Magnetic resonance imaging with combined single point and back projection data taking method
First Claim
1. A magnetic resonance method for imaging an object comprising the steps of:
- a) locating the object in a homogeneous base magnetic field;
b) acquiring, using a back projection method n>
>
1 different projections with different directions φ
(i) by carrying out the following steps ba) to bd) n times with i=1 to n;
ba) applying a gradient magnetic field Gφ
(i) having a predetermined direction φ
(i), different for every i, and a strength G(i) for acquiring a projection p(i);
bb) irradiating a high frequency excitation pulse into the object;
bc) waiting a time tw '"'"';
bd) measuring, at a predetermined sampling rate, (j-m) >
>
1 measuring points Sm+1 (i) to Sj (i), which are sequential in time, of a nuclear resonance signal from the object, the signal dephasing under the influence of the gradient magnetic field Gφ
(i), the measuring points Sm+1 (i) to Sj (i) corresponding to j-m points in k-space lying along a vector extending from a k-space origin in the direction φ
(i) of the gradient magnetic field Gφ
(i), whereby the separation of each of the j-m points Sm+1 (i) to Sj (i) in k-space from the k-space origin is given by a product of the strength G(i) of the gradient magnetic field Gφ
(i) and a time interval between the high frequency excitation pulse and the sampling time of the corresponding measuring pointsm+1 (i) to Sj (i);
c) acquiring, using a single point imaging method (S by PI), n'"'"'≦
n*m additional measuring points S(i'"'"') by carrying out the following steps ca) to cd) n'"'"' times with i'"'"'=1 to n'"'"';
ca) applying a gradient magnetic field Gφ
(i'"'"') having a predetermined direction φ
(i'"'"') and a strength G(i'"'"') for acquiring only one measuring point S(i'"'"');
cb) irrdiating the high frequency excitation pulse into the object;
cc) waiting time tw '"'"';
cd) measuring only one measuring point S(i'"'"') of a nuclear resonance signal from the object, the signal dephasing under the influence of the gradient magnetic field Gφ
(i'"'"'), the measuring point S(i'"'"') corresponding to a point in k-space lying along a vector extending from a k-space origin in the direction φ
(i'"'"') of the gradient magnetic field Gφ
(i'"'"'), whereby the separation of the point S(i'"'"') in k-space from the k-space origin is given by a product of the strength G(i'"'"') of the gradient magnetic field Gφ
(i'"'"') and the time tw '"'"';
d) reconstructing an image of the object from a total number of n*(j-m) measuring points Sm+1 (i) to Sj (i) plus n'"'"' measuring points S(i'"'"') in k-space.
1 Assignment
0 Petitions
Accused Products
Abstract
A magnetic resonance method is utilized for taking an image of an object. An initial projection is taken by applying a gradient magnetic field having a predetermined direction φ and strength G, irradiating a high frequency excitation pulse and sequentially measuring a nuclear resonance signal from the object. The signal dephases under the influence of the gradient magnetic field and the signal measuring points are assigned to points in k-space lying along a vector whose direction is determined by the direction φ of the gradient magnetic field, and whose magnitude by the product of the strength of the gradient magnetic field and the time interval between the excitation pulse and the taking of the corresponding measuring point. A further number of n-1 (n>>1) projections are obtained by changing the direction and/or strength of the gradient magnetic field. Additional excitations and measurements are carried out for an additional n'"'"'≦n projections having measuring points. The gradient strengths and the waiting time tw '"'"' of the additional excitations are adjusted and the image is reconstructed from the total number measuring points.
20 Citations
19 Claims
-
1. A magnetic resonance method for imaging an object comprising the steps of:
-
a) locating the object in a homogeneous base magnetic field; b) acquiring, using a back projection method n>
>
1 different projections with different directions φ
(i) by carrying out the following steps ba) to bd) n times with i=1 to n;ba) applying a gradient magnetic field Gφ
(i) having a predetermined direction φ
(i), different for every i, and a strength G(i) for acquiring a projection p(i);bb) irradiating a high frequency excitation pulse into the object; bc) waiting a time tw '"'"'; bd) measuring, at a predetermined sampling rate, (j-m) >
>
1 measuring points Sm+1 (i) to Sj (i), which are sequential in time, of a nuclear resonance signal from the object, the signal dephasing under the influence of the gradient magnetic field Gφ
(i), the measuring points Sm+1 (i) to Sj (i) corresponding to j-m points in k-space lying along a vector extending from a k-space origin in the direction φ
(i) of the gradient magnetic field Gφ
(i), whereby the separation of each of the j-m points Sm+1 (i) to Sj (i) in k-space from the k-space origin is given by a product of the strength G(i) of the gradient magnetic field Gφ
(i) and a time interval between the high frequency excitation pulse and the sampling time of the corresponding measuring pointsm+1 (i) to Sj (i);c) acquiring, using a single point imaging method (S by PI), n'"'"'≦
n*m additional measuring points S(i'"'"') by carrying out the following steps ca) to cd) n'"'"' times with i'"'"'=1 to n'"'"';ca) applying a gradient magnetic field Gφ
(i'"'"') having a predetermined direction φ
(i'"'"') and a strength G(i'"'"') for acquiring only one measuring point S(i'"'"');cb) irrdiating the high frequency excitation pulse into the object; cc) waiting time tw '"'"'; cd) measuring only one measuring point S(i'"'"') of a nuclear resonance signal from the object, the signal dephasing under the influence of the gradient magnetic field Gφ
(i'"'"'), the measuring point S(i'"'"') corresponding to a point in k-space lying along a vector extending from a k-space origin in the direction φ
(i'"'"') of the gradient magnetic field Gφ
(i'"'"'), whereby the separation of the point S(i'"'"') in k-space from the k-space origin is given by a product of the strength G(i'"'"') of the gradient magnetic field Gφ
(i'"'"') and the time tw '"'"';d) reconstructing an image of the object from a total number of n*(j-m) measuring points Sm+1 (i) to Sj (i) plus n'"'"' measuring points S(i'"'"') in k-space. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16)
-
-
17. A magnetic resonance method for imaging an object comprising the steps of:
-
a) locating the object in a homogeneous base magnetic field; b) acquiring, using a back projection method n >
>
1 different projections by carrying out the following steps ba) to bd) n times with i=1 to n;ba) applying a gradient magnetic field Gφ
(i);bb) irradiating a high frequency excitation pulse into the object; bc) waiting a time tw'"'"' ; bd) measuring (j-m)>
>
1 measuring points Sm+1 (i) to Sj (i), which are sequential in time, of a nuclear resonance signal from the object;c) acquiring, using a single point imaging method (SPI), n'"'"' additional measuring points S(i'"'"') by carrying out the following steps ca) to cd) n'"'"' times with i'"'"'=1 to n'"'"'; ca) applying a gradient magnetic field Gφ
(i'"'"');cb) irradiating the high excitation frequency pulse into the object; cc) waiting the time tw '"'"' cd) measuring exactly one measuring point S(i'"'"') of a nuclear resonance signal from the object; d) reconstructing an image of the object from measuring points Sm+1 (i) to Sj (i) and measuring points S(i'"'"'). - View Dependent Claims (18, 19)
-
Specification