A Study on the Comparison of Quantitative Evaluation of Uptake Ratio in 2D Planar and Auto Lung 3D Images Using SPECT/CT in Pulmonary Ventilation/Perfusion Scan

Purpose: The pulmonary ventilation/perfusion scan is used to detect pulmonary embolism before transplantation and to evaluate lung function after transplantation. Pulmonary scans can be performed using two methods: 2D planar imaging and 3D SPECT. In the case of 2D imaging, there are inherent limitations due to the overlap of anatomical lobes. Therefore, in this study, we aimed to compare the uptake ratio results between two methods: the traditional approach using 2D images to classify the lungs into three equal regions of interest (ROI) and the method using 3D SPECT/CT images with Siemens Syngo.via Auto Lung 3D's Auto Segment function. Materials & Methods: From May to September 2024, the study included 30 patients (aged 63.3±15.4 years, 10 males, 20 females) who underwent both 2D planar and 3D SPECT/CT pulmonary ventilation/perfusion scans on the one day protocol. Ventilation scans in both 2D and 3D were performed first, followed by perfusion scans in 2D and 3D. For the 2D images, rectangular ROIs were set for both the left and right lungs in the anterior and posterior views, and the geometric mean of the counts classified into three lobes was analyzed. For the 3D SPECT/CT images, the Auto Lung 3D function of the Siemens Syngo.via was used to analyze the counts classified into lobes (two in the left lung, three in the right lung) divided in three dimensions. A paired t-test was performed to compare the uptake ratio between the 2D and 3D images. Results: The uptake ratio for the left and right lungs, as well as for each lobe of the right lung, were analyzed using the ratio (%) of the geometric mean from 2D ventilation/perfusion planar images and the NM count (%) from 3D ventilation/perfusion scans. For the right lung (Rt. Total), the ventilation ratio was 56.8±3.2% in the 2D and 57.0±4.2% in the 3D and the perfusion ratio was 59.5±8.9% in the 2D and 60.3±10.6% in the 3D (denoted as Lobe/V or P/2D %/3D %). For the left lung (Lt. Total), the ventilation ratio was 43.1±3.2% in 2D and 42.9±4.2% in 3D, and the perfusion ratio was 40.4±11.4% in 2D and 39.6±12.4% in 3D. Statistical analysis showed no statistically significant differences in uptake ratio between 2D and 3D images for both Rt. Total and Lt. Total (P>0.05). For the right upper lobe, the ventilation ratio was 13.7±8.4% in 2D and 21.5±3.5% in 3D, and the perfusion ratio was 15.4±4.1% in 2D and 25.4±6.3% in 3D. For the right middle lobe, the ventilation ratio was 31.1±1.2% in 2D and 8.20±6.3% in 3D, and the perfusion ratio was 32.2±7.0% in 2D and 11.1±5.4% in 3D. For the right lower lobe, the ventilation ratio was 11.8±6.4% in 2D and 27.3±5.6% in 3D, and the perfusion ratio was 11.9±4.5% in 2D and 23.8±1.4% in 3D. Statistical analysis showed significant differences in uptake ratio between 2D and 3D images for all three lobes of the right lung (P<0.05). Conclusion: It is suggested that the 3D image analysis method, which considers anatomical structures, could replace the traditional 2D planar image analysis method. Additionally, 3D analysis, which provides a more detailed representation of the anatomical proportions of the lung lobes compared to the 2D method, may offer a more accurate evaluation not only for quantitative analysis but also for visual analysis. Therefore, it is considered that using SPECT could be more beneficial for precise evaluations.