Minimally invasive therapeutic ultrasound: Ultrasound-guided ultrasound ablation in neuro-oncology

Focused Ultrasound-Responsive Nanocomposite with Near-Infrared II Mechanoluminescence for Spatiotemporally Selective Immune Activation in Lymph Nodes

The immune regulation of the lymphatic system, especially the lymph node (LN), is of great significance for the treatment of diseases and the inhibition of pathogenic organisms spreading in the body. However, achieving precise spatiotemporal control of immune cell activation in LN in vivo remains a challenge due to tissue depth and off-target effects. Furthermore, minimally invasive and real-time feedback methods to monitor the regulation of the immune system in LN are lacking. Here, focused ultrasound responsive immunomodulator loaded nanoplatform (FURIN) with near-infrared II (NIR-II) luminescence is designed to achieve spatiotemporally controllable immune activation in LN in vivo. The NIR-II persistent luminescence of FURIN can track its delivery in LN through bioimaging. Under focused ultrasound (FUS) stimulation, the immunomodulator encapsulated in FURIN can be released locally in the LN to activate immune cells such as dendritic cells and the NIR-II mechanoluminescence of FURIN provides real-time optical feedback signals for immune activation. This work points to a FUS mediated, spatiotemporal selective immune activation strategy in vivo with the feedback control of luminescence signals via ultrasound responsive nanocomposite, which is of great significance in improving the efficacy and reducing the side effect of immune regulation for the development of potential immunotherapeutic methods in the future.

Effects of ultrasound settings on temperature changes in NiTi implants

BACKGROUND

Shape memory alloys (SMAs) are well-known for their unique ability to undergo a shape change in response to a thermal stimulus. A frequently-used SMA for biomedical devices is NiTi, although its superelastic features tend to be emphasized more than the ability to change shape. Minimally invasive NiTi implants which can reconfigure or adjust their shape across several temperature points could provide desirable surgical outcomes. For decades, therapeutic ultrasound has been used medically as a non-invasive method for tissue thermal therapy. Ultrasound's ability to quickly raise temperatures, and transcutaneously activate shape changes in NiTi implants is a novel approach for eliciting the martensitic thermoelastic transformation.

METHODS

The purpose of this study was to investigate the features of therapeutic ultrasound that correspond with temperature changes in different NiTi specimens. For this purpose, ultrasound was applied to two NiTi specimens for two minutes each at varying low- and high-frequency and power settings using a Sonicator 740 and a Dynatron 150.

FINDINGS

The baseline temperature for all 32 trials was room temperature (23.0 ± 1.7°C). This study successfully increased the specimen temperature with the application of Sonicator 740 and Dynatron 150 therapeutic ultrasound machines (2.2 ± 2.4°C and 1.5 ± 1.15°C, respectively). From the statistical analyses of the experimental data, it was clear that there is a significant difference between low- and high-power settings on mean temperature change using the Dynatron 150 (ANCOVA; p = 0.013). Interpretation Of clinical relevance, NiTi implants can quickly and easily increase in temperature when applying therapeutic ultrasound. Ultrasound power causes temperature changes and should be accounted for when designing orthopedic implants for applications where dimensional changes are desirable.

Sonolucent cranioplasty: Is therapeutic FUS the next frontier?

Focused ultrasound (FUS) has emerged as a promising area of research in neuro-oncology. Preclinical and clinical investigation has demonstrated the utility of FUS in therapeutic applications including blood brain barrier disruption for therapeutic delivery, and high intensity FUS for tumor ablation. However, FUS as it exists today is relatively invasive as implantable devices are necessary to achieve adequate intracranial penetration. Sonolucent implants, composed of materials permeable to acoustic waves, have been used for cranioplasty and intracranial imaging with ultrasound. Given the overlap in ultrasound parameters with those used for intracranial imaging, and the demonstrated efficacy of sonolucent cranial implants, we believe that therapeutic FUS through sonolucent implants represents a promising avenue of future research. The potential applications of FUS and sonolucent cranial implants may confer the demonstrated therapeutic benefits of existing FUS applications, without the drawbacks and complications of invasive implantable devices. Here we briefly summarize existing evidence regarding sonolucent implants and describe applications for therapeutic FUS.

Surgical Management of Brain Tumors with Focused Ultrasound

Focused ultrasound is a novel technique for the treatment of aggressive brain tumors that uses both mechanical and thermal mechanisms. This non-invasive technique can allow for both the thermal ablation of inoperable tumors and the delivery of chemotherapy and immunotherapy while minimizing the risk of infection and shortening the time to recovery. With recent advances, focused ultrasound has been increasingly effective for larger tumors without the need for a craniotomy and can be used with minimal surrounding soft tissue damage. Treatment efficacy is dependent on multiple variables, including blood-brain barrier permeability, patient anatomical features, and tumor-specific features. Currently, many clinical trials are currently underway for the treatment of non-neoplastic cranial pathologies and other non-cranial malignancies. In this article, we review the current state of surgical management of brain tumors using focused ultrasound.

Phase aberration correction for ultrasound imaging guided extracorporeal shock wave therapy (ESWT): Feasibility study

Image guidance of extracorporeal shock wave therapy (ESWT) is important to enhance its efficacy while lowering pain in patients. Real-time ultrasound imaging is an appropriate modality for image guidance, but its image quality substantially reduces due to severe phase aberration from the different speed of sound between soft tissues and a gel pad, which is utilized to control a therapeutic focal point in ESWT. This paper presents a phase aberration correction method for improving image quality in the ultrasound imaging guided ESWT. To correct an error from phase aberration, a time delay based on a two-layer model with different speeds of sound is calculated for dynamic receive beamforming. For the phantom and in vivo studies, a rubber type gel pad (i.e., 1400 m/s) with a specific thickness (3 or 5-cm) was placed on the top of soft tissue and full scanline RF data were acquired. In the phantom study, with phase aberration correction, image quality was highly increased compared to image reconstructions with a fixed speed of sound (i.e., 1540 or 1400 m/s), i.e., 1.1 vs. 2.2 and 1.3 mm in -6dB lateral resolution and 0.64 vs. 0.61 and 0.56 in contrast-to-noise ratio (CNR), respectively. From an in vivo musculoskeletal (MSK) imaging, the phase aberration correction method provided a clearly improved depiction of muscle fibers in a rectus femoris region. These results indicate that the proposed method enables effective imaging guidance of ESWT by improving image quality of ultrasound imaging in real-time.

Surgical Resection of Deep-Seated Arteriovenous Malformations Through Stereotactically Guided Tubular Retractor Systems: A Case Series

BACKGROUND

Arteriovenous malformations (AVMs) in the subcortical and/or periventricular regions can cause significant intraventricular and intracranial hemorrhage. These AVMs can pose a unique surgical challenge because traditional, open approaches to the periventricular region require significant cortical/white matter retraction to establish sufficient operative corridors, which may result in risk of neurological injury. Minimally invasive tubular retractor systems represent a novel, feasible surgical option for treating deep-seated AVMs.

OBJECTIVE

To explore 5 cases of NICO BrainPath-assisted resection of subcortical/periventricular AVMs.

METHODS

Five patients from a single institution were operated on for deep-seated AVMs using tubular retractor systems. Collected data included demographics, AVM specifications, preoperative neurological status, postoperative neurological status, and postoperative/intraoperative angiogram results.

RESULTS

Five patients, ranging from age 10 to 45 years, underwent mini-craniotomy for stereotactically guided tubular retractor-assisted AVM resection using neuronavigation for selecting a safe operative corridor. No preoperative embolization was necessary. Mean maximum AVM nidal diameter was 8.2 mm. All deep-seated AVMs were completely resected without complications. All AVMs demonstrated complete obliteration on intraoperative angiogram and on 6-month follow-up angiogram.

CONCLUSION

Minimally invasive tubular retractors are safe and present a promising surgical option for well-selected deep-seated AVMs. Furthermore, study may elucidate whether tubular retractors improve outcomes after microsurgical AVM resection secondary to mitigation of iatrogenic retraction injury risk.

Clinical value of pulmonary congestion detection by lung ultrasound in patients with chronic heart failure

Chronic heart failure is one of the common causes of hospitalization and death. Pulmonary congestion is the common disease feature of patients with chronic heart failure, which could be correctly diagnosed by lung ultrasound. Efficacy of lung ultrasound‐guided pulmonary congestion management for patients with acute heart failure is well documented, however, more evidence is needed to establish the clinical value of pulmonary congestion detection by lung ultrasound examination in patients with chronic heart failure. This review summarized current evidence related to the use and clinical value of pulmonary congestion assessment by lung ultrasound in patients with chronic heart failure, aiming to provide new suggestions on promoting the widespread use of lung ultrasound in patients with chronic heart failure to improve the quality of life and outcome of patients with chronic heart failure.

A Dual-Frequency Lens-Focused Endoscopic Histotripsy Transducer

A forward-looking miniature histotripsy transducer has been developed that incorporates an acoustic lens and dual-frequency stacked transducers. An acoustic lens is used to increase the peak negative pressure through focal gain and the dual-frequency transducers are designed to increase peak negative pressure by summing the pressure generated by each transducer individually. Four lens designs, each with an f -number of approximately 1, were evaluated in a PZT5A composite transducer. The finite-element model (FEM) predicted axial beamwidths of 1.61, 2.40, 2.84, and 2.36 mm for the resin conventional, resin Fresnel, silicone conventional, and silicone Fresnel lenses, respectively; the measured axial beamwidths were 1.30, 2.28, 2.71, and 2.11 mm, respectively. Radial beamwidths from the model were between 0.32 and 0.35 mm, while measurements agreed to within 0.2 mm. The measured peak negative was 0.150, 0.124, 0.160, and 0.160 MPa/V for the resin conventional, resin Fresnel, silicone conventional, and silicone Fresnel lenses, respectively. For the dual-frequency device, the 5-MHz (therapy) transducer had a measured peak negative pressure of 0.136 MPa/V for the PZT5A composite and 0.163 MPa/V for the PMN-PT composite. The 1.2-MHz (pump) transducer had a measured peak negative pressure of 0.028 MPa/V. The pump transducer significantly lowered the cavitation threshold of the therapy transducer. The dual-frequency device was tested on an ex vivo rat brain, ablating tissue at up to 4-mm depth, with lesion sizes as small as [Formula: see text].

A Robotically Steerable Guidewire With Forward-Viewing Ultrasound: Development of Technology for Minimally-Invasive Imaging

OBJECTIVE

The current standard of care for peripheral chronic total occlusions involves the manual routing of a guidewire under fluoroscopy. Despite significant improvements in recent decades, navigation remains clinically challenging with high rates of procedural failure and iatrogenic injury. To address this challenge, we present a proof-of-concept robotic guidewire system with forward-viewing ultrasound imaging to allow visualization and maneuverability through complex vasculature.

METHODS

A 0.035" guidewire-specific ultrasound transducer with matching layer and acoustic backing was designed, fabricated, and characterized. The effect of guidewire motion on signal decorrelation was assessed with simulations and experimentally, driving the development of a synthetic aperture beamforming approach to form images as the transducer is steered on the robotic guidewire. System performance was evaluated by imaging wire targets in water. Finally, proof-of-concept was demonstrated by imaging an ex vivo artery.

RESULTS

The designed custom transducer was fabricated with a center frequency of 15.7 MHz, 45.4% fractional bandwidth, and 31 dB SNR. In imaging 20 μm wire targets at a depth of 6 mm, the lateral -6 dB target width was 0.25 ± 0.03 mm. The 3D artery reconstruction allowed visualization of vessel wall structure and lumen.

CONCLUSION

Initial proof-of-concept for an ultrasound transducer-tipped steerable guidewire including 3D image formation without an additional sensor to determine guidewire position was demonstrated for a sub-mm system with an integrated ultrasound transducer and a robotically-steered guidewire.

SIGNIFICANCE

The developed forward-viewing, robotically-steered guidewire may enable navigation through occluded vascular regions that cannot be crossed with current methods.

A MINIATURE LASER SPECKLE CONTRAST IMAGER FOR MONITORING OF THE NEURO-MODULATORY EFFECT OF TRANSCRANIAL FOCUSED ULTRASOUND STIMULATION

Transcranial focused ultrasound stimulation is a neuromodulation technique that is capable of exciting or suppressing the neural network. Such neuro-modulatory effects enable the treatment of brain diseases non-invasively, such as treating stroke. The neuro-modulatory effect on cerebral hemodynamics has been monitored using laser speckle contrast imaging in animal studies. However, the bulky size and stationary nature of the imaging system constrains the application of this imaging technique on research that requires the animal to have different body positions or to be awake. We present the design of a system that combines a miniature microscope for laser speckle contrast imaging and transcranial focused ultrasound stimulation, as well as, test its capability to monitor cerebral hemodynamics during stimulation and compare the result with a benchtop imaging system.

DESIGN AND FABRICATION OF A FOCUSED ULTRASOUND DEVICE FOR MINIMALLY-INVASIVE NEUROSURGERY: REPORTING A SECOND, MINIATURIZED AND MR-COMPATIBLE PROTOTYPE WITH STEERING CAPABILITIES

Many surgeons are faced with inoperable or only partially operable brain lesions, such as tumors. Even when surgery is feasible, patient outcome is greatly affected by blood loss or infection. This has led many physicians toward non- or minimally-invasive surgery, which demands specialized toolkits. Focused ultrasound has great potential for assisting in such procedures due to its ability to focus a few cm away from the surface of the transducer. In a prior study, we developed a focused ultrasound prototype that could fit within a BrainPath trocar, specifically made for minimally invasive brain surgery. Here, we present the design and fabrication of a second prototype that reduces size, is MR-compatible, and has electronic steering capabilities.

Double-Parabolic-Reflectors Ultrasonic Transducer With Flexible Waveguide for Minimally Invasive Treatment

OBJECTIVE

To treat tissues that are difficult to access, ultrasound based minimally invasive treatment (MIT) is promising. However, high-power ultrasound delivery through waveguides had been difficult which can increase treatment duration. It is our effort to design the waveguide that can transmit powerful ultrasound.

METHODS

The waveguide with two parabolic reflectors was proposed by us to produce high-energy-density plane wave. Use of flexible and long thin waveguide was demonstrated here.

RESULTS

Double Parabolic refLectors wave-guided high-power Ultrasonic tranSducer (DPLUS) including a ϕ1 mm ×1 m Nitinol thin waveguide was fabricated. It was shown that high-power ultrasound between 1 to 2 MHz can be propagated through the thin waveguide. Low-loss waveguide material was confirmed to be important to enhance output. As ultrasound is transmitted into working medium, energy mainly flows from the side surface. Temperature of target soft tissue was demonstrated to drastically increase by 10 degree in 30 seconds.

CONCLUSION

The developed DPLUS makes high-power ultrasound transmission in long and flexible thin waveguide possible.

SIGNIFICANCE

The concept of DPLUS for delivering high-power ultrasound is powerful in the field of Ultrasonics.