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

Karius, Andre; Szkitsak, Juliane; Strnad, Vratislav; Fietkau, Rainer; Bert, Christoph

doi:10.1002/mp.16463

Cited by 5 publications

(1 citation statement)

References 46 publications

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“…To facilitate adaptive brachytherapy for cervical cancer using 3D intraoperative imaging, our institution acquires CBCT scans with a mobile CBCT scanner (ImagingRing m, medPhoton, Austria), as previously described. 17,[22][23][24] The device features a gantry with 121 cm clearance and a 43.2 × 43.2 cm 2 flat-panel detector. A battery-mode allows translations and rotations of the mobile scanner on the floor, as well as tilting of its gantry.…”

Section: System Descriptionmentioning

confidence: 99%

First implementation of an innovative infra‐red camera system integrated into a mobile CBCT scanner for applicator tracking in brachytherapy—Initial performance characterization

Karius,

Leifeld,

Strnad

et al. 2024

J Applied Clin Med Phys

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PurposeTo enable a real‐time applicator guidance for brachytherapy, we used for the first time infra‐red tracking cameras (OptiTrack, USA) integrated into a mobile cone‐beam computed tomography (CBCT) scanner (medPhoton, Austria). We provide the first description of this prototype and its performance evaluation.MethodsWe performed assessments of camera calibration and camera‐CBCT registration using a geometric calibration phantom. For this purpose, we first evaluated the effects of intrinsic parameters such as camera temperature or gantry rotations on the tracked marker positions. Afterward, calibrations with various settings (sample number, field of view coverage, calibration directions, calibration distances, and lighting conditions) were performed to identify the requirements for achieving maximum tracking accuracy based on an in‐house phantom. The corresponding effects on camera‐CBCT registration were determined as well by comparing tracked marker positions to the positions determined via CBCT. Long‐term stability was assessed by comparing tracking and a ground‐truth on a weekly basis for 6 weeks.ResultsRobust tracking with positional drifts of 0.02 ± 0.01 mm was feasible using the system after a warm‐up period of 90 min. However, gantry rotations affected the tracking and led to inaccuracies of up to 0.70 mm. We identified that 4000 samples and full coverage were required to ensure a robust determination of marker positions and camera‐CBCT registration with geometric deviations of 0.18 ± 0.03 mm and 0.42 ± 0.07 mm, respectively. Long‐term stability showed deviations of more than two standard deviations from the initial calibration after 3 weeks.ConclusionWe implemented for the first time a standalone combined camera‐CBCT system for tracking in brachytherapy. The system showed high potential for establishing corresponding workflows.

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Section: System Descriptionmentioning

confidence: 99%

First implementation of an innovative infra‐red camera system integrated into a mobile CBCT scanner for applicator tracking in brachytherapy—Initial performance characterization

Karius,

Leifeld,

Strnad

et al. 2024

J Applied Clin Med Phys

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Extension of the cone‐beam CT field‐of‐view using two complementary short scans

Belotti,

Fattori,

Baroni

et al. 2023

Medical Physics

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BackgroundRobotic C‐arm cone‐beam computed tomography (CBCT) scanners provide fast in‐room imaging in radiotherapy. Their mobility extends beyond performing a gantry rotation, but they might encounter obstructions to their motion which limit the gantry angle range. The axial field‐of‐view (FOV) of a reconstructed CBCT image depends on the acquisition geometry. When imaging a large anatomical location, such as the thorax, abdomen, or pelvis, a centered cone beam might be insufficient to acquire untruncated projection images. Some CBCT scanners can laterally displace their detector and collimate the beam to increase the FOV, but the gantry must then perform a 360° rotation to provide complete data for reconstruction.PurposeTo extend the FOV of a CBCT image with a single short scan (gantry angle range of fan angle) using two complementary short scans.MethodsWe defined an acquisition protocol using two short scans during which the source follows the same trajectory and where the detector has equal and opposite tilt and/or offset between the two scans, which we refer to as complementary scans. We created virtual acquisitions using a Monte Carlo simulator on a digital anthropomorphic phantom and on a computed tomography (CT) scan of a patient abdomen. For our proposed method, each simulation produced two complementary sets of projections, which were weighted for redundancies and used to reconstruct one CBCT image. We compared the resulting images to the ground truth phantoms and simulations of conventional scans.ResultsReconstruction artifacts were slightly more prominent in the complementary scans w.r.t. a complete scan with untruncated projections but matched those in a single short scan without truncation. When analyzing reconstructed scans from simulated projections with scatter and corrected with prior CT information, we found a global agreement between complementary and conventional scan approaches.ConclusionsWhen dealing with a limited range of motion of the gantry of a CBCT scanner, two complementary short scans are a technically valid alternative to a full 360° scan with equal FOV. This approach enables FOV extension without collisions or hardware upgrades.

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Reduction of cone‐beam CT artifacts in a robotic CBCT device using saddle trajectories with integrated infrared tracking

Wei,

Albrecht,

Rit

et al. 2024

Medical Physics

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BackgroundCone beam computed tomography (CBCT) is widely used in many medical fields. However, conventional CBCT circular scans suffer from cone beam (CB) artifacts that limit the quality and reliability of the reconstructed images due to incomplete data.PurposeSaddle trajectories in theory might be able to improve the CBCT image quality by providing a larger region with complete data. Therefore, we investigated the feasibility and performance of saddle trajectory CBCT scans and compared them to circular trajectory scans.MethodsWe performed circular and saddle trajectory scans using a novel robotic CBCT scanner (Mobile ImagingRing (IRm); medPhoton, Salzburg, Austria). For the saddle trajectory, the gantry executed yaw motion up to using motorized wheels driving on the floor. An infrared (IR) tracking device with reflective markers was used for online geometric calibration correction (mainly floor unevenness). All images were reconstructed using penalized least‐squares minimization with the conjugate gradient algorithm from RTK with voxel size. A disk phantom and an Alderson phantom were scanned to assess the image quality. Results were correlated with the local incompleteness value represented by , which was calculated at each voxel as a function of the source trajectory and the voxel's 3D coordinates. We assessed the magnitude of CB artifacts using the full width half maximum (FWHM) of each disk profile in the axial center of the reconstructed images. Spatial resolution was also quantified by the modulation transfer function at 10% (MTF10).ResultsWhen using the saddle trajectory, the region without CB artifacts was increased from 43 to 190 mm in the SI direction compared to the circular trajectory. This region coincided with low values for . When was larger than 0.02, we found there was a linear relationship between the FWHM and . For the saddle, IR tracking allowed the increase of MTF10 from 0.37 to 0.98 lp/mm.ConclusionsWe achieved saddle trajectory CBCT scans with a novel CBCT system combined with IR tracking. The results show that the saddle trajectory provides a larger region with reliable reconstruction compared to the circular trajectory. The proposed method can be used to evaluate other non‐circular trajectories.

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

Cited by 5 publications

References 46 publications

First implementation of an innovative infra‐red camera system integrated into a mobile CBCT scanner for applicator tracking in brachytherapy—Initial performance characterization

First implementation of an innovative infra‐red camera system integrated into a mobile CBCT scanner for applicator tracking in brachytherapy—Initial performance characterization

Extension of the cone‐beam CT field‐of‐view using two complementary short scans

Reduction of cone‐beam CT artifacts in a robotic CBCT device using saddle trajectories with integrated infrared tracking

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