Study design and patient enrollment

This study was a retrospective and conducted at King Saud Medical City, Riyadh City, Saudi Arabia. It is one of the largest tertiary care centers in Saudi Arabia, with a total bed capacity of 1500. The institutional review board at King Saud Medical City approved the study (H1R1-09-Mar21-02). The hospital file data of 987 patients who underwent coronary and brain vascular computed tomography (CT) radiography between September 2019 and September 2020 were retrieved.

Data collection

  • Personal information (age, gender, nationality, smoking status).

  • The presence of comorbidities (diabetes, hypertension, coronary heart disease), clinical presentation.

  • Radiological findings (CT findings, history of stroke, stroke location, type of stroke), posterior circulation calcium, and vascular findings (vertebral arteries, basilar artery, posterior cerebral artery).

The picture archiving and communication system (PACS) was searched using “coronary calcification” as a keyword to retrieve data on patients with coronary calcification.

Inclusion criteria

  • Patient who had chest and brain CT scans between September 2019 and September 2020 (n = 987).

  • Patient with coronary arteries calcifications.

  • Patient with posterior circulation calcifications.

Exclusion criteria

  • Patient with negative CAC (n = 852).

  • An interval of over 6 months between non-gated chest CT and brain CT (n = 23).

  • CT brain examinations with suboptimal image quality (e.g., posterior fossa beam-hardening) (n = 11).

The data of n = 101 patients with positive CAC who underwent non-enhanced brain CT were collected for the study.

Computed tomography (CT) examinations techniques and protocol

For non-gated chest CT, a multi-slice helical CT scanner was utilized (multi-slice 64-detector CT scanner) (Discovery CT750 HD; GE Healthcare, Chicago, IL, USA). The patients were scanned supine with their arms elevated above the head. Inspiration breathing instructions were given to reduce motion artifact (120–140 kV, Tube current–time product, 40–80 mAs depending on the patients’ habitus, and 2.5 slice thickness), and 0.625-mm thin slices were used for the chest when the data were missed.

For plain brain CT examinations, the scan was performed on either a 64-detector CT scanner (Discovery CT750 HD; GE Healthcare, Chicago, IL, USA) using a conventional CT technique (120 kV, 90 mAs, and 0.5 slice thickness) or a dual-source CT scanner (Somatom Definition Flash; Siemens; Germany) using a similar conventional CT technique (120 kV, 250 mAs, and 0.5 slice thickness).

CT examination protocol

Local CT protocols were used as follows:

  • Reconstructed axial, sagittal, coronal sets of images were utilized for chest CT scan. The spiral mode was used for calcium scoring on all patients with heart rates up to 70 bpm. For patients with heart rates greater than 70 bpm, prospective sequential imaging was used instead. All scans are performed using the ALARA principle.

  • Brain CT images used 5 mm axial reconstruction, 3 mm coronal, and 3 mm sagittal.

Image analysis

All brain images were assessed by a neuroradiologist consultant with over 20 years of experience. A set of thin-slice brain images of all included patients were reviewed. The posterior calcification was categorized according to the presence or absence of calcification in the following vascular beds: right vertebral artery, left vertebral artery, and basilar artery (Fig. 1).

Fig. 1
figure 1

Two different patients showing posterior circulation calcification. A A 46-year-old male patient with a history of posterior stroke, non-enhanced CT brain of posterior fossa demonstrating dense calcifying in the left vertebral artery. B A 55-year-old male patient with a history of stroke, non-enhanced CT brain of posterior fossa showing a dense calcification in bilateral vertebral arteries

All chest images were reviewed by radiologists with a subspecialty in thoracic imaging and over 13 years of experience. The positive CAC was assessed visually, categorizing the calcification as mild, moderate, or severe based on the guidelines suggested [13] (Fig. 2).

Fig. 2
figure 2

Two different patients showing coronary arteries calcification. A A 59-year-old male with a history of heart attack, non-contrast CT image showing severe, dense coronary calcifications involving the RCA with mild bilateral plural effusion more in the right side with associated atelectatic changes. B A 63-year-old man presented with a history of HTN, smoking and previous stroke, non-contrast CT image showing moderate-to-severe, dense coronary calcifications in the aortic route and involving the left system (LCX and LAD) as well as RCA, mild right-sided plural effusion also noted

Coronary arteries calcification scoring

The Agatston scoring system is the most quantitative scoring system for reporting the calcification of coronary arteries. Nevertheless, this technique requires special software and hardware to implement as well as standard scanning parameters, such as a small field of view (FOV) and a radiation dose necessary for a higher resolution. Therefore, the Agatston scoring system was not used. Published guidelines recommend a visual assessment and report on coronary artery calcification [13]. A visual assessment system of calcification can determine an absence of calcification, mild calcification, moderate calcification, and severe calcification. The visual estimation method has the advantage of feasibility and straightforward implementation [13].

Posterior circulation calcification scoring

To the best of our knowledge, there is no existing method for evaluating and scoring intracranial arterial calcification. A recent study reviewed the literature and discussed the assessment of intracranial calcification. The author confirmed the lack of an available method and recommended further trials to develop a consistent calcification scoring tool [14].

Statistical analysis

Descriptive and inferential statistics were used to assess the study variables. All analyses were done using SPSS version 27 (Armonk, NY: IBM Corp). A binomial logistic regression was conducted to evaluate the association between the incidence of stroke and the relevant independent variables based on previously described methods [15]. The relevant independent variables were tested for associations with stroke using the chi-square test for nominal or ordinal variables and a univariate logistic regression for continuous variables. Variables with p-values < 0.25 were subjected to a multivariate logistic regression using the backward stepwise approach. The final model included statistically significant (p < 0.05) independent variables. After removing each insignificant variable, we monitored the model fit using the log-likelihood ratio to ensure it did not significantly influence the model. The independent variables included age, gender, BMI, hypertension, diabetes, smoking, presence of a brain lesion, headache, dizziness, neurological symptoms, loss of consciousness, CAC severity, and the presence of PCC. An alpha value of 0.05 was considered significant across all tests.

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