Comparing feasibility of different tube voltages and different concentrations of contrast medium in coronary CT angiography of overweight patients

Abstract

OBJECTIVES:

To compare image quality, radiation dose, and iodine intake of coronary computed tomography angiography (CCTA) acquired by wide-detector using different tube voltages and different concentrations of contrast medium (CM) for overweight patients.

MATERIALS AND METHODS:

A total of 150 overweight patients (body mass index≥25 kg/m²) who underwent CCTA are enrolled and divided into three groups according to scan protocols namely, group A (120 kVp, 370 mgI/ml CM); group B (100 kVp, 350 mgI/ml CM); and group C (80 kVp, 320 mgI/ml CM). The CT values, signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), and figure-of-merit (FOM) of all images are calculated. Images are subjectively assessed using a 5-point scale. In addition, the CT dose index volume (CTDIvol) and dose length product (DLP) of each patient are recorded. The effective radiation dose (ED) is also calculated. Above data are then statistically analyzed.

RESULTS:

The mean CT values, SNR, CNR, and subjective image quality of group A are significantly lower than those of groups B and C (P < 0.001), but there is no significant difference between groups B and C (P > 0.05). FOMs show a significantly increase trend from group A to C (P < 0.001). The ED values and total iodine intake in groups B and C are 30.34% and 68.53% and 10.22% and 16.85% lower than those in group A, respectively (P < 0.001).

CONCLUSION:

The lower tube voltage and lower concentration of CM based on wide-detector allows for significant reduction in iodine load and radiation dose in CCTA for overweight patients comparing to routine scan protocols. It also enhances signal intensity of CCTA and maintains image quality.

Keywords

Computed tomography angiography contrast medium radiation dosage image quality

Abbreviations

CCTA Coronary computed tomography angiography

CM Contrast medium

BMI Body Mass Index

CNR Contrast-to-noise ratio

SNR Signal-to-noise ratio

DLP Dose-length product

ED Effective dose

CAD Coronary artery disease

SD Standard deviation

ROI Regions of interest

FOM Figure-of-merit

CTDI_vol Volume CT dose index

1 Introduction

Obesity is one of the main independent risk factors for ailments such as hypertension and coronary artery disease [1, 2]. Overweight patients always have high body fat content and are more likely to have coronary atherosclerosis, which increases the incidence of CAD [3]. With the progress of CT technology, coronary CT angiography (CCTA) has been regarded as a first-line imaging method for stable coronary artery disease (CAD) and has been shown to significantly improve the detection rate of coronary heart disease [4 –6]. However, exposure to ionizing radiation and the potential nephrotoxicity of iodine contrast medium intake have attracted the attention of researchers [7 –9]. Compared with ordinary patients, overweight patients are easier to receive higher doses of ionizing radiation and iodine contrast medium (CM) during CCTA examination, which poses greater risks. Currently, technological innovations can reduce the amount of radiation dose and iodine intake in CCTA examination, including automated tube voltage selection [10], tube current modulation [11], iterative reconstruction [12], and other measures such as using high pitch [13], lowing concentration of CM [14], and using dual energy CT [15]. However, the tube voltage is proportional to the square of the X-ray dose [16]. Therefore, the radiation dose can be effectively reduced by using low tube voltage.

In addition, the settings of noise index is associated with the level of image noise, which is another way of tube current modification [4]. Lowing noise index can decrease image noise by increasing applied tube current, which affects radiation dose and image quality. Moreover, based on an ECG gating three-dimensional Smart mA modulation technique, the appropriate tube current could be used automatically according to the characteristics of the patient’s cardiac cycle in different cardiac phase. The peak of tube current arose in 40–80% of the R-R interval and the lower tube current was curried out in another cardiac phase.

The purpose of our study was to compare image quality, radiation dose, and iodine intake of CCTA acquired by wide-detector using different tube voltages and different concentrations of contrast medium for overweight patients and to investigate the feasibility of using low radiation dose with a low concentration contrast medium in CCTA examination of overweight patients while maintaining image quality.

2 Materials and methods

2.1 Patient population

This study was approved by our institutional review board, and written informed consent was obtained by all patients or their immediate family members including their parents, siblings, spouse, or children.

A total of 150 adult overweight patients (mean age: 57±11 years, range: 30–87 years; BMI: 28.34±2.60 kg/m², WHO defines overweight as a BMI greater than or equal to 25 kg/m²; 61 females and 89 males) who underwent CCTA examination in our hospital from June to September 2021 were prospectively enrolled and randomly divided into groups A, B, and C with 50 participants in each group (Table 1).

Table 1
Summary of patient characteristics

Groups Number of Age Gender BMI Heart rate

patients (year) (male/female) (kg/m²) (bpm)

A 50 57±11 23/17 28.66±2.45 64±14

B 50 57±11 26/24 28.24±2.77 66±12

C 50 55±11 30/20 28.10±2.60 65±13

χ²/H value 0.697 0.677 2.53 1.487

P value P > 0.05 P > 0.05 P > 0.05 P > 0.05

Groups	Number of	Age	Gender	BMI	Heart rate
A	50	57±11	23/17	28.66±2.45	64±14
B	50	57±11	26/24	28.24±2.77	66±12
C	50	55±11	30/20	28.10±2.60	65±13
χ²/H value		0.697	0.677	2.53	1.487
P value		P > 0.05	P > 0.05	P > 0.05	P > 0.05

Exclusion criteria are for the following factors: (1) pregnancy; (2) hypersensitivity to contrast medium; (3) failure of vital organs such as the heart, liver and kidneys; (4) metal implants that seriously affect the image quality in the scanning field.

2.2 CT protocol

2.2.1 Inspection equipment

A 16-cm wide-detector CT (Revolution CT, GE Healthcare, Waukesha, WI, USA) scanner and a CT workstation (AW 4.7, GE Healthcare, IL, USA) were used to acquire diagnostic images. A high-pressure double-cylinder syringe (Ulrich XD2001, Missouri, USA) was used for injection of contrast medium.

2.2.2 Scanning parameters and contrast medium protocol

Groups A, B, and C used 120 kVp, 100 kVp, and 80 kVp and were injected with iopamidol (370 mgI/ml), iohexol (350 mgI/ml), and Ioversol (320 mgI/ml), respectively. All patients underwent CCTA examination with prospective electrocardiogram gated mode, and the scanning range covered the heart from the trachea level of the trachea to 0.5 cm below the inferior border of the heart. The axial length ranged from 120 to 160 mm, according to the cardiac length of each patient. The other parameters that were the same for each group were as follows: a three-dimensional Smart mA modulation technique was used, the mA ranged from 60 to 700 mA, 0.28 s tube rotation time, noise index based on thickness of 2.5 mm was 9, 19.2 cm DFOV, matrix of 512×512. All images were reconstructed by an iterative reconstruction technique set at 50% before scanning and 70% after scanning, which can reduce the radiation dose and cut down the image noise.

A high-pressure syringe was used to inject the agent through the right median cubical vein. Total injection amount was 0.8 ml/kg. Different patients were injected with different quantity according to their body weight at a rate of 4.5 ml/s. The contrast injection was followed by a saline flush (30 mL) at the same rate. The timing of the scan was determined with smart prep technique, with a region of interest (10±2 mm²) placed on the center of the ascending aorta root at the level of the pulmonary artery bifurcation, and scan was started 2 seconds after the ROI reached the threshold of 280 Hounsfield units. In addition, while smart monitoring began and 8 seconds delay, patients were required to hold breath until scan ending.

2.3 Data analysis and reconstruction

Image raw data was transmitted to a GE AW4.7 workstation. CCTA image data were reconstructed with a slice thickness of 0.625 mm in axial plane and processed by cardiac intelligent analysis system in GE AW4.7 workstation, including surface reconstruction, maximum intensity projection, curved projection reformation, and volume reconstruction. All reconstruction images were combined with the original horizontal axis images to diagnose and assess the image quality.

2.4 Objective image quality evaluation

Objective image quality was quantitatively measured and analyzed on an AW4.7 workstation with a slice thickness of 0.625 mm on axial CCTA images. CT attenuation values and standard deviations (SD) were measured by placing regions of interest (ROI) of 1–20 mm² in the aortic root, proximal right coronary artery, left main artery, left anterior descending branch, left circumflex branch, and the same layer of the pericardial adipose tissue to calculate the signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) (Fig. 1). All ROIs of the vessels should avoid calcified blood vessel walls and artifacts as much as possible. SNR and CNR were calculated based on the following formula: SNR = mean CT attenuation of vessels/image noise; CNR = (mean CT attenuation of vessels - CT attenuation of the pericardium adipose tissue)/image noise; image noise = mean SD value of all vessels [17, 18].

Fig. 1

Example of identical ROI measurements simultaneously placed in axial CT images. The mean CT value (signal value) and standard deviation (noise value) of left main coronary artery were measured by ROI with area size of 1∼2 mm², and CT values (signal value) and standard deviation (noise value) of aortic root and pericardial fat were measured by ROI with area size of 20 mm² (A). The mean CT value (signal value) and standard deviation (noise value) of right coronary artery and left circumflex branch by ROI with area size of 1∼2 mm² (B).The mean CT value (signal value) and standard deviation (noise value) of left anterior descending branch by ROI with area size of 1∼2 mm² (C). ROI, regions of interest; CCTA, coronary CT angiography.

Figure-of-merit (FOM) calculation, which could reflect the contribution of radiation effective dose (ED) in the objective image quality computation, was performed to compare the CNR values acquired at different tube voltages. The formula used for FOM was FOM = CNR2/ED [19, 20].

2.5 Subjective image quality evaluation

All CCTA images were scored independently by two radiologists with more than 10 years of experience in CCTA diagnosis. They were blinded to the study protocol and personal identifier information. Image noise, image artifacts, vessel sharpness, and overall quality were evaluated using a 5-point Likert scale [21, 22]. The scoring criteria are presented in Table 2. The subjective score of the overall quality that was≥3, which corresponds to the clinical diagnostic standard.

Table 2
Grading score for subjective image quality in 5-point Likert scale

Score Image noise Image artifact Vessel sharpness Vessel calcification and stenosis Overall quality

5 Mininmal or no noise Exact anatomical structure, no artifact Excellent Sharpest visibility (4nd-oeder branches or higher) Excellent

4 Common or below-average noise The anatomical stucture is clear, slight artifacts Good Better than average visibility (3nd-order branches) Good

3 Average noise Identifiable anatomical structure, artifact Morderate Average visibility (2nd-order branches) Moderate, but sufficient for diagnosis

2 Above-average noise Unclear anatomical structure, obvious artifact Poor Suboptimal overall visibility (main or 1st order branches) Poor, diagnostic confidence substantially reduced

1 Unacceptable noise Unclear anatomical structure,serious artifact Nondiagnostic Unacceptable visibility (vessels not seen) Nondiagnostic

Score	Image noise	Image artifact	Vessel sharpness	Vessel calcification and stenosis	Overall quality
5	Mininmal or no noise	Exact anatomical structure, no artifact	Excellent	Sharpest visibility (4nd-oeder branches or higher)	Excellent
4	Common or below-average noise	The anatomical stucture is clear, slight artifacts	Good	Better than average visibility (3nd-order branches)	Good
3	Average noise	Identifiable anatomical structure, artifact	Morderate	Average visibility (2nd-order branches)	Moderate, but sufficient for diagnosis
2	Above-average noise	Unclear anatomical structure, obvious artifact	Poor	Suboptimal overall visibility (main or 1st order branches)	Poor, diagnostic confidence substantially reduced
1	Unacceptable noise	Unclear anatomical structure,serious artifact	Nondiagnostic	Unacceptable visibility (vessels not seen)	Nondiagnostic

2.6 Radiation dose and iodine intake

The volume CT dose index (CTDI_vol) and dose length product (DLP) values of all patients were recorded by the system after each CCTA examination. The ED received by patients was obtained by multiplying the DLP with the conversion coefficient (K = 0.014 mSv/mGy cm) [22].

The formula to calculate iodine intake was as follows: Iodine intake (g) = [weight of patients (kg)×0.8 ml/kg×the concentration of contrast medium (mgI/ml)]/1000.

2.7 Statistical analysis

SPSS software (SPSS v. 26.0, IBM Corp, Armonk, USA) was used for statistical analysis, and continuous variables were expressed as mean±SD. Kruskall-Wallis tests were performed to evaluate differences in demographic characteristics between the three groups, including age, BMI, and average heart rate. The chi-square test was performed to assess gender differences. One-way ANOVA was used to analyze the differences in DLP, ED, iodine intake, SNR, CNR, FOM, and the average subjective score between the three groups. Multiple comparisons were adjusted with either the least significant difference test if variances were equal or the Tamhane’s test if variances were unequal. Results with p < 0.05 were considered statistically significant. Kappa’s analysis was used to assess inter-observer reliability for subjective scores, and the κ values were defined as follows: poor agreement for 0–0.20; average agreement for 0.21–0.40; moderate agreement for 0.41–0.60; substantial agreement for 0.61–0.80; excellent agreement for 0.81–1.00.

3 Results

In this study, all 150 patients completed the CCTA examination successfully. The demographic data for all patients are summarized in Table 1. Age, gender, BMI, and average heart rate did not have a significant effect on results for the three groups (P > 0.05).

3.1 Objective image quality

The mean CT attenuation values, SNR, CNR, and FOM of the ascending aorta, left main trunk, left anterior descending branch, left circumflex branch, and proximal right coronary artery are summarized in Table 3. Statistical analysis showed the mean values of CT attenuation values, SNRs, and CNRs in the groups B and C were higher than those in group A (P < 0.001), but there was no significant difference in those values for groups B and C (P > 0.05); the FOM of group C was higher than that of groups A and B (P < 0.001) (Figs. 2 and 3).

Table 3
Objective image quality and subjective image quality

Groups Objective image quality Subjective

Average CT value (HU) SNR CNR FOM score

A 401.47±60.03^‡, * 22.11±3.86^‡, * 27.37±4.38^‡, * 95.89±39.19^‡, * 4.12±0.62^‡, *

B 553.59±86.89^† 27.74±4.87^† 33.03±5.20^† 197.63±71.74^†, * 4.47±0.64^†

C 599.11±126.17^† 26.07±5.14^† 31.17±5.17^† 386.13±136.15^†, ‡ 4.39±0.66^†

F value 81.294 19.302 17.091 127.985 4.111

P value P < 0.001 P < 0.001 P < 0.001 P < 0.001 P < 0.05

Groups	Objective image quality	Subjective
A	401.47±60.03^‡, *	22.11±3.86^‡, *	27.37±4.38^‡, *	95.89±39.19^‡, *	4.12±0.62^‡, *
B	553.59±86.89^†	27.74±4.87^†	33.03±5.20^†	197.63±71.74^†, *	4.47±0.64^†
C	599.11±126.17^†	26.07±5.14^†	31.17±5.17^†	386.13±136.15^†, ‡	4.39±0.66^†
F value	81.294	19.302	17.091	127.985	4.111
P value	P < 0.001	P < 0.001	P < 0.001	P < 0.001	P < 0.05

SNR, signal-to-noise ratio; CNR, contrast-to-noise ratio; FOM, figure-of-merit; CCTA: coronary CT angiography. †: Significantly different compared with group A. ‡: Significantly different compared with group B. *: Significantly different compared with group C.

Fig. 2

SNR, CNR, Iodine intake, and ED in different protocols. Graph showing the comparisons of SNR, CNR, Iodine intake, and ED among different scan protocols. Group A showed a lower SNR and CNR than did groups B and C (all P < 0.05) in all patients, whereas there was no statistically significant difference between groups B and C in either SNR (P = 0.074) or CNR (P = 0.061). There were significant differences in ED and iodine intake among groups A, B, and C. Compared with Group A, ED and iodine intake were reduced by 30.34% and 68.53% and 10.22% and 16.85% (P < 0.001) in groups B and C, respectively.

Fig. 3

CCTA image quality schematic diagram (VR, LAD, LCX and RCA). (A1-A4) A 46-year-old man (BMI = 27.26 kg/m²) from group A scanning protocol (120 kVp + Iopromide 370 mgI/ml); the coronary arteries were shown clearly with sharp edges and no motion artifacts, and average CT value was 470.50 HU, the subjective scores of images was 4.00; (B1-B4) A 58-year-old woman (BMI = 29.30 kg/m²) from group B scanning protocol (100 kVp + iohexol 350 mgI/ml); the coronary arteries were shown clearly with sharp edges and no motion artifacts, and average CT value was 608.18 HU, the subjective scores of images was 5.00; (C1-C4) A 62-year-old woman (BMI = 26.35 kg/m2) from group C scanning protocol (80 kVp + iofoverol 320 mgI/ml); the coronary arteries were shown clearly with sharp edges and no motion artifacts, and average CT value was 658.02 HU, the subjective scores of images was 5.00. Statistical analysis showed that the mean CT value and subjective image quality scores of groups B and C were higher than those of group A (P < 0.05), but there was no significant difference between groups B C (P > 0.05).

3.2 Subjective image quality

All CCTA images for the three groups assessed by the radiologists are summarized in Table 3. The inter reader agreement was substantial agreement for image noise (κ= 0.66), moderate agreement for image artifacts (κ= 0.55), substantial agreement for vessel sharpness (κ= 0.73), and excellent agreement for overall image quality (κ= 0.89). (Fig. 3).

3.3 Radiation dose and iodine intake

The mean CTDL_vol, DLP, ED, and iodine intake of groups A, B, and C are summarized in Fig. 2 and Table 4. Statistical analysis showed that the CTDL_vol, DLP, ED, and iodine intake of groups B and C were lower than those of group A. Compared with group A, ED were reduced by 30.34% and 68.53% while iodine intake were lowered 10.22% and 16.85% (P < 0.001) in groups B and C,respectively.

Table 4
Radiation dose and iodine intake

Groups CTDI_vol (mGy) DLP (mGycm) ED (mSv) Iodine intake (g)

A 38.33±7.94^‡, 601.83±138.63^‡, * 8.42±1.94^‡, * 30.10±3.68^‡, *

B 27.11±4.80^†, * 419.15±78.05^†, * 5.87±1.09^†, * 27.02±3.51^†, *

C 12.49±2.43^†, ‡ 189.39±37.51^†, ‡ 2.65±0.53^†, ‡ 25.02±3.66^†, ‡

F value 374.83 340.674 340.763 24.969

P value P < 0.001 P < 0.001 P < 0.001 P < 0.001

Groups	CTDI_vol (mGy)	DLP (mGy*cm)	ED (mSv)	Iodine intake (g)
A	38.33±7.94^‡, *	601.83±138.63^‡, *	8.42±1.94^‡, *	30.10±3.68^‡, *
B	27.11±4.80^†, *	419.15±78.05^†, *	5.87±1.09^†, *	27.02±3.51^†, *
C	12.49±2.43^†, ‡	189.39±37.51^†, ‡	2.65±0.53^†, ‡	25.02±3.66^†, ‡
F value	374.83	340.674	340.763	24.969
P value	P < 0.001	P < 0.001	P < 0.001	P < 0.001

CTDI_vol: volume CT dose index; DLP: dose length product; ED: effective dose. †: Significantly different compared with group A. ‡: Significantly different compared with group B. *: Significantly different compared with group C.

4 Discussion

With the improvement of CT imaging technology, 16 cm wide detector CT has been rapidly developed for clinical use. Technical developments in the 16 cm wide-area-coverage CT scanner have increased the number of detector rows on the z-axis, which has enhanced the temporal and spatial resolution, free of stair-step artifacts [23]. This advancement provides an effective guarantee for the diagnostic performance of CCTA examinations.

At present, in order to reduce the risk of high ionizing radiation exposure in CCTA examinations, many researchers have proposed new methods that involve decreasing the radiation dose while maintaining image quality, including tube current modulation, prospective ECG triggering, high-pitch acquisition, and iterative reconstruction techniques [8 , 24–26]. However, since the tube voltage level is proportional to the square of the X-ray dose, decreasing the tube voltage level may still be the most effective method to reduce the radiation dose in CCTA examinations. According to Tan et al., compared with 120 kVp tube voltage, the average ED of the lower tube voltage (100kVp and 80kVp) could reduce by 41.21–74.30% [27].

The conclusion of our study was corresponded to the above report, which showed that the average ED of groups A, B and C were 8.42±1.94 mSv, 5.87±1.09 mSv and 2.65±0.53 mSv, respectively. Moreover, tube voltage determines the penetration ability of the X-rays. Overweight patients tend to have a long chest diameter. Lowering the tube voltage reduces the radiation dose while increasing the image noise, which may lead to the decrease of image quality. The results of this study showed that the average ED of patients in group C reduced by 68.53% and 54.90% respectively compared with groups A and B, but the image quality of patients in group C corresponds to the clinical diagnostic standard. This study used the third generation of adaptive statistical iterative reconstruction technology - ASIR-V. ASIR-V includes a system noise model, object model, and physical model, which can reduce image noise and improve image density resolution through multiple iterations and for enabling CT images with adequate image quality and diagnostic [28 –30]. There are two modes including pre-ASIR-V and post-ASIR-V in ASIR-V. Both two modes have different effects in 10 levels. The pre-ASIR-V can be used for reducing radiation dose by adjusting the tube current according to a three-dimensional Smart mA modulation, but cannot substantially improve image quality. The post-ASIR-V means ASIR-V reconstruction after scanning, which can effectively cut down the image noise to maintain the detail and quality of image [31]. Previous studies showed that 50% ASIR-V to 70% ASIR-V levels can significantly improve image quality among other ASIR-V levels [32]. Therefore, we combine 50% pre-ASIR-V with 70% post-ASIR-V for each patient in our study to decrease radiation dose, lower image noise and maintain image quality. The results of this study showed that using low iodine concentration of contrast medium may decline the enhancement of the target coronary artery. Our study showed that low tube voltages can compensate for the enhancement but not at the cost of lowered SNR and CNR.

The concept of FOM was proposed in order to characterize the contribution of different radiation doses to image quality, based on comprehensive assessment with image contrast, image noise, and effective dose [19, 33]. The higher the value of FOM, the greater the contribution of the effective dose to the image quality, and the better the quality of the CT images [20]. In our study, the FOM of groups A, B and C were 95.89±39.19, 197.63±71.74 and 386.13±136.15, and the CNR of groups A, B and C were 27.37±4.38, 33.03±5.20 and 31.17±5.17, respectively. When compared with group A, the average CNR of coronary vessels in groups B and C was significantly higher (P < 0.05). Although the CNR of group C was slightly lower than that of group B, there was no significant difference in the CNR between groups B C (P > 0.05). However, the FOM of group C was significantly higher than that of groups A and B. Moreover, there was no difference between groups B and C in subjective scores (P > 0.05). Our study showed that the 80 kVp tube voltage could effectively decrease the radiation dose of overweight patients in CCTA examinations, and the image quality of all patients corresponds to the clinical diagnostic standard.

To enhance the CT attenuation of vessels and obtaining diagnostic image quality in CCTA examination of overweight patients, the dose and concentration of contrast medium usually must be increased, while maintaining the iodine content in the coronary artery. In this situation, it may easily increase the risk of contrast-induced nephropathy [34, 35]. The 16 cm wide detector CT scanner can markedly reduce the whole heart scanning time to less than 1 second in a single rotation within a single beat [23]. Because the total contrast media and the injection duration can be decreased at CCTA in a shorter scanning time [14]. The total injection amount with 0.8 ml/kg and flow rate with 4.5 ml/s were applied in our study, which is smaller than previous study (1.0 ml/kg and 5.0 ml/s) [18 , 37]. In addition, when using the same flow rate, increasing the concentration of contrast agents may greatly increase the risk of extravasation due to increased viscosity of contrast medium [38].

Therefore, the use of low concentration iodine contrast medium not only decreases the risk of extravasation, but also decreases the metabolic load on the patient’s kidney. With the reduction of tube voltage, the photoelectric effect would be increased, and Compton scattering would be decreased between the X-ray and iodine atoms. At the same time, the average photon energy of X-rays is close to the K-edge of iodine (33 keV), and the ability of X-ray absorption of iodine atoms in blood vessels would be increased. Thus, the contrast between the coronary artery and surrounding tissue can be increased, and the image quality of CCTA can be improved [39, 40]. According to the above principle, a low tube voltage with low concentration of contrast medium was used in our study. None of the patients had contrast medium extravasation and other adverse events. The iodine intake of groups A, B and C were 30.10±3.68 g, 27.02±3.51 g, and 25.02±3.66 g, respectively. Compared with group A, although total iodine intake was reduced by 10.22% and 16.85% in group B and group C respectively, the CT attenuation values of the coronary artery in all groups were greater than 350, which met the requirement of clinical diagnosis.

This study also had some limitations. Firstly, we only focused on image quality, radiation dose, and iodine intake. We did not evaluate the level of coronary artery stenosis by coronary angiography as a standard in overweight patients. Secondly, the sample size of this study was small, and the overweight patients enrolled in this study did not include grades II and III as classified by WHO. These patients should be included in future studies. Thirdly, in order to avoid the impact of partial volume effects, the ROIs were only placed in the proximal coronary arteries. Finally, we investigated the comprehensive effects of tube voltage and the concentration of contrast medium in CCTA examination of overweight patients but did not analyze the independent effect of tube voltage or contrast medium separately.

5 Conclusion

Based on a wide-detector CT scanner, using 80 kVp tube voltage and 320 mgI/ml contrast medium protocol could substantially reduce the radiation dose and iodine intake in CCTA examinations for overweight patients. It can also acquire CCTA images that meet the diagnostic requirements.

6 Compliance with Ethical Standards

1. Funding: This study was funded by Key R&D projects of Hebei Province (grant number: 20377765D), Hebei province program of training and basic project of clinical medicine of China (grant number: 361007), Key R&D projects of Baoding City (grantnumber:2141ZF307), Medical Science Foundation of Hebei University (grant numbers: 2021A10 and 2021X06) and the affiliated hospital of Hebei University outstanding foundation (grant numbers: 2019Z004 and 2021Q002).

2. Conflict of Interest: we declare that we do not have any commercial or associative interest that represents a conflict of interest in connection with the work submitted.

3. Ethical approval: All procedures performed in our study involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards.

4. Informed consent: Informed consent was obtained from all individual participants included in the study. All patients signed informed consent.

5. This article does not contain any studies with animals performed by any of the authors.

6. This prospective study received institutional board approval from the affiliated hospital of Hebei University and each participant provided informed consent.

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