Carl D. Herickhoff

Dual-Mode IVUS Transducer for Image-Guided Brain Therapy: Preliminary Experiments

In this study, we investigated the feasibility of using 3.5-Fr IVUS catheters for minimally-invasive, image-guided hyperthermia treatment of tumors in the brain. Feasibility is demonstrated in two ways: 1) by fitting a 3.5-Fr IVUS catheter with a 5 × 0.5 × 0.22 mm PZT-4 transducer for 9-MHz imaging, and 2) by testing an identical transducer for therapy potential with 3.3-MHz CW excitation. The imaging transducers performance was compared to a 9-Fr, 9-MHz ICE catheter as a gold standard, visualizing a 2.5-cm cyst phantom and a postmortem ovine brain. The therapy transducer was able to maintain a power output of 700 mW, achieving a temperature rise of +19°C at a depth of 1.5 mm in excised brain tumor tissue.

Dual-mode IVUS catheter for intracranial image-guided hyperthermia: Feasibility study

In this study, we investigated the feasibility of modifying 3-Fr IVUS catheters in several designs to potentially achieve minimally-invasive, endovascular access for image-guided ultrasound hyperthermia treatment of tumors in the brain. Using a plane wave approximation, target frequencies of 8.7 and 3.5 MHz were considered optimal for heating at depths (tumor sizes) of 1 and 2.5 cm, respectively. First, a 3.5-Fr IVUS catheter with a 0.7-mm diameter transducer (30 MHz nominal frequency) was driven at 8.6 MHz. Second, for a low-frequency design, a 220-μm-thick, 0.35 × 0.35-mm PZT-4 transducer - driven at width-mode resonance of 3.85 MHz - replaced a 40-MHz element in a 3.5-Fr coronary imaging catheter. Third, a 5 × 0.5-mm PZT-4 transducer was evaluated as the largest aperture geometry possible for a flexible 3-Fr IVUS catheter. Beam plots and on-axis heating profiles were simulated for each aperture, and test transducers were fabricated. The electrical impedance, impulse response, frequency response, maximum intensity, and mechanical index were measured to assess performance. For the 5 × 0.5-mm transducer, this testing also included mechanically scanning and reconstructing an image of a 2.5-cm-diameter cyst phantom as a preliminary measure of imaging potential.

Dual-mode intracranial catheter integrating 3D ultrasound imaging and hyperthermia for neuro-oncology: feasibility study.

In this study, we investigated the feasibility of an intracranial catheter transducer with dual-mode capability of real-time 3D (RT3D) imaging and ultrasound hyperthermia, for application in the visualization and treatment of tumors in the brain. Feasibility is demonstrated in two ways: first by using a 50-element linear array transducer (17 mm × 3.1 mm aperture) operating at 4.4 MHz with our Volumetrics diagnostic scanner and custom, electrical impedance-matching circuits to achieve a temperature rise over 4°C in excised pork muscle, and second, by designing and constructing a 12 Fr, integrated matrix and linear-array catheter transducer prototype for combined RT3D imaging and heating capability. This dual-mode catheter incorporated 153 matrix array elements and 11 linear array elements diced on a 0.2 mm pitch, with a total aperture size of 8.4 mm × 2.3 mm. This 3.64 MHz array achieved a 3.5°C in vitro temperature rise at a 2 cm focal distance in tissue-mimicking material. The dual-mode catheter prototype was compared with a Siemens 10 Fr AcuNav™ catheter as a gold standard in experiments assessing image quality and therapeutic potential and both probes were used in an in vivo canine brain model to image anatomical structures and color Doppler blood flow and to attempt in vivo heating.

Intracranial Dual-Mode IVUS and Hyperthermia Using Circular Arrays Preliminary Experiments

In this study, we investigated the feasibility of using 3.5-Fr (3 Fr = 1 mm) circular phased-array intravascular ultrasound (IVUS) catheters for minimally invasive, image-guided hyperthermia treatment of tumors in the brain. Feasibility was demonstrated in two ways: (1) by inserting a 3.5-Fr IVUS catheter through skull burr holes, for 20 MHz brain imaging in the pig model, and (2) by testing a modified circular array for therapy potential with 18.5-MHz and 9-MHz continuous wave (CW) excitation. The imaging transducer’s performance was superior to our previous 9-MHz mechanical IVUS prototype. The therapy catheter transducer was driven by CW electrical power at 18.5 MHz, achieving temperature changes reaching +8°C at a depth of 2 mm in a human glioblastoma grown on the flank of a mouse with minimal transducer resistive heating of +2°C. Further hyperthermia trials showed that 9-MHz CW excitation produced temperature changes of +4.5°C at a depth of 12 mm—a sufficient temperature rise for our long-term goal of targeted, controlled drug release via thermosensitive liposomes for therapeutic treatment of 1-cm-diameter glioblastomas.

Dual-mode intracranial catheters for minimally-invasive neuro-oncology feasibility study

In this study, we investigated the feasibility of dual-mode intracranial catheter transducers for visualization and treatment of tumors in the brain. Feasibility is demonstrated in two ways: 1) by developing a 12 Fr, integrated matrix and linear array catheter transducer prototype for combined real-time 3D imaging and heating, and 2) by testing 3.5 Fr IVUS-catheter-packageable transducers for therapeutic potential. The 3.6 MHz, 12 Fr catheter acquired real-time 3D images of canine brain structures in vivo while placed in the superior sagittal sinus via a burr hole in the skull, and achieved a 3.5°C temperature rise in tissue-mimicking material at a 2 cm focus in vitro. The IVUS-sized prototype transducers were tested for maximum intensity and mechanical index, and a thermal model was used to extrapolate and estimate each transducers maximum potential temperature rise in brain tissue.

4A-3 Intracranial Catheter for Integrated 3D Ultrasound Imaging & Hyperthermia: Feasibility Study

In this study, we investigate the feasibility of developing an intracranial catheter transducer capable of real time 3D (RT3D) imaging and ultrasound hyperthermia, for application in the visualization and treatment of tumors in the brain. Feasibility is demonstrated by acquiring RT3D images in a canine model using a 10 Fr, matrix array catheter transducer, and by achieving a temperature rise over 4degC in excised pork muscle using a linear array transducer with our diagnostic scanner. An integrated matrix and linear array catheter transducer prototype was constructed and used to acquire images of test phantoms.

Low-cost Volumetric Ultrasound by Augmentation of 2D Systems: Design and Prototype:

Conventional two-dimensional (2D) ultrasound imaging is a powerful diagnostic tool in the hands of an experienced user, yet 2D ultrasound remains clinically underutilized and inherently incomplete, with output being very operator dependent. Volumetric ultrasound systems can more fully capture a three-dimensional (3D) region of interest, but current 3D systems require specialized transducers, are prohibitively expensive for many clinical departments, and do not register image orientation with respect to the patient; these systems are designed to provide improved workflow rather than operator independence. This work investigates whether it is possible to add volumetric 3D imaging capability to existing 2D ultrasound systems at minimal cost, providing a practical means of reducing operator dependence in ultrasound. In this paper, we present a low-cost method to make 2D ultrasound systems capable of quality volumetric image acquisition: we present the general system design and image acquisition method, including the use of a probe-mounted orientation sensor, a simple probe fixture prototype, and an offline volume reconstruction technique. We demonstrate initial results of the method, implemented using a Verasonics Vantage research scanner.

Low-cost 3D ultrasound with any probe: A sensor-based approach

Volumetric 3D ultrasound captures a region of interest more completely than cross-sectional 2D imaging, but 3D implementation has been limited. Mechanical wobbler and matrix-array probes can do 3D imaging, but these probes tend to be bulky and/or expensive, and precise orientation of the image with respect to the patient is not measured. In this work, we present a method of acquiring volumetric 3D ultrasound images with known patient orientation by utilizing a low-cost sensor. This method enables 3D imaging with any 2D imaging probe; this versatile and practical approach may increase the clinical utilization of 3D ultrasound.

Image-guided ultrasound/microbubble-mediated drug delivery platform with passive cavitation mapping

Ultrasound/microbubble (US/MB)-mediated drug delivery is a promising approach to effectively deliver therapeutic agents to target tumors by increasing vascular permeability through sonoporation. Equipped with focused ultrasound, drug delivery platforms can increase site-specificity. To move toward clinical translation, such a platform requires both image guidance for accurate location of tumor targets and quantitative mapping of the therapeutic dose for effective treatment.

Low cost 3D Doppler ultrasound: Preliminary in vivo results

Conventional 2D Doppler ultrasound is a valuable screening tool for early detection of cardiovascular disease, including aneurysm of the abdominal aorta (AA) and stenosis of the carotid artery (CA). However, vascular ultrasound screening rates remain low and vary widely among physicians, due to the need for a skilled sonographer, equipment costs and scan time. We have recently developed a low-cost method to acquire 3D B-mode images using existing 2D clinical ultrasound systems, and 3D Doppler is a necessary feature for the application of this technology in vascular screening. Volumetric 3D Doppler ultrasound could enable faster scans by untrained users, and while 3D Doppler is available on some high-end systems, these are prohibitively expensive for deployment at the point-of-care. We demonstrate a fast and reliable method to enable comprehensive 3D Doppler acquisition using low-cost, peripheral hardware.