Radiation Therapy : Ablation

Radiation Therapy Portfolios


Real-Time 3-D Elastography

The researchers have now developed an enhancement to their technique that works especially well with a 2-D ultrasound array to provide real-time 3-D imaging. The improvement derives from a new reconstruction scheme that uses sparse data.

The new scheme imposes two key requirements – interpolation and smoothing. Essentially, raw ultrasonic echo data is acquired over many imaging planes. Then, an efficient algorithm tracks frame to frame displacement of the underlying tissue at each pixel in the imaging plane. Mechanical properties such as strain can be estimated by a calculation along the ultrasound scan line direction. The 3-D reconstruction algorithm rapidly reconstructs a complete 3-D visualization from a sparse collection of scattered data points.

Minimally Invasive Microwave Ablation Antennas

UW–Madison researchers have developed two minimally invasive, balun-free antenna designs that are small enough to treat cancers otherwise out of the reach of microwave ablation.

The first design can take any base-fed monopole, spiral or bent wire configuration. Alternatively, the antenna can use a structure more suitable for higher frequencies (five GHz to 30 GHz). This design uses cable shielding over a balanced two-wire transmission line. The design protects surrounding tissue and eliminates the need for baluns.

Monitoring Tumor Ablation in Real Time

UW–Madison researchers have developed a method that uses radiofrequency signals transmitted from a microwave ablation probe to monitor the boundaries between a tumor, ablation zone and background healthy tissue.

The probe emits and then detects the signals as they echo off the different tissue boundaries. Since the boundary between a tumor and background tissue becomes less distinct as the ablation progresses, clinicians can determine when treatment is complete based on these echoes.

Rapid Three-Dimensional Elasticity Imaging

UW–Madison researchers have developed an ultrasonic probe assembly and a reconstruction technique for rapid three-dimensional elasticity imaging using limited data.

The probe sends an ultrasonic beam of energy into tissue and receives echoes from the displaced material generally along an axis. Ultrasound data is acquired over a set of planes (between four and six in number) angularly spaced and sharing a common axis. A computer receives the ultrasound data and determines elasticity of the material at multiple points within each plane. A three-dimensional reconstruction then is generated. This reconstruction is faster than the traditional sequential data acquisition for three-dimensional visualization.

Degrading Tumors with Microwave Heat Probes

UW–Madison researchers have developed an improved design for “dual-slot” antennas that incorporates a cooling sleeve and rigid ceramic tip. The coaxially fed, embedded delivery system focuses energy specifically to the tissue surrounding the antenna tip.

Accommodating long, short or even customized shafts, this flexible design facilitates the practical implementation of antenna technology for clinicians seeking safer, more controlled heating patterns. The heating pattern could be tailored to specific clinical applications that require more spherical or more narrow ablation zones.

Fan-Beam Microwave Horn for Improved Organ Resection

UW-Madison researchers have developed a dielectric-filled microwave waveguide-fed horn antenna applicator for bloodless surgery and resection, especially resection of the liver.  The applicator is placed against the surface of the liver and microwave power is applied.  The horn antenna applicator radiates microwaves uniformly into the tissue, causing coagulation.  This design provides fast and efficient control of coagulation while allowing a bloodless resection area. 

The planar design of the horn antenna application is superior to small or cylindrical radiator sources in that it provides less attenuation and a more constant temperature range in the coagulation region.  The surface applicator also offers the user control because there is no need for imaging modalities such as ultrasound to confirm placement or coagulation.

Improved Method and Apparatus for Monitoring Tissue Ablation in Minimally Invasive Tumor Treatment

UW-Madison researchers now have developed an ablation electrode that can vibrate ablated tissue and utilize the propagating shear wave velocities to obtain quantitative stiffness measurements.  The electrode is used in a new method that improves definition of tissue boundaries and quantization of tissue stiffness by measuring both conventional axial compression and perpendicular shear wave velocity changes.  The change in shear wave velocity provides direct measurement of Young’s modulus, the ratio of tensile stress to tensile strain, which may be used to define the stiffness of the treated region. 

Specifically, the device for monitoring the progress of ablation comprises an RF or microwave electrode to ablate tissue, an actuator to produce ultrasonic vibration of the RF or microwave electrode, a tissue imager to detect axial displacement data and a computer to receive and analyze displacement data.  The displacement data is used to compute the velocity change in the orthogonal shear wave, which characterizes the ablated lesion.  Analysis of the displacement data allows a real-time tissue image to be generated, indicating the size of the ablated and non-ablated regions. 

The new electrode displacement imaging method to assist tumor ablation provides accurate quantization of a tissue’s Young’s modulus through an improved computer algorithm that calculates shear wave velocity.  Further analysis of discontinuities in the Young’s modulus data enables multidimensional imaging of the tumor and ablated lesion boundaries.  The improved technique can be coupled with conventional quasi-static elastography monitoring methods to greatly enhance the quality of elastographic images and quantization of tissue stiffness to assist minimally invasive ablation procedures.

Radiofrequency Ablation Using Independently Controlled Ground Pads

A team of researchers has now created a radiofrequency (RF) ablation system that rapidly switches power between several ground pads to disperse power and heat more effectively and prevent burns to the patient. Unlike current systems, this technology doesn’t attempt to disperse power to all ground pads simultaneously. Instead, this system briefly disperses all of the probe’s power first at ground pad 1, then at ground pad 2, and so on. As a result, the exiting power is evenly distributed among all the ground pads, preventing excessive heating of any one pad.

Floating Sleeve Microwave Antenna for Tumor Ablation

UW-Madison researchers have developed a novel microwave antenna that uses a floating sleeve to suppress the tail of the SAR pattern, allowing more energy to be delivered locally and evenly to the tumor while reducing the risk of detrimental backward heating. The antenna consists of coaxial antenna conductors surrounded by a floating metal sleeve that is electrically isolated from the antenna by a Teflon layer. The metal sleeve promotes destructive interference of axial microwave energy passing inside and outside of the sleeve, thus suppressing the tail of the SAR pattern and minimizing damage to healthy tissue along the antenna tail.

Electrode Array for Radiofrequency Tissue Ablation

UW-Madison researchers have developed a faster method of bipolar RF ablation that uses an electrode array to heat tissue between electrodes. The electrodes are inserted into the tissue along a resection cut line. To heat the tissue, RF energy is applied in bipolar mode between pairs of probes set in a comb-like configuration. Power is switched between pairs of electrodes in half-second intervals, allowing all probes to heat the tissue, but avoiding increased impedance, which compromises effective heating.

Radiofrequency Ablation System Using Multiple-Prong Probes

The researchers have now described an RF ablation system that provides the benefits of multiple probe ablation within a single multi-prong probe. The system includes a multi-pronged probe device that allows both monopolar and bipolar RF ablation from the prongs of a single probe. For efficient ablation, the prongs are electrically isolated from each other. Current can be rapidly switched between the prongs (in monopolar or bipolar mode), between a prong and a ground pad, or both.

Radio Frequency Ablation System Using Multiple Electrodes

UW-Madison researchers have developed an efficient method of RF ablation using multiple electrodes. The technique involves simultaneous operation of multiple mono-polar probes. An electric circuit switches power rapidly between individual probes so that on an instantaneous basis, each probe is operating in isolation. At the same time, each probe can be considered to be operating simultaneously for the purpose of heating.

Elastographic Imaging of Soft Tissue in Vivo

UW-Madison researchers have now discovered that by using an RF ablation probe to internally compress tissue, they can generate 3-D elastographic images of the liver in vivo. Thus, this technique provides a simple and effective way of monitoring the RF ablation of soft tissue inside the body, without the lateral slippage caused by external compression. Elastography may be performed either during RF ablation or after the procedure is complete.