Dose reduction in CT urography and vasculature phantom studies using model-based iterative reconstruction

Area of Science:

• Radiological imaging and medical physics
• Computed tomography (CT) reconstruction algorithms
• Radiation dose reduction strategies

Background:

• Current CT protocols for evaluating ureters and vasculature may involve significant radiation exposure.
• Model-based iterative reconstruction (MBIR) offers potential for improved image quality at lower doses compared to filtered back-projection (FBP).
• Evaluating the feasibility of dose reduction is crucial for patient safety and clinical practice.

Purpose of the Study:

• To assess the effectiveness of MBIR in reducing radiation dose for CT imaging of ureters and vasculature.
• To compare image noise and contrast-to-noise ratio (CNR) between MBIR and FBP at various dose levels.
• To determine the minimum radiation dose achievable with MBIR while maintaining diagnostic image quality.

Main Methods:

• A tissue-equivalent CT phantom with simulated ureters and vasculature (tubes with varying diameters and contrast dilutions) was scanned.
• Scans were performed using a 64-channel CT scanner at 140 kVp and 120 kVp, with display volumetric CT dose index (CTDIvol) ranging from 24 mGy down to 0.8 mGy.
• Images were reconstructed using both FBP and MBIR; noise and CNR were measured and compared using a factorial design.

Main Results:

• MBIR consistently produced lower image noise than FBP across all tested CTDIvol levels (p < 0.0001).
• For a 12 mm object (HU 600), MBIR at 1.7 mGy achieved higher CNR than FBP at 24 mGy (p < 0.0001).
• MBIR at 1.7 mGy demonstrated equivalent CNR to FBP at 24 mGy for 5 mm (HU 250) and 2 mm (HU 100) simulated vessels.

Conclusions:

• Low-dose CT (3.6 mGy) using MBIR for vasculature and ureter phantoms yields comparable noise and CNR to FBP at approximately one-sixth the dose.
• MBIR facilitates significant radiation dose reduction, suggesting that a 1 mSv CT examination of the ureters and vasculature may be clinically feasible.
• This study highlights MBIR's potential for maintaining diagnostic image quality in low-dose CT applications for urinary and vascular systems.