Current Medical Issues

REVIEW ARTICLE
Year
: 2018  |  Volume : 16  |  Issue : 4  |  Page : 148--154

Role of nuclear medicine in evaluation of renal system


Julie Hephzibah 
 Department of Nuclear Medicine, Christian Medical College, Vellore, Tamil Nadu, India

Correspondence Address:
Julie Hephzibah
Department of Nuclear Medicine, Christian Medical College, Vellore - 632 004, Tamil Nadu
India

Abstract

The aim of this article is to highlight the importance of Nuclear Medicine imaging in the diagnosis and management of common renal conditions. Nuclear Medicine procedures provide useful information on renal blood flow and individual kidney functions and drainage. The advantages of these procedures are that there is low radiation burden, no sedation or no special pre-procedural preparations are required and are easy to perform and interpret. It is a valuable asset in the imaging of renal system in both adults and children. Renal radiopharmaceuticals are categorized by their uptake and clearance mechanisms for studying glomerular filtration, tubular secretion, or cortical binding.



How to cite this article:
Hephzibah J. Role of nuclear medicine in evaluation of renal system.Curr Med Issues 2018;16:148-154


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Hephzibah J. Role of nuclear medicine in evaluation of renal system. Curr Med Issues [serial online] 2018 [cited 2019 Jul 16 ];16:148-154
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Full Text

 Introduction



Nuclear scintigraphy provides useful information on renal blood flow and individual kidney functions and drainage. The advantages of Nuclear Medicine Imaging procedures are that there is low radiation burden, no sedation or no special pre-procedural preparations are required and are easy to perform and interpret, and hence, it is a valuable asset in the imaging of renal system in both adults and children.

Renal radiopharmaceuticals are categorized by their uptake and clearance mechanisms for studying glomerular filtration, tubular secretion, or cortical binding.

 Terminologies



Renogram/renography: Time–activity curve was derived historically from renal probe (nonimaging) or in the current practice from computer-processed dynamic renal imaging studies after drawing region of interest (ROI)Renal scan/scintigram: Images were acquired using radiopharmaceuticals that fix to the cortex and timed sequential images acquired of radiotracer uptake and clearance in the dynamic renal studyDifferential/individual renal function: Percentage of the right/left renal cortical uptake or retention as a percentage of total renal uptakes was derived from renal scintigraphyQuantitative glomerular filtration rate (GFR)/effective renal plasma flow (ERPF): Clearance (ml/min) was derived from either blood sampling of radiotracer or computer-derived quantitative estimates of renal cortical uptake from scintigraphy.

 Clinical Indications for Radionuclide Scintigraphy



Perfusion abnormalitiesAcute/chronic renal failureRenal transplant: Rejection, obstruction, and status of anastomosisRenal trauma or surgical complicationsRenovascular hypertension/renal artery stenosis (RAS)Quantification of renal function: GFR/ERPFPyelonephritisMass versus column of BertinUreteral obstructionVesicoureteral reflux (VUR)Congenital anomalies.

 Radiotracers in Renal Scintigraphy



Renal radiopharmaceuticals can be divided into four groups:

To estimate renal plasma flowTo measure GFRTo estimate “functional renal mass” by tubular fixation in the parenchymaTo diagnose infectious or malignant lesions.

The other tracers that are available and not in wide applications are given below:

Hydroxyacetyltriglycine (HAG3)

Slightly higher urinary extractionFaster renal transitLower hepatobiliary uptake than mercaptoacetyltriglycine (MAG3)Clearance of HAG3 in humans has been shown to be 72% of that of orthoiodohippurate (OIH).

N-mercaptoacetylglycine

Properties similar to those of dimercaptosuccinic acid (DMSA) reaching renal activity plateau more rapidly than DMSA [Table 1] and [Table 2]{Table 1}{Table 2}

Organic cations labeled with Tc99m: No clinical experience has been reported to date, for example:

DACH – DiaminocyclohexaneCyclam.

Positron emission tomography radiopharmaceuticals[1]

For imaging renal blood flow

i. 15O-water, 82Rb, 13zN-ammonia, 64Cu-PTSM, 62Cu-PTSM, and 64Cu-ETS.

Renal blood volume

i. Radiolabeled carbon monoxide [15O] CO.

Metabolism

i. Carbon-11-labeled acetate

ii. 18F-fluoroacetate.

Receptor

i. [11C] MK-996 and [11C] L-159,884

ii.Radiolabeled angiotensin converting enzyme (ACE) inhibitors: 18F-Fluorocaptopril and11 C-zofenoprilat.

 Cortical Study



Technetium-99m DMSA agent of choice for renal parenchymal imaging due to its high cortical accumulation and high sensitivity.

It concentrates predominantly in the proximal convoluted tubules for adequately a long time, thus enabling a comprehensive scintigraphic evaluation. About 90% of Tc-99m DMSA is plasma protein, and hence, glomerular filtration is restricted. The main disadvantage is its relatively more radiation dose in comparison with other renal agents because of tubular fixation of DMSA and hence the longer duration in the renal cortex. However, in practice, Tc-99m DMSA is a remarkable renal parenchymal imaging agent, wherein 50% of the dose administered is located in the kidneys at 1-h injection [Figure 1].{Figure 1}

Tc-99m DMSA scintigraphy is significantly more sensitive than intravenous urography and ultrasonography and even color Doppler in the detection of renal parenchymal diseases.[2],[3]

Sensitivity for detection of parenchymal defects secondary to infection is from 80% to 100%, but acute pyelonephritis cannot be differentiated from renal scars.[4],[5]

Technetium-99m ethylene dicysteine (EC) scintigraphy gives almost the same details on relative renal function of each kidney as Tc-99m DMSA scintigraphy. In addition, it also gives more information of the perfusion, excretion pattern, and collecting system.

In 52%–78% of children during acute pyelonephritis, abnormal findings on cortical scintigraphy are found and risk of renal scarring can reach 60%.[6] The positive predictive value was raised from 62% to 85% in a semi-quantitative analysis of 99mTc-DMSA for detection of the development of renal scars in children at a high risk.[7]

 Renogram and Diuretic Renography



Tubular tracers such as 99mTc-MAG3, EC, and 123I-OIH are commonly preferred to the glomerular agent 99mTc-Diethylenetriaminepentaacetic acid (DTPA) due to their higher renal extraction ratio and rapid plasma clearance, particularly in infants and young children and also in patients with renal impairment. Bearing in mind the immaturity of nephrons in newborns, the standard recommendation is that diuretic renography should be delayed until 4 weeks of age as renal tubules will not be responding to the effect of furosemide. Renal function maturation gradually occurs in the first 2 years of life. In India, only EC is available and hence widely used [Table 4].{Table 4}

Renogram phase

I – Vascular phase (flow study): Aorta to kidney ~3"II – Parenchymal phase (kidney to background): Tpeak <5' (MAG3) and 2–3' (EC), 3–4' (DTPA)III – Washout (excretory) phase.

The guidelines published by the Society of Nuclear Medicine and the European Nuclear Medicine Association recommend the use of furosemide at a dose of 1 mg/kg, up to a maximum of 40 mg.[8]

To inject furosemide at the same time, i.e. F0 as the radiopharmaceutical is a recent proposal. It has gained much acceptance, especially in children, as it avoids repeated punctures during injection and reduces the study time.[9],[10] Simultaneous injection of radiotracer and furosemide does not interfere with the study of renal function. The diuretic effect begins 1–2 min postinjection of the diuretic, and parenchymal extraction of tubular tracers occurs in the 1st min after bolus injection, with a normal time to peak of usually <3 min.

Diuretic response is evaluated by visual and quantitative interpretation of the dynamic acquisition. Postvoid images are a must as a full bladder may delay urinary flow even if there is an unobstructed system. The effect a change from the supine position to erect or prone due to gravity is recommended in situ ations of incomplete drainage [Figure 2], [Figure 3], [Figure 4]. The role of bladder catheterization is still under debate usually not recommended in routine practice.{Figure 2}{Figure 3}{Figure 4}

Oral hydration (15 ml/kg during the 30 min prior to study) is usually sufficient. Infants will receive their feeds before the test.

Background-corrected time–activity renal curves are applied to assess urinary drainage and to calculate differential renal function [Figure 5].[11] An obstructed system is evaluated by prompt tracer washout, whereas a rising curve is generally indicative of true obstruction.{Figure 5}

In an adequately hydrated patient, the normal time to peak is <3 min with tubular tracers. Differential renal function should accordingly be measured during the extraction phase of the renogram, i.e. during the first 2 min.

Differential renal function (DRF) is the contribution of each kidney to sum of both left and right renal activities, normally ranging from 45% to 55%.[12] A DRF <40% or a decrease of DRF of >5% on successive diuretic renography studies is indicative of renal function deterioration.

Using DRF to assess renal function is also inapt in patients with solitary kidney, bilateral hydronephrosis, urethral valves, or chronic kidney disease and renal failure.

 Radionuclide Cystography



Direct radionuclide cystography is an alternative to the micturating cystourethrogram and it delivers a reduced radiation burden [Table 3].[4],[13],[14] The guidelines published by the Society of Nuclear Medicine for radionuclide cystography in children elaborate in detail the procedures in recommending, performing, interpreting, and reporting the results [Figure 6] and [Figure 7].[15]{Table 3}{Figure 6}{Figure 7}

 Other Indications



Renovascular hypertension

Patient preparation

Off Angiotensin converting enzyme inhibitors (ACEI) and Angiotensin II (ATII) receptor blockers × 3–7 daysOff diuretics × 5–7 daysNo solid food × 4 hPatient well hydrated10-ml/kg water 30–60 min pre and during testTablet Captopril 0.5-1mg/Kg given per orally 1 hour prior to imagingMonitor BPTracer: Tc-99m DTPAProtocol: 1-day versus 2-day test

1-day test: Baseline scan (1–2 mCi) followed by postcaptopril scan (8–10 mCi)2-day test: Postcaptopril scan, only if abnormal >> baseline.

Image acquisition: Flow and dynamic imaging is for 20-30minutes [Figure 8]. The interpretation of captopril renogram is given in [Table 5].[15]{Figure 8}{Table 5}

 Renal Transplant



Scintigraphy plays a vital role in identifying the complications postrenal transplant. The indications for nuclear imaging in renal transplant are the following [Figure 9]:{Figure 9}

Early complications

Perfusion status in renal arterial or venous thrombosisAcute tubular necrosis (ATN).

Late complications

Obstruction

RASVURUrine leakHematoma.

 Congenital Anomalies



Nuclear Medicine imaging is useful in congenital anomalies such as hoseshoe kidney, ectopic and duplex kidneys etc., [Figure 10], [Figure 11], [Figure 12].{Figure 10}{Figure 11}{Figure 12}

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

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