**Core Concept**
Reversible myocardial ischemia is a condition where the heart muscle temporarily lacks oxygen and nutrients due to reduced blood flow, often caused by coronary artery disease. The key principle here is identifying a test that can detect this temporary reduction in blood flow and subsequent myocardial dysfunction.

**Why the Correct Answer is Right**
The test used to detect reversible myocardial ischemia is a **Stress Echocardiogram**. This test involves imaging the heart while it is under stress, typically induced by exercise or pharmacologically. During stress, the heart muscle requires more oxygen, and areas with reduced blood flow will not function properly, leading to reversible ischemia. The echocardiogram can visualize these areas of dysfunction, allowing for early detection of coronary artery disease.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because a **Cardiac CT Angiogram** is used to visualize the coronary arteries and detect fixed stenosis or blockages, not reversible ischemia.

**Option B:** This option is incorrect because a **24-hour Holter Monitor** is used to detect arrhythmias, not reversible myocardial ischemia.

**Option C:** This option is incorrect because a **Cardiac MRI** is a sensitive tool for assessing cardiac function and structure but is not the primary test for detecting reversible myocardial ischemia.

**Clinical Pearl / High-Yield Fact**
A stress echocardiogram is a useful test for patients with suspected coronary artery disease, especially those who cannot undergo exercise stress testing due to physical limitations.

**Correct Answer:** C. Cardiac Stress Echocardiogram is used to detect reversible myocardial ischemia.