**Core Concept**
Gamma cameras are medical imaging devices that utilize the principle of scintigraphy to detect and visualize the distribution of radioactive tracers within the body. This technique involves the use of a scintillator material that converts gamma rays emitted by the tracer into visible light, which is then captured by a camera to produce images.

**Why the Correct Answer is Right**
The gamma camera is specifically designed to detect gamma rays emitted by radioactive tracers, which are used to visualize various physiological processes and diseases in the body. When a radioactive tracer is administered to a patient, it accumulates in specific tissues or organs, emitting gamma rays that are detected by the gamma camera. The intensity of the gamma rays is directly proportional to the concentration of the tracer in the tissue, allowing for the creation of detailed images of the tracer distribution. This technique is particularly useful for imaging organs such as the thyroid, liver, and bone.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because gamma cameras are not used for X-ray imaging, which requires a different type of detector and imaging technique.
**Option B:** This option is incorrect because positron emission tomography (PET) scanners use a different type of detector and reconstruction algorithm to image the body, although they also use radioactive tracers.
**Option C:** This option is incorrect because ultrasound imaging uses sound waves to produce images of the body, rather than detecting gamma rays.

**Clinical Pearl / High-Yield Fact**
Gamma cameras are a crucial tool in nuclear medicine for visualizing the distribution of radioactive tracers, which can provide valuable information about various physiological processes and diseases in the body.

**Correct Answer:** C. Gamma cameras are used in nuclear medicine to detect and visualize the distribution of radioactive tracers within the body.