Electricity: measuring and testing – Particle precession resonance – Spectrometer components
Reexamination Certificate
1998-12-16
2001-05-22
Patidar, Jay (Department: 2862)
Electricity: measuring and testing
Particle precession resonance
Spectrometer components
C324S322000, C324S300000
Reexamination Certificate
active
06236205
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a magnetic resonance (MR) device which is provided with a medical instrument which is to be introduced into an object to be examined, and also with a coil system which is arranged in or on the instrument and includes at least one coil for receiving and/or transmitting an RF signal. The invention also relates to a medical instrument to be introduced into an object to be examined, notably a catheter or an endoscope, provided with a coil system which is arranged in or on the instrument and includes at least one coil for receiving and/or transmitting an RF signal, as well as to a method of determining the position of a medical instrument that can be introduced into an object to be examined.
2. Description of Related Art
Such an MR device, medical instrument and method of determining the position thereof are known from U.S. Pat. No. 5,353, 795. Therein, a small RF coil, being a so-called microcoil, is arranged in a catheter which is introduced into a patient. During operation of the MR device, an RF signal is induced into the microcoil after excitation of the examination zone, which RF signal is applied, via an RF lead, to a receiver device which processes the signal and determines the position of the coil. The position can be superposed on an image, for example an MR image or a computer tomography (CT) image.
It has been found that the RF lead required between the transmitter and/or receiver device, arranged outside the object to be examined, to a microcoil which is preferably attached to the tip of the medical instrument constitutes a drawback. There is a risk of heating of tissue due to resonance (notably X/4 resonance) occurring in the vicinity of the RF lead during the transmission phase (RF excitation) of the MR examination. Furthermore, the RF lead must inherently be formed by very thin wires, because the medical instrument must also be introduced into very thin veins for various applications. Consequently, substantial signal losses may occur during the transmission of the signal received by the microcoil to a receiving device. Moreover, in conjunction with the RF lead the microcoil must form a stable resonant circuit; therefore, the length of the RF lead cannot be changed at random. Moreover, the known device requires a separate receiving channel for the microcoil or (when a single receiving channel is used) a switching device is required for switching over between the receiving coil system and the microcoil.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an improved MR device, an improved medical instrument and an improved method of determining the position of such a medical instrument while avoiding notably said drawbacks.
In respect of the MR device and in respect of the medical instrument this object is achieved according to the invention in that the coil system constitutes a resonant circuit in conjunction with a capacitor, and that there is provided a modulation unit for modulating an RF signal coupled into the coil system.
The RF lead to a transmitter device which is arranged outside the object to be examined as well as the transmitter device itself can be dispensed with in the MR device according to the invention, because the signal induced into the coil system is modulated, after RF excitation of the part of the object to be examined which is present in an examination zone, and emitted again with this modulated frequency and/or phase. Using a receiving coil system which forms part of the MR device, the (modulated) coil signal transmitted by the coil system as well as an object signal from the excited zone of the object to be examined are received as an MR signal. Because these signals have different frequencies and/or phases, the coil signal and the object signal can be simply separated, so that the determination of the position of the coil system, and hence of the position of the medical instrument, is also simply possible.
The drawbacks described for an RF lead no longer occur in the MR device according to the invention, because low-loss transmission of RF signals is necessary neither from the coil system to the receiving system nor in the opposite direction. The low-ohmic RF leads required in the known MR device, therefore, may be replaced by extremely thin, high-ohmic leads. Thus, the risk of heating of tissue is also eliminated in the MR device according to the invention and no additional receiving channel or switching device is required either.
The elements of the resonant circuit and the modulation unit in the preferred embodiment defined in claim
2
neighbor one another; for example, they are situated at a distance of a few millimeters to centimetres from one another, offering the advantage that no or only very short RF leads are required between these elements.
The control lead in the further embodiment of the invention as defined in claim
3
preferably consists of a high-ohmic two-wire lead whose length may be chosen at random and via which a low-frequency control signal is applied to the modulation unit by the control unit. The control unit is preferably arranged outside the object to be examined.
A particularly simple implementation of the control lead is that disclosed in claim
4
in which the control signal is supplied in an optical manner and is converted into an electrical control signal by means of suitable means, for example a type of optocoupler.
The modulation unit may have a very simple and compact construction and comprises essentially a switch arrangement as disclosed in claim
5
which can be manufactured so as to be very compact. The switch arrangement is preferably switched between two states for the modulation of the oscillation of the resonant circuit.
The preferred embodiment disclosed in claim
6
constitutes a fully wireless solution in which the control signal is induced into an RF receiving system as an RF control signal and the actual control signal for the resonant circuit is converted. The frequency of the RF control signal is then substantially higher or lower than the frequency of the signal induced into the coil system and also substantially higher or lower than the resonant frequency of the resonant circuit so as to avoid disturbances. Preferably, the RF receiving system is also arranged very close to the modulation unit and the resonant circuit, for example at a distance of a few centimeters.
The embodiment defined in claim
8
enables notably determination of the position of the medical instrument in a rather large zone, in which the coils are arranged, by determining the position of the individual coils whose position in or on the instrument is known.
In accordance with claim
9
, it is also possible to provide a plurality of resonant circuits which are also modulated in a different manner, for example with different frequencies, so that the position of each individual coil system can be unambiguously determined, for example by reproducing each coil system in a different image zone.
The object in respect of the method of determining the position of a medical instrument is achieved in that the coil system constitutes a resonant circuit in conjunction with a capacitor, that an RF signal which is coupled into the coil system is modulated in such a manner that the MR signal contains a modulated coil signal, and that the position of the instrument is determined from the coil signal.
The method according to the invention enables significantly simpler determination of the position of the coil system in comparison with the known method. As a result of the modulation according to the invention, in which a frequency shift or a phase shift is imposed on the signal induced into the coil system, the modulated coil signal emitted again by the coil system can be separated from the MR signal received by the receiving coil system by means of a simple calculation method.
The claims
12
to
14
disclose attractive versions of the method according to the invention, especially attractive versions of the modulation.
REFERENCES:
pa
Ludeke Kai-Michael
Rasche Volker
Patidar Jay
Shrivastav Brij B.
U.S. Philips Corporation
Vodopia John F.
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