What is a 4 phase renal CT study?
A four phase CT study comprises of: non-contrast, cortico-medullary, nephrographic and excretory phases. Variations of the 4 phases may be performed depending on the clinical indication. In addition the dose may be limited by performing a split bolus technique or where available the use of dual source CT, with reiterative techniques.
What is the role of MAG-3 imaging for PUJ obstruction?
MAG-3 imaging offers a dynamic quantative assessment to confirm the PUJ obstruction as real ( on occasion a so called 'baggy pelvis' may mimic a PUJ obstruction. It also offers a quantative indication of the obstruction, typically illustrated in graph form.
A three-phase CT study of the kidneys has been performed (corticomedullary, nephrographic and excretory) phases. The excretory phase equates to a CT-IVU, typically undertaken at 8-10 minutes following IV contrast administration.
The pelvis of both kidneys are expanded by water density spaces. The right kidney is atrophic with a reduced bipolar diameter (BPD). The left is larger. The cortex of both kidneys enhances normally.
On the delayed excretory phase images, the kidneys behaviour differently. On the right contrast pools dependently within a distended renal pelvis, consistent with a PUJ obstruction. On the left the calyces are outlined, compressed by numerous para-pelvic cysts (which do not contain contrast).