Maximizing the sensitivity of the indirect radionuclide cystogram: a retrospective audit.

BACKGROUND: The indirect radionuclide cystogram (IRC) has generally been reported as being less sensitive for detecting vesico-ureteric reflux (VUR) than the micturating cystourethrogram (MCUG), so we modified it in an attempt to increase its sensitivity. METHODS: We altered our routine IRC protocol by including the data obtained during failed voids, adding extra imaging sequences at intervals during bladder filling, and by using simple mathematical criteria to determine if VUR was present when visual imaging results were equivocal. We then retrospectively compared the VUR detection rates using the standard and modified techniques. RESULTS: We assessed 707 renal units in 356 children over 3 years. We identified 91 cases of VUR using standard methodology, and 134 (47% more) with the modified technique. Of the extra 43 cases detected, 11 were noted during failed voids, ten were seen within a filling sequence, and 22 were inferred because the renal pelvic activity increased during an interval between two imaging sequences, while the bladder was filling. Mathematical evaluation was helpful in the 39 cases where the increase in activity due to VUR was ≤6 standard deviations greater than the level of background variation in activity. CONCLUSIONS: Additional imaging and mathematical assessment can significantly increase the sensitivity of the IRC for detecting VUR, possibly to equal that of the MCUG.

A comparison of the renal handling of 99Tcm-DTPA and 99Tcm-MAG3 in hypertensive patients using an uptake technique.

The renal uptake and outflow of 99Tcm-DTPA and 99Tcm-MAG3 were compared by analysing renal studies performed in two different departments, but with analysis techniques and computer programs using algorithms that were almost identical. Comparison was performed by a retrospective review of results from patients who were referred for renal investigations because of hypertension but who had apparently normal kidneys. The analysis of tracer outflow rates in the form of whole-kidney transit times and renal cortical transit times showed no significant difference between the two tracers. The fractional uptake rate of tracer for each patient (both kidneys) indicated that MAG3 was extracted from the blood 3.3 times faster than DTPA in patients aged 20-69 years, with a lower ratio above the age of 70. When used to measure relative renal function, there was no overall difference between the two tracers. The fractional uptake rates were also converted to flow rates, producing values of 95.8 +/- 28.0 ml.min(-1).1.73 m-2 for DTPA and 320 +/- 75 ml.min(-1).1.73 m-2 for MAG3, in hypertensive patients aged 20-40 years. These values showed a good correlation with other published GFR and MAG3 clearance rates (obtained using blood sampling methods) in normal patients of similar ages.

Assessment of various parameters in the estimation of differential renal function using technetium-99m mercaptoacetyltriglycine.

Differential renal function (DRF) is an important parameter that should be assessed from virtually every dynamic renogram. With the introduction of technetium-99m mercaptoacetyltriglycine (99mTc-MAG3), a tracer with a high renal extraction, the estimation of DRF might hopefully become accurate and reproducible both between observers in the same institution and also between institutions. The aim of this study was to assess the effect of different parameters on the estimation of DRF. To this end we investigated two groups of children: group A, comprising 35 children with a single kidney (27 of whom had poor renal function), and group B, comprising 20 children with two kidneys and normal global function who also had an associated 99mTc-dimercaptosuccinic acid scan (99mTc-DMSA). The variables assessed for their effect on the estimation of DRF were: different operators, the choice of renal regions of interest (ROIs), the applied background subtraction, and six different techniques for analysis of the renogram. The six techniques were based on: linear regression of the slopes in the Rutland-Patlak plot, matrix deconvolution, differential method, integral method, linear regression of the slope of the renograms, and the area under the curve of the renogram. The estimation of DRF was less dependent upon both observer and method in patients with two normally functioning kidneys than in patients with a single kidney. The inter-observer comparison among children in either group was not dependent on either ROI or background subtraction. However, in patients with poor renal function the method of choice for the estimation of DRF was dependent on background subtraction, though not ROI. In children with two kidneys and normal renal function, the estimation of DRF from the 24 techniques gave similar results. Methods that produced DRF values closest to expected results, from either group of children, were the Rutland-Patlak plot and matrix deconvolution methods.

Prediction of urinary excretion of technetium-99m-MAG3.

UNLABELLED: The urinary excretion of 99mTc-mercaptotriacetylglycine (MAG3), like that of 131I-orthoiodohippurate (OIH), can be used to identify acute renal transplant rejection and measure its severity. This parameter is often quantitated as the excretory index (observed excretion/predicted excretion). A new method for predicting the urinary excretion of 99mTc-MAG3 is presented. METHODS: The expected excretion was calculated from multisample plasma time-activity curves in 122 subjects, with correction for the first pass of the initial bolus. The resulting formula was tested prospectively against actual urine measurements in an additional 466 subjects. RESULTS: Least-squares fitting led to the following equation: Predicted excretion = 0.79(1-exp(-0.0066CMAG3), with residual s.d. 0.06, where CMAG3 is MAG3 clearance in ml/min and the predicted excretion is expressed as a fraction of the administered dose. Tested prospectively in the additional 466 subjects, the s.d. was 0.09. CONCLUSION: A new formula to predict the urinary excretion of 99mTc-MAG3 has been developed and prospectively validated. Based on our data, the normal range for the excretory index using MAG3 is the same as that of 131I-OIH, 0.8-1.2.