Comparison of low energy and medium energy collimators in the quantitative assessment of 123I-MIBG cardiac sympathetic innervation imaging

Abstract

Abstract Funding Acknowledgements Type of funding sources: Public hospital(s). Main funding source(s): University Clinic Hospital of Valencia Aim The assessment of cardiac sympathetic innervation by 123I-metayodobenzylguanidine (123I-MIBG) has proved useful in patients with heart failure and neurodegenerative disorders. The standard quantification of global cardiac uptake is to obtain the heart to mediastinum (HM) ratio in planar images, while SPECT images provide better evaluation of regional extent of denervated areas. Although low energy (LE) collimator has been widely used in these patients, septal penetration of high-energy photons of 123I could affect image quality and quantification accuracy. We have compared in the same patients the effect of collimator type on image quality and quantitative assessment of HM ratio. Methods In a group of 14 patients (11 men, 57-77 y/o, 66.4 ± 5.6) submitted for cardiac sympathetic study, we obtained successive planar anterior chest images 4h after the IV administration of 10 mCi of 123I-MIBG with a low-energy-high-resolution (LEHR) and a medium-energy (ME) collimators. Images were obtained with the same gammacamera Brightview Philips for 10 min on 256x256 matrix, with 159 Kev photopeak and unchanged patient position. For quantification of HM ratio, we use in each patient the same manual heart ROI and rectangular upper mediastinum ROI in the two acquired images to obtain the corresponding HM ratio. Results The image quality was better in all the patients with ME collimator acquisition than with LEHR collimator acquisition, and the HM ratio showed higher values with ME: 1.65-2.61 (mean 2.15 ± 0.28) than with LEHR: 1.27-1.85 (mean: 1.51 ± 0.18) with a mean difference of 0.64 ± 0.15 (0.38-0.88) between ME and LEHR and a mean ratio LEHR/ME of 0.70 ± 0.04 (0.64-0.79). In 9 patients with HM ratio ≤ 1.60 obtained from LEHR collimator acquisition, the mean difference with HM ratio obtained with ME collimator was 0.61 ± 0.12 and mean ratio LEHR/ME was 0.69 ± 0.03 and in 5 patients with HM ratio(LEHR) >1.60, mean difference with HM ratio(ME) was 0.69 ± 0.19 and mean ratio LEHR/ME was 0.71 ± 0.02. Conclusion Use of a ME collimator provides better image quality than LEHR collimator in planar images and higher values of HM ratio, providing a more accurate quantification of cardiac uptake in the patients submitted for evaluation of cardiac sympathetic innervation by 123I-MIBG, and could also improve the evaluation of regional impairment and extent of denervated areas by SPECT.