Method of projection reconstruction imaging with reduced sensitivity to motion-related artifacts

Claim 2

In a method of imaging a slice of an object undergoing examination, which method utilizes a scan composed of a plurality of projections, each of said projections measured at a predetermined point in time and at a predetermined projection angle relative to a reference direction within said slice, wherein the minimum and maximum projection angle values differ by at least 180°, the improvement wherein projections measured in following ones of a plurality of successive time segments, each of said time segments being a time interval during which at least two projections are measured and being short compared to the total scan time, include the measurement of projections at the minimum and the maximum projection angle values for projections not yet measured.

Claim 3

The method of claim 1 wherein said method comprises measuring parallel-ray projections.

Claim 4

The method of claim 2 wherein the direction of each projection measurement within said imaging slice is determined by the direction of a magnetic-field gradient.

Claim 5

The method of claim 3 wherein said imaging slice is positioned in a static homogeneous magnetic field and includes the steps of: selectively exiting a plurality of nuclear spins situated in said imaging slice such that said nuclear spins produce an NMR signal; and observing said NMR signal in the presence of said magnetic-field gradient wherein isochromats perpendicular to the gradient direction represent projections of points along the isochromats onto said gradient.

Claim 6

The method of claim 1 wherein said method comprises measuring fan-beam projections.

Claim 7

The method of claim 5 wherein said fan beam comprises a beam of ultrasonic energy.

Claim 8

The method of claim 6 wherein said projection measurements comprise measuring the intensity o the ultrasonic energy not absorbed or scattered within said imaging slice along a plurality of ray paths within said fan beam.

Claim 9

The method of claim 6 wherein said projection measrements comprise measuring the propagation velocity of said ultrasonic beam along a plurality of ray paths within said fan beam.

Claim 10

The method of claim 6 wherein projection measurements are made to corespond to at least a 360° scan of the object.

Claim 11

The method of claim 6 wherein sid step of measuring a projection comprises the steps of: positioning said object in an annular array of ultrasonic transducers each capable of transmitting and receiving ultrasonic energy; irradiating said imaging slice with a substantially coplanar beam of ultrasonic energy produced by one of said transducers; and detecting the ultrasonic energy not attenuated or scattered within said slice at a plurality of transducers situated within an angle subtended by said fan beam.

Claim 12

In a method of imaging a slice of an object undergoing examination, which method utilizes a scan composed of a plurality of projections, each of said projections measured at a predetermined point in time and at a predetermined projection angle relative to a reference direction within said slice, wherein the minimum and maximum projection angle values differ by at least 180°, the improvement wherein a first one of said plurality of projections is measured at a first predetermined projection angle and wherein a second one of said plurality of projections is measured at a second predetermined projection angle and wherein predetermined ones of the remaining ones of said plurality of projections are measured in each of a plurality of successive time segments, each of said time segments being a time interval during which at least two projections are measured and being short compared to the total scan time, such that projections measured in a preceding one of said plurality of successive time segments include measurement of projections at the minimum and maximum projection angle values for the projection already measured.

Claim 13

In a method of imaging a slice of an object undergoing examination, which method utilizes a scan composed of a plurality of projections, each of said projections measured at a predetermined point in time and at a predetermined projection angle relative to a reference direction within said slice, wherein the minimum and maximum projection angle values differ by at least 180°, the improvement wherein a first one of said plurality of projections is measured at a first predetermined projection angle and wherein a second one of said plurality of projections is measured at a second predetermined projection angle and wherein predetermined ones of the remaining ones of said plurality of projections are measured in each of a plurality of successive time segments, each of said time segments being a time interval during which at least two projections are measured and being short compared to the total scan time, such that projections measured in a preceding one of said plurality of successive time segments include measurement of projections at the minimum and maximum projection angle values for the projection already measured.

Claim 14

The method of claim 11 wherein said first predetermined projection angle is approximately equal to the average of the values of said minimum and maximum projection angles.

Claim 15

The method of claim 11 wherein said second predetermined projection angle is angularly adjacent to said first projection angle.

Claim 16

The method of claim 11 wherein said method comprises measuring parallel-ray projections.

Claim 17

The method of claim 14 wherein the direction of each projection measurement within said imaging slice is determined by the direction of a magnetic-field gradient.

Claim 18

The method of claim 15 wherein said imaging slice is positioned in a static homogeneous magnetic field and includes the steps of: selectively exciting a plurality of nuclear spins situated in said imaging slice such that said nuclear spins produce an NMR signal; and observing said NMR signal in the presence of said magnetic-field gradient wherein isochromats perpendicular to the gradient direction represent projections of points along the isochromats onto said gradient.

Claim 19

The method of claim 11 wherein said method comprises measuring fan-beam projections.

Claim 20

The method of claim 17 wherein said fan beam comprises a beam of ultrasonic energy.

Claim 21

The method of claim 18 wherein said projection measurements comprise measuring the intensity of the ultrasonic energy not absorbed or scattered within said imaging slice along a plurality of ray paths within said fan beam.

Claim 22

The method of claim 18 wherein said projection measurements comprise measuring the propagation velocity of said ultrasonic beam along a plurality of ray within said fan beam.

Claim 23

The method of claim 18 wherein projection measurements are made to correspond to at least 360° scan of the object.

Claim 24

The method of claim 18 wherein said step of measuring a projection comprises the steps of: positioning said object in an annular array of ultrasonic transducers each capable of transmitting and receiving ultrasonic energy; irradiating said imaging slice with a substantially coplanar beam of ultrasonic energy produced by one of said transducers; and detecting the utlrasonic energy not attenuated or scattered within said slice at a plurality of transducers situated within an angle subtended by said fan beam.