Use of repeated gradient echoes for noise reduction and improved NMR imaging

Claim 1

A method for producing a spin echo and a gradient echo signal to produce an image, the steps comprising: (a) applying a polarity magnetic field to the object to be imaged; (b) exciting the nuclei in the object with an RF excitation pulse; (c) applying a spin echo producing RF pulse to produce a spin echo signal at a first time T; (d) acquiring the spin echo signal at the first time T during the application of a first read out gradient; and (e) acquiring a gradient echo signal at at least one time T+τ and T-τ during the application of a second read out gradient.

Claim 2

A method for producing a spin echo and a gradient echo signal to produce an image, the steps comprising: (a) applying a polarity magnetic field to the object to be imaged; (b) exciting the nuclei in the object with an RF excitation pulse; (c) applying a spin echo producing RF pulse to produce a spin echo signal at a first time T; (d) acquiring the spin echo signal at the first time T during the application of a first read out gradient; and (e) acquiring a gradient echo signal at at least one time T+τ and T-τ during the application of a second read out gradient.

Claim 7

A method of improving the quality of an NMR image comprising the steps of: (a) acquiring a spin echo signal array and a gradient echo signal array; (b) reconstructing the spin echo signal array and the gradient echo signal array to produce spin echo image and a gradient echo image respectively; and (c) combining the gradient echo image and the spin echo image to produce a composite image.

Claim 8

A method of improving the quality of an NMR image comprising the steps of: (a) acquiring a spin echo signal array and a gradient echo signal array; (b) reconstructing the spin echo signal array and the gradient echo signal array to produce spin echo image and a gradient echo image respectively; and (c) combining the gradient echo image and the spin echo image to produce a composite image.

Claim 10

A method of improving the quality of an NMR image comprising the steps of: (a) acquiring a spin echo signal array and a first and second gradient echo signal array; (b) reconstructing the spin echo signal array and the first and second gradient echo signal arrays to produce a spin echo image E 3 and a first and second gradient echo image E 2 and E 4 respectively; (c) low-pass filtering the spin echo image E 3 and gradient echo images E 2 and E 4 to produce a filtered spin echo image E 3 ' and filtered gradient echo images E 2 ' and E 4 '; (d) dividing the intensity value of each pixel of the filtered spin echo image E 3 ' by the intensity value of the corresponding pixel of filtered gradient echo images E 2 ' to produce a first weighting factor image w2; (e) dividing the intensity value of each pixel of the filtered spin echo image E 3 ' by the intensity value of the corresponding pixel of filtered gradient echo images E 4 ' to produce a second weighting factor image w4; (f) multiplying each pixel of the gradient echo image E 2 by the weighting factor image w2 for that pixel to produce a modified gradient echo image E 2 *; (g) multiplying each pixel of the gradient echo image E 4 by the weighting factor image w4 for that pixel to produce a modified gradient echo image E 4 *; and (h) summing the corresponding pixels of the spin echo image E 3 and the modified gradient echo image E 2 * and the modified gradient echo image E 4 *.

Claim 11

A method of improving the quality of an NMR image comprising the steps of: (a) acquiring a spin echo signal array and a first and second gradient echo signal array; (b) reconstructing the spin echo signal array and the first and second gradient echo signal arrays to produce a spin echo image E 3 and a first and second gradient echo image E 2 and E 4 respectively; (c) low-pass filtering the spin echo image E 3 and gradient echo images E 2 and E 4 to produce a filtered spin echo image E 3 ' and filtered gradient echo images E 2 ' and E 4 '; (d) dividing the intensity value of each pixel of the filtered spin echo image E 3 ' by the intensity value of the corresponding pixel of filtered gradient echo images E 2 ' to produce a first weighting factor image w2; (e) dividing the intensity value of each pixel of the filtered spin echo image E 3 ' by the intensity value of the corresponding pixel of filtered gradient echo images E 4 ' to produce a second weighting factor image w4; (f) multiplying each pixel of the gradient echo image E 2 by the weighting factor image w2 for that pixel to produce a modified gradient echo image E 2 *; (g) multiplying each pixel of the gradient echo image E 4 by the weighting factor image w4 for that pixel to produce a modified gradient echo image E 4 *; and (h) summing the corresponding pixels of the spin echo image E 3 and the modified gradient echo image E 2 * and the modified gradient echo image E 4 *.

Claim 16

A method of producing an NMR image based on T 2 ' comprising the steps of: (a) applying a polarizing magnetic field to the object to be imaged; (b) exciting the nuclei in the object with an RF excitation pulse; (c) applying a spin echo producing RF pulse to produce a spin echo signal at a first time T; (d) acquiring the spin echo signal at the first time T during the application of a first read out gradient along an axis; (e) acquiring a first and second gradient echo signal at a time τ prior to T and a time τ subsequent to T during the application of a second and third read out gradient along an axis; (f) repeating steps (a)-(e) to compile a spin echo data set from the spin echo signals and a first and second gradient echo data set from the first and second gradient echo signals; (g) reconstructing the spin echo data set and first and second gradient echo data sets to produce spin echo images E 3 and gradient echo images E 2 and E 4 respectively; and (h) combining the corresponding pixels of the images to produce a composite image dependent on T 2 '.

Claim 17

A method of producing an NMR image based on T 2 ' comprising the steps of: (a) applying a polarizing magnetic field to the object to be imaged; (b) exciting the nuclei in the object with an RF excitation pulse; (c) applying a spin echo producing RF pulse to produce a spin echo signal at a first time T; (d) acquiring the spin echo signal at the first time T during the application of a first read out gradient along an axis; (e) acquiring a first and second gradient echo signal at a time τ prior to T and a time τ subsequent to T during the application of a second and third read out gradient along an axis; (f) repeating steps (a)-(e) to compile a spin echo data set from the spin echo signals and a first and second gradient echo data set from the first and second gradient echo signals; (g) reconstructing the spin echo data set and first and second gradient echo data sets to produce spin echo images E 3 and gradient echo images E 2 and E 4 respectively; and (h) combining the corresponding pixels of the images to produce a composite image dependent on T 2 '.

Claim 19

A method producing an NMR image based on T 2 comprising the steps of: (a) applying a polarizing magnetic field to the object to be imaged; (b) exciting the nuclei in the object with an RF excitation pulse; (c) applying a spin echo producing RF pulse to produce a spin echo signal at a time T; (d) acquiring a first and second gradient echo signal at a time t prior to T and a time t subsequent to T during the application of a first and second read out gradient along an axis; (e) repeating steps (a)-(d) to compile a first and second gradient echo data sets from the first and second gradient echo signals; (f) reconstructing the first and second gradient echo data sets to produce gradient echo images E 2 and E 4 respectively; and (g) calculating a composite image dependent on T 2 .

Claim 20

A method producing an NMR image based on T 2 comprising the steps of: (a) applying a polarizing magnetic field to the object to be imaged; (b) exciting the nuclei in the object with an RF excitation pulse; (c) applying a spin echo producing RF pulse to produce a spin echo signal at a time T; (d) acquiring a first and second gradient echo signal at a time t prior to T and a time t subsequent to T during the application of a first and second read out gradient along an axis; (e) repeating steps (a)-(d) to compile a first and second gradient echo data sets from the first and second gradient echo signals; (f) reconstructing the first and second gradient echo data sets to produce gradient echo images E 2 and E 4 respectively; and (g) calculating a composite image dependent on T 2 .

Claim 22

A method of estimating the effect of imperfections in a spin echo producing RF pulse comprising the steps of: (a) applying a polarizing magnetic field to the object to be imaged; (b) exciting the nuclei in the object with an RF excitation pulse; (c) applying a first spin echo producing RF pulse to produce a first spin echo signal at a first time TE 1 ; (d) acquiring the first spin echo signal at the first time TE 1 during the application of a first read out gradient; (e) applying a second spin echo producing RF pulse to produce a second spin echo signal at a second time TE 2 ; (f) acquiring the second spin echo signal at the second time TE 2 during the application of a second read out gradient; (g) acquiring a first and second gradient echo signal at a time τ prior to TE 2 and a time τ subsequent to TE 2 during the application of a third and fourth read out gradient; (h) repeating steps (a)-(g) to compile a first and second spin echo data set from the first and second spin echo signals and a first and second gradient echo data set from the first and second spin echo signals; (i) reconstructing the first and second spin echo data sets to produce spin echo images E 1 and E 3 , respectively, and reconstructing the first and second gradient echo data sets to produce gradient echo images E 2 and E 4 respectively; and (j) calculating an error factor image F from the first and second gradient echo images E 2 and E 4 and the first and second spin echo images E 1 and E 3 .

Claim 23

A method of estimating the effect of imperfections in a spin echo producing RF pulse comprising the steps of: (a) applying a polarizing magnetic field to the object to be imaged; (b) exciting the nuclei in the object with an RF excitation pulse; (c) applying a first spin echo producing RF pulse to produce a first spin echo signal at a first time TE 1 ; (d) acquiring the first spin echo signal at the first time TE 1 during the application of a first read out gradient; (e) applying a second spin echo producing RF pulse to produce a second spin echo signal at a second time TE 2 ; (f) acquiring the second spin echo signal at the second time TE 2 during the application of a second read out gradient; (g) acquiring a first and second gradient echo signal at a time τ prior to TE 2 and a time τ subsequent to TE 2 during the application of a third and fourth read out gradient; (h) repeating steps (a)-(g) to compile a first and second spin echo data set from the first and second spin echo signals and a first and second gradient echo data set from the first and second spin echo signals; (i) reconstructing the first and second spin echo data sets to produce spin echo images E 1 and E 3 , respectively, and reconstructing the first and second gradient echo data sets to produce gradient echo images E 2 and E 4 respectively; and (j) calculating an error factor image F from the first and second gradient echo images E 2 and E 4 and the first and second spin echo images E 1 and E 3 .