Acousto-optic-based time domain electric field sensor for magnetic resonance imaging applications.

An acousto-optic (AO)-based electric field sensor is presented for time domain measurement under magnetic resonance imaging (MRI). A fully MR-compatible sensor is designed and fabricated using a phase-shifted fiber Bragg grating mechanically coupled to a piezoelectric transducer. Mechanical resonance of the piezoelectric transducer is matched to the operating frequencies of commonly used MRI systems to increase the sensitivity of the sensor.

A 1.11 mm2 IVUS SoC with ±50°-Range Plane Wave Transmit Beamforming at 40 MHz.

Intravascular ultrasound (IVUS) imaging catheters are significant tools for cardiovascular interventions, and their use can be expanded by realizing IVUS imaging guidewires and microcatheters. The miniaturization of these devices creates challenges in SNR due to the need for higher frequencies to provide adequate resolution. An integrated IVUS system with transmit beamforming can mitigate these limitations.

Spatially targeted brain cancer immunotherapy with closed-loop controlled focused ultrasound and immune checkpoint blockade.

Despite the challenges in treating glioblastomas (GBMs) with immune adjuvants, increasing evidence suggests that targeting the immune cells within the tumor microenvironment (TME) can lead to improved responses. Here, we present a closed-loop controlled, microbubble-enhanced focused ultrasound (MB-FUS) system and test its abilities to safely and effectively treat GBMs using immune checkpoint blockade. The proposed system can fine-tune the exposure settings to promote MB acoustic emission-dependent expression of the proinflammatory marker ICAM-1 and delivery of anti-PD1 in a mouse model of GBM.

Integrated Hybrid Sub-Aperture Beamforming and Time-Division Multiplexing for Massive Readout in Ultrasound Imaging.

This paper demonstrates hybrid sub-aperture beamforming (SAB) with time-division multiplexing (TDM) for massive interconnect reduction in ultrasound imaging systems. A single-chip front-end system prototype has been fabricated in 180-nm HV BCD technology that combines 5×1 SAB with 8×1 TDM to efficiently reduce the number of receive signal interconnects by a factor of 40. The system includes on-chip high-voltage (HV) pulsers capable of generating unipolar pulses up to 70 V in transmit (TX) mode.

An Adaptive Element-Level Impedance-Matched ASIC With Improved Acoustic Reflectivity for Medical Ultrasound Imaging.

This paper presents an active impedance matching scheme that tries to optimize electrical power transfer and acoustic reflectivity in ultrasound transducers. Leveraging negative capacitance-based impedance matching would potentially improve the bandwidth and electrical power transfer while minimizing acoustic reflection of transducer elements and improve uniformity while reducing acoustic crosstalk of transducer arrays. A 16-element transceiver front-end is designed which employs an element-level active capacitive impedance cancellation scheme using an element-level negative impedance converter.

Towards controlled drug delivery in brain tumors with microbubble-enhanced focused ultrasound.

Brain tumors are particularly challenging malignancies, due to their location in a structurally and functionally distinct part of the human body - the central nervous system (CNS). The CNS is separated and protected by a unique system of brain and blood vessel cells which together prevent most bloodborne therapeutics from entering the brain tumor microenvironment (TME). Recently, great strides have been made through microbubble (MB) ultrasound contrast agents in conjunction with ultrasound energy to locally increase the permeability of brain vessels and modulate the brain TME.

Analysis of Negative Capacitance-Based Broadband Impedance Matching for CMUTs.

Tight integration of capacitive micromachined ultrasonic transducer (CMUT) arrays with integrated circuits can make active impedance matching feasible for practical imaging devices. In this article, negative capacitance-based impedance matching for CMUTs is investigated. Simple equivalent circuit model-based calculations show the potential of negative capacitance matching for improving the bandwidth along with electrical power transfer and acoustic reflectivity, but the model has limitations especially for acoustic reflectivity evaluation.

Real-time device tracking under MRI using an acousto-optic active marker.

Purpose: This work aims to demonstrate the use of an "active" acousto-optic marker with enhanced visibility and reduced radiofrequency (RF) -induced heating for interventional MRI.

Methods: The acousto-optic marker was fabricated using bulk piezoelectric crystal and π-phase shifted fiber Bragg grating (FBGs) and coupled to a distal receiver coil on an 8F catheter. The received MR signal is transmitted over an optical fiber to mitigate RF-induced heating.

A Power-Efficient Bridge Readout Circuit for Implantable, Wearable, and IoT Applications.

A power-efficient bridge-to-digital sensing interface is proposed, which also offers immunity against power supply noise. The interface utilizes duty-cycling to reduce the static power consumption of resistive bridge sensors, which are commonly used in implantable, wearable, and internet of things (IoT) applications, such as intracranial pressure (ICP) sensing and blood pressure (BP) monitoring. The proposed interface uses a revised version of the pseudo-pseudo differential (PPD) topology with the ping-pong technique to reduce the complexity of traditional fully-differential counterparts.

Sensitivity and phase response of FBG based acousto-optic sensors for real-time MRI applications.

Fiber Bragg grating (FBG) based sensors have recently been introduced to the field of magnetic resonance imaging (MRI). Real-time MRI applications demand highly amplitude and phase sensitive MRI compatible sensors. Thus, a model and detailed analysis of FBG based ultrasound detection are required for designing better performing sensors.

Highly Integrated Guidewire Ultrasound Imaging System-on-a-Chip.

In this article, we present a highly integrated guidewire ultrasound (US) imaging system-on-a-chip (GUISoC) for vascular imaging. The SoC consists of a 16-channel US transmitter (Tx) and receiver (Rx) electronics, on-chip power management IC (PMIC), and quadrature sampler. Using a synthetic aperture imaging algorithm, a Tx/Rx pair, connected to capacitive micromachined ultrasound transducers (CMUTs), can be activated at any time.

Supply-Inverted Bipolar Pulser and Tx/Rx Switch for CMUTs Above the Process Limit for High Pressure Pulse Generation.

A combined supply-inverted bipolar pulser and a Tx/Rx switch is proposed to drive capacitive micromachined ultrasonic transducers (CMUTs). The supply-inverted bipolar pulser adopts a bootstrap circuit combined with stacked transistors, which guarantees high voltage (HV) operation above the process limit without lowering device reliability. This circuit generates an output signal with a peak-to-peak voltage that is almost twice the supply level.

An Impulse Radio PWM-Based Wireless Data Acquisition Sensor Interface.

A sensor interface circuit based on impulse radio pulse width modulation (IR-PWM) is presented for low power and high throughput wireless data acquisition systems (wDAQ) with extreme size and power constraints. Two triple-slope analog-to-time converters (ATC) convert two analog signals, each up to 5 MHz in bandwidth, into PWM signals, and an impulse radio (IR) transmitted (Tx) with an all-digital power amplifier (PA) combines them while preserving the timing information by transmitting impulses at the PWM rising and falling edges. On the receiver (Rx) side, an RF-LNA followed by an envelope detector recovers the incoming impulses, and a T-flipflop reverts the impulse sequence back to PWM to be digitized by a time-to-digital converter (TDC).

An Analysis Method for Capacitive Micromachined Ultrasound Transducer (CMUT) Energy Conversion during Large Signal Operation.

With Capacitive Micromachined Ultrasound Transducers (CMUTs) increasingly being used for high intensity, large signal ultrasound applications and several drive methods being proposed, the efficiency of these devices in this operation regime have not been quantitatively evaluated. Since well-known frequency and capacitance-based coupling coefficients definitions are not valid for large signal, nonlinear operation, an energy-based definition should be used. In this paper, an expression for mechanical energy in a CMUT is obtained based on the assumption that CMUT is a linear time varying capacitor in all regimes of operation.

Analysis and Design of High-Frequency 1-D CMUT Imaging Arrays in Noncollapsed Mode.

High-frequency ultrasound imaging arrays are important for a broad range of applications, from small animal imaging to photoacoustics. Capacitive micromachined ultrasonic transducer (CMUT) arrays are particularly attractive for these applications as low noise receiver electronics can be integrated for an overall improved performance. In this paper, we present a comprehensive analysis of high-frequency CMUT arrays based on an experimentally verified CMUT array simulation tool.

A Reduced-Wire ICE Catheter ASIC With Tx Beamforming and Rx Time-Division Multiplexing.

This paper presents a single chip reduced-wire active catheter application-specific integrated circuit (ASIC), equipped with programmable transmit (Tx) beamforming and receive (Rx) time-division multiplexing (TDM). The proposed front-end ASIC is designed for driving a 64-channel one-dimensional transducer array in intracardiac echocardiography (ICE) ultrasound catheters. The ASIC is implemented in 60 V 0.

Acousto-Optic Catheter Tracking Sensor for Interventional MRI Procedures.

Objective: The objective of this paper is to introduce an acousto-optic optical fiber sensor for tracking catheter position during interventional magnetic resonance imaging (MRI) to overcome RF induced heating of active markers.

Methods: The sensor uses a miniature coil coupled to a piezoelectric transducer, which is in turn mechanically connected to an optical fiber. The piezoelectric transducer converts the RF signal to acoustic waves in the optical fiber over a region including a fiber Bragg grating (FBG).

Analysis and Design of Capacitive Parametric Ultrasonic Transducers for Efficient Ultrasonic Power Transfer Based on a 1-D Lumped Model.

There is an increasing interest in wireless power transfer for medical implants, sensor networks, and consumer electronics. A passive capacitive parametric ultrasonic transducer (CPUT) can be suitable for these applications as it does not require a dc bias or a permanent charge. In this paper, we present a 1-D lumped parameter model of the CPUT to study its operation and investigate relevant design parameters for power transfer applications.

Supply-Doubled Pulse-Shaping High Voltage Pulser for CMUT Arrays.

A supply-doubled pulse-shaping high voltage (HV) pulser is presented for medical ultrasound imaging applications, particularly those that use capacitive micromachined ultrasonic transducers (CMUT). The pulser employs a bootstrap circuit combined with dynamically-biased stacked transistors, which allow HV operation above process limit without lowering device reliability. The new pulser overcomes supply voltage limitation of conventional unipolar pulsers by generating output signals that are almost twice the supply level.

Low Temperature CMUT Fabrication Process with Dielectric Lift-off Membrane Support for Improved Reliability.

This paper reports an improved CMOS compatible low temperature sacrificial layer fabrication process for Capacitive Micromachined Ultrasonic Transducers (CMUTs). The process adds the fabrication step of silicon oxide evaporation which is followed by a lift-off step to define the membrane support area without a need for an extra mask. This simple addition improves reliability by reducing the electric field between the top and bottom electrodes everywhere except the moving membrane without affecting the vacuum gap thickness.

Enhanced intracellular delivery via coordinated acoustically driven shear mechanoporation and electrophoretic insertion.

Delivery of large and structurally complex target molecules into cells is vital to the emerging areas of cellular modification and molecular therapy. Inadequacy of prevailing in vivo (viral) and in vitro (liposomal) gene transfer methods for delivery of proteins and a growing diversity of synthetic nanomaterials has encouraged development of alternative physical approaches. Efficacy of injury/diffusion-based delivery via shear mechanoporation is largely insensitive to cell type and target molecule; however, enhanced flexibility is typically accompanied by reduced gene transfer effectiveness.

A Hybrid Boundary Element Model for Simulation and Optimization of Large Piezoelectric Micromachined Ultrasonic Transducer Arrays.

A hybrid boundary element model is proposed for the simulation of large piezoelectric micromachined ultrasonic transducer (PMUT) arrays in immersion. Multiphysics finite element method (FEM) simulation of a single-membrane structure is used to determine stiffness and piezoelectrically induced actuation loading of the membranes. To simulate the arrays of membranes in immersion, a boundary element method is employed, wherein membrane structures are modeled by a surface mesh that is coupled mechanically by mass, stiffness, and damping matrices, and acoustically by a mutual impedance matrix.

Efficient Broadband Simulation of Fluid-Structure Coupling for Membrane-Type Acoustic Transducer Arrays Using the Multilevel Fast Multipole Algorithm.

A boundary element model provides great flexibility for the simulation of membrane-type micromachined ultrasonic transducers (MUTs) in terms of membrane shape, actuating mechanism, and array layout. Acoustic crosstalk is accounted for through a mutual impedance matrix that captures the primary crosstalk mechanism of dispersive-guided modes generated at the fluid-solid interface. However, finding the solution to the fully populated boundary element matrix equation using standard techniques requires computation time and memory usage that scales by the cube and by the square of the number of nodes, respectively, limiting simulation to a small number of membranes.

Towards a Reduced-Wire Interface for CMUT-Based Intravascular Ultrasound Imaging Systems.

Having intravascular ultrasound (IVUS) imaging capability on guide wires used in cardiovascular interventions may eliminate the need for separate IVUS catheters and expand the use of IVUS in a larger portion of the vasculature. High frequency capacitive micro machined ultrasonic transducer (CMUT) arrays should be integrated with interface electronics and placed on the guide wire for this purpose. Besides small size, this system-on-a-chip (SoC) front-end should connect to the back-end imaging system with a minimum number of wires to preserve the critical mechanical properties of the guide wire.

Direct Digital Demultiplexing of Analog TDM Signals for Cable Reduction in Ultrasound Imaging Catheters.

In real-time catheter-based 3-D ultrasound imaging applications, gathering data from the transducer arrays is difficult, as there is a restriction on cable count due to the diameter of the catheter. Although area and power hungry multiplexing circuits integrated at the catheter tip are used in some applications, these are unsuitable for use in small sized catheters for applications, such as intracardiac imaging. Furthermore, the length requirement for catheters and limited power available to on-chip cable drivers leads to limited signal strength at the receiver end.