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

The ability of [¹²³I]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) using conventional planar imaging and assessed the contribution of [¹²³I]MIBG single-photon emission computed tomography (SPECT)-CT to the diagnosis of neurological diseases.

Seventy-two patients with neurological diseases were consecutively assessed using early and delayed [¹²³I]MIBG SPECT-CT and planar imaging. Left ventricles were manually segmented in early and delayed SPECT-CT images, then the 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 WRs defined by linear regression and that of normal planar WRs derived from a database were compared with neurological diagnoses of the patients. We assigned the patients to groups according to clinical diagnoses as 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.

We found significant correlations between SPECT-CT SUV_mean and planar HMR on early and delayed images (R² = 0.69 and 0.82, p < 0.0001) and between SPECT-CT and planar WRs (R² = 0.79, p < 0.0001). A threshold of 31% for SPECT-CT WR based on linear regression resulted in agreement between planar and SPECT-CT WR 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.

Absolute heart counts and SUV_mean determined using [¹²³I]MIBG SPECT-CT correlated with findings of conventional planar images in patients with neurological diseases. Three-dimensional quantitation with [¹²³I]MIBG SPECT-CT imaging might differentiate patients with PSP and MSA from controls.