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EQUINE VETERINARY EDUCATION / AE / FEBRUARY 2022
TABLE 1: Visual grading system of the computed tomographic imaging of the distal limb in standing horses
Grade Limitations for clinical use 1
No limitations
Image quality and definition
Excellent quality: no motion artefact at anatomical region of interest (Fig 1a)
2 3 Minimal limitations
Image not usable, loss of information, image must be repeated
Good quality: mild-to- moderate motion artefact (Fig 1b)
Poor image quality: severe motion artefact (Fig 1c)
(n = 3) and sesamoiditis (n = 1). In an additional five cases, no structural changes were identified. The image quality was assessed as grade 1 in 29 horses, grade 2 in two horses (tarsus and fore PSL) and grade 3 in one horse (fore PSL). Motion artefact was the cause of reduced image quality.
The included horses were presented with the history of lameness (n = 29) or suspicion of bone pathology on a pre- purchase examination (n = 3). The anatomical regions of interest were foot/pastern (n = 14), metacarpo(tarso) phalangeal joint (n = 13), proximal suspensory ligament of front limb (n = 2; PSL), carpus (n = 2) and tarsus (n = 1). The majority of the scans were carried out in the front limbs (n = 28), and only three scans were on hindlimbs (two metatarsophalangeal regions and one tarsus). Sixteen patients had contrast-assisted CT (arthrography [n = 13] and venogram [n = 3]). A total number of 94 scan attempts were recorded for all included horses. The mean number of acquired scans per horse was three (range 1–7 scans) and for native CT two scans per horse. The horses that underwent contrast-enhanced CT showed a higher number of scan attempts (mean 5; range 4–7 scans). The radiological diagnoses included a space-occupying mass in a hoof (n = 5; Fig 2), chondropathy (n = 7; Fig 3), fissure fracture (n = 2), subchondral cystic lesions (n = 9, Fig 4), osteoarthritis
a) b)
CT system The CT scanner is a sliding helical multi-slice gantry and has 16 detector rows each is 0.5 mm wide (Aquilion LB)1. The gantry bore diameter is 90 cm, which provides a 70-cm scanning field of view (Fig 5). The tube is eccentric in position (away from CT table) and provides an output of 80–135 kV (20 kVp step) and mA of 50–400. The rotation speed per second ranges between 0.32 and 3. The maximal weight limit of the patient couch is 205 kg. The CT scanner is sliding on a special designed mobile platform, which provides the up and down movements. The platform is rectangular, measuring 2.3 9 3.9 m, and is positioned on a hydraulic lever system. It is installed in a pit in the ground (3.3 9 4 9 1.3 m) to allow bringing the gantry to the level of the distal limb. This feature enables imaging different sizes of horses in the standing position (Fig 6).
Scanning procedures Prior to image acquisition, machine-specific calibration and warm-up protocols were performed, which lasted approximately 17 min. Thereafter, the patient data were acquired from the PACS and the CT platform positioned at the level of the anatomical region of interest. The scanning protocol was chosen prior to bringing the patient to the CT room. The platform has extra extensions, which provide patient stability during the scan (Fig 5). The head is positioned on a metal extension to support the head during scanning. This extension is long on one side to prevent the horse seeing the gantry when sliding away during the scan (Fig 5B). An additional U-form wood board attached to the CT table provides limb stability. Furthermore, it protects the CT
c)
Fig 1: Multi-planar reformatted frontal reconstructed CT images using bone algorithm of the distal limb in standing horses. The images represent a grading system of image quality (Table 1). The image (a) represents excellent image quality with no motion artefact (grade 1). The image (b) shows mild-to-moderate motion artefact representing image quality grade 2. Image (c) has a severe motion artefact that significantly degrades the image quality (grade 3).
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