**Core Concept**
Functional renal tissue distribution is a critical aspect of renal imaging, particularly in assessing renal function and scarring. The distribution of functional renal tissue is essential for diagnosing and managing various renal conditions, including chronic kidney disease and renal scarring.

**Why the Correct Answer is Right**
DMSA (Dimercaptosuccinic Acid) scan is a type of renal imaging that specifically highlights the distribution of functional renal tissue. This is achieved by the uptake of DMSA in the proximal tubules of the kidneys, which is then visualized using a gamma camera. The DMSA scan provides a static image of the kidneys, allowing for the assessment of renal scarring, cortical thickness, and the distribution of functional renal tissue. The renal cortex, where DMSA is taken up, corresponds to the functional renal tissue.

**Why Each Wrong Option is Incorrect**
**Option B:** DTPA (Diethylenetriamine Pentaacetic Acid) scan is a dynamic renal imaging technique that assesses renal function and blood flow, but it does not specifically highlight the distribution of functional renal tissue.

**Option C:** MAG3 (Mercaptoacetyltriglycine) - Tc99 scan is another dynamic renal imaging technique that assesses renal function and tubular function, but it does not specifically highlight the distribution of functional renal tissue.

**Option D:** 123 Iodocholesterol scan is a type of adrenal imaging that assesses adrenal function and morphology, but it is not used for assessing the distribution of functional renal tissue.

**Clinical Pearl / High-Yield Fact**
The DMSA scan is particularly useful in assessing renal scarring and cortical thickness in children, which can help in diagnosing and managing conditions such as urinary tract infections and vesicoureteral reflux.

**✓ Correct Answer: A. DMSA**