Real-time 3D Ultrasonic Needle Tracking with a Photoacoustic Beacon

TL;DR

This work addresses the challenge of real-time 3D needle localization during ultrasound-guided interventions by introducing a tracking system that uses a fibre-optic photoacoustic beacon embedded in the needle bevel and a sparse 16-element receiver array to perform multilateration (MLAT) via a maximum-likelihood estimate ($MLE$), co-registered with 2D ultrasound. The method achieves sub-2 mm accuracy in water up to 140 mm depth and ~2 mm in an ex vivo tissue phantom, with usability testing showing a 35% reduction in biopsy failure after brief training. It is designed to integrate with standard interventional ultrasound workflows, enabling real-time 3D visualization of the needle tip even when not in the imaging plane, and has clear potential to improve diagnostic sampling and therapeutic delivery across a range of procedures. Future work will target ergonomic refinements, increased transmitter efficiency, and the possibility of truly simultaneous imaging and tracking to further enhance performance and clinical adoption.

Abstract

Many minimally invasive procedures, such as core needle biopsy of focal liver lesions, nerve blocks, and fetal and vascular interventions, are typically performed under ultrasound guidance, which provides real-time, high-resolution visualisation of tissue anatomy. Accurate and efficient localisation of the needle tip relative to patient anatomy is essential for guiding the needle towards the procedure target, avoiding adverse events and reducing the need for repeat procedures. However, the 3D nature of the procedure and poor image contrast of the needle in heterogeneous tissue or at steep insertion angles often leads to confusion over the true location of the tip within the 2D guidance images, and existing methods to enhance needle visibility largely remain limited to 2D. Here, we present a novel interventional ultrasound system capable of 2D B-mode imaging and 3D needle tracking. The tip location is determined from the time-of-flight of ultrasound generated by a photoacoustic beacon embedded in the needle bevel and received by a sparse receiver array distributed around the imaging system's curvilinear ultrasound probe. The measured tracking accuracy was better than 2 mm for depths up to 140 mm in water, and approximately 2 mm on average in an ex vivo tissue phantom, with referenced positions derived from X-ray CT. In a usability study involving 12 clinicians performing biopsy procedures in a ex vivo tissue phantom, the failure rate was reduced by 35 %, from 15.8 % to 10.3 % after only a few minutes of training. These results demonstrate that the proposed system has strong potential to support a wide range of minimally invasive procedures by enabling clinicians to accurately target anatomical structures with millimetre-level precision, improving the efficiency and effectiveness of diagnostic sampling and therapeutic delivery or ablation, and reducing the risk of adverse events.

Figures (8)

• Figure 1: Conceptual graphic and schematic of the 3D ultrasonic needle tracking system, showing how pulses of ultrasound are generated from the needle tip and detected by a sparse receiver array, enabling 3D tracking of the needle tip within or either side of the imaging plane. Includes inset photographs of: the tip of the trackable needle with integrated fibre-optic ultrasound transmitter; the trackable needle stylet and blunt introducer needle; the tracking array attached to the ultrasound imaging probe; and the clinical ultrasound imaging system.
• Figure 2: Diagram of the tracking pipeline, showing how the acquisition of tracking waveforms is triggered by the completion of an imaging frame, and the waveforms are processed to determine the distance (range) between the needle tip and each element, and then ultimately a tracked position $(x,y,z)$, which is rendered on to a frame grabbed from the imaging system.
• Figure 3: Visualisations related to registration and cursor rendering: (a) screenshot of the tracking software taken during registration, showing the unregistered tracked needle tip location (green) and the registration cross-hair (red); (b) the tracking cursor colour and orientation map used for the first usability study; (c) the tracking cursor colour and orientation map used for the second usability study.
• Figure 4: (a) Diagram of the ex vivo tissue phantoms used for the usability studies. Dark purple lesions were present in the phantoms used for both studies, while light purple lesions were only present in the phantom used for the first study. (b) Photograph of the phantom in-use during the usability tests. (c) Screenshot of the tracking software taken during the usability study, annotated (white) to show the locations of the target lesion and needle tip.
• Figure 5: Results of the measurement of tracking accuracy in water. The top row presents the magnitude of the 3D tracking error in the three elevational planes tested. The bottom row presents the standard deviation of this error (i.e. the tracking repeatability). The dashed line indicates the extent of the field of view of the ultrasound imaging system. The dotted line indicates the region of interest within which accuracy was further analysed.