Value of the Non-enhanced Cardiac Computed Tomography Scan Analysis in Determination of the Appropriate Coronary CT Angiography Scan Protocol

Abstract

Objective

Coronary computed tomography angiography (CCTA) is a cornerstone in the assessment of coronary artery disease. Despite technological advancements, balancing radiation does with diagnostic image quality remains a challenge. This study evaluates whether assessing preliminary non-enhanced CT scans allows for the optimization of CCTA gating protocols to enhance image quality and minimize radiation exposure.

Methods

We prospectively analyzed 150 patients undergoing CCTA on a 256-slice scanner. Non-enhanced scans were used to identify motion artifacts or anatomical challenges. Based on these findings, a specific gating protocol (prospective, prospective with padding, or retrospective) was selected. This cohort was compared to a control group of 150 standard CCTAs performed without protocol pre-selection. Image quality was assessed on a four-point scale, and radiation doses were recorded.

Results

The mean patient age was 49 years, with a mean heart rate (HR) of 62 ± 14 beats per minute (bpm). Subjective image quality was significantly higher in the pre-selection group, particularly for patients with HR > 65 bpm (3.5 ± 0.5 vs. 2.8 ± 0.8; p = 0.06). The mean radiation dose was significantly lower in the pre-selection group (4.9 ± 1.4 vs. 7.5 ± 1.8 mSv; p < 0.01). Furthermore, the requirement for high-radiation protocols (padding or retrospective gating) was reduced by 50% in the pre-selection group (14/150 vs. 28/150 scans).

Conclusion

Utilizing non-enhanced CT scans to tailor 256-slice CCTA protocols significantly improves image quality and reduces radiation exposure. This strategy offers a more personalized approach to cardiac imaging and should be considered for routine clinical practice.

1. Introduction

Coronary computed tomography angiography (CCTA) has become a cornerstone diagnostic technique in clinical practice, particularly for evaluating patients with an intermediate pretest probability of obstructive coronary artery disease (CAD) [1,2]. However, CCTA is associated with substantial radiation exposure, raising continuous concerns regarding the potential lifetime risk of malignancy [3–5]. Consequently, it is crucial to develop acquisition strategies that reduce radiation dose without compromising diagnostic image quality.

Various strategies have been implemented to minimize radiation exposure, with prospective electrocardiography (ECG)-gated CCTA being the most significant. In this protocol, scans are triggered by the ECG signal at predefined intervals—typically during the diastolic phase where cardiac motion is minimal. By halting the scan during the remainder of the cardiac cycle and utilizing a pitch of 1 to avoid slice overlap, this method significantly reduces the dose compared to retrospective ECG gating and invasive coronary angiography [6,7]. Despite its efficiency, prospective gating remains susceptible to heart rate (HR) fluctuations.

The introduction of a new generation of dual-source CT scanners has enabled a novel scanning mode: prospectively ECG-triggered high-pitch acquisition. This technique allows for the acquisition of the entire heart volume within a single cardiac cycle, utilizing a temporal resolution of 75 ms. In patients with low and regular HRs, high-pitch values (up to 3.4) can be used to achieve excellent image quality—free from “misalignment” or “stair-step” artifacts—while maintaining a radiation dose below 1.0 mSv [8,9].

However, both prospective and high-pitch FLASH protocols require low and stable HR. In prospective ECG gating, concerns persist regarding diagnostic accuracy due to two main factors. First, stair-step artifacts often arise from the misalignment of adjacent structures caused by HR variability, which complicates the evaluation of coronary segments [10,11]. Second, because images are acquired during only a small portion of the R-R interval, functional data regarding valvular or wall motion is lost. While “padding” can be added to prospective gating to capture more phases, this approach inherently increases the effective radiation dose.

Conversely, retrospective ECG gating provides high diagnostic accuracy by allowing image reconstruction at any point throughout the cardiac cycle [12]. This flexibility enables multi-segment reconstructions to improve temporal resolution. However, the requirement for low pitch values (typically 0.2 to 0.4) results in significantly higher radiation doses, which can reach up to 30 mSv [13]. Even with dose-reduction strategies—such as tube current modulation and voltage adaptation, the mean dose for retrospective CCTA remains approximately 12 mSv [14].

The PROTECTION I Study suggested that prospective ECG-triggered sequential CCTA significantly reduces radiation dose without compromising image quality in patients with low, stable HRs [14]. Further research has shown that prospective triggering can yield superior image quality scores compared to retrospective gating in patients with HRs below 68 beats per minute (bpm), achieving a 73% dose reduction [15]. Current clinical recommendations for 256-slice CCTA suggest that prospective acquisition should be preferred for HRs up to 75 bpm, while retrospective gating with dose modulation should be reserved for HRs exceeding 75 bpm [16].

The motivation for this study is to evaluate the clinical benefit of analyzing the image quality of the non-enhanced scan (typically performed at 70% of the cardiac cycle) to guide the pre-selection of the CCTA protocol. We hypothesize that this approach will ensure optimal image quality while preventing unnecessary exposure to high-radiation protocols, such as retrospective gating or prospective gating with padding.

2. Methods

2.1. Study design and patient selection

We conducted a prospective analysis of non-enhanced cardiac CT scans, which are usually performed prior to CCTA. The primary objective was to evaluate the presence of motion artifacts affecting the heart and coronary arteries to guide the selection of the CCTA protocol. The study utilized a prospective cohort design, randomization was not performed to reflect real-world clinical practice, and the control group was a consecutive cohort treated under the previous standard of care. The study was approved by the ethical committee in Prince Sultan Cardiac Centre. Qassim, Saudi Arabia. No AI tools were used for data analysis, only for minor grammar corrections.

The decision-making process was based on a real-time assessment of the non-enhanced images. If the analyzed phase (typically at 70% of the cardiac cycle) was free of artifacts and provided clear visibility of the coronary arteries, with particular focus on the right coronary artery (RCA), the subsequent CCTA acquisition was performed using that same phase. However, if significant artifacts were observed, an alternative protocol was selected, such as retrospective gating or prospective gating with additional padding. The patient enrollment process is illustrated in Fig. 1. The control group consisted of 150 patients whose protocols were selected using standard institutional criteria (primarily HR) without the benefit of non-enhanced scan assessment. In this group, patients with HR ≤ 65 bpm were scanned with prospective protocol, while patients with HR > 65 were scanned with retrospective or prospective with padding protocols.

Fig. 1.

Study Flowchart. Study flowchart illustrating patient screening, exclusion criteria, and allocation into the non-enhanced CT-guided experimental group and the standard-of-care control group.

Following the CCTA, image quality and radiation exposure doses were analyzed in both the pre-selection arm and a control group. To account for the impact of heart rate (HR) on image quality, patients were stratified into two groups: those with an HR ≤ 65 bpm and those with an HR > 65 bpm.

2.2. Inclusion and exclusion criteria

This study was conducted at the Prince Sultan Cardiac Center (PSCC) in Qssim, Saudi Arabia. Data collection spanned from January 2019 to February 2020. All scans were performed using a 256-slice dual-source CT (Siemens Definition FLASH). CCTA was performed on patients presenting with clinical indications including chest pain, palpitations, dyspnea, or atrial fibrillation (AF) if heart rate is ≤65 BPM (7 patients included). Patients were excluded from the study based on the following criteria: Uncontrollable arrhythmias (AF with heart rate >65 BPM), history of allergic reactions to iodinated contrast media, pregnancy, renal impairment (serum creatinine>130 μmol/L), inability to maintain a stable breath-hold, presence of significant respiratory or gating artifacts on the initial scout or non-enhanced images. All participants provided informed consent prior to inclusion in the study.

3. Data acquisition and reconstruction protocol

3.1. Imaging parameters

All scans were performed using a 256-slice dual-source CT scanner (Siemens Definition FLASH, Siemens Healthcare, Forchheim, Germany), to ensure technical consistency across all patients. The system provided a rotation time of 280 ms and a temporal resolution of 75 ms, utilizing 0.6-mm collimation. The tube current was set at 320 mAs and adjusted based on patient habitus. Tube voltage was weight-stratified: 100 kV for patients weighing <80 kg and 120 kV for those weighing >80 kg. Imaging commenced with a scout view, followed by a calcium scoring scan (3 mm slice thickness) using prospective gating at 70% of the RR interval. Of note, all the scans were performed by the same technologists and operators who are aware of the study design and protocols. In addition, all the scans were analyzed by certified cardiologists on cardiac CT.

3.2. Contrast administration

To determine the optimal delay for CCTA, a “test bolus” technique was employed. A region of interest (ROI) was placed in the ascending aorta, and 15 ml of contrast media (XENETIX® 350; 350 mg iodine/mL) was injected, followed by 20 ml of normal saline at a flow rate of 6 ml/s. The CCTA scan was subsequently initiated 4 s after peak enhancement. For the diagnostic scan, an average of 75 ml of contrast followed by 45 ml of normal saline was injected at a rate of 6 ml/s while the patient maintained an inspiratory breath-hold.

3.3. Gating protocols and image reconstruction

Three distinct acquisition protocols were employed to optimize scan quality and radiation exposure. In prospective ECG gating, data acquisition was triggered precisely at 70% of the cardiac cycle (Fig. 2A). In prospective gating with padding, the acquisition window was expanded to encompass additional cardiac phases, allowing greater reconstruction flexibility (Fig. 2B). Conversely, retrospective ECG gating involved continuous data acquisition throughout the entire cardiac cycle using helical scanning. To minimize radiation during retrospective scans, ECG-based tube current modulation was employed; the maximum mAs was delivered during the 40–70% phase, while the tube current was attenuated to 5% for the remainder of the cardiac cycle (Fig. 2C). Images were reconstructed with a slice thickness of 0.6 mm. A medium-smooth kernel (B26f) was utilized for standard diagnostic interpretation, whereas a sharper kernel (B46f) was selectively applied to mitigate blooming artifacts associated with high-density structures, such as coronary calcification or metallic stents.

Fig. 2.

Scanning protocols. Cardiac CT Acquisition Protocols and Gating Strategies. (A) Prospective ECG Gating: The X-ray beam is triggered only at a predefined phase of the cardiac cycle, typically at 70% of the R–R interval and remains off during the remainder of the cycle to minimize radiation. (B) Prospective Gating with Padding: This protocol extends the acquisition window (e.g., 40–90% of the R–R interval) to allow for minor heart rate fluctuations and provide additional phases for reconstruction. (C) Retrospective ECG Gating: Data are acquired continuously throughout the entire cardiac cycle using helical scanning. To optimize radiation safety, ECG-based tube current modulation is employed, delivering maximum tube current (mAs) between 40 and 70% of the cycle and attenuating the current to 5% during the remaining phases.

3.4. Post-processing and image analysis

Comprehensive post-processing was performed on a dedicated multi-modality workstation (MMWP; Siemens Medical Solutions, Erlangen, Germany). Multiplanar reformats (MPR) were generated in axial, coronal, sagittal, and oblique planes, supplemented by thin-slab maximum intensity projections (MIP) and volume rendering (VR) images. For prospective scans, reconstruction was focused on the 70% phase. In cases of padded prospective or retrospective gating, data from multiple phases were analyzed, specifically targeting the optimal systolic and diastolic windows, to ensure the highest diagnostic yield.

4. Data analysis and technical evaluation

4.1. Image quality

All coronary segments were systematically evaluated for diagnostic utility. Subjective image quality was graded using a 4-point Likert scale (Fig. 3), defined as follows: Score 1 (Non-diagnostic), characterized by severely impaired quality and significant motion artifacts that preclude clinical evaluation; Score 2 (Adequate), representing reduced quality that remains sufficient for interpretation; Score 3 (Good), where minor artifacts are present but coronary anatomy remains fully evaluable; and Score 4 (Excellent), defined by a complete absence of motion artifacts, high intra-luminal attenuation, and sharp delineation of the vessel walls (Fig. 3). To identify and mitigate factors degrading image quality, axial, coronal, and sagittal planes were meticulously analyzed. Diagnostic assessment was further supported by diverse post-processing techniques, including MIP, MPR, and VR.

Fig. 3.

The four point Likert scoring criteria. Representative CCTA images illustrating the 4-point Likert scoring criteria: (A) Excellent quality (Score 4), demonstrating sharp vessel delineation and no motion; (B) Good quality (Score 3), showing minor artifacts with preserved diagnostic confidence; (C) Adequate quality (Score 2), showing reduced quality that remains sufficient for interpretation; and (D) Non-diagnostic quality (Score 1), where severe artifacts preclude reliable evaluation.

4.2. Radiation dose

To quantify patient radiation exposure, we recorded the volume CT dose index (CTDI Vol) and dose-length product (DLP) for both protocols. The effective radiation dose was calculated based on the methodology proposed by the European Working Group for Guidelines on Quality Criteria in CT. The effective dose (expressed in mSv) was derived using the following formula:

$$\text{Effective\hspace{0.17em}dose}=0.014\hspace{0.17em}(\text{msv})\times \text{DLP\hspace{0.17em}}({\text{mGy}}^{-1}\hspace{0.17em}{\text{cm}}^{-1})$$[ 19,20].

4.3. Statistical analysis

Continuous variables were assessed for normality using the Kolmogorov–Smirnov test. Normally distributed data are presented as mean ± standard deviation (SD), while non-normally distributed data, such as the Agatston Calcium Score, are presented as median (interquartile range [IQR]). Comparative analyses were performed to identify significant differences between the pre-selection and standard protocol groups. All statistical evaluations were conducted using SPSS version 22 (SPSS Inc., Chicago, IL, USA). A p-value of <0.050 was established as the threshold for statistical significance.

5. Results

5.1. Patient characteristics and grouping

A total of 300 patients were analyzed (150 in the protocol pre-selection arm and 150 in the standard arm). Baseline clinical characteristics are summarized in Table 1. In the pre-selection arm, the primary indication for CCTA was chest pain (n = 120), with the remainder of patients referred for various other clinical indications. The median Agatston calcium score was 65.0 (IQR: 0–1100) in the experimental group and 75.0 (IQR: 0–950) in the control group (p = 0.090), indicating no significant difference in baseline coronary calcification between the two cohorts. There was no difference in the total procedure time between the two groups (31 vs. 32 min for Pre-Selection arm and the control group respectively), while the analysis time was slightly longer, but not significant, in the pre-selection group due to extra analysis time of the non-enhanced CT scans (32 vs 30 min for Pre-Selection arm and the control group respectively). Patients were stratified based on heart rate (HR) into Group A (HR ≤ 65 bpm) and Group B (HR > 65 bpm).

Table 1.

Patient clinical and demographic characteristics in both groups of scanning.

Patient characteristics	Nonenhanced scan and HR based selection of the protocol	HR only based selection of the protocol	P value
Number of the patients	150	150
Median age (years):	49.8	56	0.851
Male sex	65%	67 %	0.210
Risk factors
Diabetes	25 (35.3%)	22 (22.5%)	0.100
Hypertension	40 (43.9%)	35 (27.5%)	0.311
Dyslipidemia	20 (24.3%)	15 (18.7%)	0.210
Smoking	13 (13.4%)	10 (22.5%)	0.200
Family history of CAD	5 (8%)	7 (12.5)	0.300
Wight (kg)	73 ± 21	75.3 ± 22	0.431
Heart rate (bpm)	62 ± 14	64 ± 15	0.731
Calcium score	65 (0–1100)	75 (0–950)	0.090
Procedure time (min)	31 (24–38)	32 (25–40)	0.410
Analysis time	32 (20–43)	30 (21–39)	0.310

5.2. Protocol pre-selection arm (Diagram A)

Diagram A.

Pre-selection protocol arm. In this cohort, the CCTA gating protocol was tailored based on a real-time assessment of motion artifacts within the non-enhanced CT images.

In this cohort, the CCTA gating protocol was tailored based on a real-time assessment of motion artifacts within the non-enhanced CT images.

• Group A (HR < 65 bpm, n = 122): Artifact-free non-enhanced scans were observed in 118 patients (96%). These individuals underwent prospective gating at 70% of the R-R interval, achieving superior image quality (mean score: 3.6; Fig. 4). The remaining four patients (4%) exhibited artifacts on the non-enhanced scan, necessitating a transition to prospective gating with padding or retrospective gating. Despite the initial artifacts, these adjusted protocols yielded high image quality (mean score: 3.3; Fig. 5).

• Group B (HR > 65 bpm, n = 28): In this higher heart rate group, 18 patients (64%) demonstrated non-enhanced scans free of significant artifacts in the right coronary artery (RCA) or left circumflex (LCX) territories. These patients successfully underwent prospective gating (Fig. 6) with good image quality (mean score: 3.2). The remaining ten patients were managed with retrospective gating or prospective gating with padding, achieving a mean score of 3.1.

Fig. 4.

Standard low-dose prospective gating in a stable heart rate cohort. A patient with a heart rate of 60 bpm underwent both non-enhanced CT and CCTA at 70% of the cardiac cycle using prospective gating. (A, B) Multiplanar reformat (MPR) and coronal non-enhanced images demonstrate excellent visualization of the right coronary artery (RCA) at the proximal and atrioventricular groove segments, with no detectable motion artifacts. (C, D, E) Corresponding MPR CCTA images show the RCA, left circumflex (LCX), and left anterior descending (LAD) arteries to be sharply delineated and free of significant artifacts. LAD: Left anterior descending artery, RCA: Right coronary artery; LCX: Left circumflex artery; AO, Aorta.

Fig. 5.

Protocol optimization driven by pre-scan artifact detection. A patient with a heart rate of 63 bpm initially underwent non-enhanced CT at 70% of the cardiac cycle. (A, B) Multiplanar reformat (MPR) non-enhanced images demonstrate significant motion artifacts involving the right coronary artery (RCA). (C, D) CCTA reconstruction at the 70% phase confirms that these motion artifacts persist, severely degrading image quality. (E, F, G) By transitioning to retrospective gating (40–70%), curved MPR images reconstructed at the optimal 40% systolic phase show the RCA, left anterior descending (LAD), and left circumflex (LCX) arteries to be well-visualized and free of significant artifacts. This case illustrates how preselection can salvage diagnostic quality in the presence of mid-diastolic motion.

Fig. 6.

Feasibility of prospective gating at high heart rates. A patient with a heart rate of 77 bpm underwent both non-enhanced CT and CCTA at 70% of the cardiac cycle using a prospective gating protocol. (A, B) Non-enhanced CT images in multiplanar reformat (MPR) view demonstrate a well-visualized right coronary artery (RCA) at the proximal and atrioventricular groove segments, with a notable absence of motion artifacts. (C, D) Corresponding CCTA MPR images confirm a clear RCA with no significant artifacts; the distal segments and the posterior descending artery (PDA) are sharply delineated. (E) The scan achieved a high subjective image quality score.

5.3. Control group (Diagram B)

Diagram B.

Control arm. Protocols were selected based on primarily HR without the benefit of non-enhanced scan assessment.

In the control cohort, protocols were selected based on conventional institutional criteria (primarily HR) without the benefit of non-enhanced scan assessment.

• Group A (HR < 65 bpm, n = 120): While prospective gating was utilized for all 120 patients, seven (5.8%) exhibited motion artifacts that compromised the evaluation of the LCX and RCA (mean score: 3). A retrospective review of their non-enhanced scans confirmed that artifacts were already present at the 70% phase, indicating these failures were predictable and potentially avoidable via protocol adjustment.

• Group B (HR > 65 bpm, n = 30): Eight patients were scanned using prospective gating. While five achieved diagnostic quality, three (37.5%) were non-diagnostic due to severe motion (mean score: 1.7). Analysis suggests these failures could have been averted by pre-interpreting the non-enhanced scans. Furthermore, of the 22 patients who received higher-radiation protocols (padding or retrospective gating), pre-selection analysis indicated that 16 (72%) could have successfully undergone low-dose prospective gating instead.

5.4. Subjective image quality and radiation exposure

5.4.1. Subjective image quality analysis

A comparative analysis of subjective image quality across the various acquisition protocols was performed. Motion artifacts were identified as the primary determinant of image degradation, with the right coronary artery (RCA) being the segment most frequently affected during prospective gating. A strong inverse correlation was observed between heart rate (HR) and image quality, where higher HRs during acquisition were significantly associated with lower subjective quality scores. Comprehensive subjective and objective image quality metrics for both the protocol pre-selection and standard cohorts are summarized in Table 2.

Table 2.

Image quality and the overall radiation dose results in both arms of the study.

	Nonenhanced scan and HR based selection of the protocol	standard selection of the protocol	P value
Dose-length-product (DLP) (mgy)	354 ± 100	540 ± 128	0.010
Overall effective radiation dose (msv)	4.9 ± 1.4	7.5 ± 1.8	0.010
Subjective image quality score	3.5 ± 0.5	2.8 ± 0.8	0.060

5.5. Radiation dose comparison

Radiation exposure varied significantly across the different gating protocols. The mean effective radiation doses recorded were: 981 ± 358 mGy (DLP) for the retrospective protocol, 615 ± 167.7 mGy (DLP) for the prospective with padding protocol, and 298 ± 95 mGy (DLP) for the prospective protocol. The prospective gating protocol achieved a 69.6% reduction in effective radiation dose compared to the retrospective protocol and a 52% reduction compared to the prospective protocol with padding. Furthermore, the use of a lower tube voltage (100 kV) resulted in a 50% reduction in effective radiation dose compared to the 120 kV setting. Comprehensive data for the overall effective radiation doses of the two study arms are presented in Tables 2–4.

Table 3.

The effective radiation doses for the three scan protocols in the non-enhanced based selection of the CCTA protocol groups.

	Retrospective gating	Prospective gating	Prospective gating with padding	P value (retrospective vs. prospective)
Number of patients scanned with the protocol (N, %)	6 (4%)	136 (90 %)	8 (6 %)
Dose-length-product (DLP) (mgy)	981 ± 358	298 ± 95	615 ± 167.7	0.001
Effective radiation dose (msv)	13.7 ± 5	4.1 ± 1.3	8.6 ± 2.3	0.001

Table 4.

The effective radiation doses for the three scan protocols in the standard CCTA group.

	Retrospective gating	Prospective gating	Prospective gating with padding	P value (retrospective vs. prospective)
Number of patients scanned with the protocol (N, %)	13 (9 %)	122 (81 %)	15 (10 %)
Dose-length-product (DLP) (mgy)	931 ± 260	250 ± 93	543 ± 150	0.001
Effective radiation dose (msv)	13 ± 3.6	3.5 ± 1.3	7.6 ± 2.1	0.001

6. Discussion

Computed tomography (CT) technology is evolving rapidly, with a primary focus on minimizing radiation exposure without compromising diagnostic integrity. This prospective study investigated the clinical utility of analyzing preliminary non-enhanced CT images, typically acquired at 70% of the cardiac cycle, to determine the optimal CCTA gating protocol. Our findings support the hypothesis that this pre-selection strategy enhances image quality while significantly reducing the reliance on high-radiation protocols, such as retrospective gating and prospective gating with padding [11]. A central challenge in CCTA remains the delicate balance between image quality and radiation dose. Motion artifacts are the primary drivers of image degradation and are influenced by the acquisition protocol, heart rate (HR), specific cardiac phase, and total scan duration [17,18]. Furthermore, patient-specific factors, such as coronary calcification, can introduce blooming and beam-hardening artifacts. Coronary artery motion dynamics vary significantly throughout the cardiac cycle and typically accelerate at higher HR. Our results align with existing literature identifying optimal ECG-trigger windows for various HR ranges, further clarifying the complexities of coronary motion. While HR is a traditional predictor of motion, clinical practice frequently encounters unexpected artifacts that compromise diagnostic accuracy despite stable HR. Previous studies have optimized CCTA by comparing protocols based strictly on HR thresholds. For instance, Smettei et al. demonstrated that 256-slice CCTA utilizing a high-pitch FLASH protocol provided superior image quality and lower radiation doses in patients with stable HRs below 65 bpm [15]. Similarly, the PROTECTION IV trial established that a high-pitch helical strategy could achieve a 58% reduction in radiation dose while maintaining diagnostic quality in select patients [16]. Our study builds upon these findings by utilizing non-enhanced scans to move beyond HR-centric selection. By stratifying patients into two groups (HR < 65 bpm and >65 bpm) and pre-analyzing non-enhanced images, we tailored the protocol to each individual’s specific motion profile. In Group A (HR < 65 bpm), 96% of patients achieved diagnostic results using low-dose prospective gating. In Group B (HR > 65 bpm), over half of the patients were successfully scanned with prospective gating despite their elevated HR, an outcome that would likely have been missed using standard HR, based algorithms. This individualized strategy significantly reduced radiation exposure while maintaining high diagnostic performance, offering a clear advantage over conventional, rigid protocols.

7. Study limitations

While this study demonstrates significant radiation dose reduction using non-enhanced CT scan analysis, several limitations must be acknowledged: Non-Randomized Design: This was a prospective, non-randomized observational study. Although a Randomized Controlled Trial (RCT) is the gold standard for clinical evidence, our parallel-group design was chosen to evaluate the real-world integration of a refined clinical workflow in a high-volume cardiac center. To minimize potential selection bias, we utilized consecutive patient enrollment with identical inclusion and exclusion criteria for both cohorts. Furthermore, the lack of statistically significant differences in baseline variables-including Age, BMI, and Mean Heart Rate-suggests that the two groups were well-matched and that the observed dose reduction was a direct result of the protocol refinement rather than baseline patient variability. Other limitations: The study was conducted at a single tertiary cardiac center utilizing a specific 256-slice dual-source CT scanner with a relatively small number of patients. While this ensured high technical consistency and eliminated inter-scanner variability, it may limit the generalizability of our findings to smaller centers using different scanner technologies or varying levels of expertise. Although we captured total procedure time and radiation metrics, we did not perform a formal cost-benefit analysis regarding the additional time required for the non-enhanced scan analysis versus the long-term clinical benefit of reduced radiation exposure. As noted in larger trials such as PROTECTION IV, individualized protocol selection is paramount. Future multi-center randomized trials are warranted to further validate the clinical impact of non-enhanced scan assessment across diverse patient populations and different CT platforms.

8. Conclusions

Utilizing 256-slice CCTA protocols informed by a preliminary assessment of non-enhanced CT images significantly enhances subjective image quality and reduces the cumulative radiation burden. This individualized strategy facilitates the more frequent application of low-dose prospective gating, even among patients traditionally assigned to high-dose protocols based strictly on heart rate thresholds. By identifying patient-specific motion profiles prior to contrast injection, clinicians can better balance diagnostic accuracy with radiation safety. We recommend incorporating the routine analysis of non-enhanced scans into clinical workflows to optimize protocol selection and maximize patient safety in cardiac imaging.

Abbreviations

CAD

Coronary artery disease

CCTA

Coronary computed tomography angiography

CT

Computed tomography

DLP

Dose-Length-Product

ECG

Electrocardiography

HR

Heart rate

LAD

Left anterior descending artery

LCX

Left circumflex artery

MIP

Maximum intensity projection

MPR

Multi-planar reformates

MPR

Curved multiplanar reformates

RCA

Right coronary artery

VR

Volume rendering