Monolithic Multiband CMUTs for Photoacoustic Computed Tomography With <italic>In Vivo</italic> Biological Tissue Imaging

Abstract

Among the biomedical imaging modalities, photoacoustic computed tomography (PACT) was one of the emerging hybrid techniques in recent years. In designing the PACT imaging system, a finite-bandwidth transducer is one of the limited factors for the overall performance. As the target size is inversely proportional to the dominant frequency components of the generated photoacoustic (PA) signal, a broad bandwidth transducer is desired for different scales' imaging. In this paper, a monolithic multiband capacitive micromachined ultrasonic transducer (CMUT) array was designed and fabricated for the reception of the wideband PA signals so as to provide high-resolution images with high-frequency CMUT arrays and present the high signal-to-noise-ratio major structure with low-frequency CMUT arrays. To demonstrate its performance, a phantom experiment was conducted to show and evaluate the various qualities of multiresolution images. In addition, an in vivo mouse model experiment was also carried out for revealing the multiscale PA imaging capability with the multiband CMUTs on biological tissues. From the obtained results, the images from different CMUT arrays could show the structures of the mouse brain in different scales. In addition, the images from the high-frequency CMUT arrays were able to reveal the major blood vasculatures, whereas the images from low-frequency CMUT arrays showed the gross macroscopic anatomy of the brain with higher contrast.

Experimental Characterization of an Embossed Capacitive Micromachined Ultrasonic Transducer Cell

“…Capacitive Micromachined Ultrasonic Transducer (CMUT) is a promising ultrasonic transducer [1] and has been widely applied in medical imaging [2,3], nondestructive measurement [4], chemical sensing [5], and photoacoustic tomography [6]. CMUT is an electronic transducer based on micro-electro-mechanical system (MEMS) technology so that it owns intrinsic advantages, such as compatible process with integrated circuits, wide bandwidth, and excellent stability of electrical and thermal.…”

Fabrication of embossed capacitive micromachined ultrasonic transducers using sacrificial release process

“…In the past years, CMUTs have been utilized in medical areas, such as ultrasonic imaging [5,6] and therapeutic applications [7,8]. Recently, owing to the features of wide bandwidth and fabricated by micro-electro-mechanical systems (MEMS) technique, CMUTs have also been used in photoacoustic imaging and achieved high quality images [9,10].…”

Photoacoustic Characterization of Custom-Made thin Film A1N MEMS Ultrasound Transducers

“…These miniaturised ultrasound transducers include capacitive micro-machined ultrasonic transducers (cMUT) and micro ring resonators (MRR). In the former, a cavity is etched into a silicon substrate which releases a thin film on which metal is deposited and which acts as a capacitor whose capacitance changes with applied pressure [2]. In the latter, the pressure wave deforms a micro ring structure and the resulting changes in optical resonance modes can be measured [3].…”

“…In the latter, the pressure wave deforms a micro ring structure and the resulting changes in optical resonance modes can be measured [3]. Both these methods offer a broad bandwidth but need to be actively operated by either applying a high bias voltage V > 70 V (cMUT) [2] or coupling narrow band laser light into the sensor (MRR) [3]. Piezoelectric ultrasound transducers do not require to be actively driven but rather generate a voltage due to a pressure wave induced deformation of the piezoelectric material.…”