Opposed-phase Sequences Research Articles

Focal fatty sparing areas of the pediatric steatotic liver: pseudolesions on hepatobiliary phase magnetic resonance images.

Focal fatty sparing in liver can be detected as hyperintense pseudolesions on hepatobiliary phase magnetic resonance imaging (MRI). Distinguishing these pseudolesions from liver lesions may make diagnosis challenging. The aim of this study was to evaluate the imaging features of fatty sparing areas on liver MRI in pediatric patients who have been administered gadoxetate disodium. A total of 63 patients between January 2018 and June 2023 underwent gadoxetate disodium-enhanced liver MRI, and 9 (14%) patients with a focal fatty sparing were included in the study. The fat spared areas were evaluated qualitatively and quantitatively including signal intensity measurements and fat fraction calculations. The liver MRI examinations of 9 patients (5 boys, 4 girls; aged 8-18 years, median age: 14.4) using gadoxetate disodium were evaluated. Based on in-phase and opposed-phase sequences, 13 areas of focal fatty sparing were identified. The mean fat fraction of the liver and fat spared areas were 26.2% (range, 15-47) and 9% (range, 2-17), respectively. All fat spared areas were hyperintense in the hepatobiliary phase images. The mean relative enhancement ratios of the liver and fat spared areas were 0.78 (range, 0.35-1.6) and 1.11 (range, 0.45-1.9), respectively. Focal fatty sparing in liver in children was observed as hyperintense on hepatobiliary phase MRI, and it should not be identified as a focal liver lesion.

Comparison of in-phase and opposed-phase T1W gradient echo and T2W fast spin echo dixon chemical shift imaging for the assessment of non-neoplastic, benign neoplastic and malignant marrow lesions.

The objective of this study is to compare T1-weighted gradient echo (T1W GrE: control technique) chemical shift imaging (CSI) with T2-weighted fast spin echo (T2W FSE: experimental technique) CSI for differentiating non-neoplastic and neoplastic marrow lesions. Patients undergoing MRI for various marrow lesions were investigated with T1W GrE and T2W FSE Dixon CSI. Signal intensity (SI) change between in-phase (IP) and opposed-phase (OP) sequences was calculated, and SI drop > 20% considered to represent non-neoplastic lesions while SI drop < 20% considered to represent neoplastic lesions. Final diagnosis was based on imaging features (n = 42) or histology (n = 43) and classified as non-neoplastic, benign neoplastic, and malignant neoplastic. Inter-observer and inter-technique agreement between 2 readers was calculated. The study included 85 patients (44 males and 41 females; mean age 41.1years, range 2-83years). Final diagnosis included 19 (22.4%) non-neoplastic lesions, 27 (31.8%) benign neoplasms, and 39 (45.9%) malignant neoplasms. On T1W GrE CSI, 19-21 lesions were classed as non-neoplastic and 64-66 as neoplastic, while on T2W FSE Dixon CSI, 22-24 lesions were classed as non-neoplastic and 61-64 as neoplastic. Lesion classification matched between the 2 techniques in 91.8-96.5% of cases. Sensitivity, specificity, positive predictive value, negative predictive value, and accuracy of T1W GrE CSI for differentiating non-neoplastic and neoplastic marrow lesions were 66.7-72.2%, 88.1-89.6%, 61.9-63.2%, 90.9-92.2%, and 84.7%, and of T2W FSE Dixon CSI were 72.2-77.8%, 85.1-86.6%, 58.3-59.1%, 92.1-93.4%, and 83.5%. T1W GrE CSI and T2W FSE Dixon CSI produce similar results in the assessment of non-neoplastic and neoplastic marrow lesions.

Water Only Sequence: An Accurate Method to Estimate Hepatic Siderosis in Patients with Thalassemia Major and Intermedia

Background: Thalassemia is a common hemoglobinopathy in Iran. Iron overload is a major complication of thalassemia, and an accurate quantification of iron deposition is the mainstay of treatment planning. The liver is the main organ for storage of iron, and quantification of hepatic siderosis is a reliable estimation of total iron overload. Objectives: The aim of this study was to determine the accuracy of chemical shift sequences (CSS), especially a water only sequence (WOS), to estimate hepatic siderosis in thalassemia patients. Patients and Methods: During a seven-month period, from May to December 2016, one hundred and two known cases of thalassemia major and intermedia underwent liver MRI. The liver iron concentration was estimated using T2* MR relaxometry. The iron signal percentage and fraction were calculated using chemical shift sequences and correlated with estimated liver iron concentration (LIC). Results: The correlation coefficient of in-phase and opposed-phase sequences was 0.566 in estimating hepatic siderosis, which was improved by employing water only sequence (0.640). The sensitivity, specificity and positive predictive value were 90.5%, 94.4% and 98.7% for the in-phase and opposed-phase sequences and 82.1%, 94.4% and 98.6% for the water only sequence, respectively. Conclusion: Chemical shift sequences, including a water only sequence, are accurate for the assessment of hepatic siderosis. Water only sequences can effectively minimize the confounding effect of fatty liver.

Lipid Fraction Derived From MRI In- and Opposed-Phase Sequence as a Novel Biomarker for Predicting Survival Outcome of Glioma

Our study evaluated the capability of magnetic resonance imaging in- and opposed-phase (IOP) derived lipid fraction as a novel prognostic biomarker of survival outcome in glioma. We analyzed 46 histologically proven glioma (WHO grades II-IV) patients using standard 3T magnetic resonance imaging brain tumor protocol and IOP sequence. Lipid fraction was derived from the IOP sequence signal-loss ratio. The lipid fraction of solid nonenhancing region of glioma was analyzed, using a three-group analysis approach based on volume under surface of receiver-operating characteristics to stratify the prognostic factors into three groups of low, medium, and high lipid fraction. The survival outcome was evaluated, using Kaplan-Meier survival analysis and Cox regression model. Significant differences were seen between the three groups (low, medium, and high lipid fraction groups) stratified by the optimal cut-off point for overall survival (OS) (p ≤ 0.01) and time to progression (p ≤ 0.01) for solid nonenhancing region. The group with high lipid fraction had five times higher risk of poor survival and earlier time to progression compared to the low lipid fraction group. The OS plot stratified by lipid fraction also had a strong correlation with OS plot stratified by WHO grade (R = 0.61, p < 0.01), implying association to underlying histopathological changes. The lipid fraction of solid nonenhancing region showed potential for prognostication of glioma. This method will be a useful adjunct in imaging protocol for treatment stratification and as a prognostic tool in glioma patients.

The utility of chemical shift imaging and related fat suppression as standalone technique in cryptorchidism using low field MRI

Cryptorchidism is failure of one or both testes to descend completely into the scrotum. The testis can be located anywhere along its journey of descent, between the lower pole of the kidney and the inguinal canal. Objective: The aim of this study was to assess the effectiveness of chemical shift imaging and Dixon based fat suppression using low field MRI in non-palpable undescended testicle. Patients and methods: From July 2017 through February 2018, Twenty eight boys, presented by either unilateral or bilateral cryptorchidism, with total number of forty testicles, underwent MRI study using low field machine in T1-weighted dual gradient-echo in-phase and opposed-phase sequence with Dixon based fat suppression. Results: Based on the laparoscopic/operative data, twenty one testes were located at the inguinal region, whereas fifteen testes were pelvi-abdominal and four were absent. The whole image sets of CSI and Dixon fat suppression had the highest specificity and positive predictive value (100%) and the highest overall accuracy (95%) for detection of undescended testes. Conclusion: chemical shift imaging combined with Dixon based fat suppression is reliable imaging tool as a standalone technique for evaluating cryptorchidism, providing high specificity and diagnostic accuracy.

Chemical shift imaging with in-phase and opposed-phase sequences at 3T: what is the optimal threshold, measurement method, and diagnostic accuracy for characterizing marrow signal abnormalities?

To determine the threshold signal drop on 3-T chemical shift imaging (CSI), with in-phase (IP) and opposed-phase (OP) sequences, for accurately identifying bone marrow replacement with 100% sensitivity, and determine a clinically useful measurement method for deriving such a threshold. From a convenience series of 157 MRIs, 36 cases with histologically proven marrow-replacing lesions and 22 sites of red marrow (histologically proven (2) or with minimum 6-month stability) with 3-Tesla CSI were included. Two musculoskeletal radiologists performed two measurement methods (first: multiple algorithmic ROIs at the top, middle, and bottom of lesions (M-ROI); second: an ROI was drawn where there appeared to be the least opposed-phase signal reduction qualitatively/visually (Q-ROI)). Lesional and red marrow signal change (%,[(IP-OP)signal/IP signal]*100) was determined. Statistical analyses included Student's t test, Cohen's kappa, and receiver operator characteristic curve generation. By M-ROI, lesion signal change was -0.508% (confidence interval (CI) = -5.537:4.521) and 1.348% (CI = -3.541:6.311) for readers 1 and 2. By Q-ROI, lesion signal change was -11.03% (CI = -17.01:- 5.046) and - 5.657% (CI = -12.36:1.048) for readers 1 and 2. For all M-ROI and Q-ROI measurement strategies, signal change between lesional tissue and red marrow was significantly different (p < 0.0001). QROI produced the best composite sensitivities and specificities with a maximized Youden index of 0.955-1. A threshold signal drop of 25% with Q-ROI produced at least 100%/86% sensitivity/specificity for both readers for identifying marrow replacement. For 3-T CSI, a single visually targeted measurement using a 25% threshold is accurate for identifying marrow-replacing lesions.

Quantification and visualization of lipid landscape in glioma using in -and opposed-phase imaging.

ObjectivesThis study maps the lipid distributions based on magnetic resonance imaging (MRI) in-and opposed-phase (IOP) sequence and correlates the findings generated from lipid map to histological grading of glioma.MethodsForty histologically proven glioma patients underwent a standard MRI tumour protocol with the addition of IOP sequence. The regions of tumour (solid enhancing, solid non-enhancing, and cystic regions) were delineated using snake model (ITK-SNAP) with reference to structural and diffusion MRI images. The lipid distribution map was constructed based on signal loss ratio (SLR) obtained from the IOP imaging. The mean SLR values of the regions were computed and compared across the different glioma grades.ResultsThe solid enhancing region of glioma had the highest SLR for both Grade II and III. The mean SLR of solid non-enhancing region of tumour demonstrated statistically significant difference between the WHO grades (grades II, III & IV) (mean SLRII = 0.04, mean SLRIII = 0.06, mean SLRIV = 0.08, & p < .01). A strong positive correlation was seen between WHO grades with mean SLR on lipid map of solid non-enhancing (ρ=0.68, p < .01).ConclusionLipid quantification via lipid map provides useful information on lipid landscape in tumour heterogeneity characterisation of glioma. This technique adds to the surgical diagnostic yield by identifying biopsy targets. It can also be used as an adjunct grading tool for glioma as well as to provide information about lipidomics landscape in glioma development.

Role of quantitative chemical shift magnetic resonance imaging and chemical shift subtraction technique in discriminating adenomatous from non adenomatous adrenal solid lesions

PurposeTo evaluate role of quantitative assessment of chemical shift MR imaging and chemical shift subtraction technique in differentiating adenomatous from non-adenomatous adrenal lesions with comparison of accuracy level of each technique. Materials and methodsA prospective study was carried out from 4-2014 to 5-2016 using 1.5T MRI. In-phase/opposed phase MRI sequences were applied for 52 patients having 58 adrenal lesions, 18 were hyper functioning and 40 were non-functioning. Lesions signal changes between in- and opposed phase sequences and post processing was done to calculate different quantitative chemical shift parameters using spleen, paraspinal muscle, and liver as a reference tissues. Additionally subtraction chemical shift MR technique on selected 16 cases was applied. ResultsSignal intensity index and the two formulas of adrenal to spleen ratio were more accurate than other quantitative chemical shift MRI parameters in discrimination between adenomatous and nonadenomatous adrenal lesions with selected cutoff value 23.4% for the signal intensity index, 0.72 and −27.82% for adrenal to spleen ratio% using the old and new formulas respectively. Chemical shift subtraction technique expressed significant difference between adenomas and non-adenomatous adrenal lesions where adenomas had ratio of 108.87 or more, and the non-adenomatous lesions had ratio of 47.74 or less with selected cutoff value 173.0475. ConclusionThe signal intensity index and adrenal to spleen ratio are the most reliable quantitative chemical shift MRI methods in differentiation of adrenal adenomas from other non-adenomatous adrenal solid lesions. Chemical shift subtraction MRI is a recent technique that gives highly confident discrimination between two categories of pathology without using of any reference organ.

Novel application of chemical shift gradient echo in- and opposed-phase sequences in 3 T MRI for the detection of H-MRS visible lipids and grading of glioma.

ObjectivesWe evaluated the feasibility of using chemical shift gradient-echo (GE) in- and opposed-phase (IOP) imaging to grade glioma.MethodsA phantom study was performed to investigate the correlation of 1H MRS-visible lipids with the signal loss ratio (SLR) obtained using IOP imaging. A cross-sectional study approved by the institutional review board was carried out in 22 patients with different glioma grades. The patients underwent scanning using IOP imaging and single-voxel spectroscopy (SVS) using 3T MRI. The brain spectra acquisitions from solid and cystic components were obtained and correlated with the SLR for different grades.ResultsThe phantom study showed a positive linear correlation between lipid quantification at 0.9 parts per million (ppm) and 1.3 ppm with SLR (r = 0.79–0.99, p < 0.05). In the clinical study, we found that SLR at the solid portions was the best measure for differentiating glioma grades using optimal cut-points of 0.064 and 0.086 with classification probabilities for grade II (SII = 1), grade III (SIII = 0.50) and grade IV (SIV = 0.89).ConclusionsThe results underscore the lipid quantification differences in grades of glioma and provide a more comprehensive characterization by using SLR in chemical shift GE IOP imaging. SLR in IOP sequence demonstrates good performance in glioma grading.Key Points• Strong correlation was seen between lipid concentration and SLR obtained using IOP• IOP sequence demonstrates significant differences in signal loss within the glioma grades• SLR at solid tumour portions was the best measure for differentiation• This sequence is applicable in a research capacity for glioma staging armamentarium

The value of added opposed/in phase MRI sequences in characterization of the focal vertebral bone marrow lesions in oncology patients

ObjectiveThis study aimed to evaluate the value of added opposed/in phase MRI sequences with signal intensity ratio (SIR) calculations in differentiation malignant and benign vertebral focal marrow lesions in oncology patients. Patients and methodsFrom January 2013 to December 2014, a total of 50 oncology patients with 63 focal spinal bone marrow lesions underwent MRI examination with added opposed/in-phase sequences. A computation of SIR of the marrow on the opposed phase to signal intensity measured on the in-phase images was made. ResultsThe examined 50 oncology patients showed 63 focal lesions, 39 proved to be malignant and 24 diagnosed as benign. The majority of malignant lesions (32/39) showed persistence of the high signals at the opposed phase sequences while signal loss was noted on all benign lesions. SIR values were ranged between 1.1 and 2.6 in malignant lesions while it ranged from 0.47 to 0.9 in benign lesions; when a SIR of 1 as a cutoff was chosen, it showed high sensitivity and specificity (96.8% and 93.65% respectively). ConclusionThe added opposed/in phase MRI sequences with SIR cut-off value of 1, were proved to be a non-invasive sensitive tool to differentiate between malignant and benign lesions in oncology patients.

Comparison of Qualitative and Quantitative Evaluation of Diffusion-Weighted MRI and Chemical-Shift Imaging in the Differentiation of Benign and Malignant Vertebral Body Fractures

The objective of our study was to compare the diagnostic value of qualitative diffusion-weighted imaging (DWI), quantitative DWI, and chemical-shift imaging in a single prospective cohort of patients with acute osteoporotic and malignant vertebral fractures. The study group was composed of patients with 26 osteoporotic vertebral fractures (18 women, eight men; mean age, 69 years; age range, 31 years 6 months to 86 years 2 months) and 20 malignant vertebral fractures (nine women, 11 men; mean age, 63.4 years; age range, 24 years 8 months to 86 years 4 months). T1-weighted, STIR, and T2-weighted sequences were acquired at 1.5 T. A DW reverse fast imaging with steady-state free precession (PSIF) sequence at different delta values was evaluated qualitatively. A DW echo-planar imaging (EPI) sequence and a DW single-shot turbo spin-echo (TSE) sequence at different b values were evaluated qualitatively and quantitatively using the apparent diffusion coefficient. Opposed-phase sequences were used to assess signal intensity qualitatively. The signal loss between in- and opposed-phase images was determined quantitatively. Two-tailed Fisher exact test, Mann-Whitney test, and receiver operating characteristic analysis were performed. Sensitivities, specificities, and accuracies were determined. Qualitative DW-PSIF imaging (delta = 3 ms) showed the best performance for distinguishing between benign and malignant fractures (sensitivity, 100%; specificity, 88.5%; accuracy, 93.5%). Qualitative DW-EPI (b = 50 s/mm(2) [p = 1.00]; b = 250 s/mm(2) [p = 0.50]) and DW single-shot TSE imaging (b = 100 s/mm(2) [p = 1.00]; b = 250 s/mm(2) [p = 0.18]; b = 400 s/mm(2) [p = 0.18]; b = 600 s/mm(2) [p = 0.39]) did not indicate significant differences between benign and malignant fractures. DW-EPI using a b value of 500 s/mm(2) (p = 0.01) indicated significant differences between benign and malignant vertebral fractures. Quantitative DW-EPI (p = 0.09) and qualitative opposed-phase imaging (p = 0.06) did not exhibit significant differences, quantitative DW single-shot TSE imaging (p = 0.002) and quantitative chemical-shift imaging (p = 0.01) showed significant differences between benign and malignant fractures. The DW-PSIF sequence (delta = 3 ms) had the highest accuracy in differentiating benign from malignant vertebral fractures. Quantitative chemical-shift imaging and quantitative DW single-shot TSE imaging had a lower accuracy than DW-PSIF imaging because of a large overlap. Qualitative assessment of opposed-phase, DW-EPI, and DW single-shot TSE sequences and quantitative assessment of the DW-EPI sequence were not suitable for distinguishing between benign and malignant vertebral fractures.

Taking advantage of chemical shift imaging: using opposed-phase images to locate the normal appendix on MR

Multiple sequences of 50 consecutive adult pelvic MRI exams were retrospectively reviewed by two radiologists to determine if opposed-phase T1 gradient echo imaging can assist in locating the normal appendix on pelvic MRI. If the appendix was visualized, it was always seen on the T2 sequence, except for one exam. The opposed-phase sequence had the second highest visualization rate, and the appendix was identified the least on the post-gadolinium sequence. The presence of a “button nose” sign was also assessed and was present in one third of cases.

ACR Appropriateness Criteria® on Metastatic Bone Disease

Appropriate imaging modalities for screening, staging, and surveillance of patients with suspected and documented metastatic disease to bone include (99m)Tc bone scanning, MRI, CT, radiography, and 2-[(18)F]fluoro-2-deoxyglucose-PET. Clinical scenarios reviewed include asymptomatic stage 1 breast carcinoma, symptomatic stage 2 breast carcinoma, abnormal bone scan results with breast carcinoma, pathologic fracture with known metastatic breast carcinoma, asymptomatic well-differentiated and poorly differentiated prostate carcinoma, vertebral fracture with history of malignancy, non-small-cell lung carcinoma staging, symptomatic multiple myeloma, osteosarcoma staging and surveillance, and suspected bone metastasis in a pregnant patient. No single imaging modality is consistently best for the assessment of metastatic bone disease across all tumor types and clinical situations. In some cases, no imaging is indicated. The recommendations contained herein are the result of evidence-based consensus by the ACR Appropriateness Criteria((R)) Expert Panel on Musculoskeletal Radiology.

Liver Steatosis Quantification Using Magnetic Resonance Imaging

To prospectively determine the accuracy of liver fat quantification with magnetic resonance imaging (MRI). The population consisted of 40 patients (mean age, 52.5 years; range, 23-78 years). The same day, all patients underwent MRI and ultrasonography-guided liver biopsy. The histological evaluation of steatosis was performed by an experienced liver pathologist blinded to the MRI results. On T1-weighted in- and opposed-phase images, one radiologist, experienced in abdominal imaging, blinded to the clinical and pathological results, recorded signal intensity (SI) by mean regions of interest placed at same locations in both phases. Fat-water ratio was obtained by dividing SI of liver in opposed-phase sequence by SI of liver in in-phase sequence. The fat-water ratio and the histological grade of steatosis were compared by linear regression. Receiver operating characteristic curve was used to define the sensitivity and specificity of fat-water ratio as a diagnostic tool for evaluation of steatosis. Diagnoses were nonalcoholic fatty liver disease (n = 25), alcoholic liver disease (n = 10), cholangiopathy (n = 2), and autoimmune hepatitis (n = 3). Fatty liver infiltration was present in 80% of patients. The mean (SD) percentage of fatty hepatocytes was 38.7% (29.2). Fat-water ratio and steatosis grade were highly correlated (r = 0.852, P < 0.0001). Sensitivity and specificity of fat-water ratio to detect fatty infiltration greater than 20% were 96% and 93%, respectively. This prospective study demonstrates that MRI can be proposed as a noninvasive method to screen and quantify liver steatosis.

Radiological Reasoning: Bone Marrow Changes on MRI

Differentiating neoplastic from nonneoplastic bone marrow changes on imaging can be challenging. MRI provides the most helpful information when using T1-weighted and opposed-phase (chemical shift) sequences. We discuss the MRI assessment of bone marrow in the context of a complex clinical case. The case shows a false-positive result of opposed-phase imaging of bone marrow, which was a postinflammatory cause resulting in marrow fibrosis that mimicked neoplastic marrow infiltration and necessitated biopsy for definitive diagnosis.

Opposed-phase MR imaging of lipid storage myopathy in a case of Chanarin–Dorfman disease

Chanarin-Dorfman disease (CDD) is a rare genetic disorder characterized by ichthyosis, myopathy, central nervous system disturbances, and intracellular lipid storage in muscle fibers, hepatocytes, and granulocytes. We describe skeletal muscle magnetic resonance imaging findings in a case of CDD, outlining the potential role of GE T1-weighted opposed-phase sequence (chemical shift imaging) in the evaluation of lipid storage myopathies.

Abdominal Magnetic Resonance Imaging at 3.0 T: What Is the Ultimate Gain in Signal-to-Noise Ratio?

The purpose of this study was to calculate the gain in signal-to-noise ratio (SNR) of four human abdominal tissues at 3.0 Tesla (T) compared with standard 1.5 T and to validate this calculation in vivo. The expected gain in SNR at 3.0 T in the liver, pancreas, spleen, and kidney compared with standard 1.5 T was approximated theoretically for a T2-weighted HASTE (half-Fourier acquisition single-shot turbo spin-echo) and a T1-weighted gradient-echo in- and opposed-phase sequence. Fifteen healthy male subjects underwent abdominal MR imaging using a 1.5 T and 3.0 T scanner. Coronal T2-weighted HASTE images and axial T1-weighted gradient-echo in- and opposed-phase images were acquired using the sequence parameters optimized by the vendor. Except for opposed-phased imaging of pancreatic tissue, in vivo adjusted SNR values of all abdominal tissues were significantly higher at 3.0 T for all sequences (P < .05). The highest overall gain in SNR was achieved with the HASTE sequence ranging from 3.8-fold for renal imaging to 7.4-fold for hepatic imaging. The theoretical calculation of SNR gain was in good agreement with the experimentally measured gain in SNR for the HASTE and the in-phase sequence. High-field abdominal MR imaging at 3.0 T offers significantly higher SNR compared with standard 1.5 T MR imaging.

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.

New coil concept for endoluminal MR imaging

Our aim was to conduct a prospective study to evaluate staging accuracy of a new coil concept for endoluminal magnetic resonance imaging (MRI) on ex vivo gastric carcinomas. Twenty-eight consecutive patients referred to surgery with a clinically proven primary gastric malignancy were included. Surgical specimens were examined with a foldable and self-expanding loop coil (8-cm diameter) at 1.5 Tesla immediately after total gastrectomy. T1- and T2-weighted and opposed-phase sequences (axial, frontal sections; 3- to 4-mm slice thickness) were acquired. Investigators blinded to any patient information analyzed signal intensity of normal gastric wall, gastric tumor, and lymph nodes. Findings were compared with histopathological staging. On surgical specimens, 2–5 gastric wall layers could be visualized. All gastric tumors (26 carcinomas, two lymphomas) were identified on endoluminal MR data (100%). Overall accuracy for T staging was 75% (18/24); sensitivity to detect serosal involvement was 80% and specificity 89%. N staging correlated in 58% (14/24) with histopathology (N+ versus N−). The endoluminal coil concept is feasible and applicable for an ex vivo setting. Endoluminal MR data provided sufficient detail for gastric wall layer differentiation, and therefore, identification of T stages in gastric carcinoma is possible. Further investigations in in vivo settings should explore the potential of our coil concept for endoluminal MR imaging.

Characterization of adrenal adenomas and metastases: correlation between unenhanced computed tomography and chemical shift magnetic resonance imaging

To evaluate the correlation of absolute attenuation values of unenhanced computed tomography (CT) with signal intensity (SI) quantitative analysis on chemical shift (CS) magnetic resonance (MR) imaging in differentiating adrenal adenomas from metastases. Forty-one adrenal masses (27 adenomas, 14 metastases) were studied with CS MR imaging and unenhanced CT. MR included T1-weighted breathhold gradient-echo in-phase (IP) and opposed-phase (OP) sequences. The SI index (SI-i) [(SIIP-SIOP/SIIP)] x 100% and chemical-shift ratio (CS-r) relative to the spleen [(SIlesion/ SIspleen)OP/(SIlesion/SIspleen)IP] were calculated for each lesion. CT absolute attenuation values were also determined. The mean attenuation value of metastases was significantly greater than that of adenomas (< 0.0001). On MR, the mean SI-i of adenomas was significantly greater than that of metastases (P < 0.0001) and no overlaps were evident. The CS-r of malignant and benign lesions overlapped considerably, and five adenomas (all with indeterminate Hounsfield Unit values at CT) were misclassified as potentially malignant. CT attenuation values were significantly correlated with both MR quantitative analyses. Since CS MR imaging and CT both depict the presence of lipids within adrenal lesions, absolute attenuation values are highly correlated with MR quantitative analysis. SI-i is the most reliable tool for differentiating adrenal adenomas from metastases, showing better accuracy than lesion-to-spleen CS-r, in particular for adenomas with indeterminate absolute attenuation values.