MRI systems and receive coil arrangements

An MRI system receive coil arrangement 3 for use with a main MRI scanner arrangement, the receive coil arrangement 3 including support structure and at least one receives coil 7 carried on the support structure 40. The support structure 40 includes a receive coil housing portion 43 which defines a channel portion 43a which houses at least a portion of the at least one receive coil 7. The channel having a mouth 43b for allowing the introduction of said at least a portion of the at least one receive coil 7 through the mouth 43b and into the channel 43a and a closing portion 45 moveable between a first position in which the mouth 43b of the channel portion is open for allowing introduction of the at least a portion of the at least one receive coil 7 into the channel portion 43a and a second, closing, position in which the mouth 43b of the channel is blocked by the closing portion 45.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims foreign priority benefits under U.S.C. § 119 from British Patent Application No. 2208591.4, filed Jun. 13, 2022, the content of which is hereby incorporated by reference in its entirety.

TECHNICAL FIELD

This invention relates to MRI systems including receive coil arrangements and to receive coil arrangements for use in MRI systems as well as in some embodiments, combined systems such as MR-Linac and PET-MR systems where there is an MRI system used in combination with another system which relies on a source of radiation.

BACKGROUND

An MRI system typically comprises a main MRI scanner arrangement, a patient support or bed on which a patient lies during scanning and in at least some cases a separate, local, receive coil arrangement (or body part specific receive coil) which is arranged for location in the region of a particular body part which it is desired to scan.

The main MRI scanner arrangement typically comprises a main magnet, gradient coils, RF transmit coils, and receive coils all arranged in a main unit with a bore in which the patient is positioned during scanning. Where present, a body part specific receive coil will typically also be positioned in the bore during scanning.

As is well known MRI (magnetic resonance imaging) systems are widely used for imaging subjects and can also be used in combination systems such as MR-Linac and PET-MR systems. These combine magnetic resonance imaging with other techniques making use of radiation say for treatment, say in MR-Linac or to provide functional imaging say in PET-MR. In MRI operation, the magnet creates a large static magnetic field B0, the RF transmit coils generate an alternating magnetic field B1and the receive coils, whether provided in the main unit or in a body part specific receive coil are arranged for collecting a magnetic resonance signal (that is to say acquiring magnetic resonance data). The gradient coils are used to allow spatial encoding on the B0field to enable tomographic imaging.

When an MRI system is operated using just the receive coils provided in the main unit of the scanning apparatus, the resolution and accuracy of the results can be limited in some cases. This leads to the use of separate, one may say local, receive coils, say body part specific coils as mentioned above which aim to improve imaging of a selected location/body part.

However there are limitations with existing body part specific receive coil arrangements. These include that it may be a cumbersome operation to position the receive coil arrangement around the specific body part or position the specific body part in the arrangement and/or the receive coil arrangement may give inadequate imaging results for an area of interest and/or the receive coil arrangement may be incompatible with the use of other systems such as systems using a source of radiation, for example, a linear accelerator or positron emission tomography system.

A further issue is the ease of manufacture and/or set up of such receive coil arrangements whilst facilitating for example production of arrangements with desired properties such as say shape, operational receive performance, or radio transparency.

Thus, it would be desirable to provide MRI system receive coil arrangements which are aimed at addressing at least one of these issues as well as MRI systems and combined therapy and/or imaging systems which include such an MRI system receive coil arrangement.

SUMMARY

According to a first aspect of the invention there is provided an MRI system receive coil arrangement for use with a main MRI scanner arrangement, the receive coil arrangement comprising support structure and at least one receive coil carried on the support structure, wherein the support structure comprises:a receive coil housing portion which defines a channel portion which houses at least a portion of the at least one receive coil, said channel having a mouth for allowing the introduction of said at least a portion of the at least one receive coil through the mouth and into the channel; anda closing portion moveable between a first position in which the mouth of the channel portion is open for allowing introduction of said at least a portion of the at least one receive coil into the channel portion and a second, closing, position in which the mouth of the channel is blocked by the closing portion.

This provides a convenient way to allow the production of an appropriately shaped and dimension support structure and subsequently the introduction and retention of the desired receive coil(s). It can also help avoid the need for processing of the material of the support structure in securing the desired receive coils—for example it can avoid the use of heating, use of adhesives, or the application of a second material to a base material of the support structure—eg avoid the need to coat a base material plus coil portions with a foam material. This in turn can be helpful since it increases flexibility in choice of materials for the support structure—compatibility with heating, adhesives etc. need not be considered—rather the material can be selected based on its suitability for supporting the receive coil(s) and suitability for use in MRI and companion processes/treatments that may be used alongside MRI.

Further this arrangement facilitates production of a housing portion in which deformation of the housing portion by a user is possible as the closing portion is moved to the closed position and in which moving of the closing portion into the closed position can serve to hold the housing portion in said deformed position. This in turn can allow subtle adjustment of the relative position of the at least one receive coil carried in the housing portion which can be used to fine tune the response of the receive coil.

In such an arrangement the channel portion and closing portion may co-operate together to retain the at least one receive coil. The channel portion may hold the at least one receive coil in a desired position. The closing portion may assist in holding the at least one receive coil in a desired position. The interaction between the channel portion and closing portion may assist in holding the at least one receive coil in a desired position.

The closing portion may be a push fit closing portion which is push fittable into the second, closed, position from the first position.

This helps to further enhance convenience by providing a simple way to secure the closing portion in the closed position.

The support structure may be arranged so that the closing portion is locked against movement back towards the first position once moved, for example push fitted, into the second position.

The locking may be releasable. Thus in other words—The support structure may be arranged so that the closing portion is releasably locked against movement back towards the first position once moved, for example push fitted, into the second position.

The support structure may be arranged so that the closing portion latches into the second position.

Amongst other things, these features can help enhance the provision of a housing which facilitates adjustment of the positioning of carried receive coils as the receive coil arrangement is assembled.

In one set of embodiments the closing portion may be arranged to be a push fit with the housing portion, such that in moving the closing portion to the closing position, the closing portion is push fitted into position on the housing portion and blocks the mouth of the channel portion.

The closing portion may be arranged to be a push fit with the mouth of the of the channel portion. The closing portion may be arranged to be push fittable into the mouth.

In another set of embodiments the closing portion may comprise first and second engaging portions which are a push fit with one another, such that in moving the closing portion to the closing position, the first and second engaging portions are push fitted together to block the mouth of the channel portion.

In either or both of the above sets of embodiments, the support structure may be arranged so that at least one of:i) the closing portion is locked against movement back towards the first position once push fitted into the second position;ii) the closing portion is releasably locked against movement back towards the first position once push fitted into the second position; andiii) the closing portion latches into the second position.

The closing portion and the housing portion may be arranged so that at least one of:i) the closing portion is locked against movement back towards the first position once push fitted into position on the housing portion;ii) the closing portion is releasably locked against movement back towards the first position once push fitted into position on the housing portion; andiii) the closing portion latches into position on the housing portion.

The first and second engaging portions of the closing portion may be arranged so that at least one of:i) the closing portion is locked against movement back towards the first position once the first and second engaging portions are push fitted together;ii) the closing portion is releasably locked against movement back towards the first position once the first and second engaging portions are push fitted together; andiii) the first and second engaging portions latch together when they are push fitted together.

The mouth of the channel portion may have a receiving region which has a re-entrant shape in cross-section and the closing portion may comprise a correspondingly shaped insertion portion which fits in the receiving region when the closing portion is push fitted into the mouth.

For the avoidance of doubt, the following features are equally applicable to each of the two sets of embodiments mentioned above and in general.

The closing portion may be integral with housing portion.

The closing portion may be a separate component from the housing portion.

The closing portion may be connected to the housing portion when in the first position.

The closing portion may be separate from the housing portion when in the first position.

The housing portion may be shaped so as to conform with a predetermined body part. If say the receive coil arrangement is designed for use in scanning a patient's head and/or neck, the housing portion may be shaped so as to fit over and around at least part of a patient's head and/or neck.

In some instances the support structure may comprise a base portion and a cover portion. The base portion may be more rigid than the cover portion. The cover portion may comprise said receive coil housing portion.

Preferably the receive coil arrangement comprises a plurality of receive coils carried on the support structure.

Preferably the receive coil housing portion houses a plurality of the receive coils.

The housing portion may define a plurality of channel portions, each of which channel portions houses at least a portion of a respective receive coil from the plurality of receive coils.

The support structure may comprise a plurality of closing portions, each closing portion for blocking the mouth of a respective channel portion.

The plurality of channel portions may be defined in a one-piece portion of the housing portion.

The plurality of closing portions may be provided in a one-piece portion of the support structure.

In some cases the whole of the housing portion, or at least the whole of a part of the housing portion that defines coil receiving channels, may have a one-piece construction. In other cases the housing portion may be of a plurality of pieces, but yet a plurality of channel portions be defined in a one-piece part of the housing portion. In such a case there may be plural sets of channel portions, each set being defined in a respective one-piece part of the housing portion.

In some cases a one-piece portion of the support structure may comprise all of the closing portions. In other cases there may be plural sets of closing portions with each set of closing portions being provided in a respective one-piece portion of the support structure.

The housing portion may comprise a web of channel defining portions. Apertures through the housing portion may be provided between the channel defining portions.

The support structure may comprise a web of closing portions. Apertures through material making up the web of closing portions may be provided between the closing portions.

The web of channel defining portions and the web of closing portions may be dimensioned and arranged so as to register with one another such that respective closing portions in the web of closing portions are aligned or alignable with respective channels in the web of channel defining portions.

The provision of webs in the support structure can help enhance the provision a housing which facilitates adjustment of the positioning of carried receive coils.

The housing portion, or at least part of the housing portion, may be of resilient material. A part of the housing portion in the region of the or each channel may be of resilient material. The or each closing portion may be of resilient material.

The web of channel defining portions may be of resilient material. The web of closing portions may be of resilient material.

The use of resilient material in the housing portion and/or closing portion may facilitate push fitting of the closing portion into the closing position. The use of resilient material in the housing portion and/or closing portion may also facilitate shaping of at least part of the support structure, say cover portion, to conform with a body part with which the receive coil arrangement is designed to be used.

The use of resilient material in the housing portion and/or closing portion can help enhance the provision of a housing which facilitates adjustment of the positioning of carried receive coils. It noted that in some instances resilience may be provided or enhanced by the shape and configuration of components as well as the material of which they are made.

The housing portion may be additively manufactured.

The closing portion may be additively manufactured.

The cover portion may be additively manufactured.

The use additive manufacturing may be particularly advantageous when a web of channel defining portions and/or a web of closing portions is provided. Further, additive manufacturing can be convenient in providing support structures shaped and dimensioned to conform to a particular body part or even for a particular size of patient.

The housing portion may be of plastics material, say a thermoplastic, for example a thermoplastic polyurethane.

The closing portion may be of plastics material, say a thermoplastic, for example a thermoplastic polyurethane.

The cover portion may be of plastics material, say a thermoplastic, for example a thermoplastic polyurethane.

The at least one receive coil may comprise a length of co-axial cable, which may be arranged in a loop.

In some embodiments the receive coil arrangement comprises at least two receive coils, a first, main receive coil which is mounted on the base portion and a second, auxiliary, receive coil which comprises said at least a portion of the at least one receive coil which is provided in the receive coil housing portion, and the housing portion comprises the cover portion.

The main receive coil provided on the base portion may be more rigid than the auxiliary receive coil provided in the receive coil housing portion.

The auxiliary receive coil may comprise a length of co-axial cable which may be arranged in a loop.

The main receive coil may comprise a length of unshielded conductor.

Preferably the receive coil arrangement comprise a plurality of auxiliary receive coils.

According to another aspect of the invention there is provided a method of manufacturing an MRI system receive coil arrangement as defined above, the method comprising the steps of:making the housing portion;introducing the coil portion of the at least one receive coil into the channel portion of the housing portion; andmoving the closing portion to the second position.

According to another aspect of the invention there is provided a method of manufacturing an MRI system receive coil arrangement as defined above, the receive coil arrangement comprising a plurality of receive coils and a respective plurality of closing portions and the method comprising the steps of:making the housing portion;introducing coil portions of the plurality of receive coils into the respective channel portions of the housing portion;moving the plurality of closing portions to the second position;checking the receiving operation of the receive coil arrangement; andwhere said checking indicates that a first predetermined standard of receiving operation has not been achieved, carrying out the further steps of:a) moving at least one of the closing portions back out of the second position;b) returning the at least one of the closing portions to the second position with the positioning of at least one of the receive coils adjusted;c) re-checking the receiving operation of the receive coil arrangement; andd) carrying out steps a) to c) in sequence until a second predetermined standard receiving operation is achieved.

The first and second predetermined standards of receiving operation may be the same as one another or different from one another—where they are different from one another, in different embodiments either may be set to be higher than the other.

The method may comprise the step of making the housing portion using an additive manufacturing process.

The method may comprise the step of making the closing portion using an additive manufacturing process.

According to another aspect of the invention there is provided a cover portion arrangement for use in a receive coil arrangement as defined above which cover portion arrangement comprises a plurality of receive coils of the receive coil arrangement and a cover portion which carries and supports each of the receive coils.

According to another aspect of the invention there is provided an MRI system comprising a main MRI scanner arrangement, a patient support, and an MRI system receive coil arrangement as defined above provided on the patient support and electrically connected to the main MRI scanner arrangement.

According to another aspect of the invention there is provided an MR-Linac system comprising an MRI system as defined above and a medical linear accelerator system.

According to another aspect of the invention there is provided a PET-MR system comprising an MRI system as defined above and a positron emission tomography system.

According to another aspect of the invention there is provided a stereotactic mask arrangement for treatment planning comprising an MRI system as defined above and a stereotactic mask to ensure the subjects position is well defined and transferable to stereotactic treatments using the same mask thereby guided by the MRI data.

Note that, in general terms and with any necessary modifications in wording, all of the further features defined above following any aspect of the invention above are applicable as further features of all other aspects of the invention defined above. These further features are not restated after each aspect of the invention merely for the sake of brevity.

DETAILED DESCRIPTION

FIG.1shows an MRI system comprising a main scanner arrangement1, a patient support2which is arranged for supporting a patient when in the scanner arrangement1and an MRI system receive coil arrangement3which is separate from the main scanner arrangement and which in this embodiment is a body part specific receive coil arrangement. More generally such a receive coil arrangement3may be termed a local receive coil arrangement.

As alluded to above, in some instances an MRI system will be used in combination with other systems so as to provide for example, an MR-Linac system which comprises an MRI system and a medical linear accelerator system; or in another example, so as to provide a PET-MR system comprising an MRI system and a positron emission tomography system. In such a case, the MRI system shown inFIG.1may be supplemented by a linear accelerator system or positron emission tomography system S illustrated in dotted lines only in highly schematic form inFIG.1. In another alternative the present system may be used in combination with a stereotactic mask S (again illustrated in dotted lines only in highly schematic form inFIG.1) for stereotactic treatment/planning. The stereotactic mask being arranged to ensure the subject's position is well defined and transferable to stereotactic treatments using the same mask as well as the present receive coil arrangement3described herein such that the stereotactic treatments can thereby be guided by MRI data.

The main MRI scanner arrangement1may be an entirely conventional main MRI scanner arrangement comprising a main magnet11which will typically be a superconducting electromagnet, RF transmit coils12, gradient coils13and main unit receive coils14. These components are provided in a main body of the MRI scanner arrangement1which has a main bore B in which the patient support2is provided or, more typically, into which the patient support2can be moved carrying a patient until an operative position is reached.

At least in use the body part specific receive coil arrangement3is also provided in this main bore B. Where present at least part of a medical linear accelerator system or positron emission tomography system S may also be located in this main bore B during operation.

As well as being located in the main bore B of the main MRI scanner1during operation, the receive coil arrangement3is electrically connected to the main scanner arrangement1such that the magnetic resonance signals picked up by the receive coil arrangement3may be fed into the main scanner arrangement1for processing.

The signals picked up by the receive coil arrangement3may be used alone or in combination with signals picked up by the main unit receive coils14in processing and generating images. In some instances a main MRI scanner arrangement1without its own main unit receive coils14could be used with the present type of receive coil arrangement3.

The structure and operation of MRI scanner arrangements is well developed and understood and the present ideas relate to the receive coil arrangement3for use with such an MRI scanner arrangement. Therefore, further description of the structure and operation of the MRI scanner arrangement1is not necessary and the remainder of this description relates to the receive coil arrangement3.

FIG.2schematically shows the body part specific receive coil arrangement3in some more detail but still in schematic form. The body part specific receive coil arrangement3comprises a cover portion4and base portion5. The base portion5is arranged to either be rested upon the patient support2or in some embodiments may be made to be an integral part of the patient support2. On the other hand, the cover portion4is removably mounted on the base portion5so that it may be fitted over a subject and then secured in position on the base portion5.

As may be seen by consideringFIGS.3to10the body specific receive coil arrangement3comprises a primary receive coil6(seeFIGS.5and6) and a plurality of auxiliary receive coils7(seeFIGS.4and8to10). The base portion5is arranged for supporting the primary receive coil6and the cover portion4is arranged for supporting the auxiliary receive coils7.

In this embodiment, the cover portion4and base portion5can be considered together to comprise support structure of the receive coil arrangement. The combination of the cover portion4and auxiliary receive coils7can be considered a cover portion arrangement. The combination of the base portion5and main receive coil6can be considered a base portion arrangement.

Note that whilst in the present embodiment, the receive coil arrangement comprises a base portion and a cover portion, in other embodiments this is not necessary. Thus, for example, the receive coil arrangement may comprise one support portion which may for example be arranged in the same way as the cover portion4in the present embodiment. Similarly there may be only one set of receive coils in other embodiments, which may comprise coils which correspond to the auxiliary coils7in the present embodiment.

Thus in an alternative embodiment the body specific receive coil arrangement3may comprise a cover portion arrangement4,7as described herein without a base portion arrangement as described herein.

The base portion5comprises a plate portion51and two upstanding portions52. The upstanding portions52can be seen for example inFIGS.3and5. The plate portion51has two layers51aand51b. The upstanding portions52are carried on the upper layer51aas visible inFIGS.3and5. InFIG.6the upper layer51ais raised to show the lower layer51band to better show the primary receive coil6.

The base portion5is provided with a plurality of channels52a,52bfor supporting the primary receive coil6and holding it in a predefined position. A respective channel52a(only one of which can be seen in the drawings i.e. inFIG.5) is provided in each of the upstand portions52for holding a respective portion of the primary receive coil6in position in the upstand portion52.

As will be appreciated by considering together for example,FIGS.2,3,4and5, in use this portion of the primary receive coil6will be in close proximity to the subject, in particular the subject's head in the specific embodiment shown. The particular shape and path of the coil6is chosen to give desired receive characteristics for example to maximize penetration depth and ensure relatively constant electromagnetic coupling of energy to the tissue of the subject.

The lower layer51bof the plate portion51includes respective channels52bfor holding the other parts of the primary receive coil6in position.

The primary receive coil6comprises unshielded lengths of conductor. In the present embodiment, two portions of unshielded conductor61are provided. The first of which runs in the channel52aof the first of the upstands52and the second of which runs in the channel52aof the other upstand52. First ends of these conductor portions61are connected to a detune board62whilst other respective ends of the two conductor portions61are connected to a matching board63. The detune board62and matching board63each comprise at least one electronic component, such as at least one tuning capacitor in the case of the matching board63.

As seen inFIG.6the detune board62and matching board63are kept out of a central region of the coil6, that is they are away from the location of the upstand portions52and those portions of the coil6which will be nearest a portion of interest in the subject. This creates an electronic component free zone in the region of interest of the subject. This is of particular interest where the body specific receive coil arrangement3is to be used in a combination system of the type described above where radiation is used in the combination system. Radiation may pass through this central region i.e. the region of interest in the subject without being adversely affected by the presence of electrical components and/or without risk of damage to such electrical components. Thus, this arrangement of the primary receive coil6helps the use of the present receive coil arrangement in systems such as PET-MR and MR-Linac systems.

The base portion5, that is the plate portion51and the upstand portion52are of a relatively rigid plastics material for holding the primary receive coil6in a pre-defined position.

As alluded to above, this is important because alteration of the shape of the primary receive coil6will tend to affect tuning and matching that will negatively impact the sensitivity of the primary receive coil6. The rigid construction and the coil's6shape and positioning have been chosen to minimise these effects.

Each of the auxiliary receive coils7has a different structure from the primary receive coil6. Whilst the primary receive coil6is made of an unshielded conductor and has relatively low impedance, the auxiliary receive coils7are arranged as high impedance coils. In particular these coils7have higher impedance (as will be clear, what is referred to here is the magnitude of the impedance including both the resistive and reactive elements of the impedance) than that of the primary receive coil6. Furthermore, the size of the auxiliary receive coils7is smaller than that of the primary receive coil6, in particular the area which the auxiliary receive coils7bound is smaller than the area which the primary receive coil6bounds. This means that the primary receive coil6is better suited for receiving signals emanating from deep inside the subject whereas the auxiliary receive coils7are better suited for picking up signals emanating from a region of the subject close to the auxiliary receive coil7itself.

Further, due to the nature of the high impedance coils used for the auxiliary receive coils7, they couple much less with their environment and thus the precise positioning is less important. This leads to the possibility of more accurately locating these auxiliary receive coils7in relation to a subject and allowing these receive coils7to conform to the shape necessary to put them into close contact with the relevant regions of interest in the subject.

FIG.7schematically shows the connection arrangement of each of the auxiliary receive coils7. Each auxiliary receive coil7is made out of a length of coaxial cable comprising a central conductor71and an outer shield conductor72. In the receive coil the central conductor71is continuous around the coil and the ends of the central conductor71are connected to a respective matching board73(seeFIG.4). On the other hand, the shield conductor72is provided with a gap at a location remote from the ends of the inner conductor71whilst the two ends of the shield72near the ends of the inner conductor71are connected together. The matching boards73each comprise at least one electronic component, such as at least one tuning capacitor.

Due to the nature of the high impedance coils, the total length of each coaxial cable that defines the coil is restricted to close proximity to a half wavelength, thereby limiting the overall size of the auxiliary receive coils7.

In the present embodiment the cover portion4arrangement comprises a coil housing portion43which comprises a lattice work or web40of support members41. Open apertures42are defined between the support members41. Thus overall the cover portion4is very open and includes a minimised amount of support material. This can help save material, make the cover portion more acceptable/comfortable for a patient, and can help in achieving good radio transparency characteristics.

The coil housing portion43and in particular the web40of support members41supports each of the auxiliary receive coils7in a respective desired location. The support members41in the present embodiment are of two kinds. There are first support members41awhich house portions of the receive coils7(seeFIG.9) and second support members41bwhich do not house coil portions but help to support the first support members41ain the overall web40of support members41.

The cover portion4further comprises at least one terminal housing portion44(in the present embodiment there are two terminal housing portions44)—seeFIG.4—to which the ends of the auxiliary coils7lead and which house the respective matching boards73.

The receive coil housing portion43comprises a plurality of channel portions43aeach of which holds a respective portion of at least one of the auxiliary coils7. The location of the auxiliary coil7in the channel portion43ahelps hold the respective auxiliary coil7in position.

Each channel portion43acomprises a respective mouth43b, through which the auxiliary coil7can be introduced into the channel43a.

The cover portion4further comprises a web45of closing portions45a. Each closing portion45ais arranged to be push fitted into a mouth43bof a respective channel portion43ato block the mouth43band hence cover and help retain the auxiliary coil7which is located in the respective channel portion43a.

FIG.10shows part of the web45of closing portions45awhen partially push fitted into respective mouths43bof the receive coil housing portion43.

In the present embodiment the closing portions45aare arranged to completely fill the respective mouths43bof all of the channel portions43a. Together the channels43aof the coil housing portion43and closing portions45ain the present embodiment surround and encase the auxiliary coils7. In combination the terminal housing portions44, the coil housing portion43and closing portions45ain the present embodiment completely encase the auxiliary coils7and associated matching boards73. In the present embodiment no part of the auxiliary coils7is exposed or indeed visible in the assembled cover portion.

This is achieved without the need for processing of the support structure after the coils7are provided in position and without the need for adhesive or use of a coating material such as foam.

The closing portions45aand mouths43bare arranged to engage with one another to when push fitted into a closing position as shown inFIG.9from a first, open, position as partially shown inFIG.10. This engagement resists movement of the closing portions45aback out of the closing position but does not prevent it. Thus the closing portions45aare releasably locked or latched into the second, closing position.

Each mouth43bhas a re-entrant shape in cross-section as can be seen inFIG.9and each closing portion45ahas a correspondingly shaped insertion portion which engages with the re-entrant shaped mouth when the closing portion45ais pushed into the mouth43b.

The material of the closing portions45aand/or housing portion43is selected to be sufficiently resilient to allow this latching of the components together.

In the present embodiment the web40of support members and web45of closing portions are of a thermoplastic polyurethane. This can provide suitable resilience for the above described mouth closing system.

The relative flexibility of the web40of support members and web45of closing portions as well as the relative flexibility of the auxiliary receive coils7can provide advantages. The cover portion arrangement4,7is significantly more flexible than the base portion arrangement5,6.

As the webs40,45are flexible, the auxiliary coils7are flexible, and the auxiliary coils7can operate effectively when taking up a desired position this means that the cover portion4can be designed to closely fit the area of a subject which is of interest. Further the cover portion arrangement4,7may be flexed to some degree when being used with an individual patient, which can help allow positioning of the auxiliary coils7in an optimal position for the patient.

The flexibility of the arrangement plus the releasably lockable nature of the support structure gives another possibility.

When assembling the cover portion arrangement4,7, the appropriate receive coils7are introduced into the respective channel portions43aand then the closing portions45aare push fitted into place. The interaction of the housing portion43, closing portions45aand their interlocking serves to stiffen up the cover portion4to some degree. Because there is flexibility in the arrangement, the precise way that the closing portions45aare push fitted into place will subtly affect the relative positioning of the receive coils7supported in the cover portion4in this stiffened interlocked condition. This in turn can have an impact on the receive characteristics of the receive coil arrangement as a whole.

Thus when the closing portions45ahave been put in their closing positions, the receive characteristics may be checked (ie by using the receive coil arrangement in combination with an MRI machine to scan a test object or “phantom”). If these differ from what is expected and/or there is a desire to optimise performance, at least one of the closing portions45amay be moved back out of the second, closing, position and then reclosed so as to subtly move one or more of the auxiliary coils7relative to the others. After this the receive characteristics may be checked again. This process can then be stopped or continued until a desired level of receive performance is obtained.

The web40of support members and web45of closing portions are additively manufactured (for example “3D printed”) in the present embodiment. This facilitates producing a support structure that can be shaped and dimensioned to conform with a selected body part.

In alternatives different types of closing portions may be provided. First the closing portions may be made integral with or at least connected to the housing portion even when in the first, open, position. Second, irrespective of the above, a different type of closing approach may be taken in alternatives where the closing portion has two parts which can be push fitted together above or across the mouths of the housing portion to cover and/or retain a housed receive coil portion.

In the present embodiment the web45of closing portions45ais in one piece and includes a respective closing portion45afor each channel portion43ain the receive coil housing portion43. In alternatives however, individual closing portions45a, or a plurality of webs45of closing portions45amight be provided. Similarly in alternatives a plurality of webs40of support members41might be provided.

In the present embodiment the cover portion4is arranged for location on the head, face and neck of a patient. It correspondingly includes portions of the cover for covering the head, face and neck of the subject when in position.

The locations of the primary coil6and auxiliary coils7in relation to a subject when the subject is positioned on the base portion5and cover portion4, of the same general kind as shown inFIGS.8to10is in position, may be best seen inFIGS.11A and11B. Note that the actual set of auxiliary coils7illustrated inFIGS.11A and11Bis different in number and/or arrangement from that included in the cover portion arrangement4,7shown inFIGS.8to10, but the overall effect is similar, and it will be noted that various different forms of cover portion arrangements4,7and receive coil arrangements can embody the present invention.

In this instance, the primary coil6can be seen located in the region of the patient's head. The primary coil6has greater facility for acquiring data from a greater depth within the subject. This receive coil6may usefully pick up signals generated from any region within the patient's head and neck.

On the other hand, the auxiliary coils7(both in the arrangement shown inFIGS.4&8to10and the arrangement shown inFIGS.11A and11B) are located at differing locations over the patient's face and neck. There is partial overlapping between each auxiliary coil7but largely each auxiliary coil7is looking to pick up signals from a different area of face and neck of the subject.

In the arrangement shown inFIGS.11A and11Bthere are seven auxiliary coils7, three of which are arranged for location over a subject's face and four of which are arranged for location over a subject's neck and shoulder.

Correspondingly, if one thinks of the cover portion4as illustrated for example, inFIG.2, four of auxiliary coils7are provided on the neck covering portion of the cover and three of the auxiliary coils7are provided on the face covering portion of the cover4.

The auxiliary coils7are arranged, in both in the arrangement shown inFIGS.4&8to10and the arrangement shown inFIGS.11A and11B, to overlap each other by in the region of 10-15% to further reduce residual inductive coupling.

Again, in both cases the matching boards73for the auxiliary coils7are kept out of the central region i.e. the region of interest in the subject so that there is an electronic component free zone giving the benefits described above.

Note that the flexible design of the cover4as well as the fact that the auxiliary coils7are tolerant to being provided in different positions and bent into slightly different shapes, facilitates the provision of a cover portion arrangement4,7which may be used over a mask or other jig which needs to be used in a combined system. For example, in a MR-Linac system where a patient specific immobilization mask or jig is provided for appropriately directing the radiation used in the radiotherapy to be delivered by the MR-Linac system, a cover portion4of the present kind may be used in conjunction with that existing mask or jig without needing to modify it. Further of course using additive manufacturing—eg 3D printing—allows production in almost any shape configuration. The receive coil arrangement or at least the cover portion arrangement will typically be flexible—ie deformable in use or fitting by an operator. Moreover the receive coil arrangement can be made lightweight and/or can be made wearable.

As well as more conventional MRI, MR-Linac and PET MR as mentioned above, the present type of receive coil arrangement is also suitable for use in MR Sim (Simulation) systems and in general can be designed for use with pretty much all MR/MRI systems using different fields/radiation/particles since a relatively low volume of material can be used in the support structure, or at least the cover portion, and there is freedom in choice of the material to be used—thus for example good radio-translucent or radio-transparent properties can be obtained.

FIG.12is a schematic showing the overall connection arrangement of the receive coil arrangement shown inFIGS.2-10. The low impedance primary coil6and the high impedance auxiliary coils7are connected via appropriate cable traps8to preamp boards9, the output of which is fed to a driver malfunction board10and the output of this becomes the output of the receive coil arrangement3as a whole for feeding into the main MRI scanner arrangement1.