**Core Concept**
Structural heart diseases, such as valvular heart disease, involve abnormalities in the heart's chambers, valves, or septa. Accurate diagnosis of these conditions requires imaging modalities that can provide detailed visualization of the heart's anatomy.

**Why the Correct Answer is Right**
The correct answer is **Echocardiography**. Echocardiography uses high-frequency sound waves to produce images of the heart's structure and function. It is particularly useful for diagnosing valvular heart disease, as it can visualize the movement and morphology of the heart valves. Echocardiography can also assess the hemodynamic consequences of valvular disease, such as regurgitation or stenosis.

**Why Each Wrong Option is Incorrect**
**Option A:** Chest X-ray is a basic imaging modality that can show cardiac enlargement or pulmonary congestion, but it is not specific for structural heart disease.

**Option B:** Electrocardiography (ECG) can show signs of arrhythmias or ischemia, but it is not a direct diagnostic tool for structural heart disease.

**Option C:** Cardiac magnetic resonance imaging (MRI) is a powerful tool for visualizing cardiac structure and function, but it is not as widely available or as quick as echocardiography for initial diagnosis.

**Clinical Pearl / High-Yield Fact**
Echocardiography is a valuable tool for diagnosing structural heart disease, but it requires proper technique and interpretation to avoid false positives or false negatives. A thorough understanding of cardiac anatomy and physiology is essential for accurate echocardiographic diagnosis.

**Correct Answer:** E. Echocardiography.