Renal isotope scan

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

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

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

15. 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.

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

17. 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.

18. 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.

19. Vesicoureteral Reflux

20. 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

21. 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

22. 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.

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

24. Renal Transplant Evaluation

25. 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

26. 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

27. 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)

28. 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.

29. 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.

30. 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 .

31. Renovascular Hypertension

32. 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)

33. 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

34. 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

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

36. 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.