**Core Concept**
Early renal tuberculosis is a challenging diagnosis due to its non-specific symptoms and the subtle changes it causes in renal anatomy. The disease often presents as a focal or diffuse interstitial nephritis, which can be difficult to detect with conventional imaging modalities.

**Why the Correct Answer is Right**
The correct answer is **D. MRI with Gadolinium enhancement**. MRI with gadolinium enhancement is highly sensitive in detecting early renal tuberculosis due to its ability to visualize the subtle changes in renal parenchyma and the enhancement of the affected areas. Gadolinium-based contrast agents accumulate in areas of inflammation, making it easier to detect the early stages of tuberculosis. Additionally, MRI can provide detailed images of the renal collecting system and the ureters, which are often affected in renal tuberculosis.

**Why Each Wrong Option is Incorrect**
**Option A:** CT scan with contrast is less sensitive than MRI in detecting early renal tuberculosis. While CT scans can provide detailed images of the renal parenchyma, they often miss the subtle changes associated with early tuberculosis.

**Option B:** Ultrasound is not sensitive in detecting early renal tuberculosis. Ultrasound is often used as a first-line imaging modality, but it has limited sensitivity in detecting early changes in renal parenchyma.

**Option C:** Plain radiography is not useful in detecting early renal tuberculosis. Plain radiographs are often used to detect calcifications and other gross abnormalities, but they are not sensitive in detecting early changes associated with tuberculosis.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that early renal tuberculosis often presents as a focal or diffuse interstitial nephritis, which can be difficult to detect with conventional imaging modalities. A high index of suspicion and the use of sensitive imaging modalities like MRI with gadolinium enhancement are essential in making an early diagnosis.

**Correct Answer:** D. MRI with Gadolinium enhancement