**Core Concept**
Ultrasound (US) is a critical imaging modality in the evaluation of pancreatic lesions, including insulinomas. It is essential to identify the most sensitive and specific initial imaging modality for detecting these lesions.

**Why the Correct Answer is Right**
The initial imaging modality of choice for insulinoma is indeed Endoscopic Ultrasound (EUS). EUS offers high-resolution images of the pancreas and surrounding tissues, allowing for accurate detection and localization of insulinomas. EUS is particularly useful in visualizing small lesions that may not be evident on other imaging modalities. Additionally, EUS-guided fine-needle aspiration can be performed to obtain tissue samples for histological examination, which is crucial for confirming the diagnosis of insulinoma.

**Why Each Wrong Option is Incorrect**
**Option A:** USG (Ultrasound) is less sensitive than EUS for detecting small pancreatic lesions and may not provide sufficient detail for accurate localization.
**Option B:** CT abdomen is a useful imaging modality for detecting larger pancreatic lesions, but it may not be as sensitive as EUS for detecting small insulinomas.
**Option C:** Somatostatin Receptor Scan (SRS) is a useful diagnostic tool for detecting neuroendocrine tumors, including insulinomas, but it is typically used as an adjunct to EUS or CT scans, rather than as the initial imaging modality.

**Clinical Pearl / High-Yield Fact**
When evaluating a patient with suspected insulinoma, it is essential to consider the timing of symptoms. Insulinomas typically present with episodic hypoglycemia, and symptoms may be triggered by fasting or exercise. A high index of suspicion and prompt imaging with EUS can lead to early diagnosis and treatment.

✓ **Correct Answer:** D. E.U.S