Which procedure involves the examination of a living tissue sample?

The procedure that involves the examination of a living tissue sample is a biopsy. During a biopsy, a small sample of tissue is removed from the body and examined under a microscope to identify any abnormal cells or diseases, such as cancer. This process provides valuable information that can aid in diagnosis and treatment planning.

In contrast, an autopsy is performed after death to determine the cause of death and to examine disease processes, making it unrelated to living tissue samples. Sonography, also known as ultrasound, is a diagnostic imaging technique that uses sound waves to visualize organs and structures within the body, but it does not involve taking tissue samples. Endoscopy is a procedure that uses a flexible tube with a camera to view the interior of a body cavity or organ, which may allow for the collection of tissue samples, but the act of examining a tissue sample itself specifically characterizes a biopsy. Thus, the unique role of a biopsy in directly analyzing living tissue samples distinguishes it as the correct answer.