Compact transverse magnetic gradient coils and dimensioning method therefor

Claim 2

A compact transverse magnetic gradient coil structure for use in a magnetic resonance in aging system having a static magnetic field H o directed along a predetermined z-axis, said coil structure comprising: an outer arc located so as to produce negligible net transverse gradient in H o at a predetermined observation point along the z-axis; and an inner arc located so as to produce a second derivative of the transverse gradient which substantially cancels the second derivative produced by the outer arc at said predetermined observation point.

Claim 3

A compact transverse magnetic gradient saddle coil structure for use in a magnetic resonance imaging system having a static magnetic field H o directed along a predetermined z-axis, said saddle coil structure comprising: an inner arc of radius r 1 located at a first distance z 1 from a predetermined point z o on the z-axis, and an outer arc of radius r 2 located at a second distance z 2 from z o , z 2 /r 2 being substantially less than 2.57.

Claim 4

A compact transverse magnetic gradient saddle coil structure for use in a magnetic resonance imaging system having a static magnetic field H o directed along a predetermined z-axis, said saddle coil structure comprising: an inner arc of radius r 1 located at a first distance z 1 from a predetermined point z o on the z-axis, and an outer arc of radius r 2 located at a second distance z 2 from z o , z 2 /r 2 being substantially less than 2.57.

Claim 5

A compact transverse magnetic gradient saddle coil structure for use in a magnetic resonance imaging system having a static magnetic field H o directed along a predetermined z-axis, said saddle coil structure comprising: an inner arc of radius r 1 located at a first distance z 1 from a predetermined point z o on the z-axis, z 1 /r 1 being greater than 0.389; and an outer arc of radius r 2 located at a second distance z 2 from z o , z 2 /r 2 substantially less than 2.57.

Claim 6

A compact transverse magnetic gradient saddle coil structure for use in a magnetic resonance imaging system having a static magnetic field H o directed along a predetermined z-axis, said saddle coil structure comprising: an inner arc of radius r 1 located at a first distance z 1 from a predetermined point z o on the z-axis, z 1 /r 1 being greater than 0.389; and an outer arc of radius r 2 located at a second distance z 2 from z o , z 2 /r 2 substantially less than 2.57.

Claim 7

A compact transverse magnetic gradient saddle coil structure as in claim 3 wherein z 1 /r r is approximately equal to 0.45 and z 2 /r is approximately equal to 1.4.

Claim 8

A transverse gradient coil structure for creating a transverse gradient in the static magnetic field H o of a magnetic resonance imaging system, said coil structure comprising: a first set of opposingly directed partial turns having radius r 1 and located at a first distance z 1 from a predetermined observation point, z 1 /r 1 being greater than about 0.389; and a second set of opposingly directed partial turns having radius r 2 and located at a second distance z 2 from said predetermined observation point, z 2 /r 2 being substantially less than about 2.57.

Claim 9

A transverse gradient coil structure for creating a transverse gradient in the static magnetic field H o of a magnetic resonance imaging system, said coil structure comprising: a first set of opposingly directed partial turns having radius r 1 and located at a first distance z 1 from a predetermined observation point, z 1 /r 1 being greater than about 0.389; and a second set of opposingly directed partial turns having radius r 2 and located at a second distance z 2 from said predetermined observation point, z 2 /r 2 being substantially less than about 2.57.

Claim 10

A transverse gradient coil structure as in claim 5 further comprising: a symmetrical further first set of opposingly directed partial turns located at a distance -z 1 on the opposite side of said observation point; and a symmetrical further second set of opposingly directed partial turns located at a distance -z 2 also on the opposite side of said observation point.

Claim 11

A transverse gradient coil structure as in claim 6 wherein r 1 =r 2 .

Claim 12

A transverse gradient coil structure as in claim 6 wherein each of the sets of partial turns includes plural partial turns directed in a clockwise sense and plural partial turns directed in a counter clockwise sense, said partial turns in said first and second sets being connected together by horizontal parallel conductors.

Claim 13

A transverse gradient coil structure as in claim 5, 6, or 7 wherein each of said partial turns is formed into an approximately circular arc subtending an angle of about 120° and with its axis aligned with said static magnetic field.

Claim 14

A transverse gradient coil structure as in claim 9 wherein: z 2 /r 2 is approximately equal to 1.4 and z 1 /r 1 is approximately equal to 0.45. said first and second sets thereby producing approximately equal second derivatives with respect to z of the transverse gradient field at said observation point.

Claim 15

A magnetic coil assembly for use in magnetic resonance imaging, said coil assembly comprising: a static field coil producing a static H o field directed along a z-axis; z-gradient coils disposed symmetrically about a predetermined observation point on said z-axis for producing a gradient in said static field in the z-axis direction; y-gradient coils disposed symmetrically about said observation point for producing a gradient in said static field in a y-axis direction orthogonal to said z-axis direction, and x-gradient coils, disposed symmetrically about said observation point for producing a gradient in said static field in an x-axis direction orthogonal to both said z-axis and y-axis directions; each of said y-gradient and x-gradient coils including first and second saddle coil pairs disposed symmetrically on either side of said observation point, each of said saddle coil pairs including a plurality of partial arcuate turns of radius r subtending an angle of about 120 degrees centered about said z-axis and connected together in series by horizontal conductors approximately parallel to the z-axis; said partial arcuate turns being situated in a first axially aligned group disposed at a distance z 1 from said observation point and a second axially aligned group disposed at a distance z 2 from said observation point, said distance z 2 /r for being substantially less than 2.57 and yet sufficiently large so as to produce negligible contribution to the transverse gradient at said observation point; and said distance z 1 /r being sufficiently greater than 0.389 so as to produce a second derivative of the first group's transverse magnetic gradient with respect to z which approximately equals in magnitude the second derivative of the second group's transverse magnetic gradient with respect to z.

Claim 16

A magnetic coil assembly for use in magnetic resonance imaging, said coil assembly comprising: a static field coil producing a static H o field directed along a z-axis; z-gradient coils disposed symmetrically about a predetermined observation point on said z-axis for producing a gradient in said static field in the z-axis direction; y-gradient coils disposed symmetrically about said observation point for producing a gradient in said static field in a y-axis direction orthogonal to said z-axis direction, and x-gradient coils, disposed symmetrically about said observation point for producing a gradient in said static field in an x-axis direction orthogonal to both said z-axis and y-axis directions; each of said y-gradient and x-gradient coils including first and second saddle coil pairs disposed symmetrically on either side of said observation point, each of said saddle coil pairs including a plurality of partial arcuate turns of radius r subtending an angle of about 120 degrees centered about said z-axis and connected together in series by horizontal conductors approximately parallel to the z-axis; said partial arcuate turns being situated in a first axially aligned group disposed at a distance z 1 from said observation point and a second axially aligned group disposed at a distance z 2 from said observation point, said distance z 2 /r for being substantially less than 2.57 and yet sufficiently large so as to produce negligible contribution to the transverse gradient at said observation point; and said distance z 1 /r being sufficiently greater than 0.389 so as to produce a second derivative of the first group's transverse magnetic gradient with respect to z which approximately equals in magnitude the second derivative of the second group's transverse magnetic gradient with respect to z.