Localization of needle tip with color doppler during pericardiocentesis: In vitro validation and initial clinical application

A power Doppler ultrasound method for improving intraoperative tip localization for visually obstructed needles in interstitial prostate brachytherapy

PURPOSE

High-dose-rate (HDR) interstitial brachytherapy (BT) is a common treatment technique for localized intermediate to high-risk prostate cancer. Transrectal ultrasound (US) imaging is typically used for guiding needle insertion, including localization of the needle tip which is critical for treatment planning. However, image artifacts can limit needle tip visibility in standard brightness (B)-mode US, potentially leading to dose delivery that deviates from the planned dose. To improve intraoperative tip visualization in visually obstructed needles, we propose a power Doppler (PD) US method which utilizes a novel wireless mechanical oscillator, validated in phantom experiments and clinical HDR-BT cases as part of a feasibility clinical trial.

METHODS

Our wireless oscillator contains a DC motor housed in a 3D printed case and is powered by rechargeable battery allowing the device to be operated by one person with no additional equipment required in the operating room. The oscillator end-piece features a cylindrical shape designed for BT applications to fit on top of the commonly used cylindrical needle mandrins. Phantom validation was completed using tissue-equivalent agar phantoms with the clinical US system and both plastic and metal needles. Our PD method was tested using a needle implant pattern matching a standard HDR-BT procedure as well as an implant pattern designed to maximize needle shadowing artifacts. Needle tip localization accuracy was assessed using the clinical method based on ideal reference needles as well as a comparison to computed tomography (CT) as a gold standard. Clinical validation was completed in five patients who underwent standard HDR-BT as part of a feasibility clinical trial. Needle tips positions were identified using B-mode US and PD US with perturbation from our wireless oscillator.

RESULTS

Absolute mean ± standard deviation tip error for B-mode alone, PD alone, and B-mode combined with PD was respectively: 0.3 ± 0.3 mm, 0.6 ± 0.5 mm, and 0.4 ± 0.2 mm for the mock HDR-BT needle implant; 0.8 ± 1.7 mm, 0.4 ± 0.6 mm, and 0.3 ± 0.5 mm for the explicit shadowing implant with plastic needles; and 0.5 ± 0.2 mm, 0.5 ± 0.3 mm, and 0.6 ± 0.2 mm for the explicit shadowing implant with metal needles. The total mean absolute tip error for all five patients in the feasibility clinical trial was 0.9 ± 0.7 mm using B-mode US alone and 0.8 ± 0.5 mm when including PD US, with increased benefit observed for needles classified as visually obstructed.

CONCLUSIONS

Our proposed PD needle tip localization method is easy to implement and requires no modifications or additions to the standard clinical equipment or workflow. We have demonstrated decreased tip localization error and variation for visually obstructed needles in both phantom and clinical cases, including providing the ability to visualize needles previously not visible using B-mode US alone. This method has the potential to improve needle visualization in challenging cases without burdening the clinical workflow, potentially improving treatment accuracy in HDR-BT and more broadly in any minimally invasive needle-based procedure.

Localization Accuracy of Ultrasound-Actuated Needle with Color Doppler Imaging

An ultrasonic needle-actuating device for tissue biopsy and regional anaesthesia offers enhanced needle visibility with color Doppler imaging. However, its specific performance is not yet fully determined. This work investigated the influence on needle visibility of the insertion angle and drive voltage, as well as determined the accuracy and agreement of needle tip localization by comparing color Doppler measurements with paired photographic and B-mode ultrasound measurements. Needle tip accuracy measurements in a gelatin phantom gave a regression trend, where the slope of trend is 0.8808; coefficient of determination (R²) is 0.8877; bias is −0.50 mm; and the 95% limits of agreement are from −1.31 to 0.31 mm when comparing color Doppler with photographic measurements. When comparing the color Doppler with B-mode ultrasound measurements, the slope of the regression trend is 1.0179; R² is 0.9651; bias is −0.16 mm; and the 95% limits of agreement are from −1.935 to 1.605 mm. The results demonstrate the accuracy of this technique and its potential for application to biopsy and ultrasound guided regional anaesthesia.

Enhancement of needle visualization and localization in ultrasound

PURPOSE

This scoping review covers needle visualization and localization techniques in ultrasound, where localization-based approaches mostly aim to compute the needle shaft (and tip) location while potentially enhancing its visibility too.

METHODS

A literature review is conducted on the state-of-the-art techniques, which could be divided into five categories: (1) signal and image processing-based techniques to augment the needle, (2) modifications to the needle and insertion to help with needle-transducer alignment and visibility, (3) changes to ultrasound image formation, (4) motion-based analysis and (5) machine learning.

RESULTS

Advantages, limitations and challenges of representative examples in each of the categories are discussed. Evaluation techniques performed in ex vivo, phantom and in vivo studies are discussed and summarized.

CONCLUSION

Greatest limitation of the majority of the literature is that they rely on original visibility of the needle in the static image. Need for additional/improved apparatus is the greatest limitation toward clinical utility in practice.

SIGNIFICANCE

Ultrasound-guided needle placement is performed in many clinical applications, including biopsies, treatment injections and anesthesia. Despite the wide range and long history of this technique, an ongoing challenge is needle visibility in ultrasound. A robust technique to enhance ultrasonic needle visibility, especially for steeply inserted hand-held needles, and while maintaining clinical utility requirements is needed.

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.

Silica Shells/Adhesive Composite Film for Color Doppler Ultrasound Guided Needle Placement

Ultrasound (US) guided medical devices placement is a widely used clinical technology, yet many factors affect the visualization of these devices in the human body. In this research, an ultrasound-activated film was developed that can be coated on the surface of medical devices. The film contains 2 μm silica microshells and poly(methyl 2-cyanoacrylate) (PMCA) adhesive. The air sealed in the hollow space of the microshells acted as the US contrast agent. Ozone and perfluorooctyltriethoxysilane (PFO) were used to treat the surface of the film to enhance the US signals and provide durable antifouling properties for multiple passes through tissue, consistent with the dual oleophobic and hydrophobic nature of PFO. In vitro and in vivo tests showed that hypodermic needles and tumor marking wires coated with US activated film gave strong and persistent color Doppler signals. This technology can significantly improve the visibility of medical devices and the accuracy of US guided medical device placement.

Modelling and characterisation of a ultrasound-actuated needle for improved visibility in ultrasound-guided regional anaesthesia and tissue biopsy

Clear needle visualisation is recognised as an unmet need for ultrasound guided percutaneous needle procedures including regional anaesthesia and tissue biopsy. With inadequate needle visibility, these procedures may result in serious complications or a failed operation. This paper reports analysis of the modal behaviour of a previously proposed ultrasound-actuated needle configuration, which may overcome this problem by improving needle visibility in colour Doppler imaging. It uses a piezoelectric transducer to actuate longitudinal resonant modes in needles (outer diameter 0.8-1.2mm, length>65mm). The factors that affect the needle's vibration mode are identified, including the needle length, the transducer's resonance frequency and the gripping position. Their effects are investigated using finite element modelling, with the conclusions validated experimentally. The actuated needle was inserted into porcine tissue up to 30mm depth and its visibility was observed under colour Doppler imaging. The piezoelectric transducer is able to generate longitudinal vibration with peak-to-peak amplitude up to 4μm at the needle tip with an actuating voltage of 20Vpp. Actuated in longitudinal vibration modes (distal mode at 27.6kHz and transducer mode at 42.2kHz) with a drive amplitude of 12-14Vpp, a 120mm needle is delineated as a coloured line in colour Doppler images, with both needle tip and shaft visualised. The improved needle visibility is maintained while the needle is advanced into the tissue, thus allowing tracking of the needle position in real time. Moreover, the needle tip is highlighted by strong coloured artefacts around the actuated needle generated by its flexural vibration. A limitation of the technique is that the transducer mode requires needles of specific lengths so that the needle's resonance frequency matches the transducer. This may restrict the choice of needle lengths in clinical applications.

3-D ultrasound-guided robotic needle steering in biological tissue

Robotic needle steering systems have the potential to greatly improve medical interventions, but they require new methods for medical image guidance. Three-dimensional (3-D) ultrasound is a widely available, low-cost imaging modality that may be used to provide real-time feedback to needle steering robots. Unfortunately, the poor visibility of steerable needles in standard grayscale ultrasound makes automatic segmentation of the needles impractical. A new imaging approach is proposed, in which high-frequency vibration of a steerable needle makes it visible in ultrasound Doppler images. Experiments demonstrate that segmentation from this Doppler data is accurate to within 1-2 mm. An image-guided control algorithm that incorporates the segmentation data as feedback is also described. In experimental tests in ex vivo bovine liver tissue, a robotic needle steering system implementing this control scheme was able to consistently steer a needle tip to a simulated target with an average error of 1.57 mm. Implementation of 3-D ultrasound-guided needle steering in biological tissue represents a significant step toward the clinical application of robotic needle steering.

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.

Color Doppler imaging of cardiac catheters using vibrating motors

A miniature motor rotating at 11,000 rpm was attached onto the proximal end of cardiac electrophysiological (EP) catheters in order to produce vibrations at the tip that were then visualized by color Doppler on ultrasound scanners. The catheter tip was imaged within a vascular graft submerged in a water tank using the Volumetrics Medical Imaging 3D scanner, the Siemens Sonoline Antares 2D scanner and the Philips ie33 3D ultrasound scanner with TEE probe. The vibrating catheter tip was visualized in each case, although results varied with the color Doppler properties of the individual scanner.

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.

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.

Real-time 3D color flow Doppler for guidance of vibrating interventional devices

The goal of this investigation was to examine the feasibility of guiding interventional devices using piezoelectric buzzers to create velocity sources, which were imaged and tracked with real-time 3D color flow Doppler. The interventional devices examined in this study included a pacemaker lead, Brockenbrough needle for cardiac septal puncture, cardiac guidewire and radiofrequency ablation needles for cancer therapy. Each was mechanically coupled to a piezoelectric buzzer and was imaged using a commercial real-time 3D ultrasound system with either a 2.5 MHz matrix array transducer or a 5 MHz, 22 F catheter transducer equipped with a tool port. In vitro images acquired in tissue phantoms, excised liver with a 'tumor' target and an excised sheep heart show strong vibration signals in 3D color flow Doppler, enabling real-time tracking and guidance of all the devices in three dimensions. In a sheep model, in vivo tracking of the pacing lead was performed in the superior vena cava as well as the right atrium using RT3D color flow Doppler images. The vibrating rf ablation needles were guided through the liver toward "tumor" targets in vivo with real-time 3D color flow Doppler images.

Pericarditis

Pericarditis is a common disorder that has multiple causes and presents in various primary-care and secondary-care settings. New diagnostic techniques have improved the sampling and analysis of pericardial fluid and allow comprehensive characterisation of cause. Despite this advance, pericarditis is most commonly idiopathic, and radiation therapy, cardiac surgery, and percutaneous procedures have become important causes. Pericarditis is frequently self-limiting, and non-steroidal anti-inflammatory agents remain the first-line treatment for uncomplicated cases. Integrated use of new imaging methods facilitates accurate detection and management of complications such as pericardial effusion or constriction. Differentiation of constrictive pericarditis from restrictive cardiomyopathy remains a clinical challenge but is facilitated by tissue doppler and colour M-mode echocardiography. Most pericardial effusions can be safely managed with an echo-guided percutaneous approach. Pericardiectomy remains the definitive treatment for constrictive pericarditis and provides symptomatic relief in most cases. In the future, the pericardial space might become a conduit for treatments directed at the pericardium and myocardium.

"Hands-Free" continuous transthoracic monitoring of pericardiocentesis using a novel ultrasound transducer

BACKGROUND

Pericardiocentesis can be monitored with a hand-held transducer. The purpose of this study was to assess the feasibility of monitoring pericardiocentesis using a novel ultrasound transducer, which can be attached to the chest wall, developed in our laboratory (CONTISON).

METHODS

We studied nine patients with large pericardial effusions. The 2.5-MHz transducer is spherical in its distal part and mounted in an external housing to permit steering in 360 degrees. The external housing is attached to the chest wall using an adhesive patch. The CONTISON transducer was placed at the cardiac apex and an apical four-chamber view obtained. Pericardiocentesis was performed from the subcostal position. The pericardial effusion was continuously imaged. Mitral inflow velocity signals were recorded before and after pericardiocentesis. When fluid was first obtained, 50 mL of fluid were discarded after which 5 mL of agitated saline was injected through the needle.

RESULTS

In the first patient the pericardiocentesis needle was seen in the left ventricular cavity. Saline injection produced a contrast effect in the left ventricle. The needle was gradually withdrawn until contrast was seen in the pericardial sac. A total of 1100 mL was removed without further complications. The second patient had clear fluid followed by blood stained aspirate. The echocardiogram revealed gradual appearance of granular echoes within the pericardial sac, suggestive of intrapericardial clot that was subsequently surgically evacuated. In the remaining seven patients, agitated saline produced a contrast effect in the pericardial sac indicative of proper needle position. Mitral flow velocity paradoxus was noted in five patients, and it resolved after pericardiocentesis in four patients. No adjustment of the transducer was required.

CONCLUSION

The CONTISON transducer permitted continuous monitoring of pericardiocentesis. This technique could potentially facilitate pericardiocentesis.

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.