Medical device tracking and navigation

We combine ultrasonics and optics to develop technology for real time microscopy, imaging and tracking during surgical and interventional procedures. Here are our main current research topics.

Ultrasonic tracking

Ultrasound is well suited for guiding many minimally-invasive surgical and interventional procedures, but guidance is often difficult due to poor visibility of the medical device within the ultrasound image. This can result in device misplacement and therefore damage to critical structures, with life-threatening complications. At PURL, we are developing miniature ultrasonic and photoacoustic technology that can be integrated into the invasive device, communicating ultrasonically with the external ultrasound probe in order to accurately determine and visualise the location of the device within the ultrasound image.

In-plane needle tracking with an off-the-shelf ultrasound imaging system

We have developed a real-time ultrasound needle tip tracking system for guidance in fetal interventions. This system operates as an add-on to a commercial ultrasound imaging system, using a Fabry-Perot fibre-optic hydrophone (FOH) embedded in the needle tip to detect ultrasound transmissions and determine the position of the needle tip. This allows for improved visibility during procedures by superimposing a cross-hair onto the ultrasound image at the needle tip position. In testing, the system had a mean accuracy of 0.7 ± 0.4 mm in water and 1.1 ± 0.7 mm in a tissue phantom. These results show the effectiveness and clinical compatibility of our ultrasound needle tracking system, paving the way for further testing in human subjects.

3D tracking with a bespoke ultrasound probe

We have developed an ultrasound probe that can provide both 2D B-mode imaging and 3D ultrasonic needle tracking. The probe has focused and unfocused transducer elements, and a fibre-optic hydrophone is integrated into a needle to receive Golay-encoded transmissions and produce tracking images of the needle tip. The tracking accuracy in water was found to be better than 0.4 mm in all dimensions. We tested the probe in live swine and pregnant ovine models, performing insertions into the spine and uterine cavity. This probe has the potential to improve procedural outcomes by providing 3D needle tip locations that are co-registered with ultrasound images, while still being compatible with current clinical workflow.

Tracking with a needle-integrated photoacoustic beacon

We have developed a tracking system that directly visualizes the needle using an ultrasonic beacon integrated into the needle tip. The beacon transmits waves that are received by an external ultrasound imaging probe, which acquires pairs of co-registered images - a photoacoustic image and a conventional B-mode ultrasound image. The beacon consists of a custom elastomeric nanocomposite coating on the end of an optical fiber positioned within a commercial 22 gauge needle. When pulsed light is delivered to the coating, it generates ultrasonic waves through photoacoustic means. The tracking accuracy in water was found to be 0.39 ± 0.19 mm in the axial dimension and 1.85 ± 0.29 mm in the lateral dimension. We performed needle insertions in a live fetal sheep model to test the feasibility and potential clinical usefulness of this ultrasonic needle tracking system. The results demonstrated that ultrasonic needle tracking with a fiber-optic transmitter is possible in a realistic fetal surgery environment and could be useful in guiding minimally invasive procedures by providing accurate visualization of the medical device tip.