This invention relates generally to ablation systems and catheter devices, and more specifically to ablation systems with monitoring and evaluation capabilities.
Catheters are flexible, tubular devices that are widely used by physicians performing medical procedures to gain access into interior regions of the body. Certain types of catheters are commonly referred to as irrigated catheters that deliver fluid to a target site in an interior region of the body. Such irrigated catheters may deliver various types of fluid to the patient, including, for example, medications, therapeutic fluids, and even cooling fluids for certain procedures wherein heat is generated within targeted areas of the body.
For example, ablation catheters are sometimes used to perform ablation procedures to treat certain conditions of a patient. A patient experiencing arrhythmia, for example, may benefit from ablation to prevent irregular heart beats caused by arrhythmogenic electrical signals generated in cardiac tissues. By ablating or altering cardiac tissues that generate such unintended electrical signals the irregular heart beats may be stopped. Ablation catheters may include one or more ablation electrodes supplying radiofrequency (RF) energy to targeted tissue. With the aid of sensing and mapping tools, an electro-physiologist can determine a region of tissue in the body, such as cardiac tissue, that may benefit from ablation.
Once a tissue is targeted for ablation, a catheter tip having one or more ablation electrodes may be positioned over the targeted tissue. The ablation electrodes may deliver RF energy, for example, supplied from a generator, to create sufficient heat to damage the targeted tissue. By damaging and scarring the targeted tissue, aberrant electrical signal generation or transmission may be interrupted. In some instances irrigation features may be provided in ablation catheters to supply cooling fluid in the vicinity of the ablation electrodes to prevent overheating of tissue and/or the ablation electrodes.
Existing ablation catheters do not have fiber optic imaging capability to provide a physician with real-time assessment of the targeted tissue, tissue contact with the catheter tip, depth and volume of lesion, and other information.
Existing ablation systems do not have information inputs that are derived from optical signals from an ablation catheter that has fiber optic imaging capability to better monitor, assess and control the ablation process in real time.
An ablation and monitoring system comprises a catheter, an optical coherence tomography (OCT) system, and an ablation generator. The catheter comprises one or more optical fibers to transmit a light beam to a tissue material and collect a reflected light from the tissue material. The OCT system is in optical communication with the catheter via the one or more optical fibers, providing the light beam to the one or more optical fibers and receiving the reflected light from the one or more optical fibers. The ablation generator is in electrical communication with the OCT system and with the catheter. The ablation generator provides radio frequency energy to the catheter for ablating the tissue material, monitors and assesses the ablation based on an information signal received from the OCT system.
An ablation and monitoring system comprises a catheter, an optical coherence tomography (OCT) system, and an ablation generator. The catheter comprises one or more optical fibers to transmit a light beam to a tissue material and collect a reflected light from the tissue material. The OCT system is in optical communication with the catheter via the one or more optical fibers, providing the light beam to the one or more optical fibers and receiving the reflected light from the one or more optical fibers. The ablation generator is in electrical communication with the OCT system and with the catheter. The ablation generator provides radio frequency energy to the catheter for ablating the tissue material, monitors and assesses the ablation based on an information signal received from the OCT system.
In one embodiment, the ablation and monitoring system also includes a fluid pump in fluid communication with the catheter and in electrical communication with the ablation generator. The fluid pump receives instructions from the ablation generator and provides fluid to the catheter to irrigate the catheter in accordance with the instructions.
The OCT system includes at least one common-path interferometer. In one embodiment, the OCT system is a multi-channel OCT system.
The catheter 110 of the present invention is an irrigated ablation catheter that also comprises optical fibers to transmit light to and collected reflected light from the tissue undergoing ablation. The catheter 110 is in optical communication with the OCT system 120, in electrical communication with the ablation generator 130, and in fluid communication with the fluid pump 140. The catheter 110 receives an optical signal from the OCT system 120 via one or more optical fibers. The optical fibers terminate at openings or transparent windows located in the distal portion of the catheter 110. The optical fibers are bi-directional. The optical fibers transmit the optical signals from the OCT system 120 through their ends into a tissue area and receive reflected optical signals which are sent back to the OCT system 120.
The ablation generator 130 comprises a processor 132, memory 134, a graphical user interface (GUI) 136, and a RF signal generator 138. The memory 134 includes a control module 135. The generator 130 receives the signal 125 from the OCT system 120. The image data from the signal 125 are displayed on the display of the GUI 136. The control module 135 processes information in the signal 125 to provide information including at least one of the following: lesion assessment (such as depth and volume of lesion), tissue contact assessment, signal change corresponding to tissue phase change, force sensing, thermal detection, tissue differentiation, and three-dimensional imaging. This information allows automatic or manual actions to be taken to prevent undesirable effects of ablation such as over-burning, formation of steam pop, etc. The information provided by the control module 135 is also displayed on the display of the GUI 136. The control module 135 also receives and processes user input received via the GUI 136.
The processor 132 executes instructions from the control module 135. In response to a user input requesting ablation, the control module 135 instructs the processor 132 to instruct the RF signal generator 138 to output an RF signal delivering RF energy for ablation to the catheter 110. The processor may also instruct the fluid pump 140 to pump fluid into the catheter 110 to irrigate it.
The OCT system 120 uses a reference optical signal identical to the optical signal originally transmitted to the catheter 110 to process the reflected optical signals into imaging and related information data signal 125, and sends the signal 125 to the ablation generator 130. In one embodiment, the OCT system 120 uses a frequency domain OCT technique that measures the magnitude and time delay of reflected light in order to construct depth profiles in the tissue being imaged. The OCT system 120 includes a high-speed swept laser, and a fiber-based Michelson interferometer with a photodetector. The OCT system 120 uses advanced data acquisition and digital processing techniques to enable real-time video rate OCT imaging. In one embodiment, the OCT system 120 employs common-path interferometers for OCT imaging. In a common-path interferometer, the reflection from the fiber end face is used as a reference beam. As such, the reference beam and reflection lights from an imaging object propagate in the same fiber. The common-path interferometer is very stable and substantially insensitive to the surrounding temperature, vibration, and even fiber bending or twisting. Stability of the interferometer is critical for OCT imaging in catheter applications during ablation in a heart cavity, with surrounding vibrations from the heart beating, the blood flowing, and with the pressure and temperature changing.
The catheter tip 340 may be manufactured separately and attached to the rest of the elongated catheter body. The catheter tip 340 may be fabricated from suitable biocompatible materials to conduct ablation energy, such as RF energy, and to withstand temperature extremes. Suitable materials for the catheter tip include, for example, natural and synthetic polymers, various metals and metal alloys, naturally occurring materials, textile fibers, glass and ceramic materials, sol-gel materials, and combinations thereof. In an exemplary embodiment, the catheter tip 340 is fabricated from a material including 90% platinum and 10% iridium.
Referring to
Optical scanning may be used to achieve a 2-dimensional or 3-dimensional imaging. When optical scanning is very difficult to implement or not economical, a fiber array or multi-channel OCT may be used to simulate the scanning to achieve a 2-dimensional or 3-dimensional imaging.
One way to control the strength of the reference beam to optimize the interference signal is to use angle-cleaved fibers. To reduce the reflection at the optical fiber end face 508 to about 1 percent, the tip of the optical fiber 506 may be angle-cleaved. It is noted that, when the optical fiber 506 is cleaved at 90 degrees, this results in a reflection of approximately 4 percent.
Another way to control the strength of the reference beam is to use Gradient-index (GRIN) fiber lens. GRIN fiber lens can be used to focus the laser beam to illuminate the imaging object and to collect more scattering lights from the imaging object to improve the signal-noise ratio (SNR). The length of GRIN lenses can be used to control the strength of the reference beam to optimize the interference signal, i.e., the OCT signal. Experiments showed that GRIN lenses provide a more controllable method for optimizing the interference signal than the method of angle-cleaved fibers.
With the common path interferometer system shown in
where r0 is the amplitude reflectance at the fiber end face, rz is the amplitude reflectance at depth z of the imaging object, l0 is the central wavelength, Dl is wavelength sweeping range, and fsweep is the wavelength sweeping rate.
For simplicity, a top-hat spectral profile f(dl) is used to only consider the intensity I within the range of the spectral profile f(dl):
where Dlfwhm is the laser instantaneous linewidth.
Simplifying Eq. (1), and ignoring the DC component r02+rz2, the intensity of the interference signal can be expressed as:
By applying a fast Fourier Transform (FFT) to Eq. (3), it can be derived that the Fourier frequency F is directly proportional to the depth z and the amplitude of the Fourier component at Fourier frequency F is proportional to the amplitude reflectance rz. It is noted that the re-clocking operation to achieve an equidistant spacing in frequency is required for the data stream when it is captured in equidistant time spacing.
where F is the Fourier frequency, and Λ(F) is the amplitude of the Fourier component at Fourier frequency F.
The OCT system of the present invention provides monitoring and assessment of tissue contact. When the optical fiber 506 touches the imaging object 522, F=0. Equation (4) shows that the scattering from depth z can be explored by the Fourier frequency F and the amplitude A(F) of the Fourier component at Fourier frequency F.
The OCT system of the present invention provides imaging of the ablation area, lesion assessment, tissue differentiation, and three-dimensional imaging. When the tissue is ablated or charred, the light reflectance rz or scattering coefficient will be increased. The strength of the Fourier components will be significantly increased accordingly. The changes of tissue shape cause the imaging pattern to change.
The OCT system of the present invention provides warning for steam pop. It is very important to avoid steam pop during ablation since the presence of steam pop indicates that the tissue is seriously damaged. Before the steam pop actually happens, there is a lot of micro-pops generated by the overheating. The micro-pops will significantly increase the light scattering and thus can be monitored by the strength of the Fourier components, i.e., OCT intensity. Experiments have shown that OCT intensity is very sensitive to the presence of micro-pops. When micro-pops are detected, a warning for a steam pop is generated, and the ablation generator 130 reduces its ablation power and beeps for attention.
The OCT system 600 comprises an optical fiber 601, an optical switch 602, five optical fibers 604 which are connected via the fiber optic connector 270 (see
Referring to
While the invention has been described in terms of several embodiments, those of ordinary skill in the art will recognize that the invention is not limited to the embodiments described, but can be practiced with modifications and alterations within the spirit and scope of the appended claims. The description is thus to be regarded as illustrative instead of limiting.
This application claims the benefit of U.S. Provisional Application Ser. No. 61/135,872, filed on Jul. 23, 2008, entitled “Ablation and monitoring system including a fiber optic imaging catheter and an optical coherence tomography system”, which is hereby incorporated by reference in its entirety.
Number | Date | Country | |
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61135872 | Jul 2008 | US |