Timothy Peter Szczykutowicz PhD, Presenter: Equipment support, General Electric Company Research Grant, Siemens AG

Charles Anthony Mistretta PhD, Abstract Co-Author: Founder, Mistretta Medical Intellectual Property Licensing Activities Research, Siemens AG

The purpose of this study is to compare the gains in tissue compensation and dose reduction possible when using a 2D fluence field modulator compared to a 1D modulator and bowtie filtration.

A 2D fluence field modulator was simulated assuming two continuous 1D modulators could be placed orthogonal to each other. This produces an additively separable 2D fluence field. A 1D modulator was also simulated. Two different size bowtie filters were also simulated, one optimized for the head, and one optimized for the body. Comparisons were made for chest, thorax, abdomen, pelvis, and head anatomical regions. The ability to compensate for tissue was quantified by calculating the standard deviation of the sum of the attenuation from the patient anatomy and the 2D/1D modulator or bowtie. Dose comparisons were made by first setting the mA such that peak variance was minimized. The x-ray fluence incident onto the anatomy was summed and used to make relative dose comparisons between the various modulators. Lastly, a piecewise constant modulator was simulated for the 2D modulator using realistic numbers of wedges as have been previously experimentally implemented.

As expected, in terms of dose reduction and tissue compensation, the best modulation design was 2D, followed by 1D, and then bowtie filter respectively. The largest benefit from 2D modulation relative to 1D modulation was in the thorax, the smallest in the head. On average, the 2D modulated allowed for a dose reduction of 3.7 and 21 times relative to 1D and bowtie filter modulation respectively. The average increase in tissue compensation for 2D modulation was 1.2 and 3.25 times relative to 1D and bowtie modulation respectively.

2D modulation does provide large advantages over 1D tissue compensation and would likely benefit FFMCT, especially wide cone angle CT like that found on c-arm and some MDCT systems. Large dose reduction are possible when peak variance is minimized instead of average variance. 2D modulation allows for large dose reductions for large cone angle systems as z-axis dose modulation is not possible with traditional bowtie filtration/mA modulation methods for these systems.

Fluence field modulated CT (FFMCT) allows for another stride along the path of patient specific imaging dose tailoring to be realized; switching from 1D to 2D FFMCT can be done at half the dose.

Szczykutowicz, T, Mistretta, C, The Feasibility of 2D Fluence Field Modulated CT Using Attenuating Filters.  Radiological Society of North America 2014 Scientific Assembly and Annual Meeting, - ,Chicago IL. http://archive.rsna.org/2014/14004970.html