Standing CT of the equine head: Reducing radiation dose maintains image quality

Abstract

Multiple published studies involving computed tomographic (CT) examinations of the equine head utilise a wide range of mAs parameters for image acquisition. This prospective, experimental study assessed the effects of lowering mAs during CT image acquisition on image quality and scatter radiation on 10 cadaver equine heads. Each head was scanned three times at 300, 225, and 150 mAs, with all other scanning parameters remaining constant between series. An anthropomorphic phantom was positioned adjacent to each equine head during image acquisition, mimicking a human bystander, with an ionization chamber attached to the phantom at eye level. Each series was reconstructed using filtered back projection, using medium (H30) and high (H80) frequency reconstruction algorithms. Quantitative image quality assessment was performed by calculating signal to noise ratio (SNR) and contrast to noise ratio (CNR). Two qualitative image quality assessments were performed independently by three blinded board certified veterinary radiologists with a 4 week interval, using a visual grade analysis model adapted from peer reviewed medical literature. Ionization chamber measurements, calculated volume CT dose index (CTDIvol), and dose‐length product (DLP) were recorded. Halving radiation dose during image acquisition from 300 to 150mAs resulted in comparable image quality between series. There was a statistically significant and linear relationship between mAs and scatter radiation to the bystander; halving mAs during image acquisition resulted in halving of scatter radiation. Results of this cadaveric study support the use of lower mAs settings during standing CT examinations of the equine head.

Use of a novel helical fan beam imaging system for computed tomography of the head and neck in sedated standing horses: 120 cases (2019–2020)

“…Horses were presented for the following complaints: unilateral or bilateral nasal discharge (n = 41), facial or head swelling (11), epistaxis (10), draining tract (10), ataxia (10), problems with mastication or opening the mouth (9), head trauma (7), periorbital swelling (5), neck swelling or stiffness (5), pain or sensitivity of the poll (4), headshaking (4), retained tooth root (2), and reduced unilateral nasal airflow (2).…”

“…[2][3][4] CT imaging can be performed with horses in recumbency under general anesthesia or with horses sedated and standing. 3,4,[7][8][9][10][11][12][13][14][15][16] Imaging under general anesthesia is labor-intensive and time-consuming and involves higher costs and a higher risk of complications, compared…”

Standing computed tomography of the equine limb using a multi‐slice helical scanner: Technique and feasibility study

“…Radiation safety is one of the most concerning issues in equine standing CT. It is recommended to wear 0.5 mm lead protective clothes, when holding horses for scans (Dakin et al 2014;Davies et al 2019). In this study, there was no horse holder in the CT room during the imaging of the front limbs, the limb was held with a long rope from the operating room.…”

The Role of Computed Tomography in Imaging Non-neurologic Disorders of the Head in Equine Patients

“…The high exposure settings inherent to all types of computed tomography can pose a safety risk for personnel restraining sedated horses ( 5 ), especially if the handler remains next to the horse during the scan. However, scatter radiation, which is the highest radiation exposure risk for the handler, may be reduced by reducing the mAs settings; halving the mAs can reduce scatter radiation by half thereby reducing personnel exposure dose and persistently result in comparable image quality as demonstrated in an experimental cadaveric head study ( 12 ). The benefit of being able to scan standing horses without general anesthesia and its associated risks and complications and the lower costs of performing standing CT is clinically important ( 13 ) and future technical developments will likely make standing MDCT and CBCT more readily available for use in horses.…”