Adam J. Kuchnia

Computed tomography (CT) is a valuable assessment method for muscle pathologies such as sarcopenia, cachexia, and myosteatosis. However, several key underappreciated scan imaging parameters need consideration for both research and clinical use, specifically CT kilovoltage and the use of contrast material. We conducted a scoping review to assess these effects on CT muscle measures. We reviewed articles from PubMed, Scopus, and Web of Science from 1970 to 2020 on the effect of intravenous contrast material and variation in CT kilovoltage on muscle mass and density. We identified 971 articles on contrast and 277 articles on kilovoltage. The number of articles that met inclusion criteria for contrast and kilovoltage was 11 and 7, respectively. Ten studies evaluated the effect of contrast on muscle density of which nine found that contrast significantly increases CT muscle density (arterial phase 6–23% increase, venous phase 19–57% increase, and delayed phase 23–43% increase). Seven out of 10 studies evaluating the effect of contrast on muscle area found significant increases in area due to contrast (≤2.58%). Six studies evaluating kilovoltage on muscle density found that lower kilovoltage resulted in a higher muscle density (14–40% increase). One study reported a significant decrease in muscle area when reducing kilovoltage (2.9%). The use of contrast and kilovoltage variations can have dramatic effects on skeletal muscle analysis and should be considered and reported in CT muscle analysis research. These significant factors in CT skeletal muscle analysis can alter clinical and research outcomes and are therefore a barrier to clinical application unless better appreciated.

Background Computed tomography (CT)‐derived measures of tissue quality can add to frailty assessment and improve selection of candidates for heart transplant. We investigated the prognostic value of CT measures of tissue density for predicting hospital length of stay (LOS) and mortality post‐transplant. Methods All patients at a quaternary care hospital between 1999 to 2018 with preheart transplant CT scans and available data on transplant outcomes were eligible ( n = 189), including a subset within the total cohort with scans 6‐month pretransplant ( n = 103). Axial chest CT scans were analysed for liver and muscle density at the 12th thoracic vertebrae and aortic arch landmarks, respectively. Cox and linear regression models examined the risk of death and LOS, respectively, according to median (above or below) pectoral muscle density. Low‐density muscle (LDM) area and liver density were analysed as continuous variables. Results Out of 157 patients with readable CT scans (median age 55 years, interquartile range [50–60] 10% women), 31 died on 1‐year follow up. Patients with higher than and at median pectoral muscle density (39.5 Hounsfield Unit [HU]) had better 1‐year survival in the overall cohort (hazard ratio [HR] 0.82, 95% confidence interval [CI] 0.673, 0.989; p = 0.039), with the 6‐month cohort showing a trend (HR 0.79, 95% CI 0.603, 1.023; p = 0.074) towards improved survival. Conversely, every 5‐cm 2 increase in pectoral LDM area was associated with 2.4‐day lower LOS ( p = 0.045) in the overall cohort, and a 2.6‐day lower LOS in the 6‐month cohort ( p = 0.05). Patients with higher ratio of normal‐density muscle to LDM had higher LOS ( p < 0.01). Every 5‐HU increase in liver density at a region of interest was associated with 0.24‐day higher post‐transplant LOS in the overall cohort, and a 0.41 higher LOS in the 6‐month cohort ( p ≤ 0.05). Conclusions Patients with higher preheart transplant pectoral muscle density had greater 1‐year survival. Higher pectoral LDM area was associated with decreased LOS post‐transplant and higher liver density was associated with increased LOS. These findings raise possibilities that measures of muscle density as they reflect to quality of muscle may have prognostic implications. Future studies with prospective design are needed to confirm these findings.