EQUINE VETERINARY EDUCATION Equine vet. Educ. (2022) 34 (2) 77-83 doi: 10.1111/eve.13388
Original Article
Standing computed tomography of the equine limb using a multi-slice helical scanner: Technique and feasibility study
M. Mageed Tierklinik L€
usche GmbH, Bakum-L€ usche, Germany
*Corresponding author email:
Mahmoud.mageed@
hotmail.com Keywords: arthrography CT; distal limb CT; fan Beam; horse foot CT; standing CT
Summary Computed tomography (CT) is an important cross-sectional diagnostic modality for lameness localised to the equine distal limb. The necessity of general anaesthesia to perform CT scans has limited its use in the equine orthopaedic field. Therefore, many attempts have been made to perform CT of the distal limb in standing horses. This retrospective report aims to describe the technical set-up and the feasibility of using a multi-slice helical CT unit recently introduced into the equine market. The medical records of the patients undergoing a standing CT in the period between March 2019 and January 2020 were reviewed. The imaged anatomical region and the image quality were assessed. Thirty-two horses met the inclusion criteria, and the following anatomical areas have been imaged: front foot/pastern (n = 14), metacarpophalangeal joint (n = 11), front proximal suspensory ligament
(n = 2), carpus (n = 2),
metatarsophalangeal joint (n = 2) and tarsus (n = 1). In 97% of the cases, excellent imaging quality was obtained. Motion artefact is the main cause of poor image quality. The feet and the metacarpophalangeal region can be easily imaged. Imaging the proximal anatomical regions of the limb is more challenging but achievable.
Introduction
The use of computed tomography (CT) in equine veterinary medicine in a clinical setting was first documented in the late 1980s for the investigation of a brain abscess and an osteochondral cyst in the metacarpophalangeal region (Allen et al. 1987; Barbee et al. 1987a). To image these anatomical regions, it has been necessary to conduct the scans under general anaesthesia to position the anatomical region of interest in the CT scanner (Barbee et al. 1987b). However, the mortality rate associated with equine anaesthesia has been reported to range from 0.08% to 1.8% (Dugdale and Taylor 2016). A third of the deaths were attributed to limb or cervical fractures and post-anaesthesia myopathy. It is likely that at least some of the fractures occurred as a consequence of myopathy-induced pain or weakness (Dugdale and Taylor 2016). The first attempt to perform a standing CT of the equine
extremity dated back to 2002 (Desbrosse et al. 2008). Desbrosse and colleagues (2008) described the use of a small peripheral quantitative computerised tomography scanner, which is used for assessing bone mineral density. They used it on 47 clinical cases successfully to confirm a diagnosis or aid in surgical planning for conditions of the foot (Desbrosse et al. 2008). However, the procedure time was about
90 seconds per slice, and the entire scan protocol took 20 min to obtain ten slices. Not surprisingly, 11% of the slices were invalid due to the motion artefacts. A few years later, adaptation of a human CT machine for use in the standing sedated horse was designed and developed for imaging the head and cranial cervical spine (Dakin et al. 2014). The helical CT units in the standing horse have been
described using two distinct techniques, either with a sliding gantry or with a stationary gantry (Bregger et al. 2019). The CT table, with the ’patient’, moves through the gantry bore in stationary system and vice versa in sliding system. In both systems, the patient has to be placed on a platform that is suspended by air castors (Bregger et al. 2019; Riggs 2019). These systems are commonly used for imaging the head and cranial cervical spine in standing horses. Recently, a new CT machine has become available on the market to perform the CT of the distal limb in standing horses. The aim of the current retrospective study was to demonstrate the feasibility of a helical multi-slice CT unit for imaging the limb of standing horses.
Materials and methods
The electronic medical records of the horses admitted for standing limb CT in the period between March 2019 and January 2020 at Tierklinik L€
usche GmbH, Germany were
reviewed. The horses imaged for demonstration purposes were excluded. The data recorded included signalment, clinical presentation, the imaged anatomical region and diagnosis. The number of scan attempts to provide a diagnostic image quality was recorded. The image quality was evaluated subjectively using a 3-point visual grading system developed for that purpose (Table 1 and Fig 1). Both bone and soft tissue reconstructed CT images were evaluated by a German board-certified radiologist (M.M.) who was aware of the case history. The images were reviewed once in a period of 3 days using the same workstation. A detailed description of the CT scanner and the needed technical installations, and the scanning procedure are provided.
Results
Thirty-two subjects met the inclusion criteria. They were 10 mares, 17 geldings and 5 stallions, with a mean age of 8.4 years (range 3–22 years). There were 29 Warmblood horses, 2 Haflingers and one donkey. For simplicity, we describe the included subjects as equines or horses. Three horses were excluded because they were used for demonstration purposes and training of the staff members.
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