Abstract:
Proc. Amt. Sot. Ai~im. Prod. 1994 Vol. 20 A PRELIMINARY DESCRIPTION OF THE MEDIUM FREQUENCY ULTRASOUND IMAGES OF THE SKIN OF LIVESTOCK L.G. BUTLER Dept of Primary Industry and Fisheries, P.O. Box 46, Kings Meadows, Tas. 7249 Ultrasound is now being used in human dermatology to measure skin thickness and to image various skin disease states. Thus there are potential applications in animal science and production (reviewed by Butler 1991). The medium frequency ultrasound characteristics of the skin of cattle have been described by Butler and Head (1993) but no information is available on the use of ultrasound in imaging the skin of smaller livestock species, or on the ultrasound characteristics of their skins. This work aims to extend the previous work by providing a preliminary description of the medium frequency ultrasound characteristics of sheep and pig skin. Examinations were conducted as described by Butler and Head (1993) using an Aloka 500'r' with 5 or 7.5 MHz linear array probe. In 9 sheep, the area to be examined was closely clipped and thoroughly coated with vegetable oil. A water filled bag was interposed between the skin and the transducer to provide a 'stand-off' distance of about 2-3 cm and the transducer focussed at this distance. In the pig, dehaired skin on purchased loin cuts from a pi g carcase was scanned as close as practicable to the cut edge. The images were recorded on video cassette for further study. Normal sheep skin could be delineated with 5 and 7.5 MHz ultrasound as expected but finer detail could not be elucidated (Figure 1). In contrast, the lower boundary of pig skin was poorly defined and could not be measured. This may be due to the apparent poor differentiation between dermis and subcutaneous layers, an observation which is not supported by any published study. Unlike cattle skin (Butler and Head 1993) there was evidence that shavin g improved the image in sheep. With the 5 MHz probe sheep skin appeared simply as an echogenic layer 2.9 + 0.5 mm thick in adult crossbred ewes of fat score 4-5. Using 7.5 MHz, some differentiation into layers could just be discerned at about 2 mm, appearing as an intermittent darker (echolucent) layer in the skin. Figure 1. A 7.5 MHz ultrasound image of sheep skin showing the water standoff (w), skin (s) and underlying muscle (m) and fat (f). The vertical bar represents 0.5 cm. In an attempt to define the lower boundary of the skin, normal saline was injected subcutaneously to 0 generate a fluid (echo-free) gap between the skin and underlyin, tissues. This was unsuccessful in the fat sheep used as the injected saline dissipated immediately and did not provide any delineation of tissue boundaries. A shadow generated by the needle could be detected when it was left in the skin, but its origin was not distinct. It is concluded that further work with higher frequencies is required to investigate the potential for ultrasound imaging of sheep and pig skin. The oil-fibre pile layer between the skin surface and 'standoff' bag may present a problem in identifying the skin surface. Reverberation echoes were often encountered and may be a problem. Using ultrasound, it may be possible to study new skin parameters (eg. viscoelastic and mechanical) of potential interest and application. BUTLER, L.G. (1991). Proceedings of 9th Conference of Australian Association of Animal Breeding and Genetics, Melbourne, pp. 335-8. BUTLER, L.G. and HEAD, G.M. (1993). Amt. Vet. J. 70: 345-7. 405