Justin M. Ream

Dynamic contrast-enhanced MRI of the prostate with high spatiotemporal resolution using compressed sensing, parallel imaging, and continuous golden-angle radial sampling: Preliminary experience

To demonstrate dynamic contrast‐enhanced (DCE) magnetic resonance imaging (MRI) of the prostate with both high spatial and temporal resolution via a combination of golden‐angle radial k‐space sampling, compressed sensing, and parallel‐imaging reconstruction (GRASP), and to compare image quality and lesion depiction between GRASP and conventional DCE in prostate cancer patients.

Respiratory Motion-Resolved Compressed Sensing Reconstruction of Free-Breathing Radial Acquisition for Dynamic Liver Magnetic Resonance Imaging.

ObjectiveThis study aimed to demonstrate feasibility of free-breathing radial acquisition with respiratory motion-resolved compressed sensing reconstruction [extra-dimensional golden-angle radial sparse parallel imaging (XD-GRASP)] for multiphase dynamic gadolinium ethoxybenzyl diethylenetriamine pentaacetic acid (Gd-EOB-DTPA)-enhanced liver imaging, and to compare image quality to compressed sensing reconstruction with respiratory motion-averaging (GRASP) and prior conventional breath-held Cartesian-sampled data sets [BH volume interpolated breath-hold examination (VIBE)] in same patients. Subjects and MethodsIn this Health Insurance Portability and Accountability Act–compliant prospective study, 16 subjects underwent free-breathing continuous radial acquisition during Gd-EOB-DTPA injection and had prior BH-VIBE available. Acquired data were reconstructed using motion-averaging GRASP approach in which consecutive 84 spokes were grouped in each contrast-enhanced phase for a temporal resolution of approximately 14 seconds. Additionally, respiratory motion-resolved reconstruction was performed from the same k-space data by sorting each contrast-enhanced phase into multiple respiratory motion states using compressed sensing algorithm named XD-GRASP, which exploits sparsity along both the contrast-enhancement and respiratory-state dimensions.Contrast-enhanced dynamic multiphase XD-GRASP, GRASP, and BH-VIBE images were anonymized, pooled together in a random order, and presented to 2 board-certified radiologists for independent evaluation of image quality, with higher score indicating more optimal examination. ResultsThe XD-GRASP reconstructions had significantly (all P < 0.05) higher overall image quality scores compared to GRASP for early arterial (reader 1: 4.3 ± 0.6 vs 3.31 ± 0.6; reader 2: 3.81 ± 0.8 vs 3.38 ± 0.9) and late arterial (reader 1: 4.5 ± 0.6 vs 3.63 ± 0.6; reader 2: 3.56 ± 0.5 vs 2.88 ± 0.7) phases of enhancement for both readers. The XD-GRASP also had higher overall image quality score in portal venous phase, which was significant for reader 1 (4.44 ± 0.5 vs 3.75 ± 0.8; P = 0.002). In addition, the XD-GRASP had higher overall image quality score compared to BH-VIBE for early (reader 1: 4.3 ± 0.6 vs 3.88 ± 0.6; reader 2: 3.81 ± 0.8 vs 3.50 ± 1.0) and late (reader 1: 4.5 ± 0.6 vs 3.44 ± 0.6; reader 2: 3.56 ± 0.5 vs 2.94 ± 0.9) arterial phases. ConclusionFree-breathing motion-resolved XD-GRASP reconstructions provide diagnostic high-quality multiphase images in patients undergoing Gd-EOB-DTPA–enhanced liver examination.

Proposed Adjustments to PI-RADS Version 2 Decision Rules: Impact on Prostate Cancer Detection

Purpose To test the impact of existing Prostate Imaging Reporting and Data System (PI-RADS) version 2 (V2) decision rules, as well as of proposed adjustments to these decision rules, on detection of Gleason score (GS) 7 or greater (GS ≥7) prostate cancer. Materials and Methods Two radiologists independently provided PI-RADS V2 scores for the dominant lesion on 343 prostate magnetic resonance (MR) examinations. Diagnostic performance for GS ≥7 tumor was assessed by using MR imaging-ultrasonography fusion-targeted biopsy as the reference. The impact of existing PI-RADS V2 decision rules, as well as a series of exploratory proposed adjustments, on the frequency of GS ≥7 tumor detection, was evaluated. Results A total of 210 lesions were benign, 43 were GS 6, and 90 were GS ≥7. Lesions were GS ≥7 in 0%-4.1% of PI-RADS categories 1 and 2, 11.4%-27.1% of PI-RADS category 3, 44.4%-49.3% of PI-RADS category 4, and 72.1%-73.7% of PI-RADS category 5 lesions. PI-RADS category 4 or greater had sensitivity of 78.9%-87.8% and specificity of 75.5%-79.1 for detecting GS ≥7 tumor. The frequency of GS ≥7 tumor for existing PI-RADS V2 decision rules was 30.0%-33.3% in peripheral zone (PZ) lesions upgraded from category 3 to 4 based on dynamic contrast enhancement (DCE) score of positive; 50.0%-66.7% in transition zone (TZ) lesions upgraded from category 3 to 4 based on diffusion-weighted imaging (DWI) score of 5; and 71.7%-72.7% of lesions in both zones upgraded from category 4 to 5 based on size of 15 mm or greater. The frequency of GS ≥7 tumor for proposed adjustments to the decision rules was 30.0%-60.0% for TZ lesions upgraded from category 3 to 4 based on DWI score of 4; 33.3%-57.1% for TZ lesions upgraded from category 3 to 4 based on DCE score of positive when incorporating new criteria (unencapsulated sheetlike enhancement) for DCE score of positive in TZ; and 56.4%-61.9% for lesions in both zones upgraded from category 4 to 5 based on size of 10-14 mm. Other proposed adjustments yielded GS ≥7 tumor in less than 15% of cases for one or more readers. Conclusion Existing PI-RADS V2 decision rules exhibited reasonable performance in detecting GS ≥7 tumor. Several proposed adjustments to the criteria (in TZ, upgrading category 3 to 4 based on DWI score of 4 or modified DCE score of positive; in PZ or TZ, upgrading category 4 to 5 based on size of 10-14 mm) may also have value for this purpose.

Estimating liver perfusion from free-breathing continuously acquired dynamic gadolinium-ethoxybenzyl-diethylenetriamine pentaacetic acid-enhanced acquisition with compressed sensing reconstruction

ObjectiveThe purpose of this study was to estimate perfusion metrics in healthy and cirrhotic liver with pharmacokinetic modeling of high–temporal resolution reconstruction of continuously acquired free-breathing gadolinium-ethoxybenzyl-diethylenetriamine pentaacetic acid–enhanced acquisition in patients undergoing clinically indicated liver magnetic resonance imaging. Subjects and MethodsIn this Health Insurance Portability and Accountability Act–compliant prospective study, 9 cirrhotic and 10 noncirrhotic patients underwent clinical magnetic resonance imaging, which included continuously acquired radial stack-of-stars 3-dimensional gradient recalled echo sequence with golden-angle ordering scheme in free breathing during contrast injection. A total of 1904 radial spokes were acquired continuously in 318 to 340 seconds. High–temporal resolution data sets were formed by grouping 13 spokes per frame for temporal resolution of 2.2 to 2.4 seconds, which were reconstructed using the golden-angle radial sparse parallel technique that combines compressed sensing and parallel imaging. High–temporal resolution reconstructions were evaluated by a board-certified radiologist to generate gadolinium concentration-time curves in the aorta (arterial input function), portal vein (venous input function), and liver, which were fitted to dual-input dual-compartment model to estimate liver perfusion metrics that were compared between cirrhotic and noncirrhotic livers. ResultsThe cirrhotic livers had significantly lower total plasma flow (70.1 ± 10.1 versus 103.1 ± 24.3 mL/min per 100 mL; P < 0.05), lower portal venous flow (33.4 ± 17.7 versus 89.9 ± 20.8 mL/min per 100 mL; P < 0.05), and higher arterial perfusion fraction (52.0% ± 23.4% versus 12.4% ± 7.1%; P < 0.05). The mean transit time was higher in the cirrhotic livers (24.4 ± 4.7 versus 15.7 ± 3.4 seconds; P < 0.05), and the hepatocellular uptake rate was lower (3.03 ± 2.1 versus 6.53 ± 2.4 100/min; P < 0.05). ConclusionsLiver perfusion metrics can be estimated from free-breathing dynamic acquisition performed for every clinical examination without additional contrast injection or time. This is a novel paradigm for dynamic liver imaging.

Prostate Cancer: Utility of Whole-Lesion Apparent Diffusion Coefficient Metrics for Prediction of Biochemical Recurrence After Radical Prostatectomy

OBJECTIVE The purpose of this study was to investigate the additional value of whole-lesion histogram apparent diffusion coefficient (ADC) metrics, when combined with standard pathologic features, in prediction of biochemical recurrence (BCR) after radical prostatectomy for prostate cancer. MATERIALS AND METHODS The study included 193 patients (mean age, 61 ± 7 years) who underwent 3-T MRI with DWI (b values, 50 and 1000 s/mm(2)) before prostatectomy. Histogram metrics were derived from 3D volumes of interest encompassing the entire lesion on ADC maps. Pathologic features from radical prostatectomy and subsequent BCR were recorded for each patient. The Fisher exact test and Mann-Whitney test were used to compare ADC-based metrics and pathologic features between patients with and patients without BCR. Stepwise logistic regression analysis was used to construct multivariable models for prediction of BCR, which were assessed by ROC analysis. RESULTS BCR occurred in 16.6% (32/193) of patients. Variables significantly associated with BCR included primary Gleason grade, Gleason score, extraprostatic extension, seminal vesicle invasion, positive surgical margin, preoperative prostate-specific antigen level, MRI tumor volume, mean whole-lesion ADC, entropy ADC, and mean ADC of the bottom 10th, 10-25th, and 25-50th percentiles (p ≤ 0.019). Significant independent predictors of BCR at multivariable analysis were primary Gleason grade, extraprostatic extension, mean of the bottom 10th percentile ADC, and entropy ADC (p = 0.002-0.037). The AUC of this multivariable model was 0.94 for prediction of BCR; the AUC of pathologic features alone was 0.89 (p = 0.001). CONCLUSION A model integrating whole-lesion ADC metrics had significantly higher performance for prediction of BCR than did standard pathologic features alone and may help guide postoperative prognostic assessments and decisions regarding adjuvant therapy.

Prostate Cancer Detection Using Computed Very High b-value Diffusion-weighted Imaging: How High Should We Go?

RATIONALE AND OBJECTIVES The aim of this study was to assess prostate cancer detection using a broad range of computed b-values up to 5000 s/mm(2). MATERIALS AND METHODS This retrospective Health Insurance Portability and Accountability Act-compliant study was approved by an institutional review board with consent waiver. Forty-nine patients (63 ± 8 years) underwent 3T prostate magnetic resonance imaging before prostatectomy. Examinations included diffusion-weighted imaging (DWI) with b-values of 50 and 1000 s/mm(2). Seven computed DWI image sets (b-values: 1000, 1500, 2000, 2500, 3000, 4000, and 5000 s/mm(2)) were generated by mono-exponential fit. Two blinded radiologists (R1 [attending], R2 [fellow]) independently evaluated diffusion weighted image sets for image quality and dominant lesion location. A separate unblinded radiologist placed regions of interest to measure tumor-to-peripheral zone (PZ) contrast. Pathologic findings from prostatectomy served as reference standard. Measures were compared between b-values using the Jonckheere-Terpstra trend test, Spearman correlation coefficient, and generalized estimating equations based on logistic regression for correlated data. RESULTS As b-value increased, tumor-to-PZ contrast and benign prostate suppression for both readers increased (r = +0.65 to +0.71, P ≤ 0.001), whereas anatomic clarity, visualization of the capsule, and visualization of peripheral-transition zone edge decreased (r = -0.69 to -0.75, P ≤ 0.003). Sensitivity for tumor was highest for R1 at b1500-3000 (84%-88%) and for R2 at b1500-2500 (70%-76%). Sensitivities for both pathologic outcomes were lower for both readers at both b1000 and the highest computed b-values. Sensitivity for Gleason >6 tumor was highest for R1 at b1500-3000 (90%-93%) and for R2 at 1500-2500 (78%-80%). The positive predictive value for tumor for R1 was similar from b1000 to 4000 (93%-98%) and for R2 was similar from b1500 to 4000 (88%-94%). CONCLUSIONS Computed b-values in the range of 1500-2500 s/mm(2) (but not higher) were optimal for prostate cancer detection; b-values of 1000 or 3000-5000 exhibited overall lower performance.

Likert score 3 prostate lesions: Association between whole-lesion ADC metrics and pathologic findings at MRI/ultrasound fusion targeted biopsy

To assess associations between whole‐lesion apparent diffusion coefficient (ADC) metrics and pathologic findings of Likert score 3 prostate lesions at MRI/ultrasound fusion targeted biopsy.

Characterization of Adrenal Lesions at Chemical-Shift MRI: A Direct Intraindividual Comparison of In- and Opposed-Phase Imaging at 1.5 T and 3 T

OBJECTIVE. The purpose of this article is to perform an intraindividual comparison between 1.5 T and 3 T chemical-shift MRI in differentiating adrenal adenomas and nonadenomas, including comparison of quantitative thresholds. MATERIALS AND METHODS. In this retrospective study, 37 adrenal lesions in 36 patients (20 men and 16 women; mean [± SD] age, 66.7 ± 12.9 years; 27 benign adenomas in 27 patients; 10 nonadenomas in nine patients) imaged at 1.5 T and 3 T were identified. Two readers qualitatively assessed intralesional signal loss between in- and opposed-phase images. One reader placed ROIs on adrenal lesions, spleen, liver, and muscle. Quantitative measures of signal loss, such as signal intensity (SI) index, adrenal-to-spleen ratio, adrenal-to-liver ratio, and adrenal-to-muscle ratio, were calculated. Qualitative and quantitative measures between field strengths were assessed with McNemar test and ROC analysis, respectively. RESULTS. Accuracy in qualitative adenoma identification (86.5% [32/37] at 1.5 T and 81.1% [30/37] at 3 T for reader 1; 81.1% [30/37] at 1.5 T and 83.8% [31/37] at 3 T for reader 2; both p ≥ 0.180) was equivalent at both field strengths. AUCs were not statistically significantly different between field strengths for quantitative measures: AUCs at 1.5 T versus 3 T were 0.956 versus 0.915 for SI index, 0.963 versus 0.870 for adrenal-to-spleen ratio, 0.935 versus 0.852 for adrenal-to-liver ratio, and 0.948 versus 0.948 for adrenal-to-muscle ratio (all p > 0.11). The optimal threshold for SI index was lower at 3 T (> 7.4%) than at 1.5 T (> 21.6%) but had similar sensitivity (1.5 T, 92.6% [25/27]; 3 T, 88.9% [24/27]) and specificity (1.5 T, 90.0% [9/10]; 3 T, 90.0% [9/10]). CONCLUSION. Chemical-shift imaging has similar diagnostic efficacy for differentiating adrenal adenomas and nonadenomas at 1.5 T and 3 T. However, quantitative measures have different thresholds for this differentiation at 3 T; in particular, the commonly applied SI index is much lower at 3 T.

Use of MRI in Differentiation of Papillary Renal Cell Carcinoma Subtypes: Qualitative and Quantitative Analysis

OBJECTIVE The purpose of this study was to determine whether qualitative and quantitative MRI feature analysis is useful for differentiating type 1 from type 2 papillary renal cell carcinoma (PRCC). MATERIALS AND METHODS This retrospective study included 21 type 1 and 17 type 2 PRCCs evaluated with preoperative MRI. Two radiologists independently evaluated various qualitative features, including signal intensity, heterogeneity, and margin. For the quantitative analysis, a radiology fellow and a medical student independently drew 3D volumes of interest over the entire tumor on T2-weighted HASTE images, apparent diffusion coefficient parametric maps, and nephrographic phase contrast-enhanced MR images to derive first-order texture metrics. Qualitative and quantitative features were compared between the groups. RESULTS For both readers, qualitative features with greater frequency in type 2 PRCC included heterogeneous enhancement, indistinct margin, and T2 heterogeneity (all, p < 0.035). Indistinct margins and heterogeneous enhancement were independent predictors (AUC, 0.822). Quantitative analysis revealed that apparent diffusion coefficient, HASTE, and contrast-enhanced entropy were greater in type 2 PRCC (p < 0.05; AUC, 0.682-0.716). A combined quantitative and qualitative model had an AUC of 0.859. Qualitative features within the model had interreader concordance of 84-95%, and the quantitative data had intraclass coefficients of 0.873-0.961. CONCLUSION Qualitative and quantitative features can help discriminate between type 1 and type 2 PRCC. Quantitative analysis may capture useful information that complements the qualitative appearance while benefiting from high interobserver agreement.

Advances in T1-Weighted and T2-Weighted Imaging in the Abdomen and Pelvis

Utilization of abdominopelvic MR imaging continues to increase in volume and gain widespread clinical acceptance. Many factors such as diaphragmatic respiratory motion, bulk patient motion, and the need for large volumetric coverage while maintaining clinically feasible scan times have proven challenging for body applications of MRI. However, many advances in MR acquisition, including non-Cartesian T1-weighted and T2-weighted acquisitions, advanced Dixon sequences, and 3-dimensional volumetric T2-weighted imaging have helped to mitigate some of the issues which have hampered abdominopelvic MR. This article will summarize these advances in T1-weighted and T2-weighted imaging, with an emphasis on clinical applications and implementation.