Ultrasound Devices and Probes

In ophthalmology, ultrasound images are obtained using devices based on two technological principles: dedicated devices, for ophthalmology, and multipurpose devices. In this chapter, we review the various technical and technological aspects to understand how the information is generated by the transducer and then displayed as an image on the screen for both dedicated and multipurpose devices. For dedicated devices, we carefully review the transducer and the probe with all the characteristics essential for them to be optimal, but, being linked together, they must lead to an acceptable compromise; from the piezoelectric crystal to the motor/magnet/Hall effect sensor assembly allowing the movement (magnetic effect) and to the pre-amplification of the ultrasound signals in the probe, with special focus on high-frequency (50-MHz) probes and annular transducers. Then, we discuss the ultrasound system, the PC and the screen. The multipurpose ultrasound devices may be of two types: (1) a conventional multipurpose ultrasound device, with a beamformer and then processing boards, one per mode, and an integrated computer ensuring the presentation of the image for display, calculation, and transfer; and (2) a digital multipurpose ultrasound device, with acquisition boards digitizing the information from the probes; management of the beam is ensured by software in the computer terminal, separating the different modes for analysis. Here we analyze the technological evolution of transducers: piezocomposite assembly and capacitive micromachined ultrasonic transducer. Finally, we discuss fully digital imaging. Then, we review the biological effects and the safety of ultrasound scanners and probes, including the Food and Drug Administration’s September 2008 recommendations, established to limit the acoustic power of ultrasound scanners. At last, we address the cleaning and decontamination of probes, insisting on the use of customized probe covers.