An Ultrasound Array of Emitter-Receiver Stacks for Microbubble-Based Therapy.

Most therapeutic ultrasound devices place emitters and receivers in separate locations, so that the long therapeutic pulses (>1 ms) can be emitted while receivers monitor the procedure. However, with such placement, emitters and receivers are competing for the same space, producing a trade-off between emission efficiency and reception sensitivity. Taking advantage of recent studies demonstrating that short-pulse ultrasound can be used therapeutically, we aimed to develop a device that overcomes such trade-offs. The array was composed of emitter-receiver stacks, which enabled both emission and reception from the same location. Each element was made of a lead zirconate titanate (PZT)-polyvinylidene fluoride (PVDF) stack. The PZT (frequency: 500 kHz, diameter: 16 mm) was used for emission and the PVDF (thickness: 28 µm, diameter: 16 mm) for broadband reception. 32 elements were assembled in a 3D-printed dome-shaped frame (focal length: 150 mm; [Formula: see text]-number: 1) and was tested in free-field and through an ex-vivo human skull. In free-field, the array had a 4.5 × 4.5 × 32 mm focus and produced a peak-negative pressure (PNP) of 2.12 MPa at its geometric center. The electronic steering range was ±15 mm laterally and larger than ±15 mm axially. Through the skull, the array produced a PNP of 0.63 MPa. The PVDF elements were able to localize broadband microbubble emissions across the skull. We built the first multi-element array for short-pulse and microbubble-based therapeutic applications. Stacked arrays overcome traditional trade-offs between the transmission and reception quality and have the potential to create a step change in treatment safety and efficacy.

Passive Cavitation Detection With a Needle Hydrophone Array.

Therapeutic ultrasound and microbubble technologies seek to drive systemically administered microbubbles into oscillations that safely manipulate tissue or release drugs. Such procedures often detect the unique acoustic emissions from microbubbles with the intention of using this feedback to control the microbubble activity. However, most sensor systems reported introduce distortions to the acoustic signal. Acoustic shockwaves, a key emission from microbubbles, are largely absent in reported recording, possibly due to the sensors being too large or too narrowband, or having strong phase distortions. Here, we built a sensor array that countered such limitations with small, broadband sensors and a low-phase distorting material. We built eight needle hydrophones with polyvinylidene fluoride (PVDF, diameter: 2 mm) then fit them into a 3-D-printed scaffold in a two-layered, staggered arrangement. Using this array, we monitored microbubbles exposed to therapeutically relevant ultrasound pulses (center frequency: 0.5 MHz, peak-rarefactional pressure: 130-597 kPa, pulselength: four cycles). Our tests revealed that the hydrophones were broadband with the best having a sensitivity of -224.8 dB ± 3.2 dB re 1 V/ µ Pa from 1 to 15 MHz. The array was able to capture shockwaves generated by microbubbles. The signal-to-noise ratio (SNR) of the array was approximately two times higher than individual hydrophones. Also, the array could localize microbubbles (-3 dB lateral resolution: 2.37 mm) and determine the cavitation threshold (between 161 and 254 kPa). Thus, the array accurately monitored and localized microbubble activities, and may be an important technological step toward better feedback control methods and safer and more effective treatments.

Distal Re-Entry to Treat Lower Limb Chronic Total Occlusions Using a Novel Electrically Guided Re-Entry Catheter.

INTRODUCTION: Endovascular treatment of challenging infra-inguinal peripheral vascular disease is increasingly common because of new techniques and improved tools. The use of a novel electrically guided 5 F re-entry catheter is presented. By emitting a minute electrical field, detected by a target wire inserted from an opposing access, the catheter's orientation is accurately displayed to the operator, allowing precise re-entry without the need for fluoroscopic alignment. REPORT: An 84 year old man with tissue loss was treated for a long occlusion of the superficial femoral artery and tibial vessels. Successful subintimal recanalisation was achieved with the help of the ePATH re-entry catheter, restoring inline flow to the foot. CONCLUSION: This re-entry catheter benefits from an intuitive alignment method, smaller profile, and operator adjustable needle travel, making it a versatile tool for endovascular cases.

A PZT-PVDF Stacked Transducer for Short-Pulse Ultrasound Therapy and Monitoring.

Therapeutic ultrasound technologies using microbubbles require a feedback control system to perform the treatment in a safe and effective manner. Current feedback control technologies utilize the microbubble's acoustic emissions to adjust the treatment acoustic parameters. Typical systems use two separated transducers: one for transmission and the other for reception. However, separating the transmitter and receiver leads to foci misalignment. This limitation could be resolved by arranging the transmitter and receiver in a stacked configuration. Taking advantage of an increasing number of short-pulse-based therapeutic methods, we have constructed a lead zirconate titanate-polyvinylidene fluoride (PZT-PVDF) stacked transducer design that allows the transmission and reception of short-pulse ultrasound from the same location. Our design had a piston transmitter composed of a PZT disk (1 MHz, 12.7 mm in diameter), a backing layer, and two matching layers. A layer of PVDF ( [Formula: see text] in thickness, 12.7 mm in diameter) was placed at the front surface of the transmitter for reception. Transmission and reception from the same location were demonstrated in pulse-echo experiments where PZT transmitted a pulse and both PZT and PVDF received the echo. The echo signal received by the PVDF was [Formula: see text] shorter than the signal received by the PZT. Reception of broadband acoustic emissions using the PVDF was also demonstrated in experiments where microbubbles were exposed to ultrasound pulses. Thus, we have shown that our PZT-PVDF stack design has unique transmission and reception features that could be incorporated into a multielement array design that improves focal superimposing, transmission efficiency, and reception sensitivity.

3D synthetic aperture imaging with a therapeutic spherical random phased array for transcostal applications.

Experimental validation of a synthetic aperture imaging technique using a therapeutic random phased array is described, demonstrating the dual nature of imaging and therapy of such an array. The transducer is capable of generating both continuous wave high intensity beams for ablating the tumor and low intensity ultrasound pulses to image the target area. Pulse-echo data is collected from the elements of the phased array to obtain B-mode images of the targets. Since therapeutic arrays are optimized for therapy only with concave apertures having low f-number and large directive elements often coarsely sampled, imaging can not be performed using conventional beamforming. We show that synthetic aperture imaging is capable of processing the acquired RF data to obtain images of the field of interest. Simulations were performed to compare different synthetic aperture imaging techniques to identify the best algorithm in terms of spatial resolution. Experimental validation was performed using a 1 MHz, 256-elements, spherical random phased array with 130 mm radius of curvature. The array was integrated with a research ultrasound scanner via custom connectors to acquire raw RF data for variety of targets. Imaging was implemented using synthetic aperture beamforming to produce images of a rib phantom and ex vivo ribs. The array was shown to resolve spherical targets within ±15 mm of either side of the axis in the focal plane and obtain 3D images of the rib phantom up to ±40 mm of either side of the central axis and at a depth of 3-9 cm from the array surface. The lateral and axial full width half maximum was 1.15 mm and 2.75 mm, respectively. This study was undertaken to emphasize that both therapy and image guidance with a therapeutic random phased array is possible and such a system has the potential to address some major limitations in the existing high intensity focused ultrasound (HIFU) systems. The 3D images obtained with a therapeutic array can be used to identify and locate strong scattering objects aiding to image guidance and treatment planning of the HIFU procedure.

Simultaneous Ultrasound Therapy and Monitoring of Microbubble-Seeded Acoustic Cavitation Using a Single-Element Transducer.

Ultrasound-driven microbubble (MB) activity is used in therapeutic applications such as blood clot dissolution and targeted drug delivery. The safety and performance of these technologies are linked to the type and distribution of MB activities produced within the targeted area, but controlling and monitoring these activities in vivo and in real time has proven to be difficult. As therapeutic pulses are often milliseconds long, MB monitoring currently requires a separate transducer used in a passive reception mode. Here, we present a simple, inexpensive, integrated setup, in which a focused single-element transducer can perform ultrasound therapy and monitoring simultaneously. MBs were made to flow through a vessel-mimicking tube, placed within the transducer's focus, and were sonicated with therapeutic pulses (peak rarefactional pressure: 75-827 kPa, pulse lengths: [Formula: see text] and 20 ms). The MB-seeded acoustic emissions were captured using the same transducer. The received signals were separated from the therapeutic signal with a hybrid coupler and a high-pass filter. We discriminated the MB-generated cavitation signal from the primary acoustic field and characterized MB behavior in real time. The simplicity and versatility of our circuit could make existing single-element therapeutic transducers also act as cavitation detectors, allowing the production of compact therapeutic systems with real time monitoring capabilities.

Oximetry feedback flow control simulation for oxygen therapy.

OBJECTIVES: For many with Chronic Obstructive Pulmonary Disease (COPD), arterial oxygen saturation while receiving Long-Term Oxygen Therapy (LTOT) falls below an acceptable threshold (SpO(2) < 90%) for extended periods during routine daily activities. Using a closed-loop controller, we have evaluated a simulated method to automatically regulate the oxygen flow-rate in response to the measured oxygen demand. METHODS: The closed-loop control scheme was implemented in a computer simulation on Simulink. Feedback from a pulse oximeter was used to maintain a target SpO(2) of 91% by changing the oxygen flow-rate to the patient. The controller was evaluated using a model to approximate the patient's arterial oxygen saturation response, including hypoxic events from artificial disturbances as well as recorded patient oximetry data. RESULTS: The simulated controller produced improvement in arterial oxygen saturation throughout a wide range of disturbance frequencies. It suppressed disturbances with periods greater than a couple of minutes by more than -10 dB. When evaluated with patient oximetry recordings, the controller on average reduced the time spent with arterial blood saturation below threshold by 76%. Given the same volume of oxygen, the closed-loop controller also produced a 63% improvement compared to fixed flow-rate LTOT. CONCLUSIONS: The simulation findings indicate an optimized matching between oxygen supply and demand, maintaining SpO(2) above threshold to improve therapeutic efficacy compared to standard LTOT.

Removal of calcific deposits of the rotator cuff tendon using an intra-articular ultrasound probe.

Calcific tendonitis is a difficult condition to treat. In this report we describe a new technique for imaging the deposit in complicated cases. Previously the patient had an unsuccessful operation due to difficulty in visualising the deposit. An ultrasound probe was inserted arthroscopically and the calcification detected and then removed, this was later confirmed on external ultrasound.