Purpose: No data are yet available in the literature concerning 3-D [(123)I]-meta-iodobenzylguanidine ([(123)I]-MIBG) kinetics in vivo. In this study we investigated the feasibility of dynamic 3-D [(123)I]-MIBG kinetic analysis using a CZT ultrafast camera.
Methods: The study group comprised 16 patients consecutively scheduled for [(123)I]-MIBG cardiac scintigraphy for clinical purpose who were studied using a CZT camera (NM530c, GE). Dynamic acquisition in list mode was simultaneously started with a bolus injection of the radiotracer (185-370 MBq) for an overall duration of 900 s. A temporal series of 3-D volumes was reconstructed from the first 150 s of dynamic acquisition with a temporal resolution of 5 s. A summed cardiac image was also reconstructed to serve as reference for blood pool (BP) and left ventricle (LV) wall identification. BP and LV volumes of interest (VOIs) were manually drawn to cover the whole heart and automatically reported on the reframed volumes. Time-activity curves (TACs) for the BP and LV were extracted by averaging the signal intensity in the respective VOI in each time frame. BP TACs were fitted to a gamma variate model while LV TACs were fitted to a bicompartmental model.
Results: TAC analysis was feasible in all patients with good interobserver reproducibility. BP TACs were well described by a gamma variate model as they represent the first pass of the tracer. The first compartment of LV TACs corresponded to contamination spillover of the LV signal from the BP signal. The LV second compartment characterized the uptake of the tracer in the myocardium quantified in terms of maximum signal intensity value (6.95 ± 2.76 counts/mm(3)/s(2)), maximum up-slope value (0.36 ± 0.15 counts/mm(3)/s) and normalized washout of the signal value (7.0 ± 0.6 %).
Conclusion: Using CZT technology and dynamic 3-D acquisition, analysis of [(123)I]-MIBG radiotracer kinetics in vivo is feasible and may provide pathophysiological information in addition to that available with standard planar and SPECT imaging.