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A comparison study of radiations effective dose in ECG-Gated Coronary CT Angiography and calcium scoring examinations performed with a dual-source CT scanner

Akmal Sabarudin

¹Diagnostic Imaging & Radiotherapy Program, Faculty of Health Sciences, Universiti Kebangsaan Malaysia, 50300 Kuala Lumpur, Malaysia

Tiong Wei Siong

^oneDiagnostic Imaging & Radiotherapy Program, Faculty of Health Sciences, Universiti Kebangsaan Malaysia, 50300 Kuala Lumpur, Malaysia

Ang Wee Chin

²Department of Physics, Faculty of Science, Universiti Teknologi Malaysia, 81300 Johor Bharu, Johor Malaysia

Ng Kwan Hoong

³Section of Biomedical Imaging, Universiti of Malaya Medical Centre, 50603 Kuala Lumpur, Malaysia

Muhammad Khalis Abdul Karim

^fourSection of Physics, Faculty of Scientific discipline, Universiti Putra Malaysia, 43400 Serdang, Selangor Malaysia

⁵Center for Diagnostic Nuclear Imaging, Faculty of Medicine Universiti Putra Malaysia, 43400 Serdang, Selangor Malaysia

Received 2018 May 23; Accepted 2019 Feb 21.

Abstract

In this study we take evaluated radiation constructive dose received past patients during ECG-gated CCTA examinations based on gender, heart rate, tube voltage protocol and body mass alphabetize (BMI). A total of 1,824 patients were retrospectively recruited (1,139 men and 685 women) and they were divided into Group 1 (CCTA with calcium scoring), Group 2 (CCTA without calcium scoring) and Grouping 3 (only calcium scoring), where the association between gender, center rate, tube voltage protocol and body mass index (BMI) were analysed. Examinations were performed using a retrospective ECG-gated CCTA protocol and the constructive doses were calculated from the dose length product with a conversion coefficient of 0.026 mSv.mGy⁻¹cm⁻¹. No meaning differences were observed in the hateful effective dose between gender in all groups. The hateful estimated dose was significantly higher when the heart rate was lower in Group 1 (p < 0.001) and Group ii (p = 0.002). At that place were also pregnant differences between the mean constructive dose in tube voltage protocol and BMI among the three groups. The mean constructive dose was positively correlated with BMI (p < 0.001), but inversely related to the heart charge per unit. This study supported the theory that a high center rate, low tube voltage and depression BMI could significantly reduce radiations dose exposure.

Introduction

Coronary computed tomography angiography (CCTA) is a non-invasive diagnostic tool for detecting coronary middle disease that has low radiation exposure on patients compared with conventional angiography ^ane,2 . Despite its benefits, the radiation dose is still a concern among clinicians and CT browse manufacturers, and numerous techniques have been introduced to reduce its side effects on patients and medical personnel ² .

Prospective ECG-gated CCTA has been shown to be the most efficient alternative in minimising radiations exposure while maintaining image quality compared with retrospective ECG-gated CCTA. The constructive radiation dose exposure in prospective ECG-gated protocols have been proven to be between v and vii times lower compared with retrospective ECG-gated CCTA. A phantom study has plant that the effective dose in retrospective protocol could exist every bit high as 18.ii ± viii.3 mSv in dual-source CT (DSCT) scans and 28.three ± 7.0 mSv in unmarried-source CT (SSCT) scans ³ . Although prospective ECG-gating CCTA has low effective radiation dose, its use is severely restricted for cardiac patients with high and fluctuating heart rates.

The optimal center charge per unit for the process is betwixt 65 and 75 beats per infinitesimal (bpm) because that range has the best diastolic phase to capture images of coronary arteries with minimal artifacts ^iv–vi . Currently, functional analysis of the center can be performed using prospectively ECG-triggered sequential unmarried cardiac phase CT images obtained through CCTA — derived from the fractional flow reserve (FFR_CT) ⁷ or by using myocardium assay ⁸ . In contrast, retrospective ECG-gated CCTA is able to provide reconstruction of motion-costless images with greater flexibility, thus allowing coronary arteries to be viewed at any R-R interval ⁹ .

To amend the CCTA epitome of patients with loftier heart rate, beta-blockers (metoprolol) or calcium aqueduct blockers (Diltiazem and Verapamil) tin be prescribed ¹⁰ . But these drugs are contraindicated in patients with a history of significantly-impaired left ventricle role and heart failure because they reduce myocardial contractility. Currently, Ivabradine is the only drug that has pure negative chronotropic effects in inhibiting the "I" (funny) ion channels of sinoatrial nodes to lower the centre'southward natural step-making activity without binding to β-adrenergic receptors. Thus, Ivabradine provides a safer pick to reduce the patients' heart charge per unit ¹¹ . These dedicated medicines can exist used to lower the heart rate for patients undergoing prospective ECG-gated CCTA process.

Sometimes, radiographers choose to apply unoptimized CT protocols and may finish upwardly mis-centering the patients' position, leading to increased effective radiation dose exposure. For whatever reason, it is of import to apply the principle of ALARA (Every bit Depression as Reasonably Achievable) in all radiological procedures. There are several protocols that tin can be used cardiac CT inclusive contrast (CCTA) and non-contrast (calcium scoring) studies ^12,thirteen . Both protocols are being implemented in clinical practice regardless of patient condition. However, the accumulated dose for both procedures tin be loftier and it should be taken into consideration if patient condom is to be given priority. The implementation of either a single protocol or both remains debatable ¹⁴ .

Therefore, the purpose of this study is to evaluate the effective radiation doses received by patients who had undergone retrospective ECG-gated CCTA and calcium coronary CT scan, and compare them according to gender, center rate, BMI and tube voltage protocol.

Materials and Methods

Study subjects

The research protocol was approved by the ethic committee of Institut Jantung Negara (IJN) which waived patient consent class for the retrospective analysis with an approval ID: IJNEC/05/2013(01). A total of 1,824 patients comprising ane,139 men and 685 women (aged 23 to 88 with a mean of 56.56 ± 10.65 years) who underwent CCTA between February 2015 and Jan 2016 in IJN were retrospectively recruited. Paediatric patients (below age eighteen) and multiple scan area cases were excluded.

Sublingual nitro-glycerine was administered when the patient was lying down, and beta-blockers were given only if their heart rate was more than 85 bpm. Tube voltage protocol was adjusted based on patients' height and weight. Patient information (superlative, weight, heart rate, blood pressure level) were noted and the body mass index (BMI) was calculated.

In this report, patients were divided into three groups, namely Group 1 (CCTA with calcium scoring), Group 2 (CCTA without calcium scoring) and Grouping 3 (calcium scoring only). Group 1 consists of first-time patients presenting with major risks for coronary avenue disease and myocardial infarction, such as loftier claret cholesterol, family history of heart attack, diabetes, high blood force per unit area, smoking, overweight or obese, and concrete inactivity. Grouping 2 consists of patients with a history of middle attack and had undergone cardiac interventions similar coronary artery bypass graft (CABG), mail service-stenting and pacemaker implantation. Group 3 represents patients with severe/major calcifications in coronary arteries, which did not require farther CCTA and likely considered for screening purposes only.

CT conquering parameters

CT examinations were performed using the 64-slice dual-source Siemens Somatom Definition Flash scanner (Siemens Medical Solution, Erlangen, Germany) according to parameters in Tabular array1. Tube voltage protocol was selected based on the patients' BMI as indicated in Table2. These parameters were standard protocol in IJN, and details like effective mAs and scanning time were tabulated in Tabular array3. Patients were positioned supine at the centre of the scanner gantry and a coronal topogram was obtained.

Table 1

Standard conquering parameters for coronary calcium scoring and CCTA.

Acquisition parameter	Calcium scoring	CCTA
kV	100–140	100–140
mA	30–250	300–500
Constructive mAs	80	350
Slice collimation	two × 64 × 0.6 mm with Z-flying focal spot*	ii × 64 × 0.6 mm with Z-flying focal spot*
Piece thickness	3.0 mm	0.6 mm
Pitch factor	1.0	0.2–0.43

*Actual nominal beam width was ii × 32 × 0.half-dozen mm.

Table 2

Pick of tube voltage (kV) based on BMI.

Group	Category BMI	kV option	Number of patients
1	Underweight	100 or 120 kV	29
	(BMI < 18.5 kg/m²);
2	Normal weight	100 or 120 kV	547
	(eighteen.five–24.ix kg/g²);
iii	Pre-obesity	100 or 120 kV	778
	(25–29.9 kg/m²)
4	Obesity class I	120 or 140 kV	344
	(30–34.9 kg/thousand²)
5	Obesity class II	120 or 140 kV	88
	(35–39.9 kg/thou²);
6	Obesity class 3	140 or160 kV	38
	(BMI ≥ 40 kg/m²)

Table 3

Differences in hateful estimated constructive dose (mSv) between gender and heart rate.

Group	Male person	Female	p value	≤65 bpm	>65 bpm	p value
1	19.05 ± 8.74	nineteen.75 ± 9.49	0.245	xx.38 ± 9.64	18.81 ± 9.41	0.000
2	25.65 ± 12.93	23.76 ± 12.93	0.149	27.53 ± 13.23	23.37 ± 12.30	0.002
3	4.18 ± 3.03	five.ten ± 3.33	0.056	4.44 ± ane.97	4.26 ± 2.54	0.160

Based on the program, CT coronary calcium scoring and CCTA were performed, with the scanning range between the ascending aorta and heart apex to include the unabridged cardiac structure. In the CCTA scanning protocol, ECG-pulsing was used to steer the scan acquisition co-ordinate to middle rhythm and to reduce radiation dose. ECG-pulsing window was set between 30% and 80% of the R–R interval (to the lowest degree motion for the coronary arteries) with a pitch ranging from 0.2 to 0.43, which was automatically adapted to the heart charge per unit. For CT coronary calcium scoring, the ECG-pulsing window was set between 60% and 75% of the R-R interval with a pitch of i.0. The ECG-pulsing kept the tube current at the highest level for user-divers R-R interval and used a lower tube current (20% reduction) for the remaining stage that eventually led to low radiation dose exposure.

The examination bolus technique was used to calculate the scan-fourth dimension delay with top contrast enhancement. Patients were injected intravenously with twenty ml of depression osmolar iodinated dissimilarity media (Iomeron 350, Bracco, United kingdom of great britain and northern ireland) and trail scans were performed at the ascending aorta to monitor dissimilarity enhancement. Time to peak enhancement was adamant through the dissimilarity enhancement curve. Thus, the browse-time delay was calculated by adding the time to height enhancement and acquisition trigger time. Another 60 mL of contrast medium was injected into patients using a ability injector at a flow rate of 5.0–half-dozen.0 mL/south, followed by 60 ml of saline flushing at the same menstruum rate.

The CCTA scan for patients with percutaneous cardiac intervention (PCI) and CABG was made cranio-caudally with bigger scan range between the arch of aorta and the apex of the center to include the entire heart and the ligation of the grafts. The patients were instructed to concord their breath during the scan acquisition. Automated tube current modulation and automatic ECG-pulsing were used to further reduce radiations exposure.

Effective dose estimation

The dose length production (DLP) was obtained retrospectively from records of the daily patients' list. The effective dose of CCTA was estimated from the DLP production using a conversion coefficient value (yard) of 0.026 mSvmGy^−anecm⁻¹ every bit reported by Huda et al. for coronary CT examinations ¹⁵ . The estimated effective dose (E) is calculated below:

Statistical analysis

Data were analyzed using IBM SPSS version 22.0 (IBM Corporation, Armonk, New York, U.s.). The Kolmogorov-Smirnov Test was used to determine the normality of the estimated effective dose. The quantitative variables were expressed as a mean ± standard deviation. Differences between the two groups were determined using the Mann-Whitney U Test (p <0.05), while the Kruskal-Wallis H Test was used for more than two groups (p < 0.05). The mean comparisons betwixt variables were presented descriptively. Spearman's correlation analysis was used to determine the association between effective dose and centre charge per unit, as well every bit BMI.

Results

Patient characteristics and scan parameters

The patients were characterized by gender and test groups as shown in Fig.1. The boxplots in Fig.ii show the centre rate of patients, where 1,197 (65.65%) of them had more than 65 bpm., and 627 (34.35%) had less or equal to 65 bpm. The mean middle rate was 71 ± 11 bpm (range 37–123 bpm) and mean BMI was 27.54 ± 5.04 (range thirteen.62–61.14).

Distribution of gender in each exam group. The groups are divided into Grouping i: CCTA with calcium score, Group ii: CCTA merely, and Grouping iii: calcium score merely.

Boxplots indicating the center rate of patients in each group.

Radiation dose comparison

In radiations dose analysis, Fig.iii presents the estimated effective dose received by unlike groups. It was apparent that Grouping 2 patients had the highest median value and Group 3 patients received the everyman dose. In Tabular array3, the Isle of man-Whitney U exam proved that there was no difference between the mean constructive dose and gender in all examination groups. However, the estimated effective doses were significantly different between heart rate in Group 1 (p < 0.000) and Group 2 (p =0.002) patients, but not Group 3. Interestingly, the doses were college when the patients' heart rate was low.

Effective dose received by each grouping.

Table4 shows the comparison betwixt the estimated effective dose and tube voltage protocols using the Kruskal-Wallis H-test. The constructive doses in different voltage protocols were significantly different in all groups. An interesting observation was the hateful constructive dose in Group ii using a tube voltage of 120 kV, which was the highest value compared with all groups. Equally indicated in Tablev, the estimated effective dose among the BMI category was also found to be statistically significant among all groups.

Table 4

The mean estimated effective dose (mSv) and voltage protocols among groups.

Grouping	100 kV	120 kV	140 kV	160 kV	p-value
1	14.87 ± 4.36	27.96 ± 9.53	34.75 ± four.01	11.08 ± 0.00	0.000
ii	18.78 ± 7.28	37.39 ± 12.49	28.11 ± 0.00	N.A.	0.000
3	3.89 ± 2.38	4.72 ± 3.57	6.55 ± 0.00	North.A.	0.031

Tabular array 5

The hateful estimated effective dose (mSv) and BMI categories amidst groups.

BMI categories	one	2	3	4	5	6	p-value
Group 1	13.xl ± two.xx	14.86 ± 5.44	17.93 ± viii.84	27.06 ± 10.13	28.97 ± 7.82	31.63 ± 10.45	0.000
Group two	23.99 ± fifteen.37	19.36 ± 12.41	24.54 ± 11.68	32.83 ± 12.fifty	34.04 ± vii.29	32.17 ± fifteen.25	0.000
Group 3	2.67 ± 0.50	three.16 ± 0.88	4.05 ± ii.08	5.thirty ± ii.24	v.75 ± 2.09	11.90 ± 8.37	0.000

ane = Underweight (BMI < 18.5 kg/m²); 2 = Normal weight (BMI 18.5–24.ix kg/m²); 3 = Pre-obesity (BMI 25–29.9 kg/chiliad²); 4 = Obesity class I (BMI 30–34.9 kg/one thousand²); 5 = Obesity grade Two (BMI 35–39.9 kg/1000²); 6 = Obesity class Three (BMI ≥ forty kg/m²).

As illustrated in Fig.4, the Spearman's correlation analysis for all three groups showed a significant positive correlation between BMI and estimated effective dose (p < 0.001). This showed that the estimated effective dose would increase as the BMI increased. However, Fig.five showed an inverse correlation between heart rate and the estimated effective dose.

The graph shows correlation assay of the estimated effective dose depending on BMI. Positive correlation was shown in all iii groups (Group 1, r = 0.610; Group 2, r = 0.516; and, Group 3, r = 0.551).

The graph shows the correlation assay of the estimated effective dose depending on centre rate. Weak negative correlation was shown in all three groups (Group 1, r = −0.132; Group 2, r = −0.158; and, Grouping 3, r = −0.195).

Discussion

This report evaluates several factors that influence radiation dose exposure performed using routine CCTA examination protocols at IJN. We obtained compelling show that the protocols were exposing patients to considerably college radiation doses. These findings concurred with the global CTA dose survey published recently, where the DLP value of retrospective ECG-gated from a 2007 survey was higher than the latest survey, which was dominated by prospective ECG-gated scans, by a cistron of 7 ¹³ . It can, therefore, be reasonably assumed that our current imaging practices might exist causing the high radiation dose exposure rather than existing variables. Information technology should be noted that retrospective ECG-gated CCTA used a lower pitch gene, which was the reason for the loftier radiation dose exposure on patients.

It is highly recommended for a cardiac imaging eye to apply dose optimisation protocols, but that would exist highly dependent on the patients' heart rate. The main obstruction would be patients with high heart charge per unit because tube current could not be modulated fast plenty to catch upwardly with the heartbeat, which would compromise image quality ^xiii,16 . Therefore, to ensure that the ECG-gated tube current modulation was constructive in reducing radiation dose exposure, beta-blockers were prescribed to lower the patients' heart charge per unit to an optimal range ¹⁷ .

Yet, our results showed the mean estimated effective dose was lower in patients with a higher eye rate (>65 bpm). A previous study showed similar results, where the hateful effective dose for DSCT was observed to be 11.4 mSv, and information technology was reduced to three.viii mSv afterwards applying a tube voltage protocol of 100 kV with 110 ms of ECG pulsing window ^xviii .

Furthermore, previous studies besides reported a decreased dose of radiation received by patients with higher heart rates when applying the recommended ECG-pulsing window technique ^19,20 . We altered the ECG-pulsing window width based on heart rate during the examination and, therefore, the differences in estimated radiation dose might exist partly explained by the private ECG-pulsing window widths. Another variable that afflicted radiation dose exposure was tube voltage, where applying a lower voltage could exist expected to reduce the dose ²¹ . Our study adapted the tube voltage to the patients' size and weight, and a significant difference were observed in radiation doses between 140 kVp, 120 kVp and 100 kVp in Grouping i and 3 patients (except 160 kVp). Reducing the tube voltage from 120 kVp to 100 kVp could subtract the effective dose by 28%, which was corroborated by earlier findings ²² .

However, tube voltage had to be practical proportionally to BMI because higher penetration free energy required to scan patients with more torso mass. Reducing the tube voltage might compromise image quality, especially in obese patients ^23,24 . The low voltage would pb to lower photon energy beingness produced in the scanning tube, resulting in an increase of prototype noise, artifacts and a decrease of contrast range. Thus, a few studies suggested that low voltage should exist used frequently in not-obese or patients with depression BMI only ^25–27 .

In Group 2, the mean effective dose with a tube voltage of 120 kVp was shown to be college than 140 kVp. This contradictory issue could be due to the modify of acquisition protocols, where the technologist might take increased the reference mAs to reduce paradigm noise. This ascertainment was also supported by the results in Tabular array3, where the scanning fourth dimension in Group 2 was higher by a factor of one.iii compared with Group 1 due to the long scan range in post-CABG patients. The scanning range for post-CABG patients started from the arch of the aorta until the heart apex to include the ligation of the coronary artery bypass ^three . Every bit role of the optimization procedure, the radiations dose from CT scans could exist reduced with a few techniques, such every bit using an iterative reconstruction algorithm, increasing the helical pitch and lowering the tube potential energy ^27–29 . Therefore, lowering the tube voltage to reduce effective radiation dose was practical for pocket-sized- and average-sized patients, just non for those with large habitus ^15,30 .

Our study showed a significant positive correlation between BMI and constructive dose. Therefore, BMI might exist one variable that could contribute to changes in radiation dose. The automatic tube current modulation in the CT scanner would operate according to size and attenuation of torso region, and therefore, obese patients would significantly receive higher dose of scanning radiation.

Although an individual with BMI of 30 and above could exist assumed to have excess fat mass, the distribution of fat tissues was different in the chest which, in fact, was influenced by the Compton scattering effect ³¹ . The E/DLP value of 0.026 mSvmGy⁻¹cm⁻¹ used to calculate the estimated effective dose was obtained based on the International Committee on Radiological Protection (ICRP) report ^fifteen . The value was more authentic for estimating cardiac CT radiation dose compared with chest CT examination ^3,29 . The cardiac region had been reported to exist more radiosensitive than the chest and the tissue weighting factor was changed significantly from 0.05 to 0.12 for breast as reported in ICRP-103 ³² .

In retrospective ECG-gating CCTA examination, it was observed that patients with normal heart charge per unit or below 65 bpm would receive low radiations exposure with high diagnostic prototype quality produced. Simply recent development of CT scanners, peculiarly dual-source CT, a loftier heart rate would no longer be an issue in retrospective CCTA scanning ⁷ . Therefore, several methods had been suggested to overcome this issue, such as adaptive sequential scanning (prospective ECG-gated), especially when using loftier-stop scanners. In addition, padding window in prospective ECG-gated is a solution for scanning patients with higher heart rate, merely this technique might cause interference in temporal resolution.

We aware that our study might have limitations. Firstly, it was a retrospective assay, where many parameters were not strictly controlled, such as the pick of tube voltage protocols and the recording of patient data. Secondly, information technology was inevitable that the estimated effective dose values were higher when compared with other studies. The reasons were wholly understood considering of the electric current practice, which caused meaning increase in radiations dose as well as other factors. The estimated effective dose was derived from a mathematical formula, which might under- or overestimate the true radiation exposure. Therefore, a validation test should exist performed by statistically comparison the doses with the size-specific dose estimation (SSDE). But that was not performed in this study because the CT dose index (CTDI) was not recorded.

In conclusion, a higher heart rate, lower tube voltage and lower BMI might reduce radiations dose significantly in a retrospective ECG-gating protocol using DSCT. Information technology is advantageous to use ECG-pulsing protocol in DSCT for patients with a loftier eye rate. To perform CCTA safely, patient data must be taken into consideration and a lower tube voltage should be called.

Acknowledgements

The authors are grateful to Mohd Zaidi Abdul Rahman from IJN for his technical assist during data drove. The authors too wish to admit support from Geran Putra of Universiti Putra Malaysia with the project number GP/IPM/UPM/9619800.

Writer Contributions

Akmal Sabarudin, Tiong Wee Siong and Muhammad Khalis Abdul Karim wrote the main text, Ang Wee Mentum prepared the figures and tables and Ng Kwan Hoong improved the content. All authors had reviewed the manuscript.

Notes

Competing Interests

The authors declare no competing interests.

Footnotes

Publisher'southward note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

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Source: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6416329/

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