MRI analysis of fecal volume and dryness: Validation study using an experimental oxycodone-induced constipation model.

BACKGROUND: Opioids are known to affect gastrointestinal motility, but their effect on fluid absorption and secretion is poorly understood in humans. PURPOSE: To investigate the effect of oxycodone on colonic fecal volume and stool dryness by using a novel MRI-based technique. STUDY TYPE: Prospective, randomized, double-blinded, crossover study. SUBJECTS: Twenty-five healthy male volunteers (median age: 24 years [range: 21-56]; mean body mass index [BMI]: 23.9 kg/m2 [range: 22.9-25.0]) without known gastrointestinal disease. FIELD STRENGTH/SEQUENCE: T2 -weighted and two-point Dixon MRI scans of the abdomen at 1.5 T. ASSESSMENT: Subjects were treated for 5 days with prolonged-release oxycodone or a placebo. Imaging was performed on the first and last study day in each period. Images of the colon were analyzed with semiautomatic k-means-based segmentation software. Regional colonic fecal volumes were quantified excluding gas volume and colon wall. Two-point Dixon and T2 -weighted MRI signal intensity were assessed as a proxy of colonic stool dryness. Data were obtained in a previously reported study. STATISTICAL TESTS: Intraclass correlation coefficients were used to test the reliability of measurements between days, while repeated measures mixed models were applied to test treatment effects. RESULTS: After oxycodone treatment, total colonic fecal volume was significantly increased compared with placebo (mean change 100 mL vs. -13 mL; P = 0.001), with the largest increase (24%) observed in the ascending colon/cecum (P = 0.001). Dixon signal increased (less water in colon content) after oxycodone treatment compared with placebo (mean 0.09 vs. -0.02; P < 0.001). T2 -weighted signal decreased (less water in colon content) after oxycodone treatment compared with placebo (mean -0.03 vs. 0.03; P = 0.002). DATA CONCLUSION: The 5-day oxycodone treatment increased colonic fecal volume and increased stool dryness compared with placebo. This imaging-based method for noninvasive analysis of colon content has the potential to characterize gastrointestinal symptoms in general, such as in constipation. LEVEL OF EVIDENCE: 2 Technical Efficacy Stage: 1 J. Magn. Reson. Imaging 2019;50:733-745.

Postpartum computed tomography angiography of the fetoplacental macrovasculature in normal pregnancies and in those complicated by fetal growth restriction.

INTRODUCTION: Current knowledge of the fetoplacental vasculature in fetal growth restriction (FGR) due to placental dysfunction focuses on the microvasculature rather than the macrovasculature. The aim of this study was to investigate the feasibility of computed tomography angiography to analyze the fetoplacental macrovasculature in normal and FGR pregnancies. MATERIAL AND METHODS: We included 29 placentas (22-42 weeks of gestation) from normal birthweight pregnancies and eight placentas (26-37 weeks of gestation) from FGR pregnancies (birthweight < -15% and abnormal umbilical Doppler flow). We performed postpartum placental computed tomography angiography followed by semi-automatic three-dimensional image segmentation. RESULTS: A median of nine (range seven to eleven) vessel generations was identified. In normal birthweight placentas, gestational age was positively linearly correlated with macrovascular volume (p = 0.002), vascular surface area (p < 0.0005) and number of vessel junctions (p = 0.012), but not with vessel diameter and inter-branch length. The FGR placentas had a lower weight (p = 0.004) and smaller convex volume (p = 0.022) (smallest convex volume containing the macrovasculature); however, macrovascular volume was not significantly reduced. Hence, macrovascular density given as macrovascular outcomes per placental volume was increased in FGR placentas: macrovascular volume per convex volume (p = 0.004), vascular surface area per convex volume (p = 0.004) and number of vessel junctions per convex volume (p = 0.037). CONCLUSIONS: Evaluation of the fetoplacental macrovasculature is feasible with computed tomography angiography. In normal birthweight placentas, macrovascular volume and surface area increase as pregnancy advances by vessel branching rather than increased vessel diameter and elongation. The FGR placenta was smaller; however, the macrovascular volume was within normal range because of an increased macrovascular density.

High-Frame-Rate Deformation Imaging in Two Dimensions Using Continuous Speckle-Feature Tracking.

The study describes a novel algorithm for deriving myocardial strain from an entire cardiac cycle using high-frame-rate ultrasound images. Validation of the tracking algorithm was conducted in vitro prior to the application to patient images. High-frame-rate ultrasound images were acquired in vivo from 10 patients, and strain curves were derived in six myocardial regions around the left ventricle from the apical four-chamber view. Strain curves derived from high-frame-rate images had a higher frequency content than those derived using conventional methods, reflecting improved temporal sampling.

A new method to validate thoracic CT-CT deformable image registration using auto-segmented 3D anatomical landmarks.

BACKGROUND: Deformable image registrations are prone to errors in aligning reliable anatomically features. Consequently, identification of registration inaccuracies is important. Particularly thoracic three-dimensional (3D) computed tomography (CT)-CT image registration is challenging due to lack of contrast in lung tissue. This study aims for validation of thoracic CT-CT image registration using auto-segmented anatomically landmarks. MATERIAL AND METHODS: Five lymphoma patients were CT scanned three times within a period of 18 months, with the initial CT defined as the reference scan. For each patient the two successive CT scans were registered to the reference CT using three different image registration algorithms (Demons, B-spline and Affine). The image registrations were evaluated using auto-segmented anatomical landmarks (bronchial branch points) and Dice Similarity Coefficients (DSC). Deviation of corresponding bronchial landmarks were used to quantify inaccuracies in respect of both misalignment and geometric location within lungs. RESULTS: The median bronchial branch point deviations were 1.6, 1.1 and 4.2 (mm) for the three tested algorithms (Demons, B-spline and Affine). The maximum deviations (> 15 mm) were found within both Demons and B-spline image registrations. In the upper part of the lungs the median deviation of 1.7 (mm) was significantly different (p < 0.02) relative to the median deviations of 2.0 (mm), found in the middle and lower parts of the lungs. The DSC revealed similar registration discrepancies among the three tested algorithms, with DSC values of 0.96, 0.97 and 0.91, for respectively Demons, B-spline and the Affine algorithms. CONCLUSION: Bronchial branch points were found useful to validate thoracic CT-CT image registration. Bronchial branch points identified local registration errors > 15 mm in both Demons and B-spline deformable algorithms.

Cortical volumes and atrophy rates in FTD-3 CHMP2B mutation carriers and related non-carriers.

Frontotemporal dementia constitutes the third most prevalent neurodegenerative disease with dementia. We compared cortical structural changes in nine presymptomatic CHMP2B frontotemporal dementia mutation positive individuals with seven mutation negative family members. Using serial MRI scans with a mean interval of 16 months and surface based cortical segmentation we measured cortical thickness and volume, and quantified atrophy rates. Cortical thickness and atrophy rates were averaged within major lobes and focal effects were determined by parametric statistical maps. The volumetric atrophy rates in the presymptomatic CHMP2B mutation carriers were statistically significant, though of a lower magnitude than those previously reported in patients of other types of frontotemporal dementia. Cortical thickness measurements revealed cortical thinning in mutation carriers bilaterally in the frontal and occipital lobes, and in the left temporal lobe. Results indicated that cortical thickness has a higher sensitivity for detecting small changes than whole-brain volumetric measures. Comparing mutation carriers with non-carriers revealed increased atrophy rates in mutation carriers bilaterally in the inferio-temporal cortex, the superior frontal cortex, and the insular cortex. These findings indicated impairment of regions involved in both behaviour and language. The symptoms previously reported in clinical CHMP2B frontotemporal dementia patients are associated with the anatomically affected regions here found in the presymptomatic mutation carriers.

Quantitative comparison of two cortical surface extraction methods using MRI phantoms.

In the last decade several methods for extracting the human cerebral cortex from magnetic resonance images have been proposed. Studies comparing these methods have been few. In this study we compare a recent cortical extraction method with FreeSurfer, which has been widespread in the scientific community during recent years. The comparison is performed using realistic phantoms generated from surfaces extracted from original brain scans. The geometrical accuracy of the reconstructed surfaces is compared to the surfaces extracted from the original scan. We found that our method is comparable with FreeSurfer in terms of accuracy, and in some cases it performs better. In terms of speed our method is more than 25 times faster.

Active surface approach for extraction of the human cerebral cortex from MRI.

Segmentation of the human cerebral cortex from MRI has been subject of much attention during the last decade. Methods based on active surfaces for representing and extracting the cortical boundaries have shown promising results. We present an active surface method, that extracts the inner and outer cortical boundaries using a combination of different vector fields and a local weighting method based on the intrinsic properties of the deforming surface. Our active surface model deforms polygonal meshes to fit the boundaries of the cerebral cortex using a force balancing scheme. As a result of the local weighting strategy and a self-intersection constraint, the method is capable of modelling tight sulci where the image edge is missing or obscured. The performance of the method is evaluated using both real and simulated MRI data.