With the recent development of image analysis, it has become possible to measure the skeletal muscle index representing the subject's muscle mass from preoperative computed tomography (CT) images. Therefore, in this study, the investigators quantify the skeletal muscle index from preoperative CT images and analyze the correlation with the dose of neuromuscular blocking agent, rocuronium, required for maintaining deep neuromuscular blockade.

Deep neuromuscular blockade improves the condition of surgeon's surgical field during the surgery and reduces the acute postoperative pain. The dosage of neuromuscular blocking agent has been usually administered according to the patient's actual body weight, but even with the same body weight, the ratio of muscle to fat varies from individual to individual, and there are many differences depending on age, gender, and exercise level.

Therefore, if the dose of neuromuscular blocking agent is administered according to actual body weight, additional doses may be required due to insufficient neuromuscular blockade, or excessive doses may occur. However, it was difficult to quantify the muscle mass, with the recent development of image analysis, it has become possible to measure the skeletal muscle index representing the subject's muscle mass from preoperative computed tomography (CT) images. Therefore, in this study, the investigators quantify the skeletal muscle index from preoperative CT images and analyze the correlation with the dose of neuromuscular blocking agent, rocuronium, required for maintaining deep neuromuscular blockade.

Inclusion Criteria:

• Those who voluntarily agreed and signed the written consent form before participating in the study
• American Society of Anesthesiologists physical class (ASA class) 1-3
• Patients scheduled for elective colon surgery under general anesthesia
• Patients undergoing abdominal computed tomography for routine preoperative preparation

Exclusion Criteria:

• Pregnant women
• Decreased renal function (GFR<60mL/min/1.73m2).
• Patients taking drugs that affect deep neuromuscular blockade
• Patients with a history of neuromuscular and muscle disorders

Patients scheduled for elective colon surgery under general anesthesia