151751-Najiba-Chargi

79 Diagnostics: cut-off values for low skeletal muscle mass ASSESSMENT OF CROSS-SECTIONAL MUSCLE AREA AT THE LEVEL OF C3 Muscle tissue was identified using Hounsfield Unit (HU) range settings from -29 to +150 HU, which is specific for muscle tissue. Muscle tissue was delineated at the level of the third cer - vical vertebra (C3). The SMA was defined as the pixel area within the delineated area with a radiodensity between -29 and +150 HU. 21 Delineation of muscle tissue wasmanually performed using the Slice-O-matic software v 5.0. Muscle tissue delineation at the level of C3 was per - formed by selecting the first slide showing both transverse processes and the entire vertebral arc when scrolling from caudal to cranial direction. The contours of the paravertebral muscles and both sternocleidomastoid muscles were manually traced. The SMA at the level of C3 was calculated as the sum of the paravertebral muscle and both sternocleidomastoid muscles. If evident lymph node metastasis hindered accurate delineation of one sternocleidomastoid muscle, the SMA of the contralateral sternocleidomastoid muscle was used as an estimation of the SMA of the affected sternocleidomastoid muscle. After delineation, SMA was automat - ically retrieved from Slice-O-matic. For MRI, muscle area was manually segmented, and fatty tissue wasmanually excluded. The overall intraclass correlation coefficient (ICC) for themuscle SMA obtained by CT and MRI has shown to be excellent (ICC 0.9, p<0.01) 22 , and can therefore be used interchangeably for measuring CSA at the level of C3. The cervical SMI (CSMI) was calculated by dividing the SMA at the level of C3 by the squared height of the patient. Figure 1 shows muscle tissue delineation at the level of C3. Figure 1. This figure displays two identical axial CT-slides at the level of C3; in the left axial slide muscle tissue is unsegmented. The right CT slide shows both sternocleidomastoid and paravertebral muscles segmented in red. STATISTICAL ANALYSIS A test for normality (Kolmogorov-Smirnov) was performed to assess whether continuous vari - ables were normally distributed. Continuous data are represented as mean ± standard devia - tion (SD) if normally distributed, andmedian ± range if skewed. Categorical data are represent - ed as a number and percentage of total. The student’s t -test, one-way ANOVA, Mann-Whitney 5