WO2019091872A1

WO2019091872A1 - Disposable prostate coil for mri with hybrid quarter wave transformer detune circuit and wireless power

Info

Publication number: WO2019091872A1
Application number: PCT/EP2018/080041
Authority: WO
Inventors: Aasrith GANTI; Arash DABIR; Alan Leroy HOLLAND; Timothy ORTIZ; Ronald KOSAL
Original assignee: Koninklijke Philips N.V.
Priority date: 2017-11-09
Filing date: 2018-11-02
Publication date: 2019-05-16

Abstract

A magnetic resonance (MR) endo-coil designed to operate at an MR frequency includes a coil section (20) and an interface section (30). The coil section includes a coaxial cable (22) having a proximal end (24) and a distal end (26), at least one MR receive coil loop (28) connected at the distal end of the coaxial cable, and a first electrical connector (32) disposed at the proximal end of the coaxial cable. The interface section (30) includes a preamplifier (50), an impedance matching circuit (40), and a second electrical connector (34) that is configured to mate with the first electrical connector. When connected, a quarter wave transformer (44) at the MR frequency is formed, comprising the coaxial cable of the coil section and the impedance matching circuit of the interface section. The quarter wave transformer electrically connects the at least one MR receive coil loop and the preamplifier.

Description

DISPOSABLE PROSTATE COIL FOR MRI WITH HYBRID QUARTER WAVE

TRANSFORMER DETUNE CIRCUIT AND WIRELESS POWER

FIELD

[0001] The following relates generally to magnetic resonance imaging arts, the magnetic resonance receive coil arts, magnetic resonance endo-coil arts, and related arts.

BACKGROUND

[0002] Prostate cancer is a prevalent form of cancer among men in the United States. It is also a leading cause of death amongst men with cancer. Various interventional procedures are known for diagnosing, monitoring, and treating prostate cancer. Typically, a biopsy is performed to obtain histopathology samples for diagnostic or monitoring purposes. If brachytherapy is employed as a treatment, then a further interventional procedure entails implantation of radioactive seeds. In image guided interventional procedures, an imaging modality (typically ultrasound imaging) is employed to visualize the tumor and surrounding anatomy and placement of the biopsy needle or other interventional instrument during the procedure.

[0003] In a typical workflow, 30-55 biopsy samples of the prostate and tumor are collected under ultrasound guidance for analysis. However, ultrasound imaging provides relatively poor image resolution. Studies suggest that by using magnetic resonance (MR) imaging for improved visualization, the number of biopsies can be more than halved. One known image guided therapy (iGT) setup is the UroNav™ Fusion Biopsy System (available from Invivo, Gainesville, Florida, USA). This system uses MR images to increase accuracy of the target during ultrasound biopsies. This done by fusing planning MR images previously acquired using an MR scanner with real-time (i.e. "live") ultrasound images in real time.

[0004] To achieve maximal benefit, the MR images should have good Image quality and resolution, and the prostate should be positioned similarly to during the subsequent live ultrasound imaging. Currently prostate scans on the MR scanner are performed using various MR receive coil setups. In one approach, only exterior coils are used, usually including anterior and posterior coils, possibly augmented by a surface coil placed close to the prostate. As only external coils are used, the image quality can be less than ideal. Improved image quality can be obtained by additionally using an endo-rectal coil. However, the endo-rectal coil adds considerable cost and complexity to the prostate MR imaging examination. In one design, the endo-rectal coil has an inflatable balloon for positioning the coil close to the prostate. However, the inflated balloon introduces distortion of the prostate - as a consequence, the prostate is positioned differently during the MR examination as compared with during the subsequent ultrasound-guided interventional procedure. This reduces the accuracy of the cross-modality ultrasound/MR image registration which in turn substantially reduces the benefits of fusing the MR image with the live ultrasound imaging. In another design, the endo-rectal coil is designed more analogously to a traditional surface coil, and does not include an inflatable balloon. This coil design is expensive, and in view of its high cost it is designed to be reusable. However, the coil reuse requires performing a lengthy cleaning procedure between uses, which compromises patient throughput. Overall, the cost of operation is very high.

[0005] A further difficulty with the disposable balloon coil is that the electrical coupling is complex and cumbersome. A quarter wavelength cable has been used that behaves as a pick up loop in receive mode and is invisible in the transmit mode that connects to a standard port. The quarter wavelength cable is long - at 3 Tesla, which is a typical static (Bo) magnetic field used in MR imaging, the MR frequency is 128 MHz leading to a quarter wavelength cable that is almost 60 cm in length. This cable is long enough to sustain standing waves generating cable currents during the MR transmit phase of the MR imaging. For this reason, the coil is used in a specific fixed position, which complicates other aspects of the MR imaging examination workflow such as patient positioning, and can also compromise patient comfort.

[0006] The following discloses certain improvements.

SUMMARY

[0007] In one disclosed aspect, a magnetic resonance (MR) endo-coil designed to operate at an MR frequency is disclosed. The MR endo-coil comprises a coil section and an interface section. The coil section includes a coaxial cable having a proximal end and a distal end, at least one MR receive coil loop connected at the distal end of the coaxial cable, and a first electrical connector disposed at the proximal end of the coaxial cable. The interface section includes a preamplifier, an impedance matching circuit, and a second electrical connector that is configured to mate with the first electrical connector to connect the coil section and the interface section and to define a quarter wave transformer at the MR frequency. The quarter wave transformer comprises the coaxial cable of the coil section and the impedance matching circuit of the interface section. The quarter wave transformer electrically connects the at least one MR receive coil loop of the coil section and the preamplifier of the interface section.

[0008] In another disclosed aspect, a coil section of an MR endo-coil designed to operate at an MR frequency is disclosed. The coil section comprises: a coaxial cable having a proximal end and a distal end wherein the coaxial coil is not a quarter wave transformer at the MR frequency; at least one MR receive coil loop connected at the distal end of the coaxial cable; and a first electrical connector disposed at the proximal end of the coaxial cable. The coil section does not include a preamplifier.

[0009] In another disclosed aspect, an MR endo-coil designed to operate at an MR frequency is disclosed. The MR endo-coil comprise a coil section as set forth in the immediately preceding paragraph, and an interface section. The interface section includes a preamplifier, an impedance matching circuit, and a second electrical connector that is configured to mate with the first electrical connector to connect the coil section and the interface section and to define a quarter wave transformer at the MR frequency. The quarter wave transformer comprises the coaxial cable of the coil section and the impedance matching circuit of the interface section. The quarter wave transformer electrically connects the at least one MR receive coil loop of the coil section and the preamplifier of the interface section.

[0010] In another disclosed aspect, a method of receiving an MR signal at an MR frequency is disclosed. The method comprises: connecting a first electrical connector of a coil section with a second connector of an interface section wherein the connecting forms a quarter wave transformer at the MR frequency comprising a coaxial cable of the coil section and an impedance matching circuit of the interface section, the quarter wave transformer electrically connecting at least one MR receive coil loop of the coil section and a preamplifier of the interface section; and receiving an MR signal at the MR frequency using the at least one MR receive coil loop of the coil section wherein the received MR signal is communicated to the preamplifier of the interface section via the quarter wave transformer.

[0011] One advantage resides in providing an endo-coil that does not include an inflatable balloon for coil positioning and consequently does not deform proximate tissue during inflation of such a balloon.

[0012] Another advantage resides in providing an endo-coil having lower operational cost compared with other endo-coil designs. [0013] Another advantage resides in providing an endo-coil having simplified operation and consequently reduced impact on MR imaging workflow.

[0014] Another advantage resides in providing an endo-coil with reduced cable length.

[0015] Another advantage resides in providing an endo-coil with a disposable coil section having a low cost.

[0016] Another advantage resides in providing an endorectal coil having one or more of the foregoing benefits.

[0017] A given embodiment may provide none, one, two, more, or all of the foregoing advantages, and/or may provide other advantages as will become apparent to one of ordinary skill in the art upon reading and understanding the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The invention may take form in various components and arrangements of components, and in various steps and arrangements of steps. The drawings are only for purposes of illustrating the preferred embodiments and are not to be construed as limiting the invention.

[0019] FIGURE 1 diagrammatically illustrates an endorectal coil as disclosed herein in context with a suitable magnetic resonance (MR) imaging scanner with which it may be used.

[0020] FIGURE 2 diagrammatically illustrates an enlarged view of the endorectal coil of

FIGURE 1.

[0021] FIGURE 3 diagrammatically illustrates the endorectal coil of FIGURES 1 and 2 with the coil section and the interface section disconnected from each other.

[0022] FIGURE 4 diagrammatically illustrates an electrical schematic of the endorectal coil of FIGURES 1 and 2 with the coil and interface sections connected together to define a quarter wave transformer. The schematic of FIGURE 4 depicts the portion of circuitry of the interface section from the connector to the preamplifier. Insets A and B diagrammatically show two illustrative generalized topologies that may be employed for the impedance matching circuit of the quarter wave transformer.

[0023] FIGURE 5 diagrammatically illustrates the electrical schematic of the endorectal coil shown in FIGURE 4 in its high impedance state in which the endorectal coil is detuned, as appropriate during the transmit phase of an MR imaging sequence. [0024] FIGURE 6 diagrammatically illustrates the electrical schematic of the endorectal coil shown in FIGURE 4 in its impedance matched state as appropriate for use in receiving an MR signal during the receive phase of an MR imaging sequence.

[0025] FIGURE 7 diagrammatically illustrates an electrical schematic of an alternative wireless embodiment of the endorectal coil, again with the coil and interface sections connected together to define a quarter wave transformer.

[0026] FIGURE 8 diagrammatically illustrates the endorectal coil of FIGURE 7.

DETAILED DESCRIPTION

[0027] With reference to FIGURE 1 , an endo-coil 10 is employed in conjunction with a magnetic resonance (MR) imaging scanner 12 as a coil for receiving an MR signal. The MR scanner 12 includes internal components not shown in FIGURE 1 but well-known in the art such as a resistive or superconducting main magnet that generates a static (B₀) magnetic field in an examination region 14 (e.g. in a bore 14 in the illustrative horizontal-bore type MR scanner 12), and one or more transmit MR coils and associated hardware such as a radio frequency (RF) transmitter and RF amplifier for exciting magnetic resonance at an MR frequency defined in terms of the static magnetic field, e.g. a 3 Tesla static magnetic field supports magnetic resonance in ^!H protons at 128 MHz, more generally the MR frequency f_MR = γΒ₀ where γ is the gyrometric ratio (in units of Hz/Tesla) for the nuclei in which magnetic resonance is to be excited. The MR scanner 12 further typically includes magnetic field gradient coils for superimposing magnetic field gradients on the static magnetic field. Depending upon the orientation and timing of these applied gradient fields, they can serve purposes such as spatially localizing the MR excitation to a target slice, spatially encoding the phase and/or frequency of the MR resonance, spoiling residual MR resonance, and/or so forth.

[0028] The endo-coil 10 is employed as an MR receive coil, for the purpose of detecting an MR signal generated by the MR imaging scanner 12. The illustrative endo-coil 10 is an endorectal coil that is inserted into the rectum of a patient during an MR imaging examination of the prostate or other anatomy proximate to the rectum. While an endorectal coil 10 is described for illustrative purposes, the endo-coil can be configured for insertion into some other body cavity, as another example an endocervical coil is designed for insertion into the cervical passage leading into the uterus. [0029] With reference now to FIGURES 2 and 3, the illustrative endorectal coil 10 includes a coil section 20, which is a disposable component (that is, the coil section 10 is preferably used once for a single patient, and is thereafter disposed of in a sanitary manner), and an interface section 30 that is not disposable (that is, the interface section 30 is used for many patients, i.e. is not disposed of after a single use). The coil section 20 includes a coaxial cable 22 having a proximal end 24 and a distal end 26. At least one MR receive coil loop 28 is connected at the distal end 26 of the coaxial cable 22. The illustrative at least one MR receive coil loop 28 is a rigid coil, e.g. comprising one or more electrically conductive loop elements tuned to the MR frequency using a tuning capacitor or the like, and built using a rigid printed circuit board (PCB). Alternatively, a flexible PCB may be employed to provide some mechanical flexibility or flexure for the least one MR receive coil loop 28. The illustrative coil section 20 is also designed to incorporate an optional annular groove 29 that serves as a seat for engaging the sphincter of the rectum.

[0030] The endorectal coil 10 further includes the interface section 30. The coil section

20 further includes a first electrical connector 32 that is disposed at the proximal end 24 of the coaxial cable 22; and, the interface section 30 includes a second electrical connector 34 that is configured to mate with the first electrical connector 30 of the coil section 20. FIGURE 2 illustrates the coil section 20 and the interface section 30 connected together by the respective mating connectors 32, 34. FIGURE 3 illustrates the coil section 20 and the interface section 30 separated by disconnection of (or prior to connection of) of the mating connectors 32, 34 of the respective coil and interface sections 20, 30. The second electrical connector 34 is configured to mate with the first electrical connector 32 in that the two connectors 32, 34 have compatible pins and female pin receptacles to provide the intended electrical connections, or comprise an edge connector and a compatible female edge connector receptacle, or otherwise have suitable mating configurations providing the desired conduction of electrical signal across the mated connectors 32, 34.

[0031] With continuing reference to FIGURE 2 and with further reference to FIGURE 4, an electrical schematic of the endorectal coil of FIGURE 2 is diagrammatically depicted in FIGURE 4 with the coil and interface sections connected together by the mating connectors 32, 34. The illustrative at least one MR receive coil loop 28 is a single coil loop modeled as an inductance L_L and a capacitance C_L in series. These may be discrete or distributed impedances, or some combination thereof. It is contemplated for the at least one MR receive coil loop to include two or more loops, e.g. connected in series as a single channel or operating as multiple channels, e.g. with switching for selecting the channel(s) to use and/or configured as multiple channels to perform parallel imaging. As seen in FIGURE 4, the interface section 30 further includes an impedance matching circuit 40 and signal processing circuitry 42. As shown in FIGURE 4, the connection of the coil section 20 and the interface section 30 defines a quarter wave transformer 44 at the MR frequency. The quarter wave transformer 44 includes the coaxial cable 22 of the coil section 20 and the impedance matching circuit 40 of the interface section 30. These components 22, 40 are electrically connected together by the mating connectors 32, 34 to define the quarter wave transformer 44. With the coil section 20 and the interface section 30 connected together by the mating connectors 32, 34, the quarter wave transformer 44 electrically connects the at least one MR receive coil loop 28 of the coil section 20 and the signal processing circuitry 42 of the interface section 30.

[0032] The quarter wave transformer 44 is sometimes referred to herein as a hybrid quarter wave transformer 44, because it is constructed by electrical connection of the coaxial cable 22 of the coil section 20 and the impedance matching circuit 40 of the interface section 30. The coil section 20 does not include signal processing circuitry (rather, the signal processing circuitry 42 is disposed in the interface section 30), and the coil section 20 does not present a 50 ohm impedance (or other design-basis RF coupling impedance for impedance matching) at the first electrical connector 32. Rather, the combination of the coaxial cable 22 of the coil section 20 and the impedance matching circuit 40 of the interface section 30 together define the hybrid quarter wave transformer 44 that provides impedance matching of the at least one MR receive coil loop 28 to the signal processing circuitry 42.

[0033] The hybrid quarter wave transformer 44 is tuned so that it has a high impedance at the frequency of interest (e.g. 128 MHz for ^!H proton imaging in a static magnetic field of 3.0 Tesla, or 64 MHz for ^!H proton imaging in a static magnetic field of 1.5 Tesla, or so forth). To this end, the length of the coaxial cable 22 of the coil section 20 is shorter than the length required to achieve a quarter wavelength at the MR frequency. This has the additional practical advantage of providing the coil section 20 with a shorter and hence more manageable cable length. (By contrast, as a counter-example a quarter wavelength cable at the 128 MHz MR frequency of a 3 Tesla MR scanner is almost 60 cm in length, which is cumbersome for use in an MR prostate imaging examination). The impedance matching circuit 40 is tuned so that a high impedance is achieved at the coil end (i.e. distal end 26) of the coaxial cable 22. Further, the output of the impedance matching circuit 40 is matched to the signal processing circuitry 42 using any standard RF impedance matching technique.

[0034] A potential disadvantage of this design is that the MR signal travels a relatively long distance along the coaxial cable 22 before reaching the signal processing circuitry 42 that performs pre-amplification of the signal. MR signal loss along the coaxial cable 22 can be reduced to some extent since the coaxial cable 22 is made shorter than a quarter wave cable. However, to avoid unacceptably high MR signal loss over the coaxial cable 22, it is also preferable for the coaxial cable 22 to have a low impedance so as to achieve a low insertion loss. In some embodiments, the coaxial coil 22 of the coil section 20 has an insertion loss of less than 8 dB/lOOft, and more preferably less than 7.6 dB/lOOft and have low DC Resistance.

[0035] In the main illustrative embodiment, the impedance matching circuit 40 is a pi-circuit including an inductor Li, a capacitor Ci, and a capacitor C₂ in the pi-shaped circuit topology shown for the impedance matching circuit 40 of FIGURE 4. The lumped circuit elements Li, Ci, and C₂ of the impedance matching circuit 40, along with the impedance Z_cabi_e of the coaxial cable 22, are tuned to provide a high impedance at the distal end 26 of the coaxial cable 22, and to provide a desired matching impedance at the input to the signal processing circuitry 42 (e.g., a 50 ohm impedance at the input to the signal processing circuitry 42 if the 50 ohm impedance matching convention commonly used in RF and microwave engineering is adopted). The illustrative signal processing circuitry 42 includes a preamplifier 50, e.g. typically embodied as an amplifier integrated circuit (IC) and associated electronic circuitry such as a preamplifier matching circuit comprising capacitors C₃ and C4 and inductor L₂. The illustrative signal processing circuitry 42 further includes a detuning mechanism, e.g. an illustrative diode Di controlled by a DC input 52 that controls the quarter wavelength transformer 44.

[0036] With continuing reference to FIGURE 4, Insets A and B diagrammatically show two illustrative generalized topologies that may be employed for the impedance matching circuit 40 of the hybrid quarter wave transformer 44. Inset A shows a generalized pi-section impedance matching circuit including impedances Zi, Z₂, and Z₃ (which are specifically Z\=L\; Z₂=Ci; Z₃=C₂ in the illustrative pi-circuit of the main example of FIGURE 4). Inset B shows a generalized T -section impedance matching circuit including impedances Z_A, Z_b, and Zc forming a T-shaped topology. Typically, the impedances Zi, Z₂, and Z₃ (or alternatively the impedances ZA, ZB, and Zc) will comprise at least one inductor and at least one capacitor. These are merely illustrative examples, and other impedance matching circuit topologies having impedances that are tunable in combination with the impedance Z_cabi_e of the coaxial cable 22 to achieve high impedance at the distal end 26 of the coaxial cable 22 and the desired matching impedance at the input to the signal processing circuitry 42 are contemplated.

[0037] With continuing reference to FIGURE 4, the endo-coil 10 is preferably detuned to present a high impedance during the transmit phase of an MR imaging sequence. This prevents the large excitation RF field from inducing potentially harmful electrical currents in the at least one MR receive coil loop 28. Such induced currents could result in damage to the preamplifier and/or, in extreme cases, coil heating and potential patient injury. To provide for detuning, the illustrative signal processing circuitry 42 includes a connection to the signal from MR System 52 includes detuning circuitry including the switching diode Di (e.g. a PiN diode, although another switching element may be employed) and ancillary impedances L₄, C₃, C₄, and C5 and a dc detuning input 52 for activating and deactivating the detuning.

[0038] With reference to FIGURE 5, the detuned state is shown. To detune the coil a dc current is applied to the dc input 52 to turn the diode Di on so as to create a short 54 as shown in FIGURE 5. More particularly, the PiN diode Di is turned on to create the short 54 at the input of the hybrid quarter wave transformer 44 during the transmit phase of the MR imaging sequence. The short 54 converts to an open (high impedance) at the at least one MR receive coil loop 28. This high impedance reduces the currents induced in the at least one MR receive coil loop 28 and thereby protects the preamplifier 50.

[0039] With reference to FIGURE 6, the normal operational state (i.e. with the detuning deactivated) is shown. As shown in FIGURE 6, during the receive phase of the MR imaging sequence, the PiN diode Di is turned off by removing the dc current applied at the dc input 52 (and optionally by applying a negative dc bias at dc input 52), thereby creating an open 56 as shown in FIGURE 6. The open 56 is converted by the quarter wave transformer 44 to a short (or low impedance) at the at least one MR receive coil loop 28 and the MR signal is acquired. The received signal is fed to the signal processing circuitry 42, where preamplifier 50 receives the signal from at least one MR receive coil loop 28 by the quarter wave transformer 44 and is matched to the preamplifier 50 through the matching network including capacitors C₃ and C4 and inductor L₂.

[0040] With brief reference back to FIGURES 1-3, the interface section 30 in one embodiment employs an electrical cable 60 terminating in an electrical plug 62 for connection with a coils port 64 of the MR imaging scanner 12. The electrical cable 60 provides electrical power for the endorectal coil and wiring for porting the amplified MR signal off the coil. The illustrative electrical cable 60 includes one or more (illustrative two) baluns 66 for blocking induced currents at the MR frequency on the wires supplying electrical power.

[0041] With reference now to FIGURE 7, an electrical schematic of an alternative, wireless, embodiment of the endorectal coil shown. The electrical schematic of FIGURE 7 again shows the coil and interface sections 20, 30 connected together to define the quarter wave transformer 44. The schematic of FIGURE 7 is at a higher level than that of FIGURE 4 in that the detuning portion is diagrammatically indicated by the diode Di (without showing the additional components of FIGURE 4) and the signal processing circuitry 42 is shown at a higher level where the matching circuit (components C₃, C₄, L₂ of FIGURE 4) of the preamplifier 50 is generically indicated by box 53. To avoid the need for an electrical power cable, the interface section 30 of the embodiment of FIGURE 7 includes an on-board power supply 70, such as a battery (or battery compartment designed to receive a battery). The on-board power supply 70 may optionally include an energy harvesting circuit that may enable wireless charging of the battery or of a storage capacitor. When wireless power is being used, Qi standard or any other available standards are used to communicate with the charger. MR compatible batteries such as those conventionally used for patient monitoring in an MR setting are suitably employed. The wireless embodiment of FIGURE 7 further employs on-board digitization of the amplified MR signal by a digitizer 72, and a fiber optic transmitter 74 operatively connected with the signal processing circuitry 42 (via digitizer 72 in illustrative FIGURE 7) to optically output the MR signal acquired by the at least one MR receive coil 28 and amplified by the preamplifier 50 to an optical fiber 76. The fiber optic transmitter 74 may, for example, comprise a light emitting diode (LED) or laser diode emitting at a wavelength for which the optical fiber 76 has a transparency window. Such an arrangement removes the need for the electrical cable 60 of the embodiment of FIGURES 1-3 and its balun(s) 66, increasing overall patient safety, flexibility and workflow. [0042] With reference to FIGURE 8, the physical structure of the wireless embodiment of the endorectal coil of FIGURE 7 is shown. In another variant embodiment (not shown), the fiber optic transmitter 74 of the embodiment of FIGURE 7 is replaced by a radio transmitter operatively connected with the preamplifier 50 (e.g. directly connected, or via digitizer 72) to wirelessly output the MR signal acquired by the at least one MR receive coil 28 and amplified by the preamplifier 50. In embodiments employing a radio transmitter, both the electrical cable 60 of the embodiment of FIGURES 1-3 and the optical fiber 76 of the embodiment of FIGURES 7 and 8 are suitably omitted.

[0043] To use the endorectal coil, the first electrical connector 32 of the coil section 20 is connected with the second connector 34 of the interface section 30. This connecting forms the quarter wave transformer 44 at the MR frequency, comprising the coaxial cable 22 of the coil section 20 and the impedance matching circuit 40 of the interface section 30. The quarter wave transformer 44 electrically connects the at least one MR receive coil loop 28 of the coil section 20 and the signal processing circuitry 42 of the interface section 30. An MR signal at the MR frequency is then received using the at least one MR receive coil loop 28 of the coil section 20, wherein the received MR signal is communicated to the signal processing circuitry 42 of the interface section 30 via the quarter wave transformer 44. In the embodiment of FIGURE 7, the received MR signal amplified by the preamplifier 50 is optically transmitted using the fiber optic transmitter 74 of the interface section 30. Alternatively, the received MR signal amplified by the preamplifier 50 may be wirelessly transmitted using a radio transmitter of the interface section. As yet another variant, in the embodiment of FIGURES 1-3, the received MR signal amplified by the preamplifier 50 is transmitted via the electrical cable 60 to the electrical plug 62 which is connected to a destination such as the coils port 64 of the MR imaging scanner 12. Prior to the optical or wireless transmitting (or to being ported off the coil via the electrical cable 60), the received MR signal amplified by the preamplifier 50 may be digitized using the digitizer 72 of the interface section 30. In the case of an endorectal coil, prior to receiving the MR signal, the at least one MR receive coil loop 28 of the coil section 20 is inserted into the rectum of the patient undergoing prostate MR imaging or the like. (In general, the connectors 32, 34 may be connected before or after insertion of the MR receive coil loop 28 into the rectum).

[0044] The disclosed endo coil embodiments have numerous advantages. The use of the hybrid quarter wave transformer advantageously enables the length of the coaxial cable 22 to be made relatively short, which improves handling and reduces its impact on workflow. The cable section 20 is disposable, eliminating the need to perform a lengthy cleaning procedure between uses, again improving workflow throughput. At the same time, the use of the hybrid quarter wave transformer advantageously enables a construction in which the expensive signal processing circuitry 42 including the preamplifier 50 can be located in the interface section 30 which reused, thus reducing the cost of the consumable component (i.e. the coil section 20). As the coil section 20 is a one-time use disposable item, it does not need to be made of durable biocompatible material. In some embodiments the coil section 20 has an outer surface comprising a biocompatible material that is rated for a use time of no longer than 12 hours (and optionally less, e.g. rated for a use time of only 6 hours), thus further reducing cost of the consumable coil section 20. As yet another advantage, if the MR scanner operator inadvertently fails to connect the connectors 32, 34, the preamplifier 50 of the interface section 30 is not susceptible to damage from induced currents because the impedance matching circuit 40 (e.g. pi-circuit) will not go to a low impedance. This is because if the coil section 20 is not connected to the interface section 30 then the quarter wave transformer 44 is not complete as it is missing the coaxial cable 22. As yet another advantage, the coil section 20 of the disclosed endo coils do not include an inflatable balloon, thus, the prostate or other proximate anatomy is not deformed by balloon inflation.

[0045] The illustrative endo coil is an endorectal coil. In some embodiments, the at least one MR receive coil loop 28 of the coil section 20 of the endorectal coil is sized at a one inch diameter or smaller to fit inside a rectum. However, the disclosed endo coil may be configured for insertion in another body cavity, for example the endo coil may be an endocervical coil designed for insertion into the cervical passage leading into the uterus.

[0046] In bench experiments, the high impedance characteristic was measured using an

SI 1 measurement on each of the channels using a network analyzer. The PiN diode was turned on using a 100 niA current. The detune impedance obtained this way was more than sufficient to detune loop sizes of 20 cm². The effective detune for a loop size can be obtained by:

The detune impedance measured in bench experiments was around 2.5-2.8 kOhm which is much greater than what is required as described in the above formula. [0047] The invention has been described with reference to the preferred embodiments.

Modifications and alterations may occur to others upon reading and understanding the preceding detailed description. It is intended that the exemplary embodiment be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.

Claims

CLAIMS:

1. A magnetic resonance (MR) endo-coil designed to operate at an MR frequency, the MR endo-coil comprising:

a coil section (20) including a coaxial cable (22) having a proximal end (24) and a distal end (26), at least one MR receive coil loop (28) connected at the distal end of the coaxial cable, and a first electrical connector (32) disposed at the proximal end of the coaxial cable; and

an interface section (30) including a preamplifier (50), an impedance matching circuit (40), and a second electrical connector (34) that is configured to mate with the first electrical connector to connect the coil section and the interface section and to define a quarter wave transfonner (44) at the MR frequency comprising the coaxial cable of the coil section and the impedance matching circuit of the interface section, the quarter wave transformer electrically connecting the at least one MR receive coil loop of the coil section and the preamplifier of the interface section.

2. The MR endo-coil of claim 1 wherein the impedance matching circuit (44) comprises at least one inductor (Li) and at least one capacitor (Ci, C₂).

3. The MR endo-coil of any one of claims 1 -2 wherein the impedance matching circuit (44) comprises a pi circuit.

4. The MR endo-coil of any one of claims 1 -2 wherein the impedance matching circuit (44) comprises a T-section impedance matching circuit.

5. The MR endo-coil of any one of claims 1 -4 wherein the coaxial cable (22) of the coil section (20) has an insertion loss of less than 7.6 dB/l OOft.

6. The MR endo-coil of any one of claims 1 -5 wherein the interface section (30) further includes a fiber optic or radio transmitter (74) operatively connected with the preamplifier (50) to optically or wirelessly output a signal acquired by the at least one MR receive coil (28) and amplified by the preamplifier.

7. The MR endo-coil of claim 6 wherein an operative connection of the preamplifier (50) with the fiber optic or radio transmitter (74) includes a digitizer (72) configured to digitize the signal acquired by the at least one MR receive coil (28) and amplified by the preamplifier prior to being optically or wirelessly output by the fiber optic or radio transmitter.

8. The MR endo-coil of any one of claims 1 -7 wherein the interface section further includes an on-board power supply (70) comprising a battery or a receptacle for receiving a battery.

9. The MR endo-coil of any one of claims 1 -8 wherein the coil section (20) does not include an inflatable balloon.

10. The MR endo-coil of any one of claims 1 -9 wherein the coil section (20) has an outer surface comprising a biocompatible material that is rated for a use time of no longer than 12 hours.

1 1. The MR endo-coil of any one of claims 1 -10 wherein the MR endo-coil is an endorectal coil and the at least one MR receive coil loop (28) of the coil section (20) is sized at a one inch diameter or smaller to fit inside a rectum.

12. A coil section (20) of a magnetic resonance (MR) endo-coil designed to operate at an MR frequency, the coil section comprising:

a coaxial cable (22) having a proximal end (24) and a distal end (26) wherein the coaxial coil is not a quarter wave transformer at the MR frequency;

at least one MR receive coil loop (28) connected at the distal end of the coaxial cable; and a first electrical connector (32) disposed at the proximal end of the coaxial cable;

wherein the coil section does not include a preamplifier.

13. The coil section (20) of claim 12 wherein the coaxial cable (22) has an insertion loss of less than 7.66 dB/100 ft.

14. The coil section (20) of claim 12 wherein the coil section does not include an inflatable balloon.

15. The coil section (20) of any one of claims 12-14 wherein the coil section has an outer surface comprising a biocompatible material that is rated for a use time of no longer than 12 hours.

16. The coil section (20) of any one of claims 12-15 wherein the at least one MR receive coil loop (28) of the coil section is sized at a one inch diameter or smaller to fit inside a rectum.

17. A magnetic resonance (MR) endo-coil designed to operate at an MR frequency, the MR endo-coil comprising:

a coil section (20) as set forth in any one of claims 12-17; and

an interface section (30) including a preamplifier (50), an impedance matching circuit (40), and a second electrical connector (34) that is configured to mate with the first electrical connector (32) to connect the coil section and the interface section and to define a quarter wave transformer (44) at the MR frequency comprising the coaxial cable (22) of the coil section and the impedance matching circuit of the interface section, the quarter wave transformer electrically connecting the at least one MR receive coil loop (28) of the coil section and the preamplifier of the interface section.

18. A method of receiving a magnetic resonance (MR) signal at an MR frequency, the method comprising: connecting a first electrical connector (32) of a coil section (20) with a second connector (34) of an interface section (30) wherein the connecting forms a quarter wave transformer (44) at the MR frequency comprising a coaxial cable (22) of the coil section and an impedance matching circuit (40) of the interface section, the quarter wave transformer electrically connecting at least one MR receive coil loop (28) of the coil section and a preamplifier (50) of the interface section; and

receiving an MR signal at the MR frequency using the at least one MR receive coil loop of the coil section wherein the received MR signal is communicated to the preamplifier of the interface section via the quarter wave transformer.

19. The method of claim 18 further comprising one of:

optically transmitting the received MR signal amplified by the preamplifier (50) using a fiber optic transmitter (74) of the interface section (30); or

wirelessly transmitting the received MR signal amplified by the preamplifier using a radio transmitter of the interface section.

20. The method of claim 19 further comprising:

prior to the optical or wireless transmitting, digitizing the received MR signal amplified by the preamplifier using a digitizer (72) of the interface section (30).

21. The method of any one of claims 18-20 further comprising:

prior to receiving the MR signal, inserting the at least one MR receive coil loop (28) of the coil section (20) into a rectum.