The Diagnosis of Acute Deep Venous Thrombosis: Noninvasive and Radioisotopic Techniques

General review Section Editor -Marian McNarnara, MD (Detroit, Michigan)

The Diagnosis of Acute Deep Venous Thrombosis: Noninvasive and Radioisotopic Techniques Anthony J. Comerota, MD, Linda C . Knight, PhD, Alan H . Maurer, MD, Philadelphia, Pennsylvania

KEY WORDS: Deep venous thrombosis; radioisotopic diagnosis of DVT; venous Doppler imaging; impedance plethysmography;phleborheography;duplex venous imaging.

The signs and symptoms of deep venous thrombosis (DVT) are nonspecific [ 1,2] and when present may be explained by numerous other etiologies. Likewise, the complications of completely asymptomatic deep venous thrombosis can be fatal in the short-term, and associated with significant morbidity over the longterm 131. Clinicians now appreciate the necessity of objectively evaluating the deep venous system when acute thrombi are suspected. The currently available technology offers the clinician an opportunity to evaluate the deep venous system in a variety of ways. Many techniques “overlap” in their principles, however many others are complementary, particularly when radioisotopic techniques are combined with standard noninvasive methods. This review is intended to summarize the frequently performed noninvasive and radioisotopic techniques available for the diagnosis of acute deep venous thrombosis.

ANATOMY AND PHYSIOLOGY OF T H E VENOUS SYSTEM Knowledge of the anatomy and physiology of the venous system, in addition to an understanding of From the Sections of Vascular Surgery and Nuclear Medicine, Temple University Hospital, Philadelphia, Pennsylvania. Reprint requests: Anthony J. Comerota, MD, Section of Vascular Surgery, Temple University Hospital, Broad & Ontario Streets, Philadelphia, Pennsylvania 19140.

acute and chronic venous disease, is important to the proper selection of tests to be used in any particular patient. The deep veins of the lower extremity begin with the deep plantar arch which directly communicates with the paired posterior tibial veins. There are three pairs of deep veins generally present which run parallel to their corresponding arteries. A communicating set of perforating veins connects the superficial system to the deep system through a series of one way valves. When the valves are competent, blood flows only from the superficial to the deep system. Muscular veins provide drainage from the muscle mass of the calf and are represented by the soleus and gastrocnemius venous plexuses. The soleal veins drain into the peroneal and posterior tibial veins, whereas the gastrocnemius venous plexuses drain into the popliteal vein, usually above the knee joint. The remainder of the deep venous system corresponds to the arterial system. However, many variations have been noted which include paired popliteal veins and paired superficial femoral veins, as well as an unusually high or low origin of the popliteal vein. Hemodynamically, the deep venous system is characterized by low pressure gradients and large volumes of blood. In the upright position, hydrostatic pressure is primarily responsible for the venous pressure present, but the hydraulic pressure due to arterial inflow and the transmission of pressure gradients due to respiration (intrathoracic and intraabdominal) also contribute. In the recumbent position, the hydrostatic pressure is essentially eliminated and the transmitted 406

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respiratory pressure plus the hydraulic pressure are the major components. Important hemodynamic changes which occur when patients are in the supine position are the basis for the venous Doppler and phleborheographic tests. The phasic venous flow patterns corresponding to respiration are called respiratory waves. Respiratory waves are observed in all organs, as well as both upper and lower extremities. The flow velocity and volumetric response to respiration are reversed in the upper extremities compared with the lower extremities due to reversal of pressure gradients associated with inspiration and expiration. The descent of the diaphragm during inspiration causes an increased intraabdominal pressure which slows venous outflow velocity from the lower extremity with a resultant increase in its volume. As a patient exhales, the diaphragm rises and abdominal pressure diminishes with an increased venous outflow velocity from the leg and a decrease in volume. These phasic volume changes are the normal respiratory waves observed in patients with a patent, unobstructed deep venous system. Significant obstruction of the deep venous system (either anatomic or physiologic) causes venous hypertension which minimizes or eliminates these phasic volume or velocity changes. The most common cause of anatomic deep venous obstruction is deep venous thrombosis. Augmentation of venous flow velocity is an important response to distal compression. After distal compression, the normal venous system accepts this added bolus by increasing the venous flow velocity without a significant segmental volume increase. If obstruction exists in the deep venous system, there is blunting or elimination of this velocity response associated with an accompanying volumetric increase in the segments of the leg below the occlusion, due to damming of the blood distal to the obstruction. Changes in velocity and volume due to arterial pulsations are superimposed on the larger, slower velocity and volume changes due to respiration. Acute obstruction of the deep venous system will create an increased amplitude of arterial pulsation. The enlarged amplitude of these high frequency waves has been associated with the noninvasive diagnosis of acute DVT. As recanalization and collateral venous channels form, this finding subsides, respiratory waves return, and the augmentation response becomes more normalized. There is a physiologic siphoning effect of blood from the foot and calf in response to distal compression or muscular contraction. Blood is propelled cephalad with a resulting decrease in volume. This observation, termed foot emptying or calf emptying, has been incorporated in diagnostic tests assessing patency of the deep venous system. Absent or poor physiologic siphoning is noted in patients with deep venous obstruction, especially when the distal veins are

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involved. The foot refill time depends on the function of the venous valves in the resting upright person and has been useful for evaluating patients for venous insufficiency.

VENOUS DOPPLER EXAMINATION Many noninvasive tests are subject to technologist’s interpretation, but none more than the venous Doppler examination. There is little question that the trained ear will recognize abnormal venous flow patterns produced by obstruction of the underlying veins more quickly and more reliably than the untrained ear. Therefore frequent test administration is necessary to maintain optimal skill. Although we prefer to use a bidirectional Doppler which allows assessment of venous valvular insufficiency, both a 5MHz and lOMHz continuous-wave, nondirectional Doppler probe can be used to detect the presence of venous blood flow. Since this is not a quantitative measure of flow, knowledge of the previous test is valuable for comparison and detection of DVT. Methods

The examination should be performed in a warm room with the patient relaxed in a supine position. The posterior tibia1 veins, popliteal veins, superficial femoral and common femoral veins are examined. Some investigators have been able to reliably sample the profunda femoris vein, although we have been unable to consistently reproduce those results. Doppler probes in the 5-1OMHz range are used, although in obese patients the lower frequency probe is most useful. Since major veins accompany the arteries, they may be located and followed by tracing the arterial pathway. In so doing, testers can distinguish collateral flow signals from the major venous flow pattern, since collateral venous return generally does not run parallel to the artery. Inability to obtain a Doppler flow signal from a major vein is suggestive of occlusion. Finding collateral flow signals further supports diversion of venous return from the major venous pathway. Once resting flow signals have been established, respiratory variation is noted (Fig. 1). Generally, at each level, there is an appreciable decrement in velocity signal during inspiration followed by a progressive increase in velocity signal during expiration. The characteristics of the spontaneous flow signals are the most important aspect when interpreting the venous Doppler examination. Distal to an obstruction, this flow pattern will be altered to the point of a nearly continuous venous hum due to the accompanying venous hypertension created by the obstruction (Fig. 1). Occasionally, an obstructed vein will produce a continuous signal. Extremities that are hyperemic due to an

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of compression and distance between the Doppler probe and compression point. It is important to understand that absence of an augmented signal does not necessarily indicate venous obstruction. The veins may merely have been empty at the time of the compression maneuver. It has been shown that as the examiner increases the importance of augmentation, the sensitivity of the Doppler examination increases but the specificity decreases. Results

Proper diagnosis of deep venous thrombosis with the Doppler examination depends upon complete or nearly complete occlusion of the major vein with the resultant hemodynamic changes. The diagnosis of venous occlusion by Doppler examination is most accurate when there is an absence of a spontaneous flow signal from a major vein. Loss of respiratory variation and compression augmentation response are suggestive of DVT, but either criteria used alone is associated with higher false positive and false negative rates. Because this test is based on the technique and interpretation of a single examiner, its accuracy is dependent on the knowledge and experience of that Fig. 1. Venous Doppler examination in normal examiner. patient (upper tracing) and patient with acute deep venous thrombosis (lower tracing). Note absence of Table I is a compilation of the data published by respiratory phasicity and lack of augmentation investigators reporting their experience with venous response distal to compression in patient with acute Doppler examination compared with phlebography DVT. and divided according to authors reporting less than 100 extremities and more than 100 extremities. Authors reporting less than 100 extremities show a inflammatory response or recent operative procedure large number of false positive and false negative may also have a continuous venous signal; however, in results [4-lo]. On the other hand, investigators reportmost of these instances, the Doppler sounds will be ing their experience with more than 100 extremities reduced by a deep breath and eliminated by a Valsalva show a more respectable sensitivity and specificity maneuver. The Valsalva maneuver exaggerates normal [l l-151. These data strongly imply that experience is respiratory variation and may be helpful when assess- critically important when using the venous Doppler examination to diagnose DVT. ing patients with rapid or shallow breathing. Once flow signals and respiratory variation are established, distal compression of the leg or foot is performed (augmentation). In patent veins, venous flow velocity rapidly increases proximal to the site of the compression. In the presence of a competent venous valve, there should be An abrupt cessation of flow when auscultation is performed distal to the area of compression. The flow signal should then rapidly increase upon release. Occlusion of the deep venous pathway between the areas of compression and auscultation will prevent the transmission of pressures and fail to alter the Doppler signal. Listening over a patent vein distal to an obstruction and compressing beyond the area of auscultation, one will detect a lower pitched, more abrupt augmentation of the flow signal. The response during any augmentation maneuver depends upon the rapidity of compression, force of compression, quantity of blood in the veins at the time

IMPEDANCE PLETHYSMOGRAPHY Impedance plethysmography (IPG) is only one of the maximal venous outflow measurement techniques. The IPG measures changes in electrical conductivity of the lower leg (calf musculature) which directly reflects changes in blood volume. The electrical conductivity (resistance) created by changes in blood volume are measured by attaching electrodes to the patient’s lower leg and obtaining an IPG tracing. The basis for this test is Ohm’s Law: resistance = voltage/ current. The IPG provides a low-level but constant 1mAmp current which is imperceptible to the patient and incapable of stimulating the cardiac or nervous system. Electrodes attached to the lower leg detect voltage changes which directly correlate with changes

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TABLE I.-Venous

409

Doppler vs phlebography with suspected DVT

Authors reporting < 100 extremities studied

Author Milne et al Strandness et al Yao et al Holmes Johnson Bolton & Hoffman Lepore et al

Ref 4 5 6 7 8 9 10

No of Datients 35 57 50 71 32 76 40

False Dostiive P!~o) 50 5 6 15 17 21 9

False neaative (Yo) 52 21 13 0 42 24 0

Authors reporting > 100 extremifies studied

Author Evans Sigel et al McCaffrey et al Barnes et al Summer et al

Ref 11 12 13 14 15

No of patients 200 248 118 122 159

in tissue resistance. The resistance changes in the lower leg over the short period of time of the test are directly related to a change in blood volume. Therefore, the changes in electrical resistance measured by the IPG directly correlate to changes in blood volume of the extremity being examined.

False positive (Yo) 0 19 10 8 24

False negative (Yo) 13 13 3 4 2

ing the pneumatic cuff occlusion time, increasing the cuff pressure, pre-test reactive hyperemia, and the application of local heat and leg exercise.

Results

Wheeler and Anderson reported the results of impedance plethysmography in 2,561 patients underAs with all noninvasive studies, it is important that going ascending phlebography [ 181. They reported the the patient be comfortable, relaxed and warm. Any pooled data from 16 publications spanning six years. artifacts of vasoconstriction or external compression The majority of these patients suffered symptoms sugwill affect the IPG or any hemodynamic test. The IPG gestive of deep vein thrombosis. The sensitivity for is performed with the patient in the supine position detecting proximal DVT was 93% (7051755) and the with the legs elevated above the heart, the knee slightly specificity was 94% (1704/1797). Several authors have bent and the leg externally rotated. Electrodes are suggested that therapeutic decisions can be made on placed around the bulk of the calf musculature after the basis of results of impedance plethysmography in application of a conductive gel or paste. The pneu- patients suspected of having DVT [19,20]. It should be matic cuff is placed around the thigh, as high above noted that serial noninvasive tests are important in the knee as possible. The pneumatic cuff is then establishing the accurate diagnosis when suspicion inflated to a pressure of 60-65 cm of water and the continues following a negative initial study. Huisman strip chart recording observed. The objective is to and coworkers completed a study evaluating serial maximize venous filling by creating a partial external IPG in outpatients suspected of having DVT [21]. obstruction of the venous system. Once the tracing has Whereas 85% of the abnormal IPGs were detected on plateaued, the pneumatic cuff is rapidly deflated and the first test, an additional 15% of the abnormal IPGs the outflow is monitored. The relationship between were detected on subsequent studies. These data jusvenous capacitance (increased volume) versus venous outflow has been correlated by previous investigators tify serial noninvasive testing. When authors report [16,17] and guidelines proposed for normal and sensitivities of lesser magnitude, it should be clearly determined whether the false negatives were based abnormal extremities (Fig. 2). upon an initial negative study or whether serial examiIt is most important that maximal venous filling nations were performed. occur. If the first one or two tests are positive or borIt is accepted that nonocclusive thrombi and calf derline normal, additional attempts should be made to improve venous filling which will better evaluate maxi- vein thrombi will not be reliably detected by impedmal venous outflow. The techniques include prolong- ance plethysmography.

Technique

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Fig. 2. Impedance plethysmographictracing in normal extremity (upper tracing) and patient with acute deep venous thrombosis (lower tracing). Note decreased capacitance and significantly smaller maximal venous outflow in patient with the obstructed deep venous system.

PHLEBORHEOGRAPHY Phleborheography is most accurately defined as the tracing of fluids flowing within veins. The phleborheograph is a six-channel volume plethysmograph which monitors segmental volume change in the lower extremities associated with respiration and foot and calf compression (augmentation). The volume changes observed are related to changes in the segmental venous volume of the lower extremities. Technique

As with all other noninvasive studies, the patient should be relaxed and comfortable, lying supine or slightly lateral, with the bed in a 10-12" reverse Trendelenberg position, which places the heart above the lower extremities. The uppermost cuff is placed around the lower thorax to monitor respiration directly. The second cuff is placed around the thigh, the third, fourth and fifth cuffs are placed around the calf and the sixth cuff around the forefoot. The upper four cuffs record volume changes only. The fifth and sixth cuffs are used alternatively to record volume change and to apply extrinsic pulsatile contractions

used to augment venous return when evaluating whether baseline volume increases occur with such augmentation. Normal patients (Fig. 3) show smooth respiratory waves at each segment in the lower extremity corresponding to the respiratory waves recorded by the thoracic cuff. When augmentation is provided by rapid compression of the foot cuff or the lower calf cuff, the bolus of blood propelled during cuff compression is accepted in the venous system by increasing velocity without changes in the baseline volume in any segment. Augmentation provided by the lower calf cuff also results in a physiologic siphoning effect in normal individuals, resulting in a rapid drop in foot volume as well as the adjacent mid-calf cuff. Patients with deep venous thrombosis (Fig. 4) frequently have attenuated or lost respiratory volume change. Since venous hypertension can create increased outflow resistance to the arterial bed, prominent arterial pulse waves are frequently noted. Augmentation using the foot and lower calf cuff will result in a damming up of blood against the proximal obstruction, thereby creating increases in the segmental baseline volume recorded by each cuff. Patients with deep vein thrombosis will also lose the physio-

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41 1

Fig. 3. Phleborheographic tracing in patient with normal deep venous system. Notice phasic respiratory waves, no baseline elevation with augmentation and good foot emptying (physiologic siphoning effect) with low calf compression.

logic siphoning effect normally observed following augmentation. Results

Fig’ 4 m Phleborheographic tracing in patient with acute deep venous thrombosis. Note loss of respiratory waves, baseline elevation with augmentation and prominent arterial pulsations.

Cranley has recently tabulated the results from eight centers spanning seven years [22]. There were 1,252 studies with phlebographic correlation. The overall sensitivity for detection of proximal vein thrombi was 90% (413/455) and the overall specificity was 93% (732/788). The PRG, being a hemodynamic test, cannot reliably detect calf vein thrombi or nonoccluding thrombi. The PRG has been shown to accurately assess patients with suspected venous thrombosis to the point that test results can be used in clinical decision-making. Those patients with negative studies have been treated without phlebography and have been shown to have an exceedingly low incidence of subsequent venous thromboembolic complications [23]. Additionally, the PRG tracing has established the diagnosis of venous insufficiency, popliteal artery aneurysms and tricuspid valve insufficiency in patients

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with symptoms of lower extremity venous obstruction ~41.

DIAGNOSTIC VERSUS SURVEILLANCE TESTING The good results obtained with impedance plethysmography and phleborheography are reviewed above. These reports, however, conflict with data from other centers documenting high false negative and false positive rates [25-281. It was our observation that patients who were sent to the vascular laboratory with signs and symptoms of venous thrombosis were reliably studied, whereas those participating in a program for surveillance of DVT, who were not symptomatic, had a high number of false positive and false negative results with these hemodynamic techniques. A study was then performed to determine whether patient selection influenced diagnostic reliability of these noninvasive hemodynamic tests [29]. The essential findings will be summarized. Three-hundred and fifty-one patients having impedance plethysmography or phleborheography and ascending phlebography within the same 24 hour period were prospectively evaluated. The method of patient selection for the noninvasive testing and ascending phlebography varied between two distinct patient groups.

Diagnostic group: These patients were evaluated because of clinical suspicion of acute DVT. Phlebography was selectively performed by the referring physician but was not predicated upon any particular noninvasive test result. Surveillance group: These patients were at high risk for postoperative DVT since they were orthopedic patients undergoing total joint replacement. They had routine fibrinogen uptake tests and postoperative phlebography as part of an ongoing surveillance program. Noninvasive testing was performed as an adjunct to other studies and the majority of patients were asymptomatic. Noninvasive test results

Three-hundred and eight patients having IPG and ascending phlebography are summarized in Table 11. Three-hundred and two patients had PRG and ascending phlebography and are summarized in Table 111. The overall results are listed in the first column of each Table and are subsequently divided into the results obtained according to the two specific patient groups. There is a trend toward better specificity in the surveillance group for both noninvasive tests, but a significant difference exists in the ability of both IPG and PRG to detect DVT in patients in the diagnostic group

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compared to patients in the surveillance group. The difference in overall sensitivity is due to the reliable detection of above-knee thrombi in the diagnostic group compared to the poor results obtained in the surveillance group. The identification of below-knee thrombi was equally poor in the diagnostic and surveillance groups for each noninvasive test. PhlebograPhy

Two-hundred and twelve patients in the diagnostic group had ascending phlebography and 139 patients in the surveillance group had ascending phlebography (Table IV). Although the overall incidence of DVT was similar in the two groups, the distribution of thrombi was significantly different (Table V). Only 9% of patients in the diagnostic group had isolated below-knee thrombi compared with 29% in the surveillance group (p < 0.0001). Above-knee thrombi occurred in 47% of the diagnostic group and only 26% of the surveillance group (p < 0.0001) (Table VI). Only 3% of above-knee thrombi in the diagnostic group failed to create any hemodynamic alterations as determined by IPG and PRG, whereas 52% in the surveillance group had normal venous hemodynamics (Table VII). Therefore, 97% of the above-knee thrombi in the diagnostic group were detected hemodynamically compared with 48% in the surveillance group (p < 0.001). One-hundred phlebograms in patients with above-knee thrombi were available for re-review to determine whether the thrombus was occluding or nonoccluding (Table VIII). Eighty-four percent of above-knee thrombi in the diagnostic group were occluding compared with only 23% in the surveillance group (p < 0.OOOl). Discussion

Many noninvasive tests used to diagnose DVT rely on the thrombus creating some abnormality of venous hemodynamics. The analysis presented here clarifies some of the inconsistent data previously reported by integrating an analysis of the noninvasive tests with the phlebographic details which influence venous hemodynamics. It is interesting that the distribution of thrombi and the magnitude of thrombi can be influenced by the indication for patient evaluation. After reviewing these data, it appears that therapeutic decisions can be made on the basis of results when noninvasive tests are used in patients suspected of having DVT, the diagnostic group. It should be emphasized that these data are based upon a single, initial, noninvasive study. Sensitivities would be expected to further improve if serial noninvasive testing was used prior to ascending phlebography, assuming that the initial hemodynamic test was normal and clinical suspicion persisted. The majority of the patients in the surveillance

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TABLE 11.-lmpedence plethysmography compared with phlebography

SPEC SENS AIK B/K - PV + PV

Overall 85% (1 191140) 49% ( 831168) 68% ( 79/116) 8% ( 41 52) 58% (1 191204) 80% ( 831104)

Diagnostic 81% (66181) 71O/o (69197) 83% (68182) 7% ( 1/15) 70% (66/94) 82% (69184)

vs vs vs vs vs vs

Surveillance 90% (53159) 20% (14/71) 32% (1 1134) 8% ( 3137) 48% (531110) 70% (14/20)

p value NS <0.0001 <0.0001 NS

< 0.005 NS

SPEC = specificity SENS = sensitivity AIK = above-knee B/K = below-knee - PV = negative predictive value + PV = positive predictive value

TABLE Ill.-Phleborheography

SPEC SENS AIK BIK - PV + PV

Overall 78% (1161134) 59% ( 991168) 78% ( 881113) 20% ( 11155) 63% (1 16/185) 85% ( 99/117)

compared with phlebography

Diagnostic 81% (65/80) 78% (82/105) 92% (79186) 16% ( 3119) 74% (65188) 85% (82/97)

vs vs vs vs vs vs

Surveillance 94% (51154) 27% (17163) 33% ( 9127) 22% ( 8136) 53% (51197) 85% (17120)

p value <0.05 <0.0001 < 0.0001 NS <0.001 NS

SPEC = specificity SENS = sensitivity AIK = above-knee B/K = below-knee - PV = negative predictive value + PV = positive predictive value

TABLE IV.-Location of thrombi in the diagnosis and surveillance groups

Group Surveillance Diagnosis Total

Normal 63 94 157

Phlebography Below-knee 40 19 99

TABLE V.-Distribution of thrombi in patients with deep vein thrombosis

Location Above-knee Below-knee

Diagnostic (N = 118) 84% 16%

Surveillance (N = 76) 47% 53O/o

p value <0.001 <0.001

Above-knee 36 99 135

Total 139 212 351

TABLE VII.-Hemodynamic abnormalities of proximal thrombi by patient group*

IPGlPRG Neither+ One+ Both +

Diagnostic (N = 69) 3% ( 2169) 97% (67169) 74% (51169)

Surveillance (N = 25) 58% (13125) 48% (12/25) 20% ( 5/25)

p value t0.001 <0.001 <0.001

'Note: All patients had IPG and PRG and phlebography in the same 24 hours p+riod. IPG/PGR = Impedance plethysmography/phleborheography

TABLE VI.-Comparison of the phlebographic results between patient groups

Location No thrombi Above-knee Below-knee

Diagnostic (N = 118) 49% 47% 9%

Surveillance (N = 76) 45% 26% 29%

p value NS <0.0001 <0.0001

TABLE VIII.-Occluding versus nonoccluding thrombi in patients with proximal deep vein thrombosis

Diagnostic (N = 69) Occluding 84% (58169) Nonoccluding 16% (11169)

Surveillance (N = 31) 23% ( 7/31) 77% (24131)

pvalue <0.0001 <0.0001

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group have nonocclusive thrombi and, as such, these thrombi would not be expected to produce hemodynamic alterations of venous return. Therefore, it is not surprising that the sensitivity is so poor in this patient group. A major factor leading to the high incidence of nonocclusive thrombi is the early phlebography performed in the surveillance group, 94% having ascending phlebography within seven postoperative days. These data confirm the utility of noninvasive hemodynamic testing for DVT in patients who have signs and symptoms suggestive of DVT. However, noninvasive studies are inadequate for surveillance and cannot determine the true incidence of postoperative DVT, since an exceptionally high percentage of these patients have nonocclusive and below-knee thrombi. Therefore, anatomic studies will continue to be a necessary requirement for a complete surveillance program following total joint replacement.

DUPLEX VENOUS IMAGING The previously discussed diagnostic methods are physiologic in nature. Each detects some physiologic parameter of venous return, which is altered in the presence of significant venous thrombosis. The shortcomings of physiologic testing have been studied and previously reviewed. Duplex venous imaging for the diagnosis of deep venous thrombosis has the advantage of incorporating physiologic parameters based upon the integrated Doppler as well as an anatomic examination provided by real-time B-Mode imaging. The standard ultrasonic duplex imaging equipment can be used to evaluate extremity veins. A somewhat lower frequency probe may be required in particularly large thighs and to evaluate the iliac venous system. Others have used transducers at the 1.5-3MHz range to interrogate the deep abdominal venous systems and particularly the portal venous system [30]. The inherent attractiveness of obtaining direct, anatomic information in conjunction with visualizing the venous segment from which the Doppler examination is obtained has led many to adopt duplex venous imaging as an important diagnostic technique [31-36]. Technique and interpretation

Patients are examined supine on a bed placed in the reversed Trendelenberg position. As in other techniques, the patient should be comfortable and the leg slightly flexed at the knee. The transverse view is generally used initially to locate the external iliac vein, the common femoral vein and proceeding distally at each segment. The veins are studied without pressure, following light to moderate compression evaluating vein

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wall compressibility. The vessels are then examined longitudinally to confirm the findings of the transverse view and to more completely evaluate valve function. With the integrated pulsed Doppler, each major vein segment is located and a Doppler signal obtained within that segment during spontaneous and augmented venous return. The Doppler signal is interpreted according to standard diagnostic criteria. The major deep veins of the thigh to the popliteal vein are examined, and in the calf the anterior tibial, posterior tibial and peroneal veins are evaluated. Additionally, the greater saphenous, lesser saphenous and muscular veins can also be interrogated. Intraluminal echogenic material indicating partially or completely occluded veins constitutes the definitive criterion for the diagnosis of venous thrombosis (Fig. 5). Vein wall incompressibility likewise is characteristic of acute DVT, and may be found without intraluminal echoes if the thrombus is particularly acute. There are certain anatomic positions and surrounding tissue structures which normally limit compressibility. This is true of the profunda femoris vein, the superficial femoral vein as it passes through the adductor canal, and is observed in certain collagen vascular diseases which affect the skin and soft tissues. Abnormal or absent Doppler signals confirm the occlusion created by the visualized intraluminal thrombus. Likewise these abnormal Doppler signals warn the examiner of nonvisualized thrombus located just proximally or distally when the vein lumen being imaged is free of clot. Vein lumen diameter changes are normally observed during Valsalva maneuvers and distal compression. Real-time visualization of dynamic luminal changes provides indirect evidence of proximal vein patency, and has been used to assist in the diagnosis of deep venous occlusion [37]. Valve function is evaluated in the longitudinal view. Valves are normally seen to move synchronous with respiration and, to a lesser extent, with cardiac contraction. Diseased valves may be adherent to the vein wall. This technique has been adapted for use in the assessment of deep venous incompetence and compared to ambulatory venous pressures [38]. Overall results are attractive approaching a combined sensitivity and specificity of 85 Yo. Chronic venous disease is characterized by bright intraluminal echoes, a more heterogeneous pattern, greater surface irregularity, thickened vein walls, multiple lumina and increased venous collaterals. Results

The reported accuracy of the clinical experience with duplex venous imaging for acute DVT is summarized in Table IX. At our center, over 500 extremities

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Fig. 5. Real-time B-mode image of acute deep venous thrombosis. Note patent lumen (L) and acute thrombus (T).

have been evaluated with real-time venous duplex imaging and 5 1 had corresponding phlebography within 24 hours. Thirty patients were shown to have clots in the deep venous system, and of these, 29 were properly identified for a sensitivity of 97%. Twenty of 21 normal extremities were correctly identified for a specificity of 95%. The false negative occurred in a patient with a clot located in the peroneal vein which was not scanned. However, for reporting purposes this is considered an error. The patient having a false positive B-Mode venous examination had a small thrombus adherent to the wall of the popliteal vein. This was not identified by ascending phlebography. We believe the phlebogram failed to show the partially occluding thrombus. Nonetheless, to be consistent, this is reported as an error of venous duplex imaging. As the data from other centers are examined, it becomes evident that this is a highly sensitive and highly specific technique for evaluation of the deep venous system [39].

Discussion

Vascular laboratories frequently using venous duplex imaging for the diagnosis of acute DVT understand its potential. Some believe this may become the new “gold standard” in the diagnosis for acute deep venous thrombosis [40]. We continue to emphasize that the quality of the study is most critical and depends upon the diligence and expertise of the technologist and the interpreting physician. We believe that the integration of the Doppler with the B-Mode image will promote a complete examination and that physiologic and anatomic information will be additive. While enthusiasm abounds for venous duplex imaging, a complete examination which includes the main infrapopliteal and muscular veins is time consuming and on occasion difficult. Likewise, low-frequency

TABLE IX.-Duplex venous imaging compared with phlebography for acute DVT

Author Strandness Langsfeld Oliver Cornerota Sernrow Karkow Elias Total

Ref

31 32 33 -

34 35 36

No of patients

18 19 30 51 41 75

847 1,081

YO 100

100 90

97 100 96 98 97

Sensitivity (No)

YO

(13/13) (10110) (9110) (29130) (?)

(44146) (3251333) (430/442)

80 78 95 95 100 90 94 93

Specificity (No)

(415) (719) (19/20) (20121) (?)

(26129) (4831514) (5591598)

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probes must be used to completely examine the main pelvic veins. As experience is gained and good quality, complete examinations can be performed reproducibly on all patients, venous duplex imaging is likely to become the diagnostic technique of choice for deep vein thrombosis. It will undoubtedly provide information which was previously unobtainable and will certainly extend our understanding of the natural history of acute deep venous thrombosis, as well as adding an important piece to the puzzle of the patient with chronic venous disease.

RADIOISOTOPIC TECHNIQUES Most nuclear medicine techniques which employ radioisotopes for the detection and localization of thrombi utilize radiolabeled compounds which bind either specifically or nonspecifically to the structural elements within a thrombus. A brief description of the structure of thrombi is required, therefore, to understand the mechanisms of thrombus imaging currently in use and under investigation in nuclear medicine. There are at least two major mechanisms by which thrombosis may be initiated. The first requires a disruption of the endothelial lining of the blood vessel with exposure of the underlying basement membrane to clotting factors circulating in the blood. The second involves triggering of thromboses in areas of stasis with activation of the coagulation system without endothelial disruption. A venous thrombus may begin with accumulation and aggregation of platelets into a deposit which extends into the lumen of the vein. The creation of an area of relative stasis may be enough to trigger the coagulation cascade which generates nonthrombin in addition to the thrombin secreted by the aggregated platelets. Thrombin then converts fibrinogen circulating in the blood to fibrin monomers, which spontaneously polymerize to form a fibrin meshwork over the surface of the platelet aggregate. The fibrin deposit contains leukocytes and other trapped blood elements. It provides a surface on which platelets may aggregate, leading to the propagation of the structured thrombus consisting of layers of platelets and fibrin.

In an artery the morphology of a thrombus may be somewhat different than in a vein owing to the more rapid blood flow in the vessel. After an injury to an artery, platelets quickly aggregate over the exposed, nonendothelial surface. The thrombus may remain thin and friable, composed largely of platelets with only small amounts of fibrin and other cells. If the thrombus becomes thick enough to create static zones around it, layers of fibrin and platelets may deposit as described above.

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Whereas nonradioisotopic techniques detect secondary effects of thrombi such as changes in venous hemodynamics, lack of complete filling of blood vessels, noncompressible vessels, and blood volume changes, radiotracers can detect thrombi directly by their unique tendency to specifically bind to the components of a thrombus. Not all radioisotopic techniques currently in use are able to take advantage of this property. Biologic and physical factors may affect the ability of labeled compounds to detect thrombi. When fresh thrombi are actively accreting fibrin and cells, radiolabeled substances are readily incorporated into the thrombus, either by specific binding or by nonspecific entrapment. When the rate of accretion of new fibrin and cells has slowed or flow across the thrombus is absent, radioisotope detection becomes more difficult. Radiotracer remaining in the bloodstream contributes a major source of background radiation, and thus, success of detection depends on adequate concentration of the tracer at the site of the thrombus and disappearance from the blood. Radionuclide venography

The technique of radionuclide venography involves the use of nonspecific tracers injected into the dorsal veins of the feet to look for abnormal filling of the veins of the legs and for residual “hot spots” caused by adherence of the tracer to thrombi. The test is usually performed with technetium 99 (yymTc)-macroaggregated albumin (YhTc-MAA) and has been in use for a number of years [41-431. It is a rapid test and permits ascending venography to be performed safely in patients with contrast allergies. It uses readily available radiopharmaceuticals. It has come under criticism for lack of specificity because hot spots are often seen which do not correspond to thrombi [44,45]. The test is most useful in diagnosing advanced disease, because it can clearly demonstrate occlusion of venous flow [44]. If 9hT~-MAAis used as the radiopharmaceutical, a lung perfusion scan can be performed immediately after the leg study in case pulmonary embolism is suspected. Radionuclide venography using wmTc-MAAis useful as a screening procedure, but not as a substitute for contrast venography [45]. 125

I-Fibrinogen

Use of iodine 125 (125I)-fibrinogen for detection of deep vein thrombi is based on the observations of Hobbs and Davies that intravenously administered, radiolabeled fibrinogen became incorporated into an actively forming venous thrombus [46]. The 1251fibrinogen uptake test (FUT), an adaptation of that technique, is perhaps the best test today for prospective screening and detection of developing deep vein thrombosis [47-481. The FUT involves injection of

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1OOp Ci of 12sIhuman fibrinogen. At the patient's bedside, daily counts are taken of the 1251 activity over numerous locations on the patient's legs, using a portable scintillation probe coupled to a counter of radioactivity. Usually, counts over positions on the legs are expressed as a percent of the activity reading over the heart. This study results in a table of numbers rather than an image of a thrombus. Criteria for interpreting a study have been developed which make the study both sensitive and specific [48]. A study is positive if there is: (1) an increase of 20% over the same point on opposite leg; or (2) an increase of 20% over the adjacent point on same leg; or (3) an increase in 20% over the same point on the previous day.

fibrinogen or fibrinogen labeled with both 1231 and stable iodine has been shown to exhibit a thrombus-toblood uptake ratio greater than normally iodinated fibrinogen in fresh thrombi in dogs [54,55]. Images of fresh thrombi in dogs were obtained at four hours post-injection, although better images were obtained at 15 hours. This material has never been evaluated in aged thrombi or in humans. While promising, it has not been studied further, perhaps because of the difficulties with the iodination technique and the lack of widespread availability of suitable human fibrinogen.

As a label for fibrinogen IZ5Iis convenient because its long physical half-life (60 days) permits the labeled fibrinogen to have a long shelf-life and a long lifetime in-vivo for following the patient for as much as a week. On the other hand, the low-energy emissions of 1251 impair detection in the upper thighs, pelvis, or anywhere else where thick overlying tissue or a cast will significantly attenuate the radiation. If heparin therapy is begun before the FUT is completed, a false negative may result. The test is known to miss older thrombi.

The use of platelets radiolabeled with indium 1 1 1 (IlIIn) has been studied for detection of various thrombosis-related disorders [46-6 11. Thrombi that have been imaged clinically often require 24 to 48 or even up to 72 hours for visualization over the background, because platelets have a long half-life in the blood pool (five to seven days) [50]. In addition to the detection of DVT, labeled platelets have been used for the detection of thrombi and platelet deposition in areas other than the legs, including the left ventricle [62], coronary arteries [63], carotids [64], Dacron vascular grafts [65], and pulmonary emboli [66].

Fibrinogen labeled with other radionuclides

Labeling of autologous platelets is time-consuming and labor intensive, as it requires isolating the platelets from other cell types, removing or minimizing the quantity of plasma remaining and washing the cells after labeling, while maintaining sterility and nonpyrogenicity. Ongoing work continues to improve the labeling method to increase the ease and efficiency of labeling while maintaining cell viability [67].

In order to overcome the restriction associated with 1251 of examining only the calf and lower thighs, and also to provide images of thrombi, other nuclides have been used to label fibrinogen. Iodine 131 (I3lI) was first used for this by Charkes, and colleagues with success, although image resolution at that time with the high-energy 1311 was poor [49]. I3II is associated with a high radiation exposure to the subject. IZ3Iis a superior imaging radionuclide and as a radiolabel for fibrinogen provides high quality whole body images with a low radiation dose. DeNardo and associates have used 1231 fibrinogen extensively and claim to obtain diagnostic images within six to 24 hours postinjection [50]. They report detection of thrombophlebitis as long as three weeks after clinical onset.

lllln-Labeled platelets

Moser and colleagues found that fresh (up to 10 hours old) thrombi could be imaged well unless heparin had been administered [68]. Other investigators have confirmed that Il1In platelets do not bind well to older clots or to pulmonary emboli and that heparin therapy does interfere with platelet uptake in fresh thrombi. Seabold and associates [69] found that falsenegative results were obtained in patients who were on heparin or warfarin at the time of platelet imaging. In Several investigators have explored methods of patients with proven thrombi in whom anticoagulants labeling fibrinogen with 99mTc[51]. Most recently, the were discontinued at least four hours before injection improved labeling method reported by Jeghers and of labeled platelets, the platelet images eventually colleagues produced a tracer which appeared to be became positive; however, the time required was stable in-vivo and had a long half-life in the blood longer than in patients who had not received [52]. In a clinical study of this preparation of 99mTc- anticoagulants. fibrinogen by Jonckheer and associates, the blood background of radioactivity was still high at two hours after injection making visualization of thrombi diffi- 99mTc Heparin cult [53]. Several authors have observed 99mTcheparin to bind There have been attempts to modify '*3I-labeled to damaged myocardium and blood vessels [70-721. In fibrinogen in order to increase the blood clearance a clinical study to evaluate the utility of 99mTcheparin rates and thus, obtain a higher thrombus-to-blood for detection of DVT, Esquerre and associates [71] ratio much sooner than 24 hours. Highly iodinated found that 12 of 16 patients with proven DVT had

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increased activity in thrombotic vessels. Utne and coworkers [72] used 99mTcheparin radionuclide venography, by injecting the tracer in the dorsal veins of the patient’s feet and collecting images for an initial flow study (to look for filling defects and collateral circulation) and a delayed study (to look for residual hot spots). When all of these criteria were used for making a diagnosis, high correlation with contrast venography was obtained. Hot spots, however, were only seen in 50% of the patients with proven DVT. 99mTc Plasmin

Plasmin is the enzyme in blood primarily responsible for the dissolution of fresh fibrin. It, and its precursor, plasminogen, have been tested as a marker for thrombosis, but with mixed results. A study by Back and associates [73] indicated that plasmin might have the highest thrombus affinity of any of the components of the fibrinolytic system tested. There is still controversy over the mechanism of action of plasmin, and whether extrinsic radiolabeled plasmin or plasminogen should have affinity for thrombi, since Alkjaersig and his colleague [74] found that plasminogen seems to be activated and work from within a thrombus. In addition, there is evidence that any plasmin free in the circulating blood is rapidly complexed by antiplasmins, which would keep it in the circulation and delay its binding to a thrombus [75]. Despite the controversies over the mechanism of action of plasmin and plasminogen, investigators have continuously studied this enzyme and zymogen as markers of thrombi. From 1963 through 1975, radioisotopes of iodine were used to label plasminogen and plasmin [76-781. Since then, interest in plasmin has been renewed due to labeling with 99mTcand the availability (in Europe) of a kit containing purified, sterile porcine plasmin [79]. At present, the agent is not available in the U.S. Several clinical trials of 99mTc porcine plasmin have been reported. No imaging of thrombi has been reported; a scintillation probe was used at bedside to take counts over 12 to 13 points of each leg. The counts were taken at five to 15 minutes post-injection and again at 30 minutes post-injection. In 105 patients studied by both plasmin and contrast venography, Edenbrandt, and associates [80] found a sensitivity of 100% and a specificity of 51%. Deacon and coworkers [79] compared the plasmin test with either contrast venography or the FUT. In 20 patients with clinical signs of thrombosis, the plasmin missed two thrombi detected by the FUT; this was attributed to poor technetium labeling. In 20 patients at high risk of developing thrombosis, there was 100% agreement between the plasmin test and the FUT. In 20 patients clinically suspected of thrombosis, there were three cases in which a positive plasmin test result was obtained although the contrast venogram was nega-

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tive; two of these had lung scans positive for pulmonary embolism. In comparison, Adolfsson and associates [81] studied 110 patients with contrast venography and found a sensitivity of 91 070 and a specificity of 33%. Other groups agree that plasmin is most useful as a screening procedure, as it rarely misses thrombi but, it has a tendency to produce false positive results [82,83]. Radiolabeled plasminogen activators such as streptokinase and urokinase have been tested for their ability to bind to thrombi but no encouraging clinical results have been published. Fragment E,

Fragment El is a six-chain fragment derived from the controlled plasmin digestion of crosslinked human fibrin [84]. It apparently contains a dimeric binding site important in the lateral polymerization of fibrin chains [85]. In-vitro, it binds specifically to polymers of fibrin, but it does not bind to fibrin monomer nor to fibrinogen [86]. In an animal model of thrombosis, Knight and coworkers found that l3II fragment El will localize in both fresh and aged thrombi (up to five days old) with thrombus-to-blood ratios of up to 108:l [87]. Thrombus uptake studies with fragment El have also been reported by Hashimoto and associates using 67GAdeferoxamine-fragment E, and E, in rabbits with induced thrombi [88]. The ratios obtained for fragment El are attributable to its high specificity for thrombi and to its rapid rate of blood disappearance. Initial clinical trials with 123I-labeled fragment El were performed in 10 patients who also had venography or noninvasive tests for deep vein thrombosis [89]. Patients with documented DVT had rapid increased uptake of the tracer in the area of proven thrombus, within 20 to 30 minutes after injection (Fig. 6). This agent is still under investigation. Monoclonal antibodies specific for fibrin

In the 1960s, the use of polyclonal antibodies to detect thrombi in-vivo was investigated [90,91]. The antibodies were reactive with fibrinogen as well as fibrin and were observed to bind to circulating fibrinogen. Because of the incorporation of fibrinogen into forming thrombi, this method was found to be effective in permitting detection of thrombi, but the radiolabeled antibody-fibrinogen complex had a long residence time in the blood pool. This resulted in a long delay (24-48 hours) before positive images could be obtained. Recently, several monoclonal antibodies reactive with human fibrin have been prepared (Table X). Theoretically, monoclonal antibodies offer the possibility

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Fig. 6. (a) Anteroposterior radiograph of right hip of patient obtained during contrast venography. Patient had undergone total hip replacement five days earlier. Venogram shows intraluminal filling defect representing thrombus (arrows) in femoral vein. (b) Anterior gamma camera image of both hips and thighs in same patient 20 minutes following injection of I*sI-Fragment E,, demonstrating diffuse radiotracer accumulation about recently implanted right hip prosthesis (curved arrow). Focal tracer localization appears in right thigh (straight arrows), corresponding to intraluminal thrombus seen in (a). Diffuse activity represents fibrin deposition at surgical site; focal abnormality confirms presence of venous thrombosis. Patient was receiving intravenous heparin at time of Fragment El study. (Reprinted with permission from the publisher [49]).

of tailoring a radiopharmaceutical to specifically detect individual molecular sites exposed on thrombi but not exposed on species found in the circulating blood. Antibody 59D8 was raised by Hui and associates against a synthetic peptide [92]. Antibody T2Gls was raised by Kudryk and colleagues against a fragment of human fibrinogen [93]. These two antibodies appear to share the same epitope in the aminoterminus of the beta chain of fibrin, a site which is not exposed in fibrinogen but which is present in fibrin monomer. Neither antibody cross-reacts appreciably

with fibrinogen. In addition to the antibeta chain antibodies, three other monoclonal antibodies which recognize sites on fibrin not exposed on fibrinogen have been reported [94,96]. Although the published use of these latter antibodies has thus far been restricted to in-vitro assays, they have the potential for binding to thrombi in-vivo. In animal models, thrombus imaging studies with radiolabeled anti-fibrin monoclonal antibodies 59D8 and T2Gls have been reported. Rosebrough and asso-

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TABLE X.-Monoclonal antibodies which recognize antigens in thrombi Antifibrin antibodies 59D8 T2Gls

anti-fbn 17 DD-366-22 DG-1 A ntiplatelet antibodies 7E3

50H.19 P256

Epitope recognized

Ref

First seven amino acids of amino terminus of B chain of fibrin Amino terminus of B chain of fibrin Amino terminus of a chain of fibrin Crosslink region of D dimer of fibrin D dimer region in fibrin

92

Glycoprotein I1b/ll l a complex (fibrinogen binding region on platelet surface) Low molecular weight antigens on platelet surface Glycoprotein I1blll l a comdex

104

93 94 95 96

108 106

ciates studied 13lI-labeled T2Gls antifibrin IgG in a model of fresh thrombi created by placing an embolization coil in a dog's femoral vein 1971. They found that positive gamma camera images were possible within four to 48 hours following injection. Antibody fragments can be prepared by treating whole IgG with enzymes. It has been shown that fragments of antifibrin antibody retain sufficient immunoreactivity to bind to clots in-vitro [91]. Antibody fragments enhance the blood disappearance rate so that blood background is removed quickly. Knight and associates have studied 111In-labeled fragment antigen binding (Fab) fragments of antibody 59D8 in animal models of thrombi and emboli [99]. In a dog model where a coil was used to induce thrombus (Fig. 7), thrombus-to-blood ratios of approximately 8: 1 were found at 24 hours post injection, and images of fresh thrombi were achieved within four hours after injection (Fig. 7). Knight and associates [100,101] also demonstrated that Fab fragments of antifibrin T2Gls were capable of producing images of fresh thrombi in dogs within one to two hours post injection. Data in animal models [lo21 suggest that heparin interferes with the thrombus uptake of the anti-beta chain antibodies, either by inhibition of thrombus propagation or by loss of antigenic sites by fibrinolysis. Alavi and coworkers have begun clinical trials with 'llIn-59D8 Fab [lo31 in patients with suspected deep venous thrombosis. In the initial report of 31 patients, imaging of the legs was performed immediately and at four and 24 hours post injection. Fifty-three sites of

Fig. 7. Roentgenogramshowing location of coil used to induce thrombus in dog. (Reprinted with permission from the publisher [59]).

thrombi were identified by contrast venography, and 56 sites were identified by "'In-antifibrin imaging, with only 41 sites matching between the two tests. Sixteen of the patients were on heparin therapy at the time of imaging, and only 27 of 34 venographically positive sites were seen in these patients. No adverse effects were noted. Anti-platelet monoclonal antibodies

Three monoclonal antibodies which bind to human platelets have been tested for their ability to image thrombi in-vivo (Table X). Antibody 7E3 recognizes the fibrinogen binding site on the surface of human platelets [104]. The antibody (IgG) has been radiolabeled with Iz3Iand lllInand used to radiolabel platelets either in citrated whole blood or in-vivo [105]. This technique represents a major advance over the laborious cell isolation and washing procedure required for the labeling of platelets with In-oxine. Platelets labeled in this fashion have been shown to localize in fresh thrombi in dogs [105]. However, because anti-

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Fig. 8. Gamma camera images of legs of dog with thrombus induced in right leg by embolization coil placed in superficial vein, following injection of 1llln-labeled antifibrin antibody (59D8 Fabl fragments). At 24 hours post injection focal uptake at site of thrombus is seen (arrow) but no apparent uptake appears in same location on control side.

body 7E3 blocks the fibrinogen binding site on platelets and thus prevents platelet aggregation, the amount of antibody used for imaging without affecting the localizing ability of the platelets is critical. Another monoclonal antibody directed against the same antigenic site, P256, has no adverse effect on platelet aggregation if used as an l1'In-labeled Fab' fragment [106], but it was still capable of producing images of thrombi induced in primates. A comparison of IIIIn7E3 and 99mTc-MAAperfusion imaging in a dog model of pulmonary embolism did not show any improvement in pulmonary embolism detection with the specific antibody [ 1071. Another monoclonal antibody which recognizes human platelets, antibody 50H. 19, was raised against human melanoma cells, but was also found to recognize three low-molecular weight antigens on the surface of human platelets [108]. It does not recognize human erythrocytes, peripheral lymphocytes, fibroblasts, serum or plasma, so it can be used to selectively label platelets in whole blood. In the form of a mixture of F(ab')2 and Fab' fragments, it was radiolabeled with 9 9 m Tand ~ used to radiolabel platelets by direct injection of the labeled antibody [ 1081. Fresh thrombi in dogs were visualized within one hour in the peripheral veins and arteries, and within two to four hours for thrombi in the trunk, including the lungs. Heparin appears to interfere with the thrombus uptake of antibody 7E3 [102]. This is not surprising, since heparin also interferes with the uptake of IlIInoxine labeled platelets. Clinical studies with the antiplatelet antibodies have not yet been reported.

REFERENCES 1. CRANLEY JJ, CANOS AJ, SULL WJ. The diagnosis of deep venous thrombosis: fallibility of clinical symptoms and signs. Arch Surg 1976; 111:34. 2. BARNES RW, WU KK, HOAK JC. Fallibility of the clinical diagnosis of venous thrombosis. JAMA 1975; 34~605-608. 3. ATIK M. Venous thromboembolic disease. In: MOORE WS, ed. Vascular surgery: a comprehensive review. New York: Grune and Stratton, 1983:821-866. 4. MILNE RM, GUNN AA, GRIFFITHS JMT, RUCKLEY CV. Postoperative deep venous thrombosis. A comparison of diagnostic techniques. Lancet 1971; 445-447. 5 . STRANDNESS DE, SUMNER DS. Ultrasonic velocity detector in the diagnosis of thrombophlebitis. Arch Surg 1972; 104: 180- 183. 6. YAO JST, GOURMOS C, HOBBS JT. Detection of proximal vein thrombosis by Doppler ultrasound flow-detection method. Lancet 1972; 1:l-4. 7. HOLMES MCG. Deep venous thrombosis of the lower limbs diagnosed by ultrasound. Med J Aust 1973; 1:427-430. 8. JOHNSON WC. Evaluation of newer techniques for the diagnosis of venous thrombosis. J Surg Res 1974; 16:473-481. 9. BOLTON JP, HOFFMAN VJ. Incidence of early postoperative iliofemoral thrombosis. Br Med J 1975; I:247-249. 10. LEPORE TJ, SAVRAN J, VAN DE WATER J, HARROWER HW, YABLONSKI M. Screening for lower extremity deep vein thrombosis. An improved plethysmographic and Doppler approach. A m J Surg 1978; 135.529-534. 1 1 . EVANS DS. The early diagnosis of deep vein thrombosis by ultrasound. Br J Surg 1970; 57:726-728. 12. SIGEL B, FELIX WR, POPKY GL, IPSEN J. Diagnosis of lower limb venous thrombosis by Doppler ultrasound technique. Arch Surg 1972; 104:174-179. 13. McCAFFREY J, WILLIAMS 0, STATHIS M. Diagnosis of deep venous thrombosis using a Doppler ultrasonic technique. Surg Gynecol Obstet 1975; 140:740-742. 14. BARNES RW, RUSSELL HE, WILSON MR. Doppler ultrasonic evaluation of venous disease, a programmed audiovisual instruction. Iowa City: University of Iowa, 1975. 15. SUMNER D. Diagnosis of deep venous thrombosis by Doppler ultrasound. In: NICOLAIDES AN, YAO JST, (eds) Investigation of vascular disorders. New York: Churchill Livingstone, 198 1 :377-402. 16. WHEELER HB, ANDERSON FA Jr. The diagnosis of venous

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thrombosis by impedance plethysmography. In: BERNSTEIN EF, ed. Noninvasive diagnostic techniques in vascular disease, 3rd ed. St. Louis: CV Mosby Co, 1985:755-773. 17. HULL RD, HIRSH J, CARTER CJ, JAY RM, OCKELFORD PA, BULLER HR, TURPIE G, POWERS P, KINCH D, DODD PE, GILL GJ, LECLERC JR, GENT M. Diagnostic efficacy of impedance plethysmography for clinically suspected deep vein thrombosis. Ann Int Med 1985; IO2:21-28. 18. WHEELER HB, ANDERSON FA. Impedance plethysmography. In: KEMPCZINSKI R, YAO JST (eds). Practical Noninvasive Vascular Diagnosis, 2nd ed. Chicago, Year Book Med Pub 1982, 407-437. 19. WHEELER HB, ANDERSON FA, CARDULLO PA, PATAVARDHAM NA, MING LJ, CUTLER BS. Suspected deep vein thrombosis, management by impedance plethysmography. Arch Surg 1982; 117:1206-1209. 20. HULL RD, HIRSH J, CARTER CJ, et al. Diagnostic efficacy of impedance plethysmography for clinically suspected deep vein thrombosis. A randomized trial. Ann Int Med 1985; 102:2 1-28. 21. HUISMAN MV, BULLER HR, CATE JV, VREEKEN J. Serial impedance plethysmography for suspected deep venous thrombosis in outpatients. N Engl J Med 1986; 314:823-828. 22. CRANLEY JJ. Phleborheography. In: KEMPCZINSKI R, YAO JST (eds). Practical Noninvasive Vascular Diagnosis, 2nd ed. Chicago, Year Book Med Pub 1982,438-463. 23. STALLWORTH JM, PLONK GW, HORNE JB. Negative phleborheography, clinical follow-up in 593 patients. Arch Surg 1981; 116795-797. 24. COMEROTA AJ, CRANLEY JJ, COOK SE, SIPPLE P. Phleborheograph results of a ten-year experience. Surgery 1982; 91(5):573-58 1. 25. RAMCHANDANI P, SOULEN RS, FEDULLO LM, GAINES VS. Deep vein thrombosis: significant limitations of noninvasive tests. Radiology 1985; 156:47-49. 26. VACCARO P, VAN AMAN M, MILLER S, FOCHMAN J, SMEAD WL. Shortcomings of physical examination and impedance plethysmography in the diagnosis of lower extremity deep venous thrombosis. Angiology 1987:232-235. 27. YOUNG AE, HENDERSON BS, PHILLIPS DA, COUCH NP. Impedance plethysmography: its limitations as a substitute for phlebography. Cardiovasc Radio1 1978; 1:233-239. 28. BYNUM LH, WILSON JE, CROTTY CM, CURRY TS, SMITSON HL. Noninvasive diagnosis of deep venous thrombosis by phleborheography. Ann Int Med 1978; 89:162. 29. COMEROTA AJ, KATZ ML, GROSS1 RJ, WHITE JV, CZEREDARCZUK M, BOWMAN G, DESAI S, VUJIC I. The comparative value of noninvasive testing for diagnosis and surveillance of deep vein thrombosis. J Vasc Surg 1988; 7:40-49. 30. ACKROYD N, GILL R, GRIFFITHS K, KOSSOFF G, REEVE T. Duplex scanning of the portal vein and portasystemic shunts. Surgery 1986; 99(5):591-597. 31. STRANDNESS DE. Potential impact of duplex scanning for venous thrombosis. In the Leading Edge in Diagnostic Ultrasound. May 7-9, 1987, (abstract). 32. LANGSFELD M, HERSHEY FB, THORPE L, AVER Al, BINNINGTON, HB, HURLEY JJ, WOODS JJ. Duplex Bmode imaging for the diagnosis of deep venous thrombosis. Arch Surg 1987; 122587-591. 33. OLIVER MA. Duplex scanning in venous disease. Bruit 1985; 9:206-209. 34. SEMROW C, FRIEDELL M, BUCHBINDER D, ROLLINS DL. Characterization of lower extremity venous disease using real-time B-mode ultrasonic imaging. J Vasc Tech 1987; 11:187-191. 35. KARKOW WS, RUOFF BA, CRANLEY JJ. B-mode venous imaging. In KEMPCZINSKI RF, YAO JST (eds): Practical Noninvasive Vascular Diagnosis. Chicago, Year Book Med Pub 1987, pp 464-486. 36. ELIAS A, BOUVIER JL, LE CORFF G, CIOSI G, VILLIAN P, TAFANI C, SERRADIMIGNI A. A new therapeutic

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approach of deep vein thrombosis using ultrasound imaging and doppler. In BOCCALON H (ed). Angiologie Paris, John Libbey Eurotext, 1988, 113-116. 37. EFFENEY DJ, FRIEDMAN MB, GOODING GA. Iliofemoral venous thrombosis: real-time ultrasound diagnosis, normal criteria, and clinical application. Radiology 1984; 150:787-792. 38. SZENDRO G, NICOLAIDES AN, ZUKOWSKI AJ, et al. Duplex scanning the assessment of deep venous incompetence. J Vasc Surg 1986; 4:237-242. 39. COMEROTA AJ, KATZ ML. The diagnosis of acute deep venous thrombosis by venous duplex imaging. Sem Vasc Surg 1988; I(I):32-39. 40. STRANDNESS DE. Duplex scanning: past, present, and fugure. Sem Vasc Surg 1988; 1(1):2-8. 41. WEBBER MM, BENNETT LR, CRAGIN M, WEBB R. Thrombophlebitis demonstration by scintiscanning. Radiology 1969; 92:620-623. 42. HAYT DB, BLATT CJ, FREEMAN LM. Radionuclide venography: Its place as a modality for the investigation of thromboembolic phenomena. Sem Nucl Med 1977; 9:263-281. 43. VITTADINI A, FRANCHI R, BARBIERI LL. Isotope phlebography in the study of lower extremity venous thrombosis. Eur J Nucl Med 1980; 5:135-143. 44. HOLDEN RW, KLATTE EC, PARK HM, SIDDIQUI AR, BENDICK PJ, DILLEY RS, GLOVER JL. Efficacy of noninvasive modalities for diagnosis of thrombophlebitis. Radiology 1981; 141~63-66. 45. GOMES AS, WEBBER MM, BUFKIN D. Contrast venography vs radionuclide venography: a study of discrepancies and their possible significance. Radiology 1982; 142:719-728. 46. HOBBS JT, DAVIES JWL. Detection of venous thrombosis with I31I-labeled fibrinogen in the rabbit. Lancet 1960; 2:134-135. 47. KAKKAR VV. The diagnosis of deep vein thrombosis using the I-125-fibrinogen test. Arch Surg 1972; 104:152-159. 48. KAKKAR VV. Fibrinogen uptake test for the detection of deep vein thrombosis -a review of current practice. Sem Nucl Med 1977; 7:229-244. 49. CHARKES ND, DUGAN MA, MAIER WP, SOULEN R, ESCOVITZ E, LEARNER N, DUBIN R, KOZAR J, 111. Scintigraphic detection of deep vein thrombosis with I-131fibrinogen. J Nucl Med 1974; I5:1163-1166. 50. DeNARDO SJ, BOGREN HG, DeNARDO GL. Detection of thrombophlebitis in the lower extremities: A regional comparison of 123-I-fibrinogen scintigraphy and contrast venography. AJR 1985; 145:1045-1052. 51. HARWIG SSL, HARWIG JF, COLEMAN RE, WELCH MJ. In-vivo behavior of WmTc-fibrinogen and its potential as a thrombus imaging agent. J Nucl Med 1976; 17:40-46. 52. JEGHERS 0, ABRAMOVICI J, JONCKHEER M, ERMANS AM. Chemical method for the labeling of fibrinogen with 99mTc. Eur J Nucl Med 1978; 3:95-100. 53. JONCKHEER MH, ABRAMOVICI J , JEGHERS 0, DEREUME JP, GOLDSTEIN M. The interpretation of phlebograms using fibrinogen labeled with WmTc. Eur J Nucl Med 1978; 3:233-238. 54. HARWIG JF, COLEMAN RE, HARWIG SSL, SHERMAN LA, SIEGEL BA, WELCH MJ. Highly iodinated fibrinogen: a new thrombus localizing agent. J Nucl Med 1975; 16:756-763. 5 5 . HARWIG JF, WELCH MJ, COLEMAN RE. Preparation and use of 123-I-labeled highly iodinated fibrinogen for imaging deep vein thrombi. J Nucl Med 1976; 17:397-400. 56. THAKUR ML, WELCH MJ, JOIST JH, COLEMAM RE. Indium-1 11-labeledplatelets: studies on preparation and evaluation of in-vitro and in-vivo functions. Thromb Res 1976; 9:345-357. 57. HEATON WA, DAVIS HH, WELCH MJ, MATHIAS CJ, JOIST JH, SHERMAN LA, SIEGEL BA. Indium-I 11: a new radionuclide label for studying human platelet kinetics. Br J Haematol 1979; 42:613-622. 5 8 . KNIGHT LC, PRIMEAU JL, SIEGEL BA, WELCH MJ. Comparison of In-1 11-labeled platelets and iodinated fibrino-

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gen for the detection of deep vein thrombosis. JNuclMed 1978; 19391-894. 59. RIBA AL, THAKUR ML, GOTTSCHALK A, ZARET B. Imaging experimental coronary artery thrombosis with Indium111 platelets. Circulation 1979; 60:767-775. 60. POPE CF, SOSTMAN HD. Radioisotope labeled platelets in medical diagnosis. Invest Radiol 1986; 21:611-617. 61. DAVIS HH, SIEGEL BA, SHERMAN LA, HEATON WA, WELCH MJ. Scintigraphy with 111-In-labeled autologous platelets in venous thromboembolism. Radiology 1980; 136~203-207. 62. EZEKOWITZ MD, WILSON DA, SMITH EO, BUROW RD, HARRISON LH, PARKER DE, ELKINS RC, PEYTON M, TAYLOR FB. Comparison of Indium-1 11 platelet scintigraphy and two-dimensional echocardiography in the diagnosis of left ventricular thrombi. N Engl J M e d 1982; 306:1509-1513. 63. BERGMANN SR, LERCH RA, MATHIAS CJ, SOBEL BE, WELCH MJ. Noninvasive detection of coronary thrombi with In-1 11 platelets: concise communication. J Nucl Med 1983; 24: 130. 64. DAVIS H H 111, SIEGEL BA, SHERMAN LA, HEATON WA, NAIDICH TP, JOIST JH, WELCH MJ. Scintigraphic detection of carotid atherosclerosis with Indium-I 11-labeled autologous platelets. Circulation 1980; 61:982-988. 65. STRATTON JR, RITCHIE JL. Reduction of Indium-111 platelet deposition of Dacron vascular grafts in humans by aspirin plus dipyridamole. Circulation 1986; 73:325-330. 66. SOSTMAN HD, NEUMANN RD, ZOGHBI SS, LORD PF, THAKUR ML, CARBO P, GREENSPAN RH, GOTTSCHALK A. Experimental studies with 11I-Indium-labeled platelets in pulmonary embolism. Invest Radiol 1982; 17:367-374. 67. THAKUR ML, WALSH L, MALECH HL, GOTTSCHALK A. Indium-1 11-labeled human platelets: improved method, efficacy and evaluation. J Nucl Med 1981; 22:381-385. 68. MOSER KM, SPRAGG RG, BENDER F, KANOPKA R, HARTMAN MT, FEDULLO P. Study of factors that may condition scintigraphic detection of venous thrombi and pulmonary emboli with Indium-1 11-labeled platelets. J Nucl Med 1980; 21:105 1- 1058. 69. SEABOLD JE, CONRAD GR, KIMBALL DA, PONTO JA, BRICKER JA. Pitfalls in establishing the diagnosis of deep venous thrombophlebitis by Indium-111 platelet scintigraphy. J NuclMed 1988; 29:1169-1180. 70. KULKARNI PV, PARKEY RW, BUJA LM, WILSON JE 111, BONTE FJ, WILLERSON JT. Technetium-labeled heparin: preliminary report of new radiopharmaceutical with potential for imaging damaged coronary arteries and myocardium. J Nucl Med 1978; 19:810-815. 71. ESQUERRE JP, BONEU B, GUIRAUD R. Kinetics of technetium- labeled heparin in thromboembolism: preliminary report. Int J Nucl Med Biol 1979; 6:215-220. 72. UTNE HE, NIELSEN PS, KLEMP P, NIELSEN HV. A gamma camera method for the evaluation of deep-venous thrombosis in the leg. Application of 99mTc-labeled heparin. Eur J Nucl Med 1981; 6:237-240. 73. BACK N, AMBRUS JL, MINK IB. Distribution and the fate of I-131-labeled components of the fibrinolysin system. Circ Res 1961; 9:1208- 1216. 74. ALKJAERSIG N, FLETCHER AP, SHERRY S. The mechanism of clot dissolution by plasmin. J CIin Invest 1959; 38: 1086- 1095. 75. AMBRUS CM, MARKUS G. Plasmin-antiplasmin complex as a reservoir of fibrinolytic enzyme. A m J Physiol 1960; I99~491-494. 76. HARWIG SSL, HARWIG JF, SHERMAN LA, COLEMAN RE, WELCH MJ. Radioiodinated plasminogen: an imaging agent for preexisting thrombi. J Nucl Med 1977; 18:42-45. 77. OUCH1 H , WARREN R. Detection of intravascular thrombi by means of I-131-labeled plasmin. Surgery 1962; 51:42-49. 78. GOMEZ RL, WHEELER HB, BELKO JS, WARREN R.

423

Observations on the uptake of a radioactive fibrinolytic enzyme by intravascular clots. Ann Surg 1963; 158:905-911. 79. DEACON JM, ELL PJ, ANDERSON P, KHAN 0. Technetium 99m-plasmin: a new test for the detection of deep vein thrombosis. Br J Radiol 1980; 53:673-677. 80. EDENBRANDT C-M, NILSSON J, OHLIN P. Diagnosis of deep vein thrombosis by phlebography and WmTc-plasmin. Acta Med Scand 1982; 21~59-64. 81. ADOLFSSON L, NORDENFELT I, OHLSSON H, TORSTENSSON I. Diagnosis of deep vein thrombosis with 99mTcplasmin. Acta Med Scand 1982; 21~365-368. 82. SUNDREHAGEN E. Formation of 99mTc-plasmin in presence of gentisic acid using 99mTc pretreated with concentrated hydrochloric acid and vacuum evaporation. Int J Appl Radiat ISOt 1982; 33:93-97. 83. PERSSON BRR, DARTE L. Labeling plasmin with technetium-99m for scintigraphic location of thrombi. Int J Appl Radiat Isot 1977; 28:97-104. 84. OLEXA SA, BUDZYNSKI AZ, DOOLITTLE RF, COTTRELL BA, GREENE TC. Structure of fragment E species from human cross-linked fibrin. Biochemistry 1981; 2k6139-6145. 85. OLEXA SA, BUDZYNSKI AZ. Evidence for four different polymerization sites involved in human fibrin polymerization. Proc Not1 Acad Sci USA 1980;77:1374-1378. 86. OLEXA SA, BUDZYNSKI AZ. Binding phenomena of isolated unique plasmic degradation products of human crosslinked fibrin. J Biol Chem 1979; 254:4925-4932. 87. KNIGHT LC, OLEXA SA, MALMUD LS, BUDZYNSKI AZ. Specific uptake of radioiodinated fragment El by venous thrombi in pigs. J Clin Invest 1983; 72:2007-2013. 88. HASHIMOTO N, UEDA N, HAZUE M, OHMOMO Y, YOKOYAMA A. Preparation and basic study of 67Ga-DFfragment E(1,2) for the detection of thrombus. J Nucl Med 1983; 24:123. 89. KNIGHT LC, MAURER AH, ROBBINS PS, MALMUD LS, BUDZYNSKI AZ. Detection of venous thrombosis by radioiodinated fragment E l . Radiology 1985; 156:509-514. 90. SPAR IL, GOODLAND RL, SCHWARTZ SI. Detection of preformed thrombi in dogs by means of 1131-labeled antibodies to dog fibrinogen. Circ Res 1965; I7:322-329. 91. REICH T, REYNOLDS BM, HEALY M, WANG MCH, JACOBSON JH. Detection of venous thrombosis in the human by means of radioiodinated antifibrin-fibrinogen antibody. Surgery 1966; 60:1211-1215. 92. HUI KY, HABER E, MATSUEDA GR. Monoclonal antibodies to a synthetic fibrin-like peptide bind to human fibrin but not fibrinogen. Science 1983; 222:1129-1132. 93. KUDRYK B, ROHOZA A, AHADI M, CHIN J, WIEBE ME. Specificity of a monoclonal antibody for the NH2-terminal region of fibrin. Mol Immunol 1984; 21:89-94. 94. SCHEEFERS-BORCHEL U , MULLER-BERGHAUS 0, FUHGE P, EBERLE R, HEIMBURGER N. Discrimination between fibrin and fibrinogen by a monoclonal antibody against a synthetic peptide. Proc Natl Acad Sci USA 1985; 82:7091-7095. 95. RYLATT DB, BLAKE AS, COTTIS LE, MASSINGHAM DA, FLETCHER WA, MASCI PP, WHITAKER AN, ELMS M, BUNCE I, WEBBER AJ, WYATT D, BUNDESEN PG. An immunoassay for human D dimer using monoclonal antibodies. Thromb Res 1983; 31:767-778. 96. GARGAN PE, PLOPIS VA, SCHEU JD. A fibrin specific monoclonal antibody which interferes with the fibrinolytic effect of tissue plasminogen activator. Thromb Haemostas 1988; 59:426-431. 97. ROSEBROUGH SF, KUDRYK B, GROSSMAN ZK, McAFEE JG, SUBRAMANIAN G, RITTER-HRNCIRIK CA, WITANOWKI LS, TILLAPAUGH-FAY G. Radioimmunoimaging of venous thrombi using iodine-131 monoclonal antibody. Radiology 1985; 156:5 15-5 17. 98. LIAU CS, HABER E, MATSUEDA GR. Evaluation of mono-

424

NONINVASIVE DIAGNOSIS OF ACUTE DVT

clonal antifibrin antibodies by their binding to human blood clots. Thromb Haemostas (Stuttgart) 1987; 57:49-54. 99. KNIGHT LC, MAURER AH, AMMAR IA, SHEALY DJ, MATTIS JA. Evaluation of 11 1-In-labeledanti-fibrin antibody for imaging vascular thrombi. J Nucl Med 1988; 29:494-502. 100. KNIGHT LC, MAURER AH, AMMAR IA, EPPS LA, DEAN RT, BERGER HJ. Imaging venous thrombi in dogs with Tc-99m-antifibrin antibody. J Nucl Med 1988; 29:745 (abstract). 101. KNIGHT LC, MAURER AH, AMMAR IA, EPPS LA, DEAN RT, BERGER HJ. Comparison of Tc-99m and In-111 labeled antifibrin antibodies in a thrombus model. J Nucl Med 1988; 29:746 (abstract). 102. SAITO T, POWERS J, NOSSIFF ND, COLLER BS, GOLD HK, YASUDA T, MATSUEDA GR, KHAW BA, STRAUSS HW. Radioimmunoimaging of experimental thrombi in dogs using monoclonal antifibrin (AF) and antiplatelet (AP) antibodies: Effect of heparin on uptake by pulmonary emboli (PE) and venous thrombi (VT). J Nucl Med 1988; 29325 (abstract). 103. ALAVI A, GUPTA N, BERGER H, PALEVSKI H, JATLOW A, KELLEY M. Detection of venous thrombosis with In-111 labeled antifibrin (59D8) antibody imaging. J Nucl Med 1988; 29325 (abstract). 104 COLLER BS, PEERSCHKE EI, SCHUDDER LE. A murine

105.

106.

107.

108.

ANNALS OF VASCULAR SURGERY

monoclonal antibody that completely blocks the binding of fibrinogen to platelets produces a thrombasthenic-like state in normal platelets and binds to glycoproteins Ilb and/orIlla. J CIin Invest 1983; 72:325-338. OSTER ZH, SRIVASTAVA SC, SOM P, MEINKEN GE, SCUDDER LE, YAMAMOTO K, ATKINS HL, BRILL AB, COLLER BS. Thrombus radioimmunoscintigraphy: An approach using monoclonal antiplatelet scintigraphy. Proc Nut1 Acad Sci USA 1985; 82:3465-3468. STUTTLE AQJ, O’DONNELL CJ, VIRJI N, PETERS AM, HARRISON RC, MURPHY GJP, LAVENDER JP. Imaging thrombus with radiolabeled Fab’fragments of a monoclonal antibody to platelets. J Nucl Med 1988; 29:940 (abstract). SAITO T, KANKE M, KHAW BA, COLLER BA, POWERS J, NOSSIFF N, YASUDA T, STRAUSS HW. Detection of experimental pulmonary emboli: Comparison of monoclonal anti-platelet antibody imaging with perfusion scintigraphy. J Nucl Med 1987; 28.384 (abstract). SOM P, OSTER ZH, ZAMORA PO, YAMAMOTA K, SACKER DF, BRILL AB, NEWELL KD, RHODES BA. Radioimmunoimaging of experimental thrombi in dogs using technetium-99m-labeled monoclonal antibody fragments reactive with human platelets. J Nucl Med 1986; 27:1315-1320.

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