Patent Description:
A magnetic resonance/positron emission tomography (MR/PET) imaging system is a hybrid diagnostic system that includes two different imaging modalities. The integration of MR and PET imaging systems requires the location of PET detectors within a magnetic resonance imaging (MRI) system volume. Available space within an integrated MR/PET system comes at a premium of both cost and performance, with components often competing for an optimal location. For instance, a radio frequency (RF)-transmit antenna of the MRI system and the PET detectors of the PET system must both be placed as close to the patient as possible. In addition, an RF system of the MRI system and the PET electronics require electromagnetic shielding to protect each other against respective frequencies emitted by the RF system and PET detectors. As a result, a compromise solution is utilized that allows for the suitable location of the PET detectors while also allowing sufficient room for shielding and ease of access to the PET detectors during servicing or maintenance. <CIT> describes a magnetic resonance imaging and positron emission tomography device, where the positron emission tomography detection units are arranged radially within the magnetic resonance imaging gradient coil and can be inserted into the device and removed from the device along the longitudinal axis.

Referring to <FIG>, a front view of a conventional MR/PET imaging system <NUM> is shown. <FIG> is enlarged view of area <NUM> of <FIG>. The system <NUM> includes a patient bore <NUM> or tunnel that receives a patient to be scanned, RF transmit antenna or body coil <NUM> (component of the MRI system), PET gantry <NUM> (part of the PET system) that includes a gantry tube <NUM>, gradient coil <NUM> (a component of the MRI system) and superconducting magnet <NUM> (a component of the MRI system). The PET gantry <NUM> includes a plurality of PET detectors and an RF screen <NUM> (a component of the MRI system) located on an inner surface <NUM> of a gantry tube <NUM>. It would be advantageous in such systems to provide access to a single PET detector without having to disassemble or disturb substantial portions of system <NUM>, especially if leaving the PET gantry <NUM> in place. The PET detectors may be located either on a separate gantry tube <NUM> or integrated into a RF-transmit antenna tube. In both conventional arrangements, the PET detectors are installed or loaded radially into a supporting tube. In order to gain access to the PET detectors, removal of a substantial portion of the structure from the system <NUM> is required even if only one PET detector needs servicing. Referring to <FIG>, a perspective view of the system <NUM> is shown wherein the PET gantry <NUM> is in an extended position. In this position, PET detectors <NUM> of the system <NUM> are exposed thus enabling servicing of the PET detectors <NUM>. A first end <NUM> of the PET gantry <NUM> is supported by a backplane <NUM> that is moveably attached to service rails <NUM> that enable separation of the backplane <NUM> from a remaining portion <NUM> of the system <NUM> and movement of the PET gantry <NUM> to the extended position. A second end <NUM> of the PET gantry <NUM>, opposite the first end <NUM>, stays in the remaining portion <NUM> and is supported by rolling elements. The gantry tube <NUM> is configured to hold the PET detectors <NUM> such that the PET detectors <NUM> are inserted into the gantry tube <NUM>, or removed from the gantry tube <NUM> (exemplary PET detector <NUM> is shown in <FIG>), in a direction substantially transverse to a longitudinal center axis <NUM> of the system <NUM> (i.e., in a radial direction) as shown by arrow <NUM>.

The exemplary embodiments of the invention are further described in the following detailed description in conjunction with the accompanying drawings, in which:.

Although various embodiments that incorporate the teachings of the present disclosure have been shown and described in detail herein, those skilled in the art can readily devise many other varied embodiments that still incorporate these teachings. The scope of the disclosure is not limited in its application to the exemplary embodiment details of construction and the arrangement of components set forth in the description or illustrated in the drawings. The disclosure encompasses other embodiments and of being practiced or of being carried out in various ways. Unless specified or limited otherwise, the terms "mounted," "connected," "supported," and "coupled" and variations thereof are used broadly and encompass direct and indirect mountings, connections, supports, and couplings.

Referring to <FIG>, a front view of a gantry tube <NUM> used to form a PET gantry in accordance with an aspect of the invention is shown. The gantry tube <NUM> is part of an imaging system such as a magnetic resonance/positron emission tomography (MR/PET) imaging system <NUM> (see <FIG>). The gantry tube <NUM> includes a first tube <NUM> located within a second tube <NUM>. The first tube <NUM> is positioned about the longitudinal axis <NUM>. The gantry tube <NUM> further includes a plurality of wall elements <NUM> connected between the first <NUM> and second <NUM> tubes. Each wall <NUM> extends between an outer surface <NUM> of the first tube <NUM> and an inner surface <NUM> of the second tube <NUM> to form a plurality of channels <NUM> between the first <NUM> and second <NUM> tubes. In accordance with an aspect of the invention, each channel <NUM> holds an associated PET detector <NUM> of the system <NUM> (<FIG>). Further, each channel <NUM> is configured to receive an associated PET detector <NUM> in an axial direction as will be described in connection with <FIG>.

<FIG> depicts an enlarged view of an exemplary channel <NUM>. A size or width W of each wall <NUM> gradually increases as the wall <NUM> extends from the first tube outer surface <NUM> toward the second tube inner surface <NUM> to form a substantially triangularly or wedge-shaped wall <NUM>. This forms a channel <NUM> having a substantially rectangular shape suitable for receiving a single PET detector <NUM>. Alternatively, the channel <NUM> may have other shapes suitable for receiving a corresponding PET detector shape such as square shape, for example. An inner surface <NUM> (see <FIG>) of the first tube <NUM> defines the patient bore <NUM> that receives a patient to be scanned.

Referring to <FIG>, a segment <NUM> of the gantry tube <NUM> is shown. In an embodiment, the segment <NUM> has a substantially curved shape and includes first <NUM>, second <NUM>, third <NUM> and fourth <NUM> channels. The gantry tube <NUM> is formed by joining several segments <NUM>. For example, the segments <NUM> may be joined on a mandrel using adhesives and mechanical locking features. In aspect of the invention, assembly of the segments <NUM> on a mandrel provides a uniform and repeatable surface for the RF screen <NUM> (see <FIG>). In particular, the RF screen <NUM> is placed on the mandrel before the segments <NUM> are bonded together and to the RF screen <NUM>.

The segment <NUM> may be fabricated using a polymer material and is formed by a pultrusion process that enables formation of thin walls suitable for forming the channels <NUM>. It has been found by the inventors herein that the pultrusion technique may be used to form a segment <NUM> having a single channel <NUM> although the formation of additional channels <NUM>, such as three or more channels <NUM>, has been found to provide more suitable results. Further, a segment <NUM> that includes a channel <NUM> that is not desired may be removed by machining away the channel <NUM>. For example, a single channel <NUM> may be machined away from a segment <NUM> having an odd number of channels <NUM>. In an alternative method of fabrication, a large autoclave is used to join segments <NUM> that are made from pre-impregnated materials. The segments <NUM> are then cured under the vacuum and heat of the autoclave to form the gantry tube <NUM>.

Referring to <FIG>, perspective patient <NUM> and service <NUM> end views of the gantry tube <NUM> are shown. The gantry tube <NUM> and channels <NUM> are oriented in a longitudinal direction about the longitudinal axis <NUM>. In accordance with an aspect of the invention, the longitudinal orientation of each channel <NUM> enables insertion of a PET detector <NUM> (exemplary PET detector <NUM> is shown in <FIG>) in each channel <NUM>, or the removal of a PET detector <NUM> from a channel <NUM>, in an axial direction (i.e., as shown by arrow <NUM>) substantially parallel to the longitudinal axis <NUM>. The gantry tube <NUM> is stationary and thus the PET detectors <NUM> are inserted or removed without moving or extending the gantry tube <NUM> relative to a remaining portion of the system <NUM>.

A patient is received into the patient bore <NUM> via the patient end <NUM> (<FIG>). Servicing of the gantry tube <NUM> may be performed via the service end <NUM> (<FIG>) which is opposite the patient end <NUM>. The channels <NUM> extend between the patient <NUM> and service <NUM> ends. In accordance with an aspect of the invention, each PET detector <NUM> may be inserted into an associated channel <NUM> in the axial direction <NUM> via the patient end <NUM> or the service end <NUM>.

First <NUM> and second <NUM> support rings are located on the patient <NUM> and service <NUM> ends, respectively, of the gantry tube <NUM>. The support rings <NUM>, <NUM> may be removably attached to the gantry tube <NUM> and serve as an anchor point for the body coil <NUM> of the MRI portion of the system <NUM>. In an embodiment, the first <NUM> and second <NUM> support rings are attached to an outer diameter <NUM> of the second tube <NUM> at the patient end <NUM> and an inner diameter <NUM> of the first tube <NUM> at the service end <NUM>, respectively, of the gantry tube <NUM>. This enables mounting of the gantry tube <NUM> inside the gradient coil <NUM> while still allowing access to the PET detectors <NUM> positioned in the channels <NUM> and shims that are used to adjust a position the gradient coil <NUM>. Further, the support rings <NUM>, <NUM> provide additional stiffness to the gantry tube <NUM>.

The support rings <NUM>, <NUM> are located outside of a field of view of the PET detectors <NUM> such that they do not attenuate a PET signal generated by the PET portion of the system <NUM>. The support rings <NUM>, <NUM> are optimally placed for mounting the gantry tube <NUM> to the system <NUM>. In accordance with an aspect of the invention, the body coil <NUM>, a component that is easily damaged in service, may be exchanged without removing the gantry tube <NUM>.

Each segment <NUM> may be fabricated from a polymer enhanced with glass fiber such as glass reinforced plastic. Alternative materials having slight to moderate electrical conductivity, such as carbon fiber, polymers enhanced with copper or metallic additives and metallic meshes may be used to provide both structural strength and shielding against electromagnetic interference (EMI) generated during operation of the system <NUM>. In particular, a balance must be achieved between providing proper shielding and the effects of eddy current heating on a conductive structure. In accordance with an aspect of the invention, a metallic surface <NUM> may be formed on an inside surface <NUM> of at least one channel <NUM> to form a waveguide. For example, the metallic surface <NUM> may be a metallic coating that is applied to the inside surface <NUM> or a metallic foil that is laminated on to the inside surface <NUM>.

It has been found by the inventors herein that the pultrusion process produces segments <NUM> that are highly stable and precise. The geometry and reproducibility of the inner surface <NUM> of the first tube <NUM> is acceptable when a mandrel is used. A shape of an RF screen carrier should be precise and the inner surface of the segment <NUM> provides a suitable surface for the screen while adding no extra supporting features. Further, gaps between PET detectors <NUM> are minimized and the polymer profile in front of the PET detectors <NUM> has low attenuation. For example, the gaps may be approximately <NUM>-<NUM> in size.

Referring to <FIG>, a front view of an MR/PET imaging system <NUM> is shown that includes the gantry tube <NUM> of the invention. The system <NUM> includes the patient bore <NUM> that receives a patient to be scanned, body coil <NUM>, gantry tube <NUM> that forms a part of a PET gantry <NUM>, gradient coil <NUM>, superconducting magnet <NUM> and the RF screen <NUM> located on the first tube inner surface <NUM>.

In an aspect of the invention, a gantry tube <NUM> for a system <NUM> is disclosed that enables insertion or removal of PET detectors <NUM> in and out of associated channels <NUM> of the gantry tube <NUM> by sliding the PET detectors <NUM> in and out of the associated channels <NUM> in an axial direction <NUM> at either the patient end <NUM> or service <NUM> end of the gantry tube <NUM>. Access to the PET detectors <NUM> is provided without removing the gantry tube <NUM> from the magnet <NUM>, thus reducing system downtime and the risk of damage to equipment. Since the gantry tube <NUM> does not move and remains inside the gradient coil <NUM>, only a simple attachment to the magnet <NUM> is needed thus simplifying the mechanical structure of the system <NUM> (i.e., no rails, bearing, backplanes, etc. are needed). The risk of injury from moving a heavy gantry is substantially reduced and specialty tools are not required for performing service. In addition, the invention provides a known and reproducible surface to attach an RF shield of the body coil <NUM>. Further, the RF cabin (i.e., a scan room wherein system <NUM> is located) may be optimized and reduced in size since the gantry tube <NUM> does not extend from the system <NUM> and thus an extended PET gantry length does not factor into room size requirements. In addition, the material used to fabricate the gantry tube <NUM> has low attenuation for the PET signal and gantry fabrication is very precise allowing for the accurate location of each PET detector <NUM> in the gantry tube <NUM>.

In an alternative embodiment, the PET gantry <NUM> including gantry tube <NUM> may be integrated directly into the gradient coil <NUM>. In this embodiment, the effects of vibration and heat on the PET detectors <NUM> should be minimized since both are detrimental to the associated electronics and operation of the PET detector <NUM>.

Claim 1:
A gantry tube (<NUM>, <NUM>) for a medical imaging system (<NUM>, <NUM>), wherein the medical imaging system (<NUM>, <NUM>) is a magnetic resonance/positron emission tomography (MR/PET) imaging system, comprising:
a first tube (<NUM>) located within a second tube (<NUM>), wherein the first tube (<NUM>) is oriented about a longitudinal axis (<NUM>) of the system; and
a plurality of wall elements (<NUM>) that extend between the first and second tubes (<NUM>, <NUM>), to form a plurality of channels (<NUM>) that extend in an axial direction substantially parallel to the longitudinal axis (<NUM>) wherein each channel (<NUM>) is configured to hold a PET detector (<NUM>, <NUM>) of the system and wherein the PET detector (<NUM>, <NUM>) is configured to be inserted into or removed from an associated channel (<NUM>) in the axial direction,
characterized in that,
the gantry tube (<NUM>, <NUM>) is fabricated by joining a plurality of segments (<NUM>) that each include sections of the first and second tubes (<NUM>, <NUM>), wall elements (<NUM>) and a second plurality of channels (<NUM>).