WO2003093851A1 - Magnetic resonance imaging receive circuit - Google Patents
Magnetic resonance imaging receive circuit Download PDFInfo
- Publication number
- WO2003093851A1 WO2003093851A1 PCT/GB2003/001892 GB0301892W WO03093851A1 WO 2003093851 A1 WO2003093851 A1 WO 2003093851A1 GB 0301892 W GB0301892 W GB 0301892W WO 03093851 A1 WO03093851 A1 WO 03093851A1
- Authority
- WO
- WIPO (PCT)
- Prior art keywords
- circuit
- cables
- antenna
- circuitry
- mode
- Prior art date
Links
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R33/00—Arrangements or instruments for measuring magnetic variables
- G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
- G01R33/28—Details of apparatus provided for in groups G01R33/44 - G01R33/64
- G01R33/32—Excitation or detection systems, e.g. using radio frequency signals
- G01R33/36—Electrical details, e.g. matching or coupling of the coil to the receiver
- G01R33/3642—Mutual coupling or decoupling of multiple coils, e.g. decoupling of a receive coil from a transmission coil, or intentional coupling of RF coils, e.g. for RF magnetic field amplification
- G01R33/3657—Decoupling of multiple RF coils wherein the multiple RF coils do not have the same function in MR, e.g. decoupling of a transmission coil from a receive coil
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R33/00—Arrangements or instruments for measuring magnetic variables
- G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
- G01R33/28—Details of apparatus provided for in groups G01R33/44 - G01R33/64
- G01R33/285—Invasive instruments, e.g. catheters or biopsy needles, specially adapted for tracking, guiding or visualization by NMR
Definitions
- the present invention relates to a magnetic resonance imaging (MRI) receive circuit, and in particular although not exclusively to a balanced connection scheme for a small MRI antenna intended for use within the body of a patient.
- MRI magnetic resonance imaging
- the invention finds particular although not exclusive application within the field of minimally-invasive MRI.
- Magnetic resonance imaging for medical diagnosis is well known.
- the entire patient or at least that part of the patient to be studied is placed within the coils of an MRI scanner.
- radio-frequency coils within the scanner generate a very strong static magnetic field (e.g. 0.5 Tesla) which causes the hydrogen nuclei within that part of the patient being imaged to align themselves with the field.
- This primary magnetic field is very homogeneous and very time-constant.
- This primary magnetic field is then modified by three superimposed gradients, one for each of the x, y and z directions. These vary at audio frequencies, and are typically linear within the volume of interest.
- the function of the gradients is to provide a spatial modulation of the field which can then be used in signal localisation.
- the magnetic moments of the hydrogen nuclei After excitation from the radio frequency transmit coil and under the influence of the magnetic main field, the magnetic moments of the hydrogen nuclei gyrate at a frequency proportional to the local magnetic field strength, and eventually decay back to their equilibrium positions.
- one or more radio frequency coils are used as receivers.
- the transmit coil may also be used for receive, or specialised receive coils may instead be used.
- the gyration of the moments causes currents to be induced in the coils. By analysing those induced currents, and allowing for the three superimposed gradients, the body parts of interest can be imaged.
- a separate, small, receiving coil or antenna is used to receive the signal, instead of or in addition to the radio-frequency coils of the MRI apparatus itself.
- a coil may be placed either adjacent to the patient's skin or may be inserted by means of a probe into a patient's body cavity, for example into the colon.
- a magnetic resonance imaging receive circuit comprising:
- a circuit of this type has a number of specific advantages over prior art circuits such as that shown in Martin et al.
- circuits embodying the present invention there is no problem with swapping over of the cables, there is no problem with antennas which look like short circuits at DC, and there is the ability (if desired) to de-couple e.g. to ground even without having a capacitor in series with the antenna.
- the antenna and any matching circuit experiences only one voltage.
- twin-axial cable or shielded twisted pair is used, the two central conductors will not in that case experience large potential differences.
- the first portion includes matching circuitry which provides substantially complete impedance matching between the antenna and the cables. That provides the additional advantage that the cable-length becomes substantially immaterial.
- the length of the balanced cables is critical, since the decoupling impedance would otherwise vary in an unknown way.
- the cable length has to be 3.5 metres. This may be inconveniently long in the operating theatre, forcing the surgeon to tie the cable up in some way before starting work.
- Miniature coaxial cable often used in minimally invasive applications is substantially lossy and prone to interference; its length should therefore be minimised.
- the required cable length for the Martin et al system reduces as the magnetic field strength increases, making the required length inconveniently or even impossibly short for, say, a 1.5 Tesla field. If the rf antenna is fully matched proximal to the antenna, the cable length becomes largely immaterial.
- decoupling is performed by using the potential difference between equal DC biases on both signal lines and a grounded shield to substantially ground specific points of the antenna (for example, using diodes, where the antenna is electrically connected to ground only via the scanner's receiver impedance during receive mode).
- the first portion may be attached to or be incorporated within an endoscope or catheter probe, for insertion into the body cavity of a patient.
- the first portion may be attached to, or form part of, a surface coil.
- the first portion may be modular, and may be designed to plug into balanced cables of any desired length. ( The far end of the cables may, themselves, be plugged into a modular second portion.
- the modular first portion and/or the cables may be designed for single use, with the second portion (e.g. including a balun) designed for re-use.
- the invention extends to a magnetic resonance imaging device including a circuit as previously defined.
- FIG 1 shows, very schematically, the surgical context within which the preferred circuit of the present invention may be used
- Figure 2A shows a typical prior art receive circuit
- Figure 2B shows, in functional form, the arrangement of an embodiment of the present invention
- FIG. 3 shows an alternative method of decoupling the antenna
- Figure 4 shows a magnetic resonance imaging receive circuit according to a preferred embodiment of the present invention
- FIG. 5 shows, schematically, the antenna in conjunction with an endoscope probe
- Figure 6 shows a magnetic resonance imaging receive circuit according to another embodiment of the invention.
- Figure 1 shows, schematically, a typical surgical context within which the preferred circuit of the present invention may be used.
- the patient 10 who is undergoing minimally-invasive surgery or treatment has an endoscope probe 11 inserted into a body cavity (for example the colon) through a natural opening or a small wound 12 made in the skin.
- the endoscope is moved within the patient until it reaches an area 13 of interest.
- an MRI scanner 14 Surrounding the patient is an MRI scanner 14 having transmit/receive coils 15. In a transmit mode these expose the patient to a radio frequency field, exciting the nuclear spins and thereby realigning their magnetic moments away from the equilibrium position. In a receive mode, they detect RF signals back from the patient's tissues. Control circuitry, and circuitry for producing gradients (not shown) are also provided.
- the endoscope probe 11 has, associated with it, a small receive antenna 16, typically of about 1 cm in diameter. Extending from the probe 11 is a line 17 which carries both coaxial cables for controlling and receiving signals from the antenna 16, and also an optical fibre which transmits light to and receive images back from, imaging optics 19 on the probe.
- An detector/imaging unit 18 receives signals from the optics 19, the antenna 16 and the transmit/receive coils 15, and displays either separate or superimposed respective images 20,21,22.
- the position of the probe, within the field of the receive coils 15, may be tracked by means of a water-filled coil (not shown) formed within the probe.
- Some method must be provided to decouple the receive antenna during the transmit portion of the imaging cycle. This is needed both to protect the receiver from large currents directly induced in the receive coil, and also to avoid such currents distorting the homogeneous field that is created by the transmit coil 15.
- One conventional method of achieving this is with the arrangement shown in Figure 2A, using a single length of unbalanced coaxial cable as the transmission line.
- There are a number of problems with such an arrangement including the need for the inductive elements to be placed at a sufficient distance from the antenna not to induce local magnetic field disturbance.
- FIG. 2B shows, in functional form, the arrangement of an embodiment of the invention.
- Figure 4 shows an exemplary circuit in more detail.
- the circuit consists of three parts: a first part 100 which is typically contained within or forms part of a probe for insertion into the patient, a transmission line 200, and a second portion 300 which is positioned away from the first portion to avoid interfering with the signal.
- the first portion 100 has an RF antenna (MI coil) which is coupled to a matching network consisting of series matching capacitors Csi and a parallel matching capacitor C P1 .
- the antenna is matched to an impedance of 100 ⁇ .
- the matching circuitry is connected to decoupling circuitry 120, within which diodes Di short out the parallel matching capacitor when a positive DC bias is applied on the received input.
- the transmission line 200 comprises two 50 0 micro-coaxial cables 52,54.
- the antenna, matching and decoupling (detuning) circuit and the micro-coaxial cables may be implemented as a single subsystem, delivering the received signal via two ports A, B, with a 180° phase shift.
- the output from the cables feeds into a second portion 300 of the circuit which fulfils the functions of a two-way, 180° power splitter/combiner (i.e. functions to provide signal combination with common-mode rejection).
- the ports A and B feed into a conditioning section 320 which includes blocking capacitors 64,66 designed to block the negative DC bias present during the receive portion of the imaging cycle. Diodes 60,62 bypass these blocking capacitors to allow the positive bias during the transmit phase to pass. The current flow during the transmit phase is limited by resistors 56,58.
- radio frequency signals pass via the capacitors 64,66 and are received by a matching section 310.
- series matching inductors 68,70 and parallel matching capacitors 72,74 match the two micro-coaxial cables 52,54 to a half wavelength ( ⁇ 2) 50 ⁇ coaxial delay line 76.
- This delay line forms a balun 80 with output impedance of 200 ⁇ .
- the signals pass down a further coaxial cable 82 and are received at ports X, Y.
- the signals are then converted into appropriate images at a receiver 18, as shown schematically in Figure 1.
- mode-selection is achieved by applying a DC potential difference between the ports: a positive bias is applied during the transmit portion of the cycle (to decouple the circuit), and a negative bias is applied during receive.
- the circuit is manufactured entirely from non-ferromagnetic materials, to avoid interfering with the magnetic field.
- the positive bias applied between points X and Y decouples the antenna 50 and prevents it oscillating.
- the way the circuit is designed ensures that, in that state, the same bias voltage is applied to both ends of the coil.
- the central cores of the micro-coaxial cables 52,54 swing positively and negatively anti-symmetrically around ground. Since the signals passing along those cables are always 180° out of phase, there is little if any disruption caused to the surrounding magnetic field. Conversely, this also means that the effects of external interference are substantially reduced.
- anti-symmetric (differential) signals allows a simple balun at the far end to be used to sum the out-of-phase responses.
- FIG. 3 may be used to replace the decoupling circuitry 120 shown in Figure 4.
- Figure 6 shows an alternative embodiment.
- the receive antenna 16 is not necessarily used in conjunction with an endoscope, and is not, in use, inserted into a body cavity. Instead, it may be placed adjacent to the body tissue or other material to be imaged.
- the circuitry of the preferred embodiment may be manufactured as a series of distinct modules.
- the first pare 100 may comprise one module, the transmission line 200 a second module, and the second portion 300 a third module.
- the surgeon may select the appropriate modules for the surgical procedure to be undertaken.
- the surgeon selects an appropriate endoscope or catheter. He then selects an appropriate cable; where the circuit is fully matched at the antenna, the surgeon will have a choice of cable lengths.
- the cable is then plugged into appropriate circuitry for providing signal combination with common mode rejection, this circuitry itself being plugged into a suitable receiver.
- the entire catheter or endoscope and/or the cables may be disposable, and may be designed for once-only use. The more expensive far-end circuitry, including the balun, is reuseable.
- the loop antenna 50 ( Figure 4) was etched onto flexible copper clad (Crossley & Bradley Ltd, Krempel GMBH, KCL 2-35/50 FR). It was then fixed onto a cylindrical nylon former (13 mm diameter) using super glue and soldered to form the loops.
- the series capacitors C S1 each 45 pF, were implemented as a parallel combinations of a 47 pF (RS, 298-9141), 33 pF (RS, 298-9135) and a 10 pF (RS, 243-386) capacitors.
- the parallel capacitor C P1 was a parallel combination of two 100 pF (RS, 298-9157) capacitors, and a 47 pF (RS, 298- 9141) capacitor.
- All capacitors used were ceramic surface mount. All, except the 10 pF capacitors, were 1206 format packages and had a rating of 100 V DC. The 10 pF capacitors were smaller 0402 formats and had 50 V DC rating.
- the diodes Dj were low loss radio frequency switching PIN diodes (Infinion, BAR 65-02V). They had a reverse DC voltage rating of 30V and a forward current rating of 100 mA. The coil was covered using clear heat-shrink.
- the micro- coaxial cables 52,54 (Temp-Flex Cable Inc, 50 MCX-07-1) had an outer diameter of 1 mm and featured a silver only construction (no paramagnetic materials). The cables were terminated using SMB plugs (RS, 456-289).
- the power combiner was implemented on strip board and housed in a 50 mm by 160 mm by 130 mm aluminium casing (Farnell, 930-246 and 930-349).
- Inputs from the micro-coaxial cable were SMB bulkheads (RS, 295-5693).
- Signal from the bulkheads was transferred to DC blocking / transmitting sub- circuit by a short length (less than 80 mm) of 100 Ohm twinaxial copper and tinned copper cable (Belden, 9815).
- the blocking capacitors C 2 64, 66 were each comprised of 3 2200 pF ceramic surface mount capacitors with 100 V DC rating (RS, 298-9208).
- the same diodes as in the detuning circuit were used for the D 2 diodes 60, 62 (Infinion, BAR 65-02V).
- the current limiting resistors R 2 56, 58 were each constructed using two 8.20 k ⁇ resistors in parallel. Two 120 nH (Coil Craft, 1812SMS-R12J), one 100 nH (Coil Craft, 1812SMS-R10J) and one 33 nH (Coil Craft, 1812SMS-33J) air cored surface mount inductors 68, 70 were combined in series to produce the inductors L S3 .
- the parallel matching capacitors Cp 3 72, 74 were constructed from a 47 pF ceramic surface mount 100 V DC capacitor (RS, 298-9141) and a variable capacitor with range 8.5 to 40 pF and a 100 V DC rating (RS, 832-431).
- Right angle 50 Ohm Shielded BNC Socket (RS, 447-392) were used to connect to the half-wavelength delay line 76 and to the coaxial cable 82 leading to the receiver. Both these cables were constructed using RG223/U (RS, 227-564) coaxial cable with BNC plugs (RS, 193-4134) on either end.
- the 180 degree delay line was constructed by measuring an appropriate length of coaxial cable using the listed nominal velocity of propagation to produce a delay line with more than 180 degrees phase shift. This was then trimmed.
Abstract
Description
Claims
Priority Applications (3)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
AU2003233874A AU2003233874A1 (en) | 2002-04-29 | 2003-04-29 | Magnetic resonance imaging receive circuit |
US10/511,957 US7180296B2 (en) | 2002-04-29 | 2003-04-29 | Magnetic resonance imaging receive circuit |
EP03727636A EP1499907A1 (en) | 2002-04-29 | 2003-04-29 | Magnetic resonance imaging receive circuit |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
GB0209756.6 | 2002-04-29 | ||
GBGB0209756.6A GB0209756D0 (en) | 2002-04-29 | 2002-04-29 | Magnetic resonance imaging receive circuit |
Publications (1)
Publication Number | Publication Date |
---|---|
WO2003093851A1 true WO2003093851A1 (en) | 2003-11-13 |
Family
ID=9935707
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
PCT/GB2003/001892 WO2003093851A1 (en) | 2002-04-29 | 2003-04-29 | Magnetic resonance imaging receive circuit |
Country Status (5)
Country | Link |
---|---|
US (1) | US7180296B2 (en) |
EP (1) | EP1499907A1 (en) |
AU (1) | AU2003233874A1 (en) |
GB (1) | GB0209756D0 (en) |
WO (1) | WO2003093851A1 (en) |
Cited By (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
EP3242396A1 (en) * | 2016-05-03 | 2017-11-08 | Siemens Healthcare GmbH | Device for the transmission of magnetic resonance signals by means of a differential wiring arrangement |
US9814390B2 (en) | 2013-03-15 | 2017-11-14 | Synaptive Medical (Barbados) Inc. | Insert imaging device for surgical procedures |
Families Citing this family (10)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
BRPI0821278A2 (en) * | 2007-12-18 | 2015-06-16 | Koninkl Philips Electronics Nv | Magnetic resonance imaging device, image processing module, method for generating an image for display of an image portion or volume within a person |
KR101505331B1 (en) | 2010-07-01 | 2015-03-23 | 바이엘 메디컬 케어 인크. | Multi-channel endorectal coils and interface devices therefor |
US10852373B2 (en) | 2016-09-21 | 2020-12-01 | Quality Electrodynamics, Llc | Modulating magnetic resonance imaging transmit field in magnetic resonance fingerprinting using single layer transmit/receive radio frequency coil |
US10386430B2 (en) * | 2016-09-21 | 2019-08-20 | Quality Electrodynamics, Llc | Single layer magnetic resonance imaging transmit/receive radio frequency coil |
US11156682B2 (en) | 2017-03-24 | 2021-10-26 | Quality Electrodynamics, Llc | Single layer magnetic resonance imaging transmit/receive radio frequency coil for different anatomies |
US10976388B2 (en) | 2017-03-24 | 2021-04-13 | Quality Electrodynamics, Llc | Minimizing intravascular magnetic resonance imaging (MRI) guidewire heating with single layer MRI transmit/receive radio frequency coil |
US10649048B2 (en) | 2017-04-28 | 2020-05-12 | Quality Electrodynamics, Llc | Single layer magnetic resonance imaging (MRI) transmit/receive (TX/RX) radio frequency (RF) coil with integrated shimming |
US11193992B2 (en) | 2017-05-05 | 2021-12-07 | Quality Electrodynamics, Llc | Single layer magnetic resonance imaging (MRI) transmit/receive (Tx/Rx) radio frequency (RF) coil with induced current failsafe protection |
US10838028B2 (en) | 2017-06-19 | 2020-11-17 | Quality Electrodynamics, Llc | Decoupling magnetic resonance imaging (MRI) radio frequency (RF) coil elements with high acceleration factor in parallel transmit (pTx) or receive (Rx) coils using fewer channels |
EP3933426A1 (en) * | 2020-06-30 | 2022-01-05 | Koninklijke Philips N.V. | Magnetic resonance coil array and self-compensated radiofrequency choke |
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- 2003-04-29 EP EP03727636A patent/EP1499907A1/en not_active Withdrawn
- 2003-04-29 US US10/511,957 patent/US7180296B2/en not_active Expired - Fee Related
- 2003-04-29 AU AU2003233874A patent/AU2003233874A1/en not_active Abandoned
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Cited By (7)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US9814390B2 (en) | 2013-03-15 | 2017-11-14 | Synaptive Medical (Barbados) Inc. | Insert imaging device for surgical procedures |
EP3242396A1 (en) * | 2016-05-03 | 2017-11-08 | Siemens Healthcare GmbH | Device for the transmission of magnetic resonance signals by means of a differential wiring arrangement |
KR20170124966A (en) * | 2016-05-03 | 2017-11-13 | 지멘스 헬스케어 게엠베하 | Apparatus for transmission of magnetic resonance signals by means of differential cable routing |
CN107453728A (en) * | 2016-05-03 | 2017-12-08 | 西门子保健有限责任公司 | For being guided by the wire of difference to transmit the device of magnetic resonance signal |
KR101979081B1 (en) * | 2016-05-03 | 2019-05-15 | 지멘스 헬스케어 게엠베하 | Apparatus for transmission of magnetic resonance signals by means of differential cable routing |
US10481227B2 (en) | 2016-05-03 | 2019-11-19 | Siemens Healthcare Gmbh | Transmission of magnetic resonance signals by differential cable routing |
CN107453728B (en) * | 2016-05-03 | 2020-10-13 | 西门子保健有限责任公司 | Device for transmitting magnetic resonance signals by means of differential line guidance |
Also Published As
Publication number | Publication date |
---|---|
AU2003233874A1 (en) | 2003-11-17 |
US20060164089A1 (en) | 2006-07-27 |
EP1499907A1 (en) | 2005-01-26 |
US7180296B2 (en) | 2007-02-20 |
GB0209756D0 (en) | 2002-06-05 |
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