Feasibility of a Low Injection Rate Protocol for Bronchial Artery Imaging Using Spectral CT Angiography

Abstract Rationale and Objectives: Computed tomography (CT) angiography of the bronchial artery (BA) typically requires high-concentration iodine contrast agents and high injection rates to achieve adequate vessel enhancement, which increases the risks of contrast extravasation and renal burden. Spectral CT with monochromatic imaging can improve vascular contrast at lower energy levels (<70 keV) by enhancing the photoelectric effect of iodine. This study aimed to evaluate the feasibility of a low-injection-rate contrast protocol combined with spectral CT for BA imaging. Materials and Methods: One hundred nine patients (72 males, 61.05±12.72 years) who underwent chest spectral CT angiography (GE Revolution 256) with a low injection rate (≤3.0 mL/s, 60–70 mL of 350 mgI/mL iohexol) were retrospectively enrolled. Monochromatic images at the optimal keV (determined by the optimal contrast-to-noise ratio [CNR] curve), 60 keV, and 70 keV were reconstructed. The signal-to-noise ratio (SNR), CNR, and subjective image quality scores (5-point scale) of the BA were compared among the three groups using non-parametric tests with Bonferroni correction. Results: A total of 253 BAs (125 left, 128 right) were displayed. The optimal monochromatic energy for BA ranged from 40 to 50 keV (mean: 43.62±2.19 keV). Significant differences in SNR, CNR, and subjective scores were observed among the three groups (all P < 0.05). The optimal keV group (approximately 44 keV) yielded the highest CNR and best image quality on maximum intensity projection, volume rendering, and fused images. Conclusion: Under a low-contrast-injection-rate protocol, spectral CT angiography at approximately 44 keV provides optimal CNR and significantly improves BA image quality, offering a reliable imaging method for BA evaluation.