Method and apparatus for determining shim coil current in nuclear magnetic resonance imaging

• US 4,931,733 A
• Filed: 12/02/1988
• Issued: 06/05/1990
• Est. Priority Date: 12/14/1987
• Status: Expired due to Fees

• Current Assignee: Kabushiki Kaisha Toshiba (Toshiba Corporation)
• Original Assignee: Kabushiki Kaisha Toshiba (Toshiba Corporation)
• Inventors: Hanawa, Masatoshi
• Primary Examiner(s): Noland, Tom
• Assistant Examiner(s): O'Shea, Kevin D.
• Application Number:
  US07/278,716
• Time in Patent Office: 550 Days
• Field of Search: 324/318, 324/319, 324/320, 335/299
• US Class Current: 324/318
• CPC Class Codes: G01R 33/3875 using correction coil assemblies, e.g. active shimming

Abstract

A method and an apparatus for nuclear magnetic resonance imaging, using a shim coil which adjusts a static magnetic field to improve the homogeneity of the static magnetic field, capable of determining an appropriate amount of current to flow through the shim coil in accordance with a nuclear magnetic resonance signal due to water, in order to achieve an accurate adjustment of the homogeneity of the static magnetic field. The determination of the amount of current may be made by selecting current parameters for which a half-width of the nuclear magnetic resonance signal spectrum due to water is the smallest. The determination of the amount of current may be made by selecting current parameters for which a peak value of the nuclear magnetic resonance signal spectrum due to water is the largest.

Claims

1. A nuclear magnetic resonance imaging apparatus, comprising:

magnet means for producing a static magnetic field;

probe coil means for irradiating radio frequency pulses on a body to be examined and for detecting nuclear magnetic resonance signals from the body;

shim coil means for adjusting the homogeneity of the static magnetic field by generating an extra magnetic field to be superposed on the static magnetic field; and

means for determining an amount of current to be supplied to the shim coil means in accordance with a nuclear magnetic resonance signal due to water by selecting a current for which a half-width of a nuclear magnetic resonance signal spectrum due to water is the smallest.

2. A method of nuclear magnetic resonance imaging, comprising the steps of:

(a) producing a static magnetic field around a body to be examined;

(b) irradiating the body with radio frequency pulses suitable for exciting hydrogen atoms;

(c) detecting nuclear magnetic resonance signals due to hydrogen atoms;

(d) separating a nuclear magnetic resonance signal due to water from nuclear magnetic resonance signals due to hydrogen atoms;

(e) determining an amount of current to be supplied to a shim coil in accordance with the nuclear magnetic resonance signal due to water by selecting a current for which a half-width of a nuclear magnetic resonance signal spectrum due to water is the smallest;

(f) adjusting the homogeneity of the static magnetic field by an extra magnetic field, to be superposed on the static magnetic field, generated by the shim coil;

(g) irradiating the body with radio frequency pulses suitable for exciting a particular species of atoms to be used in examining the body; and

(h) detecting nuclear magnetic resonance signals due to the particular species.

3. A method of nuclear magnetic resonance imaging, comprising the steps of:

(a) producing a static magnetic field around a body to be examined;

(b) irradiating the body with radio frequency pulses suitable for exciting hydrogen atoms;

(c) detecting nuclear magnetic resonance signals due to hydrogen atoms located within the body;

(d) separating a nuclear magnetic resonance signal due to water from nuclear magnetic resonance signals due to hydrogen atoms in a form other than water;

(e) determining an amount of current to be supplied to a shim coil in accordance with the nuclear magnetic resonance signal due to water;

(f) adjusting the homogeneity of the static magnetic field by an extra magnetic field, to be superposed on the static magnetic field, generated by the shim coil; and

(g) irradiating the body with radio frequency pulses suitable for exciting a particular species of atoms to be used in examining the body; and

wherein at step (e) the amount of current is determined by selecting a current for which a half-width of a nuclear magnetic resonance signal spectrum due to water is the smallest.

4. A method of nuclear magnetic resonance imaging, comprising the steps of:

(a) producing a static magnetic field around a body to be examined;

(b) irradiating the body with radio frequency pulses suitable for exciting hydrogen atoms;

(c) detecting nuclear magnetic resonance signals due to hydrogen atoms located within the body;

(d) separating a nuclear magnetic resonance signal due to water from nuclear magnetic resonance signals due to hydrogen atoms in a form other than water;

(e) determining an amount of current to be supplied to a shim coil in accordance with the nuclear magnetic resonance signal due to water;

(f) adjusting the homogeneity of the static magnetic field by an extra magnetic field, to be superposed on the static magnetic field, generated by the shim coil; and

(g) irradiating the body with radio frequency pulses suitable for exciting a particular species of atoms to be used in examining the body; and

wherein step (e) includes the following steps;

adjusting each one of a plurality of variables of an expression for shim coil current within a predetermined range; and

determining a value for each variable which minimizes one of a half-width of a nuclear magnetic resonance signal spectrum and a peak value of a nuclear magnetic resonance signal spectrum, while keeping other variables fixed.