Method and apparatus for rapid NMR imaging of nuclear parameters with an object

Claim 2

emanating from different selected ones of said internal structures. 3. An imaging NMR scanner as in claim 2 wherein said NMR excitation means generates pulses of transmitted r.f. signals and includes: phase control means for accurately controlling the relative phase of said

Claim 3

transmitted r.f. signals at the initiation of a pulse thereof. 4. An imaging NMR scanner as in claim 3 wherein said NMR excitation means also generates reference r.f. signals for use in detecting said NMR output signals and wherein: said phase control means also includes means accurately controlling the relative phase of said reference r.f. signals at a predetermined time prior to the expected time occurrence of said NMR spin echo output

Claim 4

signals. 5. An imaging NMR scanner as in claim 4 wherein said phase control means resets the relative phase of said reference r.f. signals at

Claim 5

the termination of a pulse of said transmitted r.f. signals. 6. An imaging NMR scanner as in claim 4 wherein said phase control means resets the relative phase of said transmitted r.f. signals at the initiation of each pulse thereof and resets the relative phase of said reference r.f. signals

Claim 6

at the termination of each such pulse. 7. A cross-sectional imaging NMR scanner for deriving data representing the internal structure of an object located therewithin, said scanner comprising: magnetic field generating means for generating controlled magnetic fields having selectable magnitude within a selected measurement volume; r.f. transmitting means for selectively generating pulses of r.f. electromagnetic fields within said measurement volume having selectable frequency and phase, r.f. receiving means for selectively receiving r.f. electromagnetic fields of predetermined frequency and phase emanating from within said measurement volume; control means connected to said magnetic field generating means, to said r.f. transmitting means and to said r.f. receiving means for controlling same in predetermined controlled sequences which produce at least two spin echo r.f. signals also containing FID r.f. signal components from said object during each of successive measurement cycles with the relative signs of spin echo and FID signal components being different during at least some of such measurement cycles as compared to others of such measurement cycles; and means for coherently combining respectively corresponding ones of said spin echo r.f. signals resulting from successive measurement cycles to cumulatively enhance the spin echo signal components while simultaneously

Claim 7

reducing the FID signal components. 8. A cross-sectional imaging MNR scanner for deriving data representing the internal structure of an object located therewithin, said scanner comprising: magnetic field generating means for generating controlled magnetic fields having selectable magnitude within a selected measurement volume; r.f. transmitting means for selectively generating pulses of r.f. electromagnetic fields within said measurement volume having selectable frequency and phase, r.f. receiving means for selectively receiving r.f. electromagnetic fields of predetermined frequency and phase emanating from within said measurement volume; control means connected to said magnetic field generating means, to said r.f. transmitting means and to said r.f. receiving means for controlling same in a predetermined controlled sequence which produces at least two spin echo r.f. signals from said object during each measurement cycle; wherein said control means is adapted to cause transmission during each measurement cycle of a 90° nutation RF pulse followed by a 180° nutation RF pulse and, after a first spin echo signal occurs, to cause transmission of a further 180° nutation RF pulse which will thereafter cause a second spin echo signal to occur and wherein the relative phases of said RF pulses during any given measurement cycle are chosen from one line of the following table: ______________________________________ Phase of Phase of 1st Phase of 2nd 90° RF Pulse 180° RF Pulse 180° RF Pulse ______________________________________ a. 0° 0° 0° b. 0° 90° 0° c. 0° 180° 0° d. 0° 270° 0° e. 180° 0° 180° f. 180° 90° 180° g. 180° 180° 180° h. 180° 270° 180° ______________________________________

Claim 8

A cross-sectional imaging NMR scanner as in claim 8 wherein said control means is adapted to produce measurement cycles in multiples of four, with each such group of four measurement cycles corresponding to four selected ones of said lines a-h in said table, said four lines being chosen to produce a final combined spin echo signal which is non-zero but in which combined FID signal components substantially cancel in accordance with the following continuation of said table: ______________________________________ Sign of Sign of x Sign of y spin echo plane FID plane FID ______________________________________ a. - + + b. + + + Quadrature c. - + - d. + + - Quadrature e. + - + f. - - + Quadrature g. + - - h. - - - Quadrature ______________________________________

Claim 9

A cross-sectional imaging NMR scanner for deriving data representing the internal structure of an object located therewithin, said scanner comprising: magnetic field generating means for generating controlled magnetic fields having selectable magnitude within a selected measurement volume; r.f. transmitting means for selectively generating pulse of r.f. electromagnetic fields within said measurement volume having selectable frequency and phase, r.f. receiving means for selectively receiving r.f. electromagnetic fields of predetermined frequency and phase emanating from within said measurement volume; control means connected to said magnetic field generating means, to said r.f. transmitting means and to said r.f. receiving means for controlling same in a predetermined controlled sequence which produces at least two spin echo r.f. signals from said object during each measurement cycle; wherein each of said spin echo r.f. signals have a peak amplitude approximately proportional to exp(-a/T2)1-exp(-b/T1))/[1+exp(-b/T2)exp(-b/T1)] where a=a first time parameter corresponding to the elasped time from the beginning of a measurement cycle to the spin echo signal peak, b=a second time parameter corresponding to the elapsed time between successive measurement cycles, T1=the NMR longitudinal time constant of the measured volume, T2=the NMR transverse time constant of the measured volume; and wherein said control means is adapted to selectively vary said first and second time parameters so as to enhance the resultant contrast between

Claim 10

differing parts of said internal structure. 11. A cross-sectional imaging NMR scanner for deriving data representing the internal structure of an object located therewithin, said scanner comprising: magnetic field generating means for generating controlled magnetic fields having selectable magnitude within a selected measurement volume; r.f. transmitting means for selectively generating pulse of r.f. electromagnetic fields within said measurement volume having selectable frequency and phase, r.f. receiving means for selectively receiving r.f. electromagnetic fields of predetermined frequency and phase emanating from within said measurement volume; control means connected to said magnetic field generating means, to said r.f. transmitting means and to said r.f. receiving means for controlling same in a predetermined controlled sequence which produces at least two spin echo r.f. signals from said object during each measurement cycle; wherein said r.f. transmitting means includes phase control reset means for accurately resetting the relative phase of said r.f. fields at the

Claim 11

initiation of each of said pulses. 12. A cross-sectional imaging NMR scanner as in claim 11 wherein said transmitting means is connected to provide r.f. reference signals to said r.f. receiving means subsequent to at least selected ones of said pulses, and wherein said pulse control reset means also accurately resets the relative phase of said r.f. reference signals at the termination of or subsequent to said selected

Claim 12

ones of said pulses. 13. A cross-sectional imaging NMR scanner as in claim 10 wherein said a and b parameters are selected via said control means to enhance the contrast between a first part of said internal structure having T1' and T2' NMR parameters and a second part of said internal structure having T1" and T2" NMR parameters by causing said a parameter to have a value between the T2' and T2" values and by causing said b

Claim 13

parameter to have a value between the T1' and T1" values. 14. A cross-sectional imaging NMR scanner as in claim 13 wherein said control means includes means for selecting the a parameter value approximately as defined by the equation: a=[T2'T2"1n(T2'/T1")]/(T2'-T2"). .[.15. An imaging NMR scanner for deriving data representing internal structure of an object having corresponding T1 and T2 NMR parameters, said scanner comprising: NMR excitation means for exciting said internal structure to provide at least one NMR spin echo output signal during each of successive measurement cycles, said NMR spin echo output signals having an amplitude approximately proportional to exp(-a/T2)[1-exp(-b/T1)] where a=a first time parameter corresponding to the elapsed time from the beginning of a measurement cycle to the NMR spin echo output signal, b=a second time parameter corresponding to the elapsed time between successive measurement cycles; NMR detection means for detectin9 said NMR spin echo output signals; and measurement control means connected to said NMR excitation means for controlling at least one of said first and second time parameters so as to enhance the resultant contrast between differing parts of said internal structure..]. .[.16. An imaging NMR scanner as in claim 15 wherein said control means includes means for selecting said a and b parameters to enhance the contrast between a first part of said internal structure having T1' and T2' NMR parameters and a second part of said internal structure having T1" and T2" NMR parameters by selecting the a parameter to have a value between the T2' and T2" values and by selecting the b

Claim 14

parameter to have a value between the T1' and T1" values..]. 17. An imaging NMR scanner .[.as in claim 16.]. .Iadd.for deriving data representing internal structure of an object having corresponding T1 and T2 NMR parameters, said scanner comprising: NMR excitation means for exciting said internal structure to provide at least one NMR spin echo output signal during each of successive measurement cycles, said NMR spin echo output signals having an amplitude approximately proportional to exp(-a/T2)[1-exp(-b/T1)] where a=a first time parameter corresponding to the elapsed time from the beginning of a measurement cycle to the NMR spin echo output signal, b=a second time parameter corresponding to the elapsed time between successive measurement cycles; NMR detection means for detecting said NMR spin echo output signals; and measurement control means connected to said NMR excitation means for controlling at least one of said first and second time parameters so as to enhance the resultant contrast between differing parts of said internal structure; wherein said control means includes means for selecting said a and b parameters to enhance the contrast between a first part of said internal structure having T1' and T2' NMR parameters and a second part of said internal structure having T1" and T2" NMR parameters by selecting the a parameter to have a value between the T2' and T2" values and by selecting the b parameter to have a value between the T1' and T1" values .Iaddend.wherein said control means is adapted to cause transmission during each measurement cycle of a 90° nutation RF pulse followed by a 180° nutation RF pulse and, after a first spin echo signal occurs, to cause transmission of a further 180° RF pulse which will thereafter cause a second spin echo signal to occur and wherein the relative phases of said RF pulses during any given measurement cycle are chosen from one line of the following table: ______________________________________ Phase of Phase of 1st Phase of 2nd 90° RF Pulse 180° RF Pulse 180° RF Pulse ______________________________________ a. 0° 0° 0° b. 0° 90° 0° c. 0° 180° 0° d. 0° 270° 0° e. 180° 0° 180° f. 180° 90° 180° g. 180° 180° 180° h. 180° 270° 180° ______________________________________

Claim 15

An imaging NMR scanner as in claim .[.15, 16 or.]. 17 wherein said NMR excitation means produces successive pulses of RF fields through said object and wherein said excitation means includes an r.f. signal generator producing r.f. signals and a phase control reset means for accurately resetting the relative phase of said r.f. signals at the initiation of

Claim 16

each of said pulses. 19. An imaging NMR scanner as in claim 18 wherein said r.f. signal generator provides reference r.f. signals to said NMR detection means and said phase control reset means also accurately resets the relative phase of said reference r.f. signals at least once during

Claim 17

each measurement cycle. 20. An imaging NMR scanner as in claim 19 wherein said phase control means resets the relative phase of said reference r.f. signals at the termination of each of said pulses. .[.21. An imaging NMR scanner for deriving enhanced contrast data representing first and second internal structures of an object, said structures having T1', T2' and T1", T2" NMR parameters, respectively, said scanner comprising: NMR excitation means for exciting said object to provide NMR spin echo output signals during successive measurement cycles, said NMR output signals having an amplitude approximately proportional to exp(-a(T2)(1-exp(-b/T1))/[1+exp(-b/T2)exp(-b/T1) where a=a first time parameter corresponding to the elapsed time from the beginning of a measurement cycle to said NMR spin echo output signal, b=a second time parameter corresponding to the elapsed time between successive measurement cycles, T1=the NMR longitudinal time constant of the measured volume T2=the NMR transverse time constant of the measured volume; and excitation control means for selecting values for said first and second time parameters which enhance the contrast between NMR signals obtained from said first and second internal structures respectively..]. .[.22. An imaging NMR scanner as in claim 21 wherein said control means includes means for selecting the value of said first time parameter between the T2' and T2" values and for selecting the value of said second time parameter between the T1' and T1" values..]. .[.23. An imaging NMR scanner as in claim 22 wherein said control means includes means for selecting the a parameter value approximately as defined by the equation:

Claim 18

a=[T2'T2"1n(T2'/T2")]/(T2'-T2")..]. 24. An imaging NMR scanner .[.as in claim 21, 22, or 23.]. .Iadd.for deriving enhanced contrast data representing first and second internal structures of an object, said structures having T1', T2' and T1", T2" NMR parameters, respectively, said scanner comprising: NMR excitation means for exciting said object to provide NMR spin echo output signals during successive measurement cycles, said NMR output signals having an amplitude approximately proportional to exp(-a/T2)(1-exp(-b/T1))/[1+exp(-b/T2)exp(-b/T1)] where a=a first time parameter corresponding to the elapsed time from the beginning of a measurement cycle to said NMR spin echo output signal, b=a second time parameter corresponding to the elapsed time between successive measurement cycles, T1=the NMR longitudinal time constant of the measured volume T2=the NMR transverse time constant of the measured volume; and excitation control means for selecting values for said first and second time parameters which enhance the contrast between NMR signals obtained from said first and second internal structures respectively;.Iaddend. wherein said NMR excitation means produces successive pulses of RF fields through said object and wherein said excitation means includes an r.f. signal generator producing r.f. signals and a phase control reset means for accurately resetting the relative phase of said r.f. signals at the

Claim 19

initiation of each of said pulses. 25. An imaging NMR scanner as in claim 24 wherein said r.f. signal generator provides r.f. reference signals and said phase control reset means also accurately resets the relative phase of said reference r.f. signals at least once during each measurement

Claim 20

cycle. 26. An imaging NMR scanner as in claim 25 wherein said phase control means resets the relative phase of said reference r.f. signals at

Claim 21

the termination of each of said pulses. 27. An improved imaging NMR scanner of the type including NMR excitation means for generating r.f. NMR responses from an object to be imaged and including r.f. signal generator means generating reference r.f. signals for use in synchronously detecting said r.f. NMR responses and also generating pulses of transmitted r.f. signals to be transmitted into said object for causing the production of said r.f. NMR responses wherein the improvement comprises: phase control reset means for accurately resetting the relative phase of

Claim 22

said transmitted r.f. signals at the initiation of said pulses. 28. An improved NMR scanner of the type including NMR excitation means for generating r.f. NMR responses from an object to be imaged and including r.f. signal generator means generating reference r.f. signals for use in synchronously detecting said r.f. NMR responses and also generating pulses of transmitted r.f. signals to be transmitted into said object for causing the production of said r.f. NMR responses wherein the improvement comprises: phase control reset means for accurately resetting the relative phase of said transmitted r.f. signals at the initiation of said pulses; and wherein said phase control reset means also accurately resets the relative phase of said reference r.f. signals at the termination of or subsequent of said pulses. .[.29. An NMR imaging method for deriving at least one spin echo NMR r.f. signal from selected internal regions of an object under test in response to applied pulses of transmitted r.f. signals during each of successive measurement cycles, wherein said spin echo NMR r.f. signals have respective amplitudes dependent upon the T1 and T2 NMR parameters of the internal region under test and upon first and second time parameters representing the elapsed times from the beginning of a measurement (a) cycle until the spin echo occurrence and (b) until the beginning of the next measurement cycle, respectively, said method comprising: selectively controlling said first and second time parameters, and

Claim 23

detecting said spin echo NMR r.f. signals..]. 30. A method for deriving NMR imaging data representing the internal structures of an object having corresponding T1 and T2 NMR parameters, said method comprising: exciting said internal structure to provide plural NMR spin echo output signals during each of successive measurement cycles, said spin echo NMR output signals each having an amplitude dependent upon (1) a first time parameter corresponding to the elapsed time from the beginning of a measurement cycle to the occurrence of the NMR spin echo output signal and (2) a second time parameter corresponding to the elapsed time between the initiation of successive measurement cycles; and selectively controlling said first and second time parameters to selectively enhance the detection of differences between the NMR spin echo output signals emanating from different selected ones of said internal

Claim 24

structures. 31. A method as in claim 30 wherein said exciting step includes the generation of pulses of transmitted r.f. signals and further comprises: accurately controlling the relative phase of said transmitted r.f. signals

Claim 25

at the initiation of a pulse thereof. 32. A method as in claim 31 wherein said exciting step also generates reference r.f. signals for use in detecting said NMR output signals and includes: accurately controlling the relative phase of said reference r.f. signals at a predetermined time prior to the expected time occurrence of said NMR

Claim 26

spin echo output signals. 33. A method as in claim 32 wherein the relative phase of said reference r.f. signals is reset at the termination of a

Claim 27

pulse of said transmitted r.f. signals. 34. A method as in claim 32 wherein the relative phase of said transmitted r.f. signals is reset at the initiation of each pulse thereof and the relative phase of said reference r.f. signals is reset at the termination of each such pulse.

Claim 29

FID signal components. 36. A method of NMR imaging derived data representing the internal structure of an object located therewithin, said method comprising: generating controlled magnetic fields having selectable magnitude within a selected measurement volume; selectively generating pulses of r.f. electromagnetic fields within said measurement volume having selectable frequency and phase; selectively receiving r.f. electromagnetic fields of predetermined frequency and phase emanating from within said measurement volume; controlling the aforesaid steps in a predetermined controlled sequence which produces at least two spin echo r.f. signals from said object during each measurement cycle; wherein said controlling step causes transmission during each measurement cycle of a 90° nutation RF pulse followed by a 180° nutation RF pulse and, after a first spin echo signal occurs, causes transmission of a further 180° nutation RF pulse which will thereafter cause a second spin echo signal to occur and wherein the relative phases of said RF pulses during any given measurement cycle are chosen from one line of the following table: ______________________________________ Phase of Phase of 1st Phase of 2nd 90° RF Pulse 180° RF Pulse 180° RF Pulse ______________________________________ a. 0° 0° 0° b. 0° 90° 0° c. 0° 180° 0° d. 0° 270° 0° e. 180° 0° 180° f. 180° 90° 180° g. 180° 180° 180° h. 180° 270° 180° ______________________________________

Claim 30

A method as in claim 36 wherein said controlling step produces measurement cycles in multiples of four, with each such group of four measurement cycles corresponding to four selected ones of said lines a-h in said table, said four lines being chosen to produce a final combined spin echo signal which is non-zero but in which combined FID signal components substantially cancel in accordance with the following continuation of said table: ______________________________________ Phase of Phase of 1st Phase of 2nd 90° RF Pulse 180° RF Pulse 180° RF Pulse ______________________________________ a. 0° 0° 0° b. 0° 90° 0° c. 0° 180° 0° d. 0° 270° 0° e. 180° 0° 180° f. 180° 90° 180° g. 180° 180° 180° h. 180° 270° 180° ______________________________________

Claim 32

parts of said internal structure. 39. A method of NMR imaging deriving data representing the internal structure of an object located therewithin, said method comprising: generating controlled magnetic fields having selectable magnitude within a selected measurement volume; selectively generating pulses of r.f. electromagnetic fields within said measurement volume having selectable frequency and phase; selectively receiving r.f. electromagnetic fields of predetermined frequency and phase emanating from within said measurement volume; controlling the aforesaid steps in a predetermined controlled sequence which produces at least two spin echo r.f. signals from said object during each measurement cycle; wherein said generating pulses of r.f. step comprises accurately resetting the relative phase of said r.f. fields at the initiation of each of said

Claim 33

pulses. 40. A method as in claim 39 including the step of generating r.f. reference signals for use in said r.f. receiving step subsequent to at least selected ones of said pulses, and including the step of accurately resetting the relative phase of said r.f. reference signals at the

Claim 34

termination of or subsequent to said selected ones of said pulses. 41. A method as in claim 38 wherein said a and b parameters are selected to enhance the contrast between a first part of said internal structure having T1' and T2' NMR parameters and a second part of said internal structure having T1" and T2" NMR parameters by choosing said a parameter to have a value between the T2' and T2" values and by choosing said b

Claim 35

parameter to have a value between the T1' and T1" values. 42. A method as in claim 41 wherein said controlling step includes selecting the a parameter value approximately as defined by the equation: a=[T2'T2"1n(T2'/T1")]/(T2'-T2"). .[.43. A method for deriving NMR data representing internal structure of an object having corresponding T1 and T2 NMR parameters, said method comprising: exciting said internal structure to provide at least one NMR spin echo output signal during each of successive measurement cycles, said NMR spin echo output signals having an amplitude approximately proportional to exp(-a/T2)[1-exp(-b/T1)] where a=a first time parameter corresponding to the elapsed time from the beginning of a measurement cycle to the NMR spin echo output signal, b=a second time parameter corresponding to the elapsed time between successive measurement cycles; detecting said NMR spin echo output signals; and controlling at least one of said first and second time parameters so as to enhance the resultant contrast between differeing parts of said internal structure..]. .[.44. A method as in claim 43 wherein said controlling step includes selecting said a and b parameters to enhance the contrast between a first part of said internal structure having T1' and T2' NMR parameters and a second part of said internal structure having T1" and T2" NMR parameters by selecting the a parameter to have a value between the T2' and T2" values and by selecting the b parameter to have a value between

Claim 36

the T1' and T1" values..]. 45. A method .[.as in claim 44.]. .Iadd.for deriving NMR data representing internal structure of an object having corresponding T1 and T2 NMR parameters, and said method comprising: exciting said internal structure to provide at least one NMR spin echo output signal during each of successive measurement cycles, said NMR spin echo output signals having an amplitude approximately proportional to exp(-a/T2)[1-exp(-b/T1)] where a=a first time parameter corresponding to the elapsed time from the beginning of a measurement cycle to the NMR spin echo output signal, b=a second time parameter corresponding to the elapsed time between successive measurement cycles; detecting said NMR spin echo output signals; and controlling at least one of said first and second time parameters so as to enhance the resultant contrast between differing parts of said internal structure; wherein said controlling step includes selecting said a and b parameters to enhance the contrast between a first part of said internal structure having T1' and T2' NMR parameters and a second part of said internal structure having T1" and T2" NMR parameters by selecting the a parameter to have a value between the T2' and T2" values and by selecting the b parameter to have a value between the T1' and T1" values;.Iaddend. wherein said controlling step causes transmission during each measurement cycle of a 90° nutation RF pulse followed by a 180° nutation RF pulse and, after a first spin echo signal occurs, causes transmission of a further 180° RF pulse which will thereafter cause a second spin echo signal to occur and wherein the relative phases of said RF pulses during any given measurement cycle are chosen from one line of the following table: ______________________________________ Phase of Phase of 1st Phase of 2nd 90° RF Pulse 180° RF Pulse 180° RF Pulse ______________________________________ a. 0° 0° 0° b. 0° 90° 0° c. 0° 180° 0° d. 0° 270° 0° e. 180° 0° 180° f. 180° 90° 180° g. 180° 180° 180° h. 180° 270° 180° ______________________________________

Claim 38

the initiation of each of said pulses. 47. A method as in claim 46 wherein reference r.f. signals are generated for said NMR detection step including accurately resetting the relative phase of said reference r.f. signals at

Claim 39

least once during each measurement cycle. 48. A method as in claim 47 wherein the relative phase of said reference r.f. signals is reset at the termination of each of said pulses. .[.49. A method for deriving enhanced contrast NMR data representing first and second internal structures of an object, said structures having T1', T2' and T1", T2" NMR parameters, respectively, said method comprising: exciting said object to provide NMR spin echo output signals during successive measurement cycles, said NMR output signals having an amplitude approximately proportional to exp(-a/T2)(1-exp(-b/T1))/[1+exp(-b/T2)exp(-b/T1)] where a=a first time parameter corresponding to the elapsed time from the beginning of a measurement cycle to said NMR spin echo output signal, b=a second time parameter corresponding to the elapsed time between successive measurement cycles, T1=the NMR longitudinal time constant of the measured volume T2=the NMR transverse time constant of the measured volume; and selecting values for said first and second time parameters which enhance the contrast between NMR signals obtained from said first and second internal structures respectively..]. .[.50. A method as in claim 49 wherein said selecting step includes selecting the value of said first time parameter between the T2' and T2" values and for selecting the value of said second time parameter between the T1' and T1" values..]. .[.51. A method as in claim 50 wherein said selecting step includes selecting the a parameter value approximately as defined by the equation:

Claim 40

a=[T2'T2"1n(T2'/T2")]/(T2'-T2")..]. 52. A method .[.as in claim 49, 50 or 51.]. .Iadd.for deriving enhanced contrast NMR data representing first and second internal structures of an object, said structures having T1', T2' and T1", T2" NMR parameters, respectively, said method comprising: exciting said object to provide NMR spin echo output signals during successive measurement cycles, sand NMR output signals having an amplitude approximately proportional to exp(-1/T2)(1-exp(-b/T1))/[1-exp(-b/T2)exp(-b/T1)] where a=a first time parameter corresponding to the elapsed time from the beginning of a measurement cycle to said NMR spin echo output signal, b=a second time parameter corresponding to the elapsed time between successive measurement cycles, T1=the NMR longitudinal time constant of the measured volume T2=the NMR transverse time constant of the measured volume; and selecting values for said first and second time parameters which enhance the contrast between NMR signals obtained from said first and second internal structures respectively; .Iaddend.wherein said NMR excitation step produces successive pulses of RF fields through said object and wherein said excitation step includes producing r.f. signals and accurately resetting the relative phase of said r.f. signals at the

Claim 41

initiation of each of said pulses. 53. A method as in claim 52 wherein said r.f. signal producing step also provides r.f. reference signals and also accurately resets the relative phase of said reference r.f. signals

Claim 42

at least once during each measurement cycle. 54. A method as in claim 53 wherein the relative phase of said reference r.f. signals is reset at the

Claim 43

termination of each of said pulses. 55. An improved imaging NMR method of the type including generating r.f. NMR responses from an object to be imaged, generating reference r.f. signals for use in synchronously detecting said r.f. NMR responses and also generating pulses of transmitted r.f. signals to be transmitted into said object for causing the production of said r.f. NMR responses wherein the improvement comprises: accurately resetting the relative phase of said transmitted r.f. signals at

Claim 44

the initiation of said pulses. 56. An improved imaging NMR method of the type including generating r.f. NMR responses from an object to be imaged, generating reference r.f. signals for use in synchronously detecting said r.f. NMR responses and also generating pulses of transmitted r.f. signals to be transmitted into said object for causing the production of said r.f. NMR responses wherein the improvement comprises: accurately resetting the relative phase of said transmitted r.f. signals at the initiation of said pulses; and resetting the relative phase of said reference r.f. signals at the

Claim 45

termination of or subsequent to said pulses. 57. A method of rapidly generating NMR signal responses from plural respectively corresponding portions of an object for use in NMR imaging thereof, said method comprising the steps of: (a) selectively exciting a first predetermined volume of the object with a 90° r.f. nutation pulse; (b) subsequently selectively exciting a second predetermined volume of the object with a 180° r.f. nutation pulse; (c) said first and second predetermined volumes substantially intersecting and overlapping so as to elicit an NMR spin echo from their common overlapping volume; and (d) repeating steps (a)-(c) for further intersecting overlapping volumes outside of previously excited volumes within the spin-lattice relaxation

Claim 46

time T1 of the first predetermined volume. 58. An NMR imaging method wherein NMR signals are rapidly generated for imaging plural planar volumes, said method comprising the steps of: (a) selectively exciting a predetermined volume to generate an NMR response by successively exciting two regions which overlap to thereby define said predetermined volume; and (b) repeating step (a) for further predetermined volumes outside of previously excited regions within the spin-lattice relaxation time T1 of the first selected predetermined volume.