Abstract
3371
Introduction: <InvalidTag charset="UTF-8" />For 123I-metaiodobenzylguanidine (MIBG) imaging, heart-to-mediastinum ratio (HMR) and washout rate (WR) using planar images have been common indicators of sympathetic nervous activity. However, single-photon emission computed tomography (SPECT) generates three-dimensional images, which are potentially useful to discriminate myocardial activity from overlapped organs and background activities. Since the three-dimensional method for absolute quantitation has not been established in 123I-MIBG study, this study aimed to calculate absolute heart counts and standardized uptake value (SUV) using SPECT/computed tomography (CT) and to compare the values with conventional planar image-based quantitation.
Methods: We assessed 72 consecutive patients (male/female, n = 31 / 41; average age, 66.7 ± 12.3; range, 35-88 years; weight 59.5 ± 18.4 kg; range, 32-126 kg) with neurological and cardiac diseases, including Parkinson’s syndrome (PS), dementia with Lewy bodies (DLB), Parkinson’s disease (PD), chronic heart failure, and familial amyloid polyneuropathy. All patients were assessed by early and late 123I-MIBG planar and SPECT/CT imaging. All acquisitions were performed with Symbia Intevo and Symbia Intevo Bold SPECT/CT (Siemens Healthcare) with medium-energy collimator. After the patients received an intravenous injection of 123I-MIBG (111 MBq), images were obtained at 15–20 (early phase) and 180–240 (late phase) min. The planar images were acquired for 5 min under conditions of a 256×256 matrix, 2.4 mm/pixel, and zoom factor 1.0. The SPECT images were acquired for 30 s per view under conditions of a 128×128 matrix, 4.8 mm/pixel, zoom factor 1.0, 60 projections, 360° circular orbit, and rotation radius 24 cm. The SPECT data were reconstructed using an ordered subset conjugate gradient minimizer (OSCGM). Subsequent to the SPECT acquisition, a low-dose CT scan was acquired for attenuation correction. For planar images, the early and late HMR and WR were calculated using smartMIBG, a semiautomated ROI setting software developed under collaboration with FUJIFILM Toyama Chemical Co. Ltd., Tokyo, Japan. For SPECT/CT imaging, three-dimensional heart segmentation was manually performed on early and late SPECT/CT images, and the boundary of the heart was determined with SPECT, X-ray CT, and fused images. Then, the early and late mean standardized uptake values (early and late SUVmean) derived from SPECT/CT were compared with planar HMR. The WR in SPECT/CT images (SPECT WR) was calculated using early and late SUVmean and compared with the planar WR. All patients were classified into four groups based on clinical diagnoses of neurological and cardiac diseases: control, PS, PD and DLB, and other groups. Comparison among control, PS, and PD/DLB groups with each SPECT late SUVmean and planar late HMR were performed.
Results: <InvalidTag charset="UTF-8" />The SPECT SUVmean significantly correlated with the planar HMR in all patients (SPECT SUVmean = -1.17 + 1.70 × planar HMR; R2 = 0.63, p < 0.0001). Correlations were also significant between SPECT WR and planar WR (SPECT WR = 0.06 + 0.73 × planar WR; R2 = 0.79, p < 0.0001). Among three groups, which were comprised of the control (n=18), PS (n=22), and PD/DLB (n=7), SPECT late SUVmean and planar late HMR were lower in PD/DLB groups than the control group and PS group (p < 0.0001 and p < 0.0001, respectively). Although the control and PS groups did not differ significantly with planar late HMR (p = 0.21), significant difference was observed between the control and PS groups when the SPECT late SUVmean was utilized (p = 0.004).
Conclusions: <InvalidTag charset="UTF-8" />Three-dimensional absolute quantitation of sympathetic nervous activity is feasible using 123I-MIBG SPECT/CT imaging and significantly correlated with conventional quantitation of planar images in patients with neurological and cardiac diseases, which might be a new method to quantify the cardiac sympathetic nerve activity.