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.     

MR imaging of intracranial metastatic melanoma

Ten patients with intracerebral metastases from malignant melanoma were evaluated with magnetic resonance (MR) imaging performed at 1.5 T using spin-echo techniques. On the basis of histopathologic findings in three of 10 cases and CT appearances in all 10 cases, three patterns were identified on analysis of MR signal intensities in both short repetition time/echo time (TR/TE) and long TR/TE spin-echo scans. In comparison to normal cortex, nonhemorrhagic melanotic melanoma appeared markedly hyperintense on short TR/TE images and isointense, mildly hypointense on long TR/TE images. Nonhemorrhagic, amelanotic melanoma appeared isointense or mildly hypointense on short TR/TE and isointense or mildly hyperintense on long TR/TE images. Hemorrhagic melanoma varied in appearance, depending on the stage of hemorrhage. Melanotic, nonhemorrhagic melanoma can be distinguished from early and late subacute hemorrhage by its signal intensity on long TR/TE images. Spin-echo MR appears to be the method of choice for diagnosing melanotic metastases.     

Acute hypertensive intracranial hemorrhage: MR imaging at 1.5T

Twelve patients with acute hypertensive intracranial hemorrhage underwent magnetic resonance (MR) imaging within 7 days after the ictus. T1-weighted (TR = 400 msec; TE = 20 msec) and T2-weighted (TR = 2000 msec; TE = 80 msec) images were obtained on a 1.5 Tesla MR system. Signal intensities of hematomas were carefully evaluated and were compared with white matter intensity. A 9-hour-old hematoma was mildly hypointense on T1-weighted images, and was mildly hyperintense on T2-weighted images, suggesting a reflection of the high water content. On T2-weighted images, thin peripheral hypointense rim, probably due to deoxyhemoglobin, was also observed. Both of 15-hour-old hematoma and 21-hour-old hematoma had peripheral hypointensity on T2-weighted images. Both of 39-hour-old hematoma and 43-hour-old hematoma had central hyper-intensity on T1-weighted images and iso-to-mild central hypointensity on T2-weighted images, suggesting a reflection of decreased water content. A 3-day-old hematoma had thin peripheral iso-to-mild hyperintense rim on T1-weighted images, presumably due to intracellular methomoglobin. A 5-day-old hematoma had thin peripheral hyperintense rim on T2-weighted images, probably due to free methemoglobin. A 7-day-old hematoma was hyperintense on T1-weighted images and was mildly hypointense to hyperintense on T2-weighted images, presumably due to mixed intracellular methemoglobin and free methemoglobin.     

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.     

MR imaging of acute intracranial hemorrhage: findings on sequential spin-echo and gradient-echo images in a dog model

Seven intraparenchymal hematomas (four venous and three arterial) were placed in the brains of six dogs in order to study the MR appearance of acute hemorrhage and to evaluate the effects of several variables on the signal intensity of the hematoma. MR imaging at 0.6 and 1.5 T was performed by using standard short and long TR spin-echo and low-flip-angle gradient-echo sequences. Sequential examinations were performed during the first week following hematoma creation. MR findings were compared with CT and postmortem examinations. Three patterns of signal intensity were observed, which varied according to the size (small vs large) and location (parenchymal vs intraventricular) of the hematomas. The small parenchymal hematomas did not undergo evolutionary changes. On short TR scans they were isointense at both field strengths, and therefore not detectable; on long TR scans these hematomas were of variable intensity at 1.5 T and were hyperintense at 0.6 T. On gradient-echo scans, they were hypointense at all times at both field strengths. The large parenchymal hematomas underwent evolutionary changes typical of those seen in clinical imaging. On short TR scans they were initially isointense and became hyperintense 1-3 days later. Long TR scans demonstrated initial hyperintensity, followed by the development of hypointensity within 12 hr in the venous hematomas and within 60 hr in the arterial hematoma. The intensity changes on long TR scans were seen at both 0.6 and 1.5 T, but occurred sooner and to a greater degree at 1.5 T. Gradient-echo imaging of these large lesions demonstrated hypointensity at all times at both field strengths. The intraventricular hemorrhages demonstrated more rapid development of hyperintensity on short TR scans and slower and less pronounced development of hypointensity on long TR scans compared with the parenchymal clots in the same animal. Gradient-echo imaging of the intraventricular hemorrhages demonstrated hypointensity at all times at both field strengths. A multifactorial hypothesis is proposed to explain the differences in intensity between venous, arterial, and intraventricular blood. Gradient-echo sequences should prove to be highly useful in detecting and delineating hemorrhages and are recommended for the MR protocol of patients with acute neurologic ictus and suspected hemorrhage.     

Subdural and epidural empyemas: MR imaging

The MR images of six patients with extraaxial empyemas (five subdural and four epidural) were reviewed and compared with CT scans. MR demonstrated convexity and interhemispheric collections, which were mildly hyperintense relative to CSF and hypointense relative to white matter on short TR pulse sequences and hyperintense relative to CSF and white matter on long TR pulse sequences, allowing distinction from sterile effusions and most chronic hematomas. A hypointense rim, representing displaced dura, was depicted at the interface between the lesion and brain in epidural empyemas, a feature absent in subdural empyemas. Inflammation-induced parenchymal abnormalities, including edema, mass effect, and reversible cortical hyperintensity, were well depicted on MR imaging. MR was superior to CT in demonstrating the presence, nature, and extent of these lesions in all cases. Because early and accurate diagnosis will significantly improve the prognosis of these serious infections, MR is preferred to CT for patients in whom an acute intracranial infection is suspected.     

MR imaging of intracerebral hematomas: sequential changes of signal intensities on a 0.2T permanent magnetic system

We performed 67 examinations in 27 patients with intracerebral hemorrhage on a 0.2T permanent magnet system. MR appearance of the hematomas on T-1 weighted and T-2 weighted images (T1WIs, T2WIs) was carefully evaluated according to the chronological course of the lesions after the ictus. The signal intensity of each hematoma was classified into four stages in terms of the degradation process of hemoglobin. Four hematomas examined within 24 hours after the ictus (ultra-acute stage) appeared slightly hypointense or isointense relative to the normal brain tissue on T1WIs and markedly hyperintense on T2WIs. Three of those lesions became partially or totally hypointense on T2WIs at the acute stage (one to three days after the ictus), though all appeared in general isointense on T1WIs. The hematomas at the subacute stage (four days to two weeks after the ictus) were hyperintense on both T1WIs and T2WIs. At the chronic stage (more than two weeks after the ictus) the signal pattern of hematomas became variable: hyperintense on both T1WIs and T2WIs early at this stage; hypointense on T1WIs but mostly hyperintense on T2WIs latter. The results indicate the clinical feasibility of a low tesla system for MR evaluation of intracerebral hematomas.     

High-field MR imaging of extracranial hematomas

The MR features of 20 extracranial hematomas studied on a 1.5-T system and imaged with both short repetition-time/echo-time (TR/TE) and long TR/TE pulse sequences were reviewed. In four of five acute hematomas (those less than 7 days of age), signal intensity was markedly decreased on long TR/TE images and was either intermediate or slightly decreased on short TR/TR images. Fourteen subacute hematomas (7 days to 7 weeks of age) and one chronic hematoma (9 months) were studied. The appearance of the subacute lesions varied from intermediate to high intensity on short TR/TE sequences, but all demonstrated increased signal on long TR/TE sequences. A low-signal rim was noted at the margin of nine subacute lesions. In one patient with this finding, pathologic examination showed that the low-signal margin corresponded to a region containing hemosiderin-laden macrophages at the periphery of the hematoma. These results correlate well with those reported for intracranial hematomas examined at this field strength. We conclude that analysis of signal-intensity patterns at 1.5 T is useful in staging the evolution of hematomas.     

MR imaging of hemorrhagic intracranial neoplasms

Thirty patients with intracranial tumors containing hemorrhage of varying stages were examined with high-field-strength MR imaging and CT to determine what differences might exist between hemorrhagic tumor and pure hemorrhage. Pathology was obtained in the six patients with primary tumors and in 14 of the 24 patients with metastases. Similar to evolving intraparenchymal hematomas, hemorrhagic neoplasms undergo changes in their appearance that can be categorized into three distinct intensity patterns, or stages. Stage 1 is characterized as iso- or hypointensity on short TR sequences and as hypointensity on long TR sequences; stage 2 as developing hyperintensity on both short and long TR sequences, without evidence of a well-defined black rim; and stage 3 as a hyperintense lesion with a well-defined black rim on long TR sequences. An additional mixed-intensity pattern was identified, which contained areas corresponding to more than one stage. In all of the cases exhibiting this pattern, pathology confirmed that the appearance was due to recurrent bleeding. We found several characteristics on MR that, when present, suggest an underlying neoplasm. These include delay in evolution between stages, central or eccentric hyperintensity in stage 2, and a mixed-intensity pattern. In addition, the presence of a hemosiderin rim does not exclude an underlying neoplasm. We found that the MR patterns that characterize hemorrhagic intracranial neoplasms should help to determine the cause of the hemorrhage.     

Paradoxically decreased signal intensity on postcontrast short-TR MR images

Seven lesions are presented in which short TR/short TE images obtained immediately after IV administration of gadopentetate dimeglumine demonstrated an apparent decrease in signal intensity compared with precontrast short TR/short TE images. All seven lesions were hyperintense on precontrast short TR/short TE images. In four cases in which long TR/long TE scans were also obtained, the lesions were hypointense. This phenomenon may be due to a dominant T2 shortening effect by the contrast material that "overwhelms" T1 shortening even on short TR/short TE scans. Other compounding factors may include variations in scanning variables, receive and transmit attenuations, or a photographic phenomenon due to window widths and center levels.     

Hyaline articular cartilage: relaxation times,pulse-sequence parameters and MR appearance at 1.5 T

In order to optimize the parameters for the best visualization of the internal architecture of the hyaline articular cartilage a study both ex vivo and in vivo was performed. Accurate T1 and T2 relaxation times of articular cartilage were obtained with a particular mixed sequence and then used for the creation of isocontrast intensity graphs. These graphs subsequently allowed in all pulse sequences (spin echo, SE and gradient time (TR), echo time (TE) and flip angle (FA) for optimization of signal differences between MR cartilage zones. For SE sequences maximum contrast between cartilage zones can be obtained by using a long TR (> 1,500 ms) with a short TE (< 30 ms), whereas for GRE sequences maximum contrast is obtained with th shortest TE (< 15 ms) combined with a relatively long TR (> 400 ms) and an FA greater than 40°. A trilaminar appearance was demonstrated with a superficial and deep hypointense ozne in all sequences and an intermediate zone that was moderately hyperintense on SET1-weighted images, slightly more hyperintense on proton density Rho and SE T2-weighted images and even more hyperintense on GRE images.     

Magnetic resonance imaging of hemorrhage

The magnetic resonance imaging (MRI) characteristics of evolving hemorrhage are discussed and compared with those of computed tomography (CT). Studies of 15 hematomas were undertaken in four mongrel dogs. The hematomas were created by the injection of autologous blood into the subcutaneous tissues of the thigh. The hematomas were studied serially with both MRI and CT. Pulse sequences included spin-echo (2100 msec TR, 40 and 80 msec TE) and inversion-recovery (2100 msec TR, 400 msec TI, 40 msec TE). Relaxation times (T1 and T2) were calculated in each case. CT values (H) were also obtained. In addition, 24 single and 14 serial scans of hemorrhage were obtained from 24 patients. MRI was performed on a 0.15-T resistive magnet scanner. T1 and T2 relaxation times and CT values decreased as the hematomas resolved. T1 and T2 relaxation times of intraparenchymal hemorrhage tended to remain elevated with time. MRI seems to be more sensitive than CT for the detection of hemorrhage, primarily because of superior contrast resolution.     

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.     

Hepatic focal nodular hyperplasia: MR imaging at 1.0 and 1.5 T.

Ten cases of hepatic focal nodular hyperplasia (FNH) were studied with magnetic resonance (MR) imaging. Proof of diagnosis was by needle biopsy or follow-up of as long as 5 years. Both short TR/TE and long TR/TE images were obtained. The most common finding was isointensity of the lesion relative to liver parenchyma with all pulse sequences. A central scar was seen in only one patient and was hyperintense on long TR/TE images. Slight hyperintensity of the lesion on short TR/TE and long TR/TE images was seen in two cases. Textural heterogeneity was present in only one of these. The most common presentation in our series was a visually isointense lesion relative to liver on short TR/TE images and an isointense or slightly hyperintense lesion on long TR/TE images. A review of the literature and the present findings suggest that FNH has a variable appearance on MR images.     

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.     

Pheochromocytoma with posthemorrhagic cystic degeneration: magnetic resonance imaging findings

We describe in vivo and in vitro magnetic resonance imaging (MRI) findings of a pheochromocytoma with posthemorrhagic cystic degeneration in a 74-year-old man. The in vivo MR images showed the mass as an area of homogeneous moderate hyperintensity with a central area of intense hyperintensity outlined by a thin hypointense rim on a T2-weighted image. The in vitro MR images showed a hyperintense rim around the central cystic area consistent with hemorrhage on T1-weighted gradient-echo images with short echo times (1.6 and 4.2 msec) and more distinctly revealed the blurring effect due to susceptibility of hemosiderin on those with long echo times (6 and 8 msec). Hemosiderin deposition caused by intraparenchymal hemorrhage in the pheochromocytoma can be appreciated on spoiled gradient-echo images with different echo times, which is ordinarily included in the MRI protocol as phase-shift imaging.     

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.     

Synovial cysts of the lumbosacral spine: diagnosis by MR imaging

Intraspinal synovial or ganglion cysts are uncommon lesions associated with degenerative lumbosacral spine disease. CT usually reveals cystic lesions adjacent to a facet joint, and they may show calcification. MR imaging of four surgically confirmed cases of intraspinal synovial cysts revealed subtle signal changes compared with CSF. Short TR/TE images showed the lesions to be slightly hyperintense in three cases and isointense in one case. Long TR/TE sequences revealed a hyperintense appearance in two cases and a hypointense appearance in the others. A peripheral rim of decreased signal on long TR/TE images probably reflects fine calcification or hemorrhage in the margins of the cysts. The multiplanar and contrast characteristics of MR make this technique well suited to the diagnosis of herniated disk, degenerative facet disease, and synovial cyst.     

Synovial cysts of the lumbosacral spine: diagnosis by MR imaging

Intraspinal synovial or ganglion cysts are uncommon lesions associated with degenerative lumbosacral spine disease. CT usually reveals cystic lesions adjacent to a facet joint, and they may show calcification. MR imaging of four surgically confirmed cases of intraspinal synovial cysts revealed subtle signal changes compared with CSF. Short TR/TE images showed the lesions to be slightly hyperintense in three cases and isointense in one case. Long TR/TE sequences revealed a hyperintense appearance in two cases and a hypointense appearance in the others. A peripheral rim of decreased signal on long TR/TE images probably reflects fine calcification or hemorrhage in the margins of the cysts. The multiplanar and contrast characteristics of MR make this technique well suited to the diagnosis of herniated disk, degenerative facet disease, and synovial cyst.     

Intracranial hemorrhage studied with a high-field (1.5T) NMR apparatus

Fifty-two patients were studied with high-field magnetic resonance imaging (1.5T), with T1- and T2-weighted spin-echo pulse sequences. The study was aimed at assessing the efficacy of MR imaging in the evaluation of intracranial hematomas. Characteristic intensity patterns were observed in the evolution of the hematomas, due to the physicochemical changes in hemoglobin. No acute hematomas were observed. In 35 sub-acute hematomas, peripheral hyperintensity could be observed on T1- and T2-weighted pulse sequences. This hyperintensity eventually fills in the hematoma in the chronic stage. In 17 chronic hematomas, a peripheral hypointense ring due to hemosiderin deposits was seen on T1- and T2-weighted scans. The authors conclude that high-field MR imaging is a very sensible diagnostic method in the evaluation of sub-acute and chronic hematomas.