## **Core Concept**
The question tests the knowledge of imaging modalities used for diagnosing ureteric stones, specifically in the context of acute colic. Ureteric stones are a common cause of acute flank pain and can lead to severe complications if not promptly diagnosed and managed. The imaging modality of choice should ideally be non-invasive, readily available, and capable of accurately detecting stones.

## **Why the Correct Answer is Right**
The correct answer, **CT KUB (Computed Tomography of Kidneys, Ureters, and Bladder)**, is the gold standard for diagnosing ureteric stones, especially in acute settings. CT KUB provides detailed images of the urinary tract and is highly sensitive and specific for detecting stones, including their size and location. It can also identify complications such as hydronephrosis. The non-contrast CT is particularly useful as it does not require contrast medium, reducing the risk of adverse reactions.

## **Why Each Wrong Option is Incorrect**
- **Option A: Ultrasound**. While ultrasound is a useful initial imaging technique for assessing hydronephrosis and can sometimes visualize larger stones, it is less sensitive than CT for detecting smaller stones and may not provide detailed information about the stone's location or size.
- **Option B: X-ray**. A plain X-ray of the kidneys, ureters, and bladder (KUB) can visualize some stones, especially those that are radiopaque, but it cannot detect all types of stones (e.g., uric acid stones) and does not provide information on stone size or location.
- **Option D: MRI**. MRI is not typically used for the initial evaluation of ureteric stones due to its higher cost, limited availability compared to CT, and lesser utility in detecting calcifications.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that for acute ureteric colic, a **non-contrast helical CT** is the imaging modality of choice. This is because it provides rapid and accurate diagnosis, guiding management decisions. Additionally, be cautious of the radiation dose, but in the acute setting, the benefits often outweigh the risks.

## **Correct Answer:** . CT KUB