Lens dose in routine head CT: comparison of different optimization methods with anthropomorphic phantoms

Area of Science:

• Radiological physics
• Medical imaging
• Radiation protection

Background:

• Cranial computed tomography (CT) scans involve radiation exposure to the eye lenses.
• Minimizing radiation dose to sensitive organs like the lens is crucial for patient safety.
• Optimization techniques are continuously being explored to reduce radiation dose in CT procedures.

Purpose of the Study:

• To evaluate various optimization methods for reducing eye lens dose during head CT.
• To assess the impact of these methods on image quality parameters such as noise and contrast.

Main Methods:

• Two anthropomorphic phantoms were scanned using a standard head CT protocol.
• Techniques evaluated included bismuth shielding, gantry tilting, and organ-based tube current modulation, individually and in combination.
• High-sensitivity metal oxide semiconductor field effect transistor dosimeters measured equivalent doses in the head region.
• Region of Interest (ROI) analysis quantified changes in image noise and contrast.

Main Results:

• Gantry tilting was the most effective method, reducing lens dose by approximately 75% by excluding lenses from the primary beam, with minimal impact on image noise.
• Organ-based tube current modulation decreased lens dose by about 30% but increased image noise by up to 30% in posterior and central brain regions.
• Bismuth shields reduced lens dose by up to 25%.

Conclusions:

• Gantry tilting is a highly effective strategy for reducing eye lens dose in head CT without compromising image quality, where feasible.
• Patient geometry influences the effectiveness of dose optimization techniques.
• When gantry tilting is not fully applicable, organ-based tube current modulation and bismuth shields serve as valuable adjuncts for eye lens dose reduction.