**Core Concept**
MRI is superior to other imaging modalities for detecting focal liver lesions due to its high soft-tissue contrast resolution, excellent sensitivity for detecting small lesions, and ability to characterize lesions based on their signal intensity and enhancement patterns.

**Why the Correct Answer is Right**
MRI's superiority in detecting focal liver lesions stems from its ability to provide detailed images of the liver parenchyma and its ability to distinguish between different types of lesions, such as hepatocellular adenomas, hemangiomas, and metastases. This is achieved through the use of T1- and T2-weighted sequences, as well as contrast-enhanced sequences that highlight the vascular supply of the lesions. The high spatial resolution of MRI also allows for the detection of small lesions that may be missed by other imaging modalities.

**Why Each Wrong Option is Incorrect**
**Option B:** CT scans, while useful for detecting larger liver lesions, often struggle to distinguish between different types of lesions, leading to a higher risk of misdiagnosis.
**Option C:** USG (Ultrasound) is operator-dependent and may not provide sufficient detail for characterizing small or subtle liver lesions.
**Option D:** PET scans are more useful for detecting metastatic disease and assessing the metabolic activity of tumors, rather than providing detailed anatomical images of the liver.

**Clinical Pearl / High-Yield Fact**
When evaluating a patient with a suspected liver lesion, it's essential to remember that MRI is the imaging modality of choice for detecting and characterizing focal liver lesions, particularly in patients with a high risk of hepatocellular carcinoma.

**✓ Correct Answer: A. MRI**