Benign adrenocortical masses: diagnosis with chemical shift MR imaging.

Benign adrenocortical masses often contain lipid; metastases and pheochromocytomas do not. Standard and lipid-sensitive (chemical shift) magnetic resonance (MR) images of the adrenal glands in 31 patients with 45 adrenal masses were reviewed to determine if simple visual analysis of these images would increase diagnostic specificity. Lipid was considered present if signal intensity of the adrenal mass relative to other tissues decreased on chemical shift images relative to comparable standard images. Both myelolipomas and 26 of 27 benign cortical masses displayed a loss of signal intensity on at least one chemical shift image; all 12 metastases, the three hemorrhages, and a cyst did not. Opposed-phase images were slightly more sensitive than fat-suppressed images in depicting lipid within benign cortical masses. All masses had higher signal intensity than that of the liver on standard T2-weighted MR images. Chemical shift MR imaging can demonstrate lipid within benign adrenocortical masses and thus increase specificity, potentially obviating biopsy and aggressive follow-up.     

Fatty liver. Chemical shift phase-difference and suppression magnetic resonance imaging techniques in animals, phantoms, and humans.

In vitro animal and human models were used to evaluate the potential of chemical shift magnetic resonance imaging (MRI) for assessing fatty liver. Phantoms of varying fat content were created from mayonnaise-agar preparations. Fatty liver was induced in eight rats by feeding them ethanol for three to six weeks (36% of total calories), whereas eight control rats were fed a normal diet. T1-weighted in-phase and opposed-phase MR images were obtained of the phantoms animals, and 28 human subjects. Additional images obtained in animals included long TR images with in-phase and opposed-phase technique, and hybrid chemical shift water and fat suppression. The rats were killed and histologic status was graded blindly by a hepatopathologist as normal, mild, moderate, or severe fatty change, for correlation with MR grading. Quantitative analysis of MR images included fat signal fraction for animals, and relative signal decrease between in-phase and opposed-phase images for phantom and human data. Phantom in-phase signal increased linearly with respect to fat content, whereas opposed-phase signal decreased linearly. MRI and histologic grading of rat livers were highly correlated, especially when based on water suppression images (r = 0.91, P = .0001). Opposed-phase images were also highly correlated, while fat suppression images were less effective. There was no overlap between MR-derived fat fractions for control (2.6%-5.7%) versus ethanol-fed rats (7.7%-17.9%, P = .0002). Human liver considered to be fatty by visual inspection (n = 8) had higher relative signal decrease than nonfatty liver (n = 22) (P less than .001). Phantom, animal, and human data demonstrate that comparison of T1-weighted in-phase and opposed-phase images is both practical and sensitive in the detection and grading of fatty liver.     

Radiological assessment of mesenteric and retroperitoneal cysts in adults: is there a role for chemical shift MRI?

Objective

The purpose of this study was to assess the potential role for chemical shift magnetic resonance imaging (MRI) in identifying lymphangiomas from other cystic mesenteric and retroperitoneal masses.

Materials and methods

A retrospective search of radiology database identified 24 consecutive patients with mesenteric and retroperitoneal cysts (nine men, 15 women; mean age, 41 years; age range, 19-75 years) who had undergone MR which included in-phase and opposed-phase chemical shift imaging. Signal intensity (SI) decrease between in-phase and opposed-phase MR images of the cyst was evaluated qualitatively by two radiologists. Ultrasound (US), computed tomography (CT), and MRI findings of the morphological appearances of all the cystic lesions that demonstrated significant signal drop on chemical shift MR were also recorded.

Results

Of mesenteric and retroperitoneal cysts, 33% (8/24) revealed qualitative decrease in intensity on opposed-phase MR images relative to that seen on in-phase images. On ultrasound, these cysts demonstrated anechoic simple fluid. Their mean CT attenuation was 13 HU (range: 5-20 HU). Signal loss on fat-suppressed T1-weighted sequences was displayed only by a single cyst. None of the lesions with qualitative SI decrease on opposed-phase MR showed suggestion of lipid on US and CT.

Conclusion

The presence of intra cystic lipid detected by chemical shift MR may not be overt on cross-sectional imaging such as US and CT. Chemical shift MRI provides additional sensitivity and specificity as an imaging test for demonstration of lipid within mesenteric and retroperitoneal cysts enabling a higher diagnostic yield for lymphangioma leading to more appropriate patient management.     

Adrenocortical carcinoma: MR imaging appearance with current techniques

The purpose of the study was to define the magnetic resonance (MR) imaging appearance of adrenocortical carcinoma (ACC) with current MR techniques. Eight patients with ACC underwent high-field-strength MR imaging with the following sequences: axial T1-weighted gradient echo, fat-suppressed T1-weighted spin echo, fat-suppressed T2-weighted spin echo, and gadolinium-enhanced T1-weighted gradient echo and fat-suppressed T1-weighted spin echo. Postcontrast images were also acquired in the sagittal (six patients) and coronal (three patients) planes. Out-of-phase gradient-echo images were obtained in two patients. Lesion morphology, signal intensity features, and presence of metastatic disease were retrospectively evaluated. MR imaging features of ACC included internal hemorrhage (seven of eight patients), central necrosis (seven of eight), and peripheral enhancing nodules (seven of eight). Out-of-phase images in two of two patients demonstrated signal loss compared with in-phase images, which may be a common feature of these tumors. Liver metastases were present in four patients. Consistent MR features of ACC are Identified.     

Giant adrenal myelolipoma with minimal fat content in a patient with homozygous beta-thalassemia: appearance on MRI

Giant adrenal myelolipoma is an uncommon entity. We present the atypical MR imaging findings of a giant adrenal myelolipoma in a patient with homozygous beta-thalassemia with histopathology correlation. The tumor showed a drop in signal on the opposed-phase images, with no evidence of macroscopic fat contents, and demonstrated very high signal intensity on T2-weighted images. Giant adrenal myelolipoma should be considered in the differential diagnosis of tumors with the combination of the above MR imaging characteristics.     

Nondysplastic nodules that are hyperintense on T1-weighted gradient-echo MR imaging: frequency in cirrhotic patients undergoing transplantation

OBJECTIVE: Our objective was to determine the frequency and MR imaging findings of nondysplastic nodules that are hyperintense on T1-weighted gradient-echo imaging in patients with cirrhosis who undergo liver transplantation. MATERIALS AND METHODS: Two observers retrospectively evaluated in-phase (4-5 msec), opposed-phase gradient-echo (2.0-2.4 msec), and turbo short tau inversion recovery (STIR) MR images in 68 patients with cirrhosis--but without dysplastic nodules or hepatocellular carcinoma--who underwent MR imaging at 1.5 T within 150 days before liver transplantation. The size, number, signal characteristics, and arterial enhancement pattern of nodules that appear hyperintense on T1-weighted gradient-echo images were evaluated as well as the presence or absence of signal loss on opposed-phase imaging. These imaging findings were correlated with pathologic findings of whole explanted livers. RESULTS: Eleven (16%) of 68 patients had at least one nondysplastic nodule that was hyperintense on T1-weighted MR imaging. Three patients had diffuse nondysplastic hyperintense nodules (>10 nodules) measuring less than 0.5 cm, and the remaining eight patients had 22 nondysplastic hyperintense nodules ranging in size from 0.5 to 2.5 cm (mean, 1.2 cm), of which 13 were isointense and nine were hypointense on turbo STIR images. No lesion lost signal on opposed-phase imaging or enhanced during the hepatic arterial phase. CONCLUSION: In cirrhotic patients undergoing liver transplantation, nondysplastic nodules that are hyperintense are common findings on T1-weighted gradient-echo MR imaging and do not lose signal intensity on opposed-phase imaging or enhance during the hepatic arterial phase. These nodules may be indistinguishable from dysplastic nodules.     

The utility of in-phase/opposed-phase imaging in differentiating malignancy from acute benign compression fractures of the spine

BACKGROUND AND PURPOSE: Benign and malignant fractures of the spine may have similar signal intensity characteristics on conventional MR imaging sequences. This study assesses whether in-phase/opposed-phase imaging of the spine can differentiate these 2 entities. METHODS: Twenty-five consecutive patients who were evaluated for suspected malignancy (lymphoma [4 patients], breast cancer [3], multiple myeloma [2], melanoma [2], prostate [2], and renal cell carcinoma [1]) or for trauma to the thoracic or lumbar spine were entered into this study. An 18-month clinical follow-up was performed. Patients underwent standard MR imaging with an additional sagittal in-phase (repetition time [TR], 90-185; echo time [TE], 2.4 or 6.5; flip angle, 90 degrees ) and opposed-phase gradient recalled-echo sequence (TR, 90-185, TE, 4.6-4.7, flip angle, 90 degrees ). Areas that were of abnormal signal intensity on the T1 and T2 sequences were identified on the in-phase/opposed-phase sequences. An elliptical region of interest measurement of the signal intensity was made on the abnormal region on the in-phase as well as on the opposed-phase images. A computation of the signal intensity ratio (SIR) in the abnormal marrow on the opposed-phase to signal intensity measured on the in-phase images was made. RESULTS: Twenty-one patients had 49 vertebral lesions, consisting of 20 malignant and 29 benign fractures. There was a significant difference (P < .001, Student t test) in the mean SIR for the benign lesions (mean, 0.58; SD, 0.02) compared with the malignant lesions (mean, 0.98; SD, 0.095). If a SIR of 0.80 as a cutoff is chosen, with >0.8 defined as malignant and <0.8 defined as a benign result, in-phase/opposed-phase imaging correctly identified 19 of 20 malignant lesions and 26 of 29 benign lesions (sensitivity, 0.95; specificity, 0.89). CONCLUSION: There is significant difference in signal intensity between benign compression fractures and malignancy on in-phase/opposed-phase MR imaging.     

Curvilinear areas in the perinephric fat seen on MR images.

AIM: On magnetic resonance (MR) images, strands correspond to curvilinear areas running in the perinephric fat, and haloes to those lying on the renal surface. Our aim was to examine the diagnostic significance and histopathological basis of these areas. PATIENTS AND METHODS: MR images obtained in 46 patients without renal disease and 96 patients with renal disease were assessed for the signal intensity and extent of strands and haloes, and their degree of right-left asymmetry. RESULTS: Strands usually revealed low signal intensity on T1-weighted MR images and high signal intensity on fat-suppressed T2-weighted images and contrast-enhanced fat-suppressed T1-weighted images. Haloes revealed high signal intensity on fat-suppressed T2-weighted images, but most of haloes were not clearly depicted on T1-weighted images or contrast-enhanced fat-suppressed T1-weighted images. Strands and haloes were common and usually symmetrical or only mildly asymmetrical in both patient groups. However, in 11 of the 96 patients with renal disease, prominent strands and/or haloes appeared with remarkable asymmetry and likely represented definite changes in the perinephric fat. At histopathology, vascular loose fibrous tissue was found at the sites of strands and haloes. CONCLUSION: Strands and haloes usually represent normal anatomical variations. However, the presence of prominent strands or haloes with remarkable right-left asymmetry implies abnormality and may provide additional information in the evaluation of renal disease.     

MR imaging of renal cell carcinoma: its role in determining cell type

Chemical shift gradient-echo MR imaging (CSI) can detect a small amount of fat as signal loss on opposed-phase images as compared with in-phase images. Cytoplasmic fat in clear cell renal cell carcinoma (RCC) or interstitial histiocytic fat in papillary cell RCC can be successfully demonstrated by this technique. T2*-weighted gradient-echo or echo-planar MR imaging can detect local susceptibility, for example, due to cytoplasmic or interstitial histiocytic hemosiderin deposition in papillary cell RCC. CSI can also show this focal susceptibility as excessive signal loss on in-phase images as compared with opposed-phase images. MR imaging can thus help predict the cell types (clear cell and papillary cell) of RCC. These findings may be important in the decision-making process in the management of patients with suspected RCC, particularly those who are not indicated for radical surgery.     

Characterization of adrenal tumors by chemical shift fast low-angle shot MR imaging: comparison of four methods of quantitative evaluation

OBJECTIVE: The aim of our study was to assess quantitative methods of distinguishing adenomas from malignant adrenal lesions using chemical shift fast low-angle shot MR imaging. MATERIALS AND METHODS: We assessed 102 adrenal tumors in 88 patients (27 hyperfunctioning and 44 nonhyperfunctioning adenomas, 19 metastases, nine pheochromocytomas, and three other adrenal tumors) using chemical shift MR imaging. On the chemical shift imaging, signal intensity index, calculated as [(signal intensity on in-phase imaging - signal intensity on opposed-phase imaging) / (signal intensity on in-phase imaging)] x 100%, was compared with the adrenal-to-spleen ratio, adrenal-to-muscle ratio, and adrenal-to-liver ratio for signal change on opposed-phase fast low-angle shot MR imaging. The tissues in the spleen, paraspinal muscle, and liver were reference tissues. RESULTS: The signal intensity index had several advantages over the other three parameters calculated. We found no overlap in indexes between adenomas and metastatic tumors. The accuracy in distinguishing adenomas from metastatic tumors was 100% if the cutoff value of the signal intensity index selected was 11.2-16.5%. CONCLUSION: The signal intensity index is the most reliable evaluation method for differentiating adrenal adenomas from metastatic adrenal tumors.     

T1-weighted spoiled gradient-echo MR imaging of focal hepatic lesion: comparison of in-phase vs opposed-phase pulse sequence

The goal of our prospective study was to compare quantitatively and qualitatively in-phase and opposed-phase T1-weighted breath-hold spoiled gradient-recalled-echo (GRE) MR imaging technique for imaging focal hepatic lesion. Thirty-eight patients with 53 focal hepatic lesions had in-phase (TR = 12.3 ms, TE = 4.2 ms) and opposed-phase (TR = 10.1 ms, TE = 1.9 ms) GRE (flip angle = 30°, bandwidth ± 32 kHz, matrix size 256 × 128, one signal average) MR imaging at 1.5 T. Images were analyzed quantitatively by measuring the lesion-to-liver contrast and for lesion detection. In addition, images were reviewed qualitatively for lesion conspicuity. Quantitatively, lesion-to-liver contrast obtained with in-phase (3.22 ± 1.86) and opposed-phase pulse sequence (3.72 ± 2.32) were not statistically different (Student's t-test). No difference in sensitivity was found between in-phase and opposed-phase pulse sequence (31 of 53, sensitivity 58 % vs 30 of 53, sensitivity 57 %, respectively). Two lesions not seen with opposed-phase imaging were detected with in-phase imaging. Conversely, one lesion not seen on in-phase imaging was detected on opposed-phase imaging so that the combination of in-phase and opposed-phase imaging yielded detection of 32 of 53 lesions (sensitivity 60 %). Qualitatively, lesion conspicuity was similar with both techniques. However, in-phase images showed better lesion conspicuity than opposed-phase images in 9 cases, and opposed-phase images showed better lesion conspicuity than in-phase images in 7 cases. No definite advantage (at a significant level) emerged between in-phase and opposed-phase spoiled GRE imaging. Because differences in lesion conspicuity and lesion detection may be observed with the two techniques in individual cases, MR evaluation of patients with focal hepatic lesion should include both in-phase and opposed-phase spoiled GRE imaging. Received 30 October 1996; Revision received 6 January 1997; Accepted 8 January 1997     

MR signal intensity characteristics in Legg-Calvé-Perthes disease. Value of fat-suppressed (STIR) images and contrast-enhanced T1-weighted images

PURPOSE: To evaluate the MR signal intensity characteristics in Legg-Calvé-Perthes disease on fat-suppressed (STIR) images and contrast-enhanced T1-weighted spin-echo images, and to develop criteria for the administration of contrast material. MATERIAL AND METHODS: Twenty children with Legg-Calvé-Perthes disease underwent conventional radiography and MR imaging of the hip utilizing fat-suppressed (STIR) sequences and T1-weighted spin-echo sequences before and after i.v. contrast administration. The signal intensity characteristics of the femoral head and the proximal femoral metaphysis were assessed retrospectively by two pediatric radiologists. RESULTS: Evaluation of the MR images revealed six different signal patterns within the femoral head: 1) isointense signal on all images; 2) complete signal void on all images; 3) hyperintense signal on STIR images with; or 4) without contrast enhancement on T1-weighted spin-echo images; 5) isointense signal on STIR images with; or 6) without contrast enhancement on T1-weighted images. Within the metaphysis three different signal patterns were differentiated. CONCLUSION: Combination of fat-suppressed (STIR) sequences and T1-weighted pre- and post-contrast sequences allows an accurate evaluation of Legg-Calvé-Perthes disease. In patients without signal alterations or complete signal loss on fat-suppressed and T1-weighted spin-echo images, administration of i.v. contrast is not necessary. In case of bone marrow edema on fat-supressed images, contrast-enhanced T1-weighted images are required to identify viable osseous fragments.     

Characterization of the "red zone" of knee meniscus: MR imaging and histologic correlation

PURPOSE: To determine the extent and vascularity of knee menisci with conventional and gadolinium-enhanced magnetic resonance (MR) imaging in cadaveric specimens, with histologic findings as the reference standard, and to investigate signal intensity changes in menisci and perimeniscal soft tissues in symptomatic patients. MATERIALS AND METHODS: Radial dimensions and enhancement patterns of menisci were recorded and compared in (a) 12 cadaveric menisci examined with conventional and gadolinium-enhanced intermediate-weighted and fat-suppressed T1-weighted spin-echo MR imaging, high-spatial-resolution T1-weighted and fast low-angle shot MR imaging, and gross anatomic and histologic specimens and (b) 18 patients examined with conventional and gadolinium-enhanced fat-suppressed T1-weighted spin-echo MR imaging. RESULTS: No differences in radial measurements of the meniscus were found for different MR techniques (P =.551). Despite the presence of vessels in the peripheral 10%-15% of the menisci, no enhancement of menisci was detected in specimens or patients. Perimeniscal soft-tissue enhancement adjacent to the posterior horn was greater than that adjacent to the anterior horn (P <.05), and enhancement of the lateral meniscal body was greater than that of the medial meniscal body (P <.05). CONCLUSION: The wedge-shaped low-signal-intensity structure seen on MR images represents the entire meniscus. Intravenous injection of contrast material does not appear to be useful for differentiation of the vascularized from the nonvascularized zone of the meniscus.     

High signal peripancreatic fat on fat-suppressed spoiled gradient echo imaging in acute pancreatitis: preliminary evaluation of the prognostic significance

PURPOSE: To evaluate peripancreatic signal changes on fat-suppressed T1-weighted spoiled gradient echo images associated with acute pancreatitis and investigate potential utility in regards to relationship to clinical outcome. MATERIALS AND METHODS: The abdominal MR images in 31 patients with acute pancreatitis were reviewed, and evaluated for the presence of elevated signal intensity within the peripancreatic fat on fat-suppressed T1-weighted spoiled gradient echo images; the degree of signal changes was graded as mild, moderate, or severe. RESULTS: Ten of 31 patients demonstrated abnormal high signal intensity in the peripancreatic fat on fat-suppressed T1-weighted images. The degree of signal change was mild in three patients, moderate in one, and severe in six patients. All six patients with severe elevated peripancreatic soft tissue signal died within seven to 68 days (mean, 47 days) of their admission. All 21 patients without elevated peripancreatic fat signal survived without any complications. The correlation between the presence and severity of elevated peripancreatic MR signal and patient outcome was significant (P < 0.05). CONCLUSION: Elevated peripancreatic signal on fat-suppressed T1-weighted images is associated progressively with poor outcome in patients with acute pancreatitis, and may represent a simplified method for prognostic cross-sectional imaging.     

MR imaging of tuberculous arthritis: Clinical and experimental studies

Signal-intensity characteristics of magnetic resonance (MR) images were assessed in five patients and in 10 rabbits with tuberculous arthritis. MR imaging findings were compared with histologic findings in the animal study. In both of clinical and experimental cases, tuberculous lesions showed both intermediate and high signal intensity on T2-weighted images, while they showed heterogeneously intermediate signal intensity on T1-weighted images. As T2-weighted images were compared with pathologic specimens, intermediate signal intensity corresponded to caseous necrosis, whereas high signal intensity related to granulomas or effusion. Postcontrast T1-weighted images showed enhancement at the peripheries rather than the centers of tuberculous lesions. These results indicate that tuberculous arthritis should be included in the differential diagnosis when intra-articular lesions with low or intermediate signal intensity are found on T2-weighted images.     

Cartilaginous endplates of the spine: MRI with anatomic correlation in cadavers

PURPOSE: The purpose of this work was to describe the MR appearance of cartilaginous endplates (CEPs) with close anatomic correlation in cadavers derived from elderly subjects. METHOD: High-resolution MRI was performed on five cadaveric lumbar spines, and a total of 48 CEPs were studied with T1-weighted spin echo, T2-weighted fast spin echo, and fat-suppressed 3D spoiled GRASS gradient echo (SPGR) MR images. All specimens underwent anatomic sectioning, and gross anatomic findings were correlated with those of MRI. RESULTS: Conventional MR images allowed gross morphologic evaluation of the integrity of the CEPs and demonstrated cartilaginous nodes. In all specimens, fat-suppressed 3D-SPGR images invariably improved visualization of the fine anatomic structures at the diskovertebral junction (p < 0.01). Various morphologic abnormalities of the CEPs demonstrated on MR images, including thinning, irregularity, erosions, cartilaginous defects, and Schmorl nodes, were confirmed on anatomic inspection. CONCLUSION: Results in our study indicate that MRI may delineate the normal anatomy of CEPs and demonstrate morphologic changes occurring at the diskovertebral junction. Dedicated high-resolution technique and fat-suppressed 3D-SPGR images may significantly improve the diagnostic capabilities of MRI of this particular anatomic region.     

MR imaging of a case of adenomatoid tumor of the adrenal gland

The aim of this case report is to describe the appearance on magnetic resonance imaging (MRI) of an incidentally found adenomatoid tumor of the adrenal gland, and to evaluate the utility of MRI in characterizing this type of tumor. The appearance of the tumor was nonspecific on T1-weighted in-phase, opposed-phase, and T2-weighted images, as well as its behavior after paramagnetic contrast administration, outlining the differential diagnosis among carcinoma, metastatic tumors, and pheochromocytoma. After surgery, the pathologic diagnosis was adenomatoid benign tumor of mesothelial origin. Although MRI enables the characterization of most benign lesions of the adrenal gland, the appearance of other lesions is nonspecific. In our case, MRI did not assist in preoperative diagnosis, guiding us towards a diagnosis of malignancy. Received: 16 February 1998; Revision received: 17 April 1998; Accepted: 12 May 1998     

Incidentally discovered adrenal masses: evaluation with Gadolinium enhancement and fat-suppressed MR imaging at 0.5 T

The purpose of the study is to evaluate the ability of Gd-enhancement and fat-suppressed MR imaging operating at midfield strength to characterize incidentally discovered adrenal masses. Sixty patients with 72 adrenal masses incidentally discovered during US or CT exams were studied with a 0.51 MR unit following clinical and laboratory evaluation. After Gd-DTPA intravenous administration a modified three-point Dixon technique was performed in all patients. This technique provided three images sets: conventional T1-weighted SE images, fat-suppressed T1-weighted images and water-suppressed T1-weighted images. Diagnosis was established by means of surgery (11 lesions), fineneedle biopsy (21 lesions) and stability on ultrasonographic follow-up for at least 1 year (range, 12–87 months) from adrenal lesion discovery (40 masses). In most of adenomas (n = 55) an homogeneous enhancement was observed on postcontrast T1WI; however, 15 out of these lesions showed a small focal spot of high intensity in Gd-enhanced fat-suppressed images. On the contrary, malignant conditions (n = 6) and pheochromocytoma (n = 1), all had inhomogeneous signal intensities which were relatively higher after Gadolinium injection as compared with the liver. The fat suppression technique demonstrated areas of bright signal intensity related to high vascularity. The performance of three observers in order to differentiate malignant from benign conditions showed sensitivity, specificity, diagnostic accuracy, positive and negative predictive values of 100, 88.5, 90, 50 and 100% on the basis of gadolinium enhancement only, by utilizing the Dixon technique. In conclusion, although Gd-enhancement and fat-suppressed sequence helped correctly differentiate among the groups of incidentally discovered adrenal masses, the degree of overlap suggests that it is still difficult to characterize individual patients. However, the modified three-point Dixon technique after contrast material administration appears to be a further capability of midfield MRI in the characterization of adrenal tissue.     

Relationship between MR imaging and histopathologic findings of the brain in extremely sick preterm infants.

BACKGROUND AND PURPOSE: MR imaging can now be used safely in extremely preterm infants. The aim of this study was to compare the MR imaging appearance of the immature brain with neuropathologic findings at postmortem examination. METHODS: Seven extremely sick preterm infants, born at a median of 24 weeks' gestation, were studied using T1- and T2-weighted MR sequences. Infants died at a median of 3 days after initial MR imaging, and postmortem examinations were carried out. RESULTS: The cortex and germinal matrix were seen as areas of low signal intensity on T2-weighted images, which corresponded to their highly cellular histologic appearance. The periventricular and subcortical layers of white matter had a high signal intensity, corresponding to high fiber and relatively low cellular density; the intermediate layer of low signal intensity corresponded to a dense band of migrating cells. Regions of acute hemorrhage were seen as low signal intensity and regions of infarction as high signal intensity on T2-weighted images. One infant with mild periventricular leukomalacia had some low signal intensity on T1-weighted images, but no focal changes on T2-weighted images. Regions of neuronal mineralization, seen in association with infarction and capillary proliferation, within the basal ganglia and thalami were characterized by very low signal intensity on T2-weighted images and by very high signal intensity on T1-weighted images. There were no imaging abnormalities detected in regions with more subtle histologic abnormalities, such as increased glial or apoptotic cells. CONCLUSION: MR imaging can be used to observe normal developing brain anatomy in extremely premature infants; it can detect areas of hemorrhage and infarction within the developing brain, but conventional MR imaging may not detect more subtle histologic abnormalities.     

Liver fat: effect of hepatic iron deposition on evaluation with opposed-phase MR imaging

PURPOSE: To retrospectively determine the effect of liver iron deposition on the evaluation of liver fat by using opposed-phase magnetic resonance (MR) imaging. MATERIALS AND METHODS: Committee on Human Research approval was obtained, and compliance with HIPAA regulations was observed. Patient consent was waived by the committee. Thirty-eight patients with cirrhosis (30 men, eight women; mean age, 58 years; range, 34-76 years) who underwent abdominal MR imaging and had contemporaneous liver biopsy were retrospectively identified. Two radiologists independently quantified liver fat according to the relative loss of signal intensity and compared this loss on opposed-phase and in-phase T1-weighted gradient-echo images. Liver fat percentage and presence of iron deposition were independently recorded by a pathologist. Generalized linear models, which included a mixed-random effects model, were used to determine the effect of iron deposition on the Spearman correlation coefficient for relative signal intensity loss versus histopathologically determined fat percentage. RESULTS: Liver iron deposition was found in 25 of 38 patients. Liver fat percentage (mean, 3%; range, 0%-25%) was identified histopathologically in 14 of 38 patients and in nine of 25 patients with iron deposition. For both readers, relative signal intensity loss at opposed-phase imaging was closely and significantly correlated (P < .05) with histopathologically determined liver fat percentage in patients without iron deposition (r = 0.7 for reader 1, r = 0.6 for reader 2), but no such correlation was found in patients with iron deposition (r = 0.1 for reader 1, r = -0.31 for reader 2; P > .05). CONCLUSION: Signal intensity loss on in-phase images caused by the presence of liver iron is a potential pitfall in the determination of liver fat percentage at opposed-phase MR imaging in chronic liver disease.