# DeepSarc-US: A Deep Learning Framework for Assessing Sarcopenia Using Ultrasound Images
## 2 Methods  
### Dataset  
The dataset is based on a prospective cohort of 486 adult patients undergoing a clinically indicated cardiac US examination at the Jewish General Hospital (JGH), Montreal, Canada, between 1 October 2018, and 30 June 2019. These patients provided verbal informed consent to participate in this study. At the end of the cardiac US examination, with the patient remaining in a supine position, the sonographer acquired a static image of the left quadriceps muscles (rectus femoris and vastus intermedius) at the level of the anterior thigh, midway (approximated visually) between the anterior superior iliac spine and patella. A GE E95 machine (GE HealthCare, Chicago, IL, USA) with a sector 4 Vc-D phased-array probe was used for data acquisition, where the acquisition setting was set to standard adult transthoracic settings with the center frequency of 1.4 MHz. The phased-array probe used to image the heart was also used to image the quadriceps muscles, even though the latter are usually imaged using linear probes that are better suited for superficial structures. This was done for convenience of clinical implementation, as cardiac US systems do not typically include linear probes.  
The quadriceps US images were extracted in DICOM format and manually annotated by a trained observer ([PERSON]) to define the region of interest corresponding to the skeletal muscle tissue between the superior margin of the femur and the inferior margin of the subcutaneous fat, which is defined as QMT. Specifically, for each image, the upper border of the femur was delineated by marking nine equally spaced points (with the fifth point centered on the femur bone), and the upper border of the muscle was delineated by marking five equally spaced points (with the third point centered on the quadriceps muscle, aligning roughly with the central point of the femur). QMT was then determined by measuring the vertical distance between the central points of the femur and quadriceps. To validate the QMTs measured by J.O., referred to as the ground-truth QMTs in this study, and to prevent training the models with potentially inaccurate QMTs, the muscle thickness in each US image was additionally measured by two independent medical researchers using the same subset of images. Table 1 presents the inter-rater variabilities for redundant QMT measures. Inter-rater reliabilities were evaluated using the intraclass correlation coefficient (ICC) with a 95% confidence interval (CI) [(43; 44)]. All ICC values exceeded 0.80, indicating very good to excellent reliability.  
The size of the images was 708 \(\times\) 1080 pixels, which was resized to 224 \(\times\) 224. It is worth noting that the ground truth QMT was computed before resizing the images to 224 \(\times\) 224. Given the variability in image acquisitions across subjects, pixel spacing was duly considered in this calculation. Five-fold cross-validation was used in all the experiments. Therefore, 67% of the images (330 images) were used for training, 17% (83 images) were used for validation, and the remaining 15% (73 images) were used as the test set. Figure 1 presents three examples of US images with annotations, and Figure 1a-d present the distribution of QMT in centimeters (cm). Please note that pixel spacing varies across patients, so one pixel does not correspond to the same length in centimeters for different patients. Therefore, in Figure 1a,b, the QMT is 1.57 cm and 2.17 cm, respectively, even though the number of QMT pixels in (a) is higher than in (b).  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & \multicolumn{2}{c}{**QMT Measurement (cm)**} & & & & \\ \hline
**Rater 1** & **Rater 2** & **Rater 3** & **Rater 4** & **ICC (2,1)** & **95\% CI** & **ICC (2,3)** & **95\% CI** \\ \hline
3.29 \(\pm\) 1.07 & 2.94 \(\pm\) 0.86 & 2.99 \(\pm\) 0.87 & 3.24 \(\pm\) 1.12 & 0.83 & [0.77–0.87] & 0.95 & [0.93–0.96] \\ \hline \hline \end{tabular}
\end{table}
Table 1: Inter-rater variability of QMT measurements.