Significant Difference In Signal Intensity Research Articles

Hyperintense Cerebrospinal Fluid on FLAIR Images Induced by Ventilation with 100% Oxygen

To investigate in a prospective randomized study setting if increased signal intensity of the cerebrospinal fluid (CSF) on fast FLAIR images is caused by high oxygen concentrations or anesthetic agents used during general anesthesia. 40 children (13 females/27 males) aged 3 months to 8 years were included. The study was approved by the ethics committee of the authors' institution. Parents gave written informed consent to participation of their children. Patients were randomly allocated to one of four different anesthesia techniques: sevoflurane plus 30% oxygen, sevoflurane plus 100% oxygen, propofol plus 30% oxygen, and propofol plus 100% oxygen. Hard copies of the FLAIR sequence were used for blinded analysis of the signal intensity of the subarachnoid space. No significant difference in signal intensity of the CSF was detected between anesthesia with propofol or sevoflurane irrespective of using 30% or 100% oxygen during anesthesia. On the other hand, signal intensity of the CSF was increased when sevoflurane or propofol was combined with 100% inhaled oxygen. The difference of the CSF signal intensity was most pronounced over the cerebral convexities (p < 0.005) but was also observed in the basal cisterns. Hyperintense signal in the subarachnoid space can result from supplemental oxygen during anesthesia. To avoid misdiagnosis such as subarachnoid hemorrhage, purulent meningitis or meningeal carcinomatosis, radiologists should be aware of the phenomenon of increased cerebrospinal fluid signal intensity on T2-weighted FLAIR images caused by supplemented oxygen.

MR findings in Acute Disseminated Encephalomyelitis in Children

Purpose: We reviewed the distribution of lesion and the characteristics of the MR findings of acute disseminated encephalomyelitis (ADEM) in children. We evaluated the differences in the imaging findings and the clinical outcomes between the patients with deep gray matter involvement and the patients without deep gray matter involvement. Materials and Methods: We retrospectively reviewed the 62 MR examinations of 21 patients who were discharged with the clinical diagnosis of ADEM. The patients were aged from 13 months to 12 years old (mean age: 4.5 years). Follow-up MR examinations were done one to 5 times (mean: 3 times) for 2 weeks to 4 years (mean: 3 months) after the initial examination. We compared the signal intensity on T2WI, the enhancement and residue on the MR images and the clinical outcomes between the patients with deep gray matter involvement and the patients without deep gray matter involvement. Results: A total of 21 patients had white matter abnormalities on their initial MR. Fifteen patients (71%) had foci of increased signal intensity on T2WI in the deep gray matter: thalamus (n=15), globus pallidus (n=14) and putamen (n=10). On the followup images, all patients showed decreased signal intensity and enhancement of their lesion. We could not find the significant differences in signal intensity, enhancement and residue on the MRIs and also the clinical outcomes between the patients with deep gray matter involvement and the patients without deep gray matter involvement (<.05). Conclusion: There were no significant differences in the characteristics of the imaging and the clinical outcomes between the ADEM patients with deep gray matter involvement and those ADEM patients without deep gray matter involvement.

Functional magnetic resonance imaging during hypotension in the developing animal.

Hypotension in adult animals recruits brain sites extending from cerebellar cortex to the midbrain and forebrain, suggesting a range of motor and endocrine reactions to maintain perfusion. We hypothesized that comparable neural actions during development rely more extensively on localized medullary processes. We used functional MRI to assess neural responses during sodium nitroprusside challenges in 14 isoflurane-anesthetized kittens, aged 14-25 days, and seven adult cats. Baseline arterial pressure increased with age in kittens, and basal heart rates were higher. The magnitude of depressor responses increased with age, while baroreceptor reflex sensitivity initially increased over those of adults. In contrast to a decline in adult cats, functional MRI signal intensity increased significantly in dorsal and ventrolateral medullary regions and the midline raphe in the kittens during the hypotensive challenges. In addition, significant signal intensity differences emerged in cerebellar cortex and deep nuclei, dorsolateral pons, midbrain tectum, hippocampus, thalamus, and insular cortex. The altered neural responses in medullary baroreceptor reflex sites may have resulted from disinhibitory or facilitatory influences from cerebellar and more rostral structures as a result of inadequately developed myelination or other neural processes. A comparable immaturity of blood pressure control mechanisms in humans would have significant clinical implications.

(13)C nuclear magnetic resonance spectra of natural undiluted lipids: docosahexaenoic-rich phospholipid and triacylglycerol from fish.

In the (13)C NMR spectra of natural, unenriched docosahexaenoic acid-rich sardine oil and cod muscle glycerophosphocholine significant signal intensity differences across the 1D spectrum between undiluted and diluted samples were observed. In undiluted samples (13)C-(13)C 2D nuclear Overhauser enhancement spectroscopy (NOESY) interchain cross-peaks for CH, CH(2), CH(3), and C=C structures were observed. Results indicate that in undiluted natural lipids, NMR signal intensity is influenced by polarization transfer from the extended lipid structure. The NOE enhancement of specific molecular sites especially in unsaturated lipids is evidence that some natural lipids remain oriented relative to each other and in an orderly arrangement at the molecular level long enough for the effect to be detected by the NMR experiment. The presence of polyunsaturated fatty acids in mixtures of natural lipids could stabilize specific local molecular conformations within the remaining less saturated lipids.

High intensity focused ultrasound ablation of kidney guided by MRI

The effectiveness of magnetic resonance imaging (MRI) to monitor therapeutic protocols of high-intensity focused ultrasound (HIFU), in freshly excised pig kidney cortex is investigated. For high quality imaging, the pulse sequence fast spin echo (FSE) T1- and T2-weighted, and proton density were evaluated. For fast imaging, the pulse sequence T1-weighted fast spoiled gradient (FSPGR) was used. The main goal was to evaluate the MRI detection of large lesions (bigger than 1 cm × 1 cm × 1 cm) that is achieved by moving the transducer in a predetermined pattern. The contrast between lesion and kidney tissue is excellent with either T1-weighted or T2-weighted FSE. With T1-weighted FSE, the best contrast is observed for recovery time (TR) between 200 ms and 400 ms. With T2-weighted FSE best contrast can be achieved for echo time (TE) between 16 and 32 ms. T2-weighted FSE was proven as the best pulse sequence to detect cavitational activity. This advantage is attributed to the significant difference in signal intensity between air spaces and necrotic tissue. Air spaces appear brighter than thermal lesions. Therefore, for therapeutic protocols created using cavitational mode, T2-weighted FSE may be the optimum pulse sequence to use. The proton density pulse sequence does not provide any advantage over the T1- and T2-weighted pulse sequences. Using T1-weighted FSPGR, acquisition time as low as 5 s could be achieved. Good contrast and signal-to-noise ratio (SNR) are achieved with TR = 100 ms and flip angle between 75 to 90°. The above techniques were very successful in detecting large lesion volumes. (E-mail: cdamianou@cytanet.com.cy)

MR Distinction between Multiple Myeloma and Metastasis Involving the Spine

Purpose: To differentiate multiple myeloma from metastasis involving the spine at MR imaging. Materials and Methods: Twenty-five patients with multiple myeloma and 37 with vertebral metastasis were included in this study. MR images were retrospectively analyzed with regard to infiltration and enhancement patterns, signal intensity, the involvement of three consecutive vertebrae, the number of lesions within one vertebra, and paraspinal and epidural masses. Using a 1.5-T imager, we obtained sagittal and axial, unenhanced and enhanced T1-weighted images, and fast spin-echo images. For statistical analysis, Fisher’s exact test was used. Results: All cases of multiple myeloma and metastasis showed low signal intensity on T1-weighted images, and there were no significant differences in signal intensities or enhancement patterns. Infiltration and enhancement patterns were classified as focal (52% in multiple myeloma vs 68% in metastasis, p> 0.05), diffuse (32% vs 32%, p > 0.05) or salt and pepper (16% vs 0%, p 0.05), isointensity (36% vs 3%, p 0.05). Paraspinal and epidural masses played little part. Conclusion: The salt and pepper infiltration pattern, the presence of more than five lesions within one vertebra, and the involvement of more than three consecutive vertebrae were useful MR findings for differentiation between multiple myeloma and metastasis involving the spine. In most cases, however, it is difficult to distinguish between the two conditions.

Apparent diffusion coefficient measurements in progressive supranuclear palsy.

We measured the apparent diffusion coefficient (ADC), using diffusion-weighted imaging (DWI) and signal intensity on T2-weighted MRI in the cerebral white matter of patients with progressive supranuclear palsy (PSP) and age-matched normal subjects. In PSP, ADC in the prefrontal and precentral white matter was significantly higher than in controls. There was no significant difference in signal intensity on T2-weighted images. The ADC did correlate with signal intensity. The distribution of the elevation of ADC may be the consequence of underlying pathological changes, such as neurofibrillary tangles or glial fibrillary tangles in the cortex. Our findings suggest that ADC measurement might be useful for demonstrating subtle neuropathological changes.

MR Findings of Bowel Ischemia with Mesenteric Vascular Occlusion: Comparison with Pathologic Findings in a Cat Model

Purpose : In order to determine the characteristic MR findings for the early diagnosis of bowel ischemia, we analysed the dynamic enhanced MR images of ischemic bowel induced by mesenteric vascular occlusion in a cat model, and compared the T1-and T2- weighted images (WI) of extracted bowel with the pathologic findings. Materials and Methods : According to the ischemic period, twelve cats were assigned to either the normal control group (no ischemic period, n=2), the acute ischemic group (ligation of mesenteric vessels for 3 hours, n=6) or the subacute ischemic group (ligation of mesenteric vessels for 10 hours, n=4). Under general anes-thesia,laparotomy was performed. The ileal artery and vein were ligated, and a columnar surface coil was ap-plied to the expected bowel ischemia. Using a 4.7 T MR scanner, contrast-enhanced T1WI were obtained, after bolus injection of contrast media, at 10, 20, 30, 60, and 90minutes. After formalin fixation of the extracted bowel, T1- and T2WI were obtained, and the specimens were pathologically examined. MR signal intensity at each layer of the bowel wall was measured and compared with the histopathologic findings. Results : On contrast enhanced MR images, the submucosal layer showed most intensive enhancement, fol-lowed-in decreasing order of signal intensity- by muscle and mucosa. Time to peak enhancement of bowel wall was 10-minutes in the normal control group, and 20 and 60minutes in the acute and subacute bowel is-chemia groups, respectively. On T1WI, no significant differences in signal intensity were observed between the ischemic group and the normal control group. On T2WI, the signal intensity of the submucosal layer of the acute ischemic group was significantly higher than that of the normal control or subacute ischemic group, and the signal intensity of the muscular layer of the ischemic group was significantly higher than that of the normal control group. Conclusion : Time to peak enhancement of bowel wall was a helpful criterion for assessment of the ischemic period. Analysis of the signal intensity of the bowel wall layer was useful for the early detection of bowel ischemia.

Diffusion MR Imaging in Patients with Intracranial Tumors

Purpose: To assess the usefulness of diffusion-weighted MR imaging in patients with intracranial tumors. Materials and Methods: Using the single-shot spin echo EPI technique on a 1.5T unit and two gradient steps(b values of 0, 900 s/mm2), diffusion-weighted MR images (DW-MRI) of 76 patients with various intracranial tumors including high-grade glioma (n =20), meningioma (n =15), metastasis(n =14), lymphoma (n =6), low-grade glioma (n =5), schwannoma (n =4), cerebellar hemangioblastoma (n =3), - and others- were obtained. The signal intensity of each tumor was visually assessed as one of four grades, and this and apparent diffusion coefficient(ADC) were analyzed in the solid and cystic portions of tumors, normal gray matter, white matter and CSF. Results: Lymphomas, metastases, meningiomas, and high- and low-grade gliomas showed low ADC values in increasing order. Tumors showing high signal intensity on DW-MRI had low ADC values. Visual assessment whowed that solid portions of high-grade gliomas were significantly more hyperintense than those of low-grade gliomas. There was, however, no significant difference in ADCs between high- and low-grade gliomas. Lymphoma a and metastases showed significantly higher signal intensities on DW-MRI and lower ADCs than did high-grade gliomas. There were significant differences in signal intensities, as seen on DW-MRI, and in ADCs, between metastatic adenocarcinomas and non-adenocarcinomas. Schwannomas and cerebellar heman-gioblastomas showed low signal intensities and high ADC values. Conclusion: DW-MRI appears to provide an additional means of examining intracranial tumors, not available with conventional MRI, and may thus be helpful in the grading of gliomas and the differential diagnosis of some intracranial tumors.

Comparison of Nuclear Magnetic Resonance Microimages and Histology of Rat Ovaries.

Nuclear magnetic resonance (NMR) microscopy is a magnetic resonance imaging technique with an enhanced spatial resolution. In this study, fresh ovaries of mature rats immersed in phosphate buffered saline (PBS) were examined by NMR microscopy. Histological sections corresponding to NMR microimages were prepared, and components in ovaries were identified in microimages by comparison with light microscopic images. Signal intensities of antral follicles, corpora lutea (CL), stroma, adjacent fat tissue and PBS were measured in images with different echo times (TE) and analyzed. As TE increased, signal intensities decreased in CL and connective tissue including the stroma, while those in PBS and follicles changed less. Fat showed significantly high signals compared with other components at each TE. Stroma showed significantly low signals than other components except PBS and follicles at TE of 5 msec. There were no significant differences among CL, follicles and PBS at TE of 5 msec. At TE of 20 msec, however, there were significant differences in signal intensities between each components in the rank order fat > PBS > follicles > CL > stroma. Significant regression of signal intensity was seen on TE in follicles, CL and stroma. NMR microscopy is considered to be a useful tool to investigate the physiological function of rat ovaries.

Prediction of impending hemorrhagic transformation in ischemic stroke using magnetic resonance imaging in rats.

Hemorrhagic transformation (HT) of ischemic brain tissue may occur in stroke patients either spontaneously or after thrombolysis. A method to assess the risk of HT in ischemic tissue after stroke would improve the safety of thrombolytic therapy. As a means of predicting HT, we investigated the role of contrast-enhanced MRI at acute time points in a rat middle cerebral artery occlusion model with reperfusion. Intraluminal suture occlusion of the middle cerebral artery was used to produce transient ischemia in male Wistar rats (n=11). Reperfusion was performed by withdrawal of the occluding filament after 2 (n=4), 3 (n=6), or 4 (n=1) hours. MRI studies were performed before and after reperfusion with the use of conventional T1-weighted imaging, with and without gadolinium (Gd-DTPA) contrast agent, and T2-weighted imaging. Follow-up MRI and histological studies were obtained at 24 hours. Petechial hemorrhage occurred by 24 hours in 9 of 11 animals. All animals showed brain swelling and cellular death throughout the ischemic region at 24 hours. A hyperintense region in the preoptic area became visible after Gd-DTPA injection within minutes after reperfusion in animals with subsequent HT. All animals showing acute Gd-DTPA enhancement subsequently developed petechial hemorrhage (or died) by 24 hours. In these animals, statistically significant differences in signal intensity (P=.0005) between the ipsilateral enhancing region and a homologous contralateral region were detected on post-Gd-DTPA T1-weighted imaging. There was also a statistically significant correlation (P=.01) between the rate of Gd-DTPA uptake and the size of the enhancing area. Two animals did not enhance with Gd-DTPA and did not exhibit hemorrhage on histological examination or MRI at 24 hours. No abnormalities were seen on precontrast T1-weighted images before and shortly after reperfusion or postcontrast T1-weighted images before reperfusion. The primary finding of this study was the detection of early Gd-DTPA parenchymal enhancement in 82% of the animals after reperfusion. Enhancement was seen before any detectable hemorrhage, suggesting that early endothelial ischemic damage occurs before gross brain infarction and hemorrhage. Thus, we suggest that acute Gd-DTPA enhancement may provide an early prediction of petechial hemorrhage.

Verapamil reduces the size of reperfused ischemically injured myocardium in hypertrophied rat hearts as assessed by magnetic resonance imaging

Contrast-enhanced magnetic resonance (MR) imaging was used to detect and quantify the extent of myocardial injury after a brief coronary occlusion and reperfusion in response to verapamil treatment in a rat model of left ventricular hypertrophy (LVH). Two groups of rats were prepared by banding the abdominal aorta for 7 to 8 weeks to produce LVH. Group 1 ( n = 13) received oral verapamil for 3 days, whereas group 2 ( n = 13) received no therapy. Before MR examination was performed, each rat was subjected to 25 min of coronary artery occlusion followed by 1 hour of reperfusion. T1-weighted spin echo images were acquired before and after 0.3 mmol/kg gadoteridol was injected. Three images were acquired at contiguous levels of the LV and used to estimate the size of the myocardial injury. The size of the infarcted region was demarcated at postmortem examination by using triphenyltetrazolium chloride dye (TTC). Before contrast medium was administered, no significant difference in signal intensity was seen between nonischemic and reperfused ischemically injured myocardium. After gadoteridol was injected, a hyperintense zone indicative of myocardial injury was observed in 8 of 13 rats treated with verapamil and in all untreated animals. The size of the injury was significantly larger in untreated hearts than in hearts treated with verapamil as defined on MR images (25% ± 5% vs 18% ± 5%, p < 0.05) and TTC staining (12% ± 4% and 4% ± 1%, p < 0.05). Good correlation ( r = 0.91) was found between the two measurements. No significant difference in the size of jeopardy area was seen between the two groups as (defined by blue dye infusion). In conclusion, contrast-enhanced MR imaging is a suitable technique to evaluate the effects of therapies applied to reduce myocardial injury. Verapamil can cause reduction in the extent of ischemic injury after reperfusion of hypertrophied myocardium.

Reperfusion and irreversible myocardial injury: identification with a nonionic MR imaging contrast medium.

The potential of a new nonionic gadolinium complex--gadodiamide injection--to (a) allow distinction between reperfused and occlusive infarction and (b) enable differentiation between reperfused reversible and irreversible myocardial injury was investigated. Three groups of rats were used: 10 with reversibly reperfused myocardial injury, 10 with irreversibly reperfused injury, and 10 with occlusive infarction. Before administration of contrast material, there was no significant difference in signal intensity between normal and injured regions on T1-weighted images. After administration of gadodiamide injection (0.2 mmol/kg), the reversibly injured myocardium was indistinguishable from normal myocardium, while the reperfused irreversibly injured zone showed prominent and homogeneous enhancement. Occlusive infarcts showed three zones of differential enhancement consisting of normal, periinfarction, and infarction regions. Gadodiamide injection provides differential enhancement in reversibly reperfused, irreversibly reperfused, and occlusive infarcts. Thus, it may be useful as a marker of reperfusion and extent of infarction after thrombolytic therapy.

Formulation of radiographically detectable gastrointestinal contrast agents for magnetic resonance imaging: Effects of a barium sulfate additive on MR contrast agent effectiveness

Complete and homogeneous distribution of gastrointestinal (GI) contrast media are important factors for their effective use in computed tomography as well as in magnetic resonance (MR) imaging. A radiographic method (using fluoroscopy or spot films) could be effective for monitoring intestinal filling with GI contrast agents for MR imaging (GICMR), but it would require the addition of a radiopaque agent to most GICMR. This study was conducted to determine the minimum amount of barium additive necessary to be radiographically visible and to evaluate whether this additive influences the signal characteristics of the GICMR. A variety of barium sulfate preparations (3-12% wt/vol) were tested in dogs to determine the minimum quantity needed to make the administered agent visible during fluoroscopy and on abdominal radiographs. Solutions of 10 different potential GI contrast agents (Gd-DTPA, ferric ammonium citrate, Mn-DPDP, chromium-EDTA, gadolinium-oxalate, ferrite particles, water, mineral oil, lipid emulsion, and methylcellulose) were prepared without ("nondoped") and with ("doped") the barium sulfate additive. MR images of the solutions in tubes were obtained at 0.38 T using 10 different spin-echo pulse sequences. Region of interest (ROI) measurements of contrast agent signal intensity (SI) were made. In addition, for the paramagnetic contrast media, the longitudinal and transverse relaxivity (R1 and R2) were measured. A 6% wt/vol suspension of barium was the smallest concentration yielding adequate radiopacity in the GI tract. Except for gadolinium-oxalate, there was no statistically significant difference in SI for doped and non-doped solutions with most pulse sequences used. In addition, the doped and nondoped solutions yielded R1 and R2 values which were comparable. We conclude that barium sulfate 6% wt/vol added to MR contrast agents produces a suspension with sufficient radiodensity to be viewed radiographically, and it does not cause significant alteration in the MR signal appearance of most GICMR. These formulations can be useful for achieving optimal filling of the gastrointestinal tract prior to MRI.

In situ hybridization histochemistry of Spot 35 protein, a calcium-binding protein, in the rat brain

Using in situ hybridization, we analyzed the localization of mRNA for Spot 35 protein (Spot 35), a calcium-binding protein of the EF-hand type, in the rat cerebellum at various developmental stages. A cDNA fragment corresponding to part of the 3'-noncoding region was 35S-labeled and used as a hybridization probe. Autoradiographic signals for Spot 35 mRNA were detected in all the Purkinje cells, but not in any other neurons or glial cells in the adult rat cerebellum. There was no significant difference in signal intensity among individual cells. The signals were observed exclusively in Purkinje cell bodies, but not in their processes, in striking contrast to previous immunohistochemical studies in which Spot 35 protein was demonstrated in both cell bodies and processes. In the time-course study, signals for Spot 35 mRNA were detected in Purkinje cell bodies weakly at embryonic day 19, thereafter more intensely at more developed stages and most intensely at postnatal days 30 and 60 (adulthood). The signal intensities of individual cells were similar at each of these developmental stages except for the very early stages at which signals were weak and slightly variable among cells. These findings, especially that of the characteristic coordinated expression of Spot 35 mRNA at given stages, should prove useful in studies of degenerative diseases in the cerebellum in experimental animals and man. A weak expression of Spot 35 mRNA in some of non-Purkinje cells was also noted.

Reversible and irreversible injury in the reperfused myocardium: differentiation with contrast material-enhanced MR imaging.

Thrombolytic agents are being used with increasing frequency to produce reperfusion of acute myocardial infarction in humans. This study was designed to assess the potential of a magnetic resonance (MR) contrast agent, the manganese chelate of N,N'-bis(pyridoxal-5-phosphate) ethylenediamine-N,N'-diacetic acid (DPDP), in differentiating between reversible and irreversible myocardial injury during reperfusion. Ischemia was produced in rats by occlusion of the left coronary artery for either 15 minutes (n = 10) or 2 hours (n = 10), followed in both cases by 30 minutes of reperfusion. Signal intensity (SI) was measured before and after (every 15 minutes for 1 hour) the administration of Mn-DPDP. Prior to intravenous injection of the contrast agent, no significant difference in SI was observed between normal and reversibly or irreversibly injured myocardium. Mn-DPDP produced greater enhancement of SI of the irreversibly injured region compared with normal myocardium. There was no differential enhancement of the reversibly injured region compared with normal myocardium. Thus, Mn-DPDP is useful in discriminating reversible from irreversible injury in reperfused myocardium.

Occlusive and reperfused myocardial infarcts: differentiation with Mn-DPDP--enhanced MR imaging.

To assess whether the administration of manganese N,N'-bis(pyridoxal-5-phosphate)ethylenediamine-N,N'-diacetic acid (DPDP) permits differentiation between occlusive and reperfused infarcts, the authors subjected rats to either 6 hours of left coronary artery occlusion (n = 13) or 2 hours of occlusion followed by 4 hours of reperfusion (n = 10) before magnetic resonance (MR) imaging. Electrocardiographic-gated T1-weighted images were obtained before and for 1 hour after injection of 400 mumol/kg of Mn-DPDP. On T1-weighted images obtained before injection of Mn-DPDP. no significant differences in signal intensity were observed between normal and infarcted regions. Use of Mn-DPDP permitted delineation of the area of infarction. The pattern of enhancement in the injured zone was different for occlusive and reperfused myocardial infarcts. In rats with occlusive infarcts, In rats with occlusive infarcts, three well-defined zones were seen. Epicardium and endocardium were enhanced, while the midmyocardial zone was hypointense. The midmyocardial signal intensity gradually increased during the 60 minutes after injection. In rats with reperfused infarcts, the injured area was uniformly and intensely enhanced. Histologic examination confirmed the presence and location of myocardial infarct. Mn-DPDP may improve the detection and delineation of acute myocardial infarcts, demonstrate perfusion of the infarct, and permit discrimination between reperfused and occlusive infarcts.

Magnetic resonance imaging of malignant fibrous histiocytoma

The magnetic resonance imaging (MRI) changes in 39 patients with malignant fibrous histiocytoma (MFH) were reviewed retrospectively. Twenty-one sarcomas were in the lower extremity, five each in the upper extremity and trunk, two each in the neck and heart, and one each in the maxillary sinus, sella turcica, tongue, and spermatic cord. The examinations were performed with spin-echo sequences on a 1.5 Tesla Signa Scanner (GE, Milwaukee WI). Twenty-two tumors exhibited intermediate signal intensity on T 1-weighted images and 23 were of high signal intensity on T 2-weighted images. There was no significant difference in signal intensity of 12 preoperative and 13 recurrent neoplasms. Twelve of 13 patients were correctly diagnosed as having postoperative changes. The MR sensitivity and specificity for detecting a neoplasm were 96% and 83% respectively, but the signal changes were nonspecific for MFH. When compared to CT in 14 patients, MR better defined the extent of the MFH, its relationship to surrounding tissues and vessels, and best differentiated residual or recurrent disease from postoperative changes when examined at least 3 months after surgery.