Method of and apparatus for nuclear quadrupole resonance testing a sample
A method of nuclear quadrupole resonance testing a sample is disclosed in which the excitation applied to the sample is arranged so that phase and amplitude information may be obtained from the response signal, and in which the signal is resolved into two components. Particularly if a parameter such as radio-frequency field strength varies with position, this may give an indication of the distribution of nuclei in the sample, preferably from the phase of the response signal. Positional information can also be obtained by measuring from two or more reference points. This may be employed in imaging. The phase information may be employed to improve the signal to noise ratio obtainable in other methods where only amplitude information was previously available, for example in distinguishing genuine NQR response signals from spurious signals.
1. A method of determining position of quadrupolar nuclei in a sample comprising applying excitation to said sample to produce a detectable NQR response, detecting a first response signal from said nuclei and determining a first distance of the nuclei from a first reference point, detecting a second response signal from said nuclei and determining at least a second distance of said nuclei from at least a second reference point, and determining a positional parameter of said nuclei on the basis of said distances from said reference points.
2. A method according to claim 1 , wherein first and second receiver coils are used to detect respective ones of said response signals.
3. A method according to claim 1 , in which said excitation is selected to produce a response signal, said response signal containing detectable phase and amplitude components resulting from nuclear quadrupole resonance interaction between said excitation and said quadrupolar nuclei, and said positional information is determined from phase and amplitude components of signals detected by said receiver coils.
4. A method of determining position of quadrupolar nuclei according to claim 1 , wherein the distance of the nuclei from the first and second reference points is determined by the g phase of the NQR response.
5. A method of determining position of quadrupolar nuclei according to claim 4 , wherein the excitation applied to the sample comprises a pulse sequence arranged to lock response signals of a given phase.
6. A method of determining position of quadrupolar nuclei according to claim 4 , wherein the excitation applied to the sample is arranged to generate a field whose strength varies throughout the sample.
7. A method of determining position of quadrupolar nuclei according to claim 4 , wherein the excitation is arranged to generate a flip angle in the quadrupolar nuclei of less than 2π radian so that the phase of the NQR response is a single valued function of position.
8. A method of detecting NQR response signals emanating from quadrupolar nuclei in a given region of a sample, said method comprising exciting said sample to produce a response signal from said quadrupolar nuclei having a phase varying as a function of position of said nuclei and identifying signals of a given phase, wherein said identifying comprises applying a pulse arranged to lock response signals of said given phase.
9. A method according to claim 8 , further comprising determining a position of said quadrupolar nuclei, or an image of a sample containing the quadrupolar nuclei based on said phase.
10. A method according to claim 8 , further comprising reducing noise in said NQR response signals based on said phase.
11. An apparatus for determining position of quadrupolar nuclei in a sample, the apparatus comprising:
excitation means arranged to generate an excitation signal capable of exciting a detectable NQR response;
transmission means arranged to transmit said excitation signal to said sample;
detection means arranged to detect a first response signal generated by said sample at a first reference point to produce a first detected signal and to detect a second response signal generated by said sample at a second reference point to produce a second detected signal; and
signal processing means coupled to said detection means to receive both said first detected signal and said second detected signal and to process said signals to determine a positional parameter of said nuclei on the basis of a first distance of said nuclei from said first reference point and a second distance of said nuclei from said second reference point.
12. An apparatus according to claim 11 , further comprising first and second receiver coils arranged to detect respective ones of said response signals.
13. An apparatus according to claim 11 , wherein said transmission means is arranged to generate a field having a field strength varying according to a given pattern throughout at least a portion of said sample.
14. An apparatus according to claim 11 , wherein the signal processing means is arranged to process said signals to determine a positional parameter in response to phase of the NQR response.
15. An apparatus according to claim 14 , wherein the excitation means are operable to generate an excitation signal arranged to lock response signals of a given phase.
16. An apparatus according to claim 11 , wherein the excitation means are operable to generate an excitation signal arranged to have a field strength which varies throughout a sample.
17. An apparatus according to claim 16 , wherein the excitation means is operable to generate an excitation signal arranged to generate a flip-angle in the quadrupolar nuclei of less than 2π radians so that a phase of the NQR response is a single valued function of position.