CMUT-based, portable, handheld device analysis for diagnostic ultrasound imaging

Diagnostic ultrasound is a non-invasive imaging modality that uses high-frequency sound waves to generate images of structures inside the body. Through the advancements of biomedical technologies, medical ultrasound systems have evolved and, especially in the last two decades, the miniaturization of ultrasound machines has become feasible. The advent of portable machines and the development of handheld devices have made possible an evolution for the role of ultrasounds in healthcare system, emerging as an invaluable tool for first-level diagnosis in emergency wards. This practice is called point-of-care ultrasound (POCUS), and allows physicians to obtain immediate and quick assessments while evaluating their patients, as an aide to traditional examination techniques. The purpose of this thesis is the study of a new pocket-sized ultrasound system, Butterfly iQ+, developed by the American company Butterfly Network. This device is composed by a single probe that is connected to a smartphone or tablet to display and record real-time ultrasound images. The very innovative aspect is the technology behind the Butterfly iQ+: traditional ultrasound machines commonly use piezoelectric crystal-based transducers, which convert electrical energy into mechanical energy in the form of ultrasound waves, and vice versa. This traditional technology is very expensive and requires the use of multiple probes. Therefore, Butterfly iQ+ has introduced an innovative way to send and receive ultrasound waves: it attempts to do the same work of piezoelectric ceramics by replacing them with a single silicon chip containing 9000 capacitive micromachined ultrasound transducers (CMUTs), which act like little drums to generate vibrations. This is called Ultrasound-on-a-chip technology and since it is based on semiconductor wafers industry, it allows to drastically reduce the device’s costs. Moreover, unlike traditional piezoelectric crystals that are tuned to produce ultrasound waves at particular frequencies and image at defined depths, CMUTs provide a wider bandwidth, allowing the possibility to exploit a single probe for emulating any type of probes. As a result, the only ultrasound probe from the Butterfly iQ+ system can be used for multiple applications and can be programmed to image the whole body. After analyzing the clinical and technical features, the pros and cons, and the innovative technology behind this new device, the thesis focuses on the image quality assessment in images acquired by Butterfly iQ+ system, as a tool to quantitatively evaluate the machine’s performances. A series of parameters related to image quality in ultrasound have been measured and evaluated, and also compared to the same parameters obtained by images acquired with a traditional ultrasound machine. Finally, future applications for Butterfly iQ+ will be discussed.