Nevertheless, the best ratio for the initial tomographic section was found to be 0.33 of the abdominal thickness, which corresponds to what is perhaps the most commonly used formula. It would be useful to reconfirm this finding in a large series of IVU examinations to establish that 0.33 is in fact the optimal ratio for the height of the initial nephrotomogram.
In our study, this formula would have failed to intersect one or both kidneys at the midplane on the initial nephrotomogram in 31% of the cases.
Various studies have proposed several measurements to estimate the ideal depth for the initial nephrotomogram,[1-8] including:
The researchers in this study measured kidney location on CT images to determine a formula for establishing the proper height above the table for initial nephrotomograms. The optimal distance from the midplane of the kidney to the top of the radiographic table was determined to be one-third the thickness of the abdomen plus the thickness of the table pad, if any.
A standard IVU protocol includes a preliminary KUB radiograph prior to intravenous contrast administration which is followed by a nephrotomogram
or nephrographic images collimated to the kidneys (1 to 3 minutes after contrast injection), a KUB radiograph at 5 minutes after injection, a pyelographic image at 10 minutes with abdominal compression applied after the 5-minute film and ureter-bladder images after compression is released, and bladder images.