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Home All issues Volume 61 / No 2 (Avril-Juin 2026) Radioprotection, 61 2 (2026) 113-120 Full HTML
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Issue
Radioprotection
Volume 61, Number 2, Avril-Juin 2026
Page(s) 113 - 120
DOI https://doi.org/10.1051/radiopro/2025029
Published online 15 June 2026

© A. El Khatib et al., Published by EDP Sciences 2026

Licence Creative CommonsThis is an Open Access article distributed under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

1 Introduction

Computed tomography (CT) is a powerful diagnostic tool that provides high-quality 3D images, enabling fast and accurate diagnoses. As a specific technique, computed tomography angiography (CTA) uses an intravenous contrast medium to non-invasively produce detailed images of blood vessels, which are used to diagnose a wide range of vascular conditions, such as aneurysms, stenosis, and pulmonary embolism. It also aids interventional radiologists and surgeons during endovascular interventions or surgical procedures (Foley and Karcaaltincaba, 2003).

The technological advancements in CTA, such as enhanced spatial resolution and reduced scanning durations, have augmented its demand and broadened its clinical applications (Kumamaru et al., 2010), offering reduced invasiveness and potentially obviating the necessity for surgical intervention while providing accurate diagnostic results (Tins et al., 2001). Despite its advantages, the extensive use of this technology raises concerns about inappropriate applications and unwarranted patient radiation exposure (Hall and Brenner, 2012). The increased use of CT scans has raised concerns about patient dose and radiation exposure. While providing valuable diagnostic information, CT imaging contributes a substantial portion of the collective effective dose from medical procedures, with reports suggesting it may account for almost half of the total radiation exposure in the United States (Ataç et al., 2015; McDermott et al., 2019). Studies emphasize the importance of optimizing radiation doses in CT examinations to mitigate potential risks, especially considering the association between ionizing radiation and the development of neoplasia (Power et al., 2016). Despite ongoing debates about the cancer risks associated with CT scans, efforts towards dose reduction and optimization remain paramount in ensuring patient well-being and minimizing unnecessary radiation exposure (McCollough et al., 2015). To mitigate these risks, it is crucial to promote optimization processes aligned with the As Low As Reasonably Achievable (ALARA) principle (Kalender, 2014). One of the key optimization tools is the implementation of Diagnostic Reference Levels (DRLs), which serve as investigative thresholds to discern radiation doses that deviate significantly from the norm (Nenot et al., 2009). However, there is a notable gap in DRLs for the CTA protocols in Morocco (Mohiy et al., 2012).

DRLs, as delineated by the International Commission on Radiological Protection (ICRP) in 1996, are established based on the CT dose index volume (CTDIvol) and dose length product (DLP) (ICRP, 2001). In 2000, the mandatory incorporation of DRLs was instituted at the European level, with successive surveys conducted across various European nations, including Italy (Palorini et al., 2014), the United Kingdom ( Shrimpton, 2003), Ireland (Foley et al., 2012), and Switzerland (Treier et al., 2010). The UK study observed a notable 50% reduction in average dose from 1985 to 2000, attributed in part to the utilization of DRLs (Shrimpton, 2003; Wallace, 2010). DRLs are typically derived from the 50th or 75th percentile values of CTDIvol and DLP, with the ICRP advocating for their establishment through patient dose assessments at local, regional, or national levels (ICRP, 2017). To our knowledge, no study has been conducted to determine DRLs for CTA in Morocco.

The primary objective of this study was to establish local DRLs and assess radiation doses for CTA examinations on adult patients. The investigation was conducted at two public and two private hospitals across Morocco. Using the 75th percentile of CTDIvol and DLP distributions, local DRLs were determined and compared with international DRL values.

2 Materials and methods

2.1 Data collection

Data collection was performed retrospectively from the Picture Archiving and Communication System (PACS) for each hospital, on a cohort of 2283 adult participants (951 male and 1332 female), with a mean age of 61 yr (16 to 113 yr). The study included a minimum of 50 CT exams per hospital, covering at least three types of CTA examinations. Data was collected from two large public medical centers and two private clinics, and was categorized by CTA examination type and the CT systems used to analyze the frequency of the examinations. Patient confidentiality and anonymity were respected. Patient dosimetry was based on the CTDIvol and DLP. The 75th percentile values from their distributions were proposed as LDRLs and compared with international DRL values.

2.2 CTA protocols

The CT scanners used in this study were distributed as follows: Hospital A utilized a General Electric (GE) Healthcare Optima CT 540 (16 detectors), and Hospital B employed a GE EVO-REVO (64 detectors). Hospital C used a Philips Brilliance scanner (16 detectors), while Hospital D operated a Siemens SOMATOM go now (16 detectors). Most of the examined protocols are equipped with tube current modulation software, except for the brain CTA examinations.

2.3 Statistical analysis

Statistical analysis was performed using IBM SPSS Statistics v. 20. Descriptive statistics (mean, median, range) were calculated for the demographic and dosimetric data (CTDIvol and DLP) from each hospital. Local DRLs were determined from the 75th percentile of the CTDIvol and DLP. An Analysis of Variance (ANOVA) was used to assess dose differences for identical CTA examinations across the four CT systems.

3 Results

Dose indicator data, CTDIvol and DLP, are presented in Tables 2 and 3, respectively, which include mean values and local DRLs for the four hospitals, with LDRLs also compared to international DRL values in Table 4.

An Analysis of Variance (ANOVA) revealed a highly significant difference (p < 0.001) in CTDIvol between hospitals for all vascular examinations analyzed. The mean CTDIvol values for various CTA examinations are presented in Table 2. The variations in CTDIvol values were as follows For Brain CTA, a 42.12% difference was observed between institutions. In Carotid CTA, Hospital B recorded the highest value of 17.29 mGy, with discrepancies of 52.04%, 78.64%, and 110.69% compared to Hospitals A, C, and D, respectively. For Pulmonary Arteries CTA, Hospital C exhibited the highest value of 11.20 mGy, with differences of 40.34%, 108.12%, and 56.59% compared to Hospitals B, D, and A, respectively. In Abdominal Aorta CTA, CTDIvol values were similar between centers B and C, however Hospital A registered the highest value, with differences of 28.84% and 43.18% compared to Centers B and C, respectively. Total Aorta CTA revealed a value of 7.53 mGy at Hospital A, with a difference of 40.55% compared to center C. Lastly, Lower Limb CTA showed the highest value at Hospital B, surpassing Hospitals C, A, and D with differences of 48.53%, 75.91%, and 84.73%, respectively (as shown in Tab. 2)

An analysis of DLP values across various CTA examinations and hospitals using the analysis of Variance (ANOVA) showed significant differences for most comparisons. Notably, no significant difference was found for Brain CTA (p = 0.823) and the A-D hospital pair for lower limb CTA (p = 0.219). Conversely, significant variations (p < 0.05) were observed in mean DLP values for Carotid, Pulmonary Arteries, Abdominal Aorta, Total Aorta, and several pairs of hospitals for lower limb CTA (as shown in Tab. 3). For Brain CTA, a difference of 10.32% was observed between Hospitals A and B. In Carotid CTA, Hospital B recorded the highest values, with differences of 10.39%, 46.17%, and 60.84% compared to Hospitals A, C, and D, respectively. For Pulmonary Artery CTA, differences of 10.38%, 37.14%, and 43.43% were observed compared to Hospitals C, A, and D, respectively. In vascular explorations of the Abdominal Aorta, differences of 4.93% and 14.37% were noted compared to Hospitals A and C, respectively. In addition, for Lower Limb CTA, variations of 18.81%, 40.12%, and 45.08% were noted compared to Centers C, D, and A, respectively. Lastly, Total Aorta CTA revealed a difference of 57.24% between Centers A and C.

Table 1

The participant data classified according to CTA examinations and the respective CT systems utilized.

Table 2

Analysis of CTDIvol derived from examined CTA procedures.

Table 3

Analysis of DLP derived from examined CTA procedures.

Table 4

Comparison of IDRLs for CTA examinations with published DRL values.

4 Discussion

The comparison of LDRLs revealed that Hospital B recorded the highest LDRLs, except for the pulmonary artery protocol in terms of CTDIvol. Conversely, Hospital D generally exhibited the lowest DRL values, except for the pulmonary artery and lower limb protocols in terms of CTDIvol and DLP, respectively. The lower DRLs at Hospital D can be attributed to more optimized acquisition parameters programmed by the radiological technologist. For instance, the maximum kV used is 110 kV, and the pitch values are the highest compared to the other hospitals, favorably affecting the dose received by patients. Additionally, the protocols are 100% monophasic, which is not the case in the other hospitals. During data collection, it was observed that all CT examinations at Hospital D were conducted in the presence of a radiologist, ensuring optimization of the scan length.

In contrast to Hospital D, Hospital B generally exhibited the highest DLP values. For the Brain CTA protocol, an analysis of acquisition parameters between Hospitals A and B revealed that they are nearly identical, except for the number of phases used. Hospital A employed two phases in 86% of exams, whereas Hospital B used two phases in 97% of exams. This increase accounts for the 9% rise in DLP values (1117.85 mGy x cm vs. 1233.17 mGy x cm). Furthermore, LDRLs values in terms of CTDIvol experienced a substantial increase of approximately 45% (24.5 vs 45.06), which could be attributed to differences in the phantoms used for scanner calibration or the use of body phantoms for calibrating Brain CTA protocols. The differences in CTDIvol values can be significant due to variations in the radiation dose absorbed per unit length in a CT scan, influenced by factors like machine model and acquisition parameters (Ouma et al., 2023). Conversely, DLP values may not show significant differences because they represent the total radiation dose received by the patient over the entire scan. This is calculated by multiplying the CTDIvol by the scan length, which is greatly affected by the scan length and the number of series performed during the CT examination. In this regard, Benmessaoud et al., (2021b) demonstrated that DLP values increase linearly with the number of scan phases and the scan length. Regarding the carotid CTA protocol, the increase in DRLs at Hospital B in terms of CTDIvol and DLP can be attributed to the specific acquisition parameters used. Hospital B employs a140 kV setting, a pitch of 0.984, and multiphasic protocols with three phases in 91% of exams. These factors explain the observed rise in CTDIvol and DLP compared to Hospitals A,C, and D. Specifically, Hospital A uses a 120 kV setting, a pitch of 1.375, with three phases in 80% of exams. Hospital C uses a 120 kV setting, a pitch of 1.375, with two phases in 45% of exams. Hospital D uses a 110 kV setting, a pitch of 1.2, with one phase in 100% of exams. Tube voltage (kV) significantly influences CT scans by impacting radiation dose and image quality. Lowering the tube voltage decreases radiation doses, with dose being proportional to the square of the tube current. Nijhof et al. (2016) demonstrated that reducing tube voltage to 80 kVp reduces CTDIvol by 38% in abdominal CTA. Fanous et al. (2012) observed similar reductions with 100 kVp in pulmonary CTA for patients under 100 kg, achieving a 37% reduction in CTDIvol compared to 120 kVp. During data collection, it was revealed that Hospital D used the lowest contrast agent volume among the hospitals, this possibly explaining its lower CTDIvol values. Ippolito et al. (2015) confirmed that lower kV settings coupled with reduced contrast media volumes lower patient doses and CTDIvol. Using 100 kVp with 30 ml of contrast medium significantly reduces radiation doses while maintaining diagnostic quality.

For the pulmonary artery CTA protocol, the observed variations are attributed to the combination of adjusted parameters. Hospital C utilized the highest kV, with a voltage of 120 kV, compared to 110 kV in the other hospitals, which may account for the elevated CTDIvol observed at Hospital C. Conversely, Hospital B exhibited the highest DLP values, likely due to the use of two-phase protocols in 90% of the exams for the pulmonary artery.

With regards to the abdominal aorta CTA protocol, the DRL values in terms of CTDIvol and DLP did not show significant differences between the three hospitals. Hospital B recorded the highest values, likely due to the use of two phases in 100% of the examinations, whereas Hospitals A and C used two phases in 85% and 50% of the examinations, respectively.

With respect to the total aorta protocol, Hospital C presented the highest DRL values compared to Hospital A, with significant differences in terms of CTDIvol and DLP. This variation can be explained by the acquisition parameters: Hospital C used a voltage of 120 kV and three phases in 100% of the examinations, whereas Hospital A used 110 kV and three phases in 60% of the examinations.

As for the lower limb CTA protocol, Hospital B exhibited the highest LDRL values. This is attributed to the combination of acquisition parameters used, being the only hospital to use a voltage of 120 kV, while the other hospitals used 100 kV. Additionally, the number of phases was 2 in 88% of the examinations at Hospital B, compared to 50% at Hospital C and 1 phase in 100% of the examinations at Hospital D.The pitch was 0.969 at Hospital B, compared to 1.375 at Hospital C and 1.5 at Hospital D. Notably, The integration of a high-pitch protocol with iterative reconstruction techniques enables substantial dose reduction (Gariani et al. 2018).

The recorded LDRLs were compared to existing studies in terms of CTDIvol and DLP. Our results demonstrate variability: some DRLs are comparable to those in previous studies, while others are either lower or higher.

As far as the brain CTA protocol is concerned, Hospital A shows CTDIvol values lower than those reported by Matsunaga et al. (2019), Treier et al. (2010), and Kim et al. (2015), with differences of 65.5%, 60%, and 39%, respectively. Conversely, the values are similar to those of Cho (2013) and 47.5% higher than those of Zensen et al., (2021). In comparison with Hospital B, the values are 30% and 21% lower than those of Matsunaga et al. (2019) and Treier et al. (2010), respectively, but 16%, 26.7%, and 73% higher than those of Kim et al. (2015), Cho (2013), and Zensen et al. (2021), respectively.In terms of DLP, the results from Hospitals A and B are lower than those of Kim et al. (2015) and Cho (2013), with respective differences of 26–24% and 23–22%. However, they are higher than those of Matsunaga et al. (2019), Treier et al. (2010), and Zensen et al. (2021), with respective differences of 10-27-65% and 13-29-66%.

In relation to the carotid CTA protocol, the results from Hospitals C and D are lower than those of Treier et al. (2010) and Aberle et al. (2020) in terms of CTDIvol, with respective differences of 54.8% and 17.54%, and 70% and 45.6%, respectively. In contrast, Hospitals A and B show values 21% and 43% higher than those of Aberle et al. (2020), but 30% and 2.75% lower than those of Treier et al. (2010). In terms of DLP, the results from Hospitals A, B, C, and D are higher than those of Treier et al. (2010), with differences ranging from 16% to 62%, and higher than those of Aberle et al. (2020), with differences ranging from 39.5% to 72%.

For the pulmonary artery CTA protocol, all DRLs in terms of CTDIvol are lower than those reported in the published studies, with differences ranging from 21.8% to 80%. In terms of DLP, our results were comparable to those in previous studies, except for Hospital B, which showed a significantly higher value, with differences ranging from 19.2% to 54.1%.

As for the abdominal aorta CTA protocol, all DRLs in terms of CTDIvol are lower than those reported by Salama et al., (2017), Treier et al. (2010), and Shrimpton et al. (2018), with differences ranging from 19% to 74%. In terms of DLP, Hospital C shows a value 22.7% lower than that of Salama et al. (2017), but almost equivalent to that of Shrimpton et al., (2018). Hospitals A and B show significant differences compared to Treier et al. (2010), with differences of 55.2% and 51.4%, respectively, and compared to Shrimpton et al. (2018), with differences of 28.3% and 22.1%, respectively. The value recorded by Salama et al. (2017) is similar to that of Hospital B, but differs from that of Hospital A by 9%.

Regarding lower limb CTA, the LDRLs from our study in terms of CTDIvol and DLP are lower than the values reported in previous studies. For CTDIvol, our results show differences ranging from 56.2% to 82.2% compared to Salama et al. (2017) and from 5% to 61.5% compared to Sulieman et al. (2024). In terms of DLP, significant differences were observed when comparing the results of Sulieman et al. (2024) with those from hospitals A, B, C, and D, with percentage differences of 83%, 64.5%, 75.8%, and 79%, respectively. In contrast, the comparison with the values from Salama et al. (2017) shows differences of 54.4%, 4.27%, 34.6%, and 45%, respectively.

An important factor in this discrepancy observed is the data collection methodology. However, the sample included in this study was based in the majority of the CTA examination involving multiphasic protocols. In contrast, the majority of the previous studies doesn’t describe the protocol used.

Regarding the Brain CTA protocol, the comparison of the LDRLs from this study with those from previous studies showed comparable results, except for the study by Zensen et al. (2021). This discrepancy arises because the Brain CTA protocol in Zensen et al. (2021) was calibrated using a 32 cm body phantom. It is well established that CTDIvol measured in a head phantom is higher than that in a 32 cm phantom under identical technical parameters. Additionally, the radiation dose is influenced by beam filtration (including added filtration and shaping filter), with the shaping filter having the most significant impact, this is why the selection of beam filtration and phantom type for a CT examination must be determined by the anatomical region (head or body) and the patient’s size (large or small).

For carotids examinations, it is known that the DLP values are significantly influenced by the scan length and the number of series conducted within the same examination, with increases in these factors resulting in higher DLP values. In addition to different tube voltages was used in the current study set at 110 kV in the hospital D, 120 kV for the hospital C and A and 140 for the hospital B. however, Eller et al. (2019) reported that Carotid CTA using the lowest available voltage (70 kV) is feasible and reduce the CTDIvol by 22%, DLP by 20%, while maintaining the image quality 55. This is particularly important given that radiosensitive organs, such as the thyroid gland and eye lenses, are within the irradiated area. The combination of high kV with multiphasic protocol may be explain the discrepancies showed in terms of the DLP. Hospital A and B used 3 series in the 80% of the examinations and 3 in 91%, respectively, and Treier et al. (2010) used an examination consisting of a native phase followed by a contrast agent phase.

In the context of the CTPA and abdominal aorta protocol, the parameters used are not detailed in comparable studies, except for Harun et al. (2020) and Salama et al. (2017). Harun et al. (2020) used the kV settings manually with a low pitch protocol of 0.798 and a single-phase technique. Salama et al. (2017) used a combination of 120 kV and low pitch set at 1. Conversely, our study implemented a combination of high pitch and multiphasic protocols. Research indicates that high pitch protocols in CT imaging significantly affect the CTDIvol, with potential reductions in radiation dose by up to 48% (Atlı et al. 2018) and 68% (Ismail et al. 2017).

Regarding the protocol for lower limb examinations, the observed differences may be attributed to several factors. The use of non-optimized protocols, particularly the deactivation of the ATCM technique in 22% of the protocols, likely contributed to these higher values.

5 Conclusion

This study establishes the first national DRLs for CTA in Morocco, revealing significant variations in CTDIvol and DLP across hospitals and protocols. LDRLs varied significantly, with Hospital D having the lowest DRLs due to optimized practices and Hospital B having the highest due to more scan phases. Moroccan LDRLs were generally lower in CTDIvol but higher in DLP compared to international studies, a discrepancy attributed to specific protocols and longer scan ranges. The findings underscore the need for protocol optimization to align doses with international standards and set a foundation for future research to refine these benchmarks.

Funding

This research did not receive any specific funding.

Conflicts of interest

The authors declare that they have no conflict of interest.

Data availability statement

Data in this article are not publicly available due to confidentiality and privacy restrictions, authors can provide necessary information or clarification upon personal request.

Author contribution statement

All authors contributed to the design and implementation of the research, to the analysis of the results and to the writing of the manuscript.

Ethics approval

This study did not carry out activities that would require approval by a research ethics committee.

Informed consent

This article does not contain any studies involving human subjects.

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Cite this article as: El Khatib A, Tahiri M, El Baydaoui R, El Kafhali M, Bouadel I, Oubaddi T, Halimi A, Yassir A, Mkimel M. 2026. Establishment of local diagnostic reference level for computed tomography angiography in Morocco. Radioprotection 61(2): 113–120. https://doi.org/10.1051/radiopro/2025029

All Tables

Table 1

The participant data classified according to CTA examinations and the respective CT systems utilized.

In the text
Table 2

Analysis of CTDIvol derived from examined CTA procedures.

In the text
Table 3

Analysis of DLP derived from examined CTA procedures.

In the text
Table 4

Comparison of IDRLs for CTA examinations with published DRL values.

In the text

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