WO2004068159A1

WO2004068159A1 - Apparatus and method for detecting nuclear quadrupole resonance signals in the presence of incoherent noise

Info

Publication number: WO2004068159A1
Application number: PCT/AU2004/000108
Authority: WO
Inventors: Taras Nikolaevitch Rudakov; Paul Warrick Chisholm; Vassili Timofeevitch Mikhaltsevitch; John Harold Flexman; Peter Alaric Hayes
Original assignee: QR SCIENCES Ltd
Current assignee: QR SCIENCES Ltd
Priority date: 2003-01-30
Filing date: 2004-01-30
Publication date: 2004-08-12
Anticipated expiration: 2005-07-30
Also published as: AU2003900419A0

Abstract

An apparatus for detecting NQR signals from a substance in the presence of incoherent noise. The apparatus includes a probe (30) comprising a tank circuit (10) that in turn includes a coil (11). An antenna (20) is orthogonally oriented in relation to the coil of the tank circuit (10). The apparatus also includes a transmitter (60) for providing and applying powerful RF pulses at the output thereof to the tank circuit and a receiver (50) comprising two channels. One channel (80) is for detecting and amplifying signals received in the coil (11) and the other channel (90) is for detecting and amplifying signals received in the antenna (20). Processing means (70) is included for processing the signals amplified by the receiver (50) to distinguish the presence of any NQR signals from incoherent noise by comparing the amplified signals from both channels. Methods of detecting NQR signals in incoherent noise are also described.

Description

"Apparatus and Method for Detecting Nuclear Quadrupole Resonance Signals in the Presence of incoherent Noise"

Field of the Invention

This invention relates to an apparatus and method for detecting nuclear quadrupole resonance (NQR) signals from a substance responding to the NQR phenomenon in a sample material irradiated with radio frequency (RF) energy in the presence of incoherent noise.

Within this document the term "substance" is taken to mean those materials which respond to the NQR phenomenon. For a discussion of the NQR phenomenon, regard should be made to our co-pending International Patent Application PCT/AU00/01214, which is incorporated herein by reference.

Throughout the specification, unless the context requires otherwise, the word "comprise" or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.

Background Art

The following discussion of the background art is intended to facilitate an understanding of the present invention only. It should be appreciated that the discussion is not an acknowledgement or admission that any of the material referred to was part of the common general knowledge as at the priority date of the application.

Nuclear quadrupole resonance (NQR) is a phenomenon widely used for detection and investigation of various chemical compounds. These methods are also successfully used for detecting the presence of specific substances, such as explosives and narcotics. The probe of a pulsed NQR detection system is a device providing interaction between the radio frequency (RF) field of the resonant RF transmitter of the NQR detection system with the target substance, as well as the RF field response from the target substance with the receiving part of the NQR detection system. Strong RF pulses, typically with power of hundreds of watts are used. In practical NQR devices, when detecting specific substances (for example explosives and narcotics), the power of the RF pulses can reach several kW.

FIG. 1 illustrates a conventional system for detecting NQR signals. Transmitter unit 60' and receiver unit 50' are connected to probe 30' through a duplexer and matching circuit 40' which switches probe 30' between the transmit and the receive mode. Transmitter unit 60' generates RF pulses and applies the pulses to probe 30' to excite the response from the substance. The pulses have a frequency corresponding to the resonance frequency of the nuclei of the substance. After the RF pulse is applied, probe 30' can detect the NQR signal. This signal is received by the receiver unit 50' and processed by control and signal processing unit 70', which also generates all control and RF signals.

Usually the detected NQR signals have low intensity, therefore the presence of noise sources can present a serious problem, particularly for the detection of specific substances. In practical situations the investigated volume can contain objects which when irradiated with strong radio frequency (RF) pulses can become sources of coherent or incoherent noise (or spurious signals). The objects in which strong magneto-acoustic or piezo-electric signals are generated can be sources of coherent noise. As these signals are coherent with RF pulses, they are reduced considerably by using a special multi-pulse technique. This technique is extensively developed and described in literature. Unfortunately this technique does not achieve similar good results in cancelling any incoherent noise, sources of which can also be located in the investigated volume.

It should be noted that incoherent noise created by external sources is to a great extent diminished by screening the examined volume. Electronic devices such as calculators, cameras, laptop computers or mobile telephones located in the investigated volume can generate incoherent noise. The signals they. generate can have high intensity and are not averaged by the normally used multi-pulsed technique. As a result, the NQR signal from a substance is hidden behind the incoherent noise. The incoherent noise can be perceived by the detection system as the NQR signal, which leads to false alarms.

It is possible to try and solve the problem by deactivating these electronic devices, but this is inconvenient. It also does not always solve the problem. Indeed, strong radio frequency (RF) pulses applied to a probe for NQR signal detection within a volume targeted for NQR signals generate an electro-magnetic field in the volume, which at a certain level induces signals in the circuits of electronic devices. These signals can lead to the re-activation of the circuit even if the electronic device itself is deactivated and the resulting generation of incoherent noise. This does not cause any harm to the devices (if the level of the RF field does not exceed the permissible value). It should be noted that in some cases the RF pulses that cause the re-activation need not be very powerful.

Disclosure of the Invention

The purpose of this invention is to provide for the high probability of NQR signal detection in the presence of incoherent noise.

In accordance with one aspect of the present invention, there is provided a method for detecting an NQR signal from a volume that may also generate incoherent noise , comprising:

irradiating the volume with RF signals of a prescribed frequency and magnitude to generate an NQR signal in a substance contained within the volume;

detecting a first signal comprising a mix of NQR signals and incoherent noise, if present, in one channel; detecting a second signal comprising incoherent noise only, if present, in another channel; and

processing the first and second signals to cancel the incoherent noise.

In accordance with a second aspect of the present invention, there is provided an apparatus for detecting NQR signals from a substance, comprising:

a probe comprising a tank circuit including a coil;

an antenna orthogonally oriented in relation to the coil of the tank circuit;

a transmitter for providing and applying powerful RF pulses at the output thereof to the tank circuit;

a receiving means comprising two channels, one channel for detecting and amplifying signals received in the coil and the other channel for detecting and amplifying signals received in the antenna; and

processing means for processing the signals amplified by said receiving means to distinguish the presence of any NQR signals from incoherent noise by comparing the amplified signals from both channels.

By this method and apparatus, powerful RF pulses from the output of the transmitter may be applied to the tank circuit, where an RF magnetic field is excited in the coil with a sample placed in it. This magnetic field can act on the sample and lead to the excitation of a resonance signal in it. If there is a source of incoherent noise in the coil, then after the RF pulse stops, a resonance signal may appear in the probe and exist there together with incoherent noise. Only incoherent noise is induced in the antenna, as it is positioned orthogonally to the coil. Signals from the output of the tank circuit and antenna may then be simultaneously amplified and detected by the separate receiving channels, after which the signal processing takes place. ln accordance with a further aspect of the invention, there is provided a method for detecting an NQR signal produced by transmitting an RF magnetic field pulse and irradiating a volume therewith using: (i) a probe with a coil to excite an NQR signal in a sample disposed within the volume and receive the NQR signal so excited, and (ii) an antenna to receive any incoherent noise, the method involving the following steps:

(a) detecting incoherent noise in the probe;

(b) tuning the receiving system for the optimum cancelling of incoherent noise;

(c) transmitting the RF magnetic field pulse in the coil of the probe to excite an NQR signal in a sample;

(d) simultaneously detecting the signal in two separate receiving channels, connected respectively to the coil and the antenna,

processing both signals to distinguish the NQR signal from the incoherent noise.

Brief Description of the Drawings

FIG. 1 (prior art) is a block diagram of a conventional apparatus for detecting a resonance signal in a specimen.

FIG. 2 is a block diagram illustrating an NQR apparatus for detecting a resonance signal in the specimen, according to an embodiment of the present invention.

FIG. 3 is a flow chart illustrating a method for detecting a resonance signal in the specimen, according to an embodiment of the present invention.

FIG. 4 shows the probe, according to an embodiment of the present invention.

FIG. 5 shows the probe comprising a solenoid coil and a loop antenna, according to an embodiment of the present invention. FIG. 6 shows the probe comprising a solenoid coil and a saddle shaped antenna, according to an embodiment of the present invention.

FIG. 7 shows the probe comprising a saddle shaped coil and a saddle shaped antenna, according to an embodiment of the present invention.

FIG. 8 shows the probe comprising a spiral coil system and a loop antenna, according to an embodiment of the present invention.

Best Mode(s) for Carrying Out the Invention

The embodiments of the present invention are directed towards an apparatus and method using NQR for detecting the presence of target substances.

FIG. 2 is a block diagram illustrating an NQR apparatus for detecting a resonance signal in the specimen, according to the best mode for carrying out the present invention. As shown in FIG. 2, probe 30 is connected to channel-1 80 of receiver unit 50 and conventional transmitter unit 60 via duplexer and matching circuit 40. Probe 30 includes tank circuit 10 and antenna unit 20. Tank circuit 10 is tuned to a frequency of interest.

Duplexer and matching circuit 40 switch tank circuit 10 between the transmit and receive mode as well as match receiver unit 50 and transmitter unit 60 to tank circuit 10. Antenna unit 20 is connected to channel-2 90 of receiver unit 50.

Transmitter unit 60 generates RF pulses and transfers the pulses to tank circuit 10. These RF pulses can excite NQR signals in the specimen under investigation, which is located in probe 30. This signal is amplified and detected by channel-1 80 of receiver unit 50 and is then delivered for further mathematical processing into control and signal processing unit 70, the first input of which is connected with the output of channel-l 80 of receiver unit 50.

The signal that appears in antenna unit 20 is amplified and detected by channel-2 90 of receiver unit 50 and is then delivered for further mathematical processing into control and signal processing unit 70, the second input of which is connected with the output of channel-2 90 of receiver unit 50.

Control and signal processing unit 70 generates an RF signal, which from its first output is transmitted to one of the inputs of transmitter unit 60 for further formation of the RF carrier of RF pulses and to one of the inputs of channel-1 80 and channel-2 90 of receiver unit 50 as the reference frequency. Control and signal processing unit 70 generates control signals, which are transferred to the inputs of channel-1 80 and channel-2 90 of receiver unit 50 for tuning their parameters. Control and signal processing unit 70 also generates control signals, which are transferred to another input of transmitter unit 60 and prescribe parameters for RF

Λ pulses. Control and signal processing unit 70 usually consists of a computer, an RF signal source and electronic circuits (for producing control signals), which are not specific for the present invention and are not described here in any detail.

FIG. 3 is a flow chart illustrating a method for detecting the resonance signal in the specimen, according to the best mode of the present invention. The process starts in step S100 by determining the presence of incoherent noise in the probe without exciting the NQR signal in the sample. The RF excitation either is not transferred to the coil of the tank circuit at all, or is transferred at a frequency different from the NQR frequency of the target substance. It is desirable that this frequency is close to the NQR frequency of the target substance, but not too close so as not to excite a resonance signal in the nuclei. This excitation can activate electronic appliances that could be located together with the sample.

From step S100, the process moves to step S110, which envisages the adjustment of parameters of the receive system. Practice shows that the two channels of the receive system, with one of the channels containing a coil with a sample, and the other one containing an antenna, cannot be made absolutely identical for the purpose of detecting incoherent noise. Therefore the two signals of incoherent noise detected in those two channels usually have parameters that differ a little from each other, and this complicates their further use for diminishing the value of incoherent noise in the resulting output signal. The location and orientation of the possible source of incoherent noise are also significant. These drawbacks can be, to a certain degree, eliminated by adjusting the parameters of one or both channels of the receive system for receiving the lowest value of incoherent noise in the resulting output signal.

From step S110, the process moves to step S120, where the RF excitation at the NQR frequency is applied to the tank circuit, which has a sample in its coil.

From step S120, the process moves to step S130, when the first signal, containing the NQR signal with incoherent noise, and the second signal, consisting of only the incoherent noise, are detected simultaneously.

From step S110, the process moves to step S120, where the detected first and second signals are used to receive a resulting signal with a lower level of incoherent noise.

The purpose of the equipment presented in FIG.2, according to the flow chart presented in FIG.3, allows for the following steps:

(a) Transmitter unit 60 generates one or several RF pulses at a frequency different from the NQR frequency and provides the pulses to tank circuit 10 of probe 80.

(b) After the recovery period of probe 80 the signal from the output of tank circuit 10 is transmitted to the input of channel-1 80. Simultaneously the signal from the output of antenna unit 20 is transmitted to the input of channel-1 80.

(c) Signals transmitted to receiver unit 50 are amplified, detected and sent for further mathematical processing to control and signal processing unit 70.

(d) Transmitter unit 60 generates RF pulses on the frequency corresponding to the NQR frequency and provides the pulses to tank circuit 10 of probe 80.

(e) After the recovery period of probe 80 the signal from the output of tank circuit 10 is transmitted to the input of channel-1 80. Simultaneously the signal from the output of antenna unit 20 is transmitted to the input of channel-2 90. (f) Signals transmitted to receiver unit 50 are amplified, detected and sent for further mathematical processing to control and signal processing unit 70.

(g) Signal processing unit 70 distinguishes the NQR signal from the incoherent noise.

As one can see in FIG. 2, in the best mode of the present invention two signals are used, one of them containing the NQR signal and incoherent noise, and the other one containing only incoherent noise. The first signal appears in the direction of the exciting magnetic field ie. in tank circuit 10, with the sample placed in its coil. To receive the second signal, a special antenna, also located close to the sample, is used. In contrast to nuclear magnetic resonance (NMR), in NQR if a signal is excited in a sample in a certain direction, it cannot be detected in the direction orthogonal to it. Therefore by positioning the antenna orthogonally to the direction of the coil along which the NQR signal in the sample is excited incoherent noise without an NQR signal may be detected..

FIG. 4 is a diagram illustrating a probe, according to the best mode of the present invention. Probe 30 includes tank circuit 10 and antenna unit 20. Tank circuit 10 includes coil 11 , where the examined specimen is placed, and variable capacitance 12 for tuning to the resonance frequency. Antenna unit 20 contains antenna 21 and matching circuit 22, connected to antenna 21. NQR signal is excited in coil 11 in the direction of axis Y 24. Antenna 21 is aligned in the direction of axis X 23, orthogonal to axis Y 24.

FIG. 5 illustrates a first specific embodiment of probe 30, including tank circuit 10 and antenna unit 20. The specific feature of this embodiment of probe 30 is that tank circuit 10 includes solenoid coil 11 , where the investigated specimen is placed. Coil 11 contains n turns where n >1. Tank circuit 10 also includes variable capacitance 12 for tuning to the resonance frequency. Antenna unit 20 contains antenna 21 which is a loop type antenna, and matching circuit 22, which serves for tuning the antenna and matching it to the input of the receiver. Antenna 21 consists of two loops 25 and 26, each of them can contain k turns (where k >1). Loops 25 and 26 are placed strictly opposite each other in the internal area of coil 11 close to its sides as shown in FIG. 4. Loops 25 and 26 are aligned to receive signal in the direction of axis X 23, while the NQR signal is detected in coil 11 in the direction of axis Y 24, orthogonal to axis X 23.

FIG. 6 illustrates a second embodiment of the probe 30, including a tank circuit 10 and antenna unit 20. What differentiates this embodiment from the one presented in FIG. 5 is antenna 21, which is a saddle shaped coil, also located inside coil 11 close to its sides as shown in FIG. 5. Antenna 21 can contain k turns (where k >1) and is aligned to receive signal in the direction of axis X 23, while the NQR signal is detected in coil 11 in the direction of axis Y 24, orthogonal to axis X 23.

FIG. 7 illustrates a third embodiment of probe 30, including tank circuit 10 and antenna unit 20. The specific feature of this embodiment of probe 30 is that tank circuit 10 includes saddle shaped coil 11 , where the investigated specimen is placed. Coil 11 contains n turns, where n >1. Tank circuit 10 also includes variable capacitance 12 for tuning to the resonance frequency. Antenna unit 20 contains antenna 21 , which is also a saddle shaped coil. Antenna 21 can contain k turns (where k >1) and is aligned to receive signal in the direction of axis X 23, while the NQR signal is detected in coil 11 in the direction of axis Y 24, orthogonal to axis X 23.

FIG. 8 illustrates a forth embodiment of probe 30, including tank circuit 10 and antenna unit 20. The specific feature of this embodiment of probe 30 is that the tank circuit 10 includes coil 11 , which is a system of two spiral coils 27 and 28, between which the investigated specimen is placed. Tank circuit 10 also includes variable capacitance 12 for tuning to the resonance frequency. Antenna 21 consists of two loops 25 and 26, and each of them can contain k turns (where k >1 ). Loops 25 and 26 are placed strictly opposite each other orthogonally to the surfaces of spiral coils 27 and 28 as shown in FIG. 6. Loops 25 and 26 are aligned to receive signal in the direction of axis X 23, while the NQR signal is detected in coil 11 in the direction of axis Y 24, orthogonal to axis X 23.

According to the above embodiments of the present invention the use of an additional receiving channel with an antenna, aligned orthogonally to the direction in which the NQR signal is excited, permits to distinguish signal containing incoherent noise and not containing the NQR signal. Simultaneous detection of this signal and the signal containing the NQR signal with the subsequent signal processing permits to decrease considerably the value of the incoherent noise in the resulting signal and thus to increase the efficiency of detecting target substances.

Tests have been carried out on a probe containing a tank circuit with a 6 L solenoidal type coil and a loop antenna system, consisting of two loops, positioned inside the coil opposite each other. A source of incoherent noise was placed in the middle of the coil. Signals from the outputs of the tank circuit and the loop antenna were amplified by two independent receivers with regulated parameters. Using weighted amplification of these two signals with subsequent mutual extraction permitted to decrease the value of incoherent noise by 18 dB.

It should be appreciated that the scope of the present invention is not limited to the best mode and specific embodiments thereof for carrying out the invention, and that other modes and embodiments may be envisaged using the same principles and which are considered to fall within the scope of the present invention.

Claims

The Claims Defining the Invention are as Follows

1. A method for detecting an NQR signal from a volume that may also generate incoherent noise , comprising:

detecting a first signal comprising a mix of NQR signals and incoherent noise, if present, in one channel;

detecting a second signal comprising incoherent noise only, if present, in another channel; and

processing the first and second signals to cancel the incoherent noise.

2. A method as claimed in claim 1 , including receiving signals in said other channel in a manner that is orthogonal to receiving signals in said one channel, and cancelling the effect of said signals received in said other channel from the effect of said signals received in said one channel.

3. A method as claimed in claim 1 or 2, including simultaneously amplifying said signals received in both channels, and processing said signals to cancel the effect of said signals received in said other channel from the effect of said signals received in said one channel.

4. An apparatus for detecting NQR signals from a substance, comprising:

a probe comprising a tank circuit including a coil;

an antenna orthogonally oriented in relation to the coil of the tank circuit; a transmitter for providing and applying powerful RF pulses at the output thereof to the tank circuit;

5. A method for detecting an NQR signal produced by transmitting an RF magnetic field pulse and irradiating a volume therewith using: (i) a probe with a coil to excite an NQR signal in a sample disposed within the volume and receive the NQR signal so excited, and (ii) an antenna to receive any incoherent noise, the method involving the following steps:

(a) detecting incoherent noise in the probe;

(b) tuning the receiving system for the optimum cancelling of incoherent noise;

6. A method for detecting an NQR signal from a volume that may also generate incoherent noise substantially as herein described in any one of the embodiments with reference to the accompanying drawings. An apparatus for detecting NQR signals from a substance substantially as herein described in any one of the embodiments with reference to the accompanying drawings.