Optimization of the uptake method for estimating renal clearance of 99mTc mercaptoacetyltriglycine

Measurement of Renal Depth in Dynamic Renal Scintigraphy Using Ultralow-Dose CT

PURPOSE

Renal depths predicted using predefined formulas are commonly used for camera-based evaluation of renal function. We investigated the feasibility and utility of renal depth measurement using ultralow-dose CT images acquired in conjunction with dynamic renal scintigraphy.

METHODS

Dynamic renal scintigraphy with Tc-MAG3 was performed in 117 patients (225 kidneys) using a SPECT/CT scanner, and ultralow-dose CT (estimated effective dose of 0.17 mSv) was performed during free breathing immediately before tracer injection. The clarity of the renal contour on the CT images was evaluated visually. The renal depths were measured by 2 methods and compared with depths predicted by 2 previously reported methods. The accuracy of camera-based clearance using predicted and measured depths was evaluated using a single-sample method as a standard.

RESULTS

The clarity of the renal contour was poor in 18 of 225 kidneys, and 12 of 117 patients were considered ineligible for depth measurement. The measurement for eligible patients showed excellent intraobserver and interobserver repeatabilities. Although mean depths were similar among the 2 CT measurement methods and 2 prediction methods, absolute differences of more than 1 cm were observed in approximately 20% of kidneys between CT measurement and prediction. CT measurement of renal depth failed to improve the accuracy of camera-based clearance evaluation.

CONCLUSION

Ultralow-dose CT allowed measurement of renal depth in most patients. Substantial differences in renal depth between prediction and CT measurement indicated potential usefulness of CT measurement, although no actual improvement in the accuracy of clearance estimation was demonstrated in this study.

Estimation of Tc-99m MAG3 clearance using camera-based methods without blood sampling

PURPOSE

To establish camera-based methods for estimating Tc-99m mercaptoacetyltriglycine (MAG3) clearance without blood sampling.

MATERIALS AND METHODS

The results of renal scintigraphy with Tc-99m MAG3 obtained from 160 patients were analyzed retrospectively. Eight renogram parameters were calculated for each patient based on the area under the renogram (area method) and slope of the renogram (slope method) using different periods for analysis (1-2 and 1-2.5 minutes for the area method; 0.5-1.5 and 0.5-2 minutes for the slope method) and different backgrounds for subtraction (perirenal and subrenal backgrounds). The 8 parameters were then correlated with MAG3 clearance measured by the single-sample methods proposed by Russell et al and Bubeck et al to determine the equation for the conversion of renogram parameters to clearance.

RESULTS

All 8 renogram parameters were highly correlated with clearance measured by the single-sample methods, and the obtained equations enabled the estimation of clearance from image data. Selection between the area and slope methods, between different periods for analysis, or between perirenal and subrenal backgrounds did not cause large differences in the estimation.

CONCLUSION

The camera-based methods determined in the present study allow the estimation of MAG3 clearance with acceptable accuracy.