Ulla Nikupaavo BSC, Presenter: Nothing to Disclose

Touko Kaasalainen, Abstract Co-Author: Nothing to Disclose

Vappu Reijonen PhD, Abstract Co-Author: Nothing to Disclose

Sanna-Mari Ahonen PhD, Abstract Co-Author: Nothing to Disclose

Mika Karel Kortesniemi PhD, Abstract Co-Author: Nothing to Disclose

To study different optimization methods for reducing lens dose in computed tomography (CT) head scanning. 

Two tissue-equivalent anthropomorphic phantoms were scanned with a routine head CT protocol of the brain using bismuth shielding, gantry tilting, organ-based tube-current modulation (OBTCM), or their combinations. High sensitivity MOSFET dosimeters were used to measure local equivalent doses in the head region. The relative changes in image noise and contrast were determined using ROI analysis.

The mean absorbed lens dose varied from 4.9 mGy to 19.7 mGy, and from 10.8 mGy to 16.9 mGy in the two phantoms. The most efficient method for reducing lens dose was gantry tilting leaving lenses outside the primary radiation beam, resulting in approximately 75% decrease in the lens dose. The image noise decreased especially in the anterior part of the brain. The use of OBTCM resulted in an approximately 30% decrease in the lens dose. On the other hand, image noise increased by up to 30% in the posterior and central parts of the brain. With bismuth shields, it was possible to reduce lens dose by up to 25%. Measurements with the two different phantoms showed how patient geometry affects the optimization.

Gantry tilt is an effective method to reduce the exposure of the eye lenses in the CT scanning of the brain without compromising image quality. When lenses can only partially be cropped outside the primary beam, the OBTCM or bismuth shields can also be useful in lens dose reduction.

The patient lens dose in head CT can be efficiently reduced by optimal use of different techniques without compromising clinical image quality.

Nikupaavo, U, Kaasalainen, T, Reijonen, V, Ahonen, S, Kortesniemi, M, Lens Dose in Routine Head CT: Comparison of Different Optimization Methods with Anthropomorphic Phantoms.  Radiological Society of North America 2014 Scientific Assembly and Annual Meeting, - ,Chicago IL. http://archive.rsna.org/2014/14007665.html