Study population and design
Fifty consecutive patients who underwent CCTA for suspected or known coronary artery disease between January and April 2022 were prospectively enrolled at Iwate Medical University Hospital. Our exclusion criteria were renal insufficiency (estimated glomerular filtration rate < 30 mL/min per 1.73 m2), contrast agent allergy, history of bypass grafting, and potential pregnancy. Written informed consent was obtained from all participants, as approved by the institution’s human research committee.
Ct Scanning
CT scans were performed using a 320-detector row CT scanner (Aquilion ONE PRISM Edition, Canon Medical Systems, Otawara, Japan). All patients were administered nitroglycerin. Patients with a heart rate of 65 bpm were administered oral beta-blockers 60 min before the CCTA scan based on the Society of Cardiovascular Computed Tomography guidelines [8, 9].
Coronary calcium scoring was performed using a prospective electrocardiogram (ECG) gating axial scan at a 75% RR interval, with 120 kV tube voltage and a 300-mA tube current. We delivered 25.9 mgI/kg/s of nonionic contrast material (iopamidol [Iopamiron 370, Bayer, Osaka, Japan]) at a 10-s fixed duration, followed by a 35-mL saline flush administered using a 20-G intravenous catheter. The scan parameters were collimation of 320 × 0.5 mm; rotation time, 0.275 s; z-coverage, 120–160 mm; tube voltage, 100 or 120 kV; and tube current, 180–750 mA. Prospective ECG gating scan with an acquisition window of 35–80% or 65–80% of the RR interval was used for patients with a heart rate of > 65 or ≤ 65 bpm, respectively. Retrospective ECG gating scan was used for patients with arrhythmia or those who could not sufficiently hold their breath. Experienced cardiovascular CT technologists determined the optimal stationary cardiac phase with minimum motion-free datasets. The dose length product was recorded for each participant, and the corresponding effective radiation dose was calculated using a standard conversion factor of 0.014 mSv/mGy cm for chest CT [10]. Axial images were reconstructed with 0.5-mm slice thickness and reconstruction interval. The image reconstruction field of view and the matrix size were 160–200 mm and 512 × 512, respectively. All images were reconstructed using the SR-DLR (PIQE) and MBIR algorithm (FIRST, Canon Medical Systems Corp.).
Image Interpretation
The image datasets were transferred to an off-line workstation, processed using commercially available software (Ziostation2, Ziosoft Inc., Tokyo, Japan) and two radiologists (M.O. and K.Y.) with 5 and 25 years of experience, respectively, in cardiovascular imaging performed all measurements. The readers were blinded to the clinical information and reconstruction method. In case of data analysis disagreed, a final decision was reached by consensus. The degree of coronary stenosis was graded as minimal (< 25%), mild (25–49%), moderate (50–69%), and severe (70–99%) [11].
The overall image quality of each coronary artery segment was rated based on a four-point rating score for each coronary artery segment (4, excellent [minimal or no noise-related blurring and diagnostic information sufficient); 3, good [some noise-related blurring and diagnostic information acceptable]; 2, fair [marked noise-related blurring and diagnostic information limited]; and 1, poor [blurry and diagnostic information impaired]) [12].
For SR-DLR and MBIR images, the image noise was recorded as the standard deviation (SD) of the attenuation value in a circular region of interest (ROI) placed in the ascending aorta, left atrium, and septal wall of the ventricle. Then, signal-to-noise ratio (SNR) was calculated as signal/noise in the proximal right coronary artery and left main trunk [6]. The contrast-to-noise ratio (CNR) was calculated as follows: (mean vessel lumen signal − mean perivascular fat signal)/image noise in the ascending aorta [13, 14]. ROI measurements were performed by two radiologists on axial images, carefully preventing calcifications, plaques, and stenosis.
In-stent Lumen Assessability And Quantitative Stent Analysis
Stents were considered assessable with the absence of partial volume effects by stent struts, beam hardening, motion artifacts, calcification, or low CNR and when the lumen within the stent was clearly visible [4, 15]. Figure 1 shows the calculation methods of lumen visibility measurements using the average attenuation profile in the axial plane [4, 15]. First, the stent proximal and distal edges on the curved planar reformation (CPR) image were determined, with the first, second, and third quartiles as calculated points. Second, after determining the center of the stent on the cross-sectional image (Fig. 1a and b), attenuation profiles were calculated, and the full width at half maximum of the lumen (FWHM-lumen) and full width at half maximum of the strut (FWHM-stent) were measured (Fig. 1c and d).
Statistical analysis
Statistical analyses were performed using IBM® SPSS® 28.0.1 (IBM Corporation., Armonk, NY, USA). Continuous measurements are expressed as mean ± SD for normally distributed variables or median (interquartile range [IQR], 25th–75th percentile) for nonparametric data and compared using Student’s t-test or Mann–Whitney U-test as appropriate. Categorical variables are expressed as numbers and percentages. p-value of < 0.05 was considered statistically significant. The interobserver agreement between two radiologists regarding the qualitative evaluation was evaluated using the Cohen kappa κ coefficient. A κ value of more than 0.81 corresponded to excellent interobserver agreement, while values of 0.61–0.80 corresponded to good agreement.