Glioblastoma is a highly invasive, malignant brain tumor that affects over 13,000 patients in the United States each year, with a high rate of recurrence following resection. One possible solution to allow for long-term brain monitoring involves integrating wearable or implantable ultrasound devices with cranial implants. The objective of this study was to design, develop, and characterize and test a novel ultrasound probe that could be used in conjunction with a sonoluscent cranial implant to provide long-term brain monitoring following neurosurgery. A cranioplasty was performed on a human cadaver head and a cranial implant was placed over an ex vivo porcine brain, and ultrasound images of the brains with implanted tumors were captured using a custom, flexible ultrasound transducer. This proof of concept study lays the promising groundwork for the production of a wireless transducer housed inside of a cranial implant to provide long-term brain monitoring.

Focused ultrasound (FUS) is becoming widely researched for medical therapies due to its high penetration depth, spatial resolution, and affordability. Applications of FUS range from high intensity focused ultrasound (HIFU) for the ablation of cancerous tumors to low intensity focused ultrasound (LIFU) for the treatment of neurological conditions like essential tremors. A key step in developing these treatments and their corresponding FUS devices is characterizing the emitted ultrasound from the proposed transducer. However, a bottleneck exists at this verification and validation stage; current characterization techniques lack the robustness of reliably recording below a 5μm resolution. This level of accuracy is needed to adequately design devices which can target cells like astrocytes or other desired target tissues at this scale. Our Acoustic Measurement Platform for Localizing and Implementing Therapeutic Ultrasound Devices and Equipment (AMPLITUDE) is a solution which enables engineers, scientists, and clinicians to confidently characterize their equipment in a benchtop setting. It achieves this resolution by utilizing an all-in-one water conditioning unit, linear stepper motors with a theoretical step size of 1 μm and a 1% standard deviation on repetitive experiments, as well as signal processing techniques. This system can be used throughout the product timeline including prototyping, verifying efficacy, FDA testing, and routine check-ups during clinical use.

Many surgeons are faced with inoperable or only partially operable brain lesions, such as tumors. Even when surgery is feasible, patient outcomes are 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 centimeters 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.

ABSTRACT Introduction To improve patient outcomes (eg, reducing blood loss and infection), practitioners have gravitated toward noninvasive and minimally invasive surgeries (MIS), which demand specialized toolkits. Focused ultrasound, for example, facilitates thermal ablation from a distance, thereby reducing injury to surrounding tissue. Focused ultrasound can often be performed noninvasively; however, it is more difficult to carry out in neuro-oncological tumors, as ultrasound is dramatically attenuated while propagating through the skull. This shortcoming has prompted exploration of MIS options for intracranial placement of focused ultrasound probes, such as within the BrainPath ™ (NICO Corporation, Indianapolis, IN). Herein, we present the design, development, and in vitro testing of an image-guided, focused ultrasound prototype designed for use in MIS procedures. This probe can ablate neuro-oncological lesions despite its small size. Materials & Methods Preliminary prototypes were iteratively designed, built, and tested. The final prototype consisted of three 8-mm-diameter therapeutic elements guided by an imaging probe. Probe functionality was validated on a series of tissue-mimicking phantoms. Results Lesions were created in tissue-mimicking phantoms with average dimensions of 2.5×1.2×6.5mm and 3.4×3.25×9.36mm after 10- and 30-second sonification, respectively. 30s sonification with 118W power at 50% duty cycle generated a peak temperature of 68°C. Each ablation was visualized in real time by the built-in imaging probe. Conclusion We developed and validated an ultrasound-guided focused ultrasound probe for use in MIS procedures. The dimensional constraints of the prototype were designed to reflect those of BrainPath trocars, which are MIS tools used to create atraumatic access to deep-seated brain pathologies. HIGHLIGHTS An ultrasound-guided, focused ultrasound prototype was developed and validated The therapeutic transducer (1.5MHz) consisted of three 8-mm circular elements Elements were placed on a 9×32mm curved rectangular aperture: 45mm radius curvature Functionality was examined on tissue-mimicking phantoms 2.5×1.2×6.5mm and 3.4×3.25×9.36mm lesions were seen for 10 and 30s sonification

Neurosurgery typically requires craniectomy and meticulous dissection to achieve sufficient exposure for subsequent surgical intervention. This highly invasive process requires hours of operating time, long recovery periods and leaves patients with visible surgical scars. Non-invasive high-intensity focused ultrasound (HIFU) has shown some promise yet remains challenged by the attenuation of ultrasonic waves while passing through the skull. Consequently, the clinical impact of this technology remains limited, particularly in the treatment of neuro-oncology. In order to compensate for acoustic attenuation, excessive use of power for HIFU devices has been investigated, although it is undesirable from a regulatory and patient safety standpoint. Here, we report the design and development of a novel HIFU device prototype for neurologic lesion ablation. This device concept is envisioned to access the ventricular space via a minimally invasive ventriculostomy, allowing ultrasound to reach targets deep in the brain, while eliminating the need for high power to penetrate the skull.

Urinary stone lithotripsy critically depends on the presence of cavitation nuclei at the stone surface. We hypothesized that introduction of stone-targeting microbubbles could increase cavitation activity at a stone surface sufficiently to allow stone erosion and fragmentation at peak negative pressures much lower than in acoustic energy-based urinary stone interventions with induced cavitation nuclei alone. Gas-filled microbubbles were produced with calcium-binding moieties incorporated into an encapsulating lipid shell. Stone surface coverage with these targeting microbubbles was found to approach an optimal (considering microbubble expansion during insonation) range of 5–15% with incubation times of three minutes or less. Using high-speed photomicroscopy, we observe bound microbubbles expanding 10- to 30-fold under insonation with quasi-collimated sources at mechanical indexes below 1.9. For observed stand-off parameters in the range of 0.2–0.6, the modeled collapse-generated shockwaves exceed 100 MPa. In swine model studies with these targeting microbubbles, stone fragmentation into passable fragments occurs with treatment times around 30 minutes, while post-treatment examination of ureters and kidneys shows no evidence of urothelium damage or renal parenchymal hemorrhage. The stone-targeting microbubbles reported on here have formed the basis for a new non-invasive urinary stone treatment which recently entered human clinical trials.

Our group has previously demonstrated that increasing pulse duration lowers the accompanying peak negative pressure (PNP) required for effective gene delivery (UMGD) in mouse and cell models. This effect allows selection of conditions with minimal associated tissue damage and enables tuning to maximize the capabilities of piezo-materials. To eventually extend this finding clinically, we investigated its scalability in a pig model. In parallel, we examined several spatial effects which are important scaling considerations. According to our established UMGD protocol, the liver of each pig was exposed via a midline incision. Next, using contrast diagnostic ultrasound to confirm placement and perfusion, we catheterized a consistent branch of the portal vein. Just prior to therapeutic US exposure, the inferior vena cava was temporarily occluded. US exposure and infusion of a solution containing pGL4 plasmid and phospholipid MBs were initiated simultaneously. Therapeutic US was delivered via either H105, an unfocused 52 mm disc transducer, or H185D, a 49 mm disc transducer with three cylindrical focuses. Our US pulse durations spanned 19 µs-22 ms, with PNPs spanning 0.6-6.9 MPa. 24 hours after surgery, pigs were sacrificed to harvest treated and control liver lobes. After sectioning, spatially-mapped samples were analyzed for luciferase expression. Our ongoing experiments have added further support for a species-generalized model that increasing pulse duration enables the use of lower PNP for effective UMGD. Notably, within a paired study, increasing pulse duration from 19 µs to 200 µs at a constant 6.9 MPa PNP yielded an up to 17-fold increase in sampled luciferase gene expression. Furthermore, in the same paired study, a 200 µs pulse duration at a lower 4.5 MPa PNP still maintained up to a 9-fold increase in sampled expression versus the 19 µs, 6.9 MPa group. Despite these increases, ALT and AST values remained consistent or lowered for both groups when moving from 19 to 200 µs. When comparing spatial effects, H105 yielded significantly increased expression relative to H185D at equivalent pulse duration and focal PNP. This result suggests that focal treatment volume is also an important consideration for UMGD in larger animal models. However, comparing expression relative to energy flux shows no such discrepancy in our data, suggesting that pressure-dependent cavitation dynamics still play a role in UMGD efficacy. By manipulating US pulse durations, our group has successfully achieved increased expression, circumventing the peak power density limitations imposed by piezo-materials used in US transducers. Such tuning has also allowed us to achieve comparable expression at decreased PNPs. Since skin attenuation imposes a barrier to high PNPs in transcutaneous UMGD, this result has promising implications for advancing that modality. Our results demonstrate the advancement of UMGD technology for achieving efficient gene transfer in large animal models.

Ultrasound (US) combined with microbubble (MB) represents a promising non-viral gene delivery strategy. Previously we successfully developed US/MB mediated reporter gene delivery system in murine models and scaled up into large animal models. In order to further pursue non-invasive gene therapy strategy for clinical application, in this study we investigated alternative surgical operation and different acoustic transducers/parameters. Firstly, we investigated the optimal US protocol under transcutaneous US treatment using intraoperative procedures. Following midline incision, the plasmid/MB was injected into the portal vein branch with inferior vena cava occluded during treatment. Simultaneously, transcutaneous US treatment on the skin was applied towards the target liver lobe (20 cycle pulses, 50 Hz PRF, 6 MPa PNP). Compared with the control liver lobe, luciferase expression of the treated liver showed a significant enhancement (≈2000 RLU /mg protein, ≈200 fold higher vs. control). Previously we observed that higher acoustic pressure was required for large animals than that for mice at short pulse durations. In addition, even higher pressure will be needed to overcome the attenuation of US intensities across skin tissue layers. However, higher pressure can induce more severe liver damages and is limited by power output capacity of the transducers. Recently we found that by prolonging pulse durations, efficient gene transfer with minimized liver damage can be achieved at lower acoustic pressures in cell culture and mice. Similar strategy was employed in pigs by applying US on target liver lobe at various parameters (50μs-4ms pulse duration, 0.4-3 MPa). Significant enhancement of gene expression was achieved with 3000 RLU/mg protein at very low PNP (0.4 MPa) and >104 RLU/mg protein at 1MPa PNP. Our studies indicated a targetable range of millisecond pulse durations which is useful across small and large animal models. These new US conditions will allow for more effective transcutaneous treatment in the pig livers where attenuation across multiple intervening tissue layers poses a significant barrier to achieving high PNPs. Next, we evaluated gene transfer without laparotomy using a US imaging-guided procedure. Plasmid/MB was infused into a specific portal vein branch via a catheter guided by diagnostic US through the skin. The target liver was simultaneously treated by transcutaneous US on the skin. Although the liver damages were significantly minimized after treatment, large variations in the gene expression levels among different animals were obtained due to varied degrees of plasmid/MB distribution and retention. We are currently developing a minimally invasive interventional radiologic technique to deliver plasmid/MB into the liver combined with transcutaneous US procedure. In conclusion, the exploration of different treatment protocols and acoustic parameters for gene delivery into pig livers paves the way to potentially efficient and non-invasive clinical application of US/MB mediated gene therapy.