Acute intracranial hemorrhage: intensity changes on sequential MR scans at 0.5 T

Thirty-seven patients underwent MR imaging at 0.5 T within 7 days of a CT-documented intracranial hemorrhage. A total of 57 hematomas were evaluated. Twelve patients underwent serial scanning and 12 patients had multiple hemorrhages into different intracranial compartments. The appearances of the hematomas on spin-echo (SE) images with a short repetition time (TR) of 500 msec and short echo time (TE) of 32 msec (SE 500/32), long TR/intermediate TE (SE 2000/60), and long TR/long TE (SE 2000/120) were carefully evaluated with specific attention to the precise time after ictus. Hematomas showed heterogeneous, complex, rapidly changing intensities. There was a significant amount of variation among patients, especially between the third and seventh days. Hematomas studied between 12 and 24 hr after hemorrhage were mildly hyperintense on short TR scans and markedly hyperintense on long TR (intermediate and long TE) scans (stage I). These findings in acute hemorrhage have received little prior attention. Over the next 1-2 days, hematomas became iso- to mildly hypointense on short TR scans and markedly hypointense on long TR scans (stage II). Hypointensity on long TR scans has previously been described at high field strengths; our communication demonstrates that this phenomenon is seen routinely at intermediate field strengths as well. Hematomas became markedly hyperintense on short TR scans beginning on approximately the fourth day postictus and redeveloped hyperintensity on long TR scans approximately 5-6 days after ictus (stage III). By the end of the first week they were hyperintense on all pulse sequences (stage IV). MR findings on the first day after intracranial hemorrhage (in particular, subtle hyperintensity on short TR scans) probably allow for a specific diagnosis, while the variable, hetergeneous, and rapidly changing intensities noted between days 2 and 7 are often less specific.     

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.     

Variable appearances of subacute intracranial hematomas on high-field spin-echo MR

Subacute intracranial hematomas have variable appearances on high-field MR images. They are hyperintense on T1-weighted images owing to methemoglobin, but have variable intensities on T2-weighted images. Observation of the different high-field spin-echo MR intensity patterns of five subacute hematomas suggests that further subcategorization into different methemoglobin states may be possible. In particular, undiluted intracellular methemoglobin is hyperintense on T1-weighted images and markedly hypointense on T2-weighted images, undiluted free methemoglobin should be hyperintense on T1-weighted images and isointense or slightly hypointense on T2-weighted images, and dilute free methemoglobin is hyperintense on both T1- and T2-weighted images. However, it appears that certain regions of subacute hematomas may be difficult to differentiate, by intensity patterns alone, from melanotic melanomas or fat. We believe that, despite some limitations, MR is useful in dividing subacute intracranial hematomas into their respective methemoglobin states, and also that further subcategorization is possible.     

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.     

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.     

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.     

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.     

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.     

Spontaneous intracerebral hematoma on diffusion-weighted images: influence of T2-shine-through and T2-blackout effects

BACKGROUND AND PURPOSE: On diffusion-weighted (DW) images, primary hematomas are initially mainly hyperintense, and then hypointense during the first few days after stroke onset. As in other brain disorders, variations in the T2 relaxation time of the hematoma influence the DW imaging signal intensity. Our aim was to evaluate the contribution of the T2 signal intensity and apparent diffusion coefficient (ADC) changes to signal intensity displayed by DW imaging through the course of hematoma. METHODS: The MR images of 33 patients with primary intracranial hemorrhage were retrospectively reviewed. Variations in T2-weighted echo planar images, DW imaging signal intensity, and apparent diffusion coefficient (ADC) ratios (core of hematoma/contralateral hemisphere) were analyzed according to the putative stages of hematoma, as seen on T1- and T2-weighted images. RESULTS: On both T2-weighted echo planar and DW images, the core of the hematomas was hyperintense at the hyperacute (oxyhemoglobin, n = 11) and late subacute stages (extracellular methemoglobin, n = 4), while being hypointense at the acute (deoxyhemoglobin, n = 11) and early subacute stages (extracellular methemoglobin, n = 7). There was a positive correlation between the signal intensity ratio on T2-weighted echo planar and DW images (r = 0.93, P < .05). ADC ratios were significantly decreased in the whole population and in each of the first three stages of hematoma, without any correlation between DW imaging findings and ADC changes (r = 0.09, P = .6). CONCLUSION: Our results confirm that the core of hematomas is hyperintense on DW images with decreased ADC values at the earliest time point, and may thus mimic arterial stroke on DW images. T2 shine-through and T2 blackout effects contribute to the DW imaging findings of hyperintense and hypointense hematomas, respectively, while ADC values are moderately but consistently decreased during the first three stages of hematoma.     

MRI of pancreatic transplants

The value of MRI in assessing pancreatic transplants was studied in 37 patients. Sixty-seven MRI examinations were performed in patients with an uncomplicated transplant, a4 in patients with poorly functioning gransplant, and 10 in patients with a non-functioning graft. On the basis of 54 follow-up studies, it was shown that the volume of the graft decreased systematically during the 8 months after transplantation. On T1-weighted images the normal transplant was poorly delineated, with an almost homogeneous isointense or slightly hyperintense structure when compared with either renal transplant cortex or muscle. On T2-weighted images the organ was isointense or slightly hypointense compared with fat and hyperintense compared with muscle. T2-weighted delayed echo time image (TR = 2000 ms, TE = 150–200 ms) showed transplanted pancreas as well-delineated, hypointense and with a lobulated structure. This structure was characteristic of normal whole pancreatic grafts. Patent transplant vessels were seen as tubular structures of low signal intensity on T2-weighted short echo time images (TR = 2000 ms, TE = 50 ms). In the 10 patients with a non-functioning pancreatic transplant there were: 4 cases of focal intraparenchymal abnormalities, 6 cases in which the lobular structure was absent, and 4 cases of absence of patent graft main vessels (3 thromboses). There was no configuration of signal intensity of pancreatic parenchyma on MRI which could be considered typical for normal or non-functioning transplant. Correspondence to: A. Pinet     

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 intracerebral blood: diversity in the temporal pattern at 0.5 and 1.0 T

MR scans were obtained at 0.5 and 1.0 T in 40 patients with 46 intracerebral hematomas categorized as hyperacute (0-2 days), acute (3-7 days), subacute (8-14 days), and chronic (15 days to 6 years). In a retrospective review, the signal intensity of the lesions was compared with that of normal white matter of the brain on spin-density, T1-, and T2-weighted spin-echo and T1-weighted gradient-echo sequences. The classic appearance and evolution of hematomas described in the literature at 1.5 T were not found in a significant number of the cases reviewed. In the hyperacute group, only five of eight hematomas had signal intensities that were hypointense relative to brain on T2-weighted images. Two of eight hyperacute hematomas were hyperintense relative to brain on the T1-weighted spin-echo images. However, T1-weighted gradient-echo images reliably demonstrated a hypointense signal in some portion of the hematoma in 45 of 46 cases. We conclude that while there is no constant temporal pattern on spin-echo or gradient-echo sequences, there are signal-intensity changes suggestive of hemorrhage in nearly all hematomas imaged at 0.5 and 1.0 T. Although the inconsistency may be frustrating from a diagnostic standpoint, this variability may reveal important individual differences in hematomas and the brain that surrounds them, and thus be clinically significant. Before these data can be mechanistically analyzed, the reason for contrast on MR scans of hematoma must be better understood.     

Diffusion-Weighted MR Imaging of Intracerebral Hemorrhage

Objective

To document the signal characteristics of intracerebral hemorrhage (ICH) at evolving stages on diffusion-weighted images (DWI) by comparison with conventional MR images.

Materials and Methods

In our retrospective study, 38 patients with ICH underwent a set of imaging sequences that included DWI, T1-and T2-weighted imaging, and fluid-attenuated inversion recovery (FLAIR). In 33 and 10 patients, respectively, conventional and echo-planar T2* gradient-echo images were also obtained. According to the time interval between symptom onset and initial MRI, five stages were categorized: hyperacute (n=6); acute (n=7); early subacute (n=7); late subacute (n=10); and chronic (n=8). We investigated the signal intensity and apparent diffusion coefficient (ADC) of ICH and compared the signal intensities of hematomas at DWI and on conventional MR images.

Results

DWI showed that hematomas were hyperintense at the hyperacute and late subacute stages, and hypointense at the acute, early subacute and chronic stages. Invariably, focal hypointensity was observed within a hyperacute hematoma. At the hyperacute, acute and early subacute stages, hyperintense rims that corresponded with edema surrounding the hematoma were present. The mean ADC ratio was 0.73 at the hyperacute stage, 0.72 at the acute stage, 0.70 at the early subacute stage, 0.72 at the late subacute stage, and 2.56 at the chronic stage.

Conclusion

DWI showed that the signal intensity of an ICH may be related to both its ADC value and the magnetic susceptibility effect. In patients with acute stroke, an understanding of the characteristic features of ICH seen at DWI can be helpful in both the characterization of intracranial hemorrhagic lesions and the differentiation of hemorrhage from ischemia.     

颅内软骨瘤的CT、MRI诊断

目的总结探讨颅内软骨瘤的CT、MRI特点。方法对1994年1月至2004年9月经手术病理证实的10例颅内软骨瘤的CT、MRI特点进行回顾性分析。结果10例中，肿瘤位于颅底4例，大脑凸面4例，大脑镰区、脑实质内各1例；CT上均见到明显的钙化且边缘清楚，密度多不均匀（9例），相邻骨质可受累（5例）；于MRI上呈混杂信号（4例），其中钙化部分呈长T1、短T2信号，实质部分呈等长T1、长T2信号；CT增强扫描出现轻度强化4例，其中3例为延迟强化。结论颅内软骨瘤好发于颅底、大脑凸面及大脑镰区，多数伴有明显钙化，增强扫描呈轻度强化，延迟强化较有特点。病理仍是主要的确诊手段。     

Magnetic resonance appearance of slow flow vascular malformations of the brainstem

Summary Twelve patients with slow flow brain stem vascular malformations had magnetic resonance scans performed on a 1.5 Tesla scanner using T1 (TR=400–800 ms, TE=25 ms) and T2 (TR=2000 ms, TE=20, 25, 80 ms) weighted scans. Eight patients (70%) had solitary brainstem vascular malformations while 4 (30%) had multiple lesions both supra and infratentorially. Five patients had venous angiomas demonstrated by angiography and MR. There were 26 lesions seen on MR of which only 14 were identified by CT. These lesions demonstrated a specific MR image pattern indicative of subacute or chronic parenchymal hematoma. It was characterized by an iso to hyperintense central signal surrounded by a well defined thin band of low signal intensity. The central zone could appear to be single or multilocular. In multilocular lesions the hemorrhages within different cells could be of different ages. One patient did not have findings of a chronic hematoma but exhibited only low signal secondary to calcification and a venous angioma. None of these lesions had surrounding edema. Despite the variable etiologies of slow flow vascular malformations of the brainstem, their MRI manifestations seem to indicate a final common pathway of chronic hematoma. These lesions are quite distinct from MS or tumor, the usual clinical considerations in the differential diagnosis.     

MR imaging of body fluid collections

To evaluate the potential of magnetic resonance (MR) to characterize body fluids in vivo, we determined the relaxation times and the relative MR signal intensities of 42 body fluid collections in 42 patients. Twelve normal volunteers served as controls. We also studied albumin solutions at different concentrations and blood at various periods in vitro. Because of their long T1 relaxation times, most nonhemorrhagic fluid collections had low to intermediate intensity on images obtained with short repetition time (TR) and short echo time (TE) settings. Although the relaxation times and relative MR signal intensities of noninfected collections differed from those of infected collections, the values overlapped. On images obtained with short TR and short TE, blood in acute hemorrhages had intermediate signal intensity and serum in subacute hemorrhagic collections was the only pathologic fluid producing high signal intensity. Because of their relatively long T2 values, all the fluid collections were intense on images obtained with long TR and long TE settings; consequently, differences in intensity were less evident than on images obtained with short TR and short TE settings. Magnetic resonance allows reliable discrimination of subacute hemorrhagic collections from collections of other types, but the differentiation between acute hemorrhagic collections; nonhemorrhagic, noninfected collections; and nonhemorrhagic, infected collections is less accurate.     

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.     

Characterization of focal hepatic lesions with ferumoxides-enhanced MR imaging: utility of T1-weighted spoiled gradient recalled echo images using different echo times

PURPOSE: To evaluate the different signal characteristics of focal hepatic lesions on ferumoxides-enhanced MR imaging, including T1-weighted spoiled gradient recalled echo (GRE) images using different echo times (TE) and T2- and T2*-weighted images. MATERIALS AND METHODS: Ferumoxides-enhanced MR imaging was performed using a 1.5-T system in 46 patients who were referred for evaluation of known or suspected hepatic malignancies. One hundred and seven lesions (42 hepatocellular carcinomas [HCC], 40 metastases, 13 cysts, eight hemangiomas, three focal nodular hyperplasias [FNHs], and one cholangiocarcinoma) were evaluated. Postcontrast MR imaging included 1) T2-weighted FSE; 2) T2*-weighted GRE; 3) T1-weighted spoiled GRE using moderate (TE = 4.2-4.4 msec) TE; and 4) minimum (TE = 1.8-2.1 msec) TE. Signal intensities of the focal lesions were rated by two radiologists in conference as follows: hypointense, isointense or invisible, hyperintense, and markedly hyperintense. Lesion-to-liver contrast-to-noise ratio (C/N) was measured by one radiologist for a quantitative assessment. RESULTS: On ferumoxides-enhanced FSE images, 92% of cysts were "markedly hyperintense" and most of the other lesions were "hyperintense", and the mean C/N of cysts was significantly higher than that of other focal lesions. T2*-weighted GRE images showed most lesions with similar hyperintensities and the mean C/N was not significantly different between any two types of lesion. T1-weighted GRE images using moderate TE showed all FNHsand hemangiomas, 29 (69%) HCCs and eight (20%) metastases as "hyperintense". On T1-weighted GRE images using minimum TE, however, all HCCs and metastasis except one were iso- or hypointense, while all of the FNHs and hemangiomas were hyperintense. Ring enhancement was highly suggestive of malignant lesions, and was more commonly seen on the minimum TE images than on the moderate TE images. CONCLUSION: Addition of T1-weighted GRE images using minimum and moderate TE is helpful for characterizing focal lesions in ferumoxides-enhanced MR imaging.     

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.     

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.