Active Research Projects
While the Dalhousie Ultrasound research group has a robust research program, the primary focus of the research is developing ultrasound diagnostic and therapeutic tools for minimally invasive procedures. Minimally invasive surgical approaches in comparison to open surgery, offer drastically improved patient outcomes including less blood loss, fewer complications, reduced recovery time, and a reduced chance of infection. To allow more procedures to be performed as minimally invasive, it’s important to develop new surgical tools specific to the minimally invasive surgical procedure. As these procedures are almost always performed through a very small incision or access route, the associated tools must be developed in a miniaturized form factor.
(1) Neuroimaging Endoscope
Typical high-frequency ultrasound resolution of 30-100 microns can be achieved in soft tissue over a penetration depth of 10-20 mm. The short penetration depth and high resolution, make high-frequency ultrasound particularly suitable for use in guided endoscopic surgery. In these minimally invasive procedures, a set of surgical instruments are inserted into a small incision site along with a set of imaging tools, typically endoscopic optical cameras and light sources. The entire surgical procedure is done solely under image guidance. Such an approach has become standard of care for a very large number of surgical procedures including those of the brain, colon, pancreas, uterus, bowel, etc.. Our group has developed a high-frequency array-based forward-looking ultrasound endoscope, that is suitable for guiding endoscopic procedures and providing depth resolved information. The packaged form factor for this imaging array has been miniaturized down to just a few millimetres. We are currently evaluating the miniature high resolution imaging endoscope in a series of pre-clinical in-vivo neuroimaging studies.
(2) Miniature Histotripsy Transducer
Most brain tumor resections and clot removals are currently performed with small surgical tools passed through a small access port drilled into the skull. This minimally invasive approach, however, is quite limiting in terms of guided imaging modalities available to the neurosurgeon for real-time feedback. Navigation approaches are typically attempted using co-registered previously acquired MRI images, but the brain tissue shifts and distorts so severely after the skull is opened and the cranial pressure is released, that these approaches are recognized as providing only very coarse information. The most prevalent neurosurgical guidance tools used presently are simple optical endoscopes and microscopes, but these provide no information beyond the surface of the tissue that the surgeon is about to cut through, so, the approach is still mostly performed blind.
Using our recently developed high-resolution, forward-looking ultrasound endoscope our group will focus on developing, miniaturizing, and integrating an ultrasonic scalpel into the imaging endoscope. The ultrasonic scalpel that we are developing is based on a mechanical ablation technique called histotripsy. Histotripsy is a non-thermal, cavitational tissue ablation technique using short, bursts of high intensity focused ultrasound to break-up tissue on the cellular level. The first medically viable histotripsy transducers have been trans-dermal, focusing on ablations mainly in the abdomen (liver, prostate) but, difficulty in transmitting ultrasound energy through the skull has kept these devices from being used in neural applications. Our lab has developed small, hand-held histotripsy transducers, approximately 5 mm in diameter with co-registered high-resolution imaging, which can be directly manipulated by surgeons to carve out precise, sub-surface lesions without affecting the surrounding tissue. For neural surgery, these devices would be inserted through a small burr-hole, and their precise imaging and ablation capabilities could allow surgeons to perform tissue resection in previously inaccessible areas such as near major blood supplies, in areas of high vascular density, or proximal to the skull.
To our knowledge, this is the smallest histotripsy transducer developed to date by at least an order of magnitude. Our group is focused on further miniaturizing the histotripsy transducer to less than four millimetres in diameter, so that it can be used, along with the imaging endoscope, to simultaneously image and resect deep access tumours endoscopically.
(3) 2D Arrays for 3D Ultrasound Imaging
Conventional 3D ultrasound systems present several technical challenges, particularly due to the large number of elements and beamforming channels required for a 2D array, the high electrical impedance of each small array element, and lengthy image acquisition time. However, 3D imaging can provide valuable information with respect to the size, location and irregularities of anatomy for both diagnostics and surgical guidance that is absent in 2D images. We are developing a 3D array system that requires minimal added complexity compared to our endoscopic phased array imaging system. Our novel solution involves replacing the fixed acoustic elevation lens from the phased array with an electrically steerable lens. Using a steerable lens, we can collect multiple 2D slices to build up a 3D image.
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