Alexander Franciscus Kolen

Visualizing intramyocardial steam formation with a radiofrequency ablation catheter incorporating near-field ultrasound.

Steam pops are a risk of irrigated RF ablation even when limiting power delivery. There is currently no way to predict gas formation during ablation. It would be useful to visualize intramyocardial gas formation prior to a steam pop occurring using near‐field ultrasound integrated into a RF ablation catheter.

Effects of spatially targeted transcutaneous electrical nerve stimulation using an electrode array that measures skin resistance on pain and mobility in patients with osteoarthritis in the knee: a randomized controlled trial.

Summary An electrode array enabled transcutaneous electrical nerve stimulation (TENS) treatment at sites of lowest skin resistance which reduced movement‐related osteoarthritic knee pain more than adjacent TENS treatment sites. Abstract A novel device was developed that measured local electrical skin resistance and generated pulsed local electrical currents that were delivered across the skin around the knee for patients with osteoarthritis (termed eBrace TENS). Currents were delivered using an electrode array of 16 small circular electrode elements so that stimulation could be spatially targeted. The aim of this study was to investigate the effects of spatially targeted transcutaneous electrical nerve stimulation (TENS) to points of low skin resistance on pain relief and mobility in osteoarthritis of the knee (OAK). A randomised, controlled, 3‐arm, parallel‐group trial was designed that compared pain and function following a 30 to 45 minute intervention of TENS at specific locations depending on the local electrical skin resistance. Pain intensity by the visual analogue scale (VAS), 6‐minute walk test, maximum voluntary contraction (MVC), and range‐of‐motion (ROM) were the primary outcomes. Lowest‐resistance TENS reduced pain intensity during walking relative to resting baseline compared with random TENS (95% confidence interval of the difference: −20.8 mm, −1.26 mm). There were no statistically significant differences between groups in distance during the walk test, maximum voluntary contraction (MVC) or range‐of‐motion (ROM) measures or WOMAC scores. In conclusion, we provide evidence that use of a matrix electrode that spatially targets strong nonpainful TENS for 30 to 45 minutes at sites of low resistance can reduce pain intensity at rest and during walking.

Near-Field Ultrasound Imaging During Radiofrequency Catheter Ablation: Tissue Thickness and Epicardial Wall Visualization and Assessment of Radiofrequency Ablation Lesion Formation and Depth

Background Safe and successful radiofrequency catheter ablation depends on creation of transmural lesions without collateral injury to contiguous structures. Near-field ultrasound (NFUS) imaging through transducers in the tip of an ablation catheter may provide important information about catheter contact, wall thickness, and ablation lesion formation. Methods and Results NFUS imaging was performed using a specially designed open-irrigated radiofrequency ablation catheter incorporating 4 ultrasound transducers. Tissue/phantom thickness was measured in vitro with varying contact angles. In vivo testing was performed in 19 dogs with NFUS catheters positioned in 4 chambers. Wall thickness measurements were made at 222 sites (excluding the left ventricle) and compared with measurements from intracardiac echocardiography. Imaging was used to identify the epicardium with saline infusion into the pericardial space at 39 sites. In vitro, the measured exceeded actual tissue/phantom thickness by 13% to 20%. In vivo, NFUS reliably visualized electrode-tissue contact, but sensitivity of epicardial imaging was 92%. The chamber wall thickness measured by NFUS correlated well with intracardiac echocardiography (r=0.86; P<0.0001). Sensitivity of lesion identification by NFUS was 94% for atrial and 95% for ventricular ablations. NFUS was the best parameter to predict lesion depth in right and left ventricle (r=0.47; P<0.0001; multiple regression P=0.0025). Lesion transmurality was correctly identified in 87% of atrial lesions. Conclusions NFUS catheter imaging reliably assesses electrode-tissue contact and wall thickness. Its use during radiofrequency catheter ablation may allow the operator to assess the depth of ablation required for transmural lesion formation to optimize power delivery.

Medical Instrument Detection in 3-Dimensional Ultrasound Data Volumes

Ultrasound-guided medical interventions are broadly applied in diagnostics and therapy, e.g., regional anesthesia or ablation. A guided intervention using 2-D ultrasound is challenging due to the poor instrument visibility, limited field of view, and the multi-fold coordination of the medical instrument and ultrasound plane. Recent 3-D ultrasound transducers can improve the quality of the image-guided intervention if an automated detection of the needle is used. In this paper, we present a novel method for detecting medical instruments in 3-D ultrasound data that is solely based on image processing techniques and validated on various ex vivo and in vivo data sets. In the proposed procedure, the physician is placing the 3-D transducer at the desired position, and the image processing will automatically detect the best instrument view, so that the physician can entirely focus on the intervention. Our method is based on the classification of instrument voxels using volumetric structure directions and robust approximation of the primary tool axis. A novel normalization method is proposed for the shape and intensity consistency of instruments to improve the detection. Moreover, a novel 3-D Gabor wavelet transformation is introduced and optimally designed for revealing the instrument voxels in the volume, while remaining generic to several medical instruments and transducer types. Experiments on diverse data sets, including in vivo data from patients, show that for a given transducer and an instrument type, high detection accuracies are achieved with position errors smaller than the instrument diameter in the 0.5–1.5-mm range on average.

Frequency-agility of collapse-mode 1-D CMUT array

The size of the features, and their relative distance to the probe, vary a lot in the intracardiac echocardiography application thus challenging the design of the probe. Therefore it may be beneficial to design a versatile probe which can produce both a large image to provide overview for navigation, and a smaller but detailed anatomic image on the structures of interest. This could be achieved by a probe whose frequency range of operation can be tuned - on the fly - to the specific task. Our goal is to develop a forward-looking catheter which can change its imaging frequency in the range 5 MHz - 15 MHz, allowing for both high penetration and high resolution intracardiac imaging within a single device. Our design comprises a capacitive micromachined ultrasonic transducer (CMUT) array operated in collapse-mode, which allows tuning of the imaging frequency. Custom-made front-end electronics is integrated in a catheter tip close to the CMUT for improved performance. In this paper, we report on the frequency-agility of the fabricated collapse-mode 1-D CMUT array.

Quantitative imaging performance of frequency-tunable capacitive micromachined ultrasonic transducer array designed for intracardiac application: Phantom study

Highlights2‐D imaging probe prototype based on a collapse‐mode CMUT array developed.Imaging performance quantified at a range of bias voltage and driving pulse settings.Demonstration of frequency tunability on a tissue‐mimicking phantom.Images with different characteristics (e.g. penetration, resolution) are presented. ABSTRACT Commercially available intracardiac echo (ICE) catheters face a trade‐off between viewing depth and resolution. Frequency‐tunable ICE probes would offer versatility of choice between penetration or resolution imaging within a single device. In this phantom study, the imaging performance of a novel, frequency‐tunable, 32‐element, 1‐D CMUT array integrated with front‐end electronics is evaluated. Phased‐array ultrasound imaging with a forward‐looking CMUT probe prototype operated beyond collapse mode at voltages up to three times higher than the collapse voltage (Symbol V) is demonstrated. Imaging performance as a function of bias voltage (Symbol V to Symbol V), transmit pulse frequency (5–25 MHz), and number of transmit pulse cycles (1–3) is quantified, based on which penetration, resolution, and generic imaging modes are identified. It is shown that by utilizing the concept of frequency tuning, images with different characteristics can be generated trading‐off the resolution and penetration depth. The penetration mode provides imaging up to 71 mm in the tissue‐mimicking phantom, axial resolution of 0.44 mm, and lateral resolution of 0.12 rad. In the resolution mode, axial resolution of 0.055 mm, lateral resolution of 0.035 rad, and penetration depth of 16 mm are measured. These results show what this CMUT array has the potential versatile characteristics needed for intracardiac imaging, despite its relatively small transducer aperture size of 2 mm Symbol 2 mm imposed by the clinical application. Symbol. No caption available. Symbol. No caption available. Symbol. No caption available. Symbol. No caption available.

Feature study on catheter detection in three-dimensional ultrasound.

The usage of three-dimensional ultrasound (3D US) during image-guided interventions for e.g. cardiac catheterization has increased recently. To accurately and consistently detect and track catheters or guidewires in the US image during the intervention, additional training of the sonographer or physician is needed. As a result, image-based catheter detection can be beneficial to the sonographer to interpret the position and orientation of a catheter in the 3D US volume. However, due to the limited spatial resolution of 3D cardiac US and complex anatomical structures inside the heart, image-based catheter detection is challenging. In this paper, we study 3D image features for image-based catheter detection using supervised learning methods. To better describe the catheter in 3D US, we extend the Frangi vesselness feature into a multi-scale Objectness feature and a Hessian element feature, which extract more discriminative information about catheter voxels in a 3D US volume. In addition, we introduce a multi-scale statistical 3D feature to enrich and enhance the information for voxel-based classification. Extensive experiments on several in-vitro and ex-vivo datasets show that our proposed features improve the precision to at least 69% when compared to the traditional multi-scale Frangi features (from 45% to 76% at a high recall rate 75%). As for clinical application, the high accuracy of voxel-based classification enables more robust catheter detection in complex anatomical structures.

Improved ultrasound transducer positioning by fetal heart location estimation during Doppler based heart rate measurements

OBJECTIVE Doppler ultrasound (US) is the most commonly applied method to measure the fetal heart rate (fHR). When the fetal heart is not properly located within the ultrasonic beam, fHR measurements often fail. As a consequence, clinical staff need to reposition the US transducer on the maternal abdomen, which can be a time consuming and tedious task. APPROACH In this article, a method is presented to aid clinicians with the positioning of the US transducer to produce robust fHR measurements. A maximum likelihood estimation (MLE) algorithm is developed, which provides information on fetal heart location using the power of the Doppler signals received in the individual elements of a standard US transducer for fHR recordings. The performance of the algorithm is evaluated with simulations and in vitro experiments performed on a beating-heart setup. MAIN RESULTS Both the experiments and the simulations show that the heart location can be accurately determined with an error of less than 7 mm within the measurement volume of the employed US transducer. SIGNIFICANCE The results show that the developed algorithm can be used to provide accurate feedback on fetal heart location for improved positioning of the US transducer, which may lead to improved measurements of the fHR.

Ultrasound transducer positioning aid for fetal heart rate monitoring

Fetal heart rate (fHR) monitoring is usually performed by Doppler ultrasound (US) techniques. For reliable fHR measurements it is required that the fetal heart is located within the US beam. In clinical practice, clinicians palpate the maternal abdomen to identify the fetal presentation and then the US transducer is fixated on the maternal abdomen where the best fHR signal can be obtained. Finding the optimal transducer position is done by listening to the strength of the Doppler audio output and relying on a signal quality indicator of the cardiotocographic (CTG) measurement system. Due to displacement of the US transducer or displacement of the fetal heart out of the US beam, the fHR signal may be lost. Therefore, it is often necessary that the obstetrician repeats the tedious procedure of US transducer positioning to avoid long periods of fHR signal loss. An intuitive US transducer positioning aid would be highly desirable to increase the work flow for the clinical staff. In this paper, the possibility to determine the fetal heart location with respect to the transducer by exploiting the received signal power in the transducer elements is shown. A commercially available US transducer used for fHR monitoring is connected to an US open platform, which allows individual driving of the elements and raw US data acquisition. Based on the power of the received Doppler signals in the transducer elements, the fetal heart location can be estimated. A beating fetal heart setup was designed and realized for validation. The experimental results show the feasibility of estimating the fetal heart location with the proposed method. This can be used to support clinicians in finding the optimal transducer position for fHR monitoring more easily.