Quantitative MRCP Imaging: Accuracy, Repeatability, Reproducibility, and Cohort-Derived Normative Ranges.

BACKGROUND: Magnetic resonance cholangiopancreatography (MRCP) is an important tool for noninvasive imaging of biliary disease, however, its assessment is currently subjective, resulting in the need for objective biomarkers. PURPOSE: To investigate the accuracy, scan/rescan repeatability, and cross-scanner reproducibility of a novel quantitative MRCP tool on phantoms and in vivo. Additionally, to report normative ranges derived from the healthy cohort for duct measurements and tree-level summary metrics. STUDY TYPE: Prospective. PHANTOMS/SUBJECTS: Phantoms: two bespoke designs, one with varying tube-width, curvature, and orientation, and one exhibiting a complex structure based on a real biliary tree. Subjects Twenty healthy volunteers, 10 patients with biliary disease, and 10 with nonbiliary liver disease. SEQUENCE/FIELD STRENGTH: MRCP data were acquired using heavily T2 -weighted 3D multishot fast/turbo spin echo acquisitions at 1.5T and 3T. ASSESSMENT: Digital instances of the phantoms were synthesized with varying resolution and signal-to-noise ratio. Physical 3D-printed phantoms were scanned across six scanners (two field strengths for each of three manufacturers). Human subjects were imaged on four scanners (two fieldstrengths for each of two manufacturers). STATISTICAL TESTS: Bland-Altman analysis and repeatability coefficient (RC). RESULTS: Accuracy of the diameter measurement approximated the scanning resolution, with 95% limits of agreement (LoA) from -1.1 to 1.0 mm. Excellent phantom repeatability was observed, with LoA from -0.4 to 0.4 mm. Good reproducibility was observed across the six scanners for both phantoms, with a range of LoA from -1.1 to 0.5 mm. Inter- and intraobserver agreement was high. Quantitative MRCP detected strictures and dilatations in the phantom with 76.6% and 85.9% sensitivity and 100% specificity in both. Patients and healthy volunteers exhibited significant differences in metrics including common bile duct (CBD) maximum diameter (7.6 mm vs. 5.2 mm P = 0.002), and overall biliary tree volume 12.36 mL vs. 4.61 mL, P = 0.0026). DATA CONCLUSION: The results indicate that quantitative MRCP provides accurate, repeatable, and reproducible measurements capable of objectively assessing cholangiopathic change. Evidence Level: 1 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2020;52:807-820.

Accuracy of resting metabolic rate prediction in overweight and obese Australian adults.

OBJECTIVES: Predictive resting metabolic rate (RMR) equations in Australian populations are at least 10 years old, focused on males and do not commonly use overweight and obese weight categorisation. The aim of this study was to measure RMR via indirect calorimetry in overweight and obese Australian adults to develop population specific predictive equations and compare with other well-known international equations (Mifflin-St. Jeor, Owen and WHO/FAO/UNU). METHODS: Retrospective data from 278 participants (154 males, 124 females: 37% overweight, 63% obese) who had attended a weight management clinic were used to develop predictive RMR equations. These were then validated against another sample (from the same clinic) of 297 participants (150 males, 147 females: 47% overweight, 53% obese), and their accuracy compared with known standard equations. RESULTS: For the prediction sample, weight, BMI, resting VO2 and measured RMR were significantly greater in the obese than overweight. Using the validation sample, the predictive equations met a ±10% of measured RMR criterion 42% (females), 41% (total sample) and 40% (males) of the time. Prediction accuracy was not improved by using specific overweight and obese weight category equations, or by applying the known standard equations from the literature. CONCLUSIONS: In our sample of overweight and obese adults, RMR prediction to within ±10% of the measured value was only accurate ∼40% of the time, regardless of gender and weight classification. In clinical weight management settings direct measures of RMR should be made wherever possible.

Influence of Hormonal Profile on Resting Metabolic Rate in Normal, Overweight and Obese Individuals.

AIMS: To investigate whether blood thyroid stimulating hormone (TSH), cortisol, insulin and glucose concentrations (plus glucose:insulin ratio; GIR) could improve the accuracy of resting metabolic rate (RMR) prediction in normal, overweight and obese persons. METHODS: Predictive equations were developed and compared against indirect calorimetry measures for RMR in 217 weight-control clinic participants (n = 128 males and n = 89 females: ∼24% normal weight, ∼39% overweight and ∼37% obese). RESULTS: Using the common accuracy criteria of the proportion of predicted RMR within ±10% of measured RMR, our equations (using age, height, weight and gender, plus the blood factors, both independently and in combination) were accurate ∼36-44% of the time, for the whole sample, and when separated by gender and weight class. Specifically, the addition of the blood hormone and glucose concentrations improved the accuracy of predicted RMR by only 1-8% (NS). CONCLUSIONS: Including blood TSH, cortisol, insulin, glucose and GIR into RMR prediction equations did not significantly improve estimation accuracy, which in any case only met a criterion of ±10% of the measured RMR ∼40% of the time. Further work to refine the prediction of RMR is still needed, and at present, direct measurements should be made wherever possible.

Improving influx constant and ratio estimation in FDOPA brain PET analysis for Parkinson's disease.

UNLABELLED: PET studies using l-3,4-dihydroxy-6-(18)F-fluorophenylalanine have been applied to assess the diminished functionality of the striatum in patients with suspected Parkinson's disease. Two techniques for analyzing such studies are ratio methods and graphically computed influx constants. We propose a method for improving the consistency with which scans obtained by either of these techniques are analyzed. The method is based on a fully 3-dimensional analysis of the images. METHODS: Fifty-one dynamically acquired datasets were corrected for motion before analysis. Regions of interest (ROIs) for the analysis were determined by manual affine registration to a standard template, using a separate transformation for each ROI. Indicator values for each ROI were computed by averaging the values of voxels having the highest activity within a specified proportion of the voxels in the ROI, to increase the robustness to perturbations in the ROI position. Sensitivity was analyzed by examining the variation in results obtained when the ROIs were translated by up to 6 mm. RESULTS: We observed significant percentage differences in the computed influx constant before and after motion correction (mean variation +/- SD, -0.75% +/- 9.5% averaged over all regions of all patients). Our method was robust to placement of the cerebellum ROI, whereas a 2- dimensional analysis based on hand-drawn ROIs was associated with a 2- to 3-fold greater percentage variation in uptake for translations of 2 mm or more in ROI position. When we compared the 2 quantification techniques, our influx constants and ratios correlated at r(2) = 0.91, P < 0.0001. CONCLUSION: Motion correction is an important step for computing reliable results in dynamic studies. The robustness of the results can be increased further by using standard normalized volumetric ROIs and by using the average value of a specified proportion of the voxels with the highest activity in the ROI as an indicator for that ROI. Influx constant values computed using our analysis technique closely correlated to values computed with ratio methods using this general approach.