Nuclear Imaging in Nephrology

Nuclear Imaging in Nephrology
Wong Koh Wei

References: Oxford Textbook of Nephrology
Diagnostic Tests in Nephrology. Edited by John Bradley, Ken Smith Clinical Applications of Renal Scintigraphy. Andrew Taylor et al. AJR 1995;164:31-41 Radionuclide Investigations of the Urinary Tract in the Era of Multimodality Imaging. Ariane Boubaker et al. The Journal of Nuclear Medicine. Vol. 47 (11), November 2006 Bristish Nuclear Medicine Society Guidelines Isotopic Scan for Diagnosis of Renal Disease. Yusuke Inoue et al. Saudi Journal of Kidney Diseases and Transplantation. 15(3) 2004;

Introduction Uses pharmaceuticals – labels with radionuclides (radiophamaceuticals) - radiotracers Administers these to patients – radiation emitted is detected Formation of an image using a gamma camera or positron emission tomography Radionuclide imaging / nuclear scintigraphy Shows the physiological function of the system being investigated

Introduction Radiotracers – DTPA, MAG3, OIH etc – taken up by kidneys, then excreted into urinary tract Serial frames of posterior view – acquired min immediately after tracer injection Frame rate – 1-3s per frame for one min to assess perfusion (perfusion phase) 10-15s per frame for 4 min to assess function (function phase) 10-30s per frame to assess urinary system (excretion phase)

Overview of renal radiopharmaceuticals
Renal handling Radiopharmaceutical Imaging Clinical use Glomerular filtration 51 Cr-EDTA No GFR 99mTc-DTPA Yes Tubular secretion 123I/131I-OIH ERPF 99mTc-MAG3 99mTc-EC Tubular retention 99mTc-DMSA Cortical imaging 99mTc-GH

Glomerular filtration
Gold standard – inulin clearance Radionuclide of choice – 51Cr-EDTA – clearance closest to that of inulin 99mTc-DTPA – technetium-99m-diethylenetriamine pentaacetic acid – correlates well with 51Cr-EDTA and inulin Taken up by glomerular filtration, not secreted/reabsorbed by tubules 99mTc-DTPA can be used for gamma camera imaging Least expensive renal radiopharmaceutical Low radiation dose Small fraction may be bound to protein – not a problem for routine measurement of GFR Once reaches kidney – 20% is accumulated and remainder flows away, i.e. extraction fraction of DTPA is 20%

Tubular secretion (1) p-Aminohippuric acid (PAH) – gold standard for measurement of tubular cell function and its clearance – effective renal plasma flow (ERPF) 123I-OIH and 131I-OIH – cleared by tubular secretion (small fraction by glomerular filtration) Clearance rate – approx ml/min Extraction of 131I-OIH depends on renal plasma flow and extraction from plasma (proximal tubules) 123I-OIH – better imaging qualities, more expensive

Tubular secretion (2) 99mTc-MAG3
highly protein-bound, cleared mainly by proximal tubules High extraction fraction (50%) – better scintigraphic images 99mTc-I, I and d,d-ethylenedicysteine (EC) – better than 99mTc-MAG3

ıTc-MAG3 image (bottom row) from renal scan of 65-yearold patient with contrast nephrotoxicity superimposed on impaired baseline renal function (creatinine 2.4 mg/di, 232 iimol/1) shows better image quality than 99mTo-DTpA scan (top row) obtained 3 weeks later when contrast nephrotoxiclty had resolved (creatinine 1 .8 mgldi, 1 59 imol/1). ı“ıTc-MAG3 Images provide better quality than ı“Tc-DTPA in patients with Impaired renal function. 65 year-old with contrast nephropathy on CKD – better image of TC-MAG than DTPA scan

Tubular retention 99mTc-dimercaptosuccinic acid (DMSA)
Excellent cortical imaging agent Concentrates largely in renal cortex (lesser in liver) Strongly bound to proteins At 2h post-injection : 50% retained in kidneys, no visualization of urinary collecting system 99mTc-glucoheptonate (GH) Filtered by glomerulus and bound by tubules Highly protein-bound – glomerular filtration partial

DMSA IV injection – bound to proximal tubules Indications:
Assessment of kidneys in acute phase of UTI (acute pyelonephritis) Assessment of kidneys in late phase of UTI – detection of scar Assessment of horseshoe, solitary or ectopic kidney Localisation of poor or very poorly functioning kidney Assessment of renal function in the presence of an abdominal mass BNMS guidelines

DMSA Pitfalls Controversies
Acute and chronic pyelonephritis cannot be distinguished on the cortical scan. If a defect is present 6 months after the last UTI then this is a scar A recent UTI may cause temporary reduced uptake / focal defect and a follow-up DMSA scan should be undertaken The diagnosis of renal scars is difficult in the infant under 3-6 months of age because of renal immaturity. If appropriate the scan should be delayed Controversies To obtain the highest resolution, some centres recommend the use of a pin hole collimato, however many institutions obtain high resolution images with clear definition between cortex and medulla without the use of pin-hole collimation Currently there is no evidence to support the routine use of SPECT in children to delineate focal defects BNMS guidelines

Analytic methods Various methods
Single-sample methods and camera-based methods suitable for busy clinical practice Single-sample – single venous blood sampling after tracer injection, and plasma radioactivity is measured Plasma activity and injection dose substituted in a predefined, empiric equation = renal clearance

Analytic methods Camera-based methods – renal uptake early after tracer injection reflects renal function Calculate renal function from imaging data without blood sampling A region of interest (ROI) is drawn for each kidney to estimate activity, then do a background subtraction, then attenuation correction for depth of each kidney, then normalized to the injection dose – finally substituted to an empiric equation = renal clearance Less accurate than single-sample method Can assess right and left kidney function separately – split renal function Can do combined single-sample and camera-based methods Isotopic Scan for Diagnosis of Renal Disease. Yusuke Inoue et al. Saudi Journal of Kidney Diseases and Transplantation. 15(3) 2004;

Analytic methods Renogram curves – overview of the time course of renal radioactivity Generated by setting an ROI for each kidney Radioactivity in a kidney derives from renal parenchyma, upper tract and overlapping extrarenal tissues Do background subtraction - renal parenchyma and upper tract In normal subjects – a renogram demonstrates rapid increase during perfusion and function phases, then rapid decline during excretion phases Hypofunction flattens the slopes during the function and excretion phases Obstruction causes delayed excretion Cannot discriminate between retention in renal parenchyma and that in urinary tract – visual assessment of scintigraphy images needed…

Clinical uses: Renal clearance measurements Obstruction Infection
Renal artery stenosis Renal transplant Tumour/mass Trauma

Renal artery stenosis Renal transplant

Renal clearance measurements
GFR and estimation of split renal function Renal Plasma Flow A patient may lose up to 50% of renal function before the serum level of creatinine increases to a value deemed abnormal. Serum creatinine values have a wide range at all levels of inulin clearance (GFR), and creatinine can remain within the normal range despite inulin clearances 60-80% below normal

Glomerular Filtration Rate
Substances suitable for measuring GFR Low protein binding Negligible non-renal excretion Freely filtered Chemically stable and inert INULIN – Gold standard

GFR Radioactive tracers – simplifies sample measurements
Single injection 51Chromium ethylenediamine tetraacetic acid (51Cr-EDTA) – agent of choice 99mTc-DTPA – can be used – prepared from kits - variability in stability and protein-binding Short half-life (6 hours) Advantage – imaging and GFR measurement can be performed at the same time

GFR - 51Cr-EDTA After iv injection – EDTA rapidly diffuses throughout bloodstream, equilibrates more slowly with EVF Measure the plasma conc at 2, 3 and 4 hours after injection Back extrapolation to time of injectiondistribution volume of extacellular space, and slope of declining conc is fractional clearance of this space  GFR Expressed in ml/min or normalised to body surface area

GFR - 51Cr-EDTA A number of attempts to simplify GFR measurements
Considerable variation due to age and body dimensions High errors All single injection methods – assume patient in a steady state with respect to hemodynamics and fluid exchange Not accurate e.g. major surgery, transfusion or dialysis

EDTA GFR - plasma clearance curve - which required multiple blood samples to be taken over a period of several hours Slope-intercept method – after numerous simplification  number of sample : 1 (recommended by the Radionuclides in Nephrology Committee on Renal Clearance (Blaufox et al, 1996) ) It is recommended that the plasma clearance of EDTA from venous samples be taken as the standard measure of GFR DTPA does have some technical advantages over EDTA but normal ranges are not so well established Small systematic differences have been observed between GFR measurements obtained from EDTA and DTPA (Rehling et al, 1984, Fleming et al, 1991, Biggi et al, 1995)

Renal plasma flow Tracers that are filtered and actively secreted by renal tubules – extracted with  efficiency from plasma perfusing kidneys Ortho-idohippurate (OIH) – 90% removed by kidneys on a single pass  ERPF Less widely available 99mTc-labelled compounds – 99mTc-MAG3: Higher protein binding and lower extraction efficiency Tubular extraction rate Need multiple blood samples for accuracy GFR correlates well with ERPF – ERPF never achieved widespread utility in nephrology.

Obstruction/Urinary tract dilatation
Diuretic renography – diagnostic work-up of upper tract dilatation, and follow-up of patients with hydronephrosis Method of choice – to differentiate a dilated unobstructed urinary system from a true stenosis Can also assess urine flow and renal function

In children: Sedation should be avoided – may interfere with bladder voiding Increased radiation exposure to bladder mucosa – concern Receiving the child with parents in a dedicated, calm environment If needed – local guidelines for sedation Short inhalation of equimolar mixture of nitrous oxide and oxygen J Nucl Med 2006; 47:1819–1836

Diuretic renography 99mTc-mercaptoacetyltriglycine(MAG3) and 123I-orthoiodohippurate (OIH) are preferred higher renal extraction ratio and rapid plasma clearance, especially in infants and young children and in patients with impaired renal function Use of frusemide 1mg/kg (max 20mg in children, 40mg adults Recommended by Society of Nuclear Medicine European Nuclear Medicine Association

Diuretic renography Timing of frusemide administration
20 min or more after tracer injection – max distension of renal pelvis or ureter can be visually assessed (F+20) 15 min before tracer injection – diuretic response of kidney is maximal (F-20) Diuretic response is evaluated by visual and quantitative interpretation of the dynamic acquisition Postmicturition images are mandatory because a full bladder may delay urinary flow even in an unobstructed system

Diuretic renography The role of bladder catheterization – debated - not recommended in clinical routine practice Older children and adults - renography is performed after bladder emptying Non–toilet-trained children, spontaneous micturition is usually observed during the acquisition Adequate functioning of the affected kidney (GFR > 15 mL/min) and adequate hydration are major determinants of the response to frusemide

Limitation/pitfall of diuretic renography

6/12 old boy, febrile UTI by age of 2/12, normal ultrasound and VCUG
Diuretic renography (F10) in 6-mo-old boy who had febrile UTI by age of 2 mo. Renal sonography and VCUG had normal findings. (A) One-minute posterior views demonstrate normal tracer uptake by both kidneys and rapid washout, with bladder activity visible from third minute after injection and spontaneous micturition occurring at minute 10. (B) Left (red) and right (blue) renal time–activity curves show symmetric relative function (left, 50%; right, 50%) and normal time to peak (,180 s). 6/12 old boy, febrile UTI by age of 2/12, normal ultrasound and VCUG

9 year-old boy – febrile UTI
Bilateral duplex kidney diagnosed in 9-y-old boy after febrile UTI. (A) VCUG shows bilateral pyeloureteral reflux with opacification of incomplete systems, suggesting duplication. (B) Coronal T2-weighted MRI scan confirms presence of duplex kidneys bilaterally. Lower pyelocaliceal systems are dilated (arrows) even when upper ones remain thin (arrowheads). (C) Sagittal sonographic view of right upper quadrant shows enlarged kidney with broad layer of parenchyma on upper pole (arrowhead) and atrophic lower pole (arrow). (D) One-minute parenchymal view shows decreased tracer uptake by left lower system and parenchymal defects at both poles of right kidney. (E) Images obtained 1, 4, 9, and 15 min (from left to right) after injection show delayed urinary flow in lower moiety of left kidney due to loss of parenchymal function. (F) Renograms of left and right kidneys show symmetric function (left, 49%; right, 51%) and no significant impairment of urinary flow under furosemide. (G) Indirect radionuclide cystography demonstrate VUR in both left and right lower systems 9 year-old boy – febrile UTI

Indirect radionuclide cystography
. (E) Images obtained 1, 4, 9, and 15 min (from left to right) after injection show delayed urinary flow in lower moiety of left kidney due to loss of parenchymal function. (F) Renograms of left and right kidneys show symmetric function (left, 49%; right, 51%) and no significant impairment of urinary flow under furosemide. (G) Indirect radionuclide cystography demonstrate VUR in both left and right lower systems Indirect radionuclide cystography

Left kidney Diuretic renography (F10) obtained during follow-up of 4-y-old girl treated conservatively for left pelviureteric junction stenosis detected prenatally. (A) One-minute posterior views show dilated left kidney with preserved parenchymal function despite impaired urinary drainage above pelviureteric junction. Right kidney is normal. (B) Left (red) and right (blue) renograms confirm symmetric (left, 51%; right, 49%) and normal tracer extraction by both kidneys and abnormal urinary flow out of left kidney. (C) Images obtained 20 min after injection (left), after miction (middle), and 50 min after injection (right) show residual activity within left renal pelvis after miction and 50 min after injection. (D) Initial sonographic sagittal view of left kidney shows enlargement of pyelocaliceal system. (E) Follow-up sonogram obtained at same time as diuretic renography shows persistent enlargement, with satisfactory growth of left kidney. 4 year-old girl treated conservatively for left PUJ stenosis detected prenatally 20min after injection After miction 50 min after injection

. (D) Initial sonographic sagittal view of left kidney shows enlargement of pyelocaliceal system. (E) Follow-up sonogram obtained at same time as diuretic renography shows persistent enlargement, with satisfactory growth of left kidney.

UTI Frequent in children Affect girls 2x > boys
80% first infections diagnosed during first 2 years of life 5% in infants and young children – fever of unexplained origin Diagnosis – urine culture Risk of renal damage – delay of diagnosis/treatment, number of UTIs

UTI The Subcommittee on Urinary Tract Infection of the American Academy of Pediatric Committee on Quality Improvement recommended imaging (mainly sonography, VCUG, or radionuclide cystography) of the urinary tract in children younger than 2 y old but considered the role of cortical renal scintigraphy still to be unclear despite its recognized high sensitivity

Cortical scintigraphy
Scintigraphy with 99mTc-dimercaptosuccinic acid (DMSA) – simple and non-invasive Static imaging 2-4 hours after iv injection Delayed or post-frusemide images in hydronephrosis The sensitivity of 99mTc-DMSA for the detection of parenchymal defects due to infection - from 80% to 100% does not allow differentiation of acute pyelonephritis from renal scars

Cortical scintigraphy
Abnormal findings on cortical scintigraphy are found in 52%–78% of children during acute pyelonephritis, and the risk that a renal scar will develop can reach 60% The role of cortical scintigraphy is still largely debated in acute pyelonephritis but is widely accepted in the detection of renal scars 99mTc-DMSA scintigraphy is the reference method for detecting renal sequelae after UTI, is more sensitive than sonography, and should be performed no sooner than 6 mo after the last documented UTI Also used to detect scars in VUR

Radionuclide cystography
Direct radionuclide cystograhy A radiologic-VCUG alternative - lower radiation burden As invasive as VCUG – bladder catheterization More sensitive – acquisition is continuous in both filling and voiding phase Indirect radionuclide cystography Performed after conventional renography with 99mTc-MAG3 or 123I-OIH – high excretion rate No need catheterization Less sensitive and specific than VCUG/direct cystography

25-y-old patient with chronic renal insufficiency due to reflux nephropathy. (A) CT scan shows atrophic left kidney (arrow) with dilated pelvis. (B) First-minute parenchymal image shows small scarred left kidney and also upper and lower parenchymal defects of right kidney (differential renal function: left 31%; right, 69%). (C) Indirect radionuclide cystography shows massive left VUR. (D) VCUG shows massive left pyeloureteral reflux. (E) Sagittal sonogram shows dilatation of distal left ureter (arrow).

. (C) Indirect radionuclide cystography shows massive left VUR

Renovascular hypertension
3 – 5% of all hypertensive patients 15 – 30% of referred patients for refractory hypertension Renal hypoperfusion  secondary activation of renin-angiotension system Stenotic or obstructive lesion within renal artery Potential curable cause of hypertension 70-90% - atherosclerosis 10-30% - fibromuscular dysplasia

Renovascular hypertension
RVH is a consequence of activation of RAS with concomitant release of angiotensin II (a vasoconstrictor) and aldosterone (leading to plasma volume expansion) to maintain physiologic renal perfusion by increasing blood pressure Clinical features: abdominal bruits, rapid onset of hypertension, refractory hypertension, unilateral renal atrophy, azotemia (esp when worsened by ACEi or ARB), unexplained azotemia/hypokemia Episodes of flash pulmonary edema in patients with relatively well-preserved systolic function Gold standard – Renal angiography Clinical features traditionally associated with RVH are abdominal bruits; a rapid onset of the hypertension, which may be severe (diastolic blood pressure mmHg) and refractory to optimal pharmacologic treatment; unilateral renal atrophy; azotemia, especially when worsened by angiotensin-converting enzyme (ACE) inhibitors or angiotensin receptor blockers; and unexplained azotemia or hypokalemia (due to an aldosterone excess) (54). Episodes of flash (rapidly progressive) pulmonary edema have been observed with RVH in patients with relatively well-preserved systolic function, because of failure of the contralateral kidney to correct for volume expansion

Captopril-enhanced renography
To determine which patients can expect normalization of BP or improvement of BP control after revascularization ACEi reduce the conversion of angiotensin I  angiotensin II - diminishing the vasoconstriction of the postglomerular efferent arteriole and decreasing the GFR, which can be detected by scintigraphy Both glomerulus-filtered (99mTc-DTPA) and tubule-secreted (99mTc-MAG3 or 123I-OIH) - currently used ACEi – captopril (25-50mg) orally 60min before renography; or iv enalaprilat (40mg/kg) over 325min >15min before renography Commonly used ACE inhibitors are captopril (25250 mg) taken orally about 60 min before renography or enalaprilat (40 mg/kg; maximum, 2.5 mg) administered intravenously over 325 min more than 15 min before the beginning of renography—the latter being associated with a higher risk of hypotension

Captopril-enhanced renography
Known pitfalls  erroneous results are food ingestion within 4 h before receiving captopril, infiltration, dehydration, hypotension, or a full bladder impairing drainage ACEi enhanced renography now is rarely used as the primary imaging tool Most reliable in predicting recovery in patients with FMD ACE inhibitor renography is most reliable in predicting recovery in patients with FMD, who are likely to respond to revascularization. In these patients, renography by assessing the function of the affected kidney may contribute to the decision on therapeutic management, revascularization, or medical treatment

35 year-old : Doppler ultrasound showing parvus-tardus pattern with collapsed resistance index
Normal right kidney Stenosis related to FMD in 35-y-old man. (A) ACE inhibitor renography shows 1-min images of radiotracer uptake (99mTc-MAG3). Right kidney is perfor ing 95% of the renal function, which was decreased (tubular extraction rate, 160 mL/min/1.73 m2). (B) Time– activity curves of left (blue) and right (red) kidneys show almost no participation of the left kidney to renal function. C)Angiogram shows irregular stenosis (arrow) and beading (arrowheads). (D) Color Duplex sonography of peripheral artery of left kidney demonstrates parvus–tardus pattern with collapsed resistance index (0.35). (E) In contrast, right kidney shows normal Doppler spectrum.

Left kidney Right kidney
. (A) ACE inhibitor renography shows 1-min images of radiotracer uptake (99mTc-MAG3). Right kidney is performing 95% of the renal function, which was decreased (tubular extraction rate, 160 mL/min/1.73 m2). (B) Time– activity curves of left (blue) and right (red) kidneys show almost no participation of the left kidney to renal function Left kidney Right kidney

RAS in 63-y-old man with chronic renal insufficiency (creatinine clearance, 40 mL/min) and subrenal aortic inflammatory aneurysm with right renal hydronephrosis due to ureter compression. (A) On ACE inhibitor renography with 123IOIH, images obtained at 1, 6, 11, and 16 min (from left to right) after injection show poor function of right kidney, assuming only 10% of total renal function. (B) Time–activity renal curves were identical to baseline (not shown). (C) Coronal 3-dimensional MRA image demonstrates short stenosis on right renal artery (arrow).

75 year-old lady – OIH study
RAS due to atherosclerosis in 75-y-old woman. Baseline renography with 123I-OIH (A) and ACE inhibitor renography (B) show delayed renal parenchymal uptake in right kidney, as compared with baseline (images taken at 1, 6, 11, and 16 min [from left to right] after injection).

(B) show delayed renal parenchymal uptake in right kidney, as compared with baseline (images taken at 1, 6, 11, and 16 min [from left to right] after injection).

(C) Angiogram shows narrow stenosis at ostium of right renal artery (arrow). (D) Angiogram performed after angioplasty demonstrates successful dilatation of vessel (arrow). (E) Coronal 3-dimensional CT shows regular-sized reshaped vessel, with presence of stent (arrow).

Typical diagnostic workup for RVH
Doppler sonography, CT angiography or MRA ACE inhibitor renography Renal angiography and treatment Depending on local expertise and availability, this technique could be Doppler sonography, CT angiography (better availability and spatial resolution than MRA), or MRA (especially in patients with intolerance to iodinated contrast agents). If the results of initial investigations are negative, RAS can reasonably be excluded. If initial findings are positive, ACE inhibitor renography can be performed, followed by renal angiography and treatment (Fig. 7). If FMD is suspected on the basis of clinical features, Doppler sonography or ACE inhibitor renography can be recommended as the initial test, given the known limitations of CT and MRA for distal renal angiography

Renal transplantation
Comprehensive evaluation of renal transplants – in differential diagnosis of medical and surgical complications in early post-op and in long-term follow up Selection of patients for biopsy and for various drug regimens Anuric ATN – improving indices of renal function (ERPF, uptake of tubular tracers) – indicates resolution of tubular injury The protocol: a flow study, scintigram of kidneys, prevoid and postvoid bladder image, injection site image, time/acitivity curves of graft and bladder, and quantitative data of perfusion, function and tracer transit Flow study – 99mmercaptoacetyltriglycine or DTPA Quantitative analysis and function phase should include images and time/activity curves Serial studies: decline in function and poor perfusion indicative of acute rejection A normally appearing scintigram without cortical retention, low function – chronic rejection Diuretic renogram - to exclude obstruction Report of the Radionuclides in Nehrourology Committee for evaluationof transplanted kidney (review of techniques). Dubovsky et al. Semin Nucl Med Apr;29(2):175-88

Renal transplantation
A baseline study should be performed within 1 – 2 days of operation – to allow comparison of serial studies because of deteriorating renal function DTPA – tracer of choice in early stages DTPA/MAG3 can be used later stages

Indications for renography in transplantation

Renography in transplantation
Ultrasound – 1st line evaluation in renal graft dysfunction Renography – must be available on emergency basis Non-visualization – irremediable loss of function May not differentiate rejection from ischemia (RAS) ACEi renography – help determine whether arterial hypertension is dependent on RAS Help in diagnosis of urinary complications – obstruction or leak

Graft dysfunction 1d post-transplantation in a 41 y-old woman
Graft dysfunction 1 d after transplantation in 41-y-old woman. Baseline renography (A) and ACE inhibitor renography (B) show prolonged tracer transit in renal parenchyma on images and on renal and bladder curves, as compared with baseline. (C) Color duplex sonographic assessment of intrarenal vessels shows parvus–tardus pattern. (D) Color duplex sonographic exploration of renal artery demonstrates disturbance of flow. (E) Coronal 3-dimensional MRA image shows short narrowing of renal artery (arrow) at site of anastomosis. Laparotomy revealed kinking of renal artery graft

(B) show prolonged tracer transit in renal parenchyma on images and on renal and bladder curves, as compared with baseline.

Graft dysfunction 1 d after transplantation in 41-y-old woman
Graft dysfunction 1 d after transplantation in 41-y-old woman. Baseline renography (A) and ACE inhibitor renography (B) show prolonged tracer transit in renal parenchyma on images and on renal and bladder curves, as compared with baseline. (C) Color duplex sonographic assessment of intrarenal vessels shows parvus–tardus pattern. (D) Color duplex sonographic exploration of renal artery demonstrates disturbance of flow. (E) Coronal 3-dimensional MRA image shows short narrowing of renal artery (arrow) at site of anastomosis. Laparotomy revealed kinking of renal artery graft.

5d post-transplantation
Normal camera-based renography findings 5 d after transplantation of related-donor kidney: the first two 10-s perfusion images (left and middle) and the 1-min parenchymal image (right; upper pole irregularity is due to graft position) (A); whole kidney (red), cortical kidney (blue), and bladder curves (B); and sequential 1-min images (C). Somewhat prolonged visualization of ureter is due to postoperative hypotony, frequently observed during first days after transplantation.

6d post-transplantation – sudden anuria and abdominal pain
One-minute images after injection of 99mTc- MAG3. Images were obtained 6 d after transplantation because of sudden anuria and abdominal pain. Starting with third image, irregularly shaped urinary collection suggestive of urinary leak appears (arrow). Reintervention revealed necrosis of distal ureter and confirmed urinary leak. After resetion and reanastomosis of ureter, course was uneventful 6d post-transplantation – sudden anuria and abdominal pain

Decreased graft function 5/12 post-transplant, renogram showed an OIH accumulation within normal limits, normal peak, but delayed elimination 1-min images reveal tracer retention in parenchyma without outflow impairment – suggesting potential CNI toxicity Patient with decreased graft function 5 mo after transplantation of living-donor kidney. Creatinine level was 219 mmol/L. (A) Renogram shows an 123I-OIH accumulation within normal limits, a normal peak, but delayed elimination. Normal uptake and peak are unlikely to be seen in acute rejection. (B) Corresponding 1-min images reveal tracer retention in parenchyma without outflow impairment, suggesting potential calcineurin inhibitor toxicity; normal Doppler sonography findings made RAS unlikely. Biopsy showed thrombotic microangiopathy. After change of immunosuppressive therapy from tacrolimus to sirolimus, creatinine returned to baseline level (140 mmol/L).

Conclusion Role of nuclear medicine – in investigation of renal parenchymal function and upper urinary tract abnormalities Radiation burden low Do not require sedation or specific patient preparation Easy to perform Knowledge of renal pathophysiology and recognition of limitation and technical pitfalls essential

A 37-year-old man was referred for evaluation of distal renal tubular acidosis. Laboratory evaluation revealed a serum potassium level of 3.3 mmol per liter, a bicarbonate level of 16 mmol per liter, a calcium level of 9.3 mg per deciliter (2.3 mmol per liter), a phosphate level of 2.1 mg per deciliter (0.7 mmol per liter), a creatinine level of 3.0 mg per deciliter (265 µmol per liter), a parathyroid hormone level of 62 pg per milliliter, and an estimated glomerular filtration rate of 25 ml per minute per 1.73 m2 of body-surface area. He had been given a diagnosis of renal tubular acidosis at 9 years of age on the basis of metabolic acidosis with a high urinary pH and hypokalemia associated with nephrocalcinosis. At that time, there was evidence of bilateral nephrocalcinosis on plain abdominal radiography. The patient was treated with sodium bicarbonate and potassium supplementation and had normal growth but did not undergo medical follow-up or treatment between 15 and 37 years of age. The plain film of the abdomen obtained during the referral visit (see figure) revealed bilateral symmetric calcification of the renal parenchyma, sparing only the renal pelvis. This finding contrasts with those classically associated with type 1 distal renal tubular acidosis, in which nephrocalcinosis is present but is limited to the renal medulla. Three years after sodium bicarbonate and potassium supplementation was restarted, the patient's renal function has remained stable.

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