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 theseprocedures 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
3D Ultrasound systems based on 2D matrix arrays present several technical challenges, particularly the large number of elements in the 2D array, high electrical impedance, and image acquisition time. An alternative approach to 2D matrix arrays are a new type of array consisting of a set of linear array electrodes on one side of a piezo electric, and an orthogonal set of crossed electrodes on the opposite side of the piezoelectric. Crossed electrode arrays address some matrix array issues, especially the huge reduction in number of elements. However, creating a two-way focused 3D image in real-time is difficult with these arrays because azimuth and elevation dimensions cannot be beamformed at the same time. This typically forces one to use a synthetic aperture approach which is inherently slow and requires increased beamforming complexity over a 1D array.
We have developed a new, fast and simple 3D imaging approach for a new type of crossed electrode array. The high level principle behind this technique is to perform compound imaging using the top set of electrodes, while at the same time compounding a reconfigurable Fresnel elevation lens with the orthogonal bottom electrodes. This allows one to produce a highly focused beam in both orthogonal dimensions simultaneously. We have demonstrated that this form of simultaneous compounding can produce high quality 3D images at real-time frame rates.
(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.