Region of interest (ROI) computed tomography (CT): comparison with full field of view (FFOV) and truncated CT for a human head phantom

Abstract

Cone-beam CT reconstruction can be performed at lower integral dose, by using a non-uniform beam filter between the x-ray source and the patient to obtain good image quality within an ROI with minimal artifacts. To evaluate the method, a human head phantom was placed on a rotary stage. Cone-beam projection images of the phantom were obtained with and without an ROI filter (dose reduction factor ~7). A mapping function was established to equalize the intensity outside the ROI (to compensate for the attenuation by the filter) to the intensity inside by assuming that those features lying both inside and outside very close to the edge of the ROI are the same. Reconstructed images were obtained using equalized projection images for 2 cases: one in which the outside region was smoothed using an averaging filter and the other with no smoothing outside. In addition, a third case was simulated by calculating the average pixel value inside the ROI for each image and assigning this value to all pixels outside the ROI for that image. The images were then back projected using a Feldkamp algorithm. We found that the three cases yield results inside the ROI comparable to those obtained using FFOV projections. In addition, the ROI filter reconstruction with smoothing provides image information outside the ROI comparable to the FFOV reconstruction. CT using an ROI filter provides a means to reconstruct reliable 3D for a volume of interest with greatly reduced integral dose compared to FFOV projections and with minimal artifacts.

The Added Value of Volume-of-Interest C-Arm CT Imaging during Endovascular Treatment of Intracranial Aneurysms

“…Before ATRACT, various techniques to reconstruct meaningful VOI C-arm CT images with minimal truncation artifacts have been proposed in the literature. The common theme of these techniques is to fill in the missing information either by using preinterventional CT, 16 extrapolating missing data on the basis of some heuristic approach, 17 acquiring a low-resolution full-head scan and combining it with truncated VOI projection data with full-field data to create a full projection matrix suitable for a FDK reconstruction algorithm, 18 or using advanced filtering algorithms to eliminate truncated data. 19,20 Because most of these methods were designed for a stationary C-arm gantry and a rotating object and less robust extrapolation techniques, their utility for neurointerventional applications is …”

Region‐of‐interest image reconstruction with intensity weighting in circular cone‐beam CT for image‐guided radiation therapy

“…The accuracy of the chord-based BPF reconstruction has been verified extensively both in numerical and experimental studies. 25,16 The proposed IWROI technique can achieve more dose reduction than conventional approaches [11][12][13] without appreciably sacrificing ROI image quality because the robustness to transverse data truncation allows the illuminated region to be further reduced. The zonal filter approach 23 is not directly comparable with the IWROI technique in terms of dose saving because it cannot deal with ROI imaging tasks with transverse data truncations, although it can be considered a synergistic way to improve dose management.…”

“…23 ROI filters have also been used for diagnostic purposes such as angiography, head scan, and breast scan. [11][12][13] However, since only conventional reconstruction based on the FDK algorithm has been employed in these applications, transverse data truncation that can cause image artifacts was minimal or avoided entirely. In contrast, our proposed approach can take advantage of the robustness of the BPF algorithm against transverse data truncation and enables further dose reduction, for some imaging tasks, by reducing the field of view and purposely allowing data truncation.…”

LabVIEW graphical user interface for a new high sensitivity, high resolution micro-angio-fluoroscopic and ROI-CBCT system

“…An adjustable delay between the mask acquisition and DSA can be entered by the user. [9,10] required rotating-object geometry achieved by using a portable platform [11]. Current HSMAF system setup enables us to acquire ROI-CBCT datasets using standard rotational-DSA settings on the gantry system.…”