Ultrasound-guided System Research Articles

MO‐DE‐210‐06: Development of a Supercompounded 3D Volumetric Ultrasound Image Guidance System for Prone Accelerated Partial Breast Irradiation (APBI)

Purpose:For early‐stage breast cancer, accelerated partial breast irradiation (APBI) is a cost‐effective breast‐conserving treatment. Irradiation in a prone position can mitigate respiratory induced breast movement and achieve maximal sparing of heart and lung tissues. However, accurate dose delivery is challenging due to breast deformation and lumpectomy cavity shrinkage. We propose a 3D volumetric ultrasound (US) image guidance system for accurate prone APBIMethods:The designed system, set beneath the prone breast board, consists of a water container, an US scanner, and a two‐layer breast immobilization cup. The outer layer of the breast cup forms the inner wall of water container while the inner layer is attached to patient breast directly to immobilization. The US transducer scans is attached to the outer‐layer of breast cup at the dent of water container. Rotational US scans in a transverse plane are achieved by simultaneously rotating water container and transducer, and multiple transverse scanning forms a 3D scan. A supercompounding‐technique‐based volumetric US reconstruction algorithm is developed for 3D image reconstruction. The performance of the designed system is evaluated with two custom‐made gelatin phantoms containing several cylindrical inserts filled in with water (11% reflection coefficient between materials). One phantom is designed for positioning evaluation while the other is for scaling assessment.Results:In the positioning evaluation phantom, the central distances between the inserts are 15, 20, 30 and 40 mm. The distances on reconstructed images differ by −0.19, −0.65, −0.11 and −1.67 mm, respectively. In the scaling evaluation phantom, inserts are 12.7, 19.05, 25.40 and 31.75 mm in diameter. Measured inserts’ sizes on images differed by 0.23, 0.19, −0.1 and 0.22 mm, respectively.Conclusion:The phantom evaluation results show that the developed 3D volumetric US system can accurately localize target position and determine target volume, and is a promising image‐guidance tool for prone APBI.

MO‐DE‐210‐07: Investigation of Treatment Interferences of a Novel Robotic Ultrasound Radiotherapy Guidance System with Clinical VMAT Plans for Liver SBRT Patients

Purpose:To evaluate the proportion of liver SBRT cases in which robotic ultrasound image guidance concurrent with beam delivery can be deployed without interfering with clinically used VMAT beam configurations.Methods:A simulation environment incorporating LINAC, couch, planning CT, and robotic ultrasound guidance hardware was developed. Virtual placement of the robotic ultrasound hardware was guided by a target visibility map rendered on the CT surface. The map was computed on GPU by using the planning CT to simulate ultrasound propagation and attenuation along rays connecting skin surface points to a rasterized imaging target. The visibility map was validated in a prostate phantom experiment by capturing live ultrasound images of the prostate from different phantom locations. In 20 liver SBRT patients treated with VMAT, the simulation environment was used to place the robotic hardware and ultrasound probe at imaging locations indicated on the visibility map. Imaging targets were either entire PTV (range 5.9–679.5 ml) or entire GTV (range 0.9–343.4 ml). Presence or absence of mechanical collisions with LINAC, couch, and patient body as well as interferences with treated beams were recorded.Results:For PTV targets, robotic ultrasound guidance without mechanical collision was possible in 80% of the cases and guidance without beam interference was possible in 60% of the cases. For the smaller GTV targets, these proportions were 95% and 85% correspondingly. GTV size (1/20), elongated shape (1/20), and depth (1/20) were the main factors limiting the availability of non‐interfering imaging positions.Conclusion:This study indicates that for VMAT liver SBRT, robotic ultrasound tracking of a relevant internal target would be possible in 85% of cases while using treatment plans currently deployed in the clinic. With beam re‐planning in accordance with the presence of robotic ultrasound guidance, intra‐fractional ultrasound guidance may be an option for 95% of the liver SBRT cases.This project was funded by NIH Grant R41CA174089.

Panorama Ultrasound for Navigation and Guidance of Epidural Anesthesia

Despite the common use of epidural anesthesia in obstetrics and surgery, the procedure can be challenging, especially for obese patients. We propose the use of an ultrasound guidance system employing a transducer-mounted camera to create 3-D panorama ultrasound volumes of the spine, thereby allowing identification of vertebrae and selection of puncture site, needle trajectory and depth of insertion. The camera achieves absolute position estimation of the transducer with respect to the patient using a specialized marker strip attached to the skin surface. The guidance system is validated first on a phantom against a commercial optical tracking system and then in vivo by comparing panorama images from human subjects against independent measurements by an experienced sonographer. The results for measuring depth to the epidural space, intervertebral spacing and registration of interspinous gaps to the skin prove the potential of the system for improving guidance of epidural anesthesia. The tracking and visualization are implemented in real time using the 3D Slicer software package.

Novice performance of ultrasound-guided needling skills: effect of a needle guidance system.

Ultrasound-guided needle placement is a widely used technical skill that can be challenging to learn. The SonixGPS is a novel ultrasound needle-tracking system that has the potential to improve performance over traditional ultrasound systems. The objective of our study was to determine if the use of the SonixGPS ultrasound system improves performance of novice practitioners in ultrasound-guided needle placement compared with conventional ultrasound in the out-of-plane approach on a simulation model. Twenty-six medical students without previous ultrasound experience were randomized into 2 groups. Each group performed 30 simulated ultrasound nerve blocks on a porcine meat tissue simulation (phantom) model. Both groups used the SonixGPS ultrasound; however, the study group had the needle-tracking system activated, whereas the control group did not. The participants were assessed for success rate, technical aspects of block performance, and certain behaviors that could compromise the quality of the block. Learning curves were developed to assess competence. The needle guidance group reached competence more often. This group had fewer attempts and quality-compromising behaviors than did those using conventional ultrasound. Use of the SonixGPS ultrasound needle guidance system improves the performance of technical needling skills of novice trainees in an ex vivo model. The place of this technology in the wider education of ultrasound-guided regional anesthesia remains to be established.

Phantom study of an ultrasound guidance system for transcatheter aortic valve implantation

A guidance system using transesophageal echocardiography and magnetic tracking is presented which avoids the use of nephrotoxic contrast agents and ionizing radiation required for traditional fluoroscopically guided procedures. The aortic valve is identified in tracked biplane transesophageal echocardiography and used to guide stent deployment in a mixed reality environment. Additionally, a transapical delivery tool with intracardiac echocardiography capable of monitoring stent deployment was created. This system resulted in a deployment depth error of 3.4mm in a phantom. This was further improved to 2.3mm with the custom-made delivery tool. In comparison, the variability in deployment depth for traditional fluoroscopic guidance was estimated at 3.4mm.

Novel ultrasound guidance system for real-time central venous cannulation: safety and efficacy.

IntroductionReal-time ultrasound guidance is considered to be the standard of care for central venous access for non-emergent central lines. However, adoption has been slow, in part because of the technical challenges and time required to become proficient. The AxoTrack® system (Soma Access Systems, Greenville, SC) is a novel ultrasound guidance system recently cleared for human use by the United States Food and Drug Administration (FDA).MethodsAfter FDA clearance, the AxoTrack® system was released to three hospitals in the United States. Physicians and nurse practitioners who work in the intensive care unit or emergency department and who place central venous catheters were trained to use the AxoTrack® system. De-identified data about central lines placed in living patients with the AxoTrack® system was prospectively gathered at each of the three hospitals for quality assurance purposes. After institutional review board approval, we consolidated the data for the first five months of use for retrospective review.ResultsThe AxoTrack® system was used by 22 different health care providers in 50 consecutive patients undergoing central venous cannulation (CVC) from September 2012 to February 2013. All patients had successful CVC with the guidance of the AxoTrack® system. All but one patient (98%) had successful cannulation on the first site attempted. There were no reported complications, including pneumothorax, hemothorax, arterial puncture or arterial cannulation.ConclusionThe AxoTrack® system was a safe and effective means of CVC that was used by a variety of health care practitioners.

The use of a novel ultrasound guidance system for real-time central venous cannulation: initial report on safety and efficacy

Background Real-time ultrasound guidance is considered to be the standard of care for central venous access for non-emergent central lines. However, adoption has been slow in part because of the technical challenges and time required to acquire the skills to become proficient. The AxoTrack system (Soma Access Systems, Greenville, SC) is a novel ultrasound guidance system recently cleared for human use by the United States Food and Drug Administration (FDA).

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Introduction: Real-time ultrasound guidance is considered to be the standard of care for central venous access for non-emergent central lines. Traditional sites for ultrasound guided central line placement are the internal jugular vein and subclavian vein via an infraclavicular approach. The AxoTrack system (Soma Access Systems, Greenville, SC) recently cleared for human use by the United States Food and Drug Administration, is a novel ultrasound guidance system designed to simplify ultrasound guided central venous access by eliminating the hand-eye coordination challenges of conventional ultrasound needle guidance. The ultrasound probe houses a separate set of magnetic sensors that, in real-time, precisely monitors the depth of the needle and projects on the ultrasound system monitor a virtual image of the needle as it moves through the tissue toward and into the target vein. The design and function of the device facilitates a unique approach to ultrasound guided supraclavicular approach to cannulation of the subclavian vein. Methods: After FDA clearance, the AxoTrack system was released to three hospitals in the United States. Physicians and Nurse Practitioners who work in the Intensive Care Unit or Emergency Department and who place central venous catheters were trained to use the AxoTrack system. De-identified quality assurance data was prospectively collected at each of the three hospitals every time the AxoTrack system was used for central venous cannulation (CVC) to determine if the system was successful and to describe any complications from the procedure. After IRB review, we consolidated the data for the first 100 central line procedures for retrospective review. Results: The AxoTrack system was used in 100 consecutive patients undergoing central venous cannulation from September 2012 to July 2013. A subset of 33 patients underwent supraclavicular access with no reported complications, including pneumothorax, hemothorax, arterial puncture, or arterial cannulation. Conclusions: The AxoTrack system is a safe, straightforward, and effective tool that facilitates CVC insertion at an alternative site. Furthermore, this device can be used by a variety of health care practitioners with little additional training.

IMAGE GUIDED CATHETER HAVING REMOTELY CONTROLLED SURFACES-MOUNTED AND INTERNAL ULTRASOUND TRANSDUCERS

A remotely manipulatable ultrasound transducer element or transducer array permits an operator of an ultrasound system to be remotely located from a patient and yet remotely control the location of the element or array on a patient's body such as on the skin surface or within a body cavity. The transducer element or transducer array associated with motors and control circuits comprises an assembly within a housing for fixation to or within a human body. The transducer assembly may be fixed to a ring surrounding an image guided catheter and may rotate about the image guided catheter or move along its length to an anchoring position proximate the surface skin. Two embodiment systems for pericardial access may comprise surface and internal vision or ultrasound guidance systems that are wireless or wired one operating on suction and another on mechanical grasping of the pericardial lining.

Real-time three-dimensional guided ultrasound targeting system for microwave ablation of liver tumours: a human pilot study

ObjectivesThis study aimed to evaluate a novel three-dimensional ultrasound (US) guidance system for use in hepatic microwave ablation (MWA). MethodsAn in vitro assessment was performed in which users with different degrees of experience were evaluated for accuracy in targeting phantom lesions embedded in agar using US alone, or US in conjunction with the InVision™ System (IVS). An eight-patient pilot trial of the IVS was then performed in the setting of open hepatic MWA, in which lesions would otherwise have been targeted with conventional US. ResultsIn vitro studies demonstrated that the IVS significantly improved targeting accuracy at all levels of operator experience (novice, beginner and expert). In the human trial, a total of 31 tumours were targeted and all lesions were hit in one pass, as assessed by independent US image observations. There were no adverse operative events; however, there was minor line-of-sight interference with the infra-red tracking mechanism when some lesions high on the dome of the liver were targeted. ConclusionsThe IVS significantly increased the accuracy of complex targeting procedures of phantom lesions and enhanced targeting in an eight-patient clinical pilot study. During the accrual phase of this pilot study, the development of improved non-optical tracking hardware obviated the requirement to maintain a direct line of sight. The trial was then halted prematurely in order to focus on the application of the IVS utilizing this non-optical modality.

Popliteal catheter placement utilizing ultrasound needle guidance system

While ultrasound (US)-guided placement of peripheral nerve blocks is rapidly gaining popularity, expert practitioners agree that two of the most significant barriers to safety and efficacy are keeping the needle tip within the image and unintentional probe movement during the procedure.1 In addition, placing a nerve catheter past the needle tip under direct US observation requires two practitioners: one to hold the US probe and needle and another to advance the catheter. We present a case of a needle guidance system that attaches to the ultrasound probe and facilitates in-plane imaging. It enables a single practitioner to successfully execute a popliteal sciatic nerve block and visualize catheter placement. Therefore, a needle guidance system may represent an additional modification to ultrasound imaging that increases both time efficiency as well as safety.

SU‐HH‐BRB‐09: Real‐Time Soft‐Tissue Imaging Concurrent with External Beam Radiation Therapy Delivery

Purpose: The challenge of real‐time visualization, localization, and tracking of organ motion and deformation concurrently with external beam radiation therapy (EBRT) delivery remains unmet and unattainable by existing image guidance technologies. We propose to address this challenge in the development of a novel, minimally interfering, robotic ultrasound image guidance system that can be integrated with existing medical linear accelerators. Method and Materials: The span of ultrasound transducer motion required for trans‐abdominal prostate imaging was quantified via optical tracking of a probe during free‐hand acquisitions. This information was incorporated into the design of a customized human‐safe robotic manipulator to remotely control the transducer position and pressure while avoiding LINAC gantry collisions. The effect of accelerator‐induced electromagnetic interference on the robot was investigated. In addition, a treatment plan with beam directions restricted to sectors that do not interfere with the ultrasound transducer was evaluated. Results: Prostate image integrity was sensitive to probe pitch, thus the manipulator was designed to actively control abdominal pressure (0–10N) and transducer pitch (−40°−90°). Probe placement in other directions remains adjustable to accommodate anatomy variations. Human‐safety requirements translated into the design via a torque limiting friction clutch, lightweight backdriveable links, and remote center of motion pitch mechanism. Collision avoidance was confirmed by rotating the gantry 360° around the robot mounted on the LINAC couch in a typical treatment setup. The control system of the robot behaved similarly with the LINAC beam off and on, with mean servo cycle intervals of 1000.03 μs and 1000.06μs, respectively. For a representative prostate setup, remotely‐controlled robotic ultrasound image acquisition was successfully demonstrated on a volunteer. Dose volume histogram (DVH) for an IMRT plan with restricted sectors remained virtually identical to a clinically employed DVH. Conclusion: Remotely‐controlled robotic ultrasound imaging is feasible and may offer real‐time intra‐fractional soft‐tissue guidance concurrent with EBRT delivery.

TU‐D‐BRA‐03: Real‐Time‐Image Guidance in Radiation Therapy: Is There a Role for Ultrasound Imaging?

The curative potential of External Beam Radiation Therapy (EBRT) is critically dependent on having the ability to accurately aim radiation beams at intended targets while avoiding surrounding healthy tissues. Cone‐beam computed tomography, planar x‐ray imaging, radiographic or electromagnetic tracking of implanted fiducials, as well as operator‐performed ultrasound are currently used for EBRT image guidance. However, these technologies are incapable of addressing the challenge of real‐time volumetric (4D) visualization, localization, and tracking of soft‐tissue motion and deformation concurrent with treatment beam delivery. Thus a significant opportunity exists for improving the therapeutic ratio and the safety of EBRT. We will present and discuss two solutions that can realize this opportunity through the integration of spatially localized, remotely controlled operator‐free ultrasound imaging with radiation delivery systems.The first approach relies on a custom designed compact ultrasound probe based on two‐dimensional matrix array of capacitive micro‐machined ultrasonic transducers integrated with radiofrequency electronics. For operator‐free imaging, the probe is to be fixed to a subject by a belt with appropriate acoustical coupling. Dedicated beam forming methodology and image reconstruction is necessary to enable large volume data collection at a volume rate of 3 Hz or higher.The second approach employs a novel, minimally interfering, tele‐robotic ultrasound imaging based on commercial transducers. It uses a customized human‐safe robotic manipulator to control the pressure and pitch of an abdominal probe while avoiding gantry collisions. A haptic device is integrated to remotely control the robotic manipulator motion and image acquisition outside the therapy room.Learning objectives:1. Understand basic relationships between ultrasound imaging system design and performance parameters such as spatial resolution, frame rate, and field of view. Recognize the dependencies between these parameters.2. Identify limitations of current EBRT ultrasound guidance systems and identify physics, design and workflow causes behind them.3. Understand how remote‐operator free imaging and appropriately designed workflow can enable real‐time soft‐tissue image guidance concurrent with radiation delivery and reduce ultrasound localization uncertainties.4. Recognize potential interferences between the radiation delivery system and the operator‐free imaging system and appreciate their magnitude and mutual impact.

Dosimetric consequences of misalignment and realignment in prostate 3DCRT using intramodality ultrasound image guidance

It is common practice to correct for interfraction motion by shifting the patient from reference skin marks to better align the internal target at the linear accelerator's isocenter. Shifting the patient away from skin mark alignment causes the radiation beams to pass through a patient geometry different from that planned. Yet, dose calculations on the new geometry are not commonly performed. The intention of this work was to compare the dosimetric consequences of treating the patient with and without setup correction for the common clinical scenario of prostate interfraction motion. In order to account for prostate motion, 32 patients initially aligned to the room lasers via skin marks were realigned under the treatment beams by shifting the treatment couch based on ultrasound image guidance. An intramodality 3D ultrasound image guidance system was used to determine the setup correction, so that errors stemming from different tissue representations on different imaging modalities were eliminated. Two scenarios were compared to the reference static treatment plan: (1) Uncorrected patient alignment and (2) corrected patient alignment. Prostate displacement statistics and the dose to the clinical target volume (CTV), bladder, and rectum are reported. Monte Carlo dose calculation methods were employed. Comparing the uncorrected and corrected scenarios using the static treatment plan as the reference, the average percent difference in D95 for the CTV improved from -5.1% (range -40%, 1.3%) to 0.0% (-3.5%, 2.0%) and the average percent difference in V90 for the bladder and rectum changed from -11% (-84%, 232%) to -8.3% (-61%, 5.2%) and from -47% (-100%, 108%) to 0.9% (-62%, 102%), respectively. There was no simple correlation between displacement and dose discrepancy before correction. After patient realignment, the prescribed dose to the CTV was achieved within 1% for 75% (24/32) of the patients. After patient realignment, 50% of the patients had doses that differed from the static treatment plan by 25% for the bladder and 8% for the rectum. The dose degradation due to prostate motion (before correction) is not accurately predicted from the average trends for all patients. Outliers included smaller displacements that lead to larger dosimetric differences in the corrected scenario, especially for the bladder and rectum, which exhibited doses substantially different from that planned.

Novel treatment for necrospermia & partial ejaculatory duct obstruction: Turek vasodynamics using 3D trans rectal ultrasound guidance system

OBJECTIVE: A recent study presented a technique of trans-rectal vasodynamics (pressure flow study of the seminal vesicle) to assess for partial ejaculatory duct obstruction (EDO - Turek et al). Our goal was to utilize a 3D trans-rectal ultrasound imaging and needle targeting system to perform vasodynamics for the treatment of necrospermia with partial EDO.

Evaluation of alignment error due to a speed artifact in stereotactic ultrasound image guidance

Ultrasound (US) image guidance systems used in radiotherapy are typically calibrated for soft tissue applications, thus introducing errors in depth-from-transducer representation when used in media with a different speed of sound propagation (e.g. fat). This error is commonly referred to as the speed artifact. In this study we utilized a standard US phantom to demonstrate the existence of the speed artifact when using a commercial US image guidance system to image through layers of simulated body fat, and we compared the results with calculated/predicted values. A general purpose US phantom (speed of sound (SOS) = 1540 m s−1) was imaged on a multi-slice CT scanner at a 0.625 mm slice thickness and 0.5 mm × 0.5 mm axial pixel size. Target-simulating wires inside the phantom were contoured and later transferred to the US guidance system. Layers of various thickness (1–8 cm) of commercially manufactured fat-simulating material (SOS = 1435 m s−1) were placed on top of the phantom to study the depth-related alignment error. In order to demonstrate that the speed artifact is not caused by adding additional layers on top of the phantom, we repeated these measurements in an identical setup using commercially manufactured tissue-simulating material (SOS = 1540 m s−1) for the top layers. For the fat-simulating material used in this study, we observed the magnitude of the depth-related alignment errors resulting from the speed artifact to be 0.7 mm cm−1 of fat imaged through. The measured alignment errors caused by the speed artifact agreed with the calculated values within one standard deviation for all of the different thicknesses of fat-simulating material studied here. We demonstrated the depth-related alignment error due to the speed artifact when using US image guidance for radiation treatment alignment and note that the presence of fat causes the target to be aliased to a depth greater than it actually is. For typical US guidance systems in use today, this will lead to delivery of the high dose region at a position slightly posterior to the intended region for a supine patient. When possible, care should be taken to avoid imaging through a thick layer of fat for larger patients in US alignments or, if unavoidable, the spatial inaccuracies introduced by the artifact should be considered by the physician during the formulation of the treatment plan.

AAPM Task Group 128: Quality assurance tests for prostate brachytherapy ultrasound systems

While ultrasound guided prostate brachytherapy has gained wide acceptance as a primary treatment tool for prostate cancer, quality assurance of the ultrasound guidance system has received very little attention. Task Group 128 of the American Association of Physicists in Medicine was created to address quality assurance requirements specific to transrectal ultrasound used for guidance of prostate brachytherapy. Accurate imaging guidance and dosimetry calculation depend upon the quality and accuracy of the ultrasound image. Therefore, a robust quality assurance program for the ultrasound system is essential. A brief review of prostate brachytherapy and ultrasound physics is provided, followed by a recommendation for elements to be included in a comprehensive test phantom. Specific test recommendations are presented, covering grayscale visibility, depth of penetration, axial and lateral resolution, distance measurement, area measurement, volume measurement, needle template/electronic grid alignment, and geometric consistency with the treatment planning computer.

Hand-assisted laparoscopic ultrasound-guided radiofrequency thermal ablation of liver tumors: a technical report.

Ultrasound-guided radiofrequency thermal ablation has been performed for liver tumors by percutaneous, laparoscopic, or open surgical approaches. Each approach has specific advantages and disadvantages. Herein we describe a new technique for hand-assisted laparoscopic ultrasound-guided radiofrequency thermal ablation of liver tumors. A hand-access device is placed at the right or central portion of the abdomen, in addition to standard trocars. A conventional intraoperative ultrasound probe, with an ultrasound guidance system attached, is inserted into the peritoneal cavity together with the surgeon's hand. After pneumoperitoneum is established, an electrode-cannula for thermal ablation is introduced subcostally or intercostally, and advanced into a liver tumor under direct guidance by intraoperative ultrasound. We have used this technique in eight patients with unresectable liver tumors. Precise guidance of the cannula into tumors was possible. All tumors were well ablated. The postoperative recovery of patients was of shorter duration compared with that of an open surgical approach. A hand-assisted laparoscopic ultrasound-guided method has advantages of both laparoscopic and open surgical approaches for radiofrequency thermal ablation treatment of liver tumors. Accurate cannula insertion is possible with the ultrasound guidance system. The hand-assisted laparoscopic approach can become an additional useful technique, particularly as a valuable alternative to an open surgical method, for performing radiofrequency thermal ablation.

413 poster The accuracy of an ultrasound guidance system for positioning the prostate at radiotherapy

413 poster The accuracy of an ultrasound guidance system for positioning the prostate at radiotherapy

Evaluation of an ultrasonically guided venepuncture technique for the placement of permanent pacing electrodes.

We have evaluated a method of puncturing the subclavian vein in its extrathoracic portion using an ultrasound guidance system. Seventy consecutive patients requiring permanent pacemakers were included in the study. The method was successful in 56 (80%) cases (23 dual chamber systems) and unsuitable or unsuccessful in 14 (20%) cases (2 dual chamber systems). The time taken to achieve a successful cannulation of the vein was similar to that taken with conventional subclavian venepuncture (average time taken for each venepuncture was 31 seconds, range 5-130 seconds). There was a significant "learning curve" in that nearly all of the unsuccessful cases were in the first half of the series. There were no major complications. Computerized Tomography (CT) confirms that the point of entry into the subclavian vein using this technique lies outside the thoracic cavity, thereby minimizing the risk of pneumothorax. This approach to the subclavian vein is an easy technique to learn, with few immediate complications and there may be less chance of lead fracture due to subclavian crush in the longer term.