Determination of differential renal function by sequential renal scintigraphy

Evaluation of gamma camera-based measurement of individual kidney function using iodine-123 orthoiodohippurate

Gamma camera-based clearance techniques which use the renal uptake ratio (RUR) of the radiotracer are available to estimate the effective renal plasma flow (ERPF) and glomerular filtration rate. To evaluate the accuracy of these techniques, we measured RUR by an optimized procedure and compared it with standard ERPF. Iodine-123 orthoiodohippurate (OIH) scintigraphy and simultaneous para-aminohippurate clearance study for measuring standard ERPF were performed in three hospitals in 24 patients with normal or mildly impaired renal function. 123I-OIH was injected intravenously and 10-s consecutive imaging of the kidneys was started when the abdominal aorta was seen. The attenuation coefficient for 123I was measured in each hospital using the same water-equivalent absorption materials and used for the attenuation correction. After subtracting background radioactivity, RURs were defined as the count ratios of fractional renal uptakes based on the integral from 1 to 2, 2 to 3, 1.5 to 2.5 and 1 to 3 min after the injection of 123I-OIH in relation to injected doses using the following three procedures in respect of attenuation correction: (1) RUR without attenuation correction, (2) RUR with fractional renal uptake corrected by the measured attenuation coefficient, (3) RUR with the total injected dose corrected by the absorption material. To decide upon the appropriate correction method and time interval, RURs were compared with standard ERPF. Among the three correction methods, procedure 2 showed the highest correlation between RUR and standard ERPF, but the correlation coefficient was low (r=0.75). No significant difference was observed among the RURs of each time interval. Individual kidney function measured from early renal uptake may be inaccurate even when appropriate correction is made for attenuation, background activity or time lag between injection and data acquisition. Gamma camera-based measurement of renal function using 123I-OIH is limited with regard to accuracy and reproducibility, though it is convenient and non-invasive.

Measurement of relative renal function. A comparison of methods and assessment of reproducibility

A good correlation was found between relative uptake of 99Tcm dimercaptosuccinic acid (DMSA) and relative 131I orthoiodohippuric acid clearance in a group of 100 consecutive patients without evidence of renal failure. In the majority, attenuation correction was found to make no significant difference to relative function measurement. Those in whom it did could be readily identified by inspection of the posterior DMSA images at the time of examination. Two hundred patients were reviewed in whom serial studies had been performed over the previous 5 years. Differences in relative function greater than 5% indicated a high probability that a real change in renal function had occurred. We conclude that whilst renography and DMSA scintigraphy yield complementary information, relative function (L/L + R) can be measured equally well by either method, and the results are sufficiently reproducible to be clinically useful.

Glucoheptonate measurement of differential renal function

In previous studies using dogs whose renal function was rendered asymmetric by unilateral infarction or partial ureteral obstruction, the efficacy of technetium-99m diethylenetriamine pentaacetic acid and dimercaptosuccinic acid in the measurement of differential renal function was demonstrated. The present study was undertaken to determine if technetium-99m glucoheptonate could also be used to quantitate differential renal function in these conditions. Five dogs with partial ureteral obstruction, 4 with segmental infarction and 2 with ipsilateral combination of both were studied. Seven to 10 days following these interventions the animals were given a bolus injection of 10 mCi Tc-99m glucoheptonate. This was acquired in the posterior projection on a minicomputer at 2 seconds/frame for 3 minutes. Static images were obtained anteriorly and posteriorly between 3 and 5 hours postinjection. The following day iothalamate and creatinine clearances were measured by ureteral catheterization. There was good correlation between differential function calculated from the 1 to 3 minute portion of the bolus study and that determined by the ureteral catheter studies, r greater than 0.99. Correlations based on the static images were less satisfactory due to pelvic retention in the obstructed animals, r = 0.73. We conclude that technetium-99m glucoheptonate may be used to determine differential renal function.

Quantitation of renal function with glomerular and tubular agents

Quantitative methods to measure the glomerular and tubular function of the kidneys with radionuclides have been available for many years. They have not been widely used because the techniques and the calculations exceeded the scope of routine nuclear medicine practice. Validation of simplified methods and the introduction of computer technology have made measurement of the effective renal plasma flow (ERPF) and the glomerular filtration rate (GFR) simple enough so that they can be performed reproducibly in most nuclear medicine departments. The estimation of ERPF with radioiodinated OIH and GFR with 99mTcDTPA can be achieved in many ways, all of which yield clinically useful results. How to get the best results using the simplest methods is still unclear. The required accuracy depends on the intended clinical use. Our preference at the present time is to use a single or double plasma sample to calculate global ERPF or GFR, and to use the 1-2 min OIH or 1-3 min Tc-DTPA uptake to calculate relative function of the two kidneys (split function ERPF or GFR). The choice of method will be influenced by local factors, such as the nature of the patient population, the case volume, and the resources available. A desirable goal for future studies is to document carefully the capabilities and limitations of each alternative method, so that the choice can be rational.

Renal radiopharmaceuticals--an update

Noninvasive radionuclide procedures in the evaluation of renal disease have been accepted increasingly as effective and valuable alternatives to older clinical methods. The development of suitable radiopharmaceuticals labeled with high photon intensity radionuclides and with 99mTc in particular has stimulated this modality during the last few years. Currently several nearly ideal agents are available for anatomical and functional studies of kidney imparting very low absorbed radiation doses. These include 99mTc-GHA and 99mTc-DMSA for renal morphology and differential function evaluation, 99mTc-DTPA for GFR and 123I orthoiodohippurate for ERPF measurements. A suitable agent as a replacement for the latter labeled with 99mTc is actively being sought. Computer-assisted processing of dynamic renal function studies enables the observer to obtain a wealth of information related to the renal extraction, uptake, parenchymal transit and pelvic transit parameters of the agent administered into the bloodstream. Each of these parameters either globally or differentially contributes to a detailed evaluation of renal disease states. Several of these procedures have been validated against classical techniques clinically but more detailed information is being sought with the recently introduced radiopharmaceuticals. With the detailed validation and increasing recognition of the clinical utility of several of the radionuclidic procedures at many centers, it is hoped that radionuclide assessment of renal disorders ultimately will be made available routinely at all medical facilities.

Limitations of renal function scanning in acute obstruction

This study was designed to determine if technetium-99m penicillamine (TPEN), could be used to predict recoverable function in dogs with acute obstruction. Renal accumulation of TPEN was measured in four control dogs, in four dogs with acute obstruction lasting 7-14 days, and in the same four dogs following a variable recovery period of 15-63 days. The relative renal uptake of TPEN in vivo showed good agreement with the relative uptake in vitro and both measurements correlated closely with the relative inulin clearances in the normal and in the post obstructed kidneys. The uptake of TPEN in the obstructed kidney following 7-14 days of obstruction averaged 6.8% of the total renal uptake. After relief of the obstruction and a variable recovery period the relative uptake of TPEN in the post obstructed kidney had increased to a mean of 29.5%. These results indicate that TPEN scans should not be used during acute obstruction to predict recoverable function. The observations noted in the study almost certainly apply to similar chelating agents such as dimercaptosuccinic acid (DMSA) and probably to other renal radiopharmaceuticals as well.

Comprehensive renal scintillation procedures in spinal cord injury: comparison with excretory urography

A 131iodine orthoiodohippurate comprehensive renal scintillation procedure was performed and compared to results of excretory urography in 200 spinal cord injury patients. No severe urographic abnormalities were undetected by the comprehensive renal scintillation procedure. Only 1.4 per cent of renal units had greater than minimal pyelocaliectasis or ureterectasis in the presence of a normal radionuclide examination. A relatively large number of abnormalities were detected on the renal scintillation procedure when the excretory urogram was normal. Serial followup will be required to determine the significance of these findings but present data suggest that a comprehensive renal scintillation procedure and a plain film of the kidneys, ureters and bladder may be used for screening upper urinary tract abnormalities in lieu of an excretory urogram. This is particularly advantageous for the spinal cord injury population, since there have been no toxic or allergic reactions reported, no bowel preparation or dehydration is required and there is relatively low radiation exposure.

The dilated non-obstructed renal pelvis

This paper discusses 28 patients with renal pelvic dilatation in whom obstruction was excluded by excretion urography and diuresis renography. The clinical presentation and progress of the patients over a follow-up period of 1 to 5 years are presented. One patient required pyeloplasty, one developed 2 asymptomatic pelvic calculi and one showed some deterioration in function on the affected side. The remaining 25 patients remain well and their follow-up renograms show satisfactory renal function and excretion. Before the advent of objective means of assessing renal function and urodynamics, these patients would probably have been subjected to pyeloplasty. The present study confirms that the correct management of the dilated non-obstructed renal pelvis is conservative.

Diuretic radionuclide renography and scintigraphy in the differential diagnosis of hydroureteronephrosis

Conventional radionuclide renography has been modified to include a pharmacologic intervention by administration of intravenous furosemide. The procedure is applied in patients with hydroureteronephrosis to distinguish dilated, nonobstructed systems from those with significant mechanical obstruction. Diagnostic patterns are derived from computer-generated time-activity histograms that depict the accumulation of radiotracer prior to diuresis and in response to diuresis. In dilated, nonobstructed systems, increased urine flow following diuresis causes a decline or "washour" of activity. In significantly obstructed systems, there is a failure of tracer activity to decrease in response to diuresis. The procedure is applied most commonly in suspected ureteropelvic junction and ureterovesical junction obstruction. The significance of residual urinary tract dilatation following corrective surgery also can be readily assessed. The major current limitation to the technique is poor renal function with inadequate response of urine flow to diuresis.

99mTechnetium penicillamine scans: an index of differential renal function

The relative renal accumulation of 99mtechnetium penicillamine was evaluated as an index of differential renal function. Regions of interest were assigned over each kidney with a computer and the renal uptake of 99mtechnetium penicillamine was determined. A simple background correction was made by subtracting the renal activity at 10 minutes from that at 25 minutes. The percentage of 99mtechnetium penicillamine accumulation in the left kidney was correlated with the percentage of the total effective renal plasma flow to the left kidney. Effective renal plasma flow was determined after the intravenous injection of 131 I hippuran using a highly sophisticated computerized technique that has been validated in patients by comparison with traditional split renal function studies. The correlation coefficient between the 2 measurements was 0.97. In addition to its use as an index of differential effective renal plasma flow 99mtechnetium penicillamine is an excellent cortical imaging agent and the relative distribution of 99mtechnetium penicillamine between the 2 kidneys and within a single kidney can be assessed qualitatively by visual inspection of the scan.

Radionuclide kidney function evaluation in the management of urolithiasis

Renal and ureteral stones may cause asymmetrical renal damage that is not measured accurately by serum creatinine and blood urea nitrogen studies, excretory urography, nephrotomography and arteriography. We evaluated with a renal scintillation camera study 77 patients who had renal or ureteral calculi. The radionuclide procedure provided an accurate measure of total effective renal plasma flow and differential effective renal plasma flow. It had the additional advantages of being a non-invasive procedure, causing no allergic reactions, requiring no patient preparation and producing low radiation exposure.

A gamma camera method for quantitation of split renal function in children followed for vesicoureteric reflux

A method for quantitative estimation of split renal function using a computerized gamma camera system is described. 42 children and adolescents with existing or preexisting vesicoureteric reflux and recurrent urinary tract infection were investigated. Total renal clearance of DTPA was calculated with a disappearance curve derived from the largest extrarenal area in the field of view of a gamma camera with diverging collimator. Split renal function was estimated with the slopes of second phase renograms. The plasma disappearance clearance of DTPA, calculated using one compartment model with two late blood samples, gave similar results with the clearance estimated from the body disappearance curves. The proportional planimetric renal parenchymal areas had good correlation with the split clearance estimated from renogram slopes. The method offers data on renal function and urinary tract dynamics which is very valuable in the follow-up of children with recurrent urinary tract infection and vesicoureteric reflux.

Estimating relative renal function

Radionuclide measurements of relative renal function have been made using conventional dual-probe renography, computer assisted triple-probe renography, rectilinear kidney scanning and computer assisted gamma camera renography and kidney scanning. The relative area of each kidney from the excretory urogram also has been used to measure relative function. The best correlation between renography and kidney scanning was obtained with the gamma camera computer system. The relative function of each kidney was obtained by outlining regions of interest that corresponded closely to the renal images and subtracting the blood and tissue background activity, using a special background region. Triple-probe renography, using computer assisted blood background subtraction, provides another reliable indicator of relative function, which is considerably more accurate than conventional dual-probe renography. Relative renal function also may be determined, but with less precision, from the relative counts in a rectilinear kidney scan, from the relative scan areas and from the relative areas found on excretory urography. Both relative area methods are less reliable in the presence of outflow tract obstruction, renal tumors and renal cysts.

131I hippuran quantitative scintillation camera studies in the evaluation and management of vesicoureteral reflux

A study was made of 136 patients with vesicoureteral reflux with the conventional radiologic modalities of voiding cystourethrography and IVP. In addition, a 30-minute quantitative scintillation camera study was used. Comparison of these studies indicates that most periodic re-evaluations with IVP can be eliminated in favor of the scintillation study with its markedly reduced radiation dosage and lack of allergic type reactions. Unfortunately, as the quantitative scintillation camera study has been performed in these patients, it has been impossible to diagnose the presence of vesicoureteral reflux. Therefore, voiding cystourethrography or direct radionuclide cystography must be repeated at some time to determine if conservative management has been successful. The benefit of the routine use of the quantitative scintillation camera study in the early postoperative period seems to be strongly supported even by the small group of patients studied.