Fringe field MRI

Claim 2

A magnetic resonance imaging method comprising: generating a static, non-homogenous, magnetic fringe field having an intensity greater than 2 Tesla with a static magnetic gradient in excess of 2 Gauss/cm along a predetermined z-axis through an MRI image volume; and using said static magnetic gradient in conjunction with an NMR RF pulse during an MRI data acquisition pulse sequence to achieve volume-selective NMR nutation of nuclei within said MRI image volume.

Claim 3

A magnetic resonance imaging method as in claim 1 wherein said magnetic fringe field is generated by at least one solenoidal electromagnet and said fringe field and image volume are located at a position substantially removed from the central center region of the bore of said solenoidal electromagnet.

Claim 4

A magnetic resonance imaging method as in claim 2 wherein said position is within the bore but offset toward an end of the electromagnet.

Claim 5

A magnetic resonance imaging method as in claim 2 wherein said position is outside the bore and proximate an end of the electromagnet.

Claim 6

A magnetic resonance imaging method as in claim 1 wherein said magnetic fringe field and image volume is located at a position between the spaced-apart ends of a pair of electromagnets.

Claim 7

A magnetic resonance imaging method as in claim 1 wherein said fringe field has an intensity greater than 3 Tesla.

Claim 8

A magnetic resonance imaging method as in claim 1 wherein said fringe field has a static magnetic gradient in excess of 10 gauss/cm along said z-axis.

Claim 9

A magnetic resonance imaging method as in claim 1 wherein single quantum NMR responses are elicited from said image volume for said MRI data acquisition.

Claim 10

A magnetic resonance imaging method as in claim 1 wherein said using step utilizes at frequency modulated RF pulses.

Claim 11

A magnetic resonance imaging method as in claim 1 wherein said generating step utilizes at least one solenoidal, electromagnet having a bore of less than 60 centimeters in diameter.

Claim 12

A magnetic resonance imaging method as in claim 1 wherein said generating step utilizes at least one solenoidal electromagnet having a maximum bore diameter which is less than the minimum dimension of said image volume.

Claim 13

A magnetic resonance imaging method as in claim 1 wherein said MRI data acquisition pulse sequence utilizes pulsed magnetic gradient fields which are asymmetric with respect to said image volume.

Claim 14

A magnetic resonance imaging method for acquiring MRI image data from an image volume located within a non-homogeneous static magnetic field having a substantial static gradient with respect to a predetermined z-axis, said method comprising the steps of: (a) transmitting into said volume at least one RF nutation pulse including a predetermined range of frequencies which, in conjunction with said substantial static gradient, produces volume-selective first NMR nutation of NMR nuclei within a selected sub-volume of said image volume; (b) generating at least one phase-encoding magnetic gradient pulse to phase-encode NMR nuclei within said sub-volume with respect to at least one further axis orthogonal to said z-axis; (c) transmitting into said volume at least one further RF nutation pulse including a predetermined range of frequencies which, in conjunction with said substantial static gradient, produces volume-selective second NMR nutation of NMR nuclei within said selected sub-volume; and (d) thereafter recording NMR RF responses from said sub-volume to provide acquired MRI image data.

Claim 15

A magnetic resonance imaging method for acquiring MRI image data from an image volume located within a non-homogeneous static magnetic field having a substantial static gradient with respect to a predetermined z-axis, said method comprising the steps of: (a) transmitting into said volume at least one RF nutation pulse including a predetermined range of frequencies which, in conjunction with said substantial static gradient, produces volume-selective first NMR nutation of NMR nuclei within a selected sub-volume of said image volume; (b) generating at least one phase-encoding magnetic gradient pulse to phase-encode NMR nuclei within said sub-volume with respect to at least one further axis orthogonal to said z-axis; (c) transmitting into said volume at least one further RF nutation pulse including a predetermined range of frequencies which, in conjunction with said substantial static gradient, produces volume-selective second NMR nutation of NMR nuclei within said selected sub-volume; and (d) thereafter recording NMR RF responses from said sub-volume to provide acquired MRI image data.

Claim 16

A magnetic resonance imaging method as in claim 13 wherein during said transmitting steps (a) and (c) there is substantially no magnetic gradient present in said sub-volume except said static magnetic gradients.

Claim 17

A magnetic resonance imaging method as in claim 13 wherein, during at least step (b), a magnetic gradient field is utilized which is asymmetrically and non-homogeneously distributed within said image volume.

Claim 18

Magnetic resonance imaging apparatus comprising: means for generating a static, non-homogenous, magnetic fringe field having an intensity greater than 2 Tesla with a static magnetic gradient in excess of 2 Gauss/cm along a predetermined z-axis through an MRI image volume; and means for using said static magnetic gradient in conjunction with an NMR RF pulse during an MRI data acquisition pulse sequence to achieve volume-selective NMR nutation of nuclei within said MRI image volume.

Claim 19

Magnetic resonance imaging apparatus comprising: means for generating a static, non-homogenous, magnetic fringe field having an intensity greater than 2 Tesla with a static magnetic gradient in excess of 2 Gauss/cm along a predetermined z-axis through an MRI image volume; and means for using said static magnetic gradient in conjunction with an NMR RF pulse during an MRI data acquisition pulse sequence to achieve volume-selective NMR nutation of nuclei within said MRI image volume.

Claim 20

Magnetic resonance imaging apparatus as in claim 16 wherein said means for generating includes at least one solenoidal electromagnet and said fringe field and image volume are located at a position substantially removed from the central center region of the bore of said solenoidal electromagnet.

Claim 21

Magnetic resonance imaging apparatus as in claim 17 wherein said position is within the bore but offset toward an end of the electromagnet.

Claim 22

Magnetic resonance imaging apparatus as in claim 17 wherein said position is outside the bore and proximate an end of the electromagnet.

Claim 23

Magnetic resonance imaging apparatus as in claim 16 wherein said magnetic fringe field and image volume is located at a position between the spaced-apart ends of a pair of electromagnets.

Claim 24

Magnetic resonance imaging apparatus as in claim 16 wherein said fringe field has an intensity greater than 10 Tesla.

Claim 25

Magnetic resonance imaging apparatus as in claim 16 wherein said fringe field has a static magnetic gradient in excess of 10 gauss/cm along said z-axis.

Claim 26

Magnetic resonance imaging apparatus as in claim 16 wherein said means for using includes means for eliciting single quantum NMR responses are from said image volume for said MRI data acquisition.

Claim 27

Magnetic resonance imaging apparatus as in claim 16 wherein said means for using includes means for generating frequency modulated RF pulses.

Claim 28

Magnetic resonance imaging apparatus as in claim 16 wherein said means for generating includes at least one solenoidal, electromagnet having a bore of less than 50 centimeters in diameter.

Claim 29

Magnetic resonance imaging apparatus as in claim 16 wherein said means for generating includes at least one solenoidal electromagnet having a maximum bore diameter which is less than the minimum dimension of said image volume.

Claim 30

Magnetic resonance imaging apparatus as in claim 16 wherein said means for using includes means for generating pulsed magnetic gradient fields which are asymmetric with respect to said image volume.

Claim 31

Magnetic resonance imaging apparatus for acquiring MRI image data from an image volume located within a non-homogeneous static magnetic field having a substantial static gradient with respect to a predetermined z-axis, said apparatus comprising: (a) means for transmitting into said volume at least one RF nutation pulse including a predetermined range of frequencies which, in conjunction with said substantial static gradient, produces volume-selective first NMR nutation of NMR nuclei within a selected sub-volume of said image volume; (b) means for generating at least one phase-encoding magnetic gradient pulse to phase-encode NMR nuclei within said sub-volume with respect to at least one further axis orthogonal to said z-axis; (c) means for transmitting into said volume at least one further RF nutation pulse including a predetermined range of frequencies which, in conjunction with said substantial static gradient, produces volume-selective second NMR nutation of NMR nuclei within said selected sub-volume; and (d) means for thereafter recording NMR RF responses from said sub-volume to provide acquired MRI image data.

Claim 32

Magnetic resonance imaging apparatus for acquiring MRI image data from an image volume located within a non-homogeneous static magnetic field having a substantial static gradient with respect to a predetermined z-axis, said apparatus comprising: (a) means for transmitting into said volume at least one RF nutation pulse including a predetermined range of frequencies which, in conjunction with said substantial static gradient, produces volume-selective first NMR nutation of NMR nuclei within a selected sub-volume of said image volume; (b) means for generating at least one phase-encoding magnetic gradient pulse to phase-encode NMR nuclei within said sub-volume with respect to at least one further axis orthogonal to said z-axis; (c) means for transmitting into said volume at least one further RF nutation pulse including a predetermined range of frequencies which, in conjunction with said substantial static gradient, produces volume-selective second NMR nutation of NMR nuclei within said selected sub-volume; and (d) means for thereafter recording NMR RF responses from said sub-volume to provide acquired MRI image data.

Claim 33

Magnetic resonance imaging apparatus as in claim 28 wherein during operation of said means for transmitting there is substantially no magnetic gradient present in said sub-volume except said static magnetic gradients.

Claim 34

Magnetic resonance imaging apparatus as in claim 28 further comprising: means for generating at least one compensating magnetic gradient pulse within said sub-volume with respect to said z-axis at times other than during operation of said means for transmitting to thereby provide some compensation for the inhomogeneity of said static magnetic fields.

Claim 35

31 Magnetic resonance imaging apparatus as in claim 28 further comprising: means for generating a further phase-encoding magnetic gradient pulse during said recording step to phase-encode nuclei within said sub-volume with respect to a still further axis also orthogonal to said z-axis.

Claim 36

Magnetic resonance imaging apparatus as in claim 28 wherein, during operation of at least said means for transmitting (b) means for generating a magnetic gradient field is utilized which gradient field is asymmetrically and non-homogeneously distributed within said image volume.

Claim 37

Magnetic resonance imaging apparatus comprising: a pair of spaced-apart solenoidal electromagnets having an MRI image volume located between their respective bores within a non-homogeneous static magnetic fringe field; magnetic gradient coils and RF coils disposed about said image volume; and driving and receiving means connected to said gradient and RF coils for acquiring MRI data from said image volume while utilizing, at least in part, said non-homogeneous static field to effect volume-selective NMR nutations.

Claim 38

Magnetic resonance imaging apparatus comprising: a pair of spaced-apart solenoidal electromagnets having an MRI image volume located between their respective bores within a non-homogeneous static magnetic fringe field; magnetic gradient coils and RF coils disposed about said image volume; and driving and receiving means connected to said gradient and RF coils for acquiring MRI data from said image volume while utilizing, at least in part, said non-homogeneous static field to effect volume-selective NMR nutations.

Claim 39

Magnetic resonance imaging apparatus comprising: a solenoidal electromagnet producing a non-homogeneous static magnetic fringe field located off-center within its bore proximate one end thereof; magnetic gradient and RF coils disposed about an MRI image volume disposed within said non-homogenous fringe static magnetic field; and driving and receiving means connected to said gradient and RF coils for acquiring MRI data from said image volume.

Claim 40

Magnetic resonance imaging apparatus comprising: a solenoidal electromagnet producing a non-homogeneous static magnetic fringe field located off-center within its bore proximate one end thereof; magnetic gradient and RF coils disposed about an MRI image volume disposed within said non-homogenous fringe static magnetic field; and driving and receiving means connected to said gradient and RF coils for acquiring MRI data from said image volume.

Claim 41

Magnetic resonance imaging apparatus as in claim 33 or 34 wherein the bore of each said electromagnet is substantially less than 1 meter in diameter.

Claim 42

Magnetic resonance imaging apparatus as in claim 33 or 34 wherein the bore of each said electromagnet is less than 50 centimeters in diameter.

Claim 43

Magnetic resonance imaging apparatus as in claim 33 wherein the bore of each said electromagnet is less in maximum diameter than the minimum dimension of said image volume.

Claim 44

Magnetic resonance imaging apparatus as in claim 33 or 34 wherein said fringe field is in excess of 4 Tesla.

Claim 45

Magnetic resonance imaging apparatus as in claim 33 or 34 wherein said fringe field is in excess of 10 Tesla.

Claim 46

Magnetic resonance imaging apparatus as in claim 33 or 34 wherein said fringe field has a static gradient in excess of 2 Gauss/cm.

Claim 47

Magnetic resonance imaging apparatus as in claim 33 or 34 wherein said fringe field has a static gradient in excess of 10 Gauss/cm.

Claim 48

Magnetic resonance imaging apparatus as in claim 33 or 34 wherein said driving means includes means for generating frequency modulated RF pulses and transmitting them into said image volume to volume-selectively effect NMR nutation of NMR nuclei within a selected sub-volume defined by the range of frequencies included in said RF pulse and a static magnetic field gradient included in said fringe field.

Claim 49

Magnetic resonance imaging apparatus as in claim 33 or 34 wherein said magnetic gradient coils includes magnetic gradient coil means asymmetrically located with respect to said image volume for producing an asymmetric gradient field along a predetermined axis within said image volume during predetermined portions of an MRI data acquisition pulse sequence.