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.     

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.     

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.     

MR扩散加权成像对颅内囊性肿块的鉴别诊断价值

目的 :探讨MR扩散加权成像对颅内囊性肿块的鉴别诊断价值。方法 :搜集有手术病理结果的患者 3 1例 ,其中表皮样囊肿 9例 ,蛛网膜囊肿 15例 ,囊性颅咽管瘤 4例 ,颅底囊性变神经鞘瘤 3例。所有病例均行MR常规T1WI、T2 WI及DWI扫描 ,回顾性分析各组病例的MR常规及扩散加权成像表现。结果 :在MR扩散加权图像上 ,所有 7例表皮样囊肿均为显著高信号 ,而在指数扩散加权像及ADC图上为等信号 ;其余病变在扩散加权图像上为低信号或伴等信号。结论 :MR扩散加权成像有助于表皮样囊肿与其它颅内脑外囊性肿块的鉴别 ,表皮样囊肿的扩散加权高信号主要是由“T2余辉效应”而非水分子扩散受限所致。     

MR imaging of hyperacute intracranial hemorrhage in the cat

Hyperacute intracerebral hematomas were successfully created in five cats by injecting a prepared blood sample in which the oxygen (O2) saturation ranged from 0-80%. T1- and T2-weighted spin-echo sequences and T2-weighted gradient refocused scans were obtained 2.5-10 hr after injection on a 1.5-T imaging system. Detailed histology or electron microscopy was performed on each brain to confirm the presence of intact red blood cells in a retracted clot matrix. Areas of the hematoma were hypointense relative to brain in all five cats on the gradient refocused scans. The hematoma was isointense relative to brain on the T1- and T2-weighted spin-echo scans in all cats except one, which suffered a seizure/respiratory arrest and died during the scanning procedure. Portions of the hematoma in this animal had a hypointense T2-weighted signal and a hyperintense T1-weighted signal, which corresponded to the predicted MR properties of intracellular methemoglobin. We hypothesize that acute (less than 10 hr old) hematomas that contain virtually 100% intracellular deoxyhemoglobin may not appear hypointense relative to brain on T2-weighted scan sequences at 1.5 T unless surrounding tissue hypoxia and/or anoxia promote additional changes, one of which may be the formation of intracellular methemoglobin.     

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 offers no advantage over routine noncontrast MR imaging in the detection of vertebral metastases

BACKGROUND AND PURPOSE: Diffusion-weighted MR imaging of the spine has been used to differentiate benign from pathologic vertebral body compression fractures. We sought to determine the utility of diffusion-weighted MR imaging in the detection of vertebral metastases and to compare it with conventional noncontrast T1- and T2-weighted MR imaging. METHODS: Fifteen patients with metastases to the spine were studied using conventional MR imaging and diffusion-weighted imaging. Blinded review of all images was undertaken, and patients were categorized according to whether they had focal or multiple lesions. The signal intensity of the lesions was compared on T1-, T2- (fast spin-echo), and diffusion-weighted images. RESULTS: In five patients with focal disease, metastases were hypointense on T1-weighted images; hypointense (n = 2), isointense (n = 1), or hyperintense (n = 2) on T2-weighted images; and hypointense (n = 3) or hyperintense (n = 2) on diffusion-weighted images with respect to presumed normal bone marrow. In 10 patients with disease in multiple sites, all lesions were hypointense on T1-weighted images; hypointense (n = 2), isointense (n = 4), hyperintense (n = 2), or mixed (n = 2) on T2-weighted images; and hypointense (n = 5), hyperintense (n = 3), or mixed (n = 2) on diffusion-weighted images with respect to presumed normal bone marrow. CONCLUSION: As used in this study, diffusion-weighted MR imaging of the spine showed no advantage in the detection and characterization of vertebral metastases as compared with noncontrast T1-weighted imaging, but was considered superior to T2-weighted imaging.     

Experimental cerebral fat embolism: embolic effects of triolein and oleic acid depicted by MR imaging and electron microscopy

BACKGROUND AND PURPOSE: In fat embolism, free fatty acid is more toxic than neutral fat in terms of tissue damage. We evaluated the hyperacute embolic effects of triolein and oleic acid in cat brains by using MR imaging and electron microscopy. METHODS: T2-weighted imaging, diffusion-weighted imaging, and contrast-enhanced T1-weighted imaging were performed in cat brains after the injection of triolein (group 1, n = 8) or oleic acid (group 2, n = 10) into the internal carotid artery. MR images were quantitatively assessed by comparing the signal intensity ratios of the lesions with their counterparts on T2-weighted images, apparent diffusion coefficient (ADC) maps, and contrast-enhanced T1-weighted images. Electron microscopic findings in group 1 were compared with those in group 2. RESULTS: Qualitatively, MR images revealed two types of lesions. Type 1 lesions were hyperintense on diffusion-weighted images and hypointense on ADC maps. Type 2 lesions were isointense or mildly hyperintense on diffusion-weighted images and isointense on ADC maps. Quantitatively, the signal intensity ratios of type 1 lesions in group 2 specimens were significantly higher on T2-weighted images (P =.013)/(P =.027) and lower on ADC maps compared with those of group 1. Electron microscopy of type 1 lesions in both groups revealed more prominent widening of the perivascular space and swelling of the neural cells in group 2, in contrast to notable endothelial defects in group 1. CONCLUSION: MR and electron microscopic data on cerebral fat embolism induced by either triolein or oleic acid revealed characteristics suggestive of both vasogenic and cytotoxic edema in the hyperacute stage. Tissue damage appeared more severe in the oleic acid group than in the triolein group.     

MRI of musculoskeletal extraspinal tuberculosis

PURPOSE: The aim of this study was to describe the MR findings in extraspinal musculoskeletal tuberculosis (EMT). METHOD: A retrospective review was conducted of the MR findings of 18 patients with microbiologically and/or pathologically proven EMT. All MR studies were performed using T1-and T2-weighted spin echo sequences. T1-weighted spin echo sequences after Gd-DTPA injection were obtained for 12 patients. The MR images were evaluated for abnormalities in joints, bones, and soft tissues, and the results were grouped by anatomic localization, frequency distribution of structures affected, and morphologic patterns of involvement. RESULTS: Isolated soft tissue tuberculosis was found in 10 (55.5%) patients and involvement of more than one structure in 8 (44.4%). Pyomyositis (n = 6) and arthritis with involvement of adjacent soft tissues (n = 7) were the most common forms of presentation. One patient presented with isolated fascial superficial tissue involvement in one leg. Isolated pyomyositis involving one (n = 3) or two (n = 3) muscles was homogeneous in six cases and showed intermediate (n = 6), low (n = 2), or high (n = 1) signal intensity on T1-weighted images and a high and very hyperintense signal on T2-weighted images. The tenosynovitis synovial fluid was homogeneous (n = 1) or heterogeneous with multiple tiny hypointense nodules (n = 1) on T2-weighted images. The subdeltoid bursitis fluid was characterized by homogeneous low signal intensity with a hyperintense rim (n = 2) on T1-weighted images and homogeneous (n = 1) or heterogeneous hyperintense signals with areas of low signal intensity (n = 1) on T2-weighted images. In tuberculous arthritis, the synovial joint fluid (n = 7) showed heterogeneous (n = 4) or homogeneous (n = 3) low signal intensity on T1-weighted images and high or very high signal intensity on T2-weighted images. Where involved, the adjacent muscle(s) (n = 8) were usually hypointense on T1-weighted images and very hyperintense on T2-weighted images. Associated cellulitis was found in arthritis with involvement of neighboring soft tissues (n = 5), pyomyositis (n = 2), and tenosynovitis (n = 1). The images obtained after Gd-DTPA showed peripheral (n = 10) or heterogeneous (n = 1) enhancement or no enhancement (n = 1). CONCLUSION: The MR findings for EMT are variable. Although diagnosis is dependent largely on prior presumption and clinical context, MRI provides valuable guidelines in defining the extent of the lesions to select the appropriate treatment and for follow-up of abnormalities.     

Early hepatocellular carcinoma: MR imaging.

All areas in hepatic lesions designated as adenomatous hyperplasia (AH) with malignant foci have recently been recognized as cancer. AH with malignant foci can be classified into two types, depending on the presence of overt cancerous nodules. Lesions without macroscopic nodules are defined as early hepatocellular carcinoma (HCC), while those with a macroscopic component are defined as HCC with early components. A comparative study of early HCC and HCC with early components was performed with magnetic resonance imaging. Early HCC lesions (n = 20) were isointense (n = 11) and hyperintense (n = 9) on T1-weighted spin-echo images and isointense (n = 17), partially hyperintense (n = 2), or hypointense (n = 1) on T2-weighted spin-echo images relative to the surrounding liver. Lesions classified as HCC with early components (n = 8) were hyperintense (n = 5), isointense (n = 2), and of mixed signal intensity (n = 1) on T2-weighted images. T1-weighted imaging was superior to T2-weighted imaging in depicting early HCC, but the latter could be useful in evaluating the progression of HCC in the histopathologically early stages.     

急性期脑内血肿3.0T MR扩散加权成像表现

目的:探讨3.0T MR设备中平面回波扩散加权成像(EPI-DWI)和表观扩散系数(ADC)图对急性脑内血肿的诊断价值及与脑梗死的鉴别诊断能力。方法:对18例急性期脑内血肿患者行EPI-DWI检查,获得ADC图并与CT及常规MRI进行对比。同期选择发病时间、病变体积相近的急性脑梗死患者18例,比较急性期脑内血肿与脑梗死的MRI表现。结果:所有急性期脑内血肿在EPI-DWI及ADC图上均为混杂信号,尤其是较大血肿;不同大小血肿周边均可见低信号环。所有急性脑梗死病变均未见周边环状低信号。结论:血肿周边低信号环为急性期脑内血肿的特异性DWI表现,可资与急性脑梗死相鉴别。     

Pyogenic hepatic abscesses: MRI findings on T1- and T2-weighted and serial gadolinium-enhanced gradient-echo images

The purpose of this study was to determine the magnetic resonance imaging (MRI) features of pyogenic hepatic abscesses on T1-weighted, T2-weighted, and serial gadolinium (Gd)-enhanced T1-weighted spoiled gradient-echo (SGE) images including images acquired in the immediate, intermediate, and late phases of enhancement. The MRI studies of 20 patients with pyogenic liver abscesses were retrospectively reviewed. All patients were examined on 1.5 (n = 19) and 1.0 (n = 1) T MR scanners. MR studies included T1-weighted, T2-weighted, and serial Gd-enhanced SGE images. The following determinations were made: signal intensity of the abscess cavity and perilesional liver tissue, and the presence of internal septations, layering material, or air in the abscess cavity. The pattern of enhancement of the abscess wall, internal septae and peri-abscess liver were evaluated on serial Gd-enhanced SGE images. A total of 53 abscesses were observed in the 20 patients. Fortyeight abscesses were hypointense on T1-weighted and hyperintense on T2-weighted images. Internal septations were present in four abscesses. Lower signal intensity material was observed in a dependent location on T2-weighted images in one abscess. Signal void foci of air located on the nondependent surface was observed in two abscesses. Two other abscesses contained signal void air that occupied the entire abscess cavity, observed on all imaging sequences. On serial gadolinium-enhanced images, all abscesses revealed early enhancement of the wall, which persisted with negligible change in degree of enhancement or thickness on delayed images. Abscess walls ranged in thickness from 2 to 5 mm. Internal septations ranged in thickness from 2 to 3 mm. Abscess walls and septations were relatively uniform in thickness with no evidence of focal nodularity. Periabscess liver tissue was mildly hypointense on T1-weighted and mildly hyperintense on T2-weighted images in 20 lesions, which were either circumferential (n = 12) or wedge-shaped (n = 8). All these regions enhanced more than the remainder of the liver on immediate post-gadolinium images and remained relatively hyperintense on late phase images. Periabscess liver parenchyma was isointense on both T1- and T2-weighted images in 18 lesions, and in these lesions wedge-shaped subsegmental (n = 6) or segmental (n = 12) enhancement was observed on immediate gadolinium-enhanced images, which faded to isointensity on intermediate phase images. No perilesional signal changes and enhancement difference was observed in 15 lesions. Characteristic features of abscesses include: intense mural enhancement on early gadolinium-enhanced images, which persists with negligible change in thickness and intensity on later post-gadolinium images, and the presence of periabscess increased enhancement on immediate post-gadolinium images. These MRI features may help to distinguish abscesses from other focal liver lesions during differential diagnosis.     

Uterine fibroids: diffusion-weighted MR imaging for monitoring therapy with focused ultrasound surgery--preliminary study

PURPOSE: To prospectively determine the feasibility of using diffusion-weighted (DW) imaging and apparent diffusion coefficient (ADC) mapping before (baseline) and after treatment and at 6-month follow-up to monitor magnetic resonance (MR) image-guided focused ultrasound surgical ablation of uterine fibroids. MATERIALS AND METHODS: Informed consent was obtained from patients before treatment with our study protocol, as approved by the institutional review board, and the study complied with the Health Insurance Portability and Accountability Act. Fourteen patients (mean age, 46 years +/- 5 [standard deviation]) who underwent DW imaging were enrolled in this study, and 12 of 14 completed the inclusive MR examination with DW imaging at 6-month follow-up. Treatment was performed by one radiologist with a modified MR image-guided focused ultrasound surgical system coupled with a 1.5-T MR imager. Pre- and posttreatment and 6-month follow-up MR images were obtained by using phase-sensitive T1-weighted fast spoiled gradient-recalled acquisition, T1-weighted contrast material-enhanced, and DW imaging sequences. Total treatment time was 1-3 hours. Trace ADC maps were constructed for quantitative analysis. Regions of interest localized to areas of hyperintensity on DW images were drawn on postcontrast images, and quantitative statistics were obtained from treated and nontreated uterine tissue before and after treatment and at 6-month follow-up. Statistical analysis was performed with analysis of variance. Differences with P < .05 were considered statistically significant. RESULTS: T1-weighted contrast-enhancing fibroids selected for treatment had no hyperintense or hypointense signal intensity changes on the DW images or ADC maps before treatment. Considerably increased signal intensity changes that were localized within the treated areas were noted on DW images. Mean baseline ADC value in fibroids was 1504 mm(-6)/sec2 +/- 290. Posttreatment ADC values for nontreated fibroid tissue (1685 mm(-6)/sec2 +/- 468) differed from posttreatment ADC values for fibroid tissue (1078 mm(-6)/sec2 +/- 293) (P = .001). A significant difference (P < .001) between ADC values for treated (1905 mm(-6)/sec2 +/- 446) and nontreated (1437 mm(-6)/sec2 +/- 270) fibroid tissue at 6-month follow-up was observed. CONCLUSION: DW imaging and ADC mapping are feasible for identification of ablated tissue after focused ultrasound treatment of uterine fibroids.     

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.     

Variable MR findings in ovarian functional hemorrhagic cysts

PURPOSE: To describe the magnetic resonance (MR) findings in ovarian functional hemorrhagic cysts (FHC). MATERIALS AND METHODS: A total of 21 patients with 22 FHC, proven by follow-up ultrasound (US) in 11 women and surgery in 10 women, had US and MR examinations within 24 hours. The study was limited to cysts with obvious an echogenic pattern. All patients had T2-weighted fast spin echo (FSE), T1-weighted spin echo (SE), and T1-weighted SE fat-suppressed sequences. RESULTS: Four cysts (18%) were hypointense on T1-weighted-images without and with fat suppression, and hyperintense on T2-weighted-images. Five cysts (23%) were hypointense on T1-weighted images without and with fat suppression but heterogenous on T2-weighted images. Five cysts (23%) were hypointense on T1-weighted images but showed intermediate signal intensity on T1-weighted fat suppression images and heterogenous signal intensity on T2-weighted images. Two cysts (9%) were entirely intermediate on T1-weighted images. Five cysts (23%) displayed high signal intensity occupying less than 30% of the cystic content on T1-weighted images and one cyst (5%) displayed high signal intensity occupying more than 30% of the cystic content. CONCLUSION: Despite an obvious echogenic pattern on US, 64% of FHC were hypointense on T1-weighted images and 18% were also hyperintense on T2-weighted images. Only 36% demonstrated intermediate or high signal intensity on T1-weighted images.     

Detection of hyperacute parenchymal hemorrhage of the brain using echo-planar T2*-weighted and diffusion-weighted MRI

We investigated the usefulness of echo-planar imaging (EPI) as well as T2^*-weighted and diffusion-weighted MRI (DWI) to identify hyperacute hemorrhage (within 24 h after ictus) in the brain. Seven patients were examined 3.5 to 24 h after onset of symptoms using a whole-body 1.5-T MR system. Two diffusion-weighted sequences were run to obtain isotropic and anisotropic diffusion images. Apparent diffusion coefficients (ADC) were calculated from the isotropic diffusion images. All DWI images as well as the T2*-weighted EPI images showed the hematomas as either discrete, deeply hypointense homogeneous lesions, or as lesions of mixed signal intensity containing hypointense areas. We conclude that even in the early phase after hemorrhage, sufficient amounts of paramagnetic deoxyhemoglobin are present in intracerebral hemorrhages to cause hypointensity on EPI T2^*-weighted and DWI images; thus, use of ultrafast EPI allows identification of intracerebral hemorrhage. Received: 21 March 2000 Revised: 26 July 2000 Accepted: 27 July 2000     

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 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.     

Small nodule detection in cirrhotic livers: evaluation with US, spiral CT, and MRI and correlation with pathologic examination of explanted liver

PURPOSE: The purpose of this work was to evaluate the detection and characterization of nodules > or = 8 mm and small hepatocellular carcinomas (HCCs) in liver cirrhosis. METHOD: Pathologic examination and results of US, helical CT, and dynamic MRI with gadolinium were compared after orthotopic liver transplantation (OLT) of 43 cirrhotic patients. Nodules were classified as macroregenerative nodules (MRNs), borderline nodules (BNs), and HCC. RESULTS: Pathologic examination classified 69 nodules: 50 MRNs, 6 BNs, and 13 HCCs. Sensitivities of MRN, BN, and HCC detection were, respectively, for US imaging 2% (1/50), 33.3% (2/6), and 46.2% (6/13); for helical CT 2% (1/50), 50% (3/6), and 53.8% (7/13); and for MRI 42% (21/50), 50% (3/6), and 76.9% (10/13). MRI detected 21 MRNs. They presented on T1/T2-weighted images as hyperintense/hypointense (n = 8), hyperintense/isointense (n = 7), hypointense/hypointense (n = 4), hypointense/isointense (n = 1), and hypointense depicted only on echo planar imaging (n = 1). The three detected BNs were hyperintense/hypointense nodules. The 10 detected HCCs appeared hyperintense/isointense (n = 7), hyperintense/hypointense (n = 2), and hypointense/isointense (n = 1). None of the MRNs but eight HCCs and one BN were enhanced after gadolinium injection. CONCLUSION: Contrast-enhanced MRI is the most sensitive technique for detecting liver nodules. No MR signal intensity pattern characteristic of small HCCs enables differentiation from benign nodules, however. Gadolinium enhancement is the most sensitive and specific characteristic of HCC.     

Intracranial epidermoid cysts: diffusion-weighted, FLAIR and conventional MR findings

PURPOSE: To compare diffusion-weighted echo-planar imaging (DW) with spin-echo (SE), and fluid-attenuated inversion recovery (FLAIR) sequences in the evaluation of epidermoid cysts (ECs), and to evaluate T2 shine-through effect. MATERIALS AND METHODS: Fifteen patients were imaged prospectively in two different 1.5 T magnetic resonance (MR) units with standard head coils with SE, FLAIR and DW echo planar imaging sequences. The qualitative and quantitative assessments were performed by two radiologists in consensus. Apparent diffusion coefficient (ADC) values were obtained from all ECs. Exponential DW images are obtained in 11 cases to eliminate T2 shine-through effects. The results are analyzed with variance analysis (ANOVA) and Bonferroni t method. RESULTS: FLAIR sequence was superior to T1- and T2-weighted sequences in showing ECs. In 13 cases, the borders of the lesions could be delineated from the surrounding structures with only DW imaging where ECs were markedly hyperintense. The ADC values of ECs are significantly lower than CSF (P < 0.001), and significantly higher than deep white matter (P < 0.01). On exponential DW images, ECs had similar intensity with brain parenchyma showing that the real cause of the hyperintensity of the lesions on trace images is the enhanced T2 effect of the tissue. CONCLUSION: FLAIR sequence is superior to the conventional MR sequences in demonstrating the ECs and DW imaging is superior to other MR sequences in delineating the borders of the ECs. Exponential DW images had shown that the hyperintensity in the trace images are caused by increased T2 effect of the lesion rather than the decrease in ADC values.