Objective: Assessing the relative function of each of the three kidneys using nuclear scintigraphy with standard planar imaging in patients having undergone kidney transplant is problematic because of the different photon-attenuation factors associated with native versus transplanted kidneys. To address this, we applied a correction for the attenuation of 140-keV photons based on measurements taken on cross-sectional anatomical images. We performed a validation of the method using single-photon emission computed tomography/computed tomography (SPECT/CT).
Methods: Abdominal CT scans of 13 patients who had undergone simultaneous liver-kidney transplants were examined for kidney depth. Ten of those patients had undergone Tc-99m-mercaptoacetyltriglycine (MAG3) renal scans, using a Philips Precedence SPECT/CT scanner by which abdominal CT and renal SPECT acquisition followed the planar scintigraphic renogram. Kidney depth at the level of the renal hilum was measured on the concurrently acquired CT images, and it was used to derive an attenuation correction factor (ACF) that was applied to the background-subtracted activity in the planar scintigraphic renogram.
Results: ACFs calculated from kidney depths ranged from 1.31 to 4.33. The ratio of ACFs for transplant to native kidneys ranged from 0.63 to 1.51, with an average of 0.90. Applying attenuation correction when calculating relative function increased the value of native kidney function by as much as 40%.
Conclusion: Attenuation correction through measurements taken on anatomical images, preferably obtained concurrently using a hybrid SPECT/CT scanner, should improve the accuracy of functional measurements in renal scintigraphy. This improved accuracy is clinically important in assessing the relative function of native and transplant kidneys in recipients of simultaneous liver-kidney transplants.
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