Increased Renal Enhancement In the context of hypoperfusion and decreased flow to the kidneys, activation of the renin-angiotensin axis causes levels of ungiotensin 2 to dramatically increasc ana unc renal efferent arteriole to constrict. This is thought to explain the considerable and prolonged cortical hyperenhancement of the kidneys(Figure 7) [6]. Recently, the"black kid:ey sign denned as ennancement on tne Kuaneys