WO2004089211A2

WO2004089211A2 - Wireless digital transmission of mr signals

Info

Publication number: WO2004089211A2
Application number: PCT/IB2004/050378
Authority: WO
Inventors: Hans H. Tuithof; Johannes H. Den Boef; Johan E. W. Vrijheid; Dirk Sinnema
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2003-04-10
Filing date: 2004-04-01
Publication date: 2004-10-21
Also published as: WO2004089211A3

Abstract

A magnetic resonance examination apparatus including a receiving assembly located in the vicinity of an examination zone for producing a signal in response to spin resonance signals for transmission to a signal processing unit. To overcome problems associated with metallic cable connections between the signal generator and the signal processing unit, and to overcome problems associated with existing non-metallic connections, the receiving assembly comprises a digitizer for generating a digital electromagnetic signal for transmission to the signal processing unit.

Description

Magnetic resonance examination apparatus and method of performing an examination using magnetic resonance

The invention relates to a magnetic resonance examination apparatus comprising an examination zone arranged to receive a body for examination, magnetic field generating means for generating a magnetic field in said examination zone, a receiving assembly located in or in the vicinity of said examination zone, said receiving assembly comprising a receiver for receiving a spin resonance signal generated in said examination zone, a signal generator for generating a signal in response to said received spin resonance signal, and a transmitter for transmitting said generated signal to a signal processing unit disposed at a location remote from said receiving assembly.

The invention further relates to a receiver assembly for use in a magnetic resonance examination apparatus having an examination zone, said receiver assembly being used in or in the vicinity of said examination zone in which a magnetic field is generated by a magnetic field generating means, said receiver assembly comprising a receiver for receiving a spin resonance signal generated in an examination zone, a signal generator for generating a signal in response to said spin resonance signal, and a transmitter for transmitting said generated signal to a signal processing unit disposed at a location remote from said receiving assembly.

The invention further relates to a signal processing unit for use in a magnetic resonance examination apparatus of the kind described in the opening paragraph, said signal processing unit comprising a receiver for receiving a signal generated by a receiving assembly in response to a spin resonance signal received from an examination zone.

The invention further relates to a method of performing an examination using magnetic resonance, comprising the steps of providing an examination zone to receive a body for examination, generating a magnetic field in said examination zone, and receiving, within or in the vicinity of said examination zone, a spin resonance signal generated in said examination zone, generating a signal in response to said received spin resonance signal, and transmitting said generated signal to a signal processing unit disposed at a location remote from said receiving assembly. Magnetic resonance imaging is a technique which uses magnetic and radio waves to form an image of objects disposed in an examination zone. In particular, magnetic resonance imaging is used to image organic tissue. A magnetic resonance examination apparatus of the kind mentioned in the opening paragraph is known from US-A-5 245 288. In a conventional apparatus of this kind magnets are disposed so that a patient lying in an examination zone is exposed to a cylindrically shaped magnetic field. Radio waves are then transmitted into the body in the examination zone causing nuclei in atoms in the body to move. As the nuclei return to their original position, they emit radio waves. The imaging apparatus receives the emitted radio waves in a receiving assembly, and uses data derived from the received radio waves to form an image of the body examined in the examination zone. Organic tissue comprises a large proportion of water, and water comprises hydrogen. Thus, for imaging organic tissue, the imaging apparatus is calibrated to respond to radio waves emitted by hydrogen nuclei. However, the skilled person will realize that a magnetic resonance apparatus may be calibrated to respond to radio waves emitted by other species, depending on the application.

In conventional magnetic resonance imaging apparatus, the receiving assembly is disposed close to the patient in the magnet bore, and comprises one or more detecting coils/antennae. For each coil, a radio frequency preamplifier is provided, mounted on a panel. The assembly further includes some logic circuits for tuning and monitoring the performance of the apparatus. A multifunctional cable connects the elements comprised in the receiving assembly to a signal processing unit. The signal processing unit processes the signal received by the receiving assembly. In addition, the cable is used to transmit power to the receiver assembly from the receiver, to supply power to the preamplifier, to carry control signals to the receiver assembly, and to transmit status signals from the receiver assembly to the signal processing unit.

During examination of a body in the examination zone, a plurality of radio frequency antennae are used. Each antenna requires a respective cable. Thus, the more antennae are used, the more complex the cable handling around the body becomes. In particular, the greater the number of coils required. At a combiner box all cables from the respective coils are bundled together. The cable bundle is both bulky and subject to environmental interaction. In addition, such multifunctional cables comprise several metallic wires. It has been found that as the number of metallic wires around the body, lying in the magnet bore, increases, disturbance of the local radio frequency excitation field occurs. Further, in some circumstances this can result in a high local specific absorption rate (SAR) being generated at the surface of the examined body. This may compromise the safety of the operation of the apparatus, for example, a patient may experience local burns of the skin in areas close to the radio frequency leads in the cable. Further, the disturbed excitation field may give rise to image artefacts, which compromise the accuracy of the image obtainable by the apparatus.

In a further conventional apparatus, such as that described in US-A-5 545 999, an antenna is provided wherein the received radio signals, having been converted to electric signals, are further converted to optical signals by a transducer. The optical signals are then transmitted via an optical fibre connection from the receiving assembly to the further receiver connected to the signal processing unit. The inventors of the present invention have found, however, that the system described in US-A-5 545 999 suffers from the problem that the signal transfer function from radio to optical signal is unstable. In particular, it is susceptible to environmental changes and physical disturbances of the components of the receiving coil assembly. In particular, the transducer is susceptible to temperature changes. This is caused by instabilities and non-linearities in the function of the transducer.

In addition, the inventors have identified a further problem with conventional receiving assemblies, namely that some of the components of the assembly for dealing with the analog signals that are generated in the examination zone are also susceptible to environmental disturbances.

It is an object of the invention to provide a magnetic resonance examination apparatus, a receiver assembly, a signal processing unit, and a method of performing an examination using magnetic resonance of the kinds mentioned in the opening paragraphs in which the problems identified above are solved.

In order to achieve this object, a magnetic resonance examination apparatus according to the invention is characterized in that said signal generator further comprises a digitizer for generating a digital signal in response to said received spin resonance signal, and outputting said digitized signal to said transmitter. In order to achieve this object, a receiver assembly according to the invention is characterized in that the signal generator further comprises a digitizer for generating a digital signal in response to said received spin resonance signal and outputting said digitized signal to said transmitter. In order to achieve this object, a signal processing unit according to the invention is characterized in that said receiver is arranged to receive said digital signal and in that said signal processing unit includes a digital processor for deriving examination data from said received signal. In order to achieve this object, a method of performing an examination using magnetic resonance according to the invention is characterized in that within or in the vicinity of said examination zone said signal generated in response to said received spin resonance signal is digitized, and said digitized signal is outputted to said transmitter. The present invention provides the advantages that a digital signal is not susceptible to the non-linearity of the transfer function and the environmental instabilities of the transducer. Further, the signal is not susceptible to the environmental susceptibilities, such as performance fluctuations with temperature or physical disturbance of the analog components of the apparatus. These advantages result in a more accurate examination of the body allowing a more accurate image of the examined body to be produced. A particular embodiment of a magnetic resonance examination apparatus according to the invention is characterized in that the signal generator comprises a transducer for converting the digital signal to an electromagnetic signal. This particular embodiment has the advantage that converting the electric signal to an electromagnetic signal allows the provision of a non-metallic connection between the signal generator and the signal processing unit. This arrangement overcomes the problems associated with conventional cables.

In order that the invention may be more fully understood embodiments thereof with now be described by way of example only, with reference to the figures in which: Fig. 1 shows diagrammatically a magnetic resonance examination apparatus in which the invention can be used;

Fig. 2 shows a block diagram of components of a receiving assembly capable of performing the invention;

Fig. 3 shows a block diagram of a magnetic resonance examination apparatus according to a first embodiment incorporating the components of the receiving assembly shown in Figure 2;

Fig. 4 shows a block diagram of a magnetic resonance examination apparatus according to a second embodiment incorporating the components of the receiving assembly shown in Figure 2; and Fig. 5 shows a block diagram of a magnetic resonance examination apparatus according to a third embodiment incorporating the components of the receiving assembly shown in Figure 2.

The magnetic resonance examination apparatus shown in Figure 1 comprises a system comprised of four coils 1 for generating a steady, uniform magnetic field extending in the z-direction. The coils are concentrically situated relative to the z-axis and may be arranged on a spherical surface 2. The material to be examined, for example a patient 20, is arranged within these coils. There is also provided a high-frequency transmitter coil 11 which is constructed so that it can generate a substantially uniform high-frequency magnetic field extending perpendicularly to the z-direction. The frequency of the latter high-frequency magnetic field should correspond to the Larmor frequency fc, for which: fo₌cB Therein, B is the magnetic induction of the uniform, steady magnetic field and c is the gyromagnetic constant which amounts to approximately 42.58 MHz/T for hydrogen protons. The transmitting coil 11 is permanently mounted in the apparatus and is connected via a power supply means, described hereinbelow with reference to Figure 2, to a high- frequency generator which generates high-frequency pulses whose amplitude and duration are proportioned so that they rotate the nuclear magnetization out of the z-direction preferably in a plane extending perpendicularly thereto.

The excitation of the nuclear magnetization by the high-frequency pulses induces spin resonance signals in the examination zone influenced by the high-frequency coil, the resonance signals being dependent on the nuclear magnetization distribution. These spin resonance signals are received by an input of a receiving assembly 100, 101, 102 which is responsive to spin resonance signals received, and will be described in further detail herein below with reference to Figure 2. The receiving assembly 100, 101, 102 preferably comprises a coil 22, which is arranged on a flexible or rigid carrier. The signal induced in the coil is tuned to the Larmor Frequency fo and applied to a signal processing unit which is not shown in Figure 1, and which determines the spatial or spectral distribution of the nuclear magnetization therefrom.

There are also provided gradient coil systems which each comprise several coils 3, 5 and 7 and which are capable of generating a magnetic filed extending in the z- direction with a gradient in the x, the y or the z-direction. After the generation of the high- frequency excitation pulses, the RF coils of the receiving assembly conduct a current, upon the appearance of the spin resonance signals. These RF signals are amplified and fed to the signal processors, which are located in he technical room, which is commonly located outside the examination room. Figure 2 shows components 21 of the receiving assembly 100, 101, 102 according to the present invention. In particular, Figure 2 shows those components 21 of the receiving assembly 100, 101, 102, which are common to the first, second and third embodiments of the present invention shown in Figures 3-5, respectively.

Figure 2 shows components 21 of a receiving assembly 100, 101, 102, including a receiver 22, which may include a receiving coil or antenna, and a signal generator 24, 26, 28, 29 responsive to the spin resonance signals generated in the examination zone. The receiving assembly is disposed in the vicinity of the examination zone, preferably adjacent to the examination zone. It may also be disposed in the examination zone. Preferably, the receiving assembly is disposed close to the tissue to be examined. Preferably, the connection between the receiver 22 and the signal generator 24, 26, 28, 29 is as short as possible.

The receiver 22 preferably comprises a coil 22. A radio frequency field 12 is received by the coil 22. The receiver serves to receive the spin resonance signals and convert them to an electric signal. The signal generator 24, 26, 28, 29 preferably comprises a preamplifier 24, a band filter 26, and analog to digital converter 28 and a bandwidth reducer 29. The signal generator serves to generate a signal in response to the received spin resonance signal for transmission to a remote signal processing unit.

The signal generator 24, 26, 28, 29 is disposed in the vicinity of the examination zone. A signal incident on input 12 is received by receiver 22. Generally speaking the spin resonance signals are radio frequency analog signals. The receiver 22 preferably comprises a transducer for generating an electric signal in response to the spin resonance signal. In particular, the receiver comprises a coil 22 in which the radio frequency spin resonance signals induce electric signals. For example, the coil 22 is such that radio frequencies in the range of 60 MHz will induce electric signals in the coil corresponding to the spin resonance signals generated in the examination zone. Thus, in particular, the receiver 22 generates, from an analog radio -frequency spin-resonance signal, a corresponding analog electric signal.

The received induced electric signals are then preferably amplified by a conventional preamplifier 24. Preferably, the preamplifier has a frequency range of about 10 to 300 MHz and a dynamic range of about 140 dB. It is preferably a small signal amplifier with a maximum output of 5 volts. It is preferably coupled directly to the receiver 22, and is preferably located in the vicinity of the receiver. Preferably, as close as possible to the receiver. The preamplifier is designed such that the output signal matches with the required input voltages of the analog to digital converter 28. A band filter 26 with controlled attenuation of up to about 20dB is also preferably provided downstream of the preamplifier to condition the amplified signal in order to match the amplified signal with the input of the analog to digital converter 28.

The inventors of the present invention have found that the analog components of the receiving assembly are susceptible to enviromnental instabilities such as temperature related instabilities and also instabilities caused by physical disturbances. The inventors have further realized that by including an analog to digital converter, and converting the analog electric signal to a digital signal, analog components and their inherent instabilities can be avoided. However, it is preferable to amplify the induced electric signal and condition it using a band filter 26 prior to digitalization, since then the amplified and filtered signal matches the input of the analog to digital converter, and is thus more successfully digitalized. However, the invention is not limited in this respect, as is discussed in more detail below.

In the embodiment shown in Figure 2, an analog to digital converter is provided to convert the analog signals induced in the coil 22 to digital signals. The inventors have identified that conventional analog to digital converters are not suitable for application in or in the vicinity of the examination zone. Analog to digital converters include a sampling clock. The sampling clock generates interference which affects the MRI performance. The present invention overcomes this technical prejudice. In conventional MRI apparatuses components of the receiving assembly are electromagnetic interference (EMI) shielded. Conventional shielding materials include well conducting materials, such as copper. However, it has been found that if too much shielding material is disposed in or in the vicinity of the examination zone eddy currents are induced in the copper, which interfere with the gradient fields which are necessary in order for magnetic resonance imaging to take place. This problem is compounded if conventional analog to digital converters were to be disposed in the receiving assembly. It is therefore of importance to keep shielding components 23 as thin and as small as possible to prevent the gradient fields from being influenced. Similarly, in order to minimize the amount of copper necessary to effectively shield the analog to digital converter, the analog to digital converter is preferably as small as possible, thereby further reducing the amount of shielding material necessary to shield it. Preferably, the dimensions of the analog to digital converter are approximately 20x20x5 millimetres. The shield dimensions and thickness preferably are of the order of 21x21x6 millimetres of a conducting foil material, for example copper foil having a thickness of 50 micrometres. In particular, the analog to digital converter 28 is connected to the other components of the signal generator, preferably on the chip level on an integrated circuit. The integrated circuit has dimensions which correspond to approximately double the volume of the digitizer 28. For example, the dimensions of the signal generator are approximately 20x20x10 mm. The shield (not shown) may also be provided for the signal generator, and measures approximately 21x21x12 millimetres; preferably the shield used is a copper foil having a thickness of about 50 micrometres. In particular, using application- specific integrated circuits (ASICs) technology, it is possible to integrate the analog to digital converter 28 with the other functions carried out by the other components of the signal generator. In particular, a shielding means 11 is provided to shield the digitizer 28 from the magnetic field generated in the examination zone, the shielding means 11 and the digitizer being dimensioned to suppress any eddy currents induced in the shielding means 11.

Preferably the analog to digital converter 28 has a large dynamic range of at least 12 bits. A large dynamic range is required to balance between the required dynamic range of the spin resonance signals to be digitized. However, it will be appreciated that the larger the dynamic range of the analog to digital converter, the slower the sampling speed. The slower sampling speed is addressed by using a 12 bit analog to digital converter 28 combined with a controllable attenuator 27 disposed upstream of the analog to digital converter 28 controlled by controller 10. Preferably, the controller 10 selectively attenuates the spin resonance signals in accordance with a predicted signal level determined in accordance with the origin of the spin resonance signals in the examination zone. Alternatively, the signal processor 27 comprises a non-linear attenuator or a non-linear amplifier. In such alternative embodiments, the non-linear amplifier or non-linear attenuator are selected such that controller 10 may be dispensed with.

In the embodiment including a controllable attenuator good results are achieved because it can be predicted when a high spin resonance signal can be expected, and when a low spin resonance signal can be expected. This is because high signals are expected when imaging an object in the centre of the examination zone (Fourier space) and low signals are expected when imaging an object at the periphery of the examination zone (Fourier space). When a high signal is expected, the attenuator 27 is controlled to attenuate the signal, and the attenuated signal is input to the digitizer 28. When a low signal is expected the attenuator 27 is controlled to perform no attenuation, and the full amplification of the spin signals is input to the digitizer 28. In this way, a 12 bit digitizer functions satisfactorily. Preferably, the analog to digital converter 28 operates in the megaHertz data rate range, and has a high sampling rate of 20 MHz. It is noted that generally the information bandwidth in a magnetic resonance examination apparatus is about 500kHz, so depending on the design of the other components in the signal generator, a sampling rate of 1 MHz is also possible.

The converter 28 is preferably disposed between the band filter and a bandwidth reducer 29. For transmission as either a radio frequency or optical frequency signal, conversion to a lower bit rate may be necessary, depending on the radio or optical transmitters used. The bandwidth reducer 29 performs this function, converting the data rate output from the analog to digital converter to a data rate matching that of the transmitter.

The signal generator further comprises an output 14 for outputting the digital electric signals.

Further, as discussed in more detail with reference to Figures 3 and 5, it is preferable that the analog to digital conversion occurs prior to the electric signal conversion by a transducer 30, 50 to an electromagnetic signal. The reason for this is that the transducers 30, 50, in particular optical transducers, such as photodiodes, which convert an electric signal to an optical signal and vice versa, possess a non-linear transfer characteristic. Thus, a digital signal produces a more accurate transduced signal than an analog signal. The invention, however, is not limited in this respect and it is equally possible to dispose the analog converter 29 in the receiving assembly 100, 101, 102 downstream of the transducer 30, 50. Further, according to certain embodiments of the invention, the signal that is output from the signal generator may consist of an entirely digital signal. However, the invention is not limited in this respect, and it is envisaged that the signal output by the signal generator may comprise a digital signal. In particular, the signal may comprise at least a partly digital signal. It is not necessary for the present invention that the entire signal output by the signal generator is digital, although, this is a preferred embodiment.

As mentioned above, components of the receiving assembly 100, 101, 102 require a power supply. Conventionally, a multifunctional cable provides not only a link over which the received signals are transmitted to the signal processing unit, but also a power supply to the receiving assembly. According to embodiments of the invention, alternatives are provided which negate the need for applying a power supply via a conventional multifunctional cable. Figure 2 shows a power supply means 23. Except for the radio frequency coils 22, most of the components of the signal generator 21 are available as integrated circuits requiring little electric power. Thus, the amount of electric power required can be¹ kept to a minimum, and is preferably in the order of 1 Watt. For example, the power supply means 23 may comprise a segmented cable or rail system as described for example in our copending application (Philips reference PHN 17484) that is incorporated herein by reference. Further, the power supply means may comprise a battery, preferably a rechargeable battery which is recharged using a pick-up radio frequency coil during radio frequency transmission, however outside the radio frequency imaging band. Alternatively, the power supply means 23 may comprise a second transducer 25, whereby an optical power supply via an optical fibre or other optical waveguide is applied to the second transducer 25, which converts the optical input into an electric output. In particular, 1 Watt of optical to electric power conversion is applied via an optical link using a 100W laser input.

A further optical solution is to direct an optical source directly onto a second transducer 25, such as a photodiode. Similarly, a 100W laser source directed onto a photodiode with appropriate alignment will generate 1W of electric power. The components 21 of the receiving assembly 100, 101, 102 of Figure 2 may, for example, be incorporated in the apparatuses shown in Figures 3-5.

Figure 3 shows a magnetic resonance examination apparatus according to one embodiment of the present invention comprising receiving assembly components 21 as shown in Figure 2. The receiving assembly is labelled 101. The signal generator 24, 26, 28, 29 provides from output 14 signals in response to spin resonance signals in the form of digital electric signals. The receiving assembly 100 shown in Figure 3 further comprises a transducer 30 and transmitter 32. The electric signal from output 14 is directed to an input of a transducer 30, 50 for converting the electric generated signal to an electromagnetic signal. In Figure 3, the transducer is preferably an optical transducer, such as a photodiode. The optical transducer 30 converts the electric signals to optical signals. The optical signals are then fed to a transmitter 32 for transmission to optical receiver 36. The transmitter 32 may include in addition an optical amplifier (not shown) and a wavelength converter (not shown) to convert the optical signals to signals suitable for transmission via waveguide link 34. In Figure 3, transducer 30 and transmitter 32 are shown as two discrete entities. However, in other embodiments, the optical transducer may form the transmitter. The optical signals are coupled via an optical coupler 35 into a waveguide 23. The optical coupler preferably comprises an optical fibre splice. Index matching materials such as gel may also be necessary to achieve optimum optical coupling. The waveguide preferably comprises an optical fibre 34, however, it may also comprise other optical waveguides, such as a planar optical waveguide. The wavelength of the optical signals will depend on the optical medium chosen. For example, for a single mode optical fibre, optical signals having a wavelength of 1550nm may be used. One particular advantage of an optical communications link between the signal generator and the signal processing unit is that optical communication links, such as an optical fibre, have a very large capacity for carrying data. Consequently, by providing a digital output from the receiving assembly, the inventors have enabled high data rate technology used for optical data transmission to be suitable for use in a magnetic resonance examination apparatus. As mentioned previously, the inventors have realized that by converting the electric signals into electromagnetic radiation, a non-metallic communication link with the receiver and signal processing unit is possible. Further, the inventors have realized that a digital signal is more effectively transduced than an analog signal, thus improving the quality of the generated signal, and hence also the quality of the examination. Subsequent to transmission via optical fibre link 34 a further optical coupling means 35 is provided to couple the transmitted signal to receiver 36. The received signal is input to a further transducer 38 which converts the received optical signals to electric signals. The electric signals are then processed by signal processing unit 39. In an alternative embodiment, however, the optical signals are processed by an optical signal processing unit (not shown) using optical processing techniques. This embodiment avoids the need for transducer 38.

The signal processing unit 39 uses the signal received to derive data corresponding to the examined body. For example, the signal processing unit may use the data derived from the received signal to form images of the examined body. Data processes include memory store and reconstruction.

Figure 4 shows a block diagram of a magnetic resonance examination apparatus according to a further embodiment incorporating the components 21 of the receiving assembly shown in Figure 2. Similarly numbered components in Figure 4 correspond to those shown in Figure 3. Figure 4 differs from Figure 3 in that a digital optical signal is transmitted by an optical transmitter 40 as an optical infrared signal through free space 33 to an optical receiver 42. A particular advantage of the embodiment shown in Figure 4 is that no waveguide and no optical coupling means are necessary. However, it will be appreciated that transmitter 40 must be accurately aligned with receiver 42. If there is no direct line of sight alignment of the transmitter and receiver, suitable optical imaging components such as mirrors, are necessary. Further, the atmosphere must be relatively free of dust and other particles.

Figure 5 shows a magnetic resonance examination apparatus according to a further embodiment of the present invention comprising components 21 of the receiving assembly as shown in Figure 2. The receiving assembly is labelled 102 and includes in addition to those components described with reference to Figure 2, a transducer 50 and a transmitter 51. The signal generator 24, 26, 28, 29 provides from output 14 signals in response to spin resonance signals in the form of digital electric signals. The electric signal is directed to an input of a transducer 50 for converting the electric generated signal to an electromagnetic signal. In Figure 5, the transducer 50 is preferably a transducer for converting electric signals to digital modulated radio frequency signals. The digital bit pulses output from the analog to digital converter 28 have an amplitude of a few volts. Starting from a sampling rate of 20MHz, the maximum bit rate for a 12 bit analog to digital converter will be 12x20 Mbit/s, which is 240Mbit/s. Subsequent to the bit rate reduction, carried out by the bandwidth reducer 29 and depending on the chosen transmission technology, this value may be reduced to 12x1, which is 12Mbit/s. If the signals are to be transmitted as a radio frequency digital signal, a 2.4GHz carrier wave is preferably used. The modulated radio signals are then fed to a transmitter 51 for transmission to optical receiver 52. The transmitted signals 44 are transmitted through the atmosphere. The transmitter may include, in addition, an amplifier (not shown) . In Figure 5, transducer 50 and transmitter 51 are shown as two discrete entities. However, in other embodiments, the radio transducer may also form the transmitter.

One particular advantage of a digital modulated radio link between the signal generator and the signal processing unit is that the data rates (bandwidth) available for data transmission are high.

Consequently, by providing a digital output from the signal generators, the inventors have enabled high data rate technology used for optical data transmission to be suitable for use in a magnetic resonance examination apparatus. The further advantages of a digital electromagnetic signal, described with reference to Figure 3, also apply to the digital radio signals shown in Figure 5.

Subsequent to transmission via radio communication link 44, the transmitted signal is received by receiver 52. As with the free space optical link shown in Figure 4, it is important that the transmitter 51 is aligned with the receiver 52. If there is no direct line of sight alignment, suitable imaging components are necessary. The received signal is input to a transducer 53 which converts the received radio signals to electric signals. The electric signals are then processed by signal processing unit 39. In an alternative embodiment, however, the radio signals are processed by a radio signal processing unit (not shown) using radio processing techniques. This embodiment avoids the need for transducer 53.

As mentioned with reference to Figure 3 and 4, the signal processing unit 39 uses the signal received to generate data corresponding to the examined body. For example, the signal processing unit may generate images using data derived from the received signal. Data processes include memory store and reconstruction. Whilst specific embodiments of the invention have been described above, it will be appreciated that the invention may also be practiced otherwise. The description is not intended to limit the invention.

Claims

CLAIMS:

1. A magnetic resonance examination apparatus comprising: an examination zone arranged to receive a body for examination; magnetic field generating means for generating a magnetic field in said examination zone; a receiving assembly (100, 101, 102) located in or in the vicinity of said examination zone, said receiving assembly (100, 101, 102) comprising a receiver (22) for receiving a spin resonance signal generated in said examination zone, a signal generator (24, 26, 28, 29) for generating a signal in response to said received spin resonance signal, and a transmitter (32, 40, 51) for transmitting said generated signal to a signal processing unit (39) disposed at a location remote from said receiving assembly (100, 101, 102); characterized in that said signal generator (24, 26, 28, 29) further comprises a digitizer (28) for generating a digital signal in response to said received spin resonance signal, and outputting said digitized signal to said transmitter (32, 40, 51).

2. An apparatus as claimed in claim 1, characterized in that said receiving assembly further comprises a shielding means (11) for shielding said digitizer (28) from said magnetic field in said examination zone, said digitizer (28) and said shielding means (23) being dimensioned so that the induction of eddy currents in said shielding means (11) is suppressed.

3. An apparatus as claimed in claim 1, characterized in that said digitizer (28) is arranged to convert said spin resonance signals to a high data rate digital signal.

4. An apparatus as claimed in claim 1, characterized in that said signal generator comprises a signal processor (27) disposed upstream of said digitizer (28) for selectively processing said spin resonance signals in accordance with a signal level.

5. An apparatus as claimed in claim 4, characterized in that said signal processor comprises an attenuator (27) which is controlled by a controller (10) to selectively attenuate said spin resonance signals in accordance with a predicted signal level determined in accordance with the origin of the spin resonance signals in said examination zone.

6. An apparatus as claimed in claim 4, characterized in that said signal processor comprises a non-linear attenuator.

7. An apparatus as claimed in claim 4, characterized in that said signal processor comprises a non-linear amplifier.

8. An apparatus as claimed in claim 1, characterized in that said signal generator

(24, 26, 28, 29) comprises a transducer (30, 50) for converting said digital signal to an electromagnetic signal.

9. An apparatus as claimed in claim 1, characterized in that said transmitter (51) is a radio frequency transmitter for transmitting a modulated radio frequency signal to said signal processing unit (39).

10. An apparatus as claimed in claim 1, characterized in that said signal generator (24, 26, 28, 29) further comprises a band filter (26) for conditioning said spin resonance signals to match the input characteristics of an input of said digitizer (28).

11. An apparatus as claimed in claim 1, characterized in that said signal generator (24, 26, 28, 29) further comprises a bandwidth reducer (29) for reducing the bandwidth of the digital signal to match the input characteristics of said transmitter (32, 40, 51).

12. A receiver assembly for use in a magnetic resonance examination apparatus having an examination zone, said receiver assembly (100, 101, 102) being used in or in the vicinity of said examination zone in which a magnetic field is generated by a magnetic field generating means, said receiver assembly comprising a receiver (22) for receiving a spin resonance signal generated in an examination zone, a signal generator (24, 26, 28, 29) for generating a signal in response to said spin resonance signal, and a transmitter (32, 40, 51) for transmitting said generated signal to a signal processing unit (39) disposed at a location remote from said receiving assembly (100, 101 102), characterized in that said signal generator (24, 26, 28, 29) further comprises a digitizer (28) for generating a digital signal in response to said received spin resonance signal and outputting said digitized signal to said transmitter (32, 40, 51).

13. A signal processing unit for use in a magnetic resonance examination apparatus according to any of claims 1 to 11 , said signal processing unit (39) comprising a receiver (36, 42, 52) for receiving a signal generated by said receiving assembly (100, 101, 102) in response to a spin resonance signal received from an examination zone, characterized in that said receiver (36, 42, 52) is arranged to receive said digital signal and in that said signal processing unit (39) includes a digital processor (39) for deriving examination data from said received signal.

14. A method of performing an examination using magnetic resonance comprising the steps of: providing an examination zone to receive a body for examination; generating a magnetic field in said examination zone; and receiving, within or in the vicinity of said examination zone, a spin resonance signal generated in said examination zone; generating a signal (24, 26, 28, 29) in response to said received spin resonance signal, and transmitting (32, 40, 51) said generated signal to a signal processing unit (39) disposed at a location remote from said receiving assembly (100, 101, 102); characterized in that within or in the vicinity of said examination zone said signal generated in response to said received spin resonance signal is digitized, and said digitized signal is outputted to said transmitter (32, 40, 51).