Cancellation of ringing in magnetic resonance utilizing a composite pulse

Abstract

A magnetic resonance detection apparatus is provided that is not susceptible to acoustic ringing, and a method is provided for eliminating or canceling acoustic ringing from a detected magnetic resonance signal. Specifically, a composite pulse is utilized that allows for both efficient reduction of acoustic ringing signals and the detection of true NQR signals. The composite pulse can be used in any of the common NQR pulse sequences currently utilized simply via substitution of the original single pulses with the composite pulse. Furthermore, although a preferred application involves the spin-1 nucleus 14 N and NQR, the composite pulse will be useful for the NQR of other nuclei such as 35 CI and 39 K and in NMR applications and involving half-integer quadrupolar nuclei and spin- 1/2 nuclei. In addition, coil ringdown and piezoelectric ringing are also substantially reduced.

1. A detection apparatus comprising:
 means for generating an RF composite pulse, wherein said RF composite pulse consists essentially of two or more sub-pulses of different phase;  
 means for applying the RF composite pulse to a test sample;  
 means for detecting a nuclear resonance return signal in response to the application of the RF composite pulse to the test sample, wherein the detected nuclear resonance return signal includes a true signal component and a ringing signal component; and  
 processing means for processing the detected nuclear resonance return signal to identify the true signal component;  
 wherein the phases of each of the sub-pulses of the composite pulse, a phase of the true signal component and a phase of the ringing signal component are different.  
 
   
   
     2. A detection apparatus as claimed in  claim 1 , wherein the phase of the first sub-pulse is 0 and the phase of the second sub-pulse with respect to the first sub-pulse is x, such that the composite pulse is designated as (0, x). 
   
   
     3. A detection apparatus as claimed in  claim 2 , wherein x=45°. 
   
   
     4. A detection apparatus as claimed in  claim 1 , wherein the means for generating an RF composite pulse generates a sequence of composite pulses. 
   
   
     5. A detection apparatus as claimed in  claim 4 , wherein the sequence of composite pulses includes (0, x), (0, −x+180), (0, x−180), (0, −x). 
   
   
     6. A detection apparatus as claimed in  claim 5 , wherein the processing means sums detected nuclear resonance return signals corresponding to each of the composite pulses with weighting factors −1, +1, −1 and +1, respectively. 
   
   
     7. A detection apparatus as claimed in  claim 1 , wherein the true signal component is a nuclear quadrupole resonance signal. 
   
   
     8. A method comprising:
 generating an RF composite pulse, wherein said RF composite pulse consists essentially of two or more sub-pulses of different phase;  
 applying the RF composite pulse to a test sample;  
 detecting a nuclear resonance return signal in response to the application of the RF composite pulse to the test sample, wherein the detected nuclear resonance return signal includes a true signal component and a ringing signal component; and  
 processing the detected nuclear resonance return signal to identify the true signal component;  
 wherein the phases of each of the sub-pulses of the composite pulse, a phase of the true signal component and a phase of the ringing signal component are different.  
 
   
   
     9. A method as claimed in  claim 8 , wherein the phase of the first sub-pulse is 0 and the phase of the second sub-pulse with respect to the first sub-pulse is x, such that the composite pulse is designated as (0, x). 
   
   
     10. A method as claimed in  claim 9 , wherein x=45°. 
   
   
     11. A method as claimed in  claim 8 , wherein generating an RF composite pulse includes generating a sequence of composite pulses. 
   
   
     12. A method as claimed in  claim 11 , wherein the sequence of composite pulses includes (0, x), (0, −x+180), (0, x−180), (0, -x). 
   
   
     13. A method as claimed in  claim 12 , wherein processing includes summing detected nuclear resonance return signals corresponding to each of the composite pulses with weighting factors −1, +1, −1 and +1, respectively. 
   
   
     14. A method as claimed in  claim 8 , wherein the true signal component is a nuclear quadrupole resonance signal. 
   
   
     15. A detection apparatus comprising:
 a radio frequency source;  
 a pulse generator mechanism coupled to the radio frequency source, wherein the pulse generator mechanism generates a radio frequency composite pulse consisting essentially of two or more sub-pulses of different phase;  
 a coil coupled to receive the radio frequency composite pulse from the pulse generator mechanism;  
 a detector coupled to the coil, wherein the detector detects a nuclear resonance signal received from the coil that includes a true signal component and a ringing signal component; and  
 a processor coupled to the detector, wherein the processor identifies the true signal component within the nuclear resonance signal;  
 wherein the phases of each of the sub-pulses of the composite pulse, a phase of the true signal component and a phase of the ringing signal component are different.  
 
   
   
     16. A detection apparatus as claimed in  claim 15 , wherein the phase of the first sub-pulse is 0 and the phase of the second sub-pulse with respect to the first sub-pulse is x, such that the composite pulse is designated as (0, x). 
   
   
     17. A detection apparatus as claimed in  claim 16 , wherein x=45°. 
   
   
     18. A detection apparatus as claimed in  claim 15 , wherein the pulse generator mechanism generates a sequence of composite pulses. 
   
   
     19. A detection apparatus as claimed in  claim 18 , wherein the sequence of composite pulses includes (0, x), ( 0, −x+180 ), (0, x−180), (0, −x). 
   
   
     20. A detection apparatus as claimed in  claim 19 , wherein the processor sums detected nuclear resonance return signals corresponding to each of the composite pulses with weighting factors −1, +1, −1 and +1, respectively. 
   
   
     21. A detection apparatus as claimed in  claim 15  wherein the true signal component is a nuclear quadrupole resonance signal. 
   
   
     22. A detection apparatus as claimed in  claim 15 , wherein the pulse generator mechanism includes a pulse programmer and radio frequency gate and a radio frequency power amplifier. 
   
   
     23. A detection apparatus as claimed in  claim 15 , wherein the pulse generator mechanism is coupled to the coil via a coupling network, and wherein the detector is coupled to the coil via the coupling network. 
   
   
     24. A detection apparatus as claimed in  claim 15 , further comprising an alarm mechanism, wherein the alarm mechanism is activated by the processor with the true signal component exceeds a threshold value.