Abstract. In the past decade ultrasound (US) has become the preferred modality for a number of interventional procedures, offering excellent soft tissue visualization. The main limitation however is limited visualization of surgical tools. A new method is proposed for robust 3D tracking and US image enhancement of surgical tools under US guidance. Small US sensors are mounted on existing surgical tools. As the imager emits acoustic energy, the electrical signal from the sensor is analyzed to reconstruct its 3D coordinates. These coordinates can then be used for 3D surgical navigation, similar to current day tracking systems. A system with realtime 3D tool tracking and image enhancement was implemented on a commercial ultrasound scanner and 3D probe. Extensive water tank experiments with a tracked 0.2mm sensor show robust performance in a wide range of imaging conditions and tool position/orientations. The 3D tracking accuracy was 0.36 ± 0.16mm throughout the imaging volume of 55• × 27 • × 150mm. Additionally, the tool was successfully tracked inside a beating heart phantom. This paper proposes an image enhancement and tool tracking technology with sub-mm accuracy for US-guided interventions. The technology is non-disruptive, both in terms of existing clinical workflow and commercial considerations, showing promise for large scale clinical impact.

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In this paper, we propose a modified electronic Fresnel-based beamforming method for low-cost portable ultrasound systems. This method uses a unique combination of analog and digital beamforming methods. Two versions of Fresnel beamforming are presented in this paper: 4-phase (4 different time delays or phase shifts) and 8-phase (8 different time delays or phase shifts). The advantage of this method is that a system with 4 to 8 transmit channels and 2 receive channels with a network of switches can be used to focus an array with 64 to 128 elements. The simulation and experimental results show that Fresnel beamforming image quality is comparable to traditional delay-and-sum (DAS) beamforming in terms of spatial resolution and contrast-to-noise ratio (CNR) under certain system parameters. With an f-number of 2 and 50% signal bandwidth, the experimental lateral beamwidths are 0.54, 0.67, and 0.66 mm and the axial pulse lengths are 0.50, 0.51, and 0.50 mm for DAS, 8-phase, and 4-phase Fresnel beamforming, respectively. The experimental CNRs are 4.66, 4.42, and 3.98, respectively. These experimental results are in good agreement with simulation results.

This study demonstrates the feasibility of virtual image-guided endovascular aortic navigation using a ULS. This provides a 3D platform for virtual navigation on preoperative CT scan images during endovascular procedures that could assist in stent deployment as well as minimize or eliminate the need for procedural ionizing radiation and iodinated contrast. Future work will focus on miniaturization and refinements in accuracy that will be required to translate this technology into clinical application in endovascular procedures.

In order to enhance needle and catheter visibility under ultrasound and enable tool tracking, it has been proposed to embed ultrasound receivers near the tip of interventional tools. Using these sensors to receive and analyze signals coming from the imaging probe as its beams sweep the field of view, the position of the sensor can be estimated with <0.5mm accuracy even when the tool tip is invisible in the pulse-echo image. One crucial design parameter for these ultrasonically marked instruments is the sensitivity and directivity pattern of the sensor: the ideal sensor has to maintain adequate SNR at a wide range of depths and insonification angles depending on the clinical intervention. This paper presents the acoustical characterization of small (~1mm) high frequency (>10MHz) PZT sensors in different form factors for acoustical marking of needles and catheters. PZT-equipped tools including guidewires, steerable sheaths, and biopsy needles are also presented and the tracking capability is demonstrated ex vivo.Maximum SNRs of >50dB were found with all sensors in the water tank at an imaging depth of 8cm and insonification MI of 1.1. Complex directivity patterns were observed varying with sensor size and shape, likely owing to mode conversion inside the sensor and excitation of the materials' transverse piezoelectric modes. Small disks (≤1mm diameter) were found to be most appropriate with flattest directivity. Ex vivo experiments demonstrated reliable tracking of an ultrasoundequipped needle at depths >10cm.In conclusion, it is feasible to manufacture PZT-equipped instruments exhibiting good tracking accuracy and robustness.