Soft-tissue imaging with C-arm cone-beam CT using statistical reconstruction

Abstract

The potential for statistical image reconstruction methods such as penalized-likelihood (PL) to improve C-arm cone-beam CT (CBCT) soft-tissue visualization for intraoperative imaging over conventional filtered backprojection (FBP) is assessed in this work by making a fair comparison in relation to soft-tissue performance. A prototype mobile C-arm was used to scan anthropomorphic head and abdomen phantoms as well as a cadaveric torso at doses substantially lower than typical values in diagnostic CT, and the effects of dose reduction via tube current reduction and sparse sampling were also compared. Matched spatial resolution between PL and FBP was determined by the edge spread function of low-contrast (~40–80 HU) spheres in the phantoms, which were representative of soft-tissue imaging tasks. PL using the non-quadratic Huber penalty was found to substantially reduce noise relative to FBP, especially at lower spatial resolution where PL provides a contrast-to-noise ratio increase up to 1.4–2.2 × over FBP at 50% dose reduction across all objects. Comparison of sampling strategies indicates that soft-tissue imaging benefits from fully sampled acquisitions at dose above ~1.7 mGy and benefits from 50% sparsity at dose below ~1.0 mGy. Therefore, an appropriate sampling strategy along with the improved low-contrast visualization offered by statistical reconstruction demonstrates the potential for extending intraoperative C-arm CBCT to applications in soft-tissue interventions in neurosurgery as well as thoracic and abdominal surgeries by overcoming conventional tradeoffs in noise, spatial resolution, and dose.

A retrospective, semi-quantitative image quality analysis of cone beam computed tomography (CBCT) and MSCT in the diagnosis of distal radius fractures

“…Previous studies of dental CBCT scanners also found more beam-hardening artefacts in CBCT images than in MSCT images [23,38]. Better correction algorithms and iterative methods for CBCT are currently being investigated to reduce such beamhardening artefacts [52][53][54]. In our study, the CBCT scans also showed more motion artefacts.…”

A limit on dose reduction possible with CT reconstruction algorithms without prior knowledge of the scan subject

“…18 It has also been noted that if this a priori knowledge is eliminated and the regularizer behaves like conventional rather than edge-preserving smoothing, many of the image quality improvements in iterative reconstruction disappear. 19 A priori knowledge could increase the noise reduction seen here but may also lead to biased images, such as the vanishing effect for very low contrast lesions. Stronger forms of a priori knowledge could be used but may be dangerous because when the a priori knowledge is incorrect, the final images will be further biased.…”

Low-dose preview for patient-specific, task-specific technique selection in cone-beam CT

“…These values of δ and β served as a fairly general-purpose selection that avoided patchy image noise and preserved spatial resolution. Alternative parameter selection-for example, specifically to enhance soft-tissue imaging performance 37 -is possible and completely compatible the LDP process.…”