Opposed-phase Magnetic Resonance Imaging Research Articles

Added values of diffusion weighted imaging, Dynamic contrast enhancement and opposed phase MRI in evaluation of bony lesions around the knee & ankle joints

Background: Magnetic resonance imaging (MRI) represents the most advanced imaging technique in diagnosis of bone tumors being more sensitive in assessing bone marrow changes and extent of tumors compared to CT and plain X-ray. The distinction between malignant and benign neoplasms is mandatory for appropriate therapeutic choices and planning. MRI has the upper hand in the assessment of such tumors due to its brilliant soft tissue discrimination. The use of multiparametric MRI techniques increase accuracy of discrimination between malignant and benign lesions. Results: This prospective study included 34 patients; 16 males and 18 females with musculoskeletal complaint around the knee & ankle joints. Their age ranged from 10 to 65 years (mean age was 26.65 ± 17.23 years). The cut off value of ADC for bony lesions (by ROC curve) was ≤ 1 to be considered malignant. At this cut off point; the sensitivity of ADC to detect malignant and to exclude benign lesions was 83.3 % and the specificity was 86.4 %. The cut off value for SIR for bony lesions (by ROC curve) was ≥ 0.89 to be considered malignant.

Accuracy of Opposed-phase Magnetic Resonance Imaging for the Evaluation of Treated and Untreated Spinal Metastases

To assess whether the accuracy of opposed-phase magnetic resonance (MR) imaging to differentiate spinal metastases from benign lesions is influenced by treatment. We retrospectively evaluated 25 benign lesions, 25 untreated spinal metastases, and 89 treated spinal metastases in 101 patients who underwent opposed-phase MR spine imaging at our institution. The largest possible region of interest was placed over the lesion in question on out-of-phase and in-phase MR sequences, and the signal intensity ratio (SIR) of the lesions was calculated. The SIRs were compared between benign, untreated, and treated lesions. Receiver operator characteristic (ROC) curves were used to identify the optimal threshold to differentiate benign lesions from untreated spinal metastases, and the accuracy of this threshold was assessed for treated spinal metastases, chemotherapy-treated spinal metastases, and radiated spinal metastases. Benign lesions had lower mean SIR than untreated (P = 2.4 × 10-8, 95% confidence interval [0.29, 0.51]) and treated spinal metastases (P = .51; 95% confidence interval [-0.13, 0.06]). A cutoff SIR of 0.856 had an accuracy of 88.00% for untreated lesions, 77.48% for previously treated lesions, and 70.45% for previously radiated lesions. The ROC curve to differentiate benign lesions from radiated spinal metastases was significantly different from the ROC curve to differentiate benign lesions from untreated spinal metastases (P = .0180). The ROC curve to differentiate benign lesions from lesions treated with chemotherapy only was significantly different from the ROC curve to differentiate between benign lesions and radiated spinal metastases (P = .041). Opposed-phase imaging is less accurate for treated spinal metastases, in particular after radiation.

Comparative accuracy of CT, dual-echo MRI and MR spectroscopy for preoperative liver fat quantification in living related liver donors.

Background:It is of significant importance to assess the extent of hepatic steatosis in living donor liver transplant (LDLT) surgery to ensure optimum graft regeneration as well as donor safety.Aim:To establish the accuracy of non-invasive imaging methods including computed tomography (CT), dual-echo in- and opposed-phase magnetic resonance imaging (MRI), and MR spectroscopy (MRS) for quantification of liver fat content (FC) in prospective LDLT donors with histopathology as reference standard.Settings and Design:This retrospective study was conducted at our institution on LDLT donors being assessed for biliary and vascular anatomy depiction by Magnetic Resonance Cholangiopancreatography (MRCP) and CT scan, respectively, between July 2013 and October 2014.Materials and Methods:Liver FC was measured in 73 donors by dual-echoT1 MRI and MRS. Of these, CT liver attenuation index (LAI) values were available in 62 patients.Statistical Analysis:CT and MRI FC were correlated with histopathological reference standard using Spearman correlation coefficient. Sensitivity, specificity, positive predictive value, negative predicative value, and positive and negative likelihood ratios with 95% confidence intervals were obtained.Results:CT LAI, dual-echo MRI, and MRS correlated well with the histopathology results (r = 0.713, 0.871, and 0.882, respectively). An accuracy of 95% and 96% was obtained for dual-echo MRI and MRS in FC estimation with their sensitivity being 97% and 94%, respectively. False-positive rate, positive predictive value (PPV), and negative predicative value (NPV) were 0.08, 0.92, and 0.97, respectively, for dual-echo MRI and 0.03, 0.97, and 0.95, respectively, for MRS. CT LAI method of fat estimation has a sensitivity, specificity, PPV, and NPV of 73%, 77.7%, 70.4%, and 80%, respectively.Conclusion:Dual-echo MRI, MRS, and CT LAI are accurate measures to quantify the degree of hepatic steatosis in LDLT donors, thus reducing the need for invasive liver biopsy and its associated complications. Dual-echo MRI and MRS results correlate better with histological results in the study, as compared to CT LAI method for fat quantification.

Utility of opposed-phase magnetic resonance imaging in differentiating sarcoma from benign bone lesions

PurposeTo investigate the utility of opposed-phase magnetic resonance imaging (OP MRI) in differentiating malignant from benign bone lesions. Materials and methodsMRI scans of musculoskeletal lesions including opposed-phase imaging sequences were reviewed by both an experienced musculoskeletal attending radiologist, and a second year radiology resident. The change in signal from IP to OP images was measured. The reviewers' evaluation of the lesions based on T1 and T2-weighted images was compared to their evaluation with inclusion of the OP sequences. ResultsTwenty-seven lesions in bone were analyzed: 4 malignant primary bone lesions, 3 malignant soft tissue lesions to bone, 3 metastases from visceral malignancies, and 17 benign bone lesions. Benign lesions of bone dropped in signal on OP imaging by an average of 37.1%. Five of the benign lesions decreased in signal by less than 20%, and two increased. Malignant bone lesions dropped in signal by an average of 0.69% with one of the ten lesions showing a greater than 20% drop.When OP sequences were included, concern for malignancy decreased in benign lesions and increased in malignant lesions, for both the resident and attending. Compared with standard MRI, inclusion of these sequences increased the overall confidence in diagnosis for both reviewers. ConclusionOpposed-phase imaging is helpful in differentiating benign from malignant lesions in bone. Confidence in diagnosis rose for both the attending and the resident as result of the inclusion of OP sequences.

Angiomyolipoma with Minimal Fat: Can It Be Differentiated from Clear Cell Renal Cell Carcinoma by Using Standard MR Techniques?

To retrospectively assess whether magnetic resonance (MR) imaging with opposed-phase and in-phase gradient-echo (GRE) sequences and MR feature analysis can differentiate angiomyolipomas (AMLs) that contain minimal fat from clear cell renal cell carcinomas (RCCs), with particular emphasis on small (<3-cm) masses. Institutional review board approval and a waiver of informed consent were obtained for this HIPAA-compliant study. MR images from 108 pathologically proved renal masses (88 clear cell RCCs and 20 minimal fat AMLs from 64 men and 44 women) at two academic institutions were evaluated. The signal intensity (SI) of each renal mass and spleen on opposed-phase and in-phase GRE images was used to calculate an SI index and tumor-to-spleen SI ratio. Two radiologists who were blinded to the pathologic results independently assessed the subjective presence of intravoxel fat (ie, decreased SI on opposed-phase images compared with that on in-phase images), SI on T1-weighted and T2-weighted images, cystic degeneration, necrosis, hemorrhage, retroperitoneal collaterals, and renal vein thrombosis. Results were analyzed by using the Wilcoxon rank sum test, two-tailed Fisher exact test, and multivariate logistic regression analysis for all renal masses and for small masses. A P value of less than .05 was considered to indicate a statistically significant difference. There were no differences between minimal fat AMLs and clear cell RCCs for the SI index (8.05%±14.46 vs 14.99%±19.9; P=.146) or tumor-to-spleen ratio (-8.96%±16.6 and -15.8%±22.4; P=.227) when all masses or small masses were analyzed. Diagnostic accuracy (area under receiver operating characteristic curve) for the SI index and tumor-to-spleen ratio was 0.59. Intratumoral necrosis and larger size were predictive of clear cell RCC (P<.001) for all lesions, whereas low SI (relative to renal parenchyma SI) on T2-weighted images, smaller size, and female sex correlated with minimal fat AML (P<.001) for all lesions. The diagnostic accuracy of opposed-phase and in-phase GRE MR imaging for the differentiation of minimal fat AML and clear cell RCC is poor. In this cohort, low SI on T2-weighted images relative to renal parenchyma and small size suggested minimal fat AML, whereas intratumoral necrosis and large size argued against this diagnosis.

Assessment of Association Between Low Back Pain and Paraspinal Muscle Atrophy Using Opposed-Phase Magnetic Resonance Imaging

A cross-sectional imaging study of young adults. To evaluate whether severity of low back symptoms predicts atrophy in the paraspinal muscles of young adults. Although an increased fat content of the lumbar muscles has been observed among adults with chronic LBP, there is limited knowledge of this association in younger populations. The population-based study sample consisted of 554 subjects (321 females and 233 males) from the 1986 Northern Finland Birth Cohort. Latent Class Analysis (LCA) was used to cluster the subjects according to the low back symptoms and functional limitations at 18, 19, and 21 years. The mean age of the subjects at the time of the MRI (magnetic resonance imaging) was 21 years (range, 20-23). Muscle atrophy was evaluated by assessing the fat content of the paraspinal muscles using Opposed-Phase MRI. The cross-sectional areas (CSAs) of the erector spinae and multifidus muscles were also measured. LCA analysis produced five clusters differing in symptoms, ranging from a cluster (n = 65) in which subjects had high likelihood of symptoms and functional limitations at all time points, to a cluster (n = 165) with no pain ever. The fat content of the multifidus muscles was significantly higher among women than men (14.0% vs. 5.3%, P < 0.001), but it was not significantly associated with symptom severity. The CSA of both erector spinae and multifidus muscles were significantly larger among men than women (P < 0.001 in all of the muscles), but were not associated with pain severity. Low back symptoms and functional limitations over a 3-year period were not associated with increased fat content or a reduction in the cross-sectional area of lumbar paraspinal muscles among young adults.

Feasibility of dual gradient-echo in-phase and opposed-phase magnetic resonance imaging for the evaluation of epicardial fat

Dual gradient-echo in-phase (IP) and opposed-phase (OP) magnetic resonance imaging (MRI) can evaluate small amounts of fat, and is widely used for imaging abdominal organs. Epicardial fat has recently been revealed as having an important role in the development of heart disease, but IPOP-MRI has not been widely applied in this field, probably because of cardiac motion artifacts. To demonstrate the feasibility of IPOP-MRI with electrocardiography (ECG)-gating for evaluation of epicardial fat in the normal human heart, compared to black-blood T1-weighted imaging (T1WI). Ten healthy volunteers were studied. Epicardial fat volume was quantitatively evaluated on OP-from-IP subtraction images and T1-weighted images. Epicardial fat was clearly visualized on the subtraction images as hyperintense areas that corresponded to regions identified as epicardial fat on the T1-weighted images. Epicardial fat volume correlated well between the two methods (r = 0.93, P <0.0001), and tended to be larger on the subtraction images than on the T1-weighted images (91.4 ± 30.1 vs. 84.1 ± 30.5 mL, P = 0.07). IPOP-MRI with ECG-gating may be a useful alternative method to black-blood T1WI for evaluation of epicardial fat.

Assessing Signal Intensity Change on Well-registered Images: Comparing Subtraction, Color-encoded Subtraction, and Parallel Display Formats

To assess the sensitivity, specificity, accuracy, and interobserver reliability of subtraction, color-encoded subtraction, and parallel display formats in assessing signal intensity (SI) differences between well-registered images. Institutional ethics approval for the study and a waiver of individual patient consent were obtained. Five radiologists graded the severity of fatty liver by using a seven-point scale for four imaging sets created from 179 pairs of dual-echo in- and opposed-phase magnetic resonance images from 179 patients. The four sets contained images displayed in parallel, subtraction images, color-encoded subtraction images, and images from the three previous formats presented together. The order of the images and sets was randomized. Sensitivity and specificity were assessed with the McNemar test. Accuracy was assessed by using three-way analysis of variance, with Tukey post hoc methods used to assess differences between the four formats. Interobserver reliability was assessed by using the Fleiss κ value. Subtraction (P = .016 at a 5% SI difference threshold) and color-encoded subtraction (P = .031 at a 4% SI difference threshold) formats had higher sensitivity than did the parallel format. The accuracy of the subtraction format was superior to that of the parallel format (P < .0001). Interobserver reliability of the subtraction (κ = 0.53) and color-encoded subtraction (κ = 0.39) formats was superior to that of the parallel format (κ = 0.33) (P < .0001 and P = .0085, respectively). When images are well registered, subtraction and color-encoded subtraction techniques offer advantages over the traditional parallel presentation format for the assessment of SI differences.

Identification of Fat in Myxoid Matrix-Rich Mesenteric Lipoblastoma Using In-Phase and Opposed-Phase MRI: A Case Report

Lipoblastoma is a rare benign tumor composed of embryonic fat that most often presents in children younger than 3 years of age (1-4). Imaging findings of the tumor reflect the histopathologic features typically showing a mixture of mature and immature adipocytes, often with an abundant myxoid matrix (1-3). In most cases, the imaging diagnosis of lipoblastoma can be made in young children without difficulty by identifying fat in the tumor on CT or magnetic resonance (MR) imaging (1, 2). The presence of this fat component of lipoblastoma is generally confirmed by T1-weighted MR imaging without and with fat saturation, which usually obviates the additional use of T1-weighted gradient-echo in-phase and opposed-phase MR imaging in identifying fat in fatty tumors (5). Herein, we present a case with myxoid matrix-rich mesenteric lipoblastoma in whom the presence of fat in the tumor was identified by a diffuse signal drop on opposed-phase MR imaging, providing a valuable diagnostic clue. CASE REPORT

Dual Gradient-echo In-phase and Opposed-phase Magnetic Resonance Imaging to Evaluate Lipomatous Metaplasia in Patients with Old Myocardial Infarction

We present an alternative method for evaluating cardiac fat tissue-dual gradient-echo in-phase and opposed-phase magnetic resonance imaging (IPOP-MRI) with electrocardiographic (ECG) gating. Conventional IPOP-MRI can be used to evaluate small amounts of fat and is widely used for abdominal imaging, but cardiac motion artifacts make its use difficult for cardiac imaging. Using ECG gating prior to IPOP-MRI, we evaluated lipomatous metaplasia after myocardial infarction. The areas of lipomatous metaplasia measured by IPOP-MRI with ECG gating correlated well with those areas on black-blood T(1)-weighted imaging (r=0.82, P<0.0001, mean bias-0.29 cm(2), limit of agreement+/-2.06 cm(2)).

Evaluation of diffuse liver steatosis by ultrasound, computed tomography, and magnetic resonance imaging: which modality is best?

Purpose To compare ultrasound, computed tomography (CT), and magnetic resonance imaging (MRI) determination of diffuse liver steatosis. Materials and methods Quantification of liver steatosis on ultrasound, CT, and MRI was correlated with histopathology in 67 patients. Results Opposed-phase MRI demonstrated the highest correlation with steatosis (0.68 and 0.69, P<.01; intraclass correlation coefficient, 0.93). Spearman's correlation (and intraclass correlation) coefficients were lowest for ultrasound [0.54, 0.33 (0.40)] and enhanced CT [0.33, 0.39 (0.97)]. Conclusion Opposed-phase MRI demonstrated best overall performance for determining steatosis.

Liver Steatosis: Investigation of Opposed-Phase T1-weighted Liver MR Signal Intensity Loss and Visceral Fat Measurement as Biomarkers

To investigate if opposed-phase T1-weighted and fat-suppressed T2-weighted liver signal intensity (SI) loss and visceral fat measurement at magnetic resonance (MR) imaging and body mass index (BMI) are correlated with grade of liver steatosis in patients with nonalcoholic fatty liver disease (NAFLD) or hepatitis C virus (HCV) and human immunodeficiency virus (HIV)-related liver disease. Committee on Human Research approval and patient consent were obtained for this HIPAA-compliant study. Fifty-two patients (15 men, 37 women) with NAFLD (n = 29) or HCV and HIV-related liver disease (n = 23) underwent prospective contemporaneous MR imaging and liver biopsy. Liver SI loss was measured on opposed-phase T1-weighted and fat-suppressed T2-weighted MR images. Visceral fat area was measured at three levels on water-suppressed T1-weighted MR images (n = 44). Spearman rank correlation coefficients and recursive partitioning were used to examine correlations. Histopathologic liver steatosis correlated well with liver SI loss on opposed-phase T1-weighted MR images (rho = 0.78), fat-suppressed T2-weighted MR images (rho = 0.75), and average visceral fat area (rho = 0.77) (all P < .01) but poorly with BMI (rho = 0.53, P < .01). Liver SI losses on opposed-phase T1-weighted MR imaging of less than 3%, at least 3% but less than 35%, at least 35% but less than 49%, and at least 49% corresponded to histopathologic steatosis grades of 0 (n = 16 of 17), 1 (n = 11 of 16), 2 (n = 7 of 13), and 3 (n = 5 of 6), respectively. A visceral fat area of greater than or equal to 73.8 cm(2) was associated with the presence of histopathologic steatosis in 41 of 44 patients. Liver SI loss on opposed-phase T1-weighted MR images and visceral fat area may be used as biomarkers for the presence of liver steatosis and appear to be superior to BMI.

Effect of Echo Time Pair Selection on Quantitative Analysis for Adrenal Tumor Characterization with In-Phase and Opposed-Phase MR Imaging: Initial Experience

To determine the effect of two pairs of echo times (TEs) for in-phase (IP) and opposed-phase (OP) 3.0-T magnetic resonance (MR) imaging on (a) quantitative analysis prospectively in a phantom study and (b) diagnostic accuracy retrospectively in a clinical study of adrenal tumors, with use of various reference standards in the clinical study. A fat-saline phantom was used to perform IP and OP 3.0-T MR imaging for various fat fractions. The institutional review board approved this HIPAA-compliant study, with waiver of informed consent. Single-breath-hold IP and OP 3.0-T MR images in 21 patients (14 women, seven men; mean age, 63 years) with 23 adrenal tumors (16 adenomas, six metastases, one adrenocortical carcinoma) were reviewed. The MR protocol involved two acquisition schemes: In scheme A, the first OP echo (approximately 1.5-msec TE) and the second IP echo (approximately 4.9-msec TE) were acquired. In scheme B, the first IP echo (approximately 2.4-msec TE) and the third OP echo (approximately 5.8-msec TE) were acquired. Quantitative analysis was performed, and analysis of variance was used to test for differences between adenomas and nonadenomas. In the phantom study, scheme B did not enable discrimination among voxels that had small amounts of fat. In the clinical study, no overlap in signal intensity (SI) index values between adenomas and nonadenomas was seen (P < .05) with scheme A. However, with scheme B, no overlap in the adrenal gland SI-to-liver SI ratio between adenomas and nonadenomas was seen (P < .05). With scheme B, no overlap in adrenal gland SI index-to-liver SI index ratio between adenomas and nonadenomas was seen (P < .05). This initial experience indicates SI index is the most reliable parameter for characterization of adrenal tumors with 3.0-T MR imaging when obtaining OP echo before IP echo. When acquiring IP echo before OP echo, however, nonadenomas can be mistaken as adenomas with use of the SI index value.

Quantitative evaluation of norcholesterol scintigraphy, CT attenuation value, and chemical-shift MR imaging for characterizing adrenal adenomas

The objective of our study was to evaluate diagnostic ability and features of quantitative indices of three modalities: uptake rate on norcholesterol scintigraphy, computed tomography (CT) attenuation value, and fat suppression on chemical-shift magnetic resonance imaging (MRI) for characterizing adrenal adenomas. Image findings of norcholesterol scintigraphy, CT, and MRI were reviewed for 78 patients with functioning (n = 48) or nonfunctioning (n = 30) adrenal masses. The norcholesterol uptake rate, attenuation value on unenhanced CT, and suppression on in-phase to opposed-phase MRI were measured for adrenal masses. The norcholesterol uptake rate, CT attenuation value, and MR suppression index showed the sensitivity of 60%, 82%, and 100%, respectively, for functioning adenomas of <2.0 cm, and 96%, 79%, and 67%, respectively, for those of >or=2.0 cm. A statistically significant correlation was observed between size and norcholesterol uptake, and between CT attenuation value and MR suppression index. Regarding norcholesterol uptake, the adenoma-to-contralateral gland ratio was significantly higher in cortisol releasing than in aldosterone-releasing adenomas. The norcholesterol uptake rate was reliable for characterization of adenomas among adrenal masses of >or=2.0 cm. CT attenuation value and MR suppression index were well correlated with each other, and were useful regardless of mass size.

Perineal Angiomyxomas: Can a Differential Diagnosis Be Made with Imaging Studies?

HomeRadiologyVol. 245, No. 2 PreviousNext CommunicationsLetters to the EditorPerineal Angiomyxomas: Can a Differential Diagnosis Be Made with Imaging Studies?Mustafa Kemal Demir, Hakan Genchellac, Hüseyin ÖzdemirMustafa Kemal Demir, Hakan Genchellac, Hüseyin ÖzdemirAuthor AffiliationsDepartment of Radiology, Trakya University School of Medicine, 11 kisim, Yasemin Apt, D blok, Daire 35 Ataköy, Istanbul, Turkey 34158 e-mail: [email protected]Mustafa Kemal DemirHakan GenchellacHüseyin ÖzdemirPublished Online:Nov 1 2007https://doi.org/10.1148/radiol.2452070211MoreSectionsFull textPDF ToolsImage ViewerAdd to favoritesCiteTrack CitationsPermissionsReprints ShareShare onFacebookTwitterLinked In References1 Sinha R, Verma R. Case 106: aggressive angiomyxoma. Radiology 2007;242:625–627. Link, Google Scholar2 Ustun C, Malazgirt Z, Kandemir B, Kocak I, Bolat I, Gumus S. Angiomyofibroblastoma of the vulva: case report. Pathol Int 1998;48:964–966. Crossref, Medline, Google Scholar3 Mortele KJ, Lauwers GJ, Mergo PJ, Ros PR. Perineal angiomyofibroblastoma: CT and MR findings with pathologic correlation. J Comput Assist Tomogr 1999;23:687–689. Crossref, Medline, Google Scholar4 Fletcher CD, Tsang WY, Fisher C, Lee KC, Chan JK. Angiomyofibroblastoma of the vulva: a benign neoplasm distinct from aggressive angiomyxoma. Am J Surg Pathol 1992;16:373–382. Crossref, Medline, Google Scholar5 Stewart ST, McCarthy SM. Case 77: aggressive angiomyxoma. Radiology 2004;233:697–700. Link, Google ScholarArticle HistoryPublished in print: 2007 FiguresReferencesRelatedDetailsCited BySolución del caso 20: Angiomixoma agresivoRadiología, Vol. 52, No. 4Radiologic Evaluation of Mesenchymal Tumors of the Female Genital TractSurgical Pathology Clinics, Vol. 2, No. 4Recommended Articles Rare Mesenchymal Tumors of the Pelvis: Imaging and Pathologic CorrelationRadioGraphics2021Volume: 42Issue: 1pp. 143-158Radiologic-Pathologic Correlation of Primary Retroperitoneal NeoplasmsRadioGraphics2020Volume: 40Issue: 6pp. 1631-1657Spectrum of Fat-containing Soft-Tissue Masses at MR Imaging: The Common, the Uncommon, the Characteristic, and the Sometimes ConfusingRadioGraphics2016Volume: 36Issue: 3pp. 753-766Neurofibromatosis from Head to Toe: What the Radiologist Needs to KnowRadioGraphics2022Volume: 42Issue: 4pp. 1123-1144Pediatric Fibroblastic and Myofibroblastic Tumors: A Pictorial ReviewRadioGraphics2016Volume: 36Issue: 4pp. 1195-1214See More RSNA Education Exhibits Spectrum of Smooth Muscle Tumors in the Female Pelvis: Radiology-Pathology CorrelationDigital Posters2018Pediatric Soft Tissue Tumors and Tumor-Like Conditions: Focused Imaging Overview with Pathologic CorrelationDigital Posters2019Mesenchymal Pelvic Floor Tumors With Locally Aggressive Growth Patterns: Differentiating Benign From MalignantDigital Posters2020 RSNA Case Collection Vaginal MyofibroblastomaRSNA Case Collection2022Male mammary myofibroblastoma RSNA Case Collection2022Intramuscular SchwannomaRSNA Case Collection2021 Vol. 245, No. 2 Metrics Altmetric Score PDF download

Thymic Hyperplasia and Thymus Gland Tumors: Differentiation with Chemical Shift MR Imaging1

To prospectively evaluate chemical shift magnetic resonance (MR) imaging for differentiating thymic hyperplasia from tumors of the thymus gland. The institutional review board approved this study; informed consent was obtained and patient confidentiality was protected. The authors assessed 41 patients (17 male, 24 female; age range, 16-78 years) in whom thymic lesions were seen at chest computed tomography. Patients were assigned to a hyperplasia group (n=23) (18 patients with hyperplastic thymus associated with Graves disease and five with rebound thymic hyperplasia) and a tumor group (n=18) (seven patients with thymomas, four with invasive thymomas, five with thymic cancers, and two with malignant lymphomas). T2-weighted fast spin-echo and T1-weighted in-phase and opposed-phase MR images were obtained in all patients and visually assessed. A chemical shift ratio (CSR), determined by comparing the signal intensity of the thymus gland with that of the paraspinal muscle, was calculated for quantitative analysis. Mean CSRs for the patient groups and subgroups were analyzed by using Welch t and Newman-Keuls tests. P<.05 indicated a significant difference. The thymus gland had homogeneous signal intensity in all 23 patients in the hyperplasia group and in 12 of the 18 patients in the tumor group. The mean CSR (+/- standard deviation) was 0.614 +/- 0.130 in the hyperplasia group and 1.026 +/- 0.039 in the tumor group. Mean CSRs in the patients with a hyperplastic thymus and Graves disease, rebound thymic hyperplasia, thymoma, invasive thymoma, thymic cancer, and malignant lymphoma were 0.594 +/- 0.120, 0.688 +/- 0.154, 1.033 +/- 0.043, 1.036 +/- 0.040, 1.020 +/- 0.044, and 0.997 +/- 0.010, respectively. The difference in CSR between the hyperplasia and tumor groups was significant (P<.001). Mean CSRs in the hyperplasia subgroups were lower than those in the tumor subgroups (P<.001). All hyperplasia group patients had an apparent decrease in thymus gland signal intensity at chemical shift MR imaging; no tumor group patients had a decrease in thymus gland signal intensity. Chemical shift MR imaging can be used to differentiate thymic hyperplasia from thymic tumors.

Liver Fat: Effect of Hepatic Iron Deposition on Evaluation with Opposed-Phase MR Imaging

To retrospectively determine the effect of liver iron deposition on the evaluation of liver fat by using opposed-phase magnetic resonance (MR) imaging. 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. 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). 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.

Dual Gradient-Echo In-Phase and Opposed-Phase Hepatic MR Imaging: A Useful Tool for Evaluating More Than Fatty Infiltration or Fatty Sparing

A T1-weighted gradient-echo in-phase and opposed-phase sequence has become a routine part of every hepatic magnetic resonance (MR) imaging protocol. Although this sequence is primarily used to identify common pathologic conditions, such as diffuse or focal steatosis and focal fatty sparing, it is also helpful in detection of pathologic entities associated with T2* effects owing to the double-echo approach. Thus, pathologic conditions such as hemochromatosis or hemosiderosis can be identified and characterized with a high level of confidence. In cases of iron storage disease, the hepatic parenchymal signal intensity decreases on the image with the longer echo time due to the continued decay of the transverse magnetization. In addition, susceptibility artifacts can be easily detected and characterized with in-phase and opposed-phase MR imaging. Metallic objects demonstrate a larger susceptibility artifact on the image with the second or longer echo time, which is usually the in-phase image. Finally, intrahepatic pneumobilia can be identified with the T1-weighted gradient-echo in-phase and opposed-phase sequence because gas also causes a susceptibility artifact, which is more pronounced on the image with the longer echo time. A complete understanding of both the chemical shift cancellation artifact and the T2* effects of the in-phase and opposed-phase sequence is important for correct interpretation of hepatic MR images.

Chemical shift MR imaging of hyperattenuating (>10 HU) adrenal masses: does it still have a role?

To evaluate chemical shift magnetic resonance (MR) imaging for the characterization of hyperattenuating adrenal masses. Adrenal MR images obtained from January 1998 to February 2003 were reviewed. Patients were excluded if they did not undergo unenhanced computed tomography or did not have an adrenal mass with attenuation higher than 10 HU, adequate follow-up, or pathologic diagnosis for use as a reference standard. A diagnosis of adenoma required at least 24 weeks of stability on images. Thirty-eight masses in 36 patients were identified (27 adenomas, nine metastases, one adrenocortical oncocytoma, and one pheochromocytoma). Signal intensity (SI) decrease between in-phase and opposed-phase MR images was measured for the entire mass and normalized to the renal parenchymal SI. In 21 of 36 (58%) patients, dual-echo single-breath-hold MR imaging was used to eliminate misregistration. The attenuation of 61% (23 of 38) of all masses and 70% (19 of 27) of adenomas was 10-30 HU. With a threshold of 20% SI decrease, the sensitivity of chemical shift MR imaging for hyperattenuating adenoma was 67% (18 of 27 masses). When considering masses with attenuation of 10-30 HU, the sensitivity for adenoma was 89% (17 of 19 masses) and remained reasonable at 75% (six of eight masses) for adenomas with attenuation of 20-30 HU. Only one adenoma with attenuation higher than 30 HU had SI decrease of more than 20%. Specificity for diagnosis of adenoma was 100% (11 of 11). In certain circumstances, chemical shift MR imaging is a reasonable second imaging test for further characterization of a hyperattenuating adrenal mass.

Normal Adrenal Gland: In Vivo Observations, and High-Resolution in Vitro Chemical Shift MR Imaging–Histologic Correlation

Rationale and Objectives The purpose of this study was to determine whether adrenal cortical lipid affects signal intensity on magnetic resonance (MR) images and to evaluate contrast between cortex and medulla. Materials and Methods From their clinical database, the authors selected 37 MR imaging studies of patients with adrenal adenomas. Two independent readers compared in-phase and fat-suppressed T1-weighted images, looking for visible lipid-induced signal intensity loss in the adrenal gland. Six adrenal gland specimens obtained after radical nephrectomy were also studied with high-resolution MR imaging, including in-phase, opposed-phase, and fat-suppressed T1-weighted images, and T2-weighted images. Adjacent histologic sections were stained with oil red O for neutral fats and with hematoxylin-eosin, and they were also viewed with polarization light microscopy. The relative amount of lipid was graded as mild, moderate, or intense, and the appearance of the cortex and medulla was compared with that on the MR images. Results On the 37 clinical MR studies, there was no visible signal intensity loss within the limbs of the ipsilateral adrenal glands. T2-weighted images of the adrenal specimens showed a thin high-intensity band, corresponding to the appearance of medulla on histologic slices. This could not be seen on any of the T1-weighted images. Region-of-interest measurements were nearly identical for in-phase and opposed-phase images. Histologic analysis showed abundant cortical lipid. Conclusion Adrenal corticomedullary contrast can be depicted on high-resolution T2-weighted images but not on any T1-weighted images. There is abundant cortical lipid in adrenal specimens, but comparison of in-phase with opposed-phase MR images does not depict it.