# Optimization of Bolus-Tracking Thresholds levels in Cerebral CT Angiography: Influence of Patient Characteristics on contrast enhancement dynamics and radiation dose metrics

## TL;DR

The study finds that adjusting contrast thresholds in cerebral CT scans based on patient age and gender can reduce venous contamination and improve diagnostic accuracy.

## Contribution

The study introduces an optimized bolus-tracking threshold of 105 ± 5 HU for cerebral CTA, tailored to patient characteristics.

## Key findings

- Arterial enhancement is higher in females and older patients.
- A threshold of 105 ± 5 HU reduces venous contamination with high sensitivity and specificity.
- CTDIvol is a better dose metric than SSDE for cerebral CTA.

## Abstract

Cerebral computed tomography angiography (CTA) is widely used to assess neurovascular disorders, but venous contamination often obscures arteries. Optimizing bolus-tracking thresholds is crucial, yet patient factors influencing contrast dynamics and the value of radiation dose indices in head CTA remain unclear.

To optimize bolus-tracking thresholds in cerebral CTA by examining patient-related influences on enhancement and radiation metrics.

126 adults undergoing cerebral CTA were evaluated in this prospective study. Demographics, physiologic parameters, peak enhancement time (PET), peak enhancement attenuation (PEA), and dose indices (CTDIvol, SSDE) were recorded. Linear regression identified predictors of enhancement. Two blinded radiologists graded venous contamination. ROC analysis, including age subgroups, determined the optimal HU threshold.

Median age was 55.5 years; 70% were male. PET rose with age (+0.086 s/year, p < 0.001) and was shorter in females (–2.39 s, p = 0.003). PEA increased with threshold (+1.03 HU/unit, p < 0.001). Arterial enhancement was higher in females (+40.7 HU, p < 0.001) and patients ≥60 years (+70 HU, p < 0.001). Venous enhancement correlated with PET (p = 0.023) and systolic pressure (p = 0.002). ROC analysis showed an optimal threshold of 105 ± 5 HU (AUC = 0.634; sensitivity 88.4%, specificity 77.1%). CTDIvol, but not SSDE, correlated with weight (p = 0.015).

Intrinsic (age, gender) and extrinsic (threshold) factors shape CTA enhancement. A 105 ± 5 HU threshold reduces venous contamination, especially in younger patients. CTDIvol remains the preferred dose index. Findings support individualized, resource-efficient CTA protocols aligned with UN SDGs 3, 9, and 12.