**Core Concept**
Atheromatous plaque formation is a complex process involving the accumulation of lipids, inflammatory cells, and fibrous elements within the arterial wall. This process is characterized by the deposition of calcium salts, which are a hallmark of advanced atherosclerotic lesions. The presence of calcium in atheromatous plaques can be detected using non-invasive imaging modalities, such as computed tomography (CT) scans.

**Why the Correct Answer is Right**
Calcium deposition in atheromatous plaques is a critical pathophysiological phenomenon that occurs during plaque formation. Calcium salts are deposited within the fibrous cap of the plaque, which can lead to a hardening and stabilization of the plaque. This process is known as calcification. The detection of calcium deposits in atheromatous plaques is used as a screening tool for asymptomatic coronary plaques on CT scans. The presence of calcium is associated with increased plaque vulnerability and a higher risk of rupture, which can lead to acute coronary syndromes.

**Why Each Wrong Option is Incorrect**
**Option A:** Increased outer diameter of coronary artery - This is not a characteristic of atheromatous plaque formation, which is associated with the thickening of the arterial wall rather than an increase in diameter.

**Option B:** Decreased inner diameter of coronary artery - While atheromatous plaques can cause stenosis, which may lead to a decrease in inner diameter, this is not a direct result of plaque formation and is not the primary mechanism by which calcium deposition is detected.

**Option D:** Lipoid degeneration in the plaque - Lipoid degeneration is an early stage of atheromatous plaque formation, but it is not the phenomenon being detected by CT scans.

**Clinical Pearl / High-Yield Fact**
A key clinical correlation is that the presence of calcium in atheromatous plaques is associated with a higher risk of plaque rupture and acute coronary syndromes. This highlights the importance of early detection and management of asymptomatic coronary plaques.

**✓ Correct Answer: C. Calcium deposition in the atheromatous plaque**