During which phase do parenchymal lesions become apparent in kidney contrast enhancement?

The nephrographic phase is when parenchymal lesions in the kidney become apparent due to optimal contrast enhancement of the renal cortex and medulla. During this phase, there is peak enhancement of kidney tissue because the contrast material has been absorbed by the renal parenchyma, allowing for better visualization of abnormalities such as tumors, cysts, or areas of ischemia.

In the corticomedullary phase, the contrast is primarily present in the renal arteries and the outer cortex, and while some early lesions may be identified, they are usually not fully appreciated until the nephrographic phase, which occurs shortly after.

The excretory phase occurs later when the contrast begins to clear from the renal parenchyma and enters the collecting system. In this phase, kidney lesions may still be visible, but the clarity of the lesion appearance decreases as the contrast diminishes in the renal tissue.

The delayed phase occurs even later when the contrast opacification of the kidney has largely dissipated, making it less effective for assessing parenchymal lesions. Thus, the nephrographic phase is specifically the optimal time for identifying these lesions due to its peak contrast enhancement in the renal parenchyma.