Computed Tomography (CT) has become a mainstay in diagnostic imaging. The high utility of CT has led to increased use and, as a result, to concerns about the radiation burden to individuals and the population. Although many technologies have been developed to reduce the dose from CT, further reductions are both possible and prudent, and the ALARA principle dictates that any reduction that is reasonably achievable should be adopted. Control of the incident radiation profile through the use of a pre-patient attenuator (""""""""bowtie"""""""" filter) is known to reduce patient dose for a given level of image quality and also to reduce the dynamic range requirements and the effects of scatter. However, systems have at most a few attenuator shape choices and the filter is fixed during the scan. At best, they are optimal for circularly symmetric cylindrical objects. By contrast, patients'attenuation properties are rather irregular. In previous research we showed that dynamic control of the illumination profile can lead to significant dose reduction, but that work assumed the use of complex and expensive source arrays. By contrast, a dynamic attenuator would be a cost effective solution for achieving similar control in the illumination profile. Such a dynamic attenuator would tailor the radiation distribution for each patient, slice location, viewing directon, and clinical application. This is aligned with efforts toward personalized medicine. The key requirement is that the attenuator needs to be very adaptive and also provide smooth variation in flux. Prior designs fall short. We have developed a design concept that meets the modulation requirements by using movable wedge attenuators with triangular cross-sections that vary in the axial direction to produce piece-wise linear, dynamic profiles. Initial computer simulations predic large reductions in dose and in the dynamic range of the x-ray signal at the detector. The dose reduction would be of immediate benefit while the reduction in dynamic range would enable the earlier adoption of photon-counting detectors that would have additional benefits. In contrast to the source array approach, the dynamic bowtie is compatible with conventional CT system designs, so if viable it could be readily translated into clinical use. In the proposed research, w will conduct thorough computer simulations to optimize the design and predict performance benefits, build a portion of a dynamic attenuator array, and conduct experiments to validate the concept. Once this research is complete, the dynamic bowtie concept would be ready for adoption into commercial systems.

Public Health Relevance

Radiation dose from CT scanning is a growing public health concern. We will develop an x-ray attenuator that will customize the radiation field to each specific patient, body section and viewing direction. The result will be a low cost and very effective method to directly reduce patient dose and at the same time improve CT performance and enable the use of new x-ray detectors that should reduce dose even further.

National Institute of Health (NIH)
National Institute of Biomedical Imaging and Bioengineering (NIBIB)
Exploratory/Developmental Grants (R21)
Project #
Application #
Study Section
Biomedical Imaging Technology Study Section (BMIT)
Program Officer
Sastre, Antonio
Project Start
Project End
Budget Start
Budget End
Support Year
Fiscal Year
Total Cost
Indirect Cost
Stanford University
Biomedical Engineering
Schools of Medicine
United States
Zip Code
Hsieh, Scott S; Peng, Mark V; May, Christopher A et al. (2016) A prototype piecewise-linear dynamic attenuator. Phys Med Biol 61:4974-88
Hsieh, Scott S; Pelc, Norbert J (2014) The piecewise-linear dynamic attenuator reduces the impact of count rate loss with photon-counting detectors. Phys Med Biol 59:2829-47
Hsieh, Scott S; Pelc, Norbert J (2014) Control algorithms for dynamic attenuators. Med Phys 41:061907
Pelc, Norbert J (2014) Recent and future directions in CT imaging. Ann Biomed Eng 42:260-8
Hsieh, Scott S; Fleischmann, Dominik; Pelc, Norbert J (2014) Dose reduction using a dynamic, piecewise-linear attenuator. Med Phys 41:021910
Hsieh, Scott S; Pelc, Norbert J (2013) The feasibility of a piecewise-linear dynamic bowtie filter. Med Phys 40:031910
Liu, Fenglin; Wang, Ge; Cong, Wenxiang et al. (2013) Dynamic bowtie for fan-beam CT. J Xray Sci Technol 21:579-90