Revealing pelvic structures in the presence of metal hip prostheses via non-circular CBCT orbits

Abstract

As the expansion of Cone Beam CT (CBCT) to new interventional procedures continues, the burdensome challenge of metal artifacts remains. Photon starvation and beam hardening from metallic implants and surgical tools in the f ield of view can result in the anatomy of interest being partially or fully obscured by imaging artifacts. Leveraging the flexibility of modern robotic CBCT imaging systems, implementing non-circular orbits designed for reducing metal artifacts by ensuring data-completeness during acquisition has become a reality. Here, we investigate using non-circular orbits to reduce metal artifacts arising from metallic hip prostheses when imaging pelvic anatomy. As a f irst proof-ofconcept, we implement a sinusoidal and a double-circle-arc orbit on a CBCT test bench, imaging a physical pelvis phantom, with two metal hip prostheses, housing a 3D-printed iodine-filled radial line-pair target. A standard circular orbit implemented with the CBCT test bench acted as comparator. Imaging data collection and processing, geometric calibration and image reconstruction was completed using in-house developed software programs. Imaging with the standard circular orbit, image artifacts were observed in the pelvic bones and only 33 out of the possible 45 line-pairs of the radial line-pair target were partially resolvable in the reconstructed images. Comparatively, imaging with both the sinusoid and double-circle-arc orbits reduced artifacts in the surrounding anatomy and enabled all 45 line-pairs to be visibly resolved in the reconstructed images. These results indicate the potential of non-circular orbits to assist in revealing previously obstructed structures in the pelvic region in the presence of metal hip prosthesis.

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

“…Task‐based noncircular trajectories were also explored to eliminate the influence of CB artifacts, 15–17 with parameterized trajectories based on information on patient and metal implants to reduce metal and CB artifacts. Many other non‐circular trajectories were also proposed, for example, sinusoidal trajectory, 18–20 helical trajectory, 21–23 circle‐and‐line trajectory 24 and circle‐and‐arc trajectory 25 …”

Fully automatic online geometric calibration for non‐circular cone‐beam CT orbits using fiducials with unknown placement

“…[1][2][3][4][5][6][7][8] In recent years, non-circular scan orbits have been increasingly investigated for potential benefits such as increased field of view (FOV), [9][10][11][12] improved image quality and/or dose reduction, 7,[12][13][14][15] collision avoidance, 14,16 accom-modating upright patient positions [17][18][19] and reduced metal artifacts. 10,[20][21][22][23][24][25][26][27][28] While studies have demonstrated sufficient reproducibility for standard circular scanning orbits, [29][30][31][32] current implementations of non-circular orbits often result in a less predictable geometry due to factors such as gantry jitters, sagging, and manual data acquisition, and so forth. 8,12,[24][25][26][27]33,34 Since an accurate CBCT geometry is critical for the image quality of 3D reconstructions, we require a geometric calibration method that can address these challenges in practical implementations of non-circular or...…”