You are presented with a paragraph from a COVID-19 literature. Classify the topics of this piece of text by choosing from the following categories:

- Epidemic Forecasting: The content relates to predictions about the spread of COVID-19.
- Treatment: The paragraph discusses therapeutic methods or medication for COVID-19.
- Prevention: The content covers measures to prevent the spread of COVID-19.
- Mechanism: The paragraph explains the biological mechanisms of the virus.
- Case Report: The content is a report of a COVID-19 case.
- Transmission: The paragraph discusses how COVID-19 is transmitted.
- Diagnosis: The content is about diagnosing COVID-19 in individuals.

Your classification should be provided as an element within a JSON array. The array should be formatted with topics enclosed in double quotes and separated by commas, following the JSON format, for example: ["Topic1", "Topic2", ...]. Include all applicable topics within the array. Your output should be a valid JSON array, and no additional text should be included in your response.

Article:

BACKGROUND: Skeletal muscle mass (SMM) determined on computed tomography (CT) is emerging as a novel imaging biomarker. Cross-sectional area (CSA) of SMM at the level of the third lumbar vertebra (L3) on abdominal imaging is considered the clinical reference standard for measuring SMM. In certain patient groups, such as those with oncological or non-oncological lung disease like COVID-19, a chest CT may be available while an abdominal CT is not. The purpose of this study was to investigate whether determining SMM on a chest CT is a feasible alternative to abdominal CT. RESEARCH QUESTION: What is the correlation between SMM measurements at the level of L3 and the level of the fourth thoracic vertebra (Th4)? STUDY DESIGN AND METHODS: In this study we retrospectively analyzed abdominal and thoracic series of whole-body CT-scans of trauma patients (N = 47) and head and neck cancer patients (N = 194). All abdominal muscles were delineated on a single axial slice at the level of L3. The erector spinae, levator scapulae, rhomboideus minor and major and pectoralis minor and major muscles were delineated on a single axial slice at the level of Th4. CSA of the muscles at Th4 and the L3 level were compared using linear regression, and a multivariate linear regression model was established. RESULTS: Muscle CSA at level Th4 strongly correlates with L3 muscle CSA (r = 0.791, p < 0.05). A multivariate model incorporating the patient characteristics arm positioning, age, sex, and weight achieved a stronger correlation (r = 0.856, p < 0.05). INTERPRETATION: Skeletal muscle CSA measured at the level of Th4 is a feasible alternative to measurements at L3. This allows diagnosing low SMM using clinically available thoracic CT-scans. SMM measurements at the level of Th4 may become a prognostic or triage tool when faced with mechanical ventilator shortage.
["Diagnosis"]