The development of x-ray imaging to study renal function

The well-established role of the kidney in control of blood volume and ulti mately arterial blood pressure has been underscored by the demonstration of alterations in renal hemodynamics and function recognized as responsible f or these and other regulatory mechanisms. Nevertheless, the spatial complex ity of intrarenal structure and function has made evident the need to study these separately in different regions of the intact kidney. Because of the introduction of x-rays, assessment of renal function has indeed been one o f their attractive applications. However, despite the appeal of their nonin vasiveness, several limitations confounded the different x-ray techniques u sed, most of which remained unresolved until the development of computed to mography. Furthermore, the development of fast imaging, which allows repeti tive analysis of the same region of interest during the transit of contrast medium, holds a great potential to estimate intrarenal distribution of blo od how and the dynamic characteristics of tubular fluid how in individual n ephron segments. This latter assessment requires the administration of filt erable x-ray contrast medium, which is cleared from the plasma almost exclu sively by glomerular filtration, and the generation of contrast dilution cu rves. A historical review of the development and progress of the various x- ray techniques used will help understand the past and present of x-ray imag ing, and will make it easier to envision the importance of their future rol es in the study of renal physiology and pathophysiology.