|
Purpose: Previous work has demonstrated that structural models of surgical tools and implants can be integrated into
model-based CT reconstruction to greatly reduce metal artifacts and improve image quality. This work extends a
polyenergetic formulation of known-component reconstruction (Poly-KCR) by removing the requirement that a
physical model (e.g. CAD drawing) be known a priori, permitting much more widespread application.
Methods: We adopt a single-threshold segmentation technique with the help of morphological structuring elements
to build a shape model of metal components in a patient scan based on initial filtered-backprojection (FBP)
reconstruction. This shape model is used as an input to Poly-KCR, a formulation of known-component reconstruction
that does not require a prior knowledge of beam quality or component material composition. An investigation of
performance as a function of segmentation thresholds is performed in simulation studies, and qualitative comparisons
to Poly-KCR with an a priori shape model are made using physical CBCT data of an implanted cadaver and in patient
data from a prototype extremities scanner.
Results: We find that model-free Poly-KCR (MF-Poly-KCR) provides much better image quality compared to
conventional reconstruction techniques (e.g. FBP). Moreover, the performance closely approximates that of Poly-
KCR with an a prior shape model. In simulation studies, we find that imaging performance generally follows
segmentation accuracy with slight under- or over-estimation based on the shape of the implant. In both simulation and
physical data studies we find that the proposed approach can remove most of the blooming and streak artifacts around
the component permitting visualization of the surrounding soft-tissues.
Conclusion: This work shows that it is possible to perform known-component reconstruction without prior knowledge
of the known component. In conjunction with the Poly-KCR technique that does not require knowledge of beam
quality or material composition, very little needs to be known about the metal implant and system beforehand. These
generalizations will allow more widespread application of KCR techniques in real patient studies where the
information of surgical tools and implants is limited or not available.
|
