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Evaluation of Renal Function with ^99mTc-MAG3 Using Semiautomated Regions of Interest

Department of Radiology, Institute of Medical Science, University of Tokyo, Tokyo; Department of Radiology, Nishi-Niigata Central National Hospital, Niigata; and Department of Radiology and Second Department of Internal Medicine, Faculty of Medicine, University of Tokyo, Tokyo, Japan

The need to draw regions of interest (ROIs) manually may reduce the convenience and reliability of estimating renal function from renal scintigraphy. We developed a semiautomated method to define ROIs for renal scintigraphy with ^99mTc-mercaptoacetyltriglycine (MAG3) and evaluated the clinical applicability of the method to the estimation of renal function by camera-based methods. Methods: Dynamic renal scintigraphy with ^99mTc-MAG3 was performed on 21 patients. An operator placed a large rectangular ROI over each kidney, a circular ROI within the liver, and a rectangular ROI between the kidneys. Using these ROIs, semiautomated renal ROIs were determined on the basis of the temporal changes in counts, in addition to the absolute counts, and a subrenal background ROI was automatically assigned for each renal ROI. Background-subtracted renograms were generated using these renal and subrenal ROIs, and renogram parameters were derived from the slope of the renogram and the area under the renogram. Clearance was calculated using the renogram parameters and equations determined previously with manual ROIs and correlated with clearance measured by a single-sample method. The relative function of the right kidney determined by the semiautomated method was compared with that determined by the manual method. Data processing was performed independently by another operator to assess interoperator reproducibility. Results: ROIs defined by the semiautomated method were visually judged to be acceptable for clinical use in all patients with a wide range of renal function. Clearance was successfully predicted with the semiautomated ROIs (r = 0.968 using the slope of the renogram; r = 0.934 using the area under the renogram), and relative function calculated with the semiautomated ROIs was almost identical to that calculated with manual ROIs. There was almost complete concordance in absolute and relative function between the two operators. Conclusion: The semiautomated method can define ROIs for ^99mTc-MAG3 renal scintigraphy with limited operator intervention. Camera-based methods using the semiautomated ROIs allow estimation of renal function with high accuracy and little interoperator variability and are suggested to be suitable for clinical use.

Key Words: renal function • ^99mTc-mercaptoacetyltriglycine • region of interest • semiautomated technique • gamma camera

Received Dec. 28, 1999; revision accepted May 5, 2000.

For correspondence or reprints contact: Yusuke Inoue, MD, Department of Radiology, Institute of Medical Science, University of Tokyo, 4-6-1 Shirokanedai, Minato-ku, Tokyo 108-8639, Japan.