Skeletal muscle analyses: agreement between non-contrast and contrast CT scan measurements of skeletal muscle area and mean muscle attenuation

Low skeletal muscle area (SMA) and muscle radiation attenuation (MRA) have been associated with poor prognosis in various patient populations. Both non-contrast and contrast CT scans are used to determine SMA and MRA. The effect of the use of a contrast agent on SMA and MRA is unknown. Therefore, we investigated agreement between these two scan options. SMA and MRA of 41 healthy individuals were analysed on a paired non-contrast and contrast single CT scan, and agreement between paired scan results was assessed with use of Bland-Altman plots, intraclass correlation coefficients (ICCs), standard error of measurements (SEM) and smallest detectable differences at a 95% confidence level (SDD95). Analyses were stratified by tube voltage. Difference in SMA between non-contrast and contrast scans made with a different tube voltage was 70 +/- 75cm(2); for scans made with the same tube voltage this was 23 +/- 17cm(2). Agreement was excellent for both methods: ICC: 0952, SEM: 72cm(2), SDD95: 199cm(2) and ICC: 0997, SEM: 20cm(2), SDD95: 56cm(2), respectively. MRA of scans made with a different tube voltage differed 13 +/- 113 HU, and agreement was poor (ICC: 0207, SEM: 79 HU, SDD95: 218 HU). For scans made with the same tube voltage the difference was 67 +/- 32 HU, and agreement was good (ICC: 0682, SEM: 53 HU, SDD95: 146 HU). In conclusion, SMA and MRA can be slightly influenced by the use of contrast agent. To minimise measurement error, image acquisition parameters of the scans should be similar.