A Novel Use for Pelvic Magnetic Resonance Imaging Scans to Estimate Lean Body Mass and Screen for Sarcopenia in Patients with Rectal Cancer
Authors: Melucci Alexa D. , Lynch Olivia F. , Loria Anthony , Mustian Karen M. , Dunne Richard F. , Temple Larissa K. , Fleming Fergal J. 
Published: January 2023

BACKGROUND:
Sarcopenia, the combination of low lean body mass (LBM) and decreased muscle strength, is associated with significant morbidity and mortality among patients with colorectal cancer. Gold standard methods for assessing lean body mass and muscle strength, such as bioelectric impedance analysis (BIA) and handgrip dynamometry, are rarely obtained clinically. Per National Cancer Center Network recommendations, pelvic magnetic resonance imaging (MRI) is routinely collected for staging and surveillance among patients with rectal cancer. However, there is no data assessing the relationship of pelvic magnetic resonance imaging lean body mass measurements at the fifth lumbar vertebrae (L5) with bioelectric impedance analysis, handgrip strength (HGS), or abdominal computed tomography (CT) in patients with rectal cancer. Therefore, we aimed to assess whether pelvic magnetic resonance imaging lean body mass correlates with a gold standard for lean body mass measurement (bioelectric impedance analysis), muscle function (handgrip strength), and an imaging modality frequently used in the literature to identify sarcopenia (abdominal computed tomography at third lumbar vertebrae [L3]).

IMPACT OF INNOVATION:
Lean body mass measurements from routinely collected pelvic magnetic resonance imaging at L5 accurately and reproducibly estimates lean body mass and modestly correlate with handgrip strength. Rectal cancer pelvic magnetic resonance imaging may be repurposed for identifying sarcopenia without increasing inconvenience, ionizing radiation exposure, or expenditure to patients with rectal cancer.

TECHNOLOGY, MATERIALS, AND METHODS:
Patients with locally advanced rectal cancer with pretreatment bioelectric impedance analysis and handgrip strength measurements within 3 months of their staging pelvic magnetic resonance imaging were eligible. Axial skeletal muscle areas were segmented using T1-weighted series pelvic magnetic resonance images at L5 and abdominal computed tomography at L3 using Slice-O-matic (Tomovision, Montreal, Canada). Lean body mass (LBM) (kg) was derived from skeletal muscle area with standard equations. Handgrip strength (kg) was the maximum of three dominant hand attempts in the standing anatomical position. The primary outcome was the agreement between lean body mass measured by pelvic magnetic resonance imaging (at L5) and bioelectric impedance analysis. Secondary outcomes included the concordance of pelvic magnetic resonance imaging lean body mass (at L5) with abdominal computed tomography (at L3) and handgrip strength. Additionally, the intra- and interobserver validity, internal consistency, and the mean difference (bias) between lean body mass measurements by pelvic magnetic resonance imaging and bioelectric impedance analysis were evaluated.

PRELIMINARY RESULTS:
Sixteen patients were eligible. The average lean body mass was similar and consistent across two observers between bioelectric impedance analysis and pelvic magnetic resonance imaging. There was a strong correlation between lean body mass measured on pelvic magnetic resonance imaging, bioelectric impedance analysis, and abdominal computed tomography. The reliability of two pelvic magnetic resonance imaging lean body mass measurements (two weeks apart by blinded observers) and the correlation of lean body mass between pelvic magnetic resonance imaging and bioelectric impedance analysis was strong. Inter- and intra-observer correlation, reliability, and internal consistency were strong for the entire cohort. There was a moderate correlation between pelvic magnetic resonance imaging lean body mass and handgrip strength.

CONCLUSIONS:
Lean body mass measured at L5 on pelvic magnetic resonance imaging is reproducible and correlates strongly with measurements from bioelectric impedance analysis (gold standard), abdominal computed tomography at L3, and modestly with handgrip strength. These data suggest pelvic magnetic resonance imaging lean body mass measurements may be a method to screen patients with rectal cancer for sarcopenia.

FUTURE DIRECTIONS:
Future studies may evaluate changes in lean body mass on serial pelvic magnetic resonance imaging studies among patients with rectal cancer.