Apparatus and method for nuclear magnetic resonance scanning and mapping

Abstract

An improved apparatus and method for analyzing the chemical and structural composition of a specimen including whole-body specimens which may include, for example, living mammals, utilizing nuclear magnetic resonance (NMR) techniques. A magnetic field space necessary to obtain an NMR signal characteristic of the chemical structure of the specimen is focused to provide a resonance domain of selectable size, which may then be moved in a pattern with respect to the specimen to scan the specimen.

I claim: 
     
       1. A method of detecting selected nuclei within a specimen comprising: (a) providing a primary .[.static.]. magnetic field having a known field configuration in a three dimensional space having an "X", "Y", and "Z" dimensional frame of reference, the primary .[.static.]. magnetic field having a magnetic field orientation in the "Z" direction;   (b) .[.superimposing a.]. focusing .[.static.]. .Iadd.said .Iaddend.magnetic field .Iadd.to produce a resulting magnetic field of known magnetic configuration .Iaddend.having a magnetic field orientation in the "Z" direction and .[.having a selectable.]. .Iadd.a selected .Iaddend.gradient in the "Y" direction .[.on the primary static magnetic field to produce a resulting static magnetic field having a magnetic field orientation in the "Z" direction and having a known field configuration.]. .Iadd.and maintaining said resulting field unaltered during the generation of a nuclear magnetic resonance signal.Iaddend.;   (c) providing a source of oscillating magnetic radiation having a selectable frequency .Iadd.and of limited spacial extent in all directions in the Z-X plane.Iaddend.;   (d) selecting a frequency ω o  of the source of oscillating magnetic radiation to satisfy the equation:   ω.sub.o =|H.sub.o |γ     where:     ω o  =resonance angular frequency of the selected nuclei   |H o  |=magnitude of resulting static magnetic field at a .[.particular.]. .Iadd.chosen .Iaddend.location   γ=gyromagnetic ratio for the selected nuclei and is a constant for the selected nuclei for the selected nuclei .[.at a resonance domain located.]. within the resulting .[.static.]. magnetic field where the field strength is substantially |H o  |;     .[.(e) positioning the specimen such that the resonance domain impinges on the specimen;.].   .[.(f).]. (.Iadd.e) .Iaddend.orienting the .Iadd.source of .Iaddend.oscillating magnetic radiation having frequency ω o  in .[.a.]. .Iadd.the "Y" .Iaddend.direction such that its magnetic field orientation is orthogonal to the "Z" direction .Iadd.so as to define a three dimensional resonance domain in the region where the field strength is substantially |Ho|.Iaddend.;   (.Iadd.f) positioning the specimen such that the resonance domain impinges on the specimen; .Iaddend.   (g) directing the oscillating magnetic radiation to the resonance domain .[.whereby.]. .Iadd.to generate .Iaddend.a nuclear magnetic resonance signal .[.is generated.]. for the selected nuclei in the specimen located within the resonance domain;   (h) receiving the nuclear magnetic resonance signal generated; and   (i) processing the nuclear magnetic resonance signal to determine a nuclear magnetic resonance value representing the selected nuclei extant in the resonance domain within the specimen.   
     
     
       2. The method according to claim .[.1.]. .Iadd.25 .Iaddend.wherein the primary static magnetic field has a substantially uniform field configuration and .Iadd.wherein .Iaddend.the focusing .[.static magnetic.]. field .[.has a selectable linear gradient in the "Y" direction.]. .Iadd.is static.Iaddend.. 
     
     
       3. The method according to claim 2 further including, the step of selecting the linear gradient in the "Y" direction of the focusing static magnetic field to adjust the size of the resonance domain. 
     
     
       4. The method according to claim 1 further including the step of scanning the specimen in the "Y" direction by adjusting the frequency of the oscillating magnetic energy to a new value of ω o  whereby the resonance domain is moved to a location where the resulting static magnetic field has a field strength of |H o  | .Iadd.to .Iaddend.satisfy said equation for said new value of ω o . 
     
     
       5. The method according to claim 4 further including the step of focusing the oscillating magnetic radiation having a frequency ω o  to have a maximum intensity along a pencil beam in the "Y" direction and scanning of the specimen in the "Y" direction is along the pencil beam. 
     
     
       6. The method according to claim 5 wherein scanning along the pencil beam is accomplished in a step-wise fashion. 
     
     
       7. The method according to claim 6 further including the step of incrementally moving the specimen with respect to the pencil beam in the "X" direction a predetermined distance each time a scan of the specimen along the pencil beam has been accomplished whereby a grid of nuclear magnetic resonance values is obtained for a cross section in a "Y-X" plane through the specimen. 
     
     
       8. The method according to claim 7 further including the step of displaying the grid of values to provide a visual image of the grid. 
     
     
       9. The method according to claim 5 utilizing a pair of intersecting and mutually orthogonal planar coils having a line of intersection in the "Y" direction for forming the pencil beam along the line of intersection. 
     
     
       10. The method according to claim 1 wherein a pair of doughnut shaped superconducting magnets axially aligned in the "Z" direction and separated by a Helmholtz distance is utilized for providing the primary .[.static.]. magnetic field and wherein the specimen is positioned between the doughnut shaped superconducting magnets. 
     
     
       11. The method according to claim 1 wherein field focusing coils are used to provide the focusing .[.static.]. magnetic field. 
     
     
       12. The method according to claim 1 wherein at least one planar permanent magnet is utilized to provide the primary .[.static.]. magnetic field. 
     
     
       13. The method according to claim 1 wherein the specimen includes a live mammal and the nuclear magnetic values may include intensities of nuclear magnetic resonance signals received, spin-spin relaxation times, spin-lattice relaxation times, spin-mapping values and amplitude versus frequency spectra. 
     
     
       14. The method according to claim 1 wherein the selected nuclei may include nuclei selected from P 31 , K 39 , Na 23 , H 1 , C 13 , N 15 , N 14  or O 17 . 
     
     
       15. Apparatus for detecting selected nuclei within a specimen comprising: (a) means for providing a primary .[.static.]. magnetic field having a known field configuration in a three dimensional space having an "X" "Y" and "Z" dimensional frame of reference, the primary .[.static.]. magnetic field having a magnetic field orientation in the "Z" direction;   (b) means for .[.superimposing a.]. focusing .[.static.]. .Iadd.said primary .Iaddend.magnetic field .Iadd.to produce a resulting magnetic field of known field configuration .Iaddend.having a magnetic field orientation in the "Z" direction and .[.having.]. a selectable gradient in the "Y" direction .[.on the primary static magnetic field to produce a resulting static magnetic field having a magnetic field orientation in the "Z" direction and having a known field configuration.]. .Iadd.and maintaining said resulting field unaltered during the generation of a nuclear magnetic signal.Iaddend.;   (c) means for providing oscillating magnetic radiation having a selectable frequency .Iadd.and of limited spacial extent in all directions in the "Z-X" plane .Iaddend.;   (d) means for selecting a frequency ω o  of the oscillating magnetic radiation to satisfy the equation:   ω.sub.o =|H.sub.o |γ       ω o  =resonance angular frequency of the selected nuclei   H o  =magnitude of resulting static magnetic field at a particular location   γ=gyromagnetic ratio for the selected nuclei and is a constant for the selected nuclei for the selected nuclei .[.at a resonance domain.]. located within the resulting static magnetic field where the field strength is substantially |H o  |;     .[.(e) means for positioning the specimen such that the resonance domain impinges on the specimen;.].   .[.(f).]. (.Iadd.e) .Iaddend.means for orienting the oscillating magnetic radiation having the frequency ω o  in .[.a.]. .Iadd.the "Y" .Iaddend.direction such that its magnetic field orientation is orthogonal to the "Z" direction .Iadd.so as to define a three dimensional resonance domain in the region where the field strength is substantially |Ho|.Iaddend.;   (.Iadd.f) means for positioning the specimen such that the resonance domain impinges on the specimen; .Iaddend.   (g) means for directing the oscillating magnetic radiation to the resonance domain .[.whereby.]. .Iadd.to generate .Iaddend.a nuclear magnetic resonance signal .[.is generated.]. for the selected nuclei in the specimen located within the resonance domain;   (h) means for receiving the nuclear magnetic resonance signal generated; and   (i) means for processing the nuclear magnetic resonance signal to determine a nuclear magnetic resonance value representing the selected nuclei extant in the resonance domain within the specimen.   
     
     
       16. The apparatus according to claim .[.15.]. .Iadd.26 .Iaddend.wherein the means for providing the primary static magnetic field includes means for providing a substantially uniform field configuration and wherein the .[.means for providing the.]. focusing .[.static.]. magnetic field .[.includes means for providing a field having a selectable linear gradient in the "Y" direction.]. .Iadd.is static.Iaddend.. 
     
     
       17. The apparatus according to claim 16 further including means for selecting the linear gradient in the "Y" direction of the focusing static magnetic field to adjust the size of the resonance domain. 
     
     
       18. The apparatus according to claim 15 further including means for scanning the specimen in the "Y" direction including means for adjusting the frequency of the oscillating magnetic energy to a new value of ω o  whereby the resonance domain is moved to a new location where the resulting static magnetic field has a field strength of |H o  | to satisfy said equation for said new value for ω o . 
     
     
       19. The apparatus according to claim 18 further including means for focusing the oscillating magnetic radiation having a frequency ω o  to have a maximum intensity along a pencil beam in the "Y" direction and scanning of the specimen in the "Y" direction is along the pencil beam. 
     
     
       20. The apparatus according to claim 19 wherein the means for focusing the oscillating magnetic radiation includes a pair of intersecting and mutually orthogonal planar coils having a line of intersection in the "Y" direction for forming the pencil beam along the line of intersection. 
     
     
       21. The apparatus according to claim 20 wherein the planar coils are circular and the line of intersection comprises a common diameter. 
     
     
       22. The apparatus according to claim 15 wherein the means for providing the primary .[.static.]. magnetic field comprises a pair of doughnut shaped superconducting magnet axially aligned in the "Z" direction and separated by a Helmholtz distance. 
     
     
       23. The apparatus according to claim 15 wherein the means for superimposing a focusing .[.static.]. magnetic field comprises field focusing coils. 
     
     
       24. The apparatus according to claim 15 wherein the means for providing the primary .[.static.]. magnetic field comprises at least one planar permanent magnet. .Iadd. 
     
     
       25.  The method according to claim 1 wherein the primary magnetic field is static and focusing is provided by a focusing field oriented in the "Z" direction and having a selectable gradient in the "Y" direction, said focusing field being superimposed on said primary field to produce said resulting field. .Iaddend. .Iadd.26. The apparatus according to claim 16, wherein said primary field is static and the means for focusing comprises means for providing a focusing field oriented in "Z" direction and having a selectable gradient in the "Y" direction, said field being superimposed on said primary field to produce said resulting field. .Iaddend.