Comparative diagnostic performance of ultrasound shear wave elastography and magnetic resonance elastography for classifying fibrosis stage in adults with biopsy-proven nonalcoholic fatty liver disease.

OBJECTIVES: To compare the diagnostic accuracy of US shear wave elastography (SWE) and magnetic resonance elastography (MRE) for classifying fibrosis stage in patients with nonalcoholic fatty liver disease (NAFLD). METHODS: Patients from a prospective single-center cohort with clinical liver biopsy for known or suspected NAFLD underwent contemporaneous SWE and MRE. AUCs for classifying biopsy-determined liver fibrosis stages ≥ 1, ≥ 2, ≥ 3, and = 4, and their respective performance parameters at cutoffs providing ≥ 90% sensitivity or specificity were compared between SWE and MRE. RESULTS: In total, 100 patients (mean age, 51.8 ± 12.9 years; 46% males; mean BMI 31.6 ± 4.7 kg/m2) with fibrosis stage distribution (stage 0/1/2/3/4) of 43, 36, 5, 10, and 6%, respectively, were included. AUCs (and 95% CIs) for SWE and MRE were 0.65 (0.54-0.76) and 0.81 (0.72-0.89), 0.81 (0.71-0.91) and 0.94 (0.89-1.00), 0.85 (0.74-0.96) and 0.95 (0.89-1.00), and 0.91 (0.79-1.00) and 0.92 (0.83-1.00), for detecting fibrosis stage ≥ 1, ≥ 2, ≥ 3, and = 4, respectively. The differences were significant for detecting fibrosis stage ≥ 1 and ≥ 2 (p < 0.01) but not otherwise. At ≥ 90% sensitivity cutoff, MRE yielded higher specificity than SWE at diagnosing fibrosis stage ≥ 1, ≥ 2, and ≥ 3. At ≥ 90% specificity cutoff, MRE yielded higher sensitivity than SWE at diagnosing fibrosis stage ≥ 1 and ≥ 2. CONCLUSIONS: In adults with NAFLD, MRE was more accurate than SWE in diagnosing stage ≥ 1 and ≥ 2 fibrosis, but not stage ≥ 3 or 4 fibrosis. KEY POINTS: • For detecting any fibrosis or mild fibrosis, MR elastography was significantly more accurate than shear wave elastography. • For detecting advanced fibrosis and cirrhosis, MRE and SWE did not differ significantly in accuracy. • For excluding advanced fibrosis and potentially ruling out the need for biopsy, SWE and MRE did not differ significantly in negative predictive value. • Neither SWE nor MRE had sufficiently high positive predictive value to rule in advanced fibrosis.

Technical report: gadoxetate-disodium-enhanced 2D R2* mapping: a novel approach for assessing bile ducts in living donors.

PURPOSE: Gadoxetate-disodium (Gd-EOB-DTPA)-enhanced 3D T1- weighted (T1w) MR cholangiography (MRC) is an efficient method to evaluate biliary anatomy due to T1 shortening of excreted contrast in the bile. A method that exploits both T1 shortening and T2* effects may produce even greater bile duct conspicuity. The aim of our study is to determine feasibility and compare the diagnostic performance of two-dimensional (2D) T1w multi-echo (ME) spoiled gradient-recalled-echo (SPGR) derived R2* maps against T1w MRC for bile duct visualization in living liver donor candidates. MATERIALS AND METHODS: Ten potential living liver donor candidates underwent pretransplant 3T MRI and were included in our study. Following injection of Gd-EOBDTPA and a 20-min delay, 3D T1w MRC and 2D T1w ME SPGR images were acquired. 2D R2* maps were generated inline by the scanner assuming exponential decay. The 3D T1w MRC and 2D R2* maps were retrospectively and independently reviewed in two separate sessions by three radiologists. Visualization of eight bile duct segments was scored using a 4-point ordinal scale. The scores were compared using mixed effects regression model. RESULTS: Imaging was tolerated by all donors and R2* maps were successfully generated in all cases. Visualization scores of 2D R2* maps were significantly higher than 3D T1w MRC for right anterior (p = 0.003) and posterior (p = 0.0001), segment 2 (p < 0.0001), segment 3 (p = 0.0001), and segment 4 (p < 0.0001) ducts. CONCLUSIONS: Gd-EOB-DTPA-enhanced 2D R2* mapping is a feasible method for evaluating the bile ducts in living donors and may be a valuable addition to the living liver donor MR protocol for delineating intrahepatic biliary anatomy.

Comparison of magnetic resonance imaging and ultrasound (MRI-US) fusion-guided prostate biopsies obtained from axial and sagittal approaches.

OBJECTIVE: To compare cancer detection rates and concordance between magnetic resonance imaging and ultrasound (MRI-US) fusion-guided prostate biopsy cores obtained from axial and sagittal approaches. PATIENTS AND METHODS: Institutional records of MRI-US fusion-guided biopsy were reviewed. Detection rates for all cancers, Gleason ≥3 + 4 cancers, and Gleason ≥4 + 3 cancers were computed. Agreement between axial and sagittal cores for cancer detection, and frequency where one was upgraded the other was computed on a per-target and per-patient basis. RESULTS: In all, 893 encounters from 791 patients that underwent MRI-US fusion-guided biopsy in 2007-2013 were reviewed, yielding 4688 biopsy cores from 2344 targets for analysis. The mean age and PSA level at each encounter was 61.8 years and 9.7 ng/mL (median 6.45 ng/mL). Detection rates for all cancers, ≥3 + 4 cancers, and ≥4 + 3 cancers were 25.9%, 17.2%, and 8.1% for axial cores, and 26.1%, 17.6%, and 8.6% for sagittal cores. Per-target agreement was 88.6%, 93.0%, and 96.5%, respectively. On a per-target basis, the rates at which one core upgraded or detected a cancer missed on the other were 8.3% and 8.6% for axial and sagittal cores, respectively. Even with the inclusion of systematic biopsies, omission of axial or sagittal cores would have resulted in missed detection or under-characterisation of cancer in 4.7% or 5.2% of patients, respectively. CONCLUSION: Cancer detection rates, Gleason scores, and core involvement from axial and sagittal cores are similar, but significant cancer may be missed if only one core is obtained for each target. Discordance between axial and sagittal cores is greatest in intermediate-risk scenarios, where obtaining multiple cores may improve tissue characterisation.

Collagenase-mediated tissue modeling of corneal ectasia and collagen cross-linking treatments.

PURPOSE: Corneal collagen cross-linking (CXL) is a method for modifying the natural history of keratoconus and other corneal ectatic diseases. The authors evaluated the use of collagenase for generating an experimental model of ectasia to evaluate the topographic effects of CXL interventions. METHODS: Nine human corneoscleral specimens unsuitable for transplantation were used. After epithelial debridement, mounting, and pressurization on an artificial anterior chamber, a solution of 10 mg/mL collagenase type II with 15% dextran was applied to five corneas for three hours. Three of these corneas subsequently underwent riboflavin/UV-A CXL. Scheimpflug-based tomography was performed before collagenase exposure, after collagenase exposure, and after CXL to evaluate changes in maximum axial curvature of the anterior surface (K(max)) at three IOP levels. Results were compared to four control eyes exposed to dextran alone. RESULTS: A statistically significant increase in K(max) was seen across all IOP levels in the collagenase group compared to the control group (+6.6 ± 1.1 diopters [D] and +0.3 ± 0.8 D, respectively, at physiological IOP). After CXL, K(max) decreased (-7.6 ± 2.0 D at physiological IOP). Anterior corneal aberrations increased after collagenase exposure and decreased after CXL. Light microscopy showed loss of normal stromal collagen architecture and localized edema after collagenase exposure. CONCLUSIONS: A method for generating topographic features of corneal ectasia in human tissue is demonstrated. No significant sensitivity of K(max) to IOP was observed. CXL caused regression of steepening and induced aberrations in this model, consistent with clinical trends. The model may be useful for testing modifications to standard CXL techniques.

SHARPEN-systematic hierarchical algorithms for rotamers and proteins on an extended network.

Algorithms for discrete optimization of proteins play a central role in recent advances in protein structure prediction and design. We wish to improve the resources available for computational biologists to rapidly prototype such algorithms and to easily scale these algorithms to many processors. To that end, we describe the implementation and use of two new open source resources, citing potential benefits over existing software. We discuss CHOMP, a new object-oriented library for macromolecular optimization, and SHARPEN, a framework for scaling CHOMP scripts to many computers. These tools allow users to develop new algorithms for a variety of applications including protein repacking, protein-protein docking, loop rebuilding, or homology model remediation. Particular care was taken to allow modular energy function design; protein conformations may currently be scored using either the OPLSaa molecular mechanical energy function or an all-atom semiempirical energy function employed by Rosetta.