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Measuring broadband signals demands complex calibration of a detector over a sufficient bandwidth. For inertial cavitation emissions, the shock waves will be convolved with the transfer function of the hydrophone, and introduce artefacts to the measurement. Use of appropriately calibrated detectors would thus facilitate meaningful comparison of the cavitation emission data reported from groups using...
Accurate characterisation of ultrasound fields generated by diagnostic and therapeutic transducers is critical for patient safety. This requires hydrophones calibrated to a traceable standard. The existing implementation of the primary standard at the National Measurement Institutes, e.g., NPL and PTB, can provide accurate calibration to a maximum frequency of 40MHz. However, the increasing use of...
Combined endoscopic imaging and therapeutic tools for minimally invasive procedures may lead to increased efficacy of the procedure and reduced patient risk. Currently, our lab is investigating the use of histotripsy tissue ablation during ultrasound guided neurosurgery. In this work, we will present our progress toward the miniaturization of the histotripsy transducer for simultaneous, real-time...
High intensity focused ultrasound (HIFU) is being increasingly used in medical therapeutics. The properties of the ultrasonic fields applied entail challenging acoustic output measurement tasks: the generation of high-pressure amplitudes sufficient for cavitation; the use of high-frequency components due to the non-linear sound propagation in water; and narrow beam widths at the focus. Conventional...
The energy transduction of a Capacitive Micromachined Ultrasonic Transducer (CMUT) depends on the movement of a flexible plate, which has a low mechanical impedance compared to its bulky piezoelectric counterpart. Consequently, the output pressure of a CMUT is generally lower. This limits the penetration depth, and thus the visualization of deeper structures in the body, as well as non-linear imaging...
Portable ultrasound scanners (PUS) have shown to have advantages over stationary scanners such as ease of use, accessibility, transportability and cost. However, PUS are severely restricted on size and power which directly limits the area and power consumption of the electronics. In order to fully utilize the available area and power budget to achieve the best picture quality, application specific...
Several works carried out these last years have demonstrated the ability of ultrasound (US) to activate neurons at a systemic level. However, no complete description of the biophysical mechanisms involved in this phenomenon has been validated so far. In order to identify experimentally these mechanisms, we here present an in vivo study of the stimulating effects of US exposures on the ventral nerve...
In order to overcome the limitations of conventional ultrasound endoscope, we propose to develop a capsule ultrasound (CUS) device: an ingestible and disposable pill to inspect the multiple layers of the entire gastrointestinal (GI) tract as well as its surrounding organs, and to provide a convenient method for diagnosing GI diseases, such as abdominal cancers and lesions. The CUS device is composed...
Accurate knowledge of the electro-mechanical impulse response for each element in an ultrasound array is important for e.g. model-driven beamforming techniques, coded excitation, etc. Typically, one would use a hydrophone to measure the transmitted pulse of an element excited by a delta-pulse. However, hydrophone setups are expensive, the procedure time is costly, and the measurement is sensitive...
Detailed spatial resolution in imaging, requires high frequencies. Indeed, clinical systems with center frequencies up to 50MHz are available. However, at such frequencies, the accuracy in measurements may be compromised if the device may be of comparable size to, or larger than the smallest characteristic length scale of the wave. In such cases, spatial variations in the pressure over the surface...
With a growing number of magnetic resonance-guided high-intensity focused ultrasound (MR-HIFU) clinical applications, acoustic field characterization tools and methods for quality assurance are needed to ensure safe treatment outcomes. However, the established methods typically use equipment that cannot be used in a magnetic resonance imaging (MRI) suite. Herein, we propose a technique for convenient...
Transcranial focused ultrasound (FUS) is a noninvasive technique for therapy and study of brain neural activation. Here we report on the design and characterization of a new MR-guided FUS transducer for neuromodulation in nonhuman primates at 650kHz. Focus size and grating lobes during electronic steering were quantified using hydrophone measurements in water and a three-axis stage. Pressure output...
A highly sensitive capacitive micromachined ultrasound transducer (CMUT) cell with an ultra-narrow gap was investigated. The electromechanical coupling coefficient (kT) as a figure of merit of sensitivity of ultrasound transducers was 0.67 in a 30-MHz CMUT cell with a 30-nm height vacuum gap and in 100-nm thick dielectric layers, and the coefficient was superior to that of piezoelectric transducers...
Accurate characterization of ultrasound fields generated by diagnostic and therapeutic transducers is critical for patient safety. This requires hydrophones calibrated to a traceable standard and currently the upper calibration frequency range available to the user community is limited to a frequency of 40 MHz. However, the increasing use of high frequencies for both imaging and therapy necessitates...
The use of shock waves for enhancing thermal effects and mechanically ablating tissue is gaining increased attention in high intensity focused ultrasound (HIFU) applications such as tumor treatment, drug delivery, noninvasive biopsy, and immunotherapy. For abdominal targets, the presence of ribs and inhomogeneous adipose tissue can affect shock formation through aberration, absorption, and diffraction...
The Keller-Miksis equation (KME) is commonly used for numerical studies of inertial and stable-inertial cavitation. However, experimental validation of KME under clinically relevant exposure settings is scarce, particularly in terms of the acoustic emission signal generated by the cavitation. In this paper, the KME is validated against a cavitation cloud collapsing f0/2 and f0/3 sub-harmonically with...
Ultrasonic transducers in the frequency ranges of 20–100 MHz is not well-developed because of less applications or less suitable piezoelectric materials. PVDF are usually used for ultrasonic transducers in the 10–50 MHz ranges. However, their electromechanical coupling coefficient kt2 of 4% is not enough for the practical uses. In order to excite ultrasonic in the 20–100 MHz, 125 μm-25 μm thick piezoelectric...
This paper presents an experimental study of the acoustic performance of Capacitive Micromachined Ultrasonic Transducers (CMUTs) as function of plate dimensions. The objective is to increase the output pressure without decreasing the pulse-echo signal. The CMUTs are fabricated with a LOCOS process, followed by direct wafer fusion bonding to a Silicon-On-Insulator (SOI) wafer. In this way, the plate...
Accurate characterization of ultrasound fields generated by diagnostic and therapeutic transducers is critical for patient safety. At high frequencies, spatial variations in the pressure over the surface of the measurement device will produce a different averaged value from that at the intended location. Using a small hydrophone as an idealised point device, this paper seeks to ascertain the spatial-averaging...
High-intensity focused ultrasound (HIFU) fields can be characterized by specific hydrophones that are able to withstand the large acoustical pressures used in medical applications. Such hydrophones may show a non-flat frequency response due to their being strengthened by protection layers against cavitation damage. Therefore, hydrophone calibration data should be used in deconvolution in order to...
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