Document Type: Original Article
Research Institute for Nuclear Medicine, Tehran University of Medical Sciences, Tehran, Iran
Department of Medical Physics, Tarbiat Modarres University, Tehran, Iran
Background: Measurement of absolute or differential renal function using radiotracers plays an important role in the clinical management of various renal diseases. Gamma camera quantitative methods in approximation of renal clearance may potentially be as accurate as plasma clearance methods. However some critical factors such as kidney depth and background counts are still troublesome in the use of this technique. In this study the conjugate-view method along with some background correction techniques have been used for the measurement of renal activity in 99mTc-MAG3 renography. Transmission data were used for attenuation correction and the source volume was considered for accurate background subtraction. Material and methods: The study was performed in 35 adult patients referred to our department for conventional renography and ERPF calculation. Depending on the patient’s weight approximately 10-15 mCi 99mTc-MAG3 was injected in the form of a sharp bolus and 60 frames of 1 second followed by 174 frames of 10 seconds were acquired for each patient. Imaging was performed on a dual-head gamma camera (SOLUS; SunSpark10, ADAC Laboratories, Milpitas, CA). Anterior and posterior views were acquired simultaneously. A LEHR collimator was used to correct scatter for the emission and transmission images. Buijs factor was applied on background counts before background correction (Rutland-Patlak equation). Gamma camera clearance was calculated using renal uptake in 1-2, 1.5-2.5, 2-3 min. The same procedure was repeated for both renograms obtained from posterior projection and conjugate views. The plasma clearance was also directly calculated by three blood samples obtained at 40, 80, 120 min after injection. Results: 99mTc-MAG3 clearances using direct sampling method were used as reference values and compared to the results obtained from the renograms. The maximum correlation was found between conjugate view clearance at 2-3 min (R=0.99, R²=0.98, SE=15). Conventional posterior view acquisition at the same time had showed less correlation (R=0.956, R²=0.914). Both gamma camera methods after vascular activity subtraction revealed worse correlation (R=0.717 to 0.812). Conclusion: Conjugate view clearance can be used for calculation of renal clearance with a very good approximation. However in the presence of overlapping organs (Liver and spleen) may interfere with the results. Further work needed on to find the best method of background subtraction.