On‐the‐fly motion‐compensated cone‐beam CT using an a priori model of the respiratory motion

Abstract

Respiratory motion causes artifacts in cone-beam (CB) CT images acquired on slow rotating scanners integrated with linear accelerators. Respiration-correlated CBCT has been proposed to correct for the respiratory motion but only a subset of the CB projections is used to reconstruct each frame of the 4D CBCT image and, therefore, adequate image quality requires long acquisition times. In this article, the authors develop an on-the-fly solution to estimate and compensate for the respiratory motion in the reconstruction of a 3D CBCT image from all the CB projections. An a priori motion model of the patient respiratory cycle is estimated from the 4D planning CT. During the acquisition, the model is correlated with the respiration using a respiratory signal extracted from the CB projections. The estimated motion is next compensated for in an optimized reconstruction algorithm. The motion compensated for is forced to be null on average over the acquisition time to ensure that the compensation results in a CBCT image which describes the mean position of each organ, even if the a priori motion model is inaccurate. Results were assessed on simulated, phantom, and patient data. In all experiments, blur was visually reduced by motion-compensated CBCT. Simulations showed robustness to inaccuracies of the motion model observed on patient data such as amplitude variations, phase shifts, and setup errors, thus proving the efficiency of the compensation using an a priori motion model. Noise and view-aliasing artifacts were lower on motion-compensated CBCT images with 1 min scan than on respiration-correlated CBCT images with 4 min scan. Finally, on-the-fly motion estimation and motion-compensated reconstruction were within the acquisition time of the CB projections and the CBCT image available a few seconds after the end of the acquisition. In conclusion, the authors developed and implemented a method for correcting the respiratory motion during the treatment fractions which can replace respiration-correlated CBCT for improving image quality while decreasing acquisition time.

An image‐based method to synchronize cone‐beam CT and optical surface tracking

“…Real‐time surface data can be advantageously used for CBCT phase sorting, providing to each CBCT projection a breathing phase value robustly extracted from the synchronized external surface surrogate. Phase sorting is required to correct for respiratory motion in CBCT scans, allowing the reconstruction of motion‐compensated CBCT with reduced blurring artifacts and increased image quality (20) . Phase sorting is also applied for the reconstruction of 4D respiratory‐correlated CBCT, which allows the verification of tumor shape and motion just prior to treatment 19 , 21 …”

“…Three‐dimensional (3D) CBCT images are applied for the initial treatment setup to correct patient positioning errors and target misalignment by means of registration with the CT scan used for treatment planning. In order to reduce blurring artifacts caused by respiratory motion, a respiration‐correlated CBCT or a motion‐compensated CBCT can be reconstructed by using a breathing surrogate extracted directly from the acquired projections 19 , 20 or from external monitoring devices (21) . Several methods have also been proposed to track tumor position in the rotational CBCT projections 22 , 23 and to reconstruct the 3D tumor trajectory during the whole scan, (24) thus providing information on daily tumor motion patterns.…”

Motion-compensated cone beam computed tomography using a conjugate gradient least-squares algorithm and electrical impedance tomography imaging motion data

“…In the last decade, motion-compensated CBCT for removing motion blur artefacts in CBCT scans has attracted the interest of many research groups [7][8][9][10][11][12]. Many reconstruction methods have been proposed for compensating the motion.…”

Correction of motion artifacts in cone‐beam CT using a patient‐specific respiratory motion model

“…Clinical evaluation was limited to one CBCT acquisition done with four gantry rotations, thus considerably lengthening the acquisition time. Rit et al 8 compensate for respiratory motion during reconstruction of the projection images from a 1 min 200°CBCT scan, using a prior motion model estimated from a respiration-correlated planning CT ͑RCCT͒. Their method assumes that the phase-based respiratory motion during the CBCT acquisition is identical to that of the RCCT.…”