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A Comparison of Magnetic Resonance Angiography, Contrast Arteriography, and Duplex Arteriography for Patients Undergoing Lower Extremity Revascularization
A Comparison of Magnetic Resonance Angiography, Contrast Arteriography, and Duplex Arteriography for Patients Undergoing Lower Extremity Revascularization Anil Hingorani, MD, Enrico Ascher, MD, Natalia Markevich, RVT, MD, Sreedhar Kallakuri, MD, Richard Schutzer, MD, William Yorkovich, RPA, and Theresa Jacob, PhD, Brooklyn, New York
The objective of this study was to compare magnetic resonance angiography (MRA), contrast arteriography (CA), and duplex arteriography (DA) for defining anatomic features relevant to performing lower extremity revascularizations. From March 1, 2001 to August 1, 2001, 33 consecutive inpatients with chronic lower extremity ischemia underwent CA, MRA, and DA before undergoing lower extremity revascularization procedures. The reports of these tests were compared prospectively and the differences in the aortoiliac segment, femoral-popliteal, and infrapopliteal segments were noted. The vessels were classified as mild disease (<50%), moderate disease (50-70%), severe disease (71-99%), and occluded. These studies and treatment plans based on these data were compared. During this time period, 11 patients were not able to undergo MRA and therefore were excluded from the study. Thirty-three patients were included in this study. These patients underwent 35 procedures, as 2 patients underwent bilateral procedures. The mean age of the 33 patients was 76 ± 10 years (SD). Indications for the procedures included gangrene (20), ischemic ulcer (8), rest pain (4), and severe claudication (1). Patients’ medical history included diabetes mellitus (25), hypertension (20), and end-stage renal disease (5). No differences were noted between intraoperative findings and CA in this series. Two of the three differences between DA and CA were felt to be clinically significant whereas 9 of the 12 differences between MRA and CA were felt to be clinically significant. On the basis of these data in this series, MRA does not yet seem to be able to obtain adequate data on infrapopliteal segments, at least not for this highly selected population. When severe tibial calcification or very low flow states are identified, CA may be necessary for patients undergoing DA.
INTRODUCTION The limitations, risks, and costs associated with contrast arteriography (CA) have led several authors to investigate alternative imaging modalities
Department of Surgery, Division of Vascular Surgery, Maimonides Medical Center, Brooklyn, NY, USA. Presented at the New England Vascular Surgery Society, Providence, RI, September 20, 2001. Correspondence to: Enrico Ascher, MD, Division of Vascular Surgery, Maimonides Medical Center, 4802 Tenth Avenue, Brooklyn, NY 11219, USA, E-mail: [email protected] Ann Vasc Surg 2004; 18: 294-301 DOI: 10.1007/s10016-004-0039-0 Annals of Vascular Surgery Inc. Published online: 21 April 2004
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for the evaluation of the lower extremity arterial tree. Indeed, recent advances in preoperative imaging modalities such as magnetic resonance imaging (MRA) and duplex ultrasound arterial mapping (DA) have led some authors to challenge contrast arteriography (CA) as the gold standard for preoperative evaluation of patients undergoing lower extremity revascularization.1 Some of these authors have even suggested that MRA may be superior to CA in identification of distal target vessels.1 However, these studies have multiple deficiencies. The results suggesting the superiority of MRA over CA have not been confirmed at other centers of excellence.2,3 In other studies, the clinical utility of the exam remains in question because (1) MRA was often compared to CA at each an-
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atomic segment and the significance of the differences encountered in the types of interventions that would have resulted was not clarified; (2) criteria used, such as stenosis >50% or simply patent, are arbitrary; and (3) the data do not include the pedal vessels.4-6 Attempts to examine DA, by contrast, have varied from a mediocre correlation with CA7-10 to suggestions that DA can be used as a sole preoperative imaging tool.11-19 Some of this variation may have resulted from the fact that the technologists performing the exams did not have adequate training in terms of the surgical anatomy, preferences of the surgeon, and appreciation of the operative techniques. Furthermore, the technologists performing the exams were not shown the actual CA results after the DA exam, to help them progress along the learning curve. Performance of the exam in isolation from the CA, the intervention, and intraoperative findings casts serious doubts on the results that can be derived from these studies, as the very basis of the investigations is self-defeating and artificial. Indeed, by making a concerted effort to address these issues, we have noted an excellent correlation between DA and CA.20-22 In addition, by applying similar principles to MRA, we have noted significant improvements in the correlation between MRA and CA at our institution over the last 3 years. Since the technologies are rapidly advancing and the experience in these alternative techniques is limited, the few centers that have examined these techniques have focused on comparing CA to either MRA or DA, and there are no prospective data comparing all three technologies for the entire extremity.1,2,4 This has left a large void in the literature for exploring the alternatives to CA. In an attempt to clarify some of these issues, we prospectively entered consecutive inpatients with chronic lower extremity ischemia into a protocol consisting of preoperative lower extremity CA, MRA, and DA and compared these results. We also compared these results to intraoperative findings consisting of subjective quality of the vessels, completion angiography, and graft pressure measurements.
PATIENTS AND METHODS From March 1, 2001 to August 1, 2001, 33 consecutive inpatients with chronic lower extremity ischemia underwent three preoperative imaging modalities before undergoing lower extremity revascularization procedures. These three modalities
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included CA, MRA, and DA. Patients were excluded from the protocol if their serum creatinine was <2.0 after hydration (n = 2). Cases of acute ischemia or patients who had undergone outpatient preoperative evaluation only were excluded, as MRA is not readily available to outpatients at our institution because of the overwhelming inpatient demand. The MR radiologist, vascular technologist, and vascular surgeon who were not aware of results of the other test results made the reports of each test. The reports of these tests were collected prospectively. The reports and exams were analyzed by a vascular surgeon who was blinded to the identity of the patients but was aware of the clinical information for each patient. The differences in the aortoiliac, femoral-popliteal, and infrapopliteal segments were noted. The vessels were classified as mild disease (<50%), moderate disease (50-70%), severe disease (70-99%), or occluded. These studies and the treatment plans based on these data were compared. Duplex Arteriography The vascular ultrasound tests were all performed on either an ATL HDI 3000 or ATL HDI 5000 duplex scanner by two registered vascular technologists. The arterial segments starting from midabdominal aorta to the pedal arteries were studied in cross-sectional and longitudinal planes with a variety of scanheads of 7-4, 10-5, 12-5, 15-2, 5-2 and 3-2 MHz extended operative frequency range to obtain high-quality B-mode, color, and power Doppler images as well as velocity spectra. The power Doppler technique presents information by color-encoding the strength of the Doppler shifts. Power Doppler images do not have direction, speed, or flow character information and are insensitive to angle defects and aliasing. They are more sensitive than Doppler shifts displays in that they can present slower flows and flow in deeper or smaller vessels.23 All of these techniques were used to estimate the degree of stenosis, and any discrepancies were communicated to the operating surgeon. In general, however, color and power Doppler images were used primarily, and B-mode and velocity spectra were used to supplement these data, especially in the presence of long lesions or multiple lesions. The arteries were classified as normal or mildly diseased (<50%), significantly stenosed (‡50%), occluded, or not visualized. Peak systolic velocity ratios ‡2 and ‡3 as compared to the adjacent vessel were used to define hemodynamically significant stenoses ‡50% and ‡70%, respectively, A more precise evaluation of arterial size,
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length, and degree of narrowing as well as plaque characteristics was performed for areas that might undergo direct intervention. At the completion of the test, a color-coded map of the entire arterial tree was drawn to help develop the revascularization strategy.
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Table I. Causes of failure to undergo any MRA Cause
n
Pacemaker Severe claustrophobia/anxiety despite sedation Severe hip contracture Recent metallic implants
4 3 1 1
Contrast Arteriography Standard percutaneous retrograde preoperative CA with DSA was obtained. This was performed by the vascular surgery team in the operating room as a separate procedure from the revascularization. The distal aorta to the pedal vessels was attempted to be visualized. Interventions were made on the basis of CA. MRA MRA was performed with a 1.5 Tesla whole-body scanner (Magnatom Vision plus, Siemens Medical Systems, Iselin, NJ). Parameters for the study were a repetition time of 40 msec and an echo time of 1.6 msec. T1-weighted, three-dimensional, gadolinium-enhanced imaging of the aortoiliac system to the level of the ankle was performed in a body array coil with a flip angle of 70. Below the ankle, two-dimensional, electrocardiogram (EKG)-triggered, time-of-flight MRA was performed with a combination of phased-array coil and head coil with a flip angle of 30. Maximum intensity projections and source images were used in the interpretation of the study. MRA results were interpreted by MR radiologists with extensive experience who were not aware of the results of other lower extremity imaging modalities. Follow-up Patients were followed with duplex ultrasonography and physical examinations. Postoperative duplex was performed before discharge from the hospital or 1-2 weeks after discharge upon the follow-up visit. Serial duplex exams were performed every 3 months for the first year, every 6 months for the next year, and then annually. Hospital and office charts were reviewed and records from the New York City Department of Vital Statistics and the Social Security Death index were examined for mortality data. Data collection was via chart review and personal and telephone interviews.
RESULTS During this time period, 11 patients were not able to undergo MRA (Table I). Two patients were not
able to undergo CA because of borderline renal function despite hydration. These patients were excluded from this series. All patients were able to undergo DA. During this time period, 108 patients underwent lower extremity revascularization procedures by our group. Of these, 33 patients were included in this study. The remaining 64 patients did not meet the inclusion criteria. These 33 patients underwent 35 procedures, as 2 patients underwent bilateral procedures. Twenty-three were males. The mean age of the 33 patients was 76 ± 10 years (SD). Indications for the procedures included gangrene (20), ischemic ulcer (8), rest pain (4), and severe claudication (1). Previous bypasses had been performed in the same limb in 6 patients. Patients’ medical history included diabetes mellitus (25), hypertension (20), and end-stage renal disease (5). Difficult areas to image with MRA and DA exams and the causes for this are listed in Table II. Five patients had venous contamination of the calf vessels; two of these were corrected with an additional time-of-flight scan. Data were collected from all of the segments available and the areas of difficult exams were noted. CA was set as the gold standard and MRA and DA results were compared to CA results (Tables III and IV). One of the two clinically significant disagreements between DA and CA was due to overestimation of stenosis, whereas 9 of 12 clinically significant disagreements between MRA and CA DA were due to overestimation (Figs. 1, 2, 3). Both of the two clinically significant differences between DA and CA were also found in the differences between MRA and CA. No differences were noted between intraoperative findings and CA in this series. The types of procedures performed are listed in Table V. Concomitant inflow procedures included three iliac balloon angioplasties and stents and one femoral-femoral bypass. Secondary procedures included one graft thrombectomy, which resulted in below-knee amputations (the patient had undergone multiple prior failed revascularization attempts); one steal due to an adjunctive arteriovenous fistula that was closed but still resulted in a below-knee amputation; one episode of
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Table II. Causes of incomplete examsa MRA (n = 13)
Cause (n)
DA (n = 10)
Cause (n)
Aortoiliac segment Femoral-popliteal segment Infrageniculate segment
Noncooperative patient (5) Noncooperative patient (4) Venous contamination (3) Movement (1)
Aortoiliac segment Femoral-popliteal segment Infrageniculate segment
Gas interposition (4) Heavily scarred groin (1) Severe tibial calcification (7)
a
There were no incomplete CA exams.
Table III. Disagreements between DA and CA DA
CA
Clinical significance
Below-knee popliteal had moderate disease with 2-mm vessel, extremely low flow was noted Proximal anterior tibial was open, severely calcified tibials were noted Peroneal was normal, severely calcified tibials were noted
Normal below-knee popliteal
Yes—used below-knee popliteal for bypass
Severe focal stenosis in very proximal anterior tibial Focal severe stenosis in proximal peroneal
None—more distal severe disease, had to go to dorsalis pedis Yes—had femoral/peroneal bypass, not femoral-popliteal
Table IV. Disagreements between MRA and CA MRA
CA
Clinically significant
Distal occlusion of SFA Popliteal open
Entire SFA stenotic Severe behind-knee popliteal focal stenosis distal to above-knee popliteal stenosis Normal below-knee popliteal
Yes—proximal SFA was not used No—needed distal bypass due to more severe tibial disease Yes—used below-knee popliteal for bypass
Behind-knee popliteal focally stenotic Severe multisegmental disease Small PT diseased but open Normal peroneal Focally stenotic mid-peroneal DP open distally DP open DP open DP open
Yes—balloon angioplasty of behind-knee popliteal No—only inflow procedure performed No—no bypass performed Yes—peroneal used for bypass Yes—DP used for bypass Yes—DP used for bypass Yes—DP used for bypass Yes—DP used for bypass Yes—DP used for bypass
Below-knee popliteal had moderate disease; very small diffusely Behind-knee popliteal open AT had moderate disease focally PT was closed Diffusely stenotic peroneal Normal peroneal DP segmentally occluded DP closed proximally DP occluded DP very diseased diffusely, extremely small
AT, anterior tibial; DP, distal peroneal; PT, proximal tibial; SFA, superficial femoral artery.
heparin-induced thrombocytopenia that resulted in contralateral lower extremity compartment syndrome, lower extremity deep venous thrombosis, graft thrombosis, bilateral above-knee amputations, and myocardial infarction (the patient was found to have metastatic ovarian carcinoma upon exploration for perforation of the colon and died 2 days later); and one vein patch for a stenotic segment of vein. One patient underwent coronary artery bypass after undergoing the lower extremity
angiogram and had to have an amputation. They three deaths that occurred in this series all occurred more than 40 days after the procedures.
DISCUSSION In contrast to the excellent results reported at a growing number of institutions evaluating carotid disease and performing carotid endartectomy without preoperative CA,24-29 the shift away from
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Fig. 2. A,B CA demonstrates patency of the above-knee popliteal artery. Fig. 1. DA demonstrates patency of the above-knee popliteal artery.
CA in evaluation of the lower extremity arterial tree to alternative techniques has not been widely adopted. Many clinicians express a healthy skepticism when presented with the data investigating these techniques. Part of the reason for this may be that the expensive modern equipment and, more importantly, the expertise to set up and interpret the data from these techniques are not readily available. The validation studies necessary for these protocols are time consuming and require considerable involvement of the surgeon. The learning curve involves continued efforts to improve and maintain the quality of exams to obtain the needed information. Compared to the comfort of using and interpreting the traditional images of CA, the unfamiliar duplex images, with their limited field of view, and the maximal intensity projections of MRA take some adjustment on the part of the surgeon. We have found the representation from the aorta to the pedal vessels after compilation of DA data to be helpful in this matter. However, a conversation
with a DA technologist can yield much more useful information. The DA technologist can quantify the thickness of the wall, identify the softest portion of the vessel wall to perform the anastamoses, detail the hemodynamic disturbances, and characterize the quality of the vein to be used for the bypass. In addition, whether an occlusion is acute, chronic, or mixed can often be assessed quite easily with DA, compared to CA or MRA. Prior data from our institution and from others have suggested an excellent correlation between DA, CA, and intraoperative findings.13,18-20,30 This has led us to use DA as a sole preoperative imaging modality. However, our experience in over 500 cases has demonstrated that when the DA technologist identifies extreme calcification of the vessel or very low flow (PSV of <20 cm/sec), the degree of stenosis cannot be adequately assessed, and CA should be used if the status of these areas is crucial. This situation occurred in 7% of cases. Of note, however, is the fact that there were still other segments that were not clearly visualized but deemed to have no impact, and the intervention was performed. In general, our policy of not performing a femoral distal bypass for caludication
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Table V. Types of procedures performed Type
n
Bypass to distal vessel Bypass to popliteal artery No procedure Above-knee amputation Percutaneous balloon angioplasty SFA patch angioplasty Total
19 9 4 1 1 1 35
SFA, superficial femoral artery.
Fig. 3. MRA demonstrates moderate popliteal disease.
means that, in the presence of severe superficial femoral artery disease with at least one vessel runoff and insignificant iliac artery disease, a femoralpopliteal bypass will be planned, even if the other two tibial arteries could not be completely evaluated. If a surgeon prefers to perform a bypass to the distal anterior tibial artery rather than to the peroneal and the distal peroneal was too calcified to insonate, the lack of data on the distal peroneal has little impact on the planning of the procedure. Incomplete visualization of the iliac arteries due to obesity or gas interposition has not been a significant issue, as we have ready access to the equipment to perform an iliac angioplasty in the operating room if the graft pressure measurements reveal a gradient of >20 mmHg between the peak systolic pressure at the distal anastamosis and the peak systolic of the radial artery. These nuances notwithstanding, however, our data also suggest that in some patients, despite the methods used to obtain adequate information, we will not be able to obtain adequate data with DA and will still need to resort to CA.
Since the issue of cost control has become increasingly important, we need to examine this issue as well. At our institution, an MRA, including the physician charges, costs $2140, a CA costs $3095, and a DA, $200. Once again, this suggests an advantage for DA techniques. In addition, these data do not take into account the initial investment in the necessary equipment, which may also be in favor of DA. The estimated average time needed for exams is approximately 40 min for CA (including the time for compression), 60 min for MRA, and 44 min for DA. Some of the other benefits of pursuing these alternative techniques have been less obvious. Since establishing and maintaining these protocols requires considerable effort on the part of the surgeon and the technologist, the interaction between these parties tends to be increased. We have noted that the duplex laboratory tends to perform better arterial and venous exams in other beds, because there is more emphasis on high-resolution duplex, volume flow techniques, power Doppler, sonoCT techniques, and quality improvement focusing on correlation with intraoperative findings and CA. In addition, the surgeon learns the subtleties of the techniques and their limitations to obtain the information needed to perform the indicated procedure. This experience also demonstrated some of the less obvious limitations of these techniques. In contrast to prior authors’ experience, the number of patients who were not able to complete the MRA protocol was quite high.1 Despite the use of sedation, many of our patients were either not able or were vehemently unwilling to undergo MRA. The level of cooperation needed from the patient makes it difficult to obtain the MRA in confused patients or patients with language barriers. In addition, in these preliminary data, we have not been able to demonstrate a significant portion of angiographically occult vessels consistent with other authors’ findings.2,5 Finally, we have also encountered issues
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with venous contamination. Whether further advances in MR technology and techniques will be able to resolve these issues remains to be seen. While CA is commonly felt to be a necessary step to completely evaluate the arterial tree before intervention is undertaken, the information obtained from CA may possibly be misleading. Information obtained from CA can be incomplete because of psuedo-occlusions as a consequence of air bubbles or extremely low flow. In addition, underestimation of a stenotic area with standard CA, because of uniplanar views, and the ribbon-effect have also been noted. Poor visualization of patent vessels distal to occlusions, especially with retrograde filling of distal patent vessels, or problems with timing of the image may also result in errors. In addition, the status of dye-based studies as the gold standard for evaluating the vascular bed has been questioned. Data comparing completion intravascular ultrasound suggest that CA does not allow full evaluation of stents and stent grafts.31-33 Some of the MRA literature suggests that MRA may be able to identify ‘‘angiographically occult’’ vessels in selected patients undergoing lower extremity revascularization.1 Others have suggested that these errors may be due to problems inherent to CA, such as projection and technique.34,35 Despite some of these deficiencies, for the purpose of this study, CA was used as the point of comparison, as no other standard has been identified and CA seemed to correlate the best with the intraoperative findings. One of the major concerns with this series is the very selected patient population. These inpatients represent some of the most difficult revascularizations encountered. The high prevalence of limbthreatening ischemia seen mostly in patients with diabetes and advanced medical problems at a referral center may not represent the general experience in an outpatient setting. In a setting with more claudicants, the exact status of the distal tibial vessels may not be as much a concern if the treatment protocols for these patients largely included balloon angioplasty and aortoiliac or femoral-popliteal reconstruction. Indeed, some of the previous work comparing MRA and CA and suggesting excellent correlation did not include many patients with limb-threatening ischemia.4 If the entry criteria to this protocol were more inclusive, the issues of tibial vessel calcification and extremely low-flow issues might not be as prominent. In addition, since not every patient had complete assessment by DA or MRA, not all of the data points are complete. Even though all of the data points may not be needed in a clinical setting, for study purposes they do present an issue.
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CONCLUSIONS On the basis of the data in this series, MRA does not yet seem to be able to provide adequate data on infrapopliteal segment, at least not for this highly selected population. In this series, MRA resulted in both false negatives and false positives, whereas DA was inadequate when low flow or severe arterial calcification was identified. Prior groups have confirmed these MRA results.2,36 These problems occurred despite having experienced MR radiologists and modern equipment, upgrades of the hardware and software to keep the technology current, and the advantages of recent advancements in technique in the interval years between the prior groups’ work and ours, and despite reviewing each difference between CA an MRA results on a case-by-case basis. However, by using this constant quality improvement system, we have noted steady improvement in the data obtained from MRA. We suggest that any center that entertains investigating MRA evaluation of the lower extremity needs to establish a method of investigating the differences encountered between intraoperative findings, CA, and MRA. Since our MR radiologist was not initially familiar with surgical anatomy, available operative techniques, what kind of information the surgeon was seeking, and preferences of the vascular surgical team, the constant feedback over the last 4 years has led to improvements in the MRA protocols, reporting of the results, and cooperation between the surgical and MR teams. Given the past, striking advances in MRA technology and techniques, we remain hopeful that we will eventually be able to used this promising technique as a sole preoperative modality. REFERENCES 1. Velazquez OC, Baum RA, Carpenter JP. Magnetic resonance angiography of lower-extremity arterial disease. Surg. Clin. North Am. 1998;78:519-537. 2. Cambria RP, Kaufman JA, L’Italien GJ, et al. Magnetic resonance angiography in the management of lower extremity arterial occlusive disease: a prospective study. J. Vasc. Surg. 1997;25:380-389. 3. Snidow JJ, Harris VJ, Trerotola SO, et al. Interpretations and treatment decisions based on MR angiography versus conventional Parteriography in symptomatic lower extremity ischemia. J. Vasc. Interv. Radiol. 1995;6:595-603. 4. Sueyoshi E, Sakamoto I, Matsuoka Y, et al. Aortoiliac and lower extremity arteries: comparison of three-dimensional dynamic contrast-enhanced subtraction MR angiography and conventional angiography. Radiology 1999;210:683-688. 5. Baum RA, Rutter CM, Sunshine JH. Multicenter trial to evaluate vascular magnetic resonance angiography of the lower extremity. J.A.M.A. 1995;274:875-880.
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6. Lundin P, Svensson A, Henriksen E, et al. Imaging of aortoiliac arterial disease. Duplex ultrasound and MR angiography versus digital subtraction angiography. Acta. Radiol. 2000;41:125-132. 7. Cossman DV, Ellison JE, Wagner WH, et al. Comparison of contrast arteriography to arterial mapping with color-flow duplex imaging in the lower extremities. J. Vasc. Surg. 1989;10:522-528. 8. Larch E, Minar E, Ahmadi R, et al. Value of color duplex sonography for evaluation of tibioperoneal arteries in patients with femoropopliteal obstruction: a prospective comparison with anterograde intraarterial digital subtraction angiography. J. Vasc. Surg. 1997;25:629-66. 9. Lai DT, Huber D, Glasson R, et al. Colour duplex ultrasonography versus angiography in the diagnosis of lowerextremity arterial disease. Cardiovasc. Surg. 1996;4:384338. 10. Wain RA, Berdejo GL, Delvalle WN, et al. Can duplex scan arterial mapping replace contrast arteriography as the test of choice before infrainguinal revascularization?. J. Vasc. Surg. 1999;29:100-107. 11. Sensier Y, Hartshorne T, Thrush A, Nydahl S, Bolia A, London NJ. A prospective comparison of lower limb colourcoded Duplex scanning with arteriography. Eur. J. Vasc. Endovasc. Surg. 1996;11:170-175. 12. Ligush J, Jr, Reavis SW, Preisser JS, Hansen KJ. Duplex ultrasound scanning defines operative strategies for patients with limb-threatening ischemia. J. Vasc. Surg. 1998;28:482490. 13. Sensier Y, Fishwick G, Owen R, Pemberton M, Bell PR, London NJ. A comparison between colour duplex ultrasonography and arteriography for imaging infrapopliteal arterial lesions. Eur. J. Vasc. Endovasc. Surg. 1998;15:44-50. 14. London NJ, Sensier Y, Hartshorne T. Can lower limbultrasonography replace arteriography. Vasc. Med. 1996;1:115-119. 15. Polak JF, Karmel MI, Mannick JA, O’Leary DH, Donaldson MC, Whittemore AD. Determination of the extent of lowerextremity peripheral arterial disease with color-assisted duplex sonography: comparison with angiography. AJR. Am. J. Roentgenol. 1990;155:1085-1089. 16. Moneta GL, Yeager RA, Antonovic R, et al. Accuracy of lower extremity arterial duplex mapping. J. Vasc. Surg. 1992;15:275-283. 17. Wilson YG, George JK, Wilkins DC, Ashley S. Duplex assessment of run-off before femorocrural reconstruction. Br. J. Surg. 1997;84:1360-1363. 18. Karacagil S, Lofberg AM, Granbo A, Lorelius LE, Bergqvist D. Value of duplex scanning in evaluation of crural and foot arteries in limbs with severe lower limb ischaemia—a prospective comparison with angiography. Eur. J. Vasc. Endovasc. Surg. 1996;12:300-303. 19. Koelemay MJ, Legemate DA, Vos H de , Gurp JA van , Reekers JA, Jacobs MJ. Can cruropedal colour duplex scanning and pulse generated run-off replace angiography in candidates for distal bypass surgery. Eur. J. Vasc. Endovasc. Surg. 1998;16:13-18. 20. Mazzariol F, Ascher E, Salles-Cunha SX, Gade P, Hingorani A. Values and limitations of duplex ultrasonography as the sole imaging method of preoperative evaluation for popliteal and infrapopliteal bypasses. Ann.Vasc. Surg. 1999;13:1-10.
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21. Ascher E, Mazzariol F, Hingorani A, Salles-Cunha S, Gade P. The use of duplex ultrasound arterial mapping as an alternative to conventional arteriography for primary and secondary infrapopliteal bypasses. Am. J. Surg. 1999;178:162-165. 22. Mazzariol F, Ascher E, Hingorani A, Gunduz Y, Yorkovich W, Salles-Cunha S. Lower-extremity revascularisation without preoperative contrast arteriography in 185 cases: lessons learned with duplex ultrasound arterial mapping. Eur. J. Vasc. Endovasc. Surg. 2000;19:509-515. 23. Kremkau FW. Diagnostic Ultrasound: Principles and Instruments 6th edition. Philadelphia: WB Saunders, 2002, pp 218-219. 24. Loftus IM, McCarthy MJ, Pau H, et al. Carotid endarterectomy without angiography does not compromise operative outcome. Eur. J. Vasc. Endovasc. Surg. 1998;16:489-493. 25. Ascher E, Hingorani A. Changing characteristics of carotid endarterectomy. Ann. Vasc. Surg. 2001;15:275-280. 26. Syrek JR, Calligaro KD, Dougherty MJ, et al. Five-step protocol for carotid endarterectomy in the managed health care era. Surgery 1999;125:96-101. 27. Modaresi KB, Cox TC, Summers PE, et al. Comparison of intra-arterial digital subtraction angiography, magnetic resonance angiography and duplex ultrasonography for measuring carotid artery stenosis. Br. J. Surg. 1999;86:14221426. 28. Jackson MR, Chang AS, Robles HA, et al. Determination of 60% or greater carotid stenosis: a prospective comparison of magnetic resonance angiography and duplex ultrasound with conventional angiography. Ann. Vasc. Surg. 1998; 12:236-243. 29. Patel MR, Kuntz KM, Klufas RA, et al. Preoperative assessment of the carotid bifurcation. Can magnetic resonance angiography and duplex ultrasonography replace contrast arteriography? Stroke 1995;26:1753-1758. 30. Wilson YG, George JK, Wilkins DC, Ashley S. Duplex assessment of run-off before femorocrural reconstruction. Br. J. Surg. 1997;84:1360-1363. 31. Verbin C, Scoccianti M, Kopchok G, Donayre C, White RA. Comparison of the utility of CT scans and intravascular ultrasound in endovascular aortic grafting. Ann. Vasc. Surg. 1995;9:434-440. 32. Vogt KC, Brunkwall J, Malina M, et al. The use of intravascular ultrasound as control procedure for the deployment of endovascular stented grafts. Eur. J. Vasc. Endovasc. Surg. 1997;13:592-596. 33. White RA, Verbin C, Kopchok G, Scoccianti M, Virgilio C de , Donayre C. The role of cinefluoroscopy and intravascular ultrasonography in evaluating the deployment of experimental endovascular prostheses. J. Vasc. Surg. 1995;21:365374. 34. Beebe HG, Jackson T, Pigott JP. Aortic aneurysm morphology for planning endovascular aortic grafts: limitations of conventional imaging methods. J. Endovasc. Surg. 1995; 2:139-148. 35. Beebe HG, Kritpracha B. Screening and preoperative imaging of candidates for conventional repair of abdominal aortic aneurysm. Semin. Vasc. Surg. 1999;12:300-305. 36. Huber R, Back M, Ballinger R, et al. Utility of magnetic resonance arteriography for distal lower extremity revascularization. J. Vasc. Surg. 1997;26:415-423.
The objective of this study was to compare magnetic resonance angiography (MRA), contrast arteriography (CA), and duplex arteriography (DA) for defining anatomic features relevant to performing lower extremity revascularizations. From March 1, 2001 to August 1, 2001, 33 consecutive inpatients with chronic lower extremity ischemia underwent CA, MRA, and DA before undergoing lower extremity revascularization procedures. The reports of these tests were compared prospectively and the differences in the aortoiliac segment, femoral-popliteal, and infrapopliteal segments were noted. The vessels were classified as mild disease (<50%), moderate disease (50-70%), severe disease (71-99%), and occluded. These studies and treatment plans based on these data were compared. During this time period, 11 patients were not able to undergo MRA and therefore were excluded from the study. Thirty-three patients were included in this study. These patients underwent 35 procedures, as 2 patients underwent bilateral procedures. The mean age of the 33 patients was 76 ± 10 years (SD). Indications for the procedures included gangrene (20), ischemic ulcer (8), rest pain (4), and severe claudication (1). Patients’ medical history included diabetes mellitus (25), hypertension (20), and end-stage renal disease (5). No differences were noted between intraoperative findings and CA in this series. Two of the three differences between DA and CA were felt to be clinically significant whereas 9 of the 12 differences between MRA and CA were felt to be clinically significant. On the basis of these data in this series, MRA does not yet seem to be able to obtain adequate data on infrapopliteal segments, at least not for this highly selected population. When severe tibial calcification or very low flow states are identified, CA may be necessary for patients undergoing DA.
INTRODUCTION The limitations, risks, and costs associated with contrast arteriography (CA) have led several authors to investigate alternative imaging modalities
Department of Surgery, Division of Vascular Surgery, Maimonides Medical Center, Brooklyn, NY, USA. Presented at the New England Vascular Surgery Society, Providence, RI, September 20, 2001. Correspondence to: Enrico Ascher, MD, Division of Vascular Surgery, Maimonides Medical Center, 4802 Tenth Avenue, Brooklyn, NY 11219, USA, E-mail: [email protected] Ann Vasc Surg 2004; 18: 294-301 DOI: 10.1007/s10016-004-0039-0 Annals of Vascular Surgery Inc. Published online: 21 April 2004
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for the evaluation of the lower extremity arterial tree. Indeed, recent advances in preoperative imaging modalities such as magnetic resonance imaging (MRA) and duplex ultrasound arterial mapping (DA) have led some authors to challenge contrast arteriography (CA) as the gold standard for preoperative evaluation of patients undergoing lower extremity revascularization.1 Some of these authors have even suggested that MRA may be superior to CA in identification of distal target vessels.1 However, these studies have multiple deficiencies. The results suggesting the superiority of MRA over CA have not been confirmed at other centers of excellence.2,3 In other studies, the clinical utility of the exam remains in question because (1) MRA was often compared to CA at each an-
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atomic segment and the significance of the differences encountered in the types of interventions that would have resulted was not clarified; (2) criteria used, such as stenosis >50% or simply patent, are arbitrary; and (3) the data do not include the pedal vessels.4-6 Attempts to examine DA, by contrast, have varied from a mediocre correlation with CA7-10 to suggestions that DA can be used as a sole preoperative imaging tool.11-19 Some of this variation may have resulted from the fact that the technologists performing the exams did not have adequate training in terms of the surgical anatomy, preferences of the surgeon, and appreciation of the operative techniques. Furthermore, the technologists performing the exams were not shown the actual CA results after the DA exam, to help them progress along the learning curve. Performance of the exam in isolation from the CA, the intervention, and intraoperative findings casts serious doubts on the results that can be derived from these studies, as the very basis of the investigations is self-defeating and artificial. Indeed, by making a concerted effort to address these issues, we have noted an excellent correlation between DA and CA.20-22 In addition, by applying similar principles to MRA, we have noted significant improvements in the correlation between MRA and CA at our institution over the last 3 years. Since the technologies are rapidly advancing and the experience in these alternative techniques is limited, the few centers that have examined these techniques have focused on comparing CA to either MRA or DA, and there are no prospective data comparing all three technologies for the entire extremity.1,2,4 This has left a large void in the literature for exploring the alternatives to CA. In an attempt to clarify some of these issues, we prospectively entered consecutive inpatients with chronic lower extremity ischemia into a protocol consisting of preoperative lower extremity CA, MRA, and DA and compared these results. We also compared these results to intraoperative findings consisting of subjective quality of the vessels, completion angiography, and graft pressure measurements.
PATIENTS AND METHODS From March 1, 2001 to August 1, 2001, 33 consecutive inpatients with chronic lower extremity ischemia underwent three preoperative imaging modalities before undergoing lower extremity revascularization procedures. These three modalities
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included CA, MRA, and DA. Patients were excluded from the protocol if their serum creatinine was <2.0 after hydration (n = 2). Cases of acute ischemia or patients who had undergone outpatient preoperative evaluation only were excluded, as MRA is not readily available to outpatients at our institution because of the overwhelming inpatient demand. The MR radiologist, vascular technologist, and vascular surgeon who were not aware of results of the other test results made the reports of each test. The reports of these tests were collected prospectively. The reports and exams were analyzed by a vascular surgeon who was blinded to the identity of the patients but was aware of the clinical information for each patient. The differences in the aortoiliac, femoral-popliteal, and infrapopliteal segments were noted. The vessels were classified as mild disease (<50%), moderate disease (50-70%), severe disease (70-99%), or occluded. These studies and the treatment plans based on these data were compared. Duplex Arteriography The vascular ultrasound tests were all performed on either an ATL HDI 3000 or ATL HDI 5000 duplex scanner by two registered vascular technologists. The arterial segments starting from midabdominal aorta to the pedal arteries were studied in cross-sectional and longitudinal planes with a variety of scanheads of 7-4, 10-5, 12-5, 15-2, 5-2 and 3-2 MHz extended operative frequency range to obtain high-quality B-mode, color, and power Doppler images as well as velocity spectra. The power Doppler technique presents information by color-encoding the strength of the Doppler shifts. Power Doppler images do not have direction, speed, or flow character information and are insensitive to angle defects and aliasing. They are more sensitive than Doppler shifts displays in that they can present slower flows and flow in deeper or smaller vessels.23 All of these techniques were used to estimate the degree of stenosis, and any discrepancies were communicated to the operating surgeon. In general, however, color and power Doppler images were used primarily, and B-mode and velocity spectra were used to supplement these data, especially in the presence of long lesions or multiple lesions. The arteries were classified as normal or mildly diseased (<50%), significantly stenosed (‡50%), occluded, or not visualized. Peak systolic velocity ratios ‡2 and ‡3 as compared to the adjacent vessel were used to define hemodynamically significant stenoses ‡50% and ‡70%, respectively, A more precise evaluation of arterial size,
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length, and degree of narrowing as well as plaque characteristics was performed for areas that might undergo direct intervention. At the completion of the test, a color-coded map of the entire arterial tree was drawn to help develop the revascularization strategy.
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Table I. Causes of failure to undergo any MRA Cause
n
Pacemaker Severe claustrophobia/anxiety despite sedation Severe hip contracture Recent metallic implants
4 3 1 1
Contrast Arteriography Standard percutaneous retrograde preoperative CA with DSA was obtained. This was performed by the vascular surgery team in the operating room as a separate procedure from the revascularization. The distal aorta to the pedal vessels was attempted to be visualized. Interventions were made on the basis of CA. MRA MRA was performed with a 1.5 Tesla whole-body scanner (Magnatom Vision plus, Siemens Medical Systems, Iselin, NJ). Parameters for the study were a repetition time of 40 msec and an echo time of 1.6 msec. T1-weighted, three-dimensional, gadolinium-enhanced imaging of the aortoiliac system to the level of the ankle was performed in a body array coil with a flip angle of 70. Below the ankle, two-dimensional, electrocardiogram (EKG)-triggered, time-of-flight MRA was performed with a combination of phased-array coil and head coil with a flip angle of 30. Maximum intensity projections and source images were used in the interpretation of the study. MRA results were interpreted by MR radiologists with extensive experience who were not aware of the results of other lower extremity imaging modalities. Follow-up Patients were followed with duplex ultrasonography and physical examinations. Postoperative duplex was performed before discharge from the hospital or 1-2 weeks after discharge upon the follow-up visit. Serial duplex exams were performed every 3 months for the first year, every 6 months for the next year, and then annually. Hospital and office charts were reviewed and records from the New York City Department of Vital Statistics and the Social Security Death index were examined for mortality data. Data collection was via chart review and personal and telephone interviews.
RESULTS During this time period, 11 patients were not able to undergo MRA (Table I). Two patients were not
able to undergo CA because of borderline renal function despite hydration. These patients were excluded from this series. All patients were able to undergo DA. During this time period, 108 patients underwent lower extremity revascularization procedures by our group. Of these, 33 patients were included in this study. The remaining 64 patients did not meet the inclusion criteria. These 33 patients underwent 35 procedures, as 2 patients underwent bilateral procedures. Twenty-three were males. The mean age of the 33 patients was 76 ± 10 years (SD). Indications for the procedures included gangrene (20), ischemic ulcer (8), rest pain (4), and severe claudication (1). Previous bypasses had been performed in the same limb in 6 patients. Patients’ medical history included diabetes mellitus (25), hypertension (20), and end-stage renal disease (5). Difficult areas to image with MRA and DA exams and the causes for this are listed in Table II. Five patients had venous contamination of the calf vessels; two of these were corrected with an additional time-of-flight scan. Data were collected from all of the segments available and the areas of difficult exams were noted. CA was set as the gold standard and MRA and DA results were compared to CA results (Tables III and IV). One of the two clinically significant disagreements between DA and CA was due to overestimation of stenosis, whereas 9 of 12 clinically significant disagreements between MRA and CA DA were due to overestimation (Figs. 1, 2, 3). Both of the two clinically significant differences between DA and CA were also found in the differences between MRA and CA. No differences were noted between intraoperative findings and CA in this series. The types of procedures performed are listed in Table V. Concomitant inflow procedures included three iliac balloon angioplasties and stents and one femoral-femoral bypass. Secondary procedures included one graft thrombectomy, which resulted in below-knee amputations (the patient had undergone multiple prior failed revascularization attempts); one steal due to an adjunctive arteriovenous fistula that was closed but still resulted in a below-knee amputation; one episode of
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Table II. Causes of incomplete examsa MRA (n = 13)
Cause (n)
DA (n = 10)
Cause (n)
Aortoiliac segment Femoral-popliteal segment Infrageniculate segment
Noncooperative patient (5) Noncooperative patient (4) Venous contamination (3) Movement (1)
Aortoiliac segment Femoral-popliteal segment Infrageniculate segment
Gas interposition (4) Heavily scarred groin (1) Severe tibial calcification (7)
a
There were no incomplete CA exams.
Table III. Disagreements between DA and CA DA
CA
Clinical significance
Below-knee popliteal had moderate disease with 2-mm vessel, extremely low flow was noted Proximal anterior tibial was open, severely calcified tibials were noted Peroneal was normal, severely calcified tibials were noted
Normal below-knee popliteal
Yes—used below-knee popliteal for bypass
Severe focal stenosis in very proximal anterior tibial Focal severe stenosis in proximal peroneal
None—more distal severe disease, had to go to dorsalis pedis Yes—had femoral/peroneal bypass, not femoral-popliteal
Table IV. Disagreements between MRA and CA MRA
CA
Clinically significant
Distal occlusion of SFA Popliteal open
Entire SFA stenotic Severe behind-knee popliteal focal stenosis distal to above-knee popliteal stenosis Normal below-knee popliteal
Yes—proximal SFA was not used No—needed distal bypass due to more severe tibial disease Yes—used below-knee popliteal for bypass
Behind-knee popliteal focally stenotic Severe multisegmental disease Small PT diseased but open Normal peroneal Focally stenotic mid-peroneal DP open distally DP open DP open DP open
Yes—balloon angioplasty of behind-knee popliteal No—only inflow procedure performed No—no bypass performed Yes—peroneal used for bypass Yes—DP used for bypass Yes—DP used for bypass Yes—DP used for bypass Yes—DP used for bypass Yes—DP used for bypass
Below-knee popliteal had moderate disease; very small diffusely Behind-knee popliteal open AT had moderate disease focally PT was closed Diffusely stenotic peroneal Normal peroneal DP segmentally occluded DP closed proximally DP occluded DP very diseased diffusely, extremely small
AT, anterior tibial; DP, distal peroneal; PT, proximal tibial; SFA, superficial femoral artery.
heparin-induced thrombocytopenia that resulted in contralateral lower extremity compartment syndrome, lower extremity deep venous thrombosis, graft thrombosis, bilateral above-knee amputations, and myocardial infarction (the patient was found to have metastatic ovarian carcinoma upon exploration for perforation of the colon and died 2 days later); and one vein patch for a stenotic segment of vein. One patient underwent coronary artery bypass after undergoing the lower extremity
angiogram and had to have an amputation. They three deaths that occurred in this series all occurred more than 40 days after the procedures.
DISCUSSION In contrast to the excellent results reported at a growing number of institutions evaluating carotid disease and performing carotid endartectomy without preoperative CA,24-29 the shift away from
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Fig. 2. A,B CA demonstrates patency of the above-knee popliteal artery. Fig. 1. DA demonstrates patency of the above-knee popliteal artery.
CA in evaluation of the lower extremity arterial tree to alternative techniques has not been widely adopted. Many clinicians express a healthy skepticism when presented with the data investigating these techniques. Part of the reason for this may be that the expensive modern equipment and, more importantly, the expertise to set up and interpret the data from these techniques are not readily available. The validation studies necessary for these protocols are time consuming and require considerable involvement of the surgeon. The learning curve involves continued efforts to improve and maintain the quality of exams to obtain the needed information. Compared to the comfort of using and interpreting the traditional images of CA, the unfamiliar duplex images, with their limited field of view, and the maximal intensity projections of MRA take some adjustment on the part of the surgeon. We have found the representation from the aorta to the pedal vessels after compilation of DA data to be helpful in this matter. However, a conversation
with a DA technologist can yield much more useful information. The DA technologist can quantify the thickness of the wall, identify the softest portion of the vessel wall to perform the anastamoses, detail the hemodynamic disturbances, and characterize the quality of the vein to be used for the bypass. In addition, whether an occlusion is acute, chronic, or mixed can often be assessed quite easily with DA, compared to CA or MRA. Prior data from our institution and from others have suggested an excellent correlation between DA, CA, and intraoperative findings.13,18-20,30 This has led us to use DA as a sole preoperative imaging modality. However, our experience in over 500 cases has demonstrated that when the DA technologist identifies extreme calcification of the vessel or very low flow (PSV of <20 cm/sec), the degree of stenosis cannot be adequately assessed, and CA should be used if the status of these areas is crucial. This situation occurred in 7% of cases. Of note, however, is the fact that there were still other segments that were not clearly visualized but deemed to have no impact, and the intervention was performed. In general, our policy of not performing a femoral distal bypass for caludication
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Table V. Types of procedures performed Type
n
Bypass to distal vessel Bypass to popliteal artery No procedure Above-knee amputation Percutaneous balloon angioplasty SFA patch angioplasty Total
19 9 4 1 1 1 35
SFA, superficial femoral artery.
Fig. 3. MRA demonstrates moderate popliteal disease.
means that, in the presence of severe superficial femoral artery disease with at least one vessel runoff and insignificant iliac artery disease, a femoralpopliteal bypass will be planned, even if the other two tibial arteries could not be completely evaluated. If a surgeon prefers to perform a bypass to the distal anterior tibial artery rather than to the peroneal and the distal peroneal was too calcified to insonate, the lack of data on the distal peroneal has little impact on the planning of the procedure. Incomplete visualization of the iliac arteries due to obesity or gas interposition has not been a significant issue, as we have ready access to the equipment to perform an iliac angioplasty in the operating room if the graft pressure measurements reveal a gradient of >20 mmHg between the peak systolic pressure at the distal anastamosis and the peak systolic of the radial artery. These nuances notwithstanding, however, our data also suggest that in some patients, despite the methods used to obtain adequate information, we will not be able to obtain adequate data with DA and will still need to resort to CA.
Since the issue of cost control has become increasingly important, we need to examine this issue as well. At our institution, an MRA, including the physician charges, costs $2140, a CA costs $3095, and a DA, $200. Once again, this suggests an advantage for DA techniques. In addition, these data do not take into account the initial investment in the necessary equipment, which may also be in favor of DA. The estimated average time needed for exams is approximately 40 min for CA (including the time for compression), 60 min for MRA, and 44 min for DA. Some of the other benefits of pursuing these alternative techniques have been less obvious. Since establishing and maintaining these protocols requires considerable effort on the part of the surgeon and the technologist, the interaction between these parties tends to be increased. We have noted that the duplex laboratory tends to perform better arterial and venous exams in other beds, because there is more emphasis on high-resolution duplex, volume flow techniques, power Doppler, sonoCT techniques, and quality improvement focusing on correlation with intraoperative findings and CA. In addition, the surgeon learns the subtleties of the techniques and their limitations to obtain the information needed to perform the indicated procedure. This experience also demonstrated some of the less obvious limitations of these techniques. In contrast to prior authors’ experience, the number of patients who were not able to complete the MRA protocol was quite high.1 Despite the use of sedation, many of our patients were either not able or were vehemently unwilling to undergo MRA. The level of cooperation needed from the patient makes it difficult to obtain the MRA in confused patients or patients with language barriers. In addition, in these preliminary data, we have not been able to demonstrate a significant portion of angiographically occult vessels consistent with other authors’ findings.2,5 Finally, we have also encountered issues
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with venous contamination. Whether further advances in MR technology and techniques will be able to resolve these issues remains to be seen. While CA is commonly felt to be a necessary step to completely evaluate the arterial tree before intervention is undertaken, the information obtained from CA may possibly be misleading. Information obtained from CA can be incomplete because of psuedo-occlusions as a consequence of air bubbles or extremely low flow. In addition, underestimation of a stenotic area with standard CA, because of uniplanar views, and the ribbon-effect have also been noted. Poor visualization of patent vessels distal to occlusions, especially with retrograde filling of distal patent vessels, or problems with timing of the image may also result in errors. In addition, the status of dye-based studies as the gold standard for evaluating the vascular bed has been questioned. Data comparing completion intravascular ultrasound suggest that CA does not allow full evaluation of stents and stent grafts.31-33 Some of the MRA literature suggests that MRA may be able to identify ‘‘angiographically occult’’ vessels in selected patients undergoing lower extremity revascularization.1 Others have suggested that these errors may be due to problems inherent to CA, such as projection and technique.34,35 Despite some of these deficiencies, for the purpose of this study, CA was used as the point of comparison, as no other standard has been identified and CA seemed to correlate the best with the intraoperative findings. One of the major concerns with this series is the very selected patient population. These inpatients represent some of the most difficult revascularizations encountered. The high prevalence of limbthreatening ischemia seen mostly in patients with diabetes and advanced medical problems at a referral center may not represent the general experience in an outpatient setting. In a setting with more claudicants, the exact status of the distal tibial vessels may not be as much a concern if the treatment protocols for these patients largely included balloon angioplasty and aortoiliac or femoral-popliteal reconstruction. Indeed, some of the previous work comparing MRA and CA and suggesting excellent correlation did not include many patients with limb-threatening ischemia.4 If the entry criteria to this protocol were more inclusive, the issues of tibial vessel calcification and extremely low-flow issues might not be as prominent. In addition, since not every patient had complete assessment by DA or MRA, not all of the data points are complete. Even though all of the data points may not be needed in a clinical setting, for study purposes they do present an issue.
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CONCLUSIONS On the basis of the data in this series, MRA does not yet seem to be able to provide adequate data on infrapopliteal segment, at least not for this highly selected population. In this series, MRA resulted in both false negatives and false positives, whereas DA was inadequate when low flow or severe arterial calcification was identified. Prior groups have confirmed these MRA results.2,36 These problems occurred despite having experienced MR radiologists and modern equipment, upgrades of the hardware and software to keep the technology current, and the advantages of recent advancements in technique in the interval years between the prior groups’ work and ours, and despite reviewing each difference between CA an MRA results on a case-by-case basis. However, by using this constant quality improvement system, we have noted steady improvement in the data obtained from MRA. We suggest that any center that entertains investigating MRA evaluation of the lower extremity needs to establish a method of investigating the differences encountered between intraoperative findings, CA, and MRA. Since our MR radiologist was not initially familiar with surgical anatomy, available operative techniques, what kind of information the surgeon was seeking, and preferences of the vascular surgical team, the constant feedback over the last 4 years has led to improvements in the MRA protocols, reporting of the results, and cooperation between the surgical and MR teams. Given the past, striking advances in MRA technology and techniques, we remain hopeful that we will eventually be able to used this promising technique as a sole preoperative modality. REFERENCES 1. Velazquez OC, Baum RA, Carpenter JP. Magnetic resonance angiography of lower-extremity arterial disease. Surg. Clin. North Am. 1998;78:519-537. 2. Cambria RP, Kaufman JA, L’Italien GJ, et al. Magnetic resonance angiography in the management of lower extremity arterial occlusive disease: a prospective study. J. Vasc. Surg. 1997;25:380-389. 3. Snidow JJ, Harris VJ, Trerotola SO, et al. Interpretations and treatment decisions based on MR angiography versus conventional Parteriography in symptomatic lower extremity ischemia. J. Vasc. Interv. Radiol. 1995;6:595-603. 4. Sueyoshi E, Sakamoto I, Matsuoka Y, et al. Aortoiliac and lower extremity arteries: comparison of three-dimensional dynamic contrast-enhanced subtraction MR angiography and conventional angiography. Radiology 1999;210:683-688. 5. Baum RA, Rutter CM, Sunshine JH. Multicenter trial to evaluate vascular magnetic resonance angiography of the lower extremity. J.A.M.A. 1995;274:875-880.
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6. Lundin P, Svensson A, Henriksen E, et al. Imaging of aortoiliac arterial disease. Duplex ultrasound and MR angiography versus digital subtraction angiography. Acta. Radiol. 2000;41:125-132. 7. Cossman DV, Ellison JE, Wagner WH, et al. Comparison of contrast arteriography to arterial mapping with color-flow duplex imaging in the lower extremities. J. Vasc. Surg. 1989;10:522-528. 8. Larch E, Minar E, Ahmadi R, et al. Value of color duplex sonography for evaluation of tibioperoneal arteries in patients with femoropopliteal obstruction: a prospective comparison with anterograde intraarterial digital subtraction angiography. J. Vasc. Surg. 1997;25:629-66. 9. Lai DT, Huber D, Glasson R, et al. Colour duplex ultrasonography versus angiography in the diagnosis of lowerextremity arterial disease. Cardiovasc. Surg. 1996;4:384338. 10. Wain RA, Berdejo GL, Delvalle WN, et al. Can duplex scan arterial mapping replace contrast arteriography as the test of choice before infrainguinal revascularization?. J. Vasc. Surg. 1999;29:100-107. 11. Sensier Y, Hartshorne T, Thrush A, Nydahl S, Bolia A, London NJ. A prospective comparison of lower limb colourcoded Duplex scanning with arteriography. Eur. J. Vasc. Endovasc. Surg. 1996;11:170-175. 12. Ligush J, Jr, Reavis SW, Preisser JS, Hansen KJ. Duplex ultrasound scanning defines operative strategies for patients with limb-threatening ischemia. J. Vasc. Surg. 1998;28:482490. 13. Sensier Y, Fishwick G, Owen R, Pemberton M, Bell PR, London NJ. A comparison between colour duplex ultrasonography and arteriography for imaging infrapopliteal arterial lesions. Eur. J. Vasc. Endovasc. Surg. 1998;15:44-50. 14. London NJ, Sensier Y, Hartshorne T. Can lower limbultrasonography replace arteriography. Vasc. Med. 1996;1:115-119. 15. Polak JF, Karmel MI, Mannick JA, O’Leary DH, Donaldson MC, Whittemore AD. Determination of the extent of lowerextremity peripheral arterial disease with color-assisted duplex sonography: comparison with angiography. AJR. Am. J. Roentgenol. 1990;155:1085-1089. 16. Moneta GL, Yeager RA, Antonovic R, et al. Accuracy of lower extremity arterial duplex mapping. J. Vasc. Surg. 1992;15:275-283. 17. Wilson YG, George JK, Wilkins DC, Ashley S. Duplex assessment of run-off before femorocrural reconstruction. Br. J. Surg. 1997;84:1360-1363. 18. Karacagil S, Lofberg AM, Granbo A, Lorelius LE, Bergqvist D. Value of duplex scanning in evaluation of crural and foot arteries in limbs with severe lower limb ischaemia—a prospective comparison with angiography. Eur. J. Vasc. Endovasc. Surg. 1996;12:300-303. 19. Koelemay MJ, Legemate DA, Vos H de , Gurp JA van , Reekers JA, Jacobs MJ. Can cruropedal colour duplex scanning and pulse generated run-off replace angiography in candidates for distal bypass surgery. Eur. J. Vasc. Endovasc. Surg. 1998;16:13-18. 20. Mazzariol F, Ascher E, Salles-Cunha SX, Gade P, Hingorani A. Values and limitations of duplex ultrasonography as the sole imaging method of preoperative evaluation for popliteal and infrapopliteal bypasses. Ann.Vasc. Surg. 1999;13:1-10.
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21. Ascher E, Mazzariol F, Hingorani A, Salles-Cunha S, Gade P. The use of duplex ultrasound arterial mapping as an alternative to conventional arteriography for primary and secondary infrapopliteal bypasses. Am. J. Surg. 1999;178:162-165. 22. Mazzariol F, Ascher E, Hingorani A, Gunduz Y, Yorkovich W, Salles-Cunha S. Lower-extremity revascularisation without preoperative contrast arteriography in 185 cases: lessons learned with duplex ultrasound arterial mapping. Eur. J. Vasc. Endovasc. Surg. 2000;19:509-515. 23. Kremkau FW. Diagnostic Ultrasound: Principles and Instruments 6th edition. Philadelphia: WB Saunders, 2002, pp 218-219. 24. Loftus IM, McCarthy MJ, Pau H, et al. Carotid endarterectomy without angiography does not compromise operative outcome. Eur. J. Vasc. Endovasc. Surg. 1998;16:489-493. 25. Ascher E, Hingorani A. Changing characteristics of carotid endarterectomy. Ann. Vasc. Surg. 2001;15:275-280. 26. Syrek JR, Calligaro KD, Dougherty MJ, et al. Five-step protocol for carotid endarterectomy in the managed health care era. Surgery 1999;125:96-101. 27. Modaresi KB, Cox TC, Summers PE, et al. Comparison of intra-arterial digital subtraction angiography, magnetic resonance angiography and duplex ultrasonography for measuring carotid artery stenosis. Br. J. Surg. 1999;86:14221426. 28. Jackson MR, Chang AS, Robles HA, et al. Determination of 60% or greater carotid stenosis: a prospective comparison of magnetic resonance angiography and duplex ultrasound with conventional angiography. Ann. Vasc. Surg. 1998; 12:236-243. 29. Patel MR, Kuntz KM, Klufas RA, et al. Preoperative assessment of the carotid bifurcation. Can magnetic resonance angiography and duplex ultrasonography replace contrast arteriography? Stroke 1995;26:1753-1758. 30. Wilson YG, George JK, Wilkins DC, Ashley S. Duplex assessment of run-off before femorocrural reconstruction. Br. J. Surg. 1997;84:1360-1363. 31. Verbin C, Scoccianti M, Kopchok G, Donayre C, White RA. Comparison of the utility of CT scans and intravascular ultrasound in endovascular aortic grafting. Ann. Vasc. Surg. 1995;9:434-440. 32. Vogt KC, Brunkwall J, Malina M, et al. The use of intravascular ultrasound as control procedure for the deployment of endovascular stented grafts. Eur. J. Vasc. Endovasc. Surg. 1997;13:592-596. 33. White RA, Verbin C, Kopchok G, Scoccianti M, Virgilio C de , Donayre C. The role of cinefluoroscopy and intravascular ultrasonography in evaluating the deployment of experimental endovascular prostheses. J. Vasc. Surg. 1995;21:365374. 34. Beebe HG, Jackson T, Pigott JP. Aortic aneurysm morphology for planning endovascular aortic grafts: limitations of conventional imaging methods. J. Endovasc. Surg. 1995; 2:139-148. 35. Beebe HG, Kritpracha B. Screening and preoperative imaging of candidates for conventional repair of abdominal aortic aneurysm. Semin. Vasc. Surg. 1999;12:300-305. 36. Huber R, Back M, Ballinger R, et al. Utility of magnetic resonance arteriography for distal lower extremity revascularization. J. Vasc. Surg. 1997;26:415-423.