46. Isotope renography (indications, radiopharmaceuticals, imaging).
Renal scintigraphy, alo called nuclear renal scan, refers to using nuclear imaging to image the kidney and its function.
Static renal scintigraphy
Static renal scintigraphy is used to accurately visualise the renal morphology and to measure loss of renal cortex. One can measure relative ratio of renal function between the two kidneys. The radiopharmaceutical 99mTc-DMSA is used, which accumulates in the renal parenchyme but is not excreted. Imaging is performed 3 hours after injection
Indications:
- Pyelonephritis
- Renal infarction
- Acute renal failure
- Hydronephrosis
Dynamic renal scintigraphy
Dynamic renal scintigraphy, also called camera renography, is used to accurately measure the kidney function and perfusion. The radiopharmaceutical 99mTc-DTPA is filtered in the glomeruli and is therefore used to measure glomerular function while 99mTc-MAG3 is secreted in the tubuli and is therefore used for for tubular secretion. Imaging is performed serially from the time of the injection and for 30 min.
Indications:
- Evaluation of whether hydronephrosis is due to urinary tract obstruction or not
- Evaluation of renal perfusion
- Evaluation of renovascular hypertension
- Evaluation of kidney function loss in transplant patients
- Accurate measurement of GFR
If one is uncertain whether urinary output is decreased due to functional problems with the kidney or anatomical obstruction, one can obtain images before and after administration of a loop diuretic like furosemide. If furosemide improves excretion the obstruction is anatomical, if it doesn’t then it’s a functional problem of the kidney.
Dynamic renal scintigraphy gives a time-activity curve, a renogram with 3 phases:
- Phase I – perfusion
- Phase II – filtration or secretion function
- Phase III – excretion function