Evaluation of tilted cone-beam CT orbits in the development of a dedicated hybrid mammotomograph

Abstract

A compact dedicated 3D breast SPECT-CT (mammotomography) system is currently under development. In its initial prototype, the cone-beam CT sub-system is restricted to a fixed-tilt circular rotation around the patient’s pendant breast. This study evaluated stationary-tilt angles for the CT subsystem that will enable maximal volumetric sampling and viewing of the breast and chest wall. Images of geometric/anthropomorphic phantoms were acquired using various fixed-tilt circular and 3D sinusoidal trajectories. The iteratively reconstructed images showed more distortion and attenuation coefficient inaccuracy from tilted cone-beam orbits than from the complex trajectory. Additionally, line profiles illustrated cupping artifacts in planes distal to the central plane of the tilted cone-beam, otherwise not apparent for images acquired with complex trajectories. This indicates that undersampled cone-beam data may be an additional cause of cupping artifacts. High-frequency objects could be distinguished for all trajectories, but their shapes and locations were corrupted by out-of-plane frequency information. Although more acrylic balls were visualized with a fixed-tilt and nearly flat cone-beam at the posterior of the breast, 3D complex trajectories have less distortion and more complete sampling throughout the reconstruction volume. While complex trajectories would ideally be preferred, negatively fixed-tilt source–detector configuration demonstrates minimally distorted patient images.

Three dimensional dose distribution comparison of simple and complex acquisition trajectories in dedicated breast CT

“…Therefore, using a circular orbit would result in missing a portion of breast volume close to the chest wall, or in some cases irradiate it, but provides poor sampling. As reported in our previous studies, 26,27 using a tilted orbit allows us to remedy this shortcoming encountered by the circular orbits and provides better sampling close to the chest wall. However, to characterize trajectory-related differences, we wanted the entire breast volume to be in the FOV and easily irradiated by the circular orbit.…”

“…As has been demonstrated by us, this also leads to more nearly complete sampling throughout a larger object FOV. 8,26,27,41,44 In both cases, due to the symmetrical nature of the orbits about the 3D center of rotation (COR), the dose deposition in the volume is approximately radially symmetric. This is easily seen in the coronal Monte Carlo results [ Fig.…”

“…Based on these results, we can conclusively state that the difference in dose deposited from the two acquisition orbits is minimal, thereby mitigating the concern for over exposure of a patient breast in future clinical studies. Finally, saddle acquisition orbits have previously shown to have a significant advantage in overcoming cone beam sampling artifacts 26,27 and also promoting routine chest wall imaging of the posterior breast. 27 This capability demonstrates the superior performance of nontraditional, spherically symmetric cone beam acquisition trajectories for breast CT, which could be extended to other potential cone beam applications.…”

“…20 A comparison study has demonstrated the benefits of using complex 3D acquisition trajectories that utilize a breast CT system's polar tilting capability. 26,27 Such trajectories overcome the cone beam sampling insufficiency problem while also promoting imaging further into the breast volume, resulting in more uniformly sampled images having isotropic resolution throughout the imaged volume. With the inclusion of complex 3D acquisition trajectories in the proposed future iterations of a hybrid breast SPECT-CT system, 28 it is imperative to characterize the differences between the dose distribution within a breast volume for simple azimuthal (fixed tilt) and complex 3D (variable tilt) acquisition trajectories.…”

Dedicated breast CT: radiation dose for circle-plus-line trajectory

“…4,5 Multimodality SPECT/CT and PET/CT systems dedicated for breast imaging, wherein the CT component utilize a similar trajectory and cone-beam imaging have also been developed. 6,7 However, cone-beam imaging with a circular source trajectory does not satisfy the necessary conditions for data sufficiency. 8,9 Cone-beam imaging with such a trajectory could result in artifacts that manifest as variation in intensity and geometric distortion that are readily observed at locations away from the circular plane.…”