Dynamic detector offsets for field of view extension in C‐arm computed tomography with application to weight‐bearing imaging

Abstract

Purpose: In C-arm computed tomography (CT), the field of view (FOV) is often not sufficient to acquire certain anatomical structures, e.g., a full hip or thorax. Proposed methods to extend the FOV use a fixed detector displacement and a 360• scan range to double the radius of the FOV. These trajectories are designed for circular FOVs. However, there are cases in which the required FOV is not circular but rather an ellipsoid. Methods: In this work, the authors show that in fan-beam CT, the use of a dynamically adjusting detector offset can reduce the required scan range when using a noncircular FOV. Furthermore, the authors present an analytic solution to determine the minimal required scan ranges for elliptic FOVs given a certain detector size and an algorithmic approach for arbitrary FOVs. Results: The authors show that the proposed method can result in a substantial reduction of the required scan range. Initial reconstructions of data sets acquired with our new minimal trajectory yielded image quality comparable to reconstructions of data acquired using a fixed detector offset and a full 360• rotation. Conclusions: Our results show a promising reduction of the necessary scan range especially for ellipsoidal objects that extend the FOV. In noncircular FOVs, there exists a set of solutions that allow a trade-off between detector size and scan range. C 2015 American Association of Physicists in Medicine. [http://dx

Cone‐beam CT imaging with laterally enlarged field of view based on independently movable source and detector

“…The corresponding imaging performance was experimentally and quantitatively assessed by means of the THETIS, CatPhan, and Alderson phantom and compared to conventional isocentric and non‐isocentric full‐scans. This methodology forms a more practical approach compared to the presentation of former enlarged FOV scanning techniques, which represent in many cases only a theoretical, in‐silico based proof‐of‐principle 12,20,34 . In this study, we decided for a complete experimental and practical validation with a launched O‐arm CBCT device.…”

“…To account for this drawback, several approaches for CBCT imaging with enlarged FOVs particularly applied on C‐arms 12,16 and on‐board imaging systems 17,18 of linear accelerators for radiotherapy have been proposed, as reviewed by Hatamikia et al 19 . The most common ansatz is to shift the detector with a fixed offset tangentially to the gantry, 20,21 which allows in one single 360° acquisition capturing a FOV with up to almost doubled lateral extension compared to the conventional imaging geometry (i.e., with opposing X‐ray source and FPD).…”

Technical note: Extended longitudinal and lateral 3D imaging with a continuous dual‐isocenter CBCT scan

“…5 However, most work completed to date on robotic CBCT systems has been focused on single direction expansion (i.e., only lateral or longitudinal expansion). For example, lateral CBCT expansion on robotic CBCT systems has been previously demonstrated using offset 6 and rotated detector 7 configurations. Similarly, longitudinal CBCT expansion on robotic CBCT systems has been achieved using non-circular trajectories such as the multi-turn reverse helical 8,9 and line-ellipse-line trajectory.…”

Task-driven source–detector trajectories in cone-beam computed tomography: I. Theory and methods

“…To date, these flexible orbits have mainly been used to address the FOV and the sampling issues in interventional CBCT. For example, noncircular trajectories have been used to provide extended axial 9 and elliptical 10 FOVs and to improve 3-D sampling and data completeness [11][12][13][14] to avoid cone-beam artifacts that arise from traditional circular conebeam orbits.…”