**Question:** Radiation exposure is the least in the following procedure –

A. Chest X-ray
B. Computed Tomography (CT) scan
C. Magnetic Resonance Imaging (MRI)
D. Ultrasonography

**Core Concept:** Radiation exposure in medical imaging is a concern for patients and healthcare professionals alike. Medical imaging procedures use ionizing radiation to visualize internal structures and diagnose diseases, but they carry a risk of radiation-induced harm, including increased cancer risk.

**Why the Correct Answer is Right:**

D. Ultrasonography (USG) has the least radiation exposure among the given options. Ultrasonography uses high-frequency sound waves to create images of internal structures, avoiding the use of ionizing radiation altogether. This makes it inherently safer compared to other imaging modalities, which involve ionizing radiation.

**Why Each Wrong Option is Incorrect:**

A. Chest X-ray: Though not as high as CT scans, chest X-rays still expose patients to a significant amount of ionizing radiation, making it a higher risk option compared to Ultrasonography.

B. Computed Tomography (CT) scan: CT scans involve the use of multiple X-ray beams and detectors to create cross-sectional images, resulting in higher radiation exposure compared to Ultrasonography.

C. Magnetic Resonance Imaging (MRI): MRI does not use ionizing radiation; however, this option is incorrect because it is more time-consuming and often requires contrast agents that may cause adverse reactions in some patients.

**Clinical Pearl:** In clinical practice, healthcare professionals should consider the risk-benefit ratio when choosing imaging modalities for patients. Ultrasonography is a safe and effective alternative to other imaging modalities that utilize ionizing radiation, such as X-rays, CT scans, and chest X-rays. While MRI does not involve ionizing radiation, it may have other limitations, including longer examination times and potential contrast agent reactions.

**Correct Answer:** D. Ultrasonography