Pulsed NMR flow measurement

Claim 3

The method of claim 1 in which said radio frequency is applied under conditions to generate a free induction decay signal, said measured frequency resulting from free induction decay of said nuclear magnetic resonance.

Claim 9

The method of claim 1, 2, 3 or 4 in which said gradient increases axially in the direction of flow of said fluid.

Claim 10

The method of claim 5 in which the gradient of said first magnetic field increases axially in the direction of flow of said fluid and the gradient of said second and third magnetic fields increase axially outwardly from their point of mutual orthogonal crossing.

Claim 11

The method of claim 1 in which said conduit comprises a a blood vessel and said fluid component is hydrogen proton.

Claim 14

Apparatus for measuring flow of fluid in a conduit, the atomic nuclei of at least one component of said fluid displaying a nuclear magnetic moment and angular momentum, comprising: means establishing a first static, substantially homogenous axial magnetic field about said conduit whereby a gradient along the direction of flow of said fluid is obtainable sufficient to induce nuclear paramagnetization in said fluid; means for applying to a region within said conduit a radio frequency pulse chosen to alter the nuclear magnetization within a bolus of said fluid to thereby tag said bolus with respect to fluid preceding and following said bolus; means for measuring the frequency of nuclear magnetic resonance of the atomic nuclei of said element in said bolus over predetermined periods of time to obtain for each period of time the means instantaneous frequency of said nuclear magnetic resonance; and means for deriving the velocity of said fluid from the rate of change of said mean instantaneous frequency.

Claim 15

Apparatus for measuring flow of fluid in a conduit, the atomic nuclei of at least one component of said fluid displaying a nuclear magnetic moment and angular momentum, comprising: means establishing a first static, substantially homogenous axial magnetic field about said conduit whereby a gradient along the direction of flow of said fluid is obtainable sufficient to induce nuclear paramagnetization in said fluid; means for applying to a region within said conduit a radio frequency pulse chosen to alter the nuclear magnetization within a bolus of said fluid to thereby tag said bolus with respect to fluid preceding and following said bolus; means for measuring the frequency of nuclear magnetic resonance of the atomic nuclei of said element in said bolus over predetermined periods of time to obtain for each period of time the means instantaneous frequency of said nuclear magnetic resonance; and means for deriving the velocity of said fluid from the rate of change of said mean instantaneous frequency.

Claim 16

Apparatus for measuring flow of fluid in a conduit, the atomic nuclei of at least one component of said fluid displaying a nuclear magnetic moment and angular momentum, comprising: means for establishing first, second and third orthogonally related, static axial magnetic fields, each being substantially homogenous; means for placing said conduit within said fields whereby a gradient along the direction of flow of said fluid is obtainable sufficient to induce nuclear paramagnetization in said fluid; means for applying to said fields radio frequency pulses chosen to alter the nuclear magnetization of a selected volume within a bolus of said fluid to thereby generate a free induction decay signal and tag said bolus with respect to fluid preceding and following said bolus; means for measuring the frequency of nuclear magnetic resonance of the atomic nuclei of said element in said bolus over predetermined periods of time to obtain for each period of time the mean instantaneous frequency of said nuclear magnetic resonance; and means for deriving the velocity of said fluid from the rate of change of said mean instantaneous frequency.

Claim 17

Apparatus for measuring flow of fluid in a conduit, the atomic nuclei of at least one component of said fluid displaying a nuclear magnetic moment and angular momentum, comprising: means for establishing first, second and third orthogonally related, static axial magnetic fields, each being substantially homogenous; means for placing said conduit within said fields whereby a gradient along the direction of flow of said fluid is obtainable sufficient to induce nuclear paramagnetization in said fluid; means for applying to said fields radio frequency pulses chosen to alter the nuclear magnetization of a selected volume within a bolus of said fluid to thereby generate a free induction decay signal and tag said bolus with respect to fluid preceding and following said bolus; means for measuring the frequency of nuclear magnetic resonance of the atomic nuclei of said element in said bolus over predetermined periods of time to obtain for each period of time the mean instantaneous frequency of said nuclear magnetic resonance; and means for deriving the velocity of said fluid from the rate of change of said mean instantaneous frequency.

Claim 18

Apparatus for measuring flow of fluid in a conduit, the atomic nuclei of at least one component of said fluid displaying a nuclear magnetic moment and angular momentum, comprising: means for establishing a first static, substantially homogenous axial magnetic field; means for placing said conduit within said field whereby a gradient along the direction of flow of said fluid is obtainable sufficient to induce nuclear paramagnetization in said fluid; means for applying to a region within said conduit a radio frequency pulse chosen to alter the nuclear magnetization within a bolus of said fluid to thereby generate a free induction decay signal and tag said bolus with respect to fluid preceding and following said bolus; and feedback control means for: (a) applying a 180° radio frequency pulse to said conduit region to generate a spin echo signal; (b) measuring the maximum amplitude of said spin echo signal; (c) when said maximum amplitude is equal to or above a predetermined threshold level, measuring the frequency of said spin echo signal over a predetermined period of time to obtain for that period the mean instantaneous frequency of said nuclear magnetic resonance, if a previous spin echo measurement was made then deriving the velocity of said fluid from the rate of change of said mean instantaneous spin echo frequency from said previous spin echo measurement, and returning to step (a); (d) when said maximum amplitude is less than said predetermined thershold level, determining from previous measurements the average fluid velocity of said fluid from the beginning of free induction decay of said nuclear magnetic resonance to the present, determining the maximum time period as between (i) the time required for full free induction decay of said nuclear magnetic resonance and (ii) the time for said fluid to flow at said average fluid velocity a distance equal to the thickness of said bolus in the direction of said first magnetic field, and when time lapse from beginning of free induction decay of the nuclear magnetic resonance is greater than said maximum time period, reapplying to said conduit a radio frequency pulse chosen to generate a free induction decay signal.

Claim 19

Apparatus for measuring flow of fluid in a conduit, the atomic nuclei of at least one component of said fluid displaying a nuclear magnetic moment and angular momentum, comprising: means for establishing a first static, substantially homogenous axial magnetic field; means for placing said conduit within said field whereby a gradient along the direction of flow of said fluid is obtainable sufficient to induce nuclear paramagnetization in said fluid; means for applying to a region within said conduit a radio frequency pulse chosen to alter the nuclear magnetization within a bolus of said fluid to thereby generate a free induction decay signal and tag said bolus with respect to fluid preceding and following said bolus; and feedback control means for: (a) applying a 180° radio frequency pulse to said conduit region to generate a spin echo signal; (b) measuring the maximum amplitude of said spin echo signal; (c) when said maximum amplitude is equal to or above a predetermined threshold level, measuring the frequency of said spin echo signal over a predetermined period of time to obtain for that period the mean instantaneous frequency of said nuclear magnetic resonance, if a previous spin echo measurement was made then deriving the velocity of said fluid from the rate of change of said mean instantaneous spin echo frequency from said previous spin echo measurement, and returning to step (a); (d) when said maximum amplitude is less than said predetermined thershold level, determining from previous measurements the average fluid velocity of said fluid from the beginning of free induction decay of said nuclear magnetic resonance to the present, determining the maximum time period as between (i) the time required for full free induction decay of said nuclear magnetic resonance and (ii) the time for said fluid to flow at said average fluid velocity a distance equal to the thickness of said bolus in the direction of said first magnetic field, and when time lapse from beginning of free induction decay of the nuclear magnetic resonance is greater than said maximum time period, reapplying to said conduit a radio frequency pulse chosen to generate a free induction decay signal.

Claim 20

Apparatus for measuring flow of fluid in a conduit, the atomic nuclei of at least one component of said fluid displaying a nuclear magnetic moment and angular momentum, comprising: means for establishing first, second and third orthogonally related, static axial magnetic field, each being substantially homogenous; means for placing said conduit within said fields whereby a gradient along the direction of flow of said fluid is obtainable sufficient to induce nuclear paramagnetization in said fluid; means for applying to said fields radio frequency pulses chosen to alter the nuclear magnetization of a selected volume within a bolus of said fluid to thereby generate a free induction decay signal and tag said bolus with respect to fluid preceding and following said bolus; feedback control means for: (a) applying a 180° radio frequency pulse to said conduit region to generate a spin echo signal; (b) measuring the maximum amplitude of said spin echo signal; (c) when said maximum amplitude is equal to or above a predetermined threshold level, measuring the frequency of said spin echo signal over a predetermined period of time to obtain for that period the mean instantaneous frequency of said nuclear magnetic resonance, if a previous spin echo measurement was made then deriving the velocity of said fluid from the rate of change of said mean instantaneous spin echo frequency from said previous spin echo measurement, and returning to step (a); (d) when said maximum amplitude is less than said predetermined threshold level, determining from previous measurements the average fluid velocity of said fluid from the beginning of free induction decay of said nuclear magnetic resonance to the present, determining the maximum time period as between (i) the time required for full free induction decay of said nuclear magnetic resonance and (ii) the time for said fluid to flow at said average fluid velocity a distance equal to the thickness of said bolus in the direction of said first magnetic field, and when time lapse from beginning of free induction decay of the nuclear magnetic resonance is greater than said maximum time period, reapplying to said conduit a radio frequency pulse chosen to generate a free induction decay signal.

Claim 21

Apparatus for measuring flow of fluid in a conduit, the atomic nuclei of at least one component of said fluid displaying a nuclear magnetic moment and angular momentum, comprising: means for establishing first, second and third orthogonally related, static axial magnetic field, each being substantially homogenous; means for placing said conduit within said fields whereby a gradient along the direction of flow of said fluid is obtainable sufficient to induce nuclear paramagnetization in said fluid; means for applying to said fields radio frequency pulses chosen to alter the nuclear magnetization of a selected volume within a bolus of said fluid to thereby generate a free induction decay signal and tag said bolus with respect to fluid preceding and following said bolus; feedback control means for: (a) applying a 180° radio frequency pulse to said conduit region to generate a spin echo signal; (b) measuring the maximum amplitude of said spin echo signal; (c) when said maximum amplitude is equal to or above a predetermined threshold level, measuring the frequency of said spin echo signal over a predetermined period of time to obtain for that period the mean instantaneous frequency of said nuclear magnetic resonance, if a previous spin echo measurement was made then deriving the velocity of said fluid from the rate of change of said mean instantaneous spin echo frequency from said previous spin echo measurement, and returning to step (a); (d) when said maximum amplitude is less than said predetermined threshold level, determining from previous measurements the average fluid velocity of said fluid from the beginning of free induction decay of said nuclear magnetic resonance to the present, determining the maximum time period as between (i) the time required for full free induction decay of said nuclear magnetic resonance and (ii) the time for said fluid to flow at said average fluid velocity a distance equal to the thickness of said bolus in the direction of said first magnetic field, and when time lapse from beginning of free induction decay of the nuclear magnetic resonance is greater than said maximum time period, reapplying to said conduit a radio frequency pulse chosen to generate a free induction decay signal.

Claim 22

Apparatus for measuring flow of fluid in a conduit, the atomic nuclei of at least one component of said fluid displaying a nuclear magnetic moment and angular momentum, comprising: means for establishing a first static, substantially homogenous axial magnetic field; means for placing said conduit within said field whereby a gradient along the direction of flow of said fluid is obtainable sufficient to induce nuclear paramagentization in said fluid; means for applying to a region within said conduit a radio frequency pulse chosen to alter the nuclear magnetization within a bolus of said fluid to thereby generate a free induction decay signal and tag said bolus with respect to fluid preceding and following said bolus; and feedback control means for: (a) measuring free induction decay signals over predetermined periods of time to obtain for each period of time the mean instantaneous frequency of the nuclear magnetic resonance of said fluid; (b) deriving the velocity of said fluid from the rate of change of said mean instantaneous frequency; (c) when magnetization of said volume reaches a static value, reinstating the application of radio frequency pulse selected to generate a free induction decay signal; and (d) until magnetization of said volume has reached a static value, conducting a series of steps, comprising: (1) applying a 180° radio frequency pulse to generate a spin echo signal; (2) measuring the maximum amplitude of said spin echo signal and its mean instantaneous frequency over a predetermined period of time; (3) when said maximum amplitude is equal to or above a predetermined threshold level, obtaining from the rate of change of the mean instantaneous frequency of said nuclear magnetic resonance the velocity of said fluid, and returning to step (d) (1); (4) when said maximum amplitude is less than said predetermined thershold level, determining from previous measurements the average velocity of said fluid from the beginning of free induction decay of said nuclear magnetic resonance to the present, determining the maximum time period as between (i) the time required for full free induction decay of said nuclear magnetic resonance and (ii) the time for said fluid to flow at said average fluid velocity a distance equal to the thickness of said volume in the direction of said first magnetic field, and if time lapse from beginning of free induction decay of said nuclear magnetic resonance is less than said maximum time period then waiting, else returning to step (a).

Claim 23

Apparatus for measuring flow of fluid in a conduit, the atomic nuclei of at least one component of said fluid displaying a nuclear magnetic moment and angular momentum, comprising: means for establishing a first static, substantially homogenous axial magnetic field; means for placing said conduit within said field whereby a gradient along the direction of flow of said fluid is obtainable sufficient to induce nuclear paramagentization in said fluid; means for applying to a region within said conduit a radio frequency pulse chosen to alter the nuclear magnetization within a bolus of said fluid to thereby generate a free induction decay signal and tag said bolus with respect to fluid preceding and following said bolus; and feedback control means for: (a) measuring free induction decay signals over predetermined periods of time to obtain for each period of time the mean instantaneous frequency of the nuclear magnetic resonance of said fluid; (b) deriving the velocity of said fluid from the rate of change of said mean instantaneous frequency; (c) when magnetization of said volume reaches a static value, reinstating the application of radio frequency pulse selected to generate a free induction decay signal; and (d) until magnetization of said volume has reached a static value, conducting a series of steps, comprising: (1) applying a 180° radio frequency pulse to generate a spin echo signal; (2) measuring the maximum amplitude of said spin echo signal and its mean instantaneous frequency over a predetermined period of time; (3) when said maximum amplitude is equal to or above a predetermined threshold level, obtaining from the rate of change of the mean instantaneous frequency of said nuclear magnetic resonance the velocity of said fluid, and returning to step (d) (1); (4) when said maximum amplitude is less than said predetermined thershold level, determining from previous measurements the average velocity of said fluid from the beginning of free induction decay of said nuclear magnetic resonance to the present, determining the maximum time period as between (i) the time required for full free induction decay of said nuclear magnetic resonance and (ii) the time for said fluid to flow at said average fluid velocity a distance equal to the thickness of said volume in the direction of said first magnetic field, and if time lapse from beginning of free induction decay of said nuclear magnetic resonance is less than said maximum time period then waiting, else returning to step (a).

Claim 24

Apparatus for measuring flow of fluid in a conduit, the atomic nuclei of at least one component of said fluid displaying a nuclear magnetic moment and angular momentum:, comprising: means for establishing first, second and third or orthogonally related, static axial magnetic fields, each being substantially homogenous; means for placing said conduit within said field whereby a gradient along the direction of flow of said fluid is obtainable sufficient to induce nuclear paramagnetization in said fluid; means for applying to said fields radio frequency pulses chosen to alter the nuclear magnetization of a selected volume within a bolus of said fluid to thereby generate a free induction decay signal and tag said bolus with respect to fluid preceding and following said bolus; feedback control means for: (a) measuring free induction decay signals over predetermined periods of time to obtain for each period of time the mean instantaneous frequency of the nuclear magnetic resonance of said fluid; (b) deriving the velocity of said fluid from the rate of change of said mean instantaneous frequency; (c) when magnetization of said volume reaches a static value reinstating the application of radio frequency pulse selected to generate a free induction decay signal; and (d) until magnetization of said volume has reached a static value, conducting a series of steps, comprising: (1) applying a 180° radio frequency pulse to generate a spin echo signal; (2) measuring the maximum amplitude of said spin echo signal and its mean instantaneous frequency over a predetermined period of time; (3) when said maximum amplitude is equal to or above a predetermined threshold level, obtaining from the rate of change of the mean instantaneous frequency of said nuclear magnetic resonance the velocity of said fluid, and returning to step (d) (1); (4) when said maximum amplitude is less than said predetermined threshold level, determining from previous measurements the average velocity of said fluid from the beginning of free induction decay of said nuclear magnetic resonance to the present, determining the maximum time period as between (i) the time required for full free induction decay of said nuclear magnetic resonance and (ii) the time for said fluid to flow at said average fluid velocity a distance equal to the thickness of said volume in the direction of said first magnetic field, and if time lapse from beginning of free induction decay of said nuclear magnetic resonance is less than said maximum time period then waiting, else returning to step (a).

Claim 25

Apparatus for measuring flow of fluid in a conduit, the atomic nuclei of at least one component of said fluid displaying a nuclear magnetic moment and angular momentum:, comprising: means for establishing first, second and third or orthogonally related, static axial magnetic fields, each being substantially homogenous; means for placing said conduit within said field whereby a gradient along the direction of flow of said fluid is obtainable sufficient to induce nuclear paramagnetization in said fluid; means for applying to said fields radio frequency pulses chosen to alter the nuclear magnetization of a selected volume within a bolus of said fluid to thereby generate a free induction decay signal and tag said bolus with respect to fluid preceding and following said bolus; feedback control means for: (a) measuring free induction decay signals over predetermined periods of time to obtain for each period of time the mean instantaneous frequency of the nuclear magnetic resonance of said fluid; (b) deriving the velocity of said fluid from the rate of change of said mean instantaneous frequency; (c) when magnetization of said volume reaches a static value reinstating the application of radio frequency pulse selected to generate a free induction decay signal; and (d) until magnetization of said volume has reached a static value, conducting a series of steps, comprising: (1) applying a 180° radio frequency pulse to generate a spin echo signal; (2) measuring the maximum amplitude of said spin echo signal and its mean instantaneous frequency over a predetermined period of time; (3) when said maximum amplitude is equal to or above a predetermined threshold level, obtaining from the rate of change of the mean instantaneous frequency of said nuclear magnetic resonance the velocity of said fluid, and returning to step (d) (1); (4) when said maximum amplitude is less than said predetermined threshold level, determining from previous measurements the average velocity of said fluid from the beginning of free induction decay of said nuclear magnetic resonance to the present, determining the maximum time period as between (i) the time required for full free induction decay of said nuclear magnetic resonance and (ii) the time for said fluid to flow at said average fluid velocity a distance equal to the thickness of said volume in the direction of said first magnetic field, and if time lapse from beginning of free induction decay of said nuclear magnetic resonance is less than said maximum time period then waiting, else returning to step (a).