What is the sequence of images for an IVU?
The procedure begins with two radiographs, known as the preliminary or scout images, which are used to examine the soft tissues, bones, and bowel gas pattern. One radiograph is centered over the kidneys, and the second radiograph views the entire abdomen to the level of the pubic symphysis. Scout radiographs are particularly important for detecting radiopaque urinary tract stones because these stones have the same radiographic density as excreted contrast material and are often difficult to visualize when the collecting systems are opacified with contrast. In addition to calculi, the scout radiographs are also used to detect renal masses
The imaging sequence of IVU is aimed at evaluating the renal parenchyma for masses and the collecting systems for urothelial neoplasms and other abnormalities, such as papillary necrosis. Parenchymal evaluation is performed with a series of images called nephrotomograms , in which the x-ray tube moves over the patient in an arc with a fixed focal plane that is in sharp focus. Structures anterior or posterior to the focal point are blurred.
Evaluation of the collecting systems for subtle abnormalities is aided by distention of the collecting systems. This requires compressing the abdomen with inflatable balloons so that the ureters are obstructed. When the compression is released, contrast material floods the ureters, allowing for visualization of the entire length of the ureters. An image is also obtained in the upright position, which is very sensitive for showing low grades of obstruction. An unobstructed collecting system should drain nearly completely on an upright image. Images of the urinary bladder are obtained with the bladder distended and then after the patient voids. The latter image allows for a rough estimate of bladder function and is sensitive for showing bladder masses.
