Improved blood vessel projection imaging system using nuclear magnetic resonance

Claim 2

In a method for producing a two-dimensional projection image of moving material in a volume the steps of: insensitizing the magnetic spins in a region of the volume using saturation excitation; exciting the spins in the region with a burst so that only moving material that has traveled into the region and not experienced complete saturation will produce an output signal; and processing the output signals to produce a two-dimensional projection image of the volume.

Claim 3

The method as described in Claim 1 where the steps of producing the two-dimensional projection image of the volume includes the steps of: applying a first gradient so that the saturation excitations and burst excitations excite a planar region in the volume; applying a second gradient, normal to the first gradient following the burst excitation so that each line integral in the planar region will produce a different frequency; decomposing the output signal into its constituent frequencies to provide the intensity at each point along the line represented by the planar region; and repeating the sequence using different frequencies for the saturation and burst excitations to provide the set of line integrals for each planar region in the volume.

Claim 4

In a method for providing a two-dimensional projection image of the moving material in a volume using nuclear magnetic resonance the steps of: applying a first magnetic gradient field; exciting the nuclear magnetic resonant spins in a planar region of the volume normal to the direction of the first gradient field; applying a second magnetic gradient field normal to the first magnetic gradient field following the excitation signal during the time that free induction decay signals are received; processing the free induction decay signals to provide a projection of the moving material in the planar region of the volume; and repeating the sequence using different excitation frequencies in the presence of the first gradient field to excite the spins in different planar regions of the volume to complete the two-dimensional projection image of the volume.

Claim 5

In a method for providing a two-dimensional projection image of the moving material in a volume using nuclear magnetic resonance the steps of: applying a first magnetic gradient field; exciting the nuclear magnetic resonant spins in a planar region of the volume normal to the direction of the first gradient field; applying a second magnetic gradient field normal to the first magnetic gradient field following the excitation signal during the time that free induction decay signals are received; processing the free induction decay signals to provide a projection of the moving material in the planar region of the volume; and repeating the sequence using different excitation frequencies in the presence of the first gradient field to excite the spins in different planar regions of the volume to complete the two-dimensional projection image of the volume.

Claim 6

The method as described in Claim 3 where the step of exciting the nuclear magnetic spins in each planar region takes place when the moving material is at a first velocity and including the steps of: repeating the process at each planar region where the moving material is at a second velocity; and subtracting the processed signals to cancel all static material.

Claim 7

The method as described in Claim 3 where the step of exciting the nuclear magnetic resonant spins in a planar region of the body represents an inversion excitation whereby all static material produces no free induction decay signals.

Claim 8

The method as described in Claim 3 including the step of applying an alternating gradient field in the same direction as the first gradient field-during the time of the free induction decay signal where the null plane of the alternating gradient field is adjacent to the excited planar region whereby only moving excited nuclei which have traveled into the null plane will produce output signals.

Claim 9

Apparatus for providing a two-dimensional projection image of the moving material in a volume using nuclear magnetic resonance comprising; means for applying a first magnetic gradient field parallel to the two-dimensional projection image; means for exciting the nuclear magnetic resonant spins in a planar region of the volume normal to the first gradient field and normal to the two-dimensional projection image; means for applying a second magnetic gradient field normal to the first magnetic gradient field following the excitation signal during the time that free induction decay signals are received; means for processing the free induction decay signals to provide a projection of the moving material in the planar region of the volume; and means for repeating the sequence using different excitation signals of different frequencies to excite the spins in different planar regions of the volume to complete the two-dimensional projection of the volume.

Claim 10

Apparatus for providing a two-dimensional projection image of the moving material in a volume using nuclear magnetic resonance comprising; means for applying a first magnetic gradient field parallel to the two-dimensional projection image; means for exciting the nuclear magnetic resonant spins in a planar region of the volume normal to the first gradient field and normal to the two-dimensional projection image; means for applying a second magnetic gradient field normal to the first magnetic gradient field following the excitation signal during the time that free induction decay signals are received; means for processing the free induction decay signals to provide a projection of the moving material in the planar region of the volume; and means for repeating the sequence using different excitation signals of different frequencies to excite the spins in different planar regions of the volume to complete the two-dimensional projection of the volume.

Claim 11

Apparatus as recited in Claim 7 where the means for processing the signal to provide a projection of the moving material includes; means for exciting the nuclear magnetic resonant spins in each planar region of the volume during a time when the moving material is at a first velocity; means for-exciting the nuclear magnetic resonant spins in each planar region of the volume during a time when the moving material is at a second velocity; and means for subtracting the processed signals resulting from the two excitations in each planar region.

Claim 12

Apparatus as recited in Claim 7 where the excitation means is an inversion excitation whereby all static material produces no free induction decay signals.

Claim 13

Apparatus as recited in Claim 7 where the excitation means is a sequence of two burst excitations of amplitude and duration such that all static material produces no free induction decay signals following the second burst.

Claim 14

Apparatus as recited in Claim 7 where the excitation means is a saturation excitation having a duration substantially comparable to Tl followed by an excitation burst of duration shorter that Tl whereby the static material is saturated and fails to produce signals in response to the burst.

Claim 15

Apparatus as recited in Claim 7 including means for applying an alternating gradient field in the same direction as the first gradient field during the time of the free induction decay signal where the null plane of the alternating gradient field is adjacent to the excited planar region whereby only moving excited nuclei which have traveled into the null plane will produce output signals.