Patent Application
20080221448
The invention relates generally to medical devices. More particularly, the present invention relates to ultrasound image-guided delivery of therapeutic tools for minimally invasive medical procedures.
Minimally invasive techniques are widely used in medical procedures including cardiac, vascular, joint, abdominal, and spinal surgeries and interventions. In minimally invasive interventions, a surgical or medical tool is introduced into the body through a natural body opening or small artificial incisions. A separate endoscopic camera is typically used to obtain optical images inside of the body to help perform the minimally invasive procedure. Minimally invasive medical techniques have several advantages over open surgeries, such as minimizing incision size and trauma, and reducing recovery time. However, existing minimally invasive techniques suffer from restricted vision. Particularly, for cardiac or vascular interventions, blood poses difficulties for optical imaging.
Under conditions when optical imaging is inadequate, ultrasound imaging can be used. Existing intravascular or endoscopic ultrasound imaging devices, however, typically only provide side-looking cross-sectional images. For inserting catheters or other medical devices 20 into a body, side-looking images are inadequate if there is blockage along the direction of insertion. For example, in coronary catheterization, totally occluded or heavily stenosed vessels make it impossible to introduce catheters with strictly side-looking capabilities.
Many existing minimally invasive medical instruments are also typically limited to image only or therapy only capabilities. With separate instruments for imaging and therapy, a medical interventionist would have to either separately introduce the imaging and therapy instruments or introduce multiple catheters or tubes. In the former scenario, the accuracy and guidance capability would be limited and in the latter scenario, the size of the openings must be large enough to accommodate multiple tubes.
Recently, high intensity focused ultrasound (HIFU) techniques have been developed for medical procedures, such as tissue destruction. Traditional HIFU techniques rely on cavitation effects or thermal effects as mechanisms for tissue destruction. Low frequency HIFU is naturally preferred to induce cavitation. Even when thermal effects are desired to be the dominant mechanism of tissue destruction, low frequencies are still preferred because of the increased attenuation at higher frequencies. For at least these reasons, existing HIFU devices for medical procedures typically operate at low frequencies. However, existing low frequency HIFU devices typically do not offer sufficient focal intensity for tissue ablation, especially for HIFU transducers with small diameters. Imaging ultrasounds also typically operate at low frequencies due to the increase in attenuation at higher frequencies.
The present invention addresses the problem of imaging and applying therapy in minimally invasive interventions.
The present invention is directed to image-guided therapy using an imaging ultrasound array and a therapeutic tool positioned on the same instrument. The image-guided therapy device includes an elongate tubular member, such as an intravascular or intracardiac catheter, having an inner lumen. The elongate tubular member is dimensioned to fit inside a body lumen. An annular ultrasound array, having a central lumen formed by the annulus of the array, is positioned on a distal end of the elongate tubular member such that the central lumen of the annular ultrasound array is at least partially aligned with the inner lumen of the elongate tubular member. The elements of the annular ultrasound array include multiple capacitive micromachined ultrasonic transducers (cMUTs). The annular ultrasound array is capable of real-time forward-looking imaging. Importantly, the image-guided therapy device also includes a therapeutic tool positioned on the distal end and inside of the inner lumen of the elongate tubular member.
Minimally invasive interventions can be performed by inserting the image-guided therapy device into a body lumen or cavity, imaging a region inside the body lumen by using the annular ultrasound array, guiding the therapeutic tool to a focus spot based on the imaging, and applying therapy to the focus spot by using the therapeutic tool. The interventions can also include scanning over an area inside the body lumen or delivering an ultrasound contrast agent through the inner lumen of the elongate tubular member to enhance the imaging.
In a preferred embodiment, the cMUTs of the imaging annular ultrasound array are operable at a high frequency that is equal to or greater than about 10 MHz. Preferably, the therapeutic tool is a HIFU device, also operable at a high frequency that is equal to or greater than about 10 MHz. The HIFU device can have a diameter of about 2 mm and a focal distance of about 2 mm. The HIFU device can include a single focused transducer element or a phased array transducer. The elements of the phased array can include multiple HIFU cMUTs.
The therapeutic tool can also include medical instruments in replacement of or in addition to the HIFU device, such as a laser for tissue ablation, a device for radio-frequency ablation, a biopsy needle, an atherectomy device, or any other surgical tool. When used in combination with the HIFU device, a biopsy tool can be used to determine the efficacy of the HIFU device. An optical fiber can also be used to perform optical imaging. Correlations of the optical and acoustic imaging can be used to determine the efficacy of a therapeutic tool, particularly a HIFU device.
The present invention together with its objectives and advantages will be understood by reading the following description in conjunction with the drawings, in which:
Minimally invasive surgeries and interventions require delivery of a therapeutic tool through natural body openings or small artificial incisions. However, many instruments and methods to conduct these interventions suffer from restricted vision. Below is a detailed description of methods and devices for image-guided therapy delivery usable in minimally invasive surgeries and interventions.
Located at the distal end of the elongate tubular member are the acoustic imaging and therapy components of the image-guided therapy device 100. An annular ultrasound array 130 is positioned on the distal end for real-time forward-looking imaging. The annulus of the annular ultrasound array 130 defines a central lumen, wherein the central lumen of the annular ultrasound array 130 and the inner lumen 125 of the elongate tubular member are at least partially aligned. Positioned inside of the inner lumen 125 is a therapeutic tool 150. Optionally, electronic components and cabling 180 can also be placed inside the inner lumen 125 or between the inner wall 120 and the outer wall 110.
As shown by
It is important to note that the elements 135 of the annular ultrasound array 130 are preferably capacitive micromachined ultrasound transducers (cMUTs). The annular ultrasound array 130 can contain any number of elements. Using an array of cMUTs, the image-guided therapy device 100 has three-dimensional forward-looking capabilities. The dashed lines with arrows 140 in
Furthermore, the combination of high resolution imaging and real-time feedback enables a medical interventionist operating the device 100 to precisely position the therapeutic tool 150. Additionally, with a forward-looking annular ultrasound array 130 and a therapeutic tool 150 on the same device 100, the medical interventionist can scan an area of the inner body region 170, where scanning involves imaging the area and applying therapy to some or all of the area. With separate devices for imaging and therapy, an interventionist would be required to repeatedly remove and introduce multiple separate devices or introduce multiple catheters into the same body lumen.
In a preferred embodiment, the therapeutic tool 150 includes a high intensity focused ultrasound (HIFU) device. The HIFU device can operate at a high frequency equal to or greater than about 10 MHz. In HIFU devices, focusing gain increases with frequency. More particularly, the size of the focus spot of the HIFU device is related to the acoustic wavelength (λ) and the focal distance (z), defined as the distance from the HIFU device to the focus spot. The focus spot size is also inversely related to the diameter (d) of the HIFU device. These qualitative relations show that a decrease in λ (or, equivalently, an increase in frequency) would decrease the focus spot size. By decreasing the size of the focus spot, the focusing gain increases, thereby producing a large focal intensity necessary for certain therapeutic applications, such as tissue ablation or coagulative necrosis. Furthermore, a smaller focus spot may be desired for precise application of therapeutic acoustic energy.
Increasing the diameter of the HIFU device can also reduce the size of the focus spot and increase the total available power. Many minimally invasive interventions, such as intravascular or intracardiac procedures, however, require small devices to fit inside certain body lumens. The diameter of the HIFU device is limited in these restrictive environments as the size of the body lumen constrains device dimensions. The small size and large focal intensity requirements can be overcome by operating a small diameter HIFU device at high frequency. At high frequencies, the focus spot size can be greatly reduced giving the required large focal intensity. However, increasing the frequency of the HIFU device also increases attenuation. The competition between a decrease in spot size (i.e. an increase in focusing gain) and an increase in attenuation introduces an optimal frequency. The optimal frequency can be measured or found based on calculations or simulations.
In fact, it is found that a 2 mm diameter HIFU device operating at its optimal frequency of 60 MHz results in a focal intensity of about 8 kW/cm2 at a focus spot with a diameter of about 0.025 mm at a focal distance of about 2 mm. This focal intensity is comparable to the intensity from a 50 mm diameter HIFU operating at 2.5 MHz, resulting in a focus spot with a diameter of about 0.6 mm at a focal distance of about 50 mm. In a preferred embodiment, the high frequency HIFU device has a diameter of about 2 mm and a focal distance of about 2 mm. When operated at about 10 MHz, the focus spot diameter of the preferred HIFU device is about 0.15 mm. Alternatively, other dimensions of the HIFU device and operating frequencies can be used.
It is important to note that the cMUTs of the annular ultrasound imaging array 130 are operable at high frequency, including frequencies equal to or greater than about 10 MHz. High frequency imaging increases the resolution of the annular ultrasound array 130. The high resolution may be necessary due to the small focus spot from the high frequency HIFU device. Optionally, to enhance the quality of the acoustic imaging, one or more ultrasound contrast agents can be introduced to the inner body region 170. The ultrasound contrast agent can be delivered through the inner lumen 125 of the elongate tubular member.
In addition to a HIFU device, the therapeutic tool 130 of the image-guided therapy device 100 can include other surgical tools, such as a laser for tissue ablation, a device for radio-frequency ablation, a biopsy needle, an atherectomy device, or any other surgical tool.
As one of ordinary skill in the art will appreciate, various changes, substitutions, and alterations could be made or otherwise implemented without departing from the principles of the present invention, e.g. other surgical tools can be positioned inside the inner lumen and the imaging ultrasound array can be configured in any geometry. Accordingly, the scope of the invention should be determined by the following claims and their legal equivalents.
This application claims priority from U.S. Provisional Patent Application 60/906,097 filed Mar. 7, 2007, which is incorporated herein by reference.
This invention was made with Government support under contract NIH awarded by 1-RO1-HL7647 and grant number GPEDC0013B from OHSU. The Government has certain rights in the invention.
| Number | Date | Country | |
|---|---|---|---|
| 60906097 | Mar 2007 | US |
