Ultrasound principles and instrumentation

Abstract

Ultrasound (US) is a fundamental and inexpensive tool both for the prompt diagnosis and for the study of diverse medical conditions. Its widespread use is partly due to the availability of US devices in the daily practice of physicians. US can be performed in real-time and is instrumental in the generation of clinical algorithms for the management of situations like trauma. It also constitutes a primary approach for the study of oncological diseases, and a guidance tool for interventions such as percutaneous drainages. In addition, and specifically for HPB surgeons, US is an essential tool in the operating room: intraoperative (either open or laparoscopic) US is necessary for the accurate determination of the stage, location, number, and margins of tumors within the liver, pancreas, or biliary tree. On another note, reading and understanding US images are skills that require time and training, which should be taught during surgical residencies. However, this is not customary in most residencies globally. This chapter offers a concise yet comprehensive elucidation of the basic principles of ultrasonography, the instruments required to perform an ultrasonic assessment of a patient, and the basic ultrasound controls.

Keywords: Biliary; Liver; Pancreas; Physics; US; Ultrasound.

Fig. 1.

Graphic representing the physics of a wavelength, where all the variables involved are present. Description within the text.

Fig. 2.

Different effects that end up in the attenuation of the images (seen as decreased light blue intensity within the footprint), including reflection, refraction, absorption, scattering, and descriptions are within the text.

Fig. 3.

Pneumobilia creates an artifact called comet tail, where it can be observed thephenomenon as a comet tail, behind the air inside the biliary tract, (left image a current US image, right image a scheme to better understand the image to the left).

Fig. 4.

A giant cyst in the liver, actual image to the left, scheme image to the right.

Fig. 5.

Gallbladder with stones. Acoustic shadows can be seen behind the stone.

Fig. 6.

Doppler effect is used in a scan of the liver to assess the flows (portal, arterial) to differentiate the bile ducts and the vessels.