Cone-beam computed tomography of the head in standing equids

Abstract

Background Computed tomography in standing horses has revolutionized diagnostic imaging. The O-arm®, a cone beam computed tomography (CBCT) scanner with a gantry opening of 96.5 cm is routinely used for image-guided spine and neurosurgery in humans. The aim of this study is to describe the set-up and first experiences using the O-arm® to achieve CBCT imaging of the head in standing horses. CT imaging of the predefined region of interest (ROI) was tested on 2 cadaveric heads, concentrating on centering issues within the gantry, as well as determining the number of scans needed per ROI. All horses presented with head-related diseases and subjected to a CBCT examination between February 2015 and November 2016 for CBCT were included. Per scan, a limited field of view, i.e. a cylindrical volume of 21 cm in diameter and 16 cm in height was acquired within 13 s. Depending on the dimensions of the ROI, the minimum number of scans could range from one to six, if the entire equine head is to be examined in an adult horse. Results Sixty-eight horses were included, five of which had a follow-up CBCT exam, and two of which were presented twice for two different indications (75 clinical cases). A total number of 449 acquired three-dimensional (3D) scans were recorded for these 75 cases. Two-hundred and forty-two 3D scans (54%) were considered as diagnostic quality. The imaging procedure was generally well tolerated by the sedated, standing equid, and diagnostic studies were performed in 73 out of 75 cases (97.3%). Motion artefacts and inadequate centering of the ROI were the most common reasons for non-diagnostic quality images and repeat scans of the same ROI. Conclusions CBCT is a valuable imaging modality for the equine head. Advantages of the O-arm® compared to a conventional multi-slice helical CT for imaging of the head in standing equids include the rapid image acquisition, the gantry’s mobility in all dimensions, and the free movability of the entire imaging unit. Disadvantages include the considerable sensitivity to motion artefact, increased scatter, low soft tissue contrast and the limited dimensions of the field of view.

Feasibility, indications, and radiographically confirmed diagnoses of standing extremity cone beam computed tomography in the horse

“…The lower number of acquisitions can be explained by the smaller anatomy of extremities that usually can easily be covered by one acquisition of the fixed cylindrical volume. The extremities seem to be less affected by the respiratory swaying, which is not the case in the head and neck 8 …”

“…In comparison with standing CBCT of the head in standing sedated horses, the median number of acquisitions per region of interest is only one-half. 8 The lower number of acquisitions can be explained by the smaller anatomy of extremities that usually can easily be covered by one acquisition of the fixed cylindrical volume. The extremities seem to be less affected by the respiratory swaying, which is not the case in the head and neck.…”

“…The CBCT scanner, technical setup, and scanning procedure used in this study have been described elsewhere. 7,8 In brief, a mobile CBCT unit originally designed and FDA-approved for intraoperative applications in surgical theatres with an inner gantry diameter of 96.5 cm (Medtronic O-Arm; Medtronic AG) was used for image acquisition. The gantry itself is mobile in all three dimensions and can be tilted around its horizontal and vertical axis.…”

Computed Tomography (CT)-Assisted 3D Cephalometry in Horses: Interincisal Angulation of Clinical Crowns

“…In a study in which multislice CT and cone beam CT were compared, however, Watanabe et al ( 39 ) showed that a smaller voxel size does not always improve spatial resolution as this may also depend on both the in-plane and longitudinal directed modulation-transfer function. Nevertheless, cone beam CT has not yet become area-wide established in equine dentistry due to various limitations, such as substantial sensitivity to motion artifacts, higher scatter, or a limited dimension of the field of view (FOV) ( 31 ). Additional artifacts of cone beam CT are alias artifacts by x-ray beam divergence and a higher noise level ( 38 ).…”

“…Domanska-Kruppa et al ( 15 ) just recently introduced conventional two-dimensional (2D) x-ray based cephalometry to investigate class II malocclusion and IIA using distinct cephalometric landmarks in Warmblood foals. Current advances of head CT in standing sedated horses ( 29 – 31 ) may allow for methodical standardization as well as single tooth measurements and will make 3D cephalometry clinically applicable.…”