A system for ultrasonic beacon-guidance of catheters and other minimally-invasive medical devices

Handheld interventional ultrasound/photoacoustic puncture needle navigation based on deep learning segmentation

Interventional ultrasound (US) has challenges in accurate localization of the puncture needle due to intrinsic acoustic interferences, which lead to blurred, indistinct, and even invisible needles in handheld linear array transducer-based US navigation, especially the incorrect needle tip positioning. Photoacoustic (PA) imaging can provide complementary image contrast, without additional data acquisition. Herein, we proposed an internal illumination to solely light up the needle tip in PA imaging. Then deep-learning-based feature segmentation alleviates acoustic interferences, enhancing the needle shaft-tip visibility. Further, needle shaft-tip compensation aligned the needle shaft in US image and the needle tip in the PA image. The experiments on phantom, ex vivo chicken breast, preclinical radiofrequency ablation and in vivo biopsy of sentinel lymph nodes were piloted. The target registration error can reach the submillimeter level, achieving precise puncture needle tracking ability with in-plane US/PA navigation.

A Real-time Color Doppler Marker for Echocardiographic Guidance of an Acoustically Active Extracorporeal Membrane Oxygenation Cannula

B-mode ultrasound imaging guidance of cannulas can be compromised by noise, artifacts, and echogenicity that is not distinctive from that of surrounding anatomy. We have modified a venovenous extracorporeal membrane oxygenation cannula by embedding piezoelectric crystals into each of its 3 blood flow ports. Each vibrating crystal acoustically interacts with a Doppler imaging signal and produces an instantaneous color marker. The aim of this study was to compare identification of the extracorporeal membrane oxygenation cannula ports by B-mode imaging versus the color Doppler marker. Unlike B-mode imaging, the color Doppler marker identified the corresponding port even in highly challenging closed-chest scans in anesthetized pigs. The method could improve guidance accuracy of cannulas by ultrasound scans.

Real-Time Visualization of an Acoustically Active Injection Catheter With Ultrasound Imaging: Algorithm and In Vivo Validation in a Swine Model

OBJECTIVE

To independently visualize a catheter and needle during minimally invasive surgery in order to aid in precisely guiding them to their intended location.

METHODS

Symmetric frequency detection allows for the visualization of the acoustically active catheter tip as a unique color in live imaging. This study extends the algorithm to identify two different crystals by unique colors, validating the algorithm with in vivo pig experiments while simulating the human condition using different attenuation pads.

RESULTS

The catheter and needle tip were identified with unique colors, differentiable from common Doppler colors, with a frame rate varying between 8 and 10 Hz. Both were visible at graded levels of attenuation induced by interposed polymer pads. Reducing ensemble length increased the frame rate and decreased the signal-to-noise ratio (SNR), though not significantly. At the highest in-path attenuation of 12 dB at 5 MHz, the catheter spot marker was visible whereas the needle was not. The SNR of the catheter signal varied between 12.50 and 18.24 dB and the size of the spot marker varied between 149 and 1015 mm². The SNR of the needle signal varied between 6.37 and 16.3 dB and the size of the spot marker between 59 and 169 mm². A reliability index greater than 50% was achieved for all cases except for the needle crystal at the highest attenuation setting.

CONCLUSION

Modified symmetric frequency detection algorithm can uniquely visualize both catheter and needle in real time with in-path attenuation.

SIGNIFICANCE

Unambiguous and distinct visualization of separate locations on the catheter facilitates real-time tracking of minimally invasive procedures.

Unambiguous Identification and Visualization of an Acoustically Active Catheter by Ultrasound Imaging in Real Time: Theory, Algorithm, and Phantom Experiments

OBJECTIVE

Ultrasound-guided biopsies and minimally invasive procedures have been used in numerous medical applications, including catheter guidance. The biggest challenge for catheter guidance by ultrasound lies in distinguishing the catheter from neighboring tissue, as well as the ability to differentiate the catheter body from its tip.

METHODS

In our previous work, we introduced a functional prototype of an acoustically active catheter, in which a miniature piezoelectric crystal allowed accurate localization of the catheter tip by pulsed wave (PW) Doppler imaging and Doppler spectrogram. In this paper, the theory behind the symmetric Doppler shift due to the interaction of ultrasound wave with a vibrating piezoelectric crystal is explained. The theory is validated in an experimental continuous flow phantom setup. A novel algorithm, symmetric frequency detection algorithm, is presented for identification and visualization of the catheter tip in real time along with B-mode and PW Doppler.

RESULTS

The catheter tip is identified with a distinct color differentiable from common Doppler colors with a frame rate varying from 22 to 50 Hz. The catheter tip can be visualized in a small region of 2.4 mm in the elevational direction.

CONCLUSION

The algorithm can be implemented in most clinical ultrasound machines with minor additions to the PW Doppler processing algorithm. The algorithm is optimized to be robust for a variety of blood flow velocities and is shown to perform well when the signal from the blood is on par in amplitude with the catheter signal.

SIGNIFICANCE

Unambiguous and distinct visualization of catheter tip facilitates real-time tracking of the catheter and aids minimally invasive procedures.

Acoustically Active Catheter for Intracardiac Navigation by Color Doppler Ultrasonography

Navigation of intracardiac catheters by echocardiography is challenging because of the fundamental limitations of B-mode ultrasonography. We describe a catheter fitted with a piezoelectric crystal, which vibrates and produces an instantaneous marker in color flow Doppler scans. The navigation learning curve was explored first in six pigs. Accuracy and precision of targeting with the navigation marker "off" (i.e., B-mode imaging) and "on" were assessed in another six pigs. Paired comparisons confirmed significantly (p = 0.04) shorter mean distances achieved in each pig with the color Doppler marker. Pooled (mean ± standard deviation) distance of the catheter tip from the target crystal was 5.27 ± 1.62 mm by B-mode guidance and 3.66 ± 1.45 mm by color Doppler marker navigation. Dye injection targeted into the ischemic border zone was successful in 8 of 10 pigs. Intracardiac catheter navigation with color Doppler ultrasonography is more accurate compared with conventional guidance by B-mode imaging.

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.

Microrobots for minimally invasive medicine

Microrobots have the potential to revolutionize many aspects of medicine. These untethered, wirelessly controlled and powered devices will make existing therapeutic and diagnostic procedures less invasive and will enable new procedures never before possible. The aim of this review is threefold: first, to provide a comprehensive survey of the technological state of the art in medical microrobots; second, to explore the potential impact of medical microrobots and inspire future research in this field; and third, to provide a collection of valuable information and engineering tools for the design of medical microrobots.

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.

Needle tip localization using stylet vibration

Power Doppler ultrasound is used to localize the tip of a needle by detecting physical vibrations. Two types of vibrations are investigated, lateral and axial. The lateral vibrations are created by rotating a stylet, whose tip is slightly bent, inside a stationary cannula while the stylet is completely within the cannula. The minute deflection at the needle tip when rotated causes tissue motion. The axial vibration is induced by extending and retracting a straight stylet inside a stationary cannula. The stylet's tip makes contact with the tissue and causes it to move. The lateral vibration method was found to perform approximately the same under a variety of configurations (e.g., different insertion angles and depths) and better than the axial vibration method. Tissue stiffness affects the performance of the lateral vibration method, but good images can be obtained through proper tuning of the ultrasound machine.

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.

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

Cardiac procedures rely on fluoroscopy for catheter guidance and visualization. However, fluoroscopy provides poor contrast of myocardial structures and exposes both the patient and health care providers to ionizing radiation. As an alternative to fluoroscopy, real-time three-dimensional (3-D) ultrasound imaging has the potential to provide a safe means for tracking catheter position in 3-D while simultaneously imaging the heart's anatomy. A method is described for locating a catheter-mounted transducer in the 3-D ultrasound imaging field. The distance from the imaging transducer to the catheter transducer is measured by time of flight, while the angular position is determined by a spatial crosscorrelation of the received signals with stored receive profiles. Results from simulations with 20-dB SNR demonstrated a mean accuracy of 0.22 +/- 0.13 mm at a 70-mm range. In vitro testing showed a resolution of 0.23 +/- 0.11 mm at a range of 75 mm and a resolution of 0.47 +/- 0.47 mm at a range of 97 mm. With combined catheter position and imaging, this tracking method has the potential to replace fluoroscopy and enhance interventional procedures.

Ultrasonic six-axis deformation sensing

In this paper, we describe a newly developed deformation sensing scheme in a soft medium, which is based on precise encoding and decoding of deformation components into ultrasound wavefronts. It can detect three translational components and three rotational components of displacement around a transmitter position nearly simultaneously. We assume a cell structure that consists of a 2 x 2 ultrasonic transmitter matrix and a 2 x 2 ultrasonic receiver matrix, which are placed face to face at a distance of a few tens of wavelengths. All of the transmitter elements are driven sinusoidally and simultaneously, but they are switched into the same, reversed, or quadrature phases to generate a particular shape of wavefront on the receiver matrix. The receiver elements are connected in such a way to obtain amplitude and spatial gradients of the wavefront at a center of the receiver matrix. First, we describe the transduction theory for the six dimensions and show the orthogonality, locality, and simultaneity of this sensing scheme. Then, we describe the fabrication and experimental evaluation of the cell. We also describe a prototype tactile sensor in which a single cell is embedded in a flexible hemispherical fingertip-like body.