Locating a catheter transducer in a three-dimensional ultrasound imaging field

Photoacoustic-based visual servoing of a needle tip

In intraoperative settings, the presence of acoustic clutter and reflection artifacts from metallic surgical tools often reduces the effectiveness of ultrasound imaging and complicates the localization of surgical tool tips. We propose an alternative approach for tool tracking and navigation in these challenging acoustic environments by augmenting ultrasound systems with a light source (to perform photoacoustic imaging) and a robot (to autonomously and robustly follow a surgical tool regardless of the tissue medium). The robotically controlled ultrasound probe continuously visualizes the location of the tool tip by segmenting and tracking photoacoustic signals generated from an optical fiber inside the tool. System validation in the presence of fat, muscle, brain, skull, and liver tissue with and without the presence of an additional clutter layer resulted in mean signal tracking errors <2 mm, mean probe centering errors <1 mm, and successful recovery from ultrasound perturbations, representing either patient motion or switching from photoacoustic images to ultrasound images to search for a target of interest. A detailed analysis of channel SNR in controlled experiments with and without significant acoustic clutter revealed that the detection of a needle tip is possible with photoacoustic imaging, particularly in cases where ultrasound imaging traditionally fails. Results show promise for guiding surgeries and procedures in acoustically challenging environments with this novel robotic and photoacoustic system combination.

Delay and Standard Deviation Beamforming to Enhance Specular Reflections in Ultrasound Imaging

Although interventional devices, such as needles, guide wires, and catheters, are best visualized by X-ray, real-time volumetric echography could offer an attractive alternative as it avoids ionizing radiation; it provides good soft tissue contrast, and it is mobile and relatively cheap. Unfortunately, as echography is traditionally used to image soft tissue and blood flow, the appearance of interventional devices in conventional ultrasound images remains relatively poor, which is a major obstacle toward ultrasound-guided interventions. The objective of this paper was therefore to enhance the appearance of interventional devices in ultrasound images. Thereto, a modified ultrasound beamforming process using conventional-focused transmit beams is proposed that exploits the properties of received signals containing specular reflections (as arising from these devices). This new beamforming approach referred to as delay and standard deviation beamforming (DASD) was quantitatively tested using simulated as well as experimental data using a linear array transducer. Furthermore, the influence of different imaging settings (i.e., transmit focus, imaging depth, and scan angle) on the obtained image contrast was evaluated. The study showed that the image contrast of specular regions improved by 5-30 dB using DASD beamforming compared with traditional delay and sum (DAS) beamforming. The highest gain in contrast was observed when the interventional device was tilted away from being orthogonal to the transmit beam, which is a major limitation in standard DAS imaging. As such, the proposed beamforming methodology can offer an improved visualization of interventional devices in the ultrasound image with potential implications for ultrasound-guided interventions.

A new sensor technology for 2D ultrasound-guided needle tracking

2D Ultrasound (US) is becoming the preferred modality for image-guided interventions due to its low cost and portability. However, the main limitation is the limited visibility of surgical tools. We present a new sensor technology that can easily be embedded on needles that are used for US-guided interventions. Two different types of materials are proposed to be used as sensor--co-polymer and PZT. The co-polymer technology is particularly attractive due to its plasticity, allowing very thin depositions (10-20 μm) on a variety of needle shapes. Both sensors receive acoustic energy and convert it to an electrical signal. The precise location of the needle can then be estimated from this signal, to provide real-time feedback to the clinician. We evaluated the feasibility of this new technology using (i) a 4DOF robot in a water tank; (ii) extensive ex vivo experiments; and (iii) in vivo studies. Quantitative robotic studies indicated that the co-polymer is more robust and stable when compared to PZT. In quantitative experiments, the technology achieved a tracking accuracy of 0.14 ± 0.03mm, significantly superior to competing technologies. The technology also proved success in near-real clinical studies on tissue data. This sensor technology is non-disruptive of existing clinical workflows, highly accurate, and is cost-effective. Initial clinician feedback shows great potential for large scale clinical impact.

Stereotactic endovascular aortic navigation with a novel ultrasonic-based three-dimensional localization system

BACKGROUND

Endovascular aortic procedures have been developed to treat many aortic diseases effectively. However, these procedures are also becoming increasingly complex given the development of branched or fenestrated endografts. Part of the difficulty lies in the limitations of current imaging paradigms. A more intuitive, three-dimensional (3D) mode of intraoperative imaging is desirable to accommodate the future progression of endovascular techniques. This article describes a novel endovascular catheter tracking device that uses ultrasonic signals, not ultrasound imaging. The tracking device displays real-time in vivo location on previously acquired 3D computed tomography (CT) images in an intuitive, endoluminal view. This system was tested in two swine and validated against fluoroscopy and by delivering stent grafts.

METHODS

The ultrasonic-based localization system (ULS) provides real-time location information of a modified endovascular catheter and displays this location on preoperative 3D CT images. The 9F endovascular catheter has a small ultrasonic transmitter attached to its tip to signal its location to the ULS. Subsequent endovascular deployment of an aortic stent was carried out using only the ULS to target the stent placement position in the aorta of Yorkshire swine. System accuracy was measured against concurrent angiography as well as to deployed stents in situ.

RESULTS

We successfully displayed the endovascular catheter tip location in real time along the registered CT aortic images, providing virtual endoluminal tracking. The relative accuracy of the ULS as compared with angiography for catheter movements in the abdominal aorta was found to have a mean error less than 1 mm. The ULS coordinates tracked within the lumen of the aortic image 98% of the time, as defined by the proportion of points within one radius distance of the aortic image centerline. Finally, three aortic stents were deployed using the ULS virtual image display to locate the target position in the aorta for stent deployment. Errors between target position and actual stent position ranged from -5.0 to +7.9 mm.

CONCLUSIONS

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.

Passive markers for tracking surgical instruments in real-time 3-D ultrasound imaging

A family of passive echogenic markers is presented by which the position and orientation of a surgical instrument can be determined in a 3-D ultrasound volume, using simple image processing. Markers are attached near the distal end of the instrument so that they appear in the ultrasound volume along with the instrument tip. They are detected and measured within the ultrasound image, thus requiring no external tracking device. This approach facilitates imaging instruments and tissue simultaneously in ultrasound-guided interventions. Marker-based estimates of instrument pose can be used in augmented reality displays or for image-based servoing. Design principles for marker shapes are presented that ensure imaging system and measurement uniqueness constraints are met. An error analysis is included that can be used to guide marker design and which also establishes a lower bound on measurement uncertainty. Finally, examples of marker measurement and tracking algorithms are presented along with experimental validation of the concepts.

Design and in vitro evaluation of a real-time catheter localization system using time of flight measurements from seven 3.5 MHz single element ultrasound transducers towards abdominal aortic aneurysm procedures

Interventional surgical instrument localization is a crucial component of minimally invasive surgery. Image guided surgery researchers are investigating devices broadly categorized as surgical localizers to provide real-time information on the instrument's 3D location and orientation only. This paper describes the implementation and in vitro evaluation of a prototype real-time nonimaging ultrasound-based catheter localizer system towards use in abdominal aortic aneurysm procedures. The catheter-tip is equipped with a single element ultrasound transducer which is tracked with an array of seven external single element transducers. The performance of the system was evaluated in a water tank and additionally in the presence of pork belly tissue and also a nitinol-dacron stent graft. The mean root mean square errors were respectively 1.94±0.06, 2.54±0.31 and 3.33±0.06 mm. In addition, this paper illustrates errors induced by transducer aperture size and suggests a method for aperture error compensation. Aperture compensation applied to the same experimental data yielded mean root mean square errors of 1.05±0.07, 2.42±0.33 and 3.23±0.07mm respectively for water; water and pork; and water, pork and stent experiments. Lastly, this paper presents a video showing free-hand movement of the catheter within the water tank with data capture at 25 frames per second.

Ultrasound emitter localization in heterogeneous media

A novel algorithm to accurately determine the location of an ultrasound source within heterogeneous media is presented. The method obtains a small spacial error of 748 microm+/-310 microm for 100 different measurements inside a circular area with 140 mm diameter. The new algorithm can be used in targeted drug delivery for cancer therapies as well as to accurately locate any kind of ultrasound sources in heterogeneous media, such as ultrasonically marked medical devices or tumors.

Vibrating interventional device detection using real-time 3-D color Doppler

Ultrasound image guidance of interventional devices during minimally invasive surgery provides the clinician with improved soft tissue contrast while reducing ionizing radiation exposure. One problem with ultrasound image guidance is poor visualization of the device tip during the clinical procedure. We have described previously guidance of several interventional devices using a real-time 3-D (RT3-D) ultrasound system with 3-D color Doppler combined with the ColorMark technology. We then developed an analytical model for a vibrating needle to maximize the tip vibrations and improve the reliability and sensitivity of our technique. In this paper, we use the analytical model and improved radiofrequency (RF) and color Doppler filters to detect two different vibrating devices in water tank experiments as well as in an in vivo canine experiment. We performed water tank experiments with four different 3- D transducers: a 5 MHz transesophageal (TEE) probe, a 5 MHz transthoracic (TTE) probe, a 5 MHz intracardiac catheter (ICE) transducer, and a 2.5 MHz commercial TTE probe. Each transducer was used to scan an aortic graft suspended in the water tank. An atrial septal puncture needle and an endomyocardial biopsy forceps, each vibrating at 1.3 kHz, were inserted into the vascular graft and were tracked using 3-D color Doppler. Improved RF and wall filters increased the detected color Doppler sensitivity by 14 dB. In three simultaneous planes from the in vivo 3-D scan, we identified both the septal puncture needle and the biopsy forceps within the right atrium using the 2.5 MHz probe. A new display filter was used to suppress the unwanted flash artifact associated with physiological motion.

Analysis of a vibrating interventional device to improve 3-D colormark tracking

Ultrasound guidance of interventional devices during minimally invasive surgical procedures has been investigated by many researchers. Previously, we extended the methods used by the Colormark tracking system to several interventional devices using a real-time, three-dimensional (3-D) ultrasound system. These results showed that we needed to improve the efficiency and reliability of the tracking. In this paper, we describe an analytical model to predict the transverse vibrations along the length of an atrial septal puncture needle to enable design improvements of the tracking system. We assume the needle can be modeled as a hollow bar with a circular cross section with a fixed proximal end and a free distal end that is suspended vertically to ignore gravity effects. The initial results show an ability to predict the natural nodes and antinodes along the needle using the characteristic equation for free vibrations. Simulations show that applying a forcing function to the device at a natural antinode yields an order of magnitude larger vibration than when driving the device at a node. Pulsed wave spectral Doppler data was acquired along the distal portion of the needle in a water tank using a 2-D matrix array transesophageal echocardiography probe. This data was compared to simulations of forced vibrations from the model. These initial results suggest that the model is a good first order approximation of the vibrating device in a water tank. It is our belief that knowing the location of the natural nodes and antinodes will improve our ability to drive the device to ensure the vibrations at the proximal end will reach the tip of the device, which in turn should improve our ability to track the device in vivo.

Interactive volume rendering of real-time three-dimensional ultrasound images

Real-time, three-dimensional (RT3D) ultrasound allows video frame rate volumetric imaging. The ability to acquire full three-dimensional (3-D) image data in real-time is particularly helpful for applications such as cardiac imaging, which require visualization of complex and dynamic 3-D anatomy. Volume rendering provides a method for intuitive graphical display of the 3-D image data, but capturing the RT3D echo data and performing the necessary processing to generate a volumetric image in real time poses a significant technical challenge. We present a data capture and rendering implementation that uses off-the-shelf components to real-time volume render RT3D ultrasound images. Our approach allowed live, interactive volume rendering of RT3D ultrasound scans.

Passive markers for ultrasound tracking of surgical instruments

A family of passive markers is presented by which the position and orientation of a surgical instrument can be computed from its ultrasound image using simple image processing. These markers address the problem of imaging instruments and tissue simultaneously in ultrasound-guided interventions. Marker-based estimates of instrument location can be used in augmented reality displays or for image-based servoing. Marker design, measurement techniques and error analysis are presented. Experimentally determined in-vitro measurement errors of 0.22 mm in position and 0.089 rad in orientation were obtained using a standard ultrasound imaging system.

Guidance of cardiac pacemaker leads using real time 3D ultrasound: feasibility studies

We investigated the feasibility of the guidance of pacemaker lead implantation using the pacemaker lead stylet as an acoustic wave-guide combined with real time 3D ultrasound imaging. In one approach, with a 2.5 MHz transducer coupled to a stylet of a pacemaker lead, we used the stylet as a transmitter to track the vibrating tip in a 3D ultrasound scan. In another approach, we connected the stylet to a piezoelectric actuator vibrating in the range 0.5-5 kHz so that the tip of the stylet was imaged using the color Doppler feature of the real time 3D ultrasound scanner. In both approaches, tracking of the isolated stylet showed good accuracy. However, neither approach offered sufficient signal-to-noise ratio to detect the vibration within the lumen of an intact pacemaker lead.