Magnetic Resonance Imaging at 1.5 Tesla With a Cochlear Implant Magnet in Place: Image Quality and Usability.

OBJECTIVE: To study the quality and usability of magnetic resonance imaging (MRI) obtained with a cochlear implant magnet in situ. STUDY DESIGN: Retrospective chart review. SETTING: Tertiary care center. PATIENTS: All patients who underwent brain MRI with a cochlear implant magnet in situ from 2007 to 2016. INTERVENTION(S): None. MAIN OUTCOME MEASURE(S): Grade of view of the ipsilateral internal auditory canal (IAC) and cerebellopontine angle (CPA). RESULTS: Inclusion criteria were met by 765 image sequences in 57 MRI brain scans. For the ipsilateral IAC, significant predictors of a grade 1 (normal) view included: absence of fat saturation algorithm (p = 0.001), nonaxial plane of imaging (p = 0.01), and contrast administration (p = 0.001). For the ipsilateral CPA, significant predictors of a grade 1 view included: absence of fat saturation algorithm (p = 0.001), high-resolution images (p = 0.001), and nonaxial plane of imaging (p = 0.001). Overall, coronal T1 high-resolution images produced the highest percentage of grade 1 views (89%). Fat saturation also caused a secondary ring-shaped distortion artifact, which impaired the view of the contralateral CPA 52.7% of the time, and the contralateral IAC 42.8% of the time. MRI scans without any usable (grade 1) sequences had fewer overall sequences (N = 4.3) than scans with at least one usable sequence (N = 7.1, p = 0.001). CONCLUSION: MRI image quality with a cochlear implant magnet in situ depends on several factors, which can be modified to maximize image quality in this unique patient population.

Adrenal Adenoma and Pheochromocytoma: Comparison of Multidetector CT Venous Enhancement Levels and Washout Characteristics.

PURPOSE: The aim of the study was to compare multidetector CT venous enhancement level and washout characteristics of adrenal adenoma and pheochromocytoma, with the goal of defining a venous enhancement level predictive of pheochromocytoma. METHODS: Retrospective review of medical records between 2002 and 2012 was performed to identify adrenal masses measuring less than 4 cm. Inclusion criteria for adrenal adenomas was venous phase contrast-enhanced computed tomography (CT), confirmatory adrenal CT (precontrast ± washout), 1 to 2 years stability, and absence of clinical indicators of pheochromocytoma. All pathologically proven pheochromocytomas with venous phase CT imaging were evaluated. Nodule size and attenuation (venous ± precontrast, delayed) were recorded. Student t test analysis compared venous enhancement levels. RESULTS: One hundred eighty-three subjects with 200 adenomas were compared with 22 subjects with 26 pheochromocytomas. The mean (SD) venous enhancement level for all adenomas (58 [26] Hounsfield units [HU]) and lipid-poor adenomas (76 [25]) was lower than that of pheochromocytomas (111 [38] HU, P < 0.01). No adenomas enhanced greater than 130 HU, compared with 38% (10/26) of the pheochromocytomas. A threshold of 130 HU to identify pheochromocytoma was 38% sensitive and 100% specific for pheochromocytoma. Of the 17 pheochromocytomas with washout imaging, rapid washout was identified in all (10/10, 100%) that enhanced greater than 130 HU on the venous phase, compared with 43% (3/7) that enhanced less than 130 HU. CONCLUSIONS: An indeterminate adrenal lesion that enhances greater than 130 HU on multidetector CT cannot be assumed to be an adenoma. Hypervascular pheochromocytoma (>130 HU) mimics adenoma washout pattern; absolute venous phase enhancement level must be considered.

MDCT of adrenal masses: Can dual-phase enhancement patterns be used to differentiate adenoma and pheochromocytoma?

OBJECTIVE: The purpose of this study was to compare enhancement of adrenal adenomas and pheochromocytomas during dual-phase (arterial and venous phases) CT performed with currently used MDCT protocols with the goal of defining enhancement patterns predictive of pathologic findings. MATERIALS AND METHODS: Pathologically proven pheochromocytomas were retrospectively compared with adrenal adenomas. Inclusion criteria for adenomas, collected by searching the radiology database, were confirmatory adrenal CT (unenhanced with or without washout) and absence of clinical indicators of pheochromocytoma. A fellowship-trained attending radiologist blinded to the pathologic diagnosis reviewed existing images from dual-phase IV contrast-enhanced CT examinations to measure enhancement of adrenal lesions and characterize the appearance (homogeneous versus heterogeneous). Student t test analysis was performed to compare arterial and venous phase enhancement levels. RESULTS: The findings in 39 patients with 41 adenomas were compared with those in 10 patients with 12 pheochromocytomas. Mean arterial and venous enhancement of adenomas at 37 HU (-6 to 85 HU) and 60 HU (16-133 HU) was significantly lower than that of pheochromocytomas at 104 HU (42-190 HU) and 119 HU (61-195 HU) (p < 0.001). No adenoma was more than 85-HU enhancing in the arterial phase, and 58% of pheochromocytomas were more than 110-HU enhancing. Most adenomas (85%) were more enhancing in the venous phase. No adenoma was more enhancing in the arterial phase, but 25% (3/12) of pheochromocytomas were. Most (58%) pheochromocytomas were heterogeneous in appearance, compared with 22% of adenomas. CONCLUSION: For indeterminate adrenal masses identified at dual-phase IV contrast-enhanced CT, higher enhancement during the arterial phase, arterial phase enhancement levels greater than 110 HU, and lesion heterogeneity should prompt consideration of pheochromocytoma.

Characterization of adrenal masses with diffusion-weighted imaging.

OBJECTIVE: The purpose of this article is to assess the role of diffusion-weighted MRI in characterizing adrenal masses. MATERIALS AND METHODS: A retrospective review of the MRI database from August 2007 to July 2009 was performed. The MRI examinations of 48 patients, with 49 lesions, were reviewed independently and blindly by two experienced abdominal radiologists who measured the signal intensities on in-phase and opposed-phase T1-weighted imaging and apparent diffusion coefficient (ADC). ADC measurements and quantitative parameters of chemical shift imaging (signal intensity index and adrenal-to-spleen ratio) were assessed separately and in combination. Lesions with indeterminate signal intensity index (< 16.5%) were considered benign if ADC was greater than or equal to 1.0 × 10(-3) mm(2)/s and malignant if ADC was less than 1.0 × 10(-3) mm(2)/s. Stepwise logistic regression analysis and receiver operating characteristic curves analysis were performed. RESULTS: There were 12 malignant and 37 benign lesions. On multivariate analysis, the only significant predictors of lesion status were signal intensity index from reviewer 2 (p = 0.05) and lesion size (p = 0.04); ADC values were not found to be useful. On receiver operating characteristic curve analysis, there was no significant difference in area under the curve for ADC, signal intensity index, adrenal-to-spleen ratio, or the combined signal intensity index and ADC assessment. For lesions that were indeterminate according to signal intensity index, ADC values greater than 1.50 × 10(-3) mm(2)/s were found only in benign lesions, and nine of 11 lesions with ADC less than 1.0 × 10(-3) mm(2)/s were malignant. CONCLUSION: In general, ADC values are not useful in differentiating adrenal lesions. However, when ADC values are applied to lesions that are indeterminate on signal intensity index, they may help in differentiating a subset of benign and malignant lesions.