Highly constrained magnetic resonance spectroscopy image reconstruction method
A series of image frames are acquired in which an MR parameter such as echo time (TE) is changed and the resulting image frames are employed to produce an MRS image of a metabolite. Scan time is reduced without sacrificing image quality by reconstructing a composite image from data acquired for a plurality of the image frames and using a highly constrained image reconstruction method with the composite image to produce each image frame.
1. A method for producing an image of a subject positioned in the 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 of the subject using a pulse sequence having a set of MR parameters;
b) changing an MR parameter in the pulse sequence and repeating step a) to acquire an additional set of projection views, wherein the acquired projection views are interleaved;
c) reconstructing a composite image that indicates a value at each composite image pixel using projection views from a plurality of said sets of projection views;
d) reconstructing image frames from corresponding sets of projection views, each image frame being reconstructed by:
d)i) backprojecting each projection view in the corresponding set of projection views and weighting the value backprojected into each image frame pixel by the value of the corresponding pixel in the composite image; and
d)ii) summing the backprojected values for each image frame pixel; and
e) processing the reconstructed image frames to produce an image.
2. The method as recited in claim 1 in which step b) is repeated a plurality of times.
3. The method as recited in claim 2 in which step e) includes Fourier transforming the signal values at corresponding pixel locations in the plurality of reconstructed image frames.
4. The method as recited in claim 1 in which the MR parameter is the echo time (TE) of the pulse sequence.
5. The method as recited in claim 4 in which step e) includes producing a T 2 image by fitting a T 2 relaxation decay curve to the signal values at corresponding pixel locations in the plurality of reconstructed image frames.
6. The method as recited in claim 1 in which the image produced in step e) depicts a metabolite in the subject.
7. The method as recited in claim 6 in which the pulse sequence includes a preparatory pulse sequence which suppresses the NMR signals from spins not associated with the metabolite.
8. The method as recited in claim 7 in which the suppressed NMR signals are from spins associated with water.
9. The method as recited in claim 1 in which the pulse sequence includes pulses that selectively suppress the NMR signals from selected spins.
10. The method as recited in claim 1 in which step b) is repeated a plurality of times and one of a first MR parameter and a second MR parameter is changed for each repetition.
11. The method as recited in claim 10 in which step e) includes:
e)i) producing a first image from image frames reconstructed from sets of projection views in which the first MR parameter is changed; and
e)ii) producing a second image from image frames reconstructed from sets of projection views in which the second MR parameter is changed.