High signal regions in normal white matter shown by heavily T2-weighted CSF nulled IR sequences.

Inversion recovery (IR) sequences with an inversion time (TI) designed to markedly reduce or null the signal from CSF (TI of approximately 2,100 ms at 1.0 T) and a very long echo time (TE) of 240 ms were used to image the brain of two normal adult volunteers, one 34-year-old man with an intrinsic tumor, and one 3-month-old infant with an infarct. Using these very heavily T2-weighted pulse sequences, adult gray and white matter showed similar signal intensity in many areas of the brain, but normal white matter in regions of the centrum semiovale, posterior internal capsule, parietopontile tract, occipitothalamic radiation, and brain stem showed a much higher signal intensity than surrounding gray or white matter. The infant displayed a low signal intensity in myelinated regions in the internal capsule and occipitothalamic radiation and a high signal in unmyelinated white matter. In many of the images there were strong similarities to the distribution of high signal within white matter seen with pulsed gradient spin echo sequences (TE 130 ms) designed to demonstrate effects due to anisotropic diffusion. Arguments are advanced to support the view that the high signal intensity in white matter tracts is due to one or more long T2 components that may be associated with unmyelinated or sparsely myelinated fibres within white matter. The resemblance to diffusion weighted images may reflect the fact that both employ long TEs and both produce a low signal from CSF. If myelin possessed a different susceptibility from axoplasm so that magnetic field gradients were generated around nerve fibres when their orientation was not parallel to B0, diffusion of water might then produce the observed dependence on fibre direction. The high signal regions in white matter are a potential source of confusion in image interpretation, and measurements of T2 in white matter need to be made with these regional variations in mind. The concept of normal appearing white matter also needs to be applied with a knowledge of these differences. The IR sequences used in this study provide a very high T2 dependence with a low signal from CSF and may be useful for detecting disease in the CNS of adults and children.     

Subacute intracranial hemorrhage: contribution of spin density to appearance on spin-echo MR images

The T2 and pseudodensity (proportional to proton density) of intracranial hemorrhages and normal white matter were calculated. The mean T2 (+/- standard deviation) was 120 +/- 62 for hemorrhage and 61 +/- 11 for white matter. Pseudodensity values were normalized to a white matter value of 1, and the value for hemorrhage was 1.56 +/- 0.28. These values were used to determine which components of hemorrhage-white matter contrast are due to T1, T2, and density. The results indicate that on spin-echo (SE) images obtained with a long repetition time (TR)/short echo time (TE) (2,500/0-20 [TR msec/TE msec]), the contrast is mainly due to density differences, with a modest T2 contribution on 20-msec-TE images and nearly no T1 component. At 600/0-20, the contrast continues to be largely determined by density differences, again with a modest T2 component on 20-msec-TE images. If the T1 of hemorrhage is extremely short, the T1 component of contrast on 600/0-20 SE images will be somewhat greater than the density component. Because contrast on short TR/short TE images may be largely or entirely determined by pseudodensity or T2, it is inaccurate to refer to 600/20 images as "T1-weighted". The assumption that high signal intensity at this sequence implies a "short T1" will lead to misleading conclusions.     

MR imaging of peripheral cholangiocarcinoma.

A prospective study was performed to compare MR spin-echo (SE) sequences [repetition time/echo time (TR/TE) 2,000/80, 500/44 ms], unenhanced CT, and rapid intravenous contrast enhanced CT in eight consecutive patients with peripheral cholangiocarcinoma. All the tumors (ranging from 5 to 9.6 cm in size) were detected with all four techniques. Tumor contrast, however, was qualitatively greatest on long TR/TE SE images. With long TR/TE SE images, tumors were demonstrated as well-demarcated homogeneous regions of high signal intensity, and the anatomic relations between tumors and intrahepatic blood vessels were easily perceived. Detection of small intrahepatic metastatic foci was best on long TR/TE images. Tumor invasion of the portal vein's branches was also best seen on long TR/TE SE images. These results indicate that long TR/TE SE sequence is the most effective initial screening method in demonstrating the presence and determining resectability of peripheral cholangiocarcinoma.     

MR imaging features of medulloblastomas.

The preoperative MR studies of 25 patients with surgically proved medulloblastomas were retrospectively reviewed in order to characterize these neoplasms with regard to their MR signal intensity, size, location, and appearance after contrast enhancement. Gadopentetate dimeglumine--enhanced MR images were available in 11 patients. On short TR/short TE images, medulloblastomas generally had low to intermediate signal, and were predominantly slightly hyperintense relative to muscle and hypointense relative to white matter. On long TR/long TE images, medulloblastomas generally had intermediate to moderately high signal, predominantly hyperintense relative to muscle and white matter. Tumor signal relative to gray matter varied considerably on both short TR and long TR images. Signal heterogeneity on long TR/long TE images was observed in 91% of the lesions and resulted from intratumoral cystic zones, small blood vessels, and/or calcifications. In the patients who received gadopentetate dimeglumine, the fraction of tumor volume showing enhancement was found to be less than one third in two cases, between one third and two thirds in four cases, and greater than two thirds in five cases. The mean tumor size was 3.6 x 4.0 x 3.5 cm. The most frequent location of medulloblastoma was the mid and inferior vermis. We conclude that the unenhanced and enhanced MR characteristics of medulloblastomas are somewhat variable. Medulloblastomas should be included in the differential diagnosis when the MR findings described are present in the appropriate patient population.     

Fibrolamellar hepatocellular carcinoma: MR appearance

We report two cases of fibrolamellar hepatocellular carcinoma, each of which had lower signal intensity than normal liver on short repetition time (TR), short echo time (TE) spin-echo (SE) images and demonstrated a central scar-like area of low signal intensity which did not become hyperintense on long time TR/TE SE images.     

MR imaging of the brain in patients with migraine headaches

Forty-one patients with migraine headaches were referred for MR imaging of the brain. Intermediate and T2-weighted images were obtained to determine the frequency of areas of high intensity within the white matter. The average age of these patients was 29.8 years; only five were over 40 years old. Each patient was evaluated in the axial plane with long TR/short and long TE images. Twenty-three patients also had T1-weighted short TR/short TE MR scans; enhancement with gadopentetate dimeglumine was used in three patients. Intracranial abnormalities were seen in only six patients: foci or white matter high intensity on intermediate and T2-weighted images in five and a venous angioma in one. Prior studies have indicated that parenchymal brain abnormalities may be found in up to 46% of patients with migraines. The current study demonstrated parenchymal brain lesions in only 12%. This study suggests that the frequency of foci of high intensity seen on long TR sequences in the migraine patient is much lower than previously reported, especially in patients under 40 years old (5.5% in our series).     

MR imaging of brain abscesses

The MR images and CT scans of 14 patients with surgically verified pyogenic cerebral abscesses were reviewed. The MR findings correlated well with those seen on CT and were believed to be sufficiently characteristic to allow early and accurate diagnosis with MR alone. These features include (1) peripheral edema producing mild hypointensity on short TR/short TE and marked hyperintensity on long TR/intermediate to long TE scans; (2) central necrosis with abscess fluid hypointense relative to white matter and hyperintense relative to CSF on short TR/short TE scans and hyperintense relative to gray matter on long TR/intermediate to long TE scans (the fluid had concentric zones of varying intensity in seven cases, a finding not previously identified in other lesions); (3) extraparenchymal spread (intraventricular or subarachnoid), which was detected more easily on MR than on CT and was manifested by increased intensity relative to normal CSF on both short TR/short TE and long TR/intermediate TE scans; and (4) visualization of the abscess capsule, which was iso- to mildly hyperintense relative to brain on short TR/short TE scans and iso- to hypointense relative to white matter on long TR/intermediate to long TE scans. On the long TR scans, the relative hypointensity of the rim allowed for visualization of the typical morphologic features of the capsule, which in turn aided in differentiation of abscesses from other lesions (as it does on CT). To investigate the cause of the capsular intensity, pathologic studies of the capsules were reviewed when available (10 cases). Fibrosis was identified in all mature abscess capsules, but the combination of the intensities seen on short TR/short TE and long TR/intermediate to long TE scans as well as the temporal changes in intensity were believed to be incompatible with fibrosis as a cause of the capsular changes. Intensity patterns were suggestive of hemorrhage, but neither acute nor chronic hemorrhage was identified on routine H and E stains, while iron stain revealed scant hemorrhage in only two of the eight patients in whom these stains were used. We believe the capsular intensity (in particular the hypointense rims on long TR scans) may reflect paramagnetic T1, and to a greater extent T2, shortening, possibly due to the presence of heterogeneously distributed free radicals that are products of the respiratory burst produced by actively phagocytosing macrophages in the capsule wall. Distinctive MR features of pyogenic abscesses should afford early and accurate diagnosis.     

Pigmented villonodular synovitis: a report of MR imaging in two cases

Although magnetic resonance (MR) imaging has been used to evaluate many musculoskeletal lesions, the MR appearance of pigmented villonodular synovitis (PVNS) has not been described in detail. The authors describe two cases of PVNS in the knee imaged with both computed tomography and MR. In both cases parts of each lesion had very low signal intensity on both short repetition time (TR)/echo time (TE) sequences and long TR/TE sequences. Other portions of both lesions had intermediate signal intensity (equal to or higher than that of muscle but lower than that of fat) on short TR/TE sequences and increasing signal intensity on longer TR/TE images. In one case, the lesion also had a cystic component that showed MR changes typical of complex fluid. The authors propose that the MR signal characteristics demonstrated in these cases may be explained by the unique tissue components of the lesion, particularly hemosiderin and fat.     

The magnetic resonance imaging appearance at 1.5 Tesla of cartilaginous tumors involving the epiphysis

Three cases of lytic, calcified epiphyseal lesions with plain film and computed tomography features suggestive of chondroblastoma were imaged by magnetic resonance imaging. Histopathologic correlation was obtained in each case. Two cases of chondroblastoma showed low signal intensity on both short (TR600/TE20ms) and long (TR2500/TE80ms) spin echo (SE) images. The third case, a clear cell chondrosarcoma, demonstrated increased signal intensity on moderately T2 weighted (TR2500/TE40ms) images. These findings suggest that magnetic resonance imaging may be helpful in distinguishing these lesions.     

Nonketotic hyperglycinemia: diffusion magnetic resonance imaging findings

We report about a boy with nonketotic hyperglycinemia who was studied at 15 days of life with a follow-up examination at age 6 months. Magnetic resonance (MR) imaging revealed progressive atrophy, callosal thinning, and delayed myelination. Glycine peaks were shown by proton MR spectroscopy at 3.56 ppm with a long echo time (TE, 135 milliseconds; TR, 1500 milliseconds). Echo-planar diffusion MR imaging (TR, 5700 milliseconds; TE, 139 milliseconds) at 15 days of life revealed high-signal lesions in the pyramidal tracts, middle cerebellar pedicles, and dentate nuclei on b = 1000 s/mm2 images associated with low apparent diffusion coefficient (ADC) values. By age 6 months, the lesions became more prominent on b = 1000 s/mm2 images with lower ADC values. Diffusion MR imaging findings likely reflected the histopathologic changes of the disease which consisted of spongiosis of the myelinated brain tissue due to myelin vacuolation.     

Quantitative analysis of sodium fast and slow component in in vivo human brain tissue using MR Na image]

In vivo sodium concentrations in the normal brain tissue and a tumorous tissue were analyzed using MR Na image. The nuclear magnetic resonance enabled us to divide the signal from sodium in the living tissue into 2 parts based on the differences of T2 value. Those are fast component having the T2 value of less than 5 msec and slow component of 15-40 msec. We investigated the effect of macromolecules on T2 value of sodium image using polyvinyl alcohol (PVA) powder. MR Na image was taken with the parameters of TR/TD, 110 ms/1.9 ms (FID image) and TR/TE, 110 ms/20 ms (SE image). Saline solution showed high intensity on both FID image and SE image. Saline solution added PVA (PVA phantom) also showed high intensity on FID image, whereas the signal intensity of PVA phantom in SE image extinguished. To know the relation between the signal intensity and sodium concentration, sodium concentration--signal intensity curve was obtained using phantoms with various sodium concentrations (0.05-1.0%). This curve showed a direct proportion between sodium concentration and signal intensity on Na image. We measured further the sodium concentrations of the human brain tissue. Sodium phantoms were arranged around the heads and the MR Na images of the normal brains from 3 volunteers and a patient with a brain tumor (meningioma) were taken. The sodium concentrations of occipital lobe, basal ganglia and the tumorous tissue were calculated using the sodium concentration--signal intensity curve obtained from the phantoms arranged around the heads.(ABSTRACT TRUNCATED AT 250 WORDS)     

Brain involvement in Salla disease

BACKGROUND AND PURPOSE: Our purpose was to document the nature and progression of brain abnormalities in Salla disease, a lysosomal storage disorder, with MR imaging. METHODS: Fifteen patients aged 1 month to 43 years underwent 26 brain MR examinations. In 10 examinations, signal intensity was measured and compared with that of healthy volunteers of comparable ages. RESULTS: MR images of a 1-month-old asymptomatic child showed no pathology. In all other patients, abnormal signal intensity was found: on T2-weighted images, the cerebral white matter had a higher signal intensity than the gray matter, except in the internal capsules. In six patients, the white matter was homogeneous on all images. In four patients, the periventricular white matter showed a somewhat lower signal intensity; in five patients, a higher signal intensity. In the peripheral cerebral white matter, the measured signal intensity remained at a high level throughout life. No abnormalities were seen in the cerebellar white matter. Atrophic changes, if present, were relatively mild but were found even in the cerebellum and brain stem. The corpus callosum was always thin. CONCLUSION: In Salla disease, the cerebral myelination process is defective. In some patients, a centrifugally progressive destructive process is also seen in the cerebral white matter. Better myelination in seen in patients with milder clinical symptoms.     

A comparison between fast and conventional spin-echo in the detection of multiple sclerosis lesions

Long repetition time (TR) spin-echo (SE) with T₂- or proton density weighting is the sequence of choice to detect the brain lesions of multiple sclerosis (MS). Fast spin-echo (FSE) permits the generation of T₂-weighted images with similar contrast to SE but in a fraction of the time. We compared the sensitivity of FSE and SE in the detection of the brain lesions of MS. Six patients with clinically definite MS underwent brain imaging with both dual echo (long TR, long and short echo time (TE) SE and dual echo FSE. The SE and FSE images were first reviewed independently and then compared. A total of 404 lesions was detected on SE and 398 on FSE. Slightly more periventricular lesions were detected using SE than FSE (145 vs 127), whereas more posterior cranial fossa lesions were detected by FSE (77 vs 57). With both SE and FSE the short TE images revealed more lesions than the long echo. These results suggest that FSE could replace SE as the long TR sequence of choice in the investigation of MS.     

Evaluation of three-dimensional fast spoiled gradient recalled acquisition in the steady state (FSPGR) using ultra magnetic field 3-Tesla MRI for optimal pulse sequences of T1-weighted imaging

The advantage of the higher signal-to-noise ratio (SNR) of 3-Tesla magnetic resonance imaging (3TMRI) contributes to the improvement of spatial and temporal resolution. However, T1-weighted images of the brain obtained by the spin-echo (SE) method at 3T MR are not satisfactory for clinical use because of radiofrequency (RF) field inhomogeneity and prolongation of the longitudinal relaxation time (T1) of most tissues. We evaluated optimal pulse sequences to obtain adequate T1 contrast, high gray matter/white matter contrast, and suitable postcontrast T1-weighted images using the three-dimentional (3D) fast spoiled gradient recalled acquisition in the steady state (FSPGR) method instead of the SE method. For the optimization of T1 contrast, the Ernst angle of the optimal flip angle (FA) was obtained from the T1 value of cerebral white matter with the shortest TR and TE. Then the most appropriate FA, showing the maximum contrast-to-noise ratio (CNR) and SNR, was obtained by changing the FA every 5 degrees at about the level of the Ernst angle. Image uniformity was evaluated by a phantom showing similar T1 and T2 values of cerebral white matter. In order to evaluate the effect of the contrast enhancement, signal intensity was compared by the same method using a phantom filled with various dilutions of contrast media. Moreover, clinical studies using full (0.1 mmol/kg) and half (0.05 mmol/kg) doses of Gd-DTPA were carried out with the most appropriate parameters of the 3D-FSPGR method. These studies indicated that the optimal pulse sequences for obtaining an adequate T1-weighted image of the brain using 3D-FSPGR are 9/2 msec (TR/TE) and 13 degrees (FA).     

Multispectral analysis of MR images of the breast

Preliminary investigations were conducted into the potential of magnetic resonance (MR) images for tissue classification of the breast on the basis of relative signal intensity. Multispectral techniques originally developed by the National Aeronautics and Space Administration for satellite image analysis were used in sequence selection, image data correction, image standardization, and image interpretation. Numerous sequence combinations with varying repetition times (TR) and echo times (TE) were considered, and a triplet was selected consisting of long TR/long TE, short TR/short TE, and an opposed phase sequence with intermediate TR and TE. Correction to remove system-imposed intensity inhomogeneities was required for all images. Image standardization based on fat and pectoral muscle signals was necessary for intercase comparisons. Multispectral images obtained based on this analysis suggest the feasibility of intensity-based image classification.     

MR imaging of focal nodular hyperplasia of the liver

The magnetic resonance appearance of three lesions of focal nodular hyperplasia observed in two patients is reviewed. All three lesions demonstrated isointensity with the liver on the short repetition time (TR) and echo time (TE) spin echo images. One lesion also showed a central area of low signal intensity that pathologically corresponded to a scar. The long TR and TE images had a varied appearance, from mixed high signal intensity to predominantly isointense with the liver. The histopathology for each lesion was carefully reviewed. The primary microscopic difference between the lesion that was predominantly isointense with liver on the long time TR and TE images and the other two, which were of mixed high signal intensity on the long time TR and TE images, was the former's relative lack of fibromuscular obliteration of septal blood vessels in the scar. Focal nodular hyperplasia can have at least two possible appearances at 1.5 T; in these three lesions there was consistent isointensity with the liver on the short TR and TE images.     

MR signal intensity of parathyroid adenomas: correlation with histopathology

Recent experience has shown that parathyroid adenomas vary in their MR signal intensity, which raises the question of whether the signal intensity is related to different histologic characteristics. In order to address this question, 10 patients who had MR imaging studies (four at 0.35 T, six at 1.5 T) showing large- to medium-sized parathyroid adenomas and who subsequently underwent surgery with histologic proof of the lesion were evaluated. The MR appearance was compared with histologic characteristics. The adenomas were classified into three groups according to the MR appearance: group I, low signal intensity on short TR/TE images, high signal intensity on long TR/TE images (n = 5); group II, low signal intensity on short and long TR/TE images (n = 3); group III, high signal intensity on short and long TR/TE images (n = 2). Histologic analysis revealed that the major features of each group were different. High cellularity without degeneration or fibrosis was observed for all five adenomas from group I. In group II, all three adenomas showed cellular degenerative changes, old hemorrhage with hemosiderin-loaded macrophages, and/or fibrosis. In group III, both adenomas showed evidence of acute hemorrhage without significant degenerative or fibrotic changes. These data suggest that the signal intensity of parathyroid adenomas on T1- and T2-weighted images corresponds at least in part to differences in histologic composition.     

Recurrent thyroid carcinoma: characteristics on MR images

Magnetic resonance (MR) imaging was used in 32 patients, including eight with benign disease, after partial or total thyroidectomy to determine sensitivity and specificity of MR imaging in the detection of tumor recurrence, to compare signal intensities of scar versus recurrent tumor qualitatively and quantitatively, and to define the extent of recurrent tumor. Findings from surgery (n = 23), needle biopsy (n = 1), or clinical follow-up (n = 8) were used for verification. Of 24 patients with primary thyroid carcinoma, 15 had recurrence and nine had a normal postsurgical thyroid bed. Diagnosis from MR images was correct in 20 cases, but false positive in three and false negative in one. Local recurrence was characterized by low to medium intensity on short repetition time (TR)/short echo time (TE) images and medium to high intensity on long TR/long TE images. Scar in the normal postsurgical thyroid bed showed low intensity on both short and long TR/TE images. Local recurrence of thyroid carcinoma and lymph node metastasis produced positive contrast compared with muscle on short TR/short TE (31 + 19%) and long TR/long TE (85 + 30%) images; fibrosis produced negative contrast, particularly on long TR/long TE (-56, -80%) images. These results indicate the capability of MR imaging in the evaluation of recurrence of thyroid tumors and in the differentiation of abnormal tissue due to tumor recurrence from postoperative fibrosis by means of signal contrast relative to a reference tissue.     

MR imaging of intracranial hemorrhage in neonates and infants at 2.35 Tesla

Summary The variations of the relative signal intensity and the time dependent changing contrast of intracranial hemorrhages on high-field spin-echo magnetic resonance images (MRI) were studied in 28 pediatric patients. For T1-weighted images, a repetition time (TR) of 500 ms and an echo time (TE) of 30 or 23 ms was used. The corresponding times for T2-weighted images were TR 3000 ms and TE 120 ms. Intracranial hematomas, less than 3 days old, were iso- to mildly hypointense on short TR/TE scans and markedly hypointense on long TR/TE scans (acute stage). In the following four days the signal of the hematomas became hyperintense on short TR/TE scans, beginning in the periphery and proceeding towards the center. On long TR/TE scans the signal remained markedly hypointense (early subacute stage). 7–14 days old hematomas were of high signal intensity on short TR/TE scans. On long TR/TE scans they appeared hypointense in the center and hyperintense in the periphery (late subacute stage). By the end of the second week the hematomas were of high signal intensity on all pulse sequences (chronic stage). Chronic hematomas were surrounded by a parenchymal rim of hypointensity on long TR/TE scans. 28 neonates and infants (with 11 follow-up examinations) of 31.5–70.6 weeks postconceptional age (PCA), with an intracranial hemorrhage were examined. The etiologies of the hemorrhages were: asphyxia (17 cases), brain infarct (2), thrombocytopenia (1), clotting disorder (1) and unknown origin (7). The aim of this study was to describe the appearance of intracranial hemorrhages inneonates and infants with MRI at2.35 Tesla using spine-cho sequences.