Dynamic Attenuator

About

Summary Stanford researchers at the Pelc Lab have developed a method to personalize radiation exposure in CT scans to the specific patient and clinical indication. This method consists of a dynamic, pre-patient attenuator which replaces the traditional, static bowtie filter. This pre-patient attenuator is a significant improvement over existing methods of modulating exposure, including the bowtie filter and tube current modulation. Simulation experiments indicate that the additional dose reduction over and above existing state-of-the-art is 30% for nontargeted scanning to as high as 50% for region-of-interest scanning, without increasing the maximum variance of the scan. Further benefits may also exist for applications where dose reduction to radiosensitive organs such as the breast is desired. Scatter-to-primary ratio is also reduced. The ability to modulate exposure is especially synergistic with new, photon-counting detectors, which promise higher dose efficiencies, improved resolution and better spectral imaging, but which also exhibit non-idealities and decreased performance at high count rates. The dynamic attenuator is capable of modulating the incident count rate to avoid the performance falloff in the high flux regime. In specific applications, the reduction in variance in spectral imaging tasks can be as high as an order of magnitude.  The dynamic attenuator consists of a series of wedges which are inserted into the beam. Motors drive these wedges further into or out of the beam to change the effective cross-section of the attenuator in the beam. The net effect of the dynamic attenuator is a piecewise-linear thickness profile which can be adjusted arbitrarily, in real-time, during the scan. A prototype of this attenuator has been implemented and reconstructions have been demonstrated with low level of artifact. This package includes further disclosures as dockets S13-152, S13-228, S13-262, S13-246, S12-328. These dockets address the geometry of the wedges, algorithms to control the attenuator, methods to calibrate the attenuator using optical or other real-time feedback, k-edge material selection for the attenuator, and alternative designs for the attenuator.   Applications Dose reduction in CT scanning Enables photon counting detectors with low count rates   Advantages Reduced radiation dose by 30% Enables volume-of-interest scans with further dose reductions Enables photon counting detectors by protecting detectors from the high-count regime Reduces scatter-to-primary ratio, further improving image quality Other dockets included in package:  Calibration of the dynamic attenuator using optical linear encoders or other mechanisms to allow for very fast and accurate readout of motion Control of the dynamic attenuator in real time using a variety of possible algorithms Other geometries and configurations of the dynamic attenuator Material selection of the dynamic attenuator, including k-edge material selection in spectral imaging applications to improve dose efficiency