The present disclosure generally provides Magnetic Resonance Imaging (MRI) receiver coil devices, including a MRI receiver coil or MRI receiver coil arrays, and methods for manufacturing the same, and more particularly MRI receive coil devices useful in MRI guided High Intensity Focused Ultrasound (HIFU) therapy techniques.
In MRI, very small signals are created via excitation of hydrogen protons in the bore of an MRI machine. These signals are picked up on receiver coils adjacent to the patient inside the machine and processed to yield an image. The higher the signal-to-noise (SNR) the receiver coils can produce, the faster the scan time can be and the higher the quality of images that can be produced. MRI receiver coil arrays provide a better signal-to-noise-ratio and field of view over standard single coil receivers. However, this gain is lost when the surface coil array is at an improper distance from the patient.
MRI guided High Intensity Focused Ultrasound (HIFU) is a therapy technique used to ablate tissue or activate heat sensitive medication inside a patient's body with acoustic energy while being tracked (i.e., guided) with images from an MRI scanner. This technique successfully treats uterine fibroids, drastically reduces the pain from bone cancer metastases, and dramatically reduces essential tremor. This quickly expanding field has shown promise for the treatment of other conditions including brain conditions, where classical imaging techniques struggle to guide without using an invasive borehole in the patient's head. Currently, a major limiting factor of MRI guided HIFU is the precision and speed of the imaging hardware used to track treatment areas. Specifically, the state-of-the-art receive coils in a MRI scanner are incompatible with the ultrasonic transducer, so a less effective body coil with lower image quality must be used.
A more effective solution is a surface coil, which has extremely high signal to noise ratio and enables accurate temperature monitoring at high resolution. A surface coil is only sensitive to tissue close to the coil, so it must be placed between the transducer and the patient to be effective. However, to treat an entire target, the transducer is moved in the water bath, which would pass acoustic energy directly through different parts of the surface coil. Ultrasonic energy easily scatters and attenuates in the thick fiberglass reinforced boards, solder, and porcelain capacitors commonly used in coil construction (
There is therefore a need for MRI receiver coil devices that provide increased SNR, and which are compatible with HIFU techniques and instruments. There is also a need for cost-effective fabrication processes for forming such receiver coil devices.
The present embodiments provide surface coil arrays that are transparent to acoustic energy and which drastically increase image quality and temperature estimation. Advantageously, these device embodiments can be used in MRI guided HIFU of the head or body, specifically for the treatment of brain conditions (including essential tremor), cancer, and uterine fibroids. In certain aspects, the device is completely waterproof and able to be submerged for extended periods of time. Imaging aquatic animals may be possible without removing them from water.
According to an embodiment, a flexible magnetic resonance imaging (MRI) receive coil device for use in a MRI guided High Intensity Focused Ultrasound system is provided. The MRI receive coil device typically includes a flexible substrate having a first surface and a second surface opposite the first surface, and a pattern of conductive material formed on one or both of the first and second surfaces, the pattern including the at least one receive coil and the at least one capacitor, wherein the flexible substrate comprises a dielectric plastic material selected from the group consisting of a polyimide (PI) film, a polyethylene (PE) film, a polyethylene terephthalate (PET) film, a polyethylene naphthalate (PEN) film, a polyetherimide (PEI) film, a polyphenylene sulfide (PPS) film, a polytetrafluoroethylene (PTFE) film, and a poly ether ketone (PEEK) film. In certain aspects, the MRI receive coil device further includes at least one layer of hydrophobic material covering the at least one receive coil and the at least one capacitor. In certain aspects, the at least one receive coil and the at least one capacitor are substantially transparent to ultrasound frequencies. In certain aspects, the MRI receive coil device further includes at least one layer of material covering the at least one receive coil and the at least one capacitor, wherein the at least one layer of material has an acoustic impedance between an acoustic impedance of water and an acoustic impedance of the conductive material. In certain aspects, a thickness of the MRI receive coil device is less than about 0.1 mm (e.g., between about 0.01 mm and 0.1 mm).
Reference to the remaining portions of the specification, including the drawings and claims, will realize other features and advantages of the present invention. Further features and advantages of the present invention, as well as the structure and operation of various embodiments of the present invention, are described in detail below with respect to the accompanying drawings. In the drawings, like reference numbers indicate identical or functionally similar elements.
The detailed description is described with reference to the accompanying figures. The use of the same reference numbers in different instances in the description and the figures may indicate similar or identical items.
The following detailed description is exemplary in nature and is not intended to limit the invention or the application and uses of the invention. Furthermore, there is no intention to be bound by any expressed or implied theory presented in the following detailed description or the appended drawings.
Turning to the drawings, and as described in greater detail herein, embodiments of the disclosure provide surface coil arrays that are transparent to acoustic energy and which drastically increase image quality and temperature estimation.
In certain embodiments, screen printing techniques are used to make a coil array for an MRI scanner that is extremely thin (e.g., less than 0.1 mm) and renders the coil array nearly invisible to MRI guided High Intensity Focused Ultrasound (HIFU), a therapy used to ablate tumors inside the human body. This allows for the coil to be inserted directly in the beam path of the ultrasonic energy, drastically increasing the quality of images used to guide the treatment. (see,
In certain embodiments, MRI coils are fabricated on a flexible substrate or thin film. Examples of flexible substrate materials include thin films of PET (Polyethylene terephthalate), Kapton (polyimide or PI), PEN (Polyethylene napthalate) sheet, or PEEK (Polyether ether ketone). Prior to printing, the substrate may be preheated to the temperature experienced during annealing to relieve any stress and prevent distortion in future processing steps. The substrate is then allowed to cool to room temperature before proceeding onto the printing process.
Printing the conductive layers is accomplished in certain embodiments by printing, e.g., screen-printing a conductive ink, such as a silver microflake ink, onto the substrate followed by annealing, e.g., 125° C. anneal for 15 min. Thereafter, the substrate is overturned and the overturned substrate is loaded back into the screen printer to receive the same patterning on the back. A schematic of the processing steps is shown in
Traditional surface coils are not compatible with MRI guided ultrasound therapy, but the coils of the present disclosure advantageously fill that performance gap and would aid doctors in observing the treatment area with higher resolution than ever before (including with higher resolution in time), potentially reducing complications and surgery time.
Drastically improving the utility of MRI guided ultrasound therapy would greatly increase the market for this therapy, bringing life changing treatment to more patients.
These MRI guided ultrasound therapy compatible coils drastically increase the resolution of the images doctors use to monitor the treatment at a higher monitoring rate. These coils interface in the same way other traditional surface coils interface with the scanner, requiring little to no retrofitting of existing equipment for their use. Ultrasonic image guiding is a potential alternative to an MRI guided image (and would not require a receive array), however this tracking technique does not work well though the skull, so MRI guided ultrasound therapy is still a better alternative for the head.
The present embodiments provide surface coil arrays that are transparent to acoustic energy and which drastically increase image quality and temperature estimation. One way to fabricate an acoustically transparent coil is to use very thin polymer-based materials and solution processed conductors. These materials can be selected to have acoustic properties close to that of water reducing the amount of interaction with the acoustic energy. Such coils may be fabricated using screen-printed conductive inks on thin plastic substrates. A surface coil is a resonant loop of wire tuned to resonate at the Larmor frequency of the scanner using in-series capacitors. To fabricate these coils, solution processed conductors are selectively deposited in a loop on a flexible plastic substrate with tuning capacitors. Reference is made to U.S. Provisional Application Ser. No. 62/469,253, filed on Mar. 19, 2017, which is incorporated by reference in its entirety, for additional and supplemental information regarding MRI receiver coils, fabrication processes and materials.
In certain embodiments, polytetrafluoroethylene (PTFE), polyethylene (PE), polyimide (PI), polyphenylene sulfide (PPS), polyetherimide (PEI), polyether ether ketone (PEEK), polyethylene naphthalate (PEN) and polyethylene terephthalate (PET) are used as substrate materials.
In one embodiment, DuPont 5064 H silver ink is used for the conductive portions of the coil. Other conductive inks or conductive materials may be used for the conductive portions of the coil. After 24 hours of water submersion, the samples made of the DuPont 5064 H silver ink did not experience any significant change in resistivity; showing resistivity of 16±2 μohm-cm before and after. Furthermore, the surface roughness of the ink did not change, maintaining a root mean squared (RMS) surface roughness of 1.3±0.2 μm both times.
The coil materials used should also transmit a high percentage of incident acoustic energy without distortion. Local surface burns, damage to the transducer, and low focal heating may occur if the coils reflect or attenuate a significant amount of the acoustic energy. To characterize the films, a transducer passes acoustic power through test films to a hydrophone that records the acoustic intensity, as illustrated in
The acoustic absorption of PEEK is characterized in the thickness range of 50 μm to 254 μm to determine the optimal thickness. All film thicknesses are within 10% of the reported values.
As a result, a PEEK film thickness of 76 μm was selected to maintain acoustic transparency, handling robustness, and ease of processing. Other thicknesses of PEEK, e.g., ranging from 10 μm to 300 μm or greater, may be used, as may a variety of thicknesses of other materials as will be appreciated by one skilled in the art.
The acoustic properties of solution-processed materials are not commonly available. To determine the acoustic impedance of the conductive silver ink acoustic power was transmitted though several thicknesses (3-56 μm) of the silver film deposited on the 76 μm of PEEK film.
To protect the patient from any DC bias that might exist on the coil, an electrically isolating film is deposited over the conductive traces in an embodiment. This film should be acoustically transparent in addition to providing high electrical breakdown strength. A PTFE film was selected as an appropriate material for further characterization and optimization. Test films with 75, 127, 391, and 520 μm in thickness of PTFE were measured for transmission across a span of common MRI guided ultrasound therapy frequencies.
The optimized material stack of a 76 μm thick PEEK substrate encapsulated in 76 μm of PTFE with 15 μm of the printed conductor is further characterized by comparing it to the traditional materials used in coil construction.
To provide a comparison to a non-printed approach, two commonly available thin copper clad substrates were also evaluated using a hydrophone setup. Commercially available 9 μm copper on top of 50 μm polyimide (Pyralux AP 7156E) and 35 μm copper on top of 50 μm polyimide (Pyralux AP 9121 R) were both encapsulated in 76 μm of PTFE and characterized for comparison to the printed coil. The transmitted acoustic power for these films is shown in
To show that the coils of the present embodiments provide higher SNR than what is currently available in clinical therapy to better guide the procedure, a 4-channel array was fabricated using the optimized material stack of PEEK, PTFE, and silver ink. The SNR of the array is compared to that of the currently used body coil of a 3 T scanner on a gel phantom inside the head transducer.
To show the clinical SNR gains that a printed coil array according to the present embodiments can provide, breath-hold abdominal images were acquired with an 8-channel coil array wrapped around the abdomen of a volunteer. The comparison between the abdominal images from the body coil and the transparent arrays in
The array and body coil are used to track ultrasonic heating inside a gel phantom.
As shown in
In order to verify that the coils are not absorbing any significant amount of energy that could pose a risk to any nearby tissue, an additional 1.5 cm thick agar gel disk was placed underneath the coil completely surrounding it in material that MR thermometry could be used to measure temperature increase. Next, 54 W of acoustic power was transmitted though the gel stack for 10 seconds with and without the coil present to see if there is any measureable increase temperature near the coil.
To demonstrate the proof-of-concept of all system elements together, a 4-channel array was used to track the heating of brain tissue inside the head transducer. A 3D printed ABS plastic skull that mimics bone and containing an ex-vivo bovine brain suspended in a gel was used as a skull phantom.
The presently disclosed array embodiments advantageously outperform the currently used body coil while tracking the heating point inside the skull without significantly attenuating or visibly distorting the acoustic power.
Octagonal coils 8.75 cm in diameter are screen printed onto a plastic substrates using a conductive silver ink (e.g., Dupont 5064 H) patterned through a 165 count stainless steel mesh (e.g., Meshtec). Individual array coils are tuned (e.g., tuned to 127.73 MHz) by changing the area of the in-series capacitors. Coils are then laminated (e.g., in a PTFE film (Professional Plastics)) for water protection, abrasion resistance, and volunteer safety. Coils are connected to a non-printed interface board that contains an inductor and diode to block the coil during the high power RF transmit. A half wavelength long piece of RG-316 non-magnetic cable connects to a box containing preamplifiers (MR Solutions) which then connects to the scanner and/or other processing circuitry or computer.
Reference is also made to U.S. patent application Ser. No. 14/166,679 (US Publication No. 2014/0210466 A1), and U.S. Provisional Application Ser. No. 62/469,253, filed on Mar. 9, 2017, which are each incorporated by reference in its entirety, for additional and supplemental information regarding MRI receiver coils, fabrication processes and materials.
All references, including publications, patent applications, and patents, cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein.
The use of the terms “a” and “an” and “the” and “at least one” and similar referents in the context of describing the embodiments (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The use of the term “at least one” followed by a list of one or more items (for example, “at least one of A and B”) is to be construed to mean one item selected from the listed items (A or B) or any combination of two or more of the listed items (A and B), unless otherwise indicated herein or clearly contradicted by context. The terms “comprising,” “having,” “including,” and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to,”) unless otherwise noted. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the disclosed embodiments and does not pose a limitation on the scope of the disclosure unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the embodiments.
Exemplary embodiments are described herein. Variations of those exemplary embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the embodiments to be practiced otherwise than as specifically described herein. Accordingly, the scope of the disclosure includes all modifications and equivalents of the subject matter recited herein and in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the disclosure unless otherwise indicated herein or otherwise clearly contradicted by context.
This patent application is a Divisional of U.S. application Ser. No. 16/656,380 by Lustig et al., entitled “MAGNETIC RESONANCE IMAGING (MRI) RECEIVE COIL COMPATIBLE WITH MRI GUIDED HIGH INTENSITY FOCUSED ULTRASOUND (HIFU) THERAPY,” filed Oct. 17, 2019, which is a continuation of PCT Application No. PCT/US2018/028541 by Lustig et al., entitled “MAGNETIC RESONANCE IMAGING (MRI) RECEIVE COIL COMPATIBLE WITH MRI GUIDED HIGH INTENSITY FOCUSED ULTRASOUND (HIFU) THERAPY,” filed Apr. 20, 2018, which claims priority to U.S. Provisional Patent Application No. 62/487,900 by Lustig et al., entitled “MAGNETIC RESONANCE IMAGING (MM) RECEIVE COIL COMPATIBLE WITH MRI GUIDED HIGH INTENSITY FOCUSED ULTRASOUND (HIFU) THERAPY,” filed Apr. 20, 2017, each of which is incorporated herein by reference in its entirety.
This invention was made with Government support under Grant Number R21EB015628, awarded by the National Institute of Health. The Government has certain rights in this invention.
Number | Date | Country | |
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62487900 | Apr 2017 | US |
Number | Date | Country | |
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Parent | 16656380 | Oct 2019 | US |
Child | 18358754 | US |
Number | Date | Country | |
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Parent | PCT/US2018/028541 | Apr 2018 | US |
Child | 16656380 | US |