Nuclear: Genitourinary Flashcards
What are the main radio tracers used in renal scans?
- Tc-99m DTPA
- Tc-99m MAG3
- Tc-99m DMSA
- Tc-99m GH (glucoheptonate)
Which is the best radiotracer for estimating GFR?
Tc-99m DTPA
Note: Almost all of this radiotracer is filtered (not secreted) by the kidneys; however, since ~5% is not you are still slightly underestimating GFR.
What is the critical organ for Tc-99m DTPA?
Bladder
What is the critical organ for Tc-99m MAG3?
Bladder
What is the critical organ for Tc-99m GH (glucoheptonate)?
Bladder
What is the best radiotracer to estimate effective renal plasma flow?
Tc-99m MAG3
Note: Almost all of this radiotracer is secreted.
Which radiotracer is better for pts with poor renal function: DTPA or MAG3?
MAG3 is concentrated better by kidneys with poor renal function
Nuclear renal scans are usually obtained posteriorly. When would you want to obtain anterior images?
- Transplanted kidney
- Horseshoe kidney
What are the indications for a dynamic (functional) nuclear renal study?
- Suspected obstruction
- Evaluate differential function
- Suspected renal artery stenosis
- Suspected complication from renal transplant
- Suspected urine leak
What are the 3 phases of a dynamic nuclear renal study?
- Blood flow phase
- Cortical phase
- Clearance phase
Differential for symmetrically decreased renal flow on dynamic nuclear renal study
Technical error (e.g. poor bolus)
Note: Most pathologies will cause asymmetric flow problems.
Differential for asymmetrically decreased renal flow on dynamic nuclear renal study
- Renal artery thrombosis
- Renal vein thrombosis
- Chronic high grade obstruction
- Acute pyelonephritis
- Acute rejection (transplant)
Note: ATN, interstitial nephritis, and cyclosporin toxicity will all have normal perfusion/flow.
Which phase of a dynamic nuclear renal study is used to calculate differential renal function?
The cortical (parenchymal) phase, after flow and before tracer reaches the collecting system
Where should you place the background area of interest for a dynamic nuclear renal study?
A background area that is not overlying the liver or spleen
How can you quantify tracer retention in the renal cortex?
20/3 ratio:
(peak count at 20 min)/(peak count at 3 min)
Note: The normal value should be < 0.8.
How do you decide whether to give furosemide during a dynamic nuclear renal study looking for obstruction?
If there is still tracer activity in the kidneys/collecting system at 30 minutes, then give the furosemide
Note: If there is true obstruction, the retained tracer won’t clear. If there is a dilated but non obstructed collecting system, then at least 50% of the remaining tracer should clear within 10-20 min of giving furosemide.
When should you call “no obstruction” on a dynamic nuclear renal study?
Radiotracer clears from collecting system without the need for Lasix
OR
> 50% reduction in radio-tracer from collecting system within 10 min of giving Lassix
Note: If there is less than 50% reduction after 20 min, call obstruction. Between 10-20 min to reach the 50% threshold is considered indeterminate.
Common causes for false positive for obstruction on a dynamic nuclear renal study
- Poor response to Lasix (e.g. poor renal function at baseline or dehydration)
- Reservoir effect (very dilated renal pelvis)
- Back pressure effects (full or neurogenic bladder)
How long should it take 50% of collecting system radiotracer to washout after giving Lasix?
<10 min
Note: >20 min is considered obstruction. 10-20 min is considered indeterminate (most often due to a very dilated renal pelvis).
How is a dynamic nuclear renal study performed to look for renal artery stenosis?
Standard dynamic study followed by a repeat study with an ACE inhibitor (e.g. captopril)
Baseline dynamic study with 1/2 dose captopril followed by full dose captopril study
Note: Normally there should be no difference between the baseline and full dose captopril studies. If captopril causes reduced renal function, this is suggestive of renal artery stenosis.
Which radiotracers can be used for a renal artery stenosis dynamic nuclear renal study?
- Tc-99m DTPA
- Tc-99m MAG3
How will renal artery stenosis affect the renogram in a captopril dynamic nuclear renal scan?
DTPA tracer: Decreased radiotracer uptake on RAS side (due to decreased perfusion)
MAG3 tracer: Tracer retention with delayed excretion on RAS side (due to decreased excretion)
Pts should stop taking _____ 3-5 days prior to a dynamic nuclear renal study looking for renal artery stenosis
ACE inhibitors
Do pts need to be NPO prior to a dynamic nuclear renal study?
Only if its looking for renal artery stenosis and you’re using a PO ACE inhibitor (in which case they should be NPO for 6 hours prior)
