System and method for MRI local coil design

An MRI local coil system for use with an MRI scanner to image a breast, the system comprising a plastic housing and an RF coil system. The RF coil system comprises a conductor and electronics. The electronics comprises a capacitor and a blocking circuit. The conductor and the electronics are disposed within the plastic housing and the conductor is integrally formed with the plastic housing.

FIELD OF THE INVENTION

This application generally relates to medical imaging and more specifically to a system and method for an MRI local coil design.

BACKGROUND OF THE INVENTION

Magnetic resonance imaging (MRI) detects the faint nuclear magnetic resonance (NMR) signals given off by protons in the presence of a strong magnetic field after excitation by a radio frequency signal. The NMR signals are detected using antennae termed “coils”. The term “coil” is also commonly used to refer to the antenna(e) and its housing or support structure. Thus “coil” may refer to a structure that contains a number of coils. “Coil element(s)” is used to refer to the electrical part of the device, the radio frequency coil or antennae.

NMR signals are extremely faint. Sensitivity of a coil to these signals decreases rapidly with increasing distance between the coil and the volume of interest. Coils are therefore placed in close proximity to the region of interest of the imaged object. The size of the local coils is kept small to allow them to be easily fit to the patient on the MRI patient table and to enable imaging of only the imaging volume of interest, since imaging regions that are not required adds noise to the acquired signal unnecessarily. Coils local to the anatomy of interest tend to have a higher signal-to-noise ratio (SNR) than larger coils such as a “body coil” which is useful for obtaining large survey scans of the patient.

Use of MRI to distinguish pathologic tissue from healthy tissue has proven advantageous in some respects in comparison to other imaging modalities. For example, MRI uses non-ionizing radio frequency (RF) signals to acquire images, in contrast to the use of ionizing radiation used with computed tomography scanners. Moreover, MRI has shown improved sensitivity in comparison to other imaging modalities.

Various limitations, however, have impeded widespread adoption of the use of MRI for imaging portions of the body despite its advantages. One impediment is the cost of MRI equipment. MRI scanners are expensive. Body coils present numerous complexities and issues so local coils have developed to isolate regions of the body of interest, but MRI local coils also have cost concerns. Nonlimiting examples of MRI local coils include U.S. Pat. Nos. 7,379,769 and 7,970,452, commonly owned by the assignee for the present invention. For example, the housing of a local coil constrains resources. In addition, local coil designs often include multiple components that are complicated to assemble. The complicated assembly can affect precision and repeatability of assembly.

What is needed, then, is a MRI local coil design with fewer parts and repeatable assembly. The MRI local coil design is preferably cost-effective, reliable, easier and/or faster to manufacture, and/or easier and/or faster to assemble with more precision.

SUMMARY OF THE INVENTION

In an aspect of the invention, an MRI local coil system for use with an MRI scanner to image a breast, the system comprises a plastic housing and an RF coil system. The RF coil system comprises a conductor and electronics, the electronics comprising a capacitor and a blocking circuit, wherein the conductor and the electronics are disposed within the plastic housing and wherein the conductor is integrally formed with the plastic housing.

The foregoing aspect can include any one or more of the following embodiment. The conductor can be exposed within an interior of the plastic housing. The conductor can be integrally formed with the plastic housing by at least one of laser direct structuring and two-shot molding. The conductor can extend substantially along a length of the plastic housing. The conductor can extend substantially along a periphery of the plastic housing. The conductor can extend continuously around a corner and, optionally, around at least 2 corners. The conductor can be positioned on an interior of an exterior wall of the plastic housing. The plastic housing can comprise an outer enclosure and an insert disposed within and releasably coupled to the outer enclosure. The conductor can be integrally formed with the insert. The conductor can extend substantially along a length of the insert. The conductor can extend substantially along a periphery of the insert. The conductor can extend continuously around a corner and, optionally, around at least 2 corners on the insert. The conductor can be configured to face in the direction of the breast. The electronics can be coupled to and, optionally, disposed within the plastic housing.

In another aspect of the invention, a method of forming and/or assembling an MRI local coil system for use with an MRI scanner to image a breast, the method comprising providing a plastic housing, integrally forming a conductor of an RF coil system with the plastic housing, and providing electronics of the RF coil system such that the electronics are coupled to and, optionally, disposed within the plastic housing, wherein the electronics comprise a capacitor and a blocking circuit.

The foregoing aspect can include any or more of the following embodiments, the step of integrally forming the conductor can expose the conductor within an interior of the plastic housing. The step of integrally forming can be accomplished by at least one of laser direct structuring or two-shot molding. The step of integrally forming the conductor can form the conductor so as to extend substantially along a length of the plastic housing. The step of integrally forming the conductor can form the conductor so as to extend substantially along a periphery of the plastic housing. The step of integrally forming the conductor can form the conductor so as to extend continuously around a corner and, optionally, around at least 2 corners. The plastic housing can comprise an outer enclosure and an insert, the insert releasably coupled to the outer enclosure. The step of integrally forming the conductor can integrally form the conductor with the insert. The step of integrally forming the conductor can form the conductor so as to extend substantially along a length of the insert. The step of integrally forming the conductor can form the conductor so as to extend along a periphery of the insert. The step of integrally forming the conductor can form the conductor continuously around a corner and, optionally, around at least 2 corners. The step of integrally forming the conductor can form the conductor on the insert to face in the direction of the breast. The forming and/or assembling of the MRI local coil system is free and/or does not include manual tuning of the RF coil system.

DETAILED DESCRIPTION OF THE INVENTION

Except as otherwise notes, the articles “a,” “an,” and “the” mean “one or more.”

Referring toFIG. 1, a known MRI local coil system10comprises a plastic housing20and an RF coil system30. The plastic housing20comprises a cover22and a case24, coupled together. The RF coil system30is disposed substantially within the case24. The RF coil system30comprises a conductor32and electronics34. The electronics34may comprise a printed circuit board. The RF coil system30is separate from the case24. Preloaded against the electronics34is a retaining foam36to keep the RF coil system30in place. A retaining cover38coupled to the retaining foam36helps to keep the retaining foam36in place and to couple together the cover22and the case24. Alternatively, the RF coil system30is coupled to the case24via an adhesive.

Referring toFIG. 2, alternative component of an MRI local coil system is shown. An insert40can be used and disposed within a plastic housing20. The insert40can be made from plastic and has a curvature. Due to the curvature, at least a portion of an RF coil system50also has a curvature. The RF coil system50comprises conductors52and electronics54. Conductors52are constructed in multiple segments to conform to the plastic housing20. Multiple conductors52can be flexible to conform to the shape of the insert40and the electronics54are coupled to the insert40and/or a case. The insert40includes retention clips42extending from the surface of the insert40to retain the conductors52. Due to the size and forces of the conductors52, manufacturing tolerances need to be minimized so as not to compromise the quality of the RF coil system.

FIGS. 3 and 4depict an MRI local coil system100. The MRI local coil system100comprises a plastic housing110and an RF coil system120. The plastic housing110comprises a case102and a cover104coupled together via a retaining cover106. The RF coil system120comprises a conductor122and electronics124. The conductor122is integrally formed with the plastic housing110(e.g., the case102), that is, no other structures or features, such as retention foam or retention clips, are necessary to hold the conductor122to the plastic housing110. Additionally or alternatively, the RF coil system120may include a surface mount126for mounting components of the RF coil system120, such as the conductor122to the plastic housing110. The RF coil system120may, optionally, include pads128to fix components of the RF coil system120, such as the electronics124to the conductor122. The electronics124may include any number of components such as, but not limited to, a capacitor and a block circuit. In an embodiment, the conductor122comprises circuitry that receives signals in MRI. The circuitry can comprise an antenna, preamplifier, filter, printed circuit pads, lands, and vias. Additionally or alternatively, any one or more of the antenna, preamplifier, filter, printed circuit pads, lands, vias, and combinations thereof are integrally formed with the plastic housing.

In an embodiment, the conductor122is integrally formed with the plastic housing110to from a molded interconnect device (MID). The conductor122can be integrally formed via laser direct structuring (LDS) or two-shot molding. In an embodiment in which the conductor122is integrally formed via LDS, the material of the plastic housing110is selected such that certain properties are activated by a laser beam/chemical process so as to plate (electroplating) the surface with copper. Suitable materials include thermoplastic polymers such as Pocan® DP T 7140 LDS (available from Lanxess Corp., Leverkusen, Germany), RTP 399 X 113385 B (available from RTP Co., Winona, Minn.), and other similar materials. Integrally forming the conductor provides numerous features. As an example, fewer parts for assembly and manufacture can be used. Moreover, assembly can be more precise without requiring adhesives or preloaded foam to retain a structure against the plastic housing. The RF coil system can also have a smaller footprint and be more flexible with and conforming to designs and curves of the housing contours. With greater flexibility to housing contours, the MRI local coil system can be more easily designed to conform the MRI local coil system to patient anatomy. The conductor is the component that receives the MRI signal and, with fewer parts and more precise assembly, integrally forming the conductor can be placed that much closer to the region of interest. In an embodiment, the conductor can be placed closer to the region of interest, for example, positioned on an interior of an exterior wall of the plastic housing. In an example, the conductor can be placed up to about 1 cm closer, preferably about ¾ cm closer, and even more preferably about ½ cm to the region of interest. This facilitates and improves the signal to noise ratio (SNR) and image quality with resulting greater sensitivity. Because of fewer parts, there is greater reliability of the MRI local coil system. In addition, another advantage of assembly with fewer parts, there is reduced sensitivity to vibration as the MRI local coil system does not need separate vibration mounting of the RF coil system. That is, there are fewer parts that need to be fixed to one another and account for possible vibrations, which may lead to signal quality issues and affect SNR. Additionally, fewer parts can reduce the cost of the MRI local coil system. In an additional or alternative embodiment, each of or both of the case and cover for the plastic housing can be formed from plastic materials suitable for injection molding, further reducing cost of the MRI local coil system.

The RF coil system can be a single loop system, though the RF coil system can include any number of loops. In an embodiment, the conductor can extend substantially along a periphery of the plastic housing. Additionally or alternatively, the conductor can extend continuously around a corner and, optionally, around at least 2 corners. The conductor can be configured to face in the direction of the breast. The electronics can be coupled to and, optionally, disposed within the plastic housing.

As depicted inFIG. 3, the plastic housing includes an aperture therethrough that can, for example, be used also for biopsy procedures. Additionally or alternatively, an MRI local coil system of the present invention can be used with fixed or adjustable coils, such as that described in U.S. Pat. Nos. 7,379,769 and 7,970,452.

Referring now toFIGS. 5A and 5B, another embodiment of an MRI local coil system130comprises a plastic housing140, optionally, without an aperture therethrough for biopsy procedures. The MRI local coil system130also comprises an RF coil system150in which a conductor152is integrally formed with the plastic housing140. The conductor152can be directly formed on an interior of an exterior wall of the plastic housing140to be closer to a region of interest. In such an arrangement, an insert disposed within the plastic housing can be optional or not needed. Additionally or alternatively, the conductor152can be formed on more than one surface of the plastic housing140. The conductor152can include more than 1 loop, such as two loops. The conductor140can also include more than one corner, such as two corners, or preferably up to four corners on a surface of the plastic housing140and, optionally, at least one corner on a first surface with another corner, in a continuous loop, on another surface orthogonal to the first surface.

FIGS. 6A and 6Bdepict another embodiment of a portion of an MRI local coil system. An RF coil system160is coupled to at least one half of an insert170in which a completed insert can be placed within a plastic housing. The insert can be made of the same or similar material as previously described for a plastic housing. The conductor can be integrally formed with the insert such that the conduct faces in a direction of a region of interest. The conductor162can generally form a loop, though generally more loops can be utilized. The conductor162can be continuous along at least one corner, preferably at least two corners, and even more preferably four corners. Additionally or alternatively, the conductor162can span along a contour of one surface of the insert and, optionally, along a contour of two surfaces of the insert in which one surface is generally orthogonal to another surface. The conductor can extend substantially along a length of the insert. The conductor can extend substantially along a periphery of the insert. In the arrangement shown inFIGS. 6A and 6B, retention clips are not needed for the conductor162of the RF coil system as the conductor is formed with the plastic insert170. Moreover, generally for all of the embodiments of the present invention, fewer parts are needed, thus providing fewer parts to assemble, more cost efficiencies as to parts, more precision of assembly, greater range of manufacturing tolerances, and greater design choices for contours of the housing, improved SNR for MRI imaging, etc.

The above described fabrication techniques of embedding a conductor described herein has additional advantages and features. In additional or alternative embodiments, the above described fabrication techniques can also include embedding non-conductive components into plastic materials. Some nonlimiting examples include embedding components such as pin diodes, ceramic capacitors, etc. Embedding conductive and non-conductive components facilitiates arbitrary three dimensional configurations to enable new designs and product solutions. Nonlimiting examples for new designs and product solutions include coil arrays, decoupling or overlapping coil elements, and/or inductive and capacitive decoupling structures. Conventional coil geometries have coil elements superimposed on one another, e.g., a loop butterfly arrangement. One disadvantage of such an arrangement, in which conductive elements cross one another, can be undesirable capacitive and inductive coupling. In an embodiment, locally increasing the spacing in the region between conductive elements due to the fabrication techniques described herein can improve performance of the coil and minimize undesirable capacitive and inductive coupling. Additionally or alternatively, the fabrication techniques described herein can automate the process of geometric decoupling or overlapping of the coil elements via process monitoring and adjustment of overlapping conductor geometry parameters and other similar methods. Moreover, various designs for inductive and capacitive decoupling structures can be enabled with the fabrication techniques due to the ability to form arbitrary three dimensional or two dimensional conductive and non-conductive component arrangements. Furthermore, the fabrication techniques facilitate automation of MRI local coil designs, for example, the coils can be automatically tuned or manual tuning can be eliminated, minimized and/or reduced. The overall shape of a MRI local coil can be customized or specified for a particular patient based on a three dimensional scan of a region of interest of the patient. The arbitrary three dimensional design of MRI local coils described herein can conform or surround any region of interest.

The above specific examples and embodiments are illustrative, and many variations can be introduced on these examples and embodiments without departing from the spirit of the disclosure or from the scope of the appended claims. For example, elements and/or features of different illustrative embodiments may be combined with each other and/or substituted for each other within the scope of this disclosure and appended claims.