Sébastien Buczinski, Isabelle Masseau
Ultrasonography is an imaging technique based on the reflection and refraction of acoustic waves as they are transmitted through the tissues (Kirberger 1995). In veterinary medicine, it was initially applied to the diagnosis of pregnancy, to assess reproductive organs prior to insemination or in an attempt to determine causes of failure to induce pregnancy in cattle. Its affordable cost and ease of use have contributed to its popularity and explain that today many veterinary practitioners are equipped with an ultrasound machine dedicated to cattle reproduction management programs (King 2006, DesCôteaux et al. 2009, Fricke et al. 2016).
In parallel with the development and sophistication of ultrasonographic examinations in the field of reproduction, a number of clinical conditions have emerged for which ultrasonography has been evaluated for its potential aid as a complementary imaging diagnostic tool. Over time, numerous research studies and growing expertise have resulted in diversification of ultrasound use in cattle leading to the recognition of its diagnostic utility for various indications, including examinations of musculoskeletal structures in cases of lameness, joint instability or penetrating wounds, among others (Flückiger 1997, Buczinski 2009a, Kofler 2009, Braun and Attiger 2016, Re et al. 2016b).
Ultrasonographic evaluation of musculoskeletal structures is facilitated by the superficial location of a majority of them. Consequently,most rectal probes (transducers) employed today for ultrasonography of the reproductive system can also be utilized for the evaluation of musculoskeletal structures. Since most practitioners are already equipped with ultrasound units, they do not have to pay additional costs for acquisition of new probes. Another important advantage of ultrasonography is its portability, allowing for musculoskeletal examinations to be performed directly on the farm (Ollivett and Buczinski 2016).
Like any other diagnostic imaging tool, it is important to understand the physical principles responsible for generating ultrasound images and commonly encountered artifacts (Kirberger 1995, Blond and Buczinski 2009). Understanding how artifacts occur can help their avoidance whenever possible or to use them advantageously to document the nature of the tissues from which they originate (e. g. gas in an abscess, osteophytes, dystrophic mineralization within a tendon, etc.). A few parameter settings that optimize image quality will also be briefly discussed. Therefore, the aim of this introductory chapter is to provide the reader with a brief overview of these important topics.
Ultrasound consists of high frequency vibrations generated by the crystals within a probe. When subjected to an electric field, the crystals inside the probe become excited, which triggers a movement or vibration, generating the emission of the ultrasound wave. This phenomenon is based on the inverse piezo-electric effect of certain materials. The speed at which transmitted ultrasound waves are propagated through a structure of interest varies according to the type of medium.
Thespeed of ultrasound waves through soft tissues is generally constant at approximately 1,540 m/s (Blond and Buczinski 2009).
A wave can betransmitted through a medium, as well asreflected, refracted and attenuated. Other types of effects such asdiffraction, polarization, dispersion and interference can also occur.
The interference effect mentioned above is of particular interest for ultrasound examinations that are performed in the proximity of other wave-generating materials or electronic devices, such as ventilation fans in a barn (Kirberger 1995, Blond and Buczinski 2009, Hindi et al. 2013).
A transducer (probe) emits ultrasound waves for only a very small fraction of the time (< 0.1 %). The remaining time (99.9 %) is devoted to reception of ultrasound echoes reflected back to the probe from tissues. This returning signal will then be converted electronically to form an ultrasound image (sonogram). As a general concept, the time interval between the emission of ultrasound waves and their return as echoes is used to estimate the depth of a specific structure. Information derived from returning echoes and their depth estimation is converted into different shades of white/grey pixels over a black background, generating an image that can be displayed on an ultrasound monitor.
Tissues commonly encountered during ultrasonography of the musculoskeletal system include articular components (capsule, synovi
