Magnetic Resonance Imaging in a Routine Clinical Setting

cfe? Proceedings Vol.60

ROCHESTER, MINNESOTA

FEBRUARY 1985

Magnetic Resonance Imaging in a Routine Clinical Setting HILLIER L. BAKER, Jr., M . D . , T O M H. BERQUIST, M . D . , DAVID B. KISPERT, M . D . , DAVID F. REESE, M.D., O. WAYNE HOUSER, M . D . , FRANKLIN EARNEST IV, M . D . , GLENN S. FORBES, M . D . , GERALD R. MAY, M . D . , Department of Diagnostic Radiology

The results of magnetic resonance imaging (MRI) examinations in the first 1,000 consecutive patients who were studied by this technique at our institution were reviewed to determine the disease states encountered, the sensitivity and accuracy of results, and the value of the examination as compared with computed tomography and other imaging procedures. The MRI device was a 0.15-tesla resistive magnet that used a variety of saturation recovery, spin echo, and inversion recovery pulse sequences to produce images. MRI was found equal to or superior to other imaging techniques in most cases. Exceptions included organs or body regions that are prone to excessive respiratory or vascular motion, lesions that necessitate exquisite spatial resolution for diagnosis, and lesions in which angulation of the viewing plane is necessary for optimal depiction. Fresh blood and calcification within a lesion were also difficult to detect with use of MRI.

In the early 1980s, magnetic resonance imaging (MRI) was introduced into the clinical medical environment by several manufacturers of prototype units. Shortly thereafter, image quality, spatial resolution, and density discrimination were vastly improved, as were the flexibility and rapidity of data acquisition and display. These and other advances are still occurring and have been reported in numerous publications in the scientific literature.1"8 Considerable enthusiasm has arisen among physicians who perceive MRI as an effective diagnostic modality, and the most enthusiastic proponents have even predicted that MRI might eventually supplant most other diagnostic imaging methods. The true role of MRI in relationship to other methods of diagnostic imaging remains speculative until multiple, in-depth, long-range analyses of its utility in daily practice for routine screening and characterization of disease have been conducted. Such studies, correlated with the numerous more circumscribed observations already in the literature, 9 " 15 can be the basis for a more comprehensive understanding of MRI and its use in clinical diagnosis. In this report, we describe our results in the Mayo Clin Proc 60:75-90, 1985

first 1,000 consecutive patients who were examined with MRI at our institution in the 14 months from December 1982 to February 1984 and offer some tentative answers to the basic questions about the applications of this procedure. METHODS AND SUBJECTS Imaging Techniques.—MRI depends on the detection of weak radio-frequency (RF) signals emitted by protons, situated in a strong static external magnetic field, which have been "energized" by the application of various applied RF pulses. Because body protons have different properties in the various normal and pathologic tissues, their detected signals (with proper spatial encoding), when processed by means of techniques for reconstruction from projections, result in axial, coronal, or sagittal sectional images of the body which have exquisite contrast resolution and excellent spatial resolution. Unlike other imaging modalities, MRI responds to multiple variables that can be manipulated to obtain a tissue diagnostic image. The most notable of these variables are (1) proton density—number of nuclear signals 75

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TR = 250(+) msec

90° NMR signal

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ΙΑΑΛΤ TR = 500(+) msec

90°

180°

NMR signal

TE = 20,40,60(+) msec -► TR = 1000(+) msec 180°

Tl = 400 (+) msec

90°

»I«

180°

NMR signal

40 msec

Fig. 1. Common pulse sequences for magnetic resonance imaging. A, Free induction decay. This technique shows excellent spatial resolution. B, Spin echo sequence. This technique elicits a strong signal from pathologic processes. C, Inversion recovery sequence. This technique reveals excellent contrast between gray and white matter of the nervous system. NMR = nuclear magnetic resonance; TE = echo time; Tl = inversion time; TR = repetition time.

per unit volume; (2) T l (spin-lattice relaxation)—time for the nuclear "magnets" to return to their original alignment with the applied magnetic field; and (3) T2 (spinspin relaxation)—time for the nuclear "magnets" to lose their phase coherence. MRI uses applied RF pulses that tilt the nuclear "magnets" 90° or.180° off the direction of the applied magnetic field, after which nuclear signals are generated. Depending on the time, sequence, and frequency in which these pulses are injected, the resulting image will emphasize one of the aforementioned variables. Standard nomenclature, proposed by the American College of Radiology to promote uniform terminology, includes the following terms: TE = echo time, TR = repetition time, and Tl = inversion time. Pulse sequences in common use today (Fig. 1) are (1) free induction decay (FID)—proton density, excellent spatial resolution, but no MRI tissue characteristics; (2) spin echo (SE)—T2 weighted, strong signal from pathologic processes; and (3) inversion recovery (IR)—T1 weighted, gray

and white matter contrast, weak signal from pathologic processes. The sequences and their corresponding time values that we used are shown in Table 1. FID, a modified saturation recovery (SR) technique, mainly reflects the proton density in the tissues, gives an excellent gross anatomic outline of organs, and elicits a positive signal from blood flowing in large vessels. IR sequences are strongly dependent on T1 relaxation times (decreasing signal with increasing T1), whereas the SE techniques have a stronger T2 dependence (increasing signal with increasing T2) which is maximized as the TR is prolonged. Any of these sequences could be used to produce axial, coronal, or sagittal images. All MRI scans were performed with use of a resistive, water-cooled magnet operating at 0.15 tesla (6.4 MHz) (Picker International). A round coil with a 30-cm aperture was used to examine the head and upper five segments of the cervical spine, and an elliptic coil 60 cm long with a 30- by 50-cm aperture was used for the rest of the body, including the extremities. Image data were acquired on a 128 by 512 matrix, interpolated, reconstructed, and displayed as a 256 by 256 matrix with an approximate pixel size of 1.2 mm 2 . Because of the prototype nature of the imager, periodic modifications and repairs were made during the time of this study, and although the first 100 examinations were accumulated in 62 working days, 86 days elapsed before the second 100 studies were done—and the instrument was inoperative 33 of those days. This "down time" was necessary to replace a faulty magnet coil and reshim the magnet, to replace and recalibrate a faulty transceiver, to reprogram the computer software to accommodate a new improved head coil, and to replace the previously used Table 1.—Pulse Sequences of Magnetic Resonance Imaging and Their Time Values* Sequence Spin echo 10 20+ 30t 40t 60+ Inversion recovery 200 400+ 500+ 600 800 Free induction decay (saturation recovery)*

TR (ms)

Tl (ms)

500-4,000 500-4,000 500-4,000 500-4,000 500-4,000 500-4,000 500-4,000 500-4,000 500-4,000 500-4,000 75-1,000

TE (ms) 20 40 60 80 120

200 400 500 600 800

40 40 40 40 40 40

*TE = echo time; Tl = inversion time; TR = repetition time. tMultislice format—4, 8, or 16 contiguous slices (10-mm thickness only). ί-Single-slice system and back-projection reconstruction only.

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back-projection reconstruction method with a twodimensional Fourier transform technique. These modifications resulted in a satisfactory and reliable "singleslice" system that could accommodate 100 examinations in 19 to 21 working days. In October 1983, the more efficient multislice software became available (4, 8, or 16 contiguous 10-mm sections); thus, at present, 100 examinations can be done in 9 to 11 working days. In the single-slice mode, widths of 5-, 10-, 15-, and 20-mm were possible, whereas multislice operation was limited to 10-mm sections. The attending radiologist chose the pulse sequences to be used after the clinical problem to be solved had been determined. In the singleslice "era," the SE and IR sequences were used in virtually all cases, and the FID was used in about 25%. With the advent of the multislice capability, the patterns of utilization changed to SE 100%, IR 50%, and FID less than 5% of the cases. The TRs with the multislice procedure were fixed at a minimum of approximately 600 ms (4 sections), 2,000 ms (8 sections), and 4,000 ms (16 sections), but not infrequently, single sections through a region of interest were made at TRs of 500 to 1,500 ms. TIs of 400 or 500 ms were almost invariably chosen, and most radiologists preferred TEs of 40, 60, and 80 ms. In order to maximize the signal-to-noise ratio, two averages were taken at each of 128 projections with the head coil, and four averages were taken at the same number of projections with the body coi I. Because of this variable, an eight-slice pack of projections of the head necessitated 8 minutes of scanning time, and eight sections through the body, 16 minutes. A 16-slice pack (two averages) also encompassed 16 minutes, whereas a 4-slice series—633-ms TR and 40-ms TE—could be completed in only 2.7 minutes. Appointment schedules were arranged to provide 60% of the time for imaging of the head, neck, and nervous system and 40% of the time for imaging of the " b o d y . " Patients with suspected disease of the head and neck or central nervous system were referred by consultants in the departments of neurology, neurosurgery, ophthalmology, and otolaryngology, whereas those with lesions of the thoracic and abdominal organs or the extremities were chosen by the radiologist, frequently after an abnormality had been detected by computed tomography (CT) or other imaging modalities. This difference in approach led to some disparity in our results in that few normal findings were among the " b o d y " MRI examinations, whereas 142 (18%) of the head and neckorneuroimaging MR studies revealed no abnormality. The body examinations also reflected the specific interests of the radiologists involved.

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Patient Population.—We examined 1,000 patients (513 male and 487 female patients) whose ages ranged from 5 days to 83 years. In this overall group, 740 patients were thought to have head and neck or neurologic disease, and of these, 33 were examined twice, 5 three times, and 1 on four occasions. Of the 260 patients with lesions of the thoracic or abdominal organs or the extremities, 6 had two studies—usually of different areas of the body. Three patients had one " b o d y " and one "neuroimaging" examination. We thus completed a total of 1,052 MRI examinations. In most patients, high-resolution CT scans (2-second and 9-second scanning) were obtained during the period of clinical evaluation in which MRI was completed. Exceptions often included the very young pediatric patients, patients with musculoskeletal soft tissue injuries, and patients with spinal cord disease who were primarily examined with myelography (113 cases). Although MRI was occasionally performed before other imaging studies, interpretation was made with full knowledge of the results of any other such examinations that had been done and of all available clinical information. Subsequently, after all data, including final clinical diagnosis, were complete, CT and myelographic results were compared with the MRI results, and judgments about the relative value of each procedure to the final diagnosis and treatment were recorded. These judgments form the basis for our conclusions. RESULTS: LESIONS OF THE THORACIC OR ABDOMINAL ORGANS OR THE EXTREMITIES As stated previously, MRI of the 260 patients who had "body" lesions showed few normal results because all of these patients had a known abnormality. Our assessments, therefore, were confined to comparison of the relative diagnostic value of MRI and CT. The regions or structures of primary interest (Table 2) included virtually the entire body except the head, neck, and central nervous system. Because we had no capability for making gated images during this study period (in contrast with our current capabilities), organs susceptible to considerable motion artifact were sparsely represented. Chest Conditions.—Because spatial resolution was noticeably better with CT than with MRI and because small pulmonary tumors or mediastinal masses, such as parathyroid adenoma or thymoma, were generally obscured by the motion inherent with the prolonged collection times for MRI data, CT was preferred by most of our radiologists. The superior density discrimination and the additional data collected from the sagittal and coronal images of MRI, however, were deemed to be of considerable diagnostic value in many cases. Table 3 lists

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Table 2.—Magnetic Resonance Imaging of Lesions of the Thoracic or Abdominal Organs or the Extremities Anatomic site Chest Musculoskeletal involvement Tumor Infection Trauma Kidneys Prostate Liver Heart Pancreas Total

No. of examinations 51 44 42 29 35 21 21 15 8 266*

*ln 260 patients.

the variety of pathologic processes that were detected by MRI. Distinguishing hilar nodes or tumors from large vessels was more easily accomplished with MRI than with CT without contrast enhancement (Fig. 2). Because it entails no ionizing irradiation, MRI has become an important procedure for screening pediatric patients with mediastinal widening or suspected lymphoma, thymoma, or vascular abnormalities in the thorax. Musculoskeletal Conditions. Tumor.—Table 4 lists the various musculoskeletal neoplasms disclosed. In all cases, MRI depicted the extent of the lesion and its involvement of and distinction from normal tissue better than did CT. In the presence of a metal prosthesis (used for limb salvage), the CT image was often completely obscured by artifacts, whereas MRI was only minimally affected (Fig. 3). Infection.—The evaluation of infectious processes involving musculoskeletal structures (Table 4) was mainly related to prosthetic joints or opportunistic inflammation in immunosuppressed patients. In these situations, the superior density discrimination of MRI again proved more decisive than CT for identifying the process earlier Table 3.- -Results of Magnetic Resonance Imaging in Patients With Chest Lesions Finding

No. of examinations

Mediastinal or hilar metastasis Primary lung tumor Mediastinal widening Vascular abnormalities Lymphoma Thymoma Mesothelioma Parathyroid adenoma Total

12 12 10 5 5 3 3 1 51

Fig. 2. Axial computed tomogram (CT) (A) and magnetic resonance image (MRI) (S) in patient with bronchogenic carcinoma. Because vessels give no signal in MRI, mass is easily distinguished. Such distinction can be difficult with CT if intravenous contrast material is not used.

in its course and revealing the actual extent of involvement. In patients with pyogenic arthritis that involved prosthetic joints, the relative lack of metallic artifact in MRI also proved decisive in many cases.

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Table 4 , -Results of Magnetic Resonance Imaging in Patients With Musculoskeletal Lesions Finding Tumor Metastasis Chrondrosarcoma Osteogenic sarcoma Lymphoma Lipoma or liposarcoma Aneurysmal bone cyst Giant cell tumor Synovial sarcoma Fibrous histiocytoma Other Infection Lower extremity Pelvis and hips Spinal column Upper extremity Trauma Hematoma Injury to cruciate ligament Injury to ankle ligaments Hamstring tear Nerve compression Quadriceps tear Other

No. of examinations 44 10 10 4 4 3 2 2 2 1 6 42 20 15 5 2 29 10 9 3 2 2 1 2

Finding

Table 5.—Results of Magnetic Resonance Imaging in Patients Who Were Thought To Have Renal or Prostatic Lesions

Renal lesions Carcinoma Cyst Inflammation Prostatic lesions Carcinoma Benign hypertrophy None (normal)

No. of examinations 35 20 10 5 21 16 4 1

Pelvic Conditions.—One of the most fruitful body regions for use of MR evaluation has been the pelvis, where there is little motion to blur the image (Table 5). Our protocol for evaluation of carcinoma of the prostate seems particularly promising (Fig. 6). Other studies of carcinoma of the rectum, bladder, cervix, and uterus were begun after completion of this investigation. Involvement of Other Anatomic Regions.—Diseases of the liver, heart, and pancreas (Table 6) did not lend themselves well to definitive analysis. MRI was either equal to or, more often, inferior to CT in these situations because of motion. It is difficult to understand why pancreatic imaging was so inferior to imaging of the adjacent kidneys and liver. Perhaps transmitted aortic pulsations were an important factor—in which case, the availability of gated scanning, for pancreatic lesions as well as for cardiac disease, should eventually improve the results. Table 6.—Results of Magnetic Resonance Imaging in Patients Who Were Thought To Have Diseases of the Liver, Heart, or Pancreas

Trauma.—Both the multiplanar capabilities and the density resolution of MRI were ideal for the noninvasive display of tendinous, ligamentous, and muscular injuries (Table 4) with a clarity heretofore not possible. The technique has been particularly valuable for visualizing vascular and neural structures that may be affected in the vicinity of more obvious bony abnormalities (Fig. 4). Renal Conditions.—In patients with renal masses or inflammatory processes (Table 5), the superior tissue discrimination of MRI in comparison with CT frequently negated the deleterious effects of respiratory motion. Of equal advantage was the capability of imaging in the sagittal and coronal planes, which yielded important additional data and facilitated diagnosis (Fig. 5).

Finding

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Hepatic lesions Metastasis Metabolic condition Hemangioma Cyst Cardiac lesions Amyloidosis Pericardial fluid Myopathy Ischemia Other Pancreatic lesions Pancreatitis Carcinoma None (normal)

No. of examinations 21 10 5 3 3 15 6 3 2 1 3 3 2 3

Preliminary Comparisons of MRI and CT for ''Body" Imaging.—Preliminary clinical assessments of MRI and CT for conditions of the thoracic or abdominal organs or the extremities are indicated in Table 7. These judgments were based on consideration of such factors as the absence of ionizing irradiation with MRI, the nonavailability of gated scanning, and the deleterious effects of motion on the final image. RESULTS: LESIONS OF THE HEAD A N D NECK OR CENTRAL NERVOUS SYSTEM Patients with otorhinolaryngologic or neurologic symptoms were referred for MRI on the basis of tentative clinical diagnoses. Because of this, we were able to compare not only the relative diagnostic value of MRI

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Fig. 3. A, Roentgenogram of hip in patient with a large femoral prosthetic component. B, Midfemoral computed tomogram through the component, demonstrating extensive artifact due to the metal. Note cortical artifact in normal leg. C, Spin echo magnetic resonance image (echo time 40 ms, repetition time 2,000 ms) at same level as ß, showing no signal in region of component. No artifact or cortical streaking is present in normal leg.

and CT but also the relative clinical efficacy of the two techniques. We had difficulty in classifying some working clinical diagnoses into logical categories for ease of analysis. No questions arose for those patients thought to have a tumor, vascular disease, developmental anomaly, or traumatic, orbital, or metabolic pathologic conditions. Ultimately, we included multiple sclerosis, encephalopathy, leukodystrophy, and radiation necrosis in the "inflammatory" group on the basis that these entities exhibit inflammation in histologic specimens. More perplexing, however, was the task of classifying specific clinical symptom complexes such as seizures, signs of olivopontocerebellar degeneration, primary cerebellar degeneration, Parkinson's disease, psychiatric disorders, dementia, sleep apnea, and dyslexia. To solve our di-

lemma, we formed an artificial category, "clinical neurologic syndromes." In this manner, six groups or categories of cases were delineated. Tumors.—Of the 228 patients referred with the diagnosis of "possible tumor," 71 % proved to have a tumor (Table 8); in 18 patients (8%) the findings were normal, and in 48 patients (21%) some condition other than a tumor was detected. Among those with tumors, the cerebral hemispheres were involved in 71 cases; posterior fossa structures (such as brainstem, cerebellum, and cranial nerves) in 43; clivus, sella, and nasopharynx in 30; and spinal cord in 18. In addition, 12 tumors (8 cerebral, 3 spinal cord, and 1 brainstem) were discovered among the 512 patients with all other tentative diagnoses.

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Fig. 4. Sagittal (A) and axial (ß) spin echo magnetic resonance images (MRI) (echo time 40 ms, repetition time 2,000 ms), demonstrating normal cruciate ligaments. Ligaments give little signal and appear black (arrows). C, Axial spin echo MRI, showing torn anterior cruciate ligament (arrow). Torn ligaments contain blood, are enlarged from edema, and give increased signal. D, In another patient, sagittal view shows anterior cruciate ligament (arrows) that is thin and irregular because of partial tear.

On many occasions, MRI was more sensitive and comprehensive than CT or myelography in detecting alterations related to the presence of a neoplasm. In 10 patients (5 with long-standing seizure disorders) MRI revealed an abnormality when CT or myelography (or both) did not. In most patients, all examinations dis-

closed abnormal findings, but in seven cases (one parasellar, three thoracic cord, and three subarachnoid space tumors), results of all examinations were normal. In no instance were the findings on CT or myelography abnormal and those on MRI normal. SE sequences were almost invariably the most sensitive

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Fig. 6. Axial magnetic resonance inversion recovery image (inversion time 800 ms, repetition time 200 ms) in patient with carcinoma of prostate. Note irregular tissue consistency caused by neoplasm.

for delineating lesions although IR images often aided in characterizing tumors as cystic or solid. Sagittal views were extremely helpful for evaluation of the brainstem and cervical cord, whereas coronal images were most satisfactory for imaging the temporal lobes (Fig. 7). In general, meningiomas exhibited weak T1 and T2 signals even though their mass and the reaction of the brain to the tumor were well seen. The absence of bone artifacts was particularly helpful with lesions in the posterior fossa, base of the skull, and spine. Table 7.—Preliminary Clinical Comparison of Results of Magnetic Resonance Imaging (MRI) and Computed Tomography (CT)

Fig. 5. Magnetic resonance inversion recovery images of kidneys in patient with renal cell carcinoma. A, Axial view (inversion time 500 ms, repetition time 2,000 ms), demonstrating large necrotic mass in right kidney. Adenopathy is present near the vena cava. Note distinction of cortex and medulla in normal left kidney, ß, Sagittal view of right kidney reveals that mass involves lower half and extends into perirenal fat anteriorly.

MRI superior to CT Musculoskeletal lesions Tumors Infection Soft tissue trauma Prostatic carcinoma Certain lesions in pediatric patients Certain cardiac diseases MRI equal to CT Many chest lesions Renal lesions Hepatic lesions Prostatic hypertrophy MRI inferior to CT Pancreatic lesions Thymoma Parathyroid adenoma Small pulmonary nodules

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Table 8.—Results of Magnetic Resonance Imaging in Patients With Tumors of the Central Nervous System Finding Glioma Metastasis Meningioma Pituitary adenoma Acoustic neuroma Lymphoma Chordoma Craniopharyngioma Hemangioblastoma Teratoma or lipoma Miscellaneous (pinealoma, medulloblastoma) Total

No. of patients 84 20 14 9 7 7 7 5 5 4 12 174*

"These 174 tumors were detected in 162 of the 228 patients (71%) w h o had a tentative clinical diagnosis of tumor and in 12 of the 51 2 patients (2%) who had other clinical diagnoses.

Vascular Conditions.—Vascular disease was suspected clinically in 62 patients (Table 9), and MRI revealed "vascular" lesions in 49 of them (79%), nonvascular conditions in 10(16%), and normal findings in 3 (5%). Among the remaining 678 patients who had other tentative clinical diagnoses, 14 were found to have vascular disease, including 8 infarcts and 3 subdural hematomas. Table 9.—Results of Magnetic Resonance Imaging in Patients With Vascular Conditions of the Central Nervous System Finding Infarct Arteriovenous malformation Aneurysm Subdural hematoma Intracerebral hematoma Sinus thrombosis Arteritis Total

No. of patients 32 13 6 6 3 2 1 63*

'These 63 cases were detected in 49 of the 62 patients (79%) with suspected vascular disease and in 14 of the 678 (2%) with other clinical diagnoses.

In 10 patients, the findings were abnormal on MRI but normal on CT. Moreover, in two patients with completed strokes, both studies showed normal findings, and in one patient with a small, calcified, cryptic arteriovenous malformation of the brainstem, results were abnormal on CT but normal on MRI. Infarcts, especially those in the posterior fossa and subcortical regions, were well displayed at a considerably earlier time after ictus by either the SE or the IR technique (Fig. 8) than by CT. In patients with a hemorrhagic infarct, CT was more specific than MRI in re-

Fig. 7. Spin echo magnetic resonance images (echo time 60 ms, repetition time 2,000 ms) of meningioma of tentorium in patient with multiple sclerosis. A, Coronal view. Meningioma gives unusually strong signal near petrous tip with deformity of brainstem. Increased periventricular signals of multiple sclerosis are not prominent. B, Sagittal view, 2 cm lateral to midline. Note parasellar extension of tumor and e x t e n s i v e lesions of m u l t i p l e sclerosis in w h i t e matter supratentorially.

vealing fresh blood. Large arteriovenous malformations were clearly imaged in several planes, and use of the FID or partial saturation SE sequence often enabled the ra-

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diologist to see the vasculature, although not as well as with contrast-enhanced CT. Of all the vascular lesions, subdural hematoma was perhaps most optimally imaged by MRI for detection and diagnosis. Half of the patients with that lesion were referred for MRI with some other tentative diagnosis, and in several of the cases, CT was unrevealing. Inflammatory Diseases.—Among the 215 patients with a tentative diagnosis of "inflammatory" disease, MRI confirmed the diagnosis in 72% (Table 10). In addition, 46 of the 525 patients with other working diagnoses were ultimately classified in this category. This group included 22 patients with suspected spinal cord tumor who proved clinically to have myelitis and 18 with various other tentative diagnoses that the neurologist finally classified in the leukodystrophy, encephalopathy, or multiple sclerosis category.

H B B ^ B H B B B l

Table 10.—Results of Magnetic Resonance Imaging in Patients W i t h Inflammatory Diseases of the Central Nervous System

H B B B l

Finding

No. of patients

H B B B l

Multiple sclerosis

86

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Myelitis Leukodystrophy, radiation therapy Encephalitis

23 13

B B B B ] B B B ^ l H H H B B B B

Encephalopathy Abscess, infection of disk space Meningitis Total

B B B ^ B B ^ B ^ H B B B ^ I

'These 200 cases were detected in 154 of the 215 patients (72%) who na d a tentative clinical diagnosis of inflammatory disease and in 46 of 'he 525 patients (-9%) w h o had other clinical diagnoses.

13 8 200*

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Of the original 215 patients, 37 (17%) were found clinically to have no neurologic disease, and 28 of these patients were seeking a second opinion concerning a diagnosis of multiple sclerosis made elsewhere. The final 24 patients (11 %) were found to have noninflammatory lesions, including neoplasms or vascular disease in 5 each and Arnold-Chiari malformation with syrinx in 4. Among the 86 patients in whom the diagnosis of multipie sclerosis was established by clinical and laboratory methods, 25% had normal findings on MRI and CT, 25% had abnormal results of both studies, and the remaining 50% had abnormal results of only the MRI examination. Multiple sclerosis manifested occasionally as an acute fulminating process, more often as a chronic disease with , regions of cerebral atrophy containing demonstrable

Fig. 8. Magnetic resonance images of infarct of left cerebellum and bellum and cerebellar tonsil. A, Spin echo axial view (echo time 60 ms, repetition >, repetition time 2,033 ms). Increased T2 signal outlines vascular territory of territory of posteroinferior cerebellar artery, ß, Inversion recovery axial view (inal view (mversion time 400 ms, repetition time 1,700 ms). Lack of signal indicates prolonged Τ Ί , and mottled appearance is from hemorrhagicc regions regions in in the infarct.

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plaques, and rarely as only one or two visible lesions. Most commonly, multiple lesions with prolonged T2 w e r e f o u n c | j n the periventricular white matter (Fig. 7 and 9). Such changes were discovered in several patients with clinical signs referable only to the spinal cord. Imaging of

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Fig. 9. Patient with acute multiple sclerosis. A, Computed tomogram with intravenous contrast enhancement. Note large, peripherally enhancing lesion in right frontoparietal region with minimal mass effect. Sagittal magnetic resonance spin echo views (echo time 60 ms, repetition time 2,000 ms) to right (ß) and left (C) of midline. In addition to large acute lesion on the right, other smaller chronic multiple sclerosis plaques were evident in white matter of left hemisphere. Recognition of the latter aided in confirming diagnosis.

the brain, therefore, may be productive in some patients with clinical signs of transverse myelopathy. Developmental Pathologic Conditions.—MRI has had a dramatic impact on the evaluation of suspected developmental pathologic conditions (Table 11). As clinicians recognized that imaging of the spine and spinal cord was possible without invasive measures, referrals of patients for MRI increased even if clinical signs and symptoms were minimal. The 87 patients encountered during the 14-month period of this study were considerably more than those studied neuroradiologically in any prior similar period. That 62 (71 %) of the examinations confirmed the existence of developmental alterations emphasizes the value of MRI in these situations, as does the fact that similar changes were discovered in about 2% of all patients with other clinical diagnoses. MRI revealed nondevelopmental lesions in 17 patients (20%) and normal findings in 8 (9%). In no instance did CT or my-

Table 12.—Results of Magnetic Resonance Imaging in Patients With Traumatic, Orbital, or Metabolic Pathologic Conditions of the Central Nervous System Finding Protruded disk Orbital signs of Graves' disease Contusion Miscellaneous (rhinorrhea, Wilson'!j disease Ihepatolenticular degeneration]) Total

No. of patients 9 7 5 5 26*

*These 26 cases were detected in 21 of the 23 patients (92%) who had a tentative diagnosis of a traumatic, orbital, or metabolic condition and in 5 of the 717 patients (<1 %) who had other clinical diagnoses.

elography show abnormal results when MRI did not, but in five cases, MRI was the only revealing diagnostic study. Arnold-Chiari malformation, with or without an associated syrinx of the cervical cord, was easily and completely evaluated with use of MRI both before and after surgical treatment (Fig. 10). Tethered cord, sacral lipoTable 11.—Results of Magnetic Resonance Imaging in Patients ma, intraspinal meningocele, and arachnoid cysts were With Developmental Pathologic Conditions adequately characterized without recourse to multiple of the Central Nervous System investigations and treatment instituted at an earlier time. Finding No. of patients Although the calcium within the lesions of tuberous Arnold-Chiari malformation, syrinx 36 sclerosis was not imaged with MR, this procedure disAqueductal stenosis, hydrocephalus 15 Meningocele, dysgenesis 11 closed hamartomatous alterations in cerebral gray and Arachnoid cyst, porencephalia 7 white matter at an earlier stage than did CT. We have also Tuberous sclerosis 3 detected alterations in the brains of parents and siblings Empty-sella syndrome 1 of the primary patient even when they had none of the Total 73* usual clinical signs of the disease. Such findings have •These 73 cases were detected in 62 of the 87 patients (71 %) who had a influenced the approach to genetic counseling for these tentative diagnosis of a developmental lesion and in 11 of the 653 families. patients (2%) who had other clinical diagnoses.

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Our meager experience suggests, however, that MRI is more sensitive than CT for the detection of cerebral contusion and can delineate more completely the extent of damage during the healing phase. Although MRI can detect the orbital alterations of Graves' disease or lupus erythematosus, it seems less useful than CT, which has

Fig. 10. Magnetic resonance image of patient with Arnold-Chiari malformation and syrinx of brainstem and cervical cord. Saturation recovery midsagittal view (echo time 40 ms, repetition time 500 ms) reveals mild tonsillar hemiation and normal fourth ventricle. Syrinx involves medulla and cervical cord. Note increased thickness and signal of calvaria from Paget's disease.

Traumatic, Orbital, and Metabolic Conditions.— Although we have had minimal experience with MRI in traumatic, orbital, and metabolic conditions, the tentative diagnosis of such a condition was substantiated in 21 of 23 patients (92%); MRI showed normal findings in 1 patient (4%) and a condition not included in this classification in the other patient (Table 12). Because our MRI unit operates only during the daytime hours, patients who have sustained trauma are often not examined immediately after the incident, and pathologic conditions of the orbits or intervertebral disks are imaged so well with CT that referrals of such cases have been sparse. Table 13.—Results of Magnetic Resonance Imaging in Patients With Clinical Neurologic Syndromes Finding

No. of patients

Atrophy, dementia Seizures Parkinson's disease Psychiatric disorders Miscellaneous (movement disorders, sleep apnea, facial pain, dyslexia, headache) Total

24 17 7 4 7 59*

"These 59 cases were detected in 36 of the 125 patients (29%) who had a tentative diagnosis of clinical neurologic syndrome and in 23 of 615 patients (4%) who had other clinical diagnoses.

Fig. 1 1 . Magnetic resonance images of patients with olivopontocerebellar degeneration. A, Saturation recovery midsagittal view (echo time 40 ms, repetition time 500 ms). Note severe diffuse atrophy of cerebellar vermis and normal supratentorial structures, the " u s u a l " findings in this condition. B, Spin echo axial view (echo time 60 ms, repetition time 2,000 ms) in another patient shows increased signal confined to olivary nuclei. Although cause is unknown, similar alterations in red nuclei have been observed in cases of leukodystrophy.

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Fig. 12. Relative value of neuroimaging techniques in 174 patients with tumors of the central nervous system. CT/M = computed tomography or myelography; NMR = nuclear magnetic resonance imaging.

better spatial resolution. Studies of intervertebral disk disease have thus far been unproductive mainly because we have been unable to angle the plane of MRI slices to pass through the spinal interspaces. Clinical Neurologic Syndromes.—Not unexpectedly,

yet disappointingly, 75 (60%) of the 125 patients who exhibited clinical signs of recognizable neurologic syndromes had normal findings on MRI studies (Table 13). These patients, more than a sixth of those with neurologic disease, were examined when no fee was charged for

Percent NMR > CT/M □

:

c)

SD hematoma Infarct

NMR = CT/M ^

20

40 1

60 1

80

100

1

I

^

^

^

KÄÄÄ^M«

:

Aneurysm

NMR < CT/M M :

IC hematoma AVM

»^Ä

>«^M

^Μ^ΜΜΜ^^ΧΜΜΜΜ WMMwMMMMMmMmm,

Fig. 13. Relative value of neuroimaging techniques in 63 patients with vascular disease of the central nervous system. A V M = arteriovenous malformation; CT/M = computed tomography or myelography; IC = intracerebral; NMR = nuclear magnetic resonance imaging; SD = subdural.

88

MAGNETIC RESONANCE IMAGING

Mayo Clin Proc, February 1985, Vol 60

Percent NMR > CT/M

□

0 I

20 I

40 I

60 I

80 I

100 I

Multiple sclerosis Encephalitis WMD and leukodystrophy Meningitis Encephalopathy

NMR = CT/M

Abscess Myelitis

NMR < CT/M

Fig. 14. Relative value of neuroimaging techniques in 200 patients with inflammatory disease of the central nervous system. CT/M = computed tomography or myelography; NMR = nuclear magnetic resonance imaging; WMD = white matter disease.

MRI and reflect our clinicians' hopes that this new technique might help clarify these often baffling and frustrating conditions. We found MRI worthwhile in patients with long-standing seizure disorders. Among 60 such patients, both MRI

and CT showed abnormal findings in 11, including a glioma, an arteriovenous malformation, a region of vasculitis, and localized scarring in 8. MRI revealed abnormal results while CT showed normal findings in 14 patients, most of whom had a unilaterally increased T2

Percent NMR > CT/M

□

0

I

20

I

40

I

60

I

80

I

100

I

Arnold-Chiari, syrinx Dysgenesis, meningocele Porencephaly, arachnoid cyst Hydrocephalus, AQ stenosis

NMR = CT/M Tuberous sclerosis [_

NMR < CT/M

Fig. 15. Relative value of neuroimaging techniques in 73 patients with developmental conditions. AQ = aqueductal; CT/M computed tomography or myelography; NMR = nuclear magnetic resonance imaging.

Mayo Clin Proc, February 1985, Vol 60

MAGNETIC RESONANCE IMAGING

NMR > CT/M □ : I

40

20

Percent

I

I

89

60

I

80

100

Contusion £

NMR = CT/M

NMR < CT/M W& : Orbital disease Disc herniation

Fig. 16. Relative value of neuroimaging techniques in 26 patients with traumatic, orbital, or metabolic conditions of the central nervous system. CT/M = computed tomography or myelography; NMR = nuclear magnetic resonance imaging.

signal in the deep temporal lobe structures, but 4 lowgrade gliomas were also discovered in this group. In the remaining patients, both studies were unrevealing. In patients who have cerebellar atrophy, we have found MRI superior to CT for assessing the severity of tissue loss. This finding probably relates to the ease with which sagittal and coronal sections can be made. Several

patients with olivopontocerebellar degeneration have demonstrated a peculiar prominence ofthe olivary nuclei in SE images (Fig. 11). Although we do not understand the importance of this finding at present, we are pursuing further studies to characterize it more completely. Relative Value of MRI in Imaging of the Head and Neck or Central Nervous System.—Our tentative judg-

Percent c)

NMR > CT/M □ : Seizures Psychiatric disease Atrophy

20

I

40

I

60

I

80

I

100

P*m^

I

I I I I Ä I P »

NMR = CT/M ^ : Parkinson's Misc. neuro NMR < C T / M ^ :

IÄ^ÄM;^«M^

^«^^Ä^^

°I

Fig. 17. Relative value of neuroimaging techniques in 59 patients with certain neurologic syndromes. CT/M = computed tomography or myelography; NMR = nuclear magnetic resonance imaging.

90

Mayo Clin Proc, February 1985, Vol 60

MAGNETIC RESONANCE IMAGING

ments concerning the relative contributions of MRI, CT, and myelography to the final clinical diagnosis and treatment of various head, neck, and neurologic diseases and syndromes are recorded in Figures 12 through 17. The various conditions encountered in our brief experience were classified in 6 major categories that contained a total of 36 diagnostic-pathologic subdivisions, and we concluded that MRI was at least equal to or even superior to CT or myelography (or both) for the detection and characterization of various lesions in 30 of the 36 subdivisions. Thissuperiority of MRI was mainly the result of its exquisite sensitivity to alterations in the cellular environment of the tissues, which often were minimal. Other advantages of the MR technique which also influenced our judgments were the capability of obtaining views in several planes, the absence of artifacts due to dense bone, and the elimination of ionizing irradiation. The disadvantages of MRI were graphically illustrated in those conditions in which CT or myelography was judged superior. The inability to depict calcification was detrimental to the specific diagnosis of meningioma, craniopharyngioma, aneurysm, and other calcified lesions. The difficulty with distinguishing fresh from old bleeding with use of MRI led us to prefer CT in many acute conditions. The inferior spatial resolution of MRI (in comparison with CT), often compounded by slight motion during prolonged collection of data, was disturbing in the study of orbital and disk disease. The absence of an easily obtainable contrast medium and the inability to angle the plane of the imaging slices were other disadvantages of MRI noticed by those of us who are accustomed to these features of CT. Inevitably, our findings and conclusions will be modified as improvements and advances develop. More powerful magnetic fields, the perfection of surface coils and contrast media, and the refinement of computer programs will improve image quality and enhance diagnosis. Accumulating experience should sharpen our insights and improve our techniques. Even at this early stage, however, MRI is obviously a very powerful clinical diagnostic tool that in many applications is more sensitive than CT and myelography. As MRI instruments become more universally available and as the examination of patients becomes more expeditious and economic, MRI might become the preferred primary imaging technique in screening for disease processes.

REFERENCES 1.

2.

3.

4.

5.

6.

7.

8.

9.

10.

11.

12.

13.

14.

15.

Bydder G M , Steiner RE, Young IR, Hall AS, Thomas DJ, Marshall I, Pallis CA, Legg N): Clinical NMR imaging of the brain: 140 cases. A)NR 3:459-480, 1982 Alfidi RJ, Haaga JR, El Yousef S), Bryan P), Fletcher BD, LiPuma )P, Morrison SC, Kaufman B, Richey JB, Hinshaw WS, Kramer D M , Yeung H N , Cohen A M , Butler HE, Ament AE, Lieberman )M: Preliminary experimental results in humans and animals with a superconducting, whole-body, nuclear magnetic resonance scanner. Radiology 143:175-181, 1982 Bryan RN, Willcott MR, Schneiders N), Ford )J, Derman HS: Nuclear magnetic resonance evaluation of stroke. Radiology 149:189-192, 1983 Brady T), Buonanno FS, Pykett IL, New PFJ, Davis KR, Pohost G M , Kistler JP: Preliminary clinical results of proton (' H) imaging of cranial neoplasms: in vivo measurements of T, and mobile proton density. AJNR 4:225-228, 1983 Zimmerman RA, Bilaniuk LT, Goldberg HL, Grossman Rl, Levine RS, Lynch R, Edelstein W , Bottomley P, Redington R: Cerebral NMR imaging: early results with a 0.12 T resistive system. AJR 141:1187-1193, 1983 Webb WR, Gamsu G, Stark D D , Moore EH: Magnetic resonance imaging of the normal and abnormal pulmonary hila. Radiology 152:89-94, 1984 Ross JS, O'Donovan PB, Novoa R, Mehta A, Buonocore E, Maclntyre WJ, Golish JA, Ahmad M: Magnetic resonance of the chest: initial experience with imaging and in vivo T1 and T2 calculations. Radiology 152:95-101, 1984 Randell CP, Collins A G , Young IR, Haywood R, Thomas DJ, McDonnell MJ, OrrJS, Bydder G M , Steiner RE: Nuclear magnetic resonance imaging of posterior fossa tumors. AJR 141:489-496, 1983 Brant-Zawadzki M , Davis PL, Crooks LE, Mills C M , Norman D, Newton T H , Sheldon P, Kaufman L: NMR demonstration of cerebral abnormalities: comparison with CT. AJNR 4:117-124, 1983 Modic MT, Pavlicek W , Weinstein MA, Boumphrey F, Ngo F, Hardy R, Duchesneau PM: Magnetic resonance imaging of intervertebral disk disease: clinical and pulse sequence considerations. Radiology 152:103-111, 1984 Brant-Zawadzki M, Badami JP, Mills C M , Norman D, Newton TH: Primary intracranial tumor imaging: a comparison of magnetic resonance and CT. Radiology 150:435-440, 1984 Webb WR, Gamsu G, Crooks LE: Multisection sagittal and coronal magnetic resonance imaging of the mediastinum and hila. Radiology 150:475-478, 1984 Han JS, Bonstelle CT, Kaufman B, Benson JE, Alfidi RJ, Clampitt M, Van Dyke C, Huss RG: Magnetic resonance imaging in the evaluation of the brainstem. Radiology 150:705-712, 1984 Gamsu G, Stark D D , Webb WR, Moore EH, Sheldon PE: Magnetic resonance imaging of benign mediastinal masses. Radiology 151:709-713, 1984 Brant-Zawadzki M, Norman D, Newton T H , Kelly W M , Kjos B, Mills C M , Dillon W , Sobel D, Crooks LE: Magnetic resonance of the b r a i n : the o p t i m a l s c r e e n i n g t e c h n i q u e . Radiology 152:71-77, 1984