Absolute quantitation of sympathetic nerve activity using 123I-metaiodobenzylguanidine SPECT-CT in neurology

Objective The ability of ¹²³ I- metaiodobenzylguanidine (MIBG) sympathetic nerve imaging with three-dimensional (3D) quantitation to clinically diagnose neurological disorders has not been evaluated. This study compared absolute heart counts calculated as mean standardized uptake values (SUV _mean ) with conventional planar image-based quantitation and assessed the contribution of ¹²³ I-MIBG single-photon emission computed tomography (SPECT)-CT to the diagnosis of neurological diseases. Methods Seventy-two patients with neurological diseases were consecutively assessed using early and delayed ¹²³ I-MIBG SPECT-CT and planar imaging. Left ventricles were manually segmented in both early and delayed SPECT-CT images, and SUV _mean and washout rates (WRs) were calculated. Heart-to-mediastinum ratios (HMRs) and WRs on planar images were conventionally computed. We investigated correlations between planar HMRs and SPECT-CT SUV _means and between WRs obtained from planar and SPECT-CT images. The cutoff for SPECT-CT WR was defined by linear regression together with normal values of planar WR from a database, and the classification was compared with neurological diagnoses of the patients. We classified the patients according to clinical diagnoses of neurological diseases as follows: controls (n = 6), multiple system atrophy (MSA, n = 7), progressive supranuclear palsy (PSP, n = 17), and Parkinson’s disease or dementia with Lewy bodies (PD/DLB, n = 19), then compared SPECT-CT and planar image parameters among them. Results We found significant correlations between SPECT-CT SUV _mean and planar HMR on early and delayed images (R ²  = 0.69 and 0.82, p < 0.0001) and between SPECT-CT and planar WRs (R ²  = 0.79, p < 0.0001). When the threshold was 31% based on linear regression for SPECT-CT WR, planar and SPECT-CT WR agreed in 67 (93.1%) of 72 patients. Compared with controls, early and delayed SUV _mean in patients with PSP and MSA tended more towards significance than planar HMR. This trend was similar for SPECT-CT WRs in patients with PSP. Conclusions Absolute heart counts and SUV _mean determined using ¹²³ I-MIBG SPECT-CT correlated with findings of conventional planar images in patients with neurological diseases. Three-dimensional quantitation with ¹²³ I-MIBG SPECT-CT imaging might differentiate patients with PSP and MSA from controls.