Purpose: Atherosclerosis detection remains challenging in coronary CT angiography for patients with cardiac implants. Pacing electrodes of a pacemaker or lead components of a defibrillator can create substantial blooming and streak artifacts in the heart region, severely hindering the visualization of a plaque of interest. We present a novel reconstruction method that incorporates a deformable model for metal leads to eliminate metal artifacts and improve anatomy visualization even near the boundary of the component.
Methods: The proposed reconstruction method, referred as STF-dKCR, includes a novel parameterization of the component that integrates deformation, a 3D-2D preregistration process that estimates component shape and position, and a polyenergetic forward model for x-ray propagation through the component where the spectral properties are jointly estimated. The methodology was tested on physical data of a cardiac phantom acquired on a CBCT testbench. The phantom included a simulated vessel, a metal wire emulating a pacing lead, and a small Teflon sphere attached to the vessel wall, mimicking a calcified plaque. The proposed method was also compared to the traditional FBP reconstruction and an interpolation-based metal correction method (FBP-MAR).
Results: Metal artifacts presented in standard FBP reconstruction were significantly reduced in both FBP-MAR and STF- dKCR, yet only the STF-dKCR approach significantly improved the visibility of the small Teflon target (within 2 mm of the metal wire). The attenuation of the Teflon bead improved to 0.0481 mm<sup>-1 </sup>with STF-dKCR from 0.0166 mm<sup>-1</sup> with FBP and from 0.0301 mm<sup>-1</sup> with FBP-MAR – much closer to the expected 0.0414 mm<sup>-1</sup>.
Conclusion: The proposed method has the potential to improve plaque visualization in coronary CT angiography in the presence of wire-shaped metal components.
Acquisition of CT images with comparable diagnostic power can potentially be achieved with lower radiation exposure than the current standard of care through the adoption of hardware-based fluence-field modulation (e.g. dynamic bowtie filters). While modern CT scanners employ elements such as static bowtie filters and tube-current modulation, such solutions are limited in the fluence patterns that they can achieve, and thus are limited in their ability to adapt to broad classes of patient morphology. Fluence-field modulation also enables new applications such as region-of-interest imaging, task specific imaging, reducing measurement noise or improving image quality. The work presented in this paper leverages a novel fluence modulation strategy that uses “Multiple Aperture Devices” (MADs) which are, in essence, binary filters, blocking or passing x-rays on a fine scale. Utilizing two MAD devices in series provides the capability of generating a large number of fluence patterns via small relative motions between the MAD filters. We present the first experimental evaluation of fluence-field modulation using a dual-MAD system, and demonstrate the efficacy of this technique with a characterization of achievable fluence patterns and an investigation of experimental projection data.
Proc. SPIE. 10132, Medical Imaging 2017: Physics of Medical Imaging
KEYWORDS: Gold, 3D acquisition, 3D image reconstruction, CT reconstruction, Data modeling, Modulation, X-rays, 3D modeling, Tomography, Data acquisition, Image quality, Computed tomography, 3D scanning, 3D image processing
Purpose: Commonly 2D scouts or topograms are used prior to CT scan acquisition. However, low-dose 3D scouts
could potentially provide additional information for more effective patient positioning and selection of acquisition
protocols. We propose using model-based iterative reconstruction to reconstruct low exposure tomographic data to
maintain image quality in both low-dose 3D scouts and reprojected topograms based on those 3D scouts.
Methods: We performed tomographic acquisitions on a CBCT test-bench using a range of exposure settings from
16.6 to 231.9 total mAs. Both an anthropomorphic phantom and a 32 cm CTDI phantom were scanned. The penalized-likelihood
reconstructions were made using Matlab and CUDA libraries and reconstruction parameters were tuned to
determine the best regularization strength and delta parameter. RMS error between reconstructions and the highest
exposure reconstruction were computed, and CTDIW values were reported for each exposure setting. RMS error for
reprojected topograms were also computed.
Results: We find that we are able to produce low-dose (0.417 mGy) 3D scouts that show high-contrast and large
anatomical features while maintaining the ability to produce traditional topograms.
Conclusions: We demonstrated that iterative reconstruction can mitigate noise in very low exposure CT acquisitions
to enable 3D CT scout. Such additional 3D information may lead to improved protocols for patient positioning and
acquisition refinements as well as a number of advanced dose reduction strategies that require localization of
anatomical features and quantities that are not provided by simple 2D topograms.
We introduce a novel strategy for fluence field modulation (FFM) in x-ray CT using multiple aperture devices (MADs).
MAD filters permit FFM by blocking or transmitting the x-ray beam on a fine (0.1-1 mm) scale. The filters have a number
of potential advantages over other beam modulation strategies including the potential for a highly compact design, modest
actuation speed and acceleration requirements, and spectrally neutral filtration due to their essentially binary action. In this
work, we present the underlying MAD filtration concept including a design process to achieve a specific class of FFM
patterns. A set of MAD filters is fabricated using a tungsten laser sintering process and integrated into an x-ray CT test
bench. A characterization of the MAD filters is conducted and compared to traditional attenuating bowtie filters and the
ability to flatten the fluence profile for a 32 cm acrylic phantom is demonstrated. MAD-filtered tomographic data was
acquired on the CT test bench and reconstructed without artifacts associated with the MAD filter. These initial studies
suggest that MAD-based FFM is appropriate for integration in clinical CT system to create patient-specific fluence field
profile and reduce radiation exposures.