Basics of Renal isotope scan and excretory function

1. Renal Isotopes- Excretory
Function
OSR
Dr. Yash Kumar Achantani

2. Introduction
The majority of nuclear imaging of the urinary tract focuses on
the kidney, designed to assess 1 or more elements of renal blood
flow, structure, function, and collecting system drainage.
The other commonly performed nuclear imaging study of the
urinary tract is radionuclide cystography. Nuclear cystograms
are generally performed in children and are designed to
evaluate for vesicoureteral reflux (VUR) that might predispose
to pyelonephritis and renal scarring.

3. RADIOPHARMACEUTICALS
The radiopharmaceuticals generally available for assessment of
renal function and anatomy can be grouped into 3 broad
categories.
• Those retained in the renal tubules. E.g. - 99mTc-DMSA
• Those filtered by the glomerulus. E.g. -99mTc-DTPA
• Those primarily secreted by the renal tubules. Eg-99mTc-
MAG3

4. PATIENT PREPARATION
• The patient will receive an intravenous injection of the
radiopharmaceutical and will lie quietly on an imaging table
for 20–30 min. Depending on the protocol, there may be 2
imaging sessions.
• The patient should be told to arrive well hydrated and, in
addition, to drink 2 large glasses of water just before arrival
since good hydration minimizes the radiation dose to the
bladder and facilitates interpretation of the examination.

5. • For a basic renogram, there are no medication or dietary
restrictions.
• Unlike radiographic contrast material, there is essentially no
risk of an allergic or anaphylactic reaction.
• The patient should void immediately before the study. This
practice will lessen the possibility that the patient needs to
void during the acquisition and is essential for diuretic studies
since a full bladder may delay upper tract emptying.

6. • Renal scans are frequently performed after the intravenous
injection of approximately 370 MBq (10 mCi) of 99mTc-
MAG3 or 99mTc-DTPA.
• Injection into a limb with venous obstruction should be
avoided; positioning the arm at a 90° angle to the body will
minimize the likelihood of axillary retention of the tracer.
• Imaging is usually performed with the patient supine. The
supine position allows a more accurate estimate of relative
renal function since the kidneys are more likely to lie at the
same depth.

7. INDICATIONS
• Evaluation of renal cortex
• Assessment of renal obstruction
• Following renal transplantation.
• Renovascular Hypertension
• Vesicoureteral Reflux
• Calculation of Glomerular Filtration Rate

8. Hydronephrosis

9. • Dilation of collecting system, which can be caused by
obstruction of urinary outflow.
• Hydroureter/hydronephrosis may persist after obstruction has
resolved.
• Anatomic and functional imaging using Tc-99m
mercaptoacetyltriglycine (MAG3) with furosemide (Lasix) to
evaluate patency of collecting system.
Characterize hydronephrosis
Estimate relative renal function

10. Nuclear Medicine Findings
Relative renal mass
• Differential or split renal function
• ROI drawn around each kidney
• 1-3 min after injection, values are selected and reported as
percentage (Normal: 45-55%)
Angiographic phase
• Flow to kidneys is seen quickly after aorta
• Cortex should accumulate radiotracer over 1-3 min
– Should be homogeneous
– Cortical defects may indicate scar
• If decreased renal function, uptake will be delayed

11. Clearance phase
• Calyceal activity within 5 min
• Bladder activity within 10-15 min
Renogram curve
• Graphic representation of uptake and excretion of Tc- 99m
MAG3 by kidneys plotted on time-activity curve
• t1/2 – Amount of time it takes for 1/2 of maximum cortical
activity to clear (Normal: < 10 min)
• Must be read with images

12. Image acquisition
Patient supine, gamma camera posterior
• Angiographic sequence (1-2 sec images for 1-2 min)
• Dynamic sequence (15-60 sec images for 20-30 min)
• Diuresis sequence ( Patient given furosemide and additional 15-60
sec images for 20-30 min)
• Postvoid images
Furosemide (Differentiates between dilated without obstruction vs.
dilated with urodynamically significant obstruction) Administer IV
when collecting system well visualized on side of obstruction

14. Normal, symmetric bilateral renal function, flow, and excretion
are shown without evidence of obstruction.

15. Normal renogram of right kidney shows no obstruction. Left
kidney shows complete obstruction with progressive rise in
activity in collecting system, even after furosemide.

16. Bilateral partial obstruction is shown. Time to calyceal activity
is > 5 min and activity continues to rise until furosemide;
thereafter decreases but washout t1/2 > 10 min. Additionally, the
relative functional renal mass is greater on the right. There is
minimal bladder activity.

17. Left kidney shows patulous renal collecting system with delayed
spontaneous excretion, which normalizes after furosemide. Right
kidney shows normal renal function.

18. Nonfunctioning right kidney is shown with no appreciable blood
flow or uptake. Left kidney is nonobstructed, but fluctuant
activity in the pelvis and ureter is consistent with vesicoureteral
reflux. Relative renal mass is 100% on the left.

19. Right renal artery stenosis is shown. Relative functioning renal
mass is 62% on left, 38% on right. The right kidney is smaller
than the left with delayed time to peak with normal washout.
There is a normal left renogram curve.

20. Vesicoureteral Reflux

21. Retrograde flow of urine from bladder into ureter &/or renal
pelvis.
• Radiopharmaceutical instilled as bolus into bladder through
catheter
Tc-99m pertechnetate
• Activity of 0.25-0.5 mCi (9.25-18.5 MBq) for infants and
toddlers
• Activity 0.5-1 mCi (18.5-37 MBq) for adults
Tc-99m sulfur colloid or Tc-99m DTPA can also be used
• Bolus administration ensures entire amount of radiotracer
delivered to bladder

22. Instillation of fluid volume after radiotracer bolus (Normal saline,
water)
– Bladder volume goal: [Age in years + 2] x 30 cc
Image acquisition
Filling and voiding dynamic images at 5-10 sec/frame.
Once bladder goal volume is reached, instruct patient to void.
Prevoid and postvoid static images, 3-5 minutes each.
Reflux of radiotracer from bladder into ureter, intrarenal
collecting system is assessed
Mild: Reflux in ureter
Moderate: Reflux to nondilated ureter and renal pelvis
Severe: Reflux to dilated collecting system

23. Posterior Tc-99m pertechnetate nuclear cystogram shows
vesicoureteral reflux to the mid right ureter, which is not dilated.
Posterior Tc-99m pertechnetate nuclear cystogram shows
vesicoureteral reflux into the right renal pelvis, which is dilated.

24. Posterior indirect cystogram using Tc-99m MAG3 renogram
shows radiotracer in the left renal collecting system that increases
over time due to vesicoureteric reflux.

25. Renal Transplant Evaluation

26. • Done with Tc-99m MAG3/ DTPA renography.
• To evaluate and potentially differentiate cause of early or late
allograft dysfunction.
– Vascular complications
– Acute rejection (AR) and chronic rejection (CR)
– Acute tubular necrosis (ATN)
– Obstruction
– Urinoma and lymphocele formation

27. Interpretation
• Perfusion to allograft: Normally within 4 sec of radiotracer
bolus passing through iliac artery
• Normal peak cortical activity 3-5 min post injection
• Normal renal transit: Tracer in collecting system, bladder by 6
min
• By end of exam, cortex should clear or be significantly less
than early in exam if no cortical retention
• Cortical retention seen in ATN, AR, CR
• Cortical loss and dilated pelvis helpful identifiers in CR

28. Imaging Findings
Renal vein thrombosis (RVT)
• Lack of draining collaterals, overall perfusion ↓ causing absent
or photopenic transplant.
Acute Tubular Necrosis
• Classically presents with relatively preserved perfusion and
delayed uptake/excretion (tubular agents)

29. Acute Rejection
• Perfusion in AR generally worse than function: Often
technically difficult to visualize
• ↑ cortical retention compared with baseline from 1 week to < 1
year: Sensitive, fairly specific for AR
Chronic Rejection
• 1st sign: ↓ blood flow, ERPF with relatively spared function
• Over time, cortical thinning with worsening uptake and
clearance develop, along with ↑ calyceal dilation.

30. Excretion images from a Tc-99m MAG3 transplant renogram demonstrate
normal excretion from the transplant kidney with expected accumulation
of radiotracer in the bladder.
Normal time-activity curve in the same patient shows rapid peak uptake
and washout of radiotracer in a baseline exam of a living related donor
allograft.

31. Excretion images from a transplant Tc- 99m MAG3 renogram demonstrate
progressive cortical accumulation of the radiotracer and no significant
excretion. Also note the accumulation of background activity, including the
gallbladder , a pattern typical of acute tubular necrosis.

32. Renovascular Hypertension

33. Hypertension (HTN) caused by hemodynamically significant
renal artery stenosis (RAS) activating renin-angiotensin system.
Patient preparation
• Stop ACEI 3-7 days prior to exam; if not, sensitivity decreases
(~ 15-17%)
• Stop short-acting ACEI (e.g., captopril) 3 days before; 5-7
days for long-acting ACEI
• Also stop angiotensin II receptor blockers, e.g., losartan
Baseline Tc-99m MAG3 renogram (without ACEI)
• Blood flow usually not perceptibly altered; nonspecific small
kidney or ↓ function could be seen but scan often normal
• Nonspecific: Any abnormality could be caused by numerous
etiologies (e.g., obstruction)

34. ACEI renogram: Excellent detection of clinically significant
RAS; sensitivity > 90% and specificity 95% in those with good
renal function
• Patients without RVHT show no significant change from
baseline
• Functional deterioration after ACEI compared with baseline
identifies patients with reversible RVHT with high accuracy.
Best diagnostic clue
• ACE inhibitor (ACEI) renogram showing functional
deterioration after ACEI administration compared with
baseline renogram

35. Interpretation
Probability of RVHT caused by RAS graded as low, intermediate,
or high
• Low probability (< 10%): Pre and post renograms normal or
improvement after ACEI.
• Intermediate (indeterminate) probability: Abnormal baseline
findings that are unchanged after ACEI.
• High probability (> 90%)
– MAG-3: ↑ peak time (by 2-3 min or at least 40%)
– DTPA: ↓ peak and ↓ relative uptake or GFR > 10%
– Marked unilateral parenchymal retention of DTPA after
ACEI compared with baseline study

36. Pre-captopril posterior ACE-inhibited renography demonstrates
normal symmetric excretion bilaterally.
Post-captopril posterior ACE inhibited renography demonstrates
normal symmetric excretion bilaterally.

37. Pre-captopril posterior ACE inhibited (ACEI) renography
demonstrates normal symmetric excretion bilaterally.
Post-captopril renogram demonstrates decreased excretion from the
right kidney relative to the left.