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. 2008 Oct;35(10):4649-59.
doi: 10.1118/1.2977736.

Streaking artifacts reduction in four-dimensional cone-beam computed tomography

Shuai Leng  1 , Joseph Zambelli, Ranjini Tolakanahalli, Brian Nett, Peter Munro, Joshua Star-Lack, Bhudatt Paliwal, Guang-Hong Chen
Affiliations

Streaking artifacts reduction in four-dimensional cone-beam computed tomography

Shuai Leng et al. Med Phys. 2008 Oct.

Abstract

Cone-beam computed tomography (CBCT) using an "on-board" x-ray imaging device integrated into a radiation therapy system has recently been made available for patient positioning, target localization, and adaptive treatment planning. One of the challenges for gantry mounted image-guided radiation therapy (IGRT) systems is the slow acquisition of projections for cone-beam CT (CBCT), which makes them sensitive to any patient motion during the scans. Aiming at motion artifact reduction, four-dimensional CBCT (4D CBCT) techniques have been introduced, where a surrogate for the target's motion profile is utilized to sort the cone-beam data by respiratory phase. However, due to the limited gantry rotation speed and limited readout speed of the on-board imager, fewer than 100 projections are available for the image reconstruction at each respiratory phase. Thus, severe undersampling streaking artifacts plague 4D CBCT images. In this paper, the authors propose a simple scheme to significantly reduce the streaking artifacts. In this method, a prior image is first reconstructed using all available projections without gating, in which static structures are well reconstructed while moving objects are blurred. The undersampling streaking artifacts from static structures are estimated from this prior image volume and then can be removed from the phase images using gated reconstruction. The proposed method was validated using numerical simulations, experimental phantom data, and patient data. The fidelity of stationary and moving objects is maintained, while large gains in streak artifact reduction are observed. Using this technique one can reconstruct 4D CBCT datasets using no more projections than are acquired in a 60 s scan. At the same time, a temporal gating window as narrow as 100 ms was utilized. Compared to the conventional 4D CBCT reconstruction, streaking artifacts were reduced by 60% to 70%.

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Figures

Figure 1
Figure 1
Flow chart of the proposed correction algorithm.
Figure 2
Figure 2
Motion phantom (a) and blurred image reconstructed from all available projections without gating (b).
Figure 3
Figure 3
Motion profile used in the experiment.
Figure 4
Figure 4
Simulation studies with a 60 s gantry rotation and a 400 ms temporal resolution. Images were reconstructed using FBP (top row) and our new algorithm (bottom row) at phases of 0%, 25%, and 45%.
Figure 5
Figure 5
Simulation studies with a 60 s gantry rotation and a 200 ms temporal resolution. Images were reconstructed using FBP (top row) and our new algorithm (central row) at phases of 0%, 25%, and 45%. The bottom row shows the difference between images at the central row and the ground truth.
Figure 6
Figure 6
Comparison between uniform sampling (left) and bunching sampling (right) patterns for the same number of view angles.
Figure 7
Figure 7
Simulation studies with a 120 s gantry rotation and a 400 ms temporal resolution. Images were reconstructed using FBP (top row) and our new algorithm (bottom row) at phases of 0%, 25%, and 45%.
Figure 8
Figure 8
Simulation studies with a 120 s gantry rotation and 200 ms temporal resolution. Images were reconstructed using FBP (top row) and our new algorithm (bottom row) at phases of 0%, 25%, and 45%.
Figure 9
Figure 9
Streak reduction ratios for images gated into 20 phases (a) and 10 phases (b).
Figure 10
Figure 10
4D CBCT images of a physical phantom. Top row shows images reconstructed from all views without gating; middle row shows images reconstructed using FDK with phase gating (95 ms temporal window); bottom row shows images reconstructed using our new algorithm at the same phase as middle row. From left to right are images of axial, sagittal, and coronal views. The selected phase center for images at middle and bottom rows is 10%. The display window for all images is [0,0.04] mm−1.
Figure 11
Figure 11
Coronal view of images reconstructed using our new algorithm at phases of 9.5%, 32%, and 50% to demonstrate the dynamics. The display window is [0,0.04] mm−1.
Figure 12
Figure 12
4D CBCT images of a physical phantom. Top row shows images reconstructed using FDK with 530 ms temporal window; bottom row shows images reconstructed using our new algorithm. From left to right are images of axial, sagittal, and coronal views. The selected phase center is 10%. The display window for all images is [0,0.04] mm−1.
Figure 13
Figure 13
Streak reduction for physical motion phantom study using different gating apertures.
Figure 14
Figure 14
Axial images of the three moving objects reconstructed using FDK (top row) and our correction algorithm (bottom row).
Figure 15
Figure 15
A segment of the RPM signal for this experiment (a) and the corresponding phase information (b).
Figure 16
Figure 16
Prior images reconstructed from all measured projections without gating. (a) Axial slice. (b) Sagittal slice.
Figure 17
Figure 17
Gated reconstruction. Images reconstructed from FDK algorithm [(a), (c)] and our correction algorithm [(b), (d)]. Both axial slices (top row) and sagittal slices (bottom row) are shown.
Figure 18
Figure 18
Sagittal images reconstructed using the correction algorithm at phases of 37.5%, 62.5%, and 77.5%.
Figure 19
Figure 19
Streak reduction ratio for the patient study.
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