**Core Concept**
Diagnosing renal stones involves various imaging modalities that help identify the location, size, and composition of the stones. The choice of imaging modality depends on factors like stone location, size, and patient's overall health.

**Why the Correct Answer is Right**
The correct answer is **PET-Scan**. PET-Scan is not typically used for diagnosing renal stones. It is more commonly used for detecting cancer, assessing cancer spread, and monitoring treatment response. PET-Scan uses a radioactive tracer to visualize metabolic activity, which is not directly relevant for identifying renal stones.

**Why Each Wrong Option is Incorrect**
**Option A:** IVP (Intravenous Pyelography) is an older imaging modality that can be used to diagnose renal stones. It involves injecting a contrast agent into the bloodstream, which is then excreted by the kidneys, allowing the stones to be visualized on X-ray.

**Option B:** MRI (Magnetic Resonance Imaging) can be used to diagnose renal stones, especially in cases where other imaging modalities are contraindicated. MRI provides detailed images of the kidneys and surrounding tissues without the use of ionizing radiation.

**Option D:** USG (Ultrasound) is a commonly used imaging modality for diagnosing renal stones, especially in emergency settings. It is non-invasive, quick, and does not involve ionizing radiation.

**Clinical Pearl / High-Yield Fact**
When diagnosing renal stones, it's essential to consider the patient's overall health, stone location, and size. Ultrasound is often the first-line imaging modality due to its non-invasive nature and lack of radiation exposure.

**Correct Answer: C. PET-Scan is not typically used for diagnosing renal stones.**