Hu, Peng

ABSTRACT Skeletal muscle (SM) is an integral organ component in the pathophysiology of many acute and chronic diseases. But is there a ‘gold’ standard or accepted reference method for quantifying the amount and composition of human SM mass? Exploring that question led us to recognize the existence of a SM measurement paradigm that divides methods into two broad categories, in vitro and in vivo. In vitro methods quantify SM mass, weighing intact muscles as part of whole cadaver evaluations, only 51 of which are reported in medical literature with no recent additions. In vivo methods are used to evaluate SM in vivo, and two tiers were revealed in our analyses. An upper tier that included three methods considered ‘reference’ approaches for their accuracy and precision: computed tomography, magnetic resonance imaging and dual‐energy X‐ray absorptiometry. A lower in vivo method tier included bioimpedance analysis, three‐dimensional imaging, several approaches involving creatine metabolism, ultrasound and anthropometry. A feature common to all of the lower tier methods is their need for calibration or validation against reference approaches in the upper in vivo method tier. A critical review of the three in vivo reference methods in the upper tier revealed widely variable SM volume/mass acquisition protocols, image analysis methods and applied terminology. Some reports espouse an upper tier reference method as the ‘gold’ standard while providing minimal details of exactly how and what was measured, thus making replication in follow‐up studies difficult. Any technical issues related to an in vivo reference method are propagated to the in vivo methods in the lower tier that are calibrated or validated against them. Our review of in vivo reference methods of quantifying SM mass and composition led us to two broad recommendations. First, published reports including these reference methods should provide enough details related to acquisition and analysis protocols so that readers can replicate their findings. Second, an effort should be made to apply precise terminology in published reports in order to avoid confusion on exactly what was measured; suggestions are made on definitions of commonly used terms when referring to body composition compartments. Lastly, because there is no consensus on what constitutes a ‘gold’ standard for SM measurement, we suggest expert groups convene in the future to recommend optimum approaches and working guidelines for quantifying muscle mass and composition in vivo.

ABSTRACT Background Adolescents with youth‐onset type 2 diabetes (YO‐T2D) have an increased risk for cardiometabolic complications. The impact of vertical sleeve gastrectomy (VSG) on fat distribution and cardiac morphology/function in YO‐T2D is unknown. Objectives To evaluate changes in body composition, abdominal and cardiac fat depots, and cardiometabolic health in adolescents with YO‐T2D undergoing VSG. Methods Anthropometrics, labs and imaging were used to assess participants pre‐surgery and 3–12 months post‐surgery. MRI quantified pericardial (PAT), epicardial (EAT), subcutaneous (SAT) and visceral adipose tissue (VAT), hepatic fat fraction (HFF) and cardiac morphology/function. Mixed‐effects models assessed longitudinal changes. Results By 12 months, weight decreased from 134.3 ± 5.1 to 103.3 ± 5.2 kg, VAT 1943 ± 148 to 1248 ± 150 cm 3 , HFF 23.2% ± 2.3% to 5.3% ± 2.3% and PAT and EAT by 27% and 33% (all p < 0.01). Homeostatic model assessment of insulin resistance (HOMA‐IR) improved (7.8 ± 1.2 to 1.7 ± 1.2 [ p < 0.01]). BMI, SAT, resting heart rate (RHR), left ventricular (LV) mass and cardiac output (CO) also decreased (all p < 0.05). VAT decreases correlated with decreases in HFF ( r = 0.70, p = 0.01), HOMA‐IR ( r = 0.60, p = 0.04) and CO ( r = 0.70, p = 0.03). HFF decreases correlated with decreases in BMI ( r = 0.70, p = 0.03), HOMA‐IR ( r = 0.90, p < 0.001), RHR ( r = 0.90, p = 0.002), CO ( r = 0.80, p = 0.007) and LV mass ( r = 0.70, p = 0.02). Conclusions VSG reduces ectopic and regional fat and improves associated insulin sensitivity and cardiac health in adolescents with YO‐T2D.

Abstract In March of 2025, 145 attendees convened at the Hub for Clinical Collaboration of the Children's Hospital of Philadelphia for the inaugural International Society for Magnetic Resonance in Medicine (ISMRM) Body MRI Study Group workshop entitled “Body MRI: Unsolved Problems and Unmet Needs.” Approximately 24% of the attendees were MD or MD/PhD's, 45% were PhD's, and 30% were early‐career trainees and postdoctoral associates. Among the invited speakers and moderators, 28% were from outside the United States, with a 40:60% female‐to‐male ratio. The 2.5‐day program brought together a multidisciplinary group of scientists, radiologists, technologists, and trainees. Session topics included quantitative imaging biomarkers, low‐ and high‐field strengths, artifact and motion correction, rapid imaging and focused protocols, and artificial intelligence. Another key session focused on the importance of team science and allowed speakers from academia and industry to share their personal experiences and offer advice on how to successfully translate new MRI technology into clinical practice. This article summarizes key points from the event and perceived unmet clinical needs within the field of body MRI.

PurposeChemical shift‐encoded MRI (CSE‐MRI) is well‐established to quantify proton density fat fraction (PDFF) as a quantitative biomarker of hepatic steatosis. However, temperature is known to bias PDFF estimation in phantom studies. In this study, strategies were developed and evaluated to correct for the effects of temperature on PDFF estimation through simulations, temperature‐controlled experiments, and a multi‐center, multi‐vendor phantom study.Theory and MethodsA technical solution that assumes and automatically estimates a uniform, global temperature throughout the phantom is proposed. Computer simulations modeled the effect of temperature on PDFF estimation using magnitude‐, complex‐, and hybrid‐based CSE‐MRI methods. Phantom experiments were performed to assess the temperature correction on PDFF estimation at controlled phantom temperatures. To assess the temperature correction method on a larger scale, the proposed method was applied to data acquired as part of a nine‐site multi‐vendor phantom study and compared to temperature‐corrected PDFF estimation using an a priori guess for ambient room temperature.ResultsSimulations and temperature‐controlled experiments show that as temperature deviates further from the assumed temperature, PDFF bias increases. Using the proposed correction method and a reasonable a priori guess for ambient temperature, PDFF bias and variability were reduced using magnitude‐based CSE‐MRI, across MRI systems, field strengths, protocols, and varying phantom temperature. Complex and hybrid methods showed little PDFF bias and variability both before and after correction.ConclusionCorrection for temperature reduces temperature‐related PDFF bias and variability in phantoms across MRI vendors, sites, field strengths, and protocols for magnitude‐based CSE‐MRI, even without a priori information about the temperature.