Image acquisition and reconstruction method for functional magnetic resonance imaging
Acquisition of MR data during a fMRI study employs a hybrid PR pulse sequence to acquire projection views from which multi-slice image frames may be reconstructed that depict the BOLD response to an applied stimulus or performed task. Composite images are reconstructed at each slice using the combined interleaved projection views from all the acquired image frames. The composite images are used to reconstruct the highly undersampled image frames.
1. A method for producing an image of a subject's brain positioned in a field of view (FOV) of a magnetic resonance imaging (MRI) system, the steps comprising:
a) acquiring with the MRI system a set of projection views at each of a plurality of intervals following an event that produces brain activity in the subject;
b) producing a composite image with projection views acquired during the plurality intervals wherein the projection views are interleaved with each other;
c) reconstructing an image frame at each interval by:
c)i) backprojecting a set of projection views acquired at the interval into the FOV and weighting the value backprojected into each image pixel by the value of the corresponding pixel in the composite image; and
c)ii) summing the backprojected values for each image pixel.
2. The method as recited in claim 1 in which each image pixel backprojected value S n is calculated in step c)i) as
S
n
=
(
P
×
C
n
)
/
∑
n
=
1
N
C
n
where:
P=the projection view value being backprojected;
C n =corresponding pixel value in the composite image;
S n =the value of the n th pixel along the backprojecting path; and
N=total number of pixels along the backprojection path.
3. The method as recited in claim 1 which includes:
d) acquiring a baseline image comprised of projection views acquired during a time period in which the event is not producing brain activity; and
e) subtracting the baseline image projection views from corresponding projection views acquired in step a) prior to performing steps b) and c).
4. The method as recited in claim 1 in which step c) includes Fourier transforming each projection view prior to backprojecting the view.
5. The method as recited in claim 1 in which step a) is performed under the direction of a hybrid 2D PR pulse sequence and each set of projection views is comprised of a plurality of subsets of projection views that depict a corresponding plurality of slices of the subject.
6. The method as recited in claim 5 in which step b) includes producing a composite image for each of said plurality of slices.
7. The method as recited in claim 6 in which step c) includes reconstructing an image of the subject at each slice using the composite image corresponding to the slice.
8. The method as recited in claim 1 in which steps a), b) and c) are repeated and the method further includes:
d) averaging the reconstructed image frames at each interval.
9. A method for producing an image of a subject positioned in a field of view (FOV of a magnetic resonance imaging (MRI) system, the steps comprising:
a) acquiring with the MRI system a set of views of the subject's brain at a plurality of intervals following an event that produces brain activity;
b) reconstructing a composite image with projection views acquired at a plurality of intervals in step a), wherein said projection views used to form the composite image are interleaved; and
c) reconstructing an image frame at each interval by:
c)i) producing an image data set from projection views acquired in step a) during the interval; and
c)ii) producing an image frame of the subject's brain using the image data set and weighting each image pixel location by the corresponding pixel value in the composite image.
10. The method as recited in claim 9 in which step a) includes acquiring a plurality of phase encoded projection views during each interval, step b) includes reconstructing a composite image for each phase encoding, and the composite images are used in step c) to reconstruct said image frames of the subject.
11. The method as recited in claim 9 in which step c)ii) includes backprojecting the projection views in the image data set into the FOV and weighting the value backprojected into each image pixel by the value of the corresponding pixel in the composite image.
12. The method as recited in claim 11 in which the projection views in the image data set are normalized by corresponding projection views of the composite image.