Patent Application
20230293038
This disclosure relates to magnetic resonance imaging (MRI) guided transcranial focused ultrasound (tFUS) therapy systems and methods, and more specifically to an MRI receive coil array that is tightly integrated with the tFUS therapeutic transducer device.
High intensity focused ultrasound (HIFU) had been proposed and demonstrated as early as in 1957 to deliver focused ultrasound energy from outside of the body to a focal spot in the targeted area inside the body for thermal treatment. The temperature of the target lesion can be raised to above 60 degrees Celsius (° C.) in a few seconds causing tissue to undergo necrosis. Thus, HIFU has been used as one of several thermal ablation modalities for various tumors, even though it was initially applied to brain for neurological disorders. Comparing to other traditional surgical operations, HIFU offers a minimum invasive, outpatient alternative with no incision or exposure to ionization radiation, minimum side effect and thus fast recovery. However, the applications of HIFU had not been widely accepted clinically until the use of Magnetic Resonance Imaging (MRI) to guide and monitor tissue temperature and degree of damage.
Disclosed is a Magnetic Resonance Imaging (MRI) receiver coil device for use in an MRI guided transcranial focused ultrasound (tFUS) system, and methods for manufacturing the same. The described receiver coil device is wearable, hydrophobic, and ultrasound transparent, and comprises an MRI receiver coil or MRI receiver coil array. In one embodiment, an MRI receiver coil device includes a first inner layer of flexible substrate made of a hydrophobic and ultrasound transparent thin film and fabricated to conform to fit to a certain 3D shape, such as that of the head of a subject or individual patient. A pattern of conductive material may be formed on a first surface of the first inner layer. The pattern may include at least one receiver coil and at least one capacitor, and the conductive traces so formed may comprise multiple conducting layers and at least a layer of dielectric plastic material. A second thin-film outer layer of the same material of the first inner layer is formed over the conductive pattern. The three-dimensional (3D) geometric configuration of the receiver coil device may conform to the 3D geometric configuration of a head model rendered from a 3D image data set of the individual patient. In an alternate embodiment, the thin-film coil device is fabricated upon a fixed 3D shape, and a gel-like ultrasound transparent material is used to fabricate an individually shaped thin layer of gel pad lining that is conformed to individual patient's head on the inside and to the fixed-shape thin-film coil device on the outside. The described methods may utilize 3- to up to 6-dimensional printing technique or other precision multi-dimensional fabrication techniques.
Various embodiments are described and illustrated herein with reference to the drawing in which like items are indicated by the same reference numeral, and in which:
In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present disclosure. The present disclosure may be practiced without some or all these specific details. For the purpose of clearly describing the present disclosure, well known process operations generally practiced in the art are not described in detail so as to not unnecessarily obscure the described concepts. While some concepts will be described in conjunction with the specific embodiments, it will be understood that these embodiments are not intended to be limiting. On the contrary, it is intended to cover alternatives, modifications, and equivalents as may be included within the spirit and scope of the present disclosure as defined by the appended claims.
For example, the techniques of the present disclosure will be described in the context of focused ultrasound therapy on various body parts, such as the head and brain. However, it should be noted that the techniques and mechanisms of the present disclosure apply to various other body parts, such as the abdomen or torso. Various techniques and mechanisms of the present disclosure will sometimes be described in singular form for clarity. However, it should be noted that some embodiments include multiple iterations of a technique or multiple instantiations of a mechanism unless noted otherwise.
The advantage of magnetic resonance imaging (MRI) to guide thermal therapy goes beyond its ability to provide fast and accurate temperature imaging of the treatment target inside the patient's body during ablation procedures. As a proven imaging modality with the best soft tissue contrast, MRI scans are used to plan the treatment, to assess the treatment outcome immediately after, and for long-term follow-up. Moreover, MRI can provide various additional contrast mechanisms such as those for protein denaturation and lesion formation to enable more control over the treatment outcome even during the ablation procedure. Another MRI approach, magnetic resonance acoustic radiation force imaging (MR-ARFI), can detect small focal displacements induced by low-power ultrasound pulses. Comprehensive MRI thermometry, in conjunction with other acoustic measuring techniques, has been proven to be the ideal imaging modality to guide and navigate various focused ultrasound (FUS) therapeutic procedures, including but not limited to high intensity focused ultrasound (HIFU) ablation procedures.
Several MR-guided HIFU devices have been developed, mainly for abdominal target areas. Existing methods have utilized a general-purpose MRI-compatible robotics system to move and operate the therapeutic or diagnostic devices inside the MRI bore. Other methods have utilized a three-axes motion stage to position the HIFU transducer in an unsealed water tank, which can be put onto the MRI patient couch. An arc structure may hold the HIFU transducer and to allow mechanical movement control up to 6 degrees of freedom while being seated on the patient couch inside the bore of existing MRI systems. An MRI receive-only phased array coil may be used to improve MRI signal-to-noise ratio (SNR). A smaller coil gets higher SNR with smaller sensitivity volume, but, comparing the SNR over same region of interest, combining an array of multiple small coils exhibits better SNR than a big coil alone. Another advantage of a multiple-channel coil array is that it can be used for parallel imaging to accelerate the MRI scan. For example, a 32-channel head array coil arranged in a soccer-ball pattern with overlapping loops may demonstrate higher SNR and capability of high acceleration factor in parallel imaging.
For abdominal HIFU applications under MRI guidance, it is essential for the MRI receiving coil configuration to integrate with the HIFU transducer device which is closely positioned on the treated anatomy and can be moved during the treatment to focus on sequential sonication points in a target region of interest. An N+1 multiple-channel configuration may be used to take advantage of a hollow loop coil that moves with the transducer HIFU device while allowing the ultrasound beams to go through un-impeded as well as serving as additional parallel imaging channel to a multiple-channel (N) coil array that stays fixed in position.
However, the aforementioned systems are not designed for application within the brain. In recent years, focused ultrasound, also under MRI navigation, has been applied to treat various neurological and psychiatric disorders in a transcranial focused ultrasound (tFUS) transducer array configuration. Such a tFUS transducer device is placed on top of the patient's head, and equipped with multiple transducer elements transmitting multiple ultrasound beams through a water bath to penetrate the skull. In this transcranial configuration, tight integration of MRI head coil array with tFUS transducer device is critical for the demanding treatment precision in order to take full advantage of MRI capability for image navigation, including: targeting, positioning, aiming, real-time monitoring and dose control, immediate prognosis, and follow up. Not only does advanced MRI technology play a pivotal role in targeting defective neural circuitry to be treated in support of the soft tissue contrast provided by usual anatomic structural images, but thermometry and/or acoustic dosage monitoring have also become increasingly demanding in speed and sensitivity.
MRI guided tFUS was approved by FDA for the treatment of essential tremor in 2016, and Parkinson's disease with main symptom of tremor in 2018. However, during treatment, MRI scans can only be performed with either the large size whole body MRI coil or a simple two-loop MRI coil inserted in the water bath of the tFUS transducer device. A typical MRI multiple-channel head coil is itself a helmet like structure and cannot be placed simultaneously with the tFUS transducer helmet. Thus, MRI images may be obtained prior to ultrasound treatment. However, where the images used for targeting or treatment planning are acquired with head coil prior to treatment, the actual position of the head during treatment when tFUS transducer is in place could exhibit a mis-registration on the images used for planning. A stereotactic frame is required and anchored onto patient skull to ensure the precision of the treatment target locations. Additionally, once the tFUS is in place, MRI sensitivity can no longer be fully realized with body coil or simple two-loop coil let alone full signal-to-noise ratio (SNR) and acceleration performance.
Some methods have proposed using a soft 8-channel coil wrapped around the lower part of the head and face of the patient and positioned external to the water bath of the tFUS transducer placed over the top of the head, in an effort to minimize direct interference between the magnetic field of view of the coil and the acoustic field of coverage from the hemispherical tFUS transducer. Because the coil is placed externally to the tFUS transducer, this configuration prevents complete imaging of certain substantive portions of the brain that may be the target of treatment. Additionally, even though the thin wire coil exhibited high acoustic transparency, the fabric like material used to embed thin wire coil elements and wrap around the patient's face is air permeable and therefore not hydrophobic or ultrasound transparent. Thus, the coil cannot be immersed in the water bath within the tFUS transducer, or otherwise placed within the tFUS transducer, to improve imaging of the treatment target.
However, with proper choice of thin enough layers of conducting and dielectric material for coil fabrication, a coil can be placed within the tFUS transducer and can yield low attenuation of the ultrasound beams through the coil traces for tFUS transducer. The present disclosure provides a configuration for a thin-film coil array that is positioned within a tFUS transducer device that provides improved signal-to-noise-ratio (SNR) performance and allows for parallel imaging acceleration to enable a high temporal resolution for the navigation MRI scans. The described systems and methods achieve a tight integration of the MRI coil array into the tFUS transducer device, while preserving or satisfying the following requirements:
In a nutshell, the described systems and devices may include or implement the following elements:
The fabrication technique used for this thin-film layers and conducting material is not the silk-screen planar printing typically used for flexible printed circuit board on a planar substrate surface. Instead, it employs high-precision multi-dimensional (3D up to 6D) printing technology. The thin-film coil array assembly may then be placed onto patient's head before sealing onto the frame of the tFUS device.
In an alternate embodiment, a convex mold is constructed based on a defined 3D shape, on which to fabricate a universal thin-film coil array, and its concave counterpart is used with the head mold to form a void space in which to fill with an ultrasound transparent gel-like material to fabricate a customized gel pad liner. As an alternative embodiment, a gel-material layer of liner can be fabricated on top of the head mold to conform externally to the defined 3D shape of the universal coil array.
Since coils need to be placed inside of the transducer device and close to the head, it has become quite a challenge to address the issue associated with the coil array being positioned in the path of ultrasound beams emitted from the transducer device and thus often inevitably submersed in the water bath, which is used as an ideal interface media to patient head for ultrasound beam emitted from the transducer elements.
With reference to
In example embodiments, the coil array assembly includes a minimum of 8 channels. The number of channels is not limited to 8 and the described coil array assemblies may have fewer channels, or more channels, than 8 (such as 4 or 16 channels depending on specific applications). As shown in
However, as technology moves into advanced MRI functional and structural studies of the cortical regions of the brain near the top, a coil array with 32 or more channels having a soccer-ball like configuration may demonstrate enhancement in sensitivity or acceleration. In this case, some of the element coil loops are exactly on the path of the ultrasound beams produced by the central transducer elements and minimizing ultrasound attenuation is one critical issue to resolve to integrate the two modalities. Notwithstanding careful selection of thin-film material and maintaining thinnest possible thickness for conductive traces and dielectric segments, as an alternate embodiment, disclosed herein is a ring-shaped tFUS transducer array with elements distributed in a cylindrical symmetry, which is shown as 200-B in
The described coil array assemblies also address another critical issue to minimize eddy current induced by the coil loops on the transducer hemisphere where a conducting electrode surface may exist. In reducing the eddy current effects, the electrode plate of the tFUS transducer's common ground is cut or grooved into a number of thin radial strips on the inside of the hemispherical transducer array, shown as 100-A in
To ensure no or minimum ultrasound impeding, deflection, or attenuation, the thin-film coil array assembly, such as 200-A shown, is fabricated to be “worn” onto individual subject's head with tight fit and close contact. In some embodiments, the described coil array assembly, such as 200-B, is placed over a customized gel pad worn over the subject's head or with a close-fit gel-pad liner attached to the inside of the thin-film cap. A customized liner may allow for a close fit to the subject's head while maintaining ultrasound transparency. Furthermore, the coil array assembly must be placed inside of a tFUS transducer device and submersed within the water bath used as the interface media between the subject's head and ultrasound beams emitted by the transducer. Thus, the coil array assembly requires hydrophobic and waterproof properties to protect the coil elements from the water or other fluids. The present disclosure describes the configuration, and method of manufacturing, of a coil array assembly that is positioned close to the patient's head to satisfy the proximity principle in achieving the optimal SNR on one hand and, on the other, to meet requirements of hydrophobicity and ultrasound transparency
In some embodiments, the coil array assembly is customized to fit a particular subject head. This ensures the closest overall positioning of the coil elements around the target area (i.e., subject's head). With reference to
In some embodiments, a 3D model of the subject's head is obtained to construct such a customized coil array assembly. For example, at operation 302, a 3D model of the subject's head is constructed. The 3D model is customized to a particular head and corresponding geometric configuration of a subject (or patient). Various techniques are implemented to generate the 3D model.
In one example, a 3D model is rendered using MRI image data. With reference to
The 3D surface rendering 420 is then used to generate a physical model which functions as a mold for the coil array assembly to be built upon.
At operation 304, a first thin-film layer is constructed upon the head mold.
Then, at operation 306, a coil array is constructed on the first thin-film layer.
With reference to
These three layers of coil element 600 (traces of conductors and distributed serial capacitors) are sandwiched between two layers of thin film 510 and 512. In various embodiments, the conductive layer 610 comprises the base conductive trace of a loop with one or more gaps at selected locations along the loop. Conductive layer 610 is fabricated onto the first or inner thin-film layer. The dielectric layer 620 is fabricated on top of the conductive layer 610. The dielectric layer 620 comprises one or more dielectric segments overlapping the position of the gap or gaps in layer 610. Subsequently, a second conductive layer 630, comprising conductive segments matching the dielectric segments, is fabricated on top of the dielectric layer 620.
For the purpose of minimizing the attenuation of through-film ultrasound, the thickness of single layer in an example embodiment may be no thicker than 0.02 millimeters (mm) for conductive material (layers 610 and 630), no thicker than 0.1 mm for dielectric material (layer 620), and no thicker than 0.1 mm for thin-film layer material (layers 510 and 512). However, it should be recognized that the thicknesses of each of the layers and components are not limited in the described ranges and may be varied to achieve various conductive or wave transparency characteristics, as well as various structural or mechanical characteristics. For example, the dielectric material may be provided at a thickness of greater than 0.1 mm.
The described systems may employ multi-dimensional printing techniques to fabricate both thin-film layers and multiple layers of the coil array onto the thin-film layers. As such, the layers are constructed to conform to the 3D shape of the head mold. Unlike the solid head mold 502 which may be constructed by conventional 3D printing techniques, each thin-film layer (510 and 512) and the coil array traces (610, 620, 630) are constructed using multi-dimensional printers, such as 5-dimensional or up to 6-dimensional printers, which are capable of performing three orthogonal translational dimensional motion in conjunction with two to three-dimensional rotational motion, on a physical 3D mold. This can be achieved by modifying a conventional 3D printer with additional fixtures for rotational control or utilizing a 6-axis robotic arm. This ensures that the thickness of a layer, such as the thin-film substrate layer, is an even thickness throughout the layer over the 3D contour of the mold.
The described fabrication techniques are distinctly different from two-dimensional (2D) planar screen-printing techniques and other planar fabrication techniques commonly used to print traces onto a thin flat substrate sheet (i.e., flexible printed circuit boards), which were then folded into non-planar shapes after printing. Because of the flexible nature of such printed circuit boards, there is a lack of mechanical stability, especially when submerged in a water bath and subjected to water pressure. Such printed circuit boards are also unable to conform accurately to a subject's head shape.
As shown in
In some embodiments, the dimensions of curved trace structures 612 are identical. In some embodiments, the dimensions of gaps 614-A and 614-B are the same. In some embodiments, dielectric segments 622-A and 622-B are the same. In some embodiments, the dimensions of overlap traces 632-A and 632-B are the same.
In an array of multiple coil loop elements, adjacent loops are often overlapped slightly to eliminate mutual inductance, which can interfere with the resonance.
Once the coil pattern is constructed upon the first thin-film layer, a second thin-film layer is constructed over the coil elements at operation 308 for additional dielectric isolation and waterproofing.
The second thin-film layer is fabricated directly upon the first thin-film layer and coil elements. In some embodiments, air pockets or gaps between the thin-film layers and the coil elements are eliminated or reduced to the greatest extent possible. While the second thin-film layer may comprise the same material as the first thin-film layer, in some embodiments, different materials may be utilized for each thin-film layer. Although the previously discussed operations construct the thin-film cap layer by layer upon a physical head mold, in some embodiments, a physical 3D head mold may not be required. Instead, the thin-film layers and the coil array may be constructed based on the merged 3D head rendering data with 3D CAD (Computer-aided design) model.
At operation 310, an end ring is attached to the thin-film layers of thin-film coil array cap 550. In this way, the coil elements are completely sealed within the two thin-film layers and the end ring. Additionally, each coil element of the coil array is electrically connected, or otherwise coupled, to one channel of the signal receiving unit of the MRI system through a tune and match circuit board (TMCB) enclosed or housed in the end ring.
The magnetic resonance signal picked up by the coil elements is amplified by multi-stage amplifiers, including low-input-impedance preamplifier, middle amplifier, and various gain amplifiers. Then, the signal from each coil element is carried to a channel of a receiver where the magnetic resonance signal is processed by analog-to-digital sampling and digital down converter before being re-ordered to form the time-domain data. Finally, the time-domain data is Fourier transformed to reconstruct an MR imaging. The above MRI signal processing chain can be independent for each channel.
The end ring is coupled to the thin-film cap at a lip or edge structure of each thin-film layer. FIG. SC shows end ring 800 attached to the thin-film coil cap 550 forming coil array assembly 50- customized to a particular subject's head.
Each TMCB in the end ring may be electrically coupled to a coil element through an additional conducting trace 850 embedded within the thin-film layers extending from the tightly, fitted coil array. Such conducting traces may be fabricated along with the coil elements upon the thin-film layer in a similar fashion. Another terminal of the TCMB is connected to corresponding low-input-impedance preamplifier with a half-wavelength, 50-ohm-impedance coaxial cable, as shown in
In some embodiments, the end ring may be completely sealed to the edge structures to form a watertight seal. In some embodiments, the end ring clamps down against the flexible material of the thin-film layers with enough pressure to prevent water or other liquids from passing the interface of the end ring and edge structures. In turn, the end ring is configured to engage and interface totally sealed with a tFUS transducer with a watertight seal. As such, water may be contained within a cavity formed between at least the outer thin-film layer, the tFUS transducer device, and the edge ring.
The example customized thin-film coil array assembly 200-A (or 500) as described is wearable and fabricated to conform to the head of a particular patient. Coil array assembly 200-A provides the closest fit to minimize ultrasound attenuation, is best mechanically supported by the head, and satisfies MRI requirements of close proximity as well as multiple-channel parallel acceleration. It can also be reused by the same patient for subsequent or follow-up treatment. As an alternative embodiment, a thin-film coil array assembly may be fabricated to conform to one or more universally defined shapes in conjunction with a customized thin layer of gel pad lining.
In another embodiment, instead of being customized to specific subject's head, the thin-film coil array assembly is fabricated over a fixed mold with a defined geometric shape of one or more sizes for the closest possible fit to the specific subject. This approach of a universal coil array assembly configuration is facilitated by a customized gel pad liner, fabricated to form a close fit to subject's head to ensure no void space is formed between the subject's head and the thin-film coil array cap thus avoiding ultrasound deflection or reflection.
At operation 1002, a convex mold of defined shape is constructed, such as convex mold 1102 shown in
At operation 1004, a first thin-film layer is constructed upon the convex mold. Similar to operation 304, first layer, or inner layer, of material is fabricated upon the convex mold to form first thin-film layer 1110. As described, such material may comprise TPU thin film. Next, a coil array is constructed upon the first thin-film layer at operation 1006. Coil array 1120 is shown positioned upon first thin-film layer 1110 in
As previously described with reference to operation 306, the coil array may comprise one or more conducting material layers for coil trace and one or more dielectric layers for distributed capacitors. In various embodiments, the coil pattern comprises a pattern of conductive traces and distributed capacitors configured into one or more coil elements. Coil array 1120 is shown as a configuration of overlapping rows of overlapping circular element loops, similar to that described in
As one example embodiment shown in
At operation 1008, a second, or outer, thin-film layer is constructed over the coil elements, as well as the first thin-film layer to complete the thin-film coil array cap 1150.
The completed thin-film coil array cap may then be removed from the convex mold and an end ring, such as end ring 800, is attached to the thin-film layers of the thin-film coil array cap at operation 1010, as previously discussed with reference to
Coil array assembly 1100 may be universally used for any user with a head of appropriate size to fit within assembly 1100. However, because the universal coil array assembly is constructed to have a configuration corresponding to a mold 1102 of a predefined size and geometry, such assembly may not precisely fit any one particular subject or patient's head to allow for adequate elimination of any air gaps that may deflect the ultrasound beam or cause skin burn at the location of air gaps. Therefore, additional structures described herein may be constructed and implemented within such universal coil array assembly. For example, a personalized lining layer may be constructed and worn on patient's head, or otherwise placed on the inside of the thin-film coil array cap, before the assembly is put on top of patient's head to provide and maintain the closest possible fit without compromising the ultrasound transmitted by the transducers. The construction of personalized lining layers may be faster and much more economical than construction of a personalized thin-film coil array cap containing complex conductive traces. As such, creating a personalized lining layer allows the cost-effective use of a single universal thin-film coil array assembly by multiple patients along with respective personalized liners.
In some embodiments, an ultrasound transparent gel material is used to fill in the void space formed between the patient's head mold (502 shown in
In various embodiments, concave mold 1202 and the patient-specific head mold 502 are used together to form a customized liner at operation 1016. As the concave mold 1202 is a counterpart to convex mold 1102, the inner surface of mold 1202 should correspond exactly to the surface of convex mold 1102. When the patient-specific head mold is placed inside of the fixed- shape concave mold, a void space is formed. In some embodiments, head mold 502 may be positioned within the concave mold at a particular distance to maintain a minimum distance from the surface of the concave mold at every point along head mold 502. In some embodiments, head mold 502 may be positioned to within the concave mold to minimize the distance between all points of head mold 502 from the surface of the concave mold, while maintaining the minimum distance requirement. In some implementation, a landmark on the head mold may be devised to align the molds.
100751 The customized liner may be formed by filling the void space with an ultrasound transparent material that will cure into a flexible or semi-rigid structure. For example, a selected ultrasound gel material may be filled into the void space and allowed to form into a semi-rigid thin gel pad, or customized liner 1220. In various embodiments, the material may be cured at room temperature or with heat. Once the customized liner has formed, head mold 502 may be removed to allow access to remove the customized liner, as shown in
Another way the customized liner can be fabricated is by constructing the liner layer directly onto the head mold. For example, the head mold may be coated with liner material such that the interior surface of the liner conforms to the shape of the head mold. Then excess liner material may be shaped or machined such that the exterior surface conforms to the shape of the universal thin-film coil array cap. As another example, liner material may be 3D or higher dimensionally printed directly onto the head mold to have the required exterior geometric shape. In some embodiments, in order to provide more structural support for the liner layer during manufacturing, additional thin-film layers may be implemented. For example, an inner thin-film layer, such as TPU, may first be constructed onto the head mold much like the first thin-film layer. Then, the liner material may be constructed over the inner thin-film layer as discussed above. In certain embodiments, an additional outer thin-film layer may be constructed over the formed liner layer to seal the liner layer within the inner and outer thin-film layers.
At operation 1020, the customized liner is attached to the coil array assembly.
With reference to
This disclosure is not limited by the design of the coil array, number of coil elements or loops, the shape or trace of the loops, or its spatial distribution. The 8-channel array shown in
Different examples of the apparatus(es) and method(s) disclosed herein include a variety of components, features, and functionalities. It should be understood that the various examples of the apparatus(es) and method(s) disclosed herein may include any of the components, features, and functionalities of any of the other examples of the apparatus(es) and method(s) disclosed herein in any combination, and all possible variations are intended to be within the spirit and scope of the present disclosure. Many modifications of examples set forth herein will come to mind to one skilled in the art to which the present disclosure pertains having the benefit of the teachings presented in the foregoing descriptions and the associated drawings.
Therefore, it is to be understood that the present disclosure is not to be limited to the specific examples illustrated and that modifications and other examples are intended to be included within the scope of the appended claims. Moreover, although the foregoing description and the associated drawings describe examples of the present disclosure in the context of certain illustrative combinations of elements and/or functions, it should be appreciated that different combinations of elements and/or functions may be provided by alternative implementations without departing from the scope of the appended claims. Accordingly, parenthetical reference numerals in the appended claims are presented for illustrative purposes only and are not intended to limit the scope of the claimed subject matter to the specific examples provided in the present disclosure.
This Patent Application is a Non-provisional Application and claims the Priority Date of Mar. 21, 2022 based on a previously filed Provisional Application 63/322,069. The disclosures made in the Provisional Application 63/322,069 are hereby incorporated by reference in this Patent Application.
| Number | Date | Country | |
|---|---|---|---|
| 63322069 | Mar 2022 | US |
