A method for distance accuracy evaluation on the reformatted oblique plane of CT images

This study proposes a new method for evaluating distance accuracy on the reformatted oblique plane using the American College of Radiology (ACR) computed tomography (CT) phantom. Evaluations were performed on oblique images reformatted from axial, sagittal, and coronal images. Oblique images from axial images were reformatted through two radiopaque markers commonly used for distance accuracy on the axial image. Oblique images from sagittal and coronal images were reformatted through eight radiopaque markers at the edge of the phantom usually used to perform centering of the phantom in the x, y, and z directions. Axial images were scanned with two pitches of 0.86 and 1.0. Oblique images were reformatted using IndoQCT and RadiAnt. The distance accuracy was evaluated on the reformatted oblique plane using an electronic caliper available in these two platforms. The percentage differences of measured distances on the reformatted oblique image using IndoQCT were within 2% of the actual distances. The average percentage differences for a pitch of 0.86 was 0.78%, and for pitch of 1.0, it was 0.57%. The percentage differences of measured distances using RadiAnt were within 1% of the actual distances. The average percentage differences for a pitch of 0.86 was 0.22%, and for a pitch of 1.0, it was 0.29%. The proposed method for evaluating distance accuracy on reformatted oblique images using the ACR CT phantom is easily implemented. We found that the percentage difference of distances from the IndoQCT and RadiAnt was within 2%. It is recommended that distance accuracy on the reformatted oblique plane is performed in regular quality control (QC).