Fully automated aortic diameter measurements on SPECT/CT attenuation maps in patients undergoing myocardial perfusion imaging
Authors: Shanbhag A , Michalowska A N N A , Zhang W E N H A O , Miller R J H , Lemley M A R K , Einstein A N D R E W , Liang J O A N N A , Builoff V A L E R I , Berman D A N I E L , Dey D A M I N I , Slomka P I O T R 
Published: June 2024

Abstract

Background
SPECT/CT integrates functional nuclear medicine imaging with anatomic CT characteristics. Aortic diameter provides important information when increased, indicating patients at higher risk of aortic dissection or rupture, and is routinely evaluated on CT scans but rarely on CT attenuation correction (CTAC) maps from SPECT/CT.

Purpose
We aimed to develop a deep learning (DL) method for fully automatic aortic diameter measurements on CTAC in patients undergoing SPECT/CT myocardial perfusion imaging (MPI).

Methods
Figure 1 shows the study design. We included CTAC from patients undergoing SPECT/CT MPI from 2 sites participating in the REFINE SPECT registry. An open-source multi-structure CT segmentation was used to segment the aorta, pulmonary artery (PA), and 3 thoracic vertebrae (Th4-Th6). The diameter of the ascending (Asc) and descending (Desc) aorta was measured automatically at each slice (on average 7 slices) at the level of the PA bifurcation (Th4-Th6). The median value of all obtained measurements of the diameter of the Asc and Desc aorta was used in further analysis. The abnormal diameter of the Asc aorta was defined as an aortic diameter &gt;40 mm whereas the abnormal diameter of the Desc aorta &gt;30 mm. Abnormal myocardial perfusion was defined as total perfusion deficit (TPD) &gt;5%.

Results
In total 4,589 patients were included, of whom 2,596 (56.6%) were male, and the median age was 66.0 (interquartile range [IQR] 57.0-74.0). During the median 3.6 years (2.0-5.0) follow-up, 352 (7.7%) patients died. The median Asc aorta diameter was 36.4 mm (33.6-39.4), whereas the median Desc aorta diameter was 30.8 mm (28.6-33.3). Patients with abnormal Asc and Desc aortic diameter were at higher risk of death compared to subjects with normal aortic diameter (Asc aorta - unadjusted hazard ratio [HR] 1.37, 95% CI 1.08-1.74, p=0.01; Desc aorta – unadjusted HR 1.9, 95% CI 1.51-2.40, p&lt;0.001) (Figure 2). Abnormal TPD was present in 2,302 (50.2%) patients. Patients with normal TPD and abnormal Asc aortic diameter were at higher risk of death compared to patients with normal TPD and normal Asc aorta diameter (unadjusted HR 1.26, 95% CI 0.83-1.90, p=0.27). Subjects with normal TPD and abnormal Desc aorta diameter had an elevated risk of death compared to patients with abnormal TPD and normal Desc aorta diameter (unadjusted HR 2.10, 95% CI 1.43-3.08, p&lt;0.001). Patients with abnormal TPD and abnormal Asc aortic diameter were at higher risk of death compared to patients with abnormal TPD and normal Asc aorta diameter (unadjusted HR 1.35, 95% CI 1.00-1.81, p=0.04). Moreover, subjects with abnormal TPD and abnormal Desc aorta diameter had an elevated risk of death compared to patients with abnormal TPD and normal Desc aorta diameter (unadjusted HR 1.57, 95% CI 1.18-2.10, p&lt;0.001).

Conclusion
DL-based aortic diameter measurements on CTAC in patients undergoing SPECT/CT MPI can help identify patients at higher risk of death due to abnormal aortic diameter.