INCLUSION OF CERVICAL RADIOGRAPHS IN PRE PURCHASE EXAMINATIONS
so the significance of spondylosis in this region is unknown. In the cervical spine, spondylosis is even more uncommon with two clini- cal cases described (Draper & Finno, 2016 ). In both cases, the os- seous proliferation was marked and both horses had severe neck stiffness, while one was ataxic. This disease process would be a rare finding on PPE and due to the lack of published data, its sig- nificance would be unknown. However, based on information from other species, if mild to moderate, it is likely to be insignificant.
ACQUISITION OF CERVICAL RADIOGRAPHS FOR A PRE- PURCHASE EXAMINATION
Patient positioning
Patient positioning is crucial to the acquisition of diagnostic radiographs, and never more so than with radiography of the neck (Butler et al., 2017 ). The value of an even surface for the horse to stand on, and use of a headstand, cannot be understated. The horse should be appropriately sedated, standing square, with the head and neck in a neutral position. Professional personnel handling the horse can greatly assist the radiographer in ensuring the horse is evenly weight- bearing and the spine is straight. This is important as different neck positions can affect the appearance of some structures and certain measurements, such as vertebral alignment angles and intervertebral sagittal ratios (Beccati et al., 2018 ; Berner et al., 2012 ; Veraa et al., 2021 ). Geometric distortion can also affect the shape of the vertebra positioned at the periphery of a radiograph (Djernæs et al., 2014 ). Therefore, if abnormalities are present at the periphery of an image,
it is worth acquiring a projection centred on the
region of interest. Ideal facilities are rarely afforded to ambulatory veterinarians who may have to compromise on patient positioning which will reduce the diagnostic value of cervical radiographs.
Equipment
In the ambulatory setting, the main limitation of the radiographic technique is the power of the X- ray generator. Hospital- based ceiling- mounted generators typically have a high power rating (50– 80 kW) while commonly used lightweight portable generators have a moderate power rating (30 kW). The ability of the generator to acquire certain images depends on the power rating and therefore the kV and mAs output the generator can produce. As a result, PPE cervical radiographs of the caudal cervical spine, taken in an am- bulatory setting are often underexposed due to the inability of the generator to produce sufficient exposure factors, causing quantum mottle artefact (Figure 3 ). Additionally, the increased exposure time makes the image acquisition susceptible to motion artefacts. These artefacts greatly reduce image quality and hinder thorough evaluation. Thicker regions of anatomy, such as the caudal neck, produce more scatter radiation which degrades image quality. A grid is then required to prevent this scatter radiation from reaching
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FIGURE 3 Laterolateral radiographs of the caudal cervical spine of an adult Warmblood horse. (a) Acquired using a portable generator, without a grid, at 80 kVp and 4 mAs. There is a diffuse quantum mottle artefact due to underexposure, which becomes more pronounced at C7 due to the muscle mass of the shoulders. (b) Acquired using a hospital- based high- power generator, with a grid, at 93 kVp and 45 mAs. The improved exposure results in increased spatial resolution, contrast resolution and image sharpness. Note the bilateral partial transposition of the ventral lamina of C6–C7 (arrow).
the detector and improve the signal–to- noise ratio. However, with- out the ability to increase the exposure factors sufficiently, the use of a grid will decrease the signal too much, resulting in a non- diagnostic radiograph. A grid will only provide assistance when using higher exposure factors. As the caudal neck (including C7- T1) is often a region of particular interest, inadequate exposure factors will limit the diagnostic utility of cervical radiographs ac- quired in an ambulatory setting. Finally, a plate stand and genera- tor stand will minimise motion artefact which can occur when a person is holding an X- ray plate with a plate holder. Furthermore, when working with ionising radiation, it is essential to consider the A.L.A.R.A. principal and subject personnel to a radiation dose that is As Low As Reasonably Achievable. According to guidance from the International Atomic Energy Agency (IAEA, 2021 ) a generator stand should always be used, with exceptions depending on local regulations. A plate stand is advisable when radiographing the spine to eliminate the need for personnel holding the plate during these high exposures.
CONCLUSION
Current evidence suggests that most findings present on cervi- cal radiographs acquired at PPEs are of unknown or low clinical
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