SYSTEM AND METHOD FOR SUPERFAST CHEMICAL EXCHANGE SATURATION TRANSFER SPECTRAL IMAGING

• US 20160356870A1
• Filed: 06/03/2016
• Published: 12/08/2016
• Est. Priority Date: 06/03/2015
• Status: Active Grant

• Current Assignee: The General Hospital Corporation (Mass General Brigham, Inc.)
• Original Assignee: The General Hospital Corporation (Mass General Brigham, Inc.)
• Inventors: Sun, Phillip Z., Zhou, Iris Y.
• Granted Patent: US 10,048,340 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: G01R 33/4833 using spatially selective excitation of the volume of interest, e.g. selecting non-orthogonal or inclined slices
• CPC Class Codes: G01R 33/5605 by transferring coherence or polarization from a spin species to another, e.g. creating magnetization transfer contrast [MTC], polarization transfer using nuclear Overhauser enhancement [NOE]

Abstract

A system and method for creating magnetic resonance images are provided. The system applies an RF irradiation during a saturation time period at a reference frequency that saturates a range of selected labile spin species of the subject. The system encodes frequency offsets by applying a gradient G1 at least during the saturation time period. The system applies a plurality of slice selection gradients accompanied by a train of RF pulses during a voxel selection time period and a gradient G3 during an acquisition time period. One or more spin/gradient echo signals having information pertaining to at least one of metabolites and metabolite byproducts is acquired to form a CEST medical imaging data set and the CEST medical imaging data set is reconstructed to form a CEST image of the subject including information about the at least one of metabolites and metabolite byproducts within the subject.

Claims

1. A magnetic resonance imaging (MRI) system comprising:

a magnet system configured to generate a polarizing magnetic field about at least a region of interest (ROI) in a subject arranged in the MRI system;

a plurality of gradient coils configured to apply a gradient field to the polarizing magnetic field;

a radio frequency (RF) system configured to apply an excitation field to the subject and acquire MR image data from the ROI,

a computer system programmed to;

control the RF system to apply a saturation radiofrequency (RF) irradiation during a saturation time period at a reference frequency that saturates a selected labile spin species of the subject;

control the plurality of gradient coils to encode frequency offsets by applying a gradient G1, along slice selection or a preset direction, at least during the saturation time period;

control the plurality of gradient coils to apply a plurality of slice selection gradients accompanied by a train of RF pulses during a voxel selection time period, wherein a padding gradient G2 is applied to control the signal formation;

control the plurality of gradient coils to apply a third gradient G3 during an acquisition time period;

control the RF system and the plurality of gradient coils, during the acquisition time period, to acquire one or more spin echo signals having spatial and spectral information pertaining to at least one of metabolites and metabolite byproducts within the ROI to form a chemical exchange saturation transfer (CEST) medical imaging data set during an acquisition time period; and

reconstruct the CEST medical imaging data set to form a CEST image of the subject including information about the at least one of metabolites and metabolite byproducts within the subject.

2. The MRI system of claim 1 wherein the computer system is programmed to apply an RF pulse with a flip angle of 180°

and readout gradient before the acquisition time period.

3. The MRI system of claim 2 wherein the computer system is programmed to select one or more voxels by applying a plurality of slice selection gradients accompanied by a train of RF pulses during a voxel selection time period.

4. The MRI system of claim 3 wherein the computer system is further configured to calculate magnitude and polarity of the padding gradient G2 based on the signal formation during G3.

5. The MRI system of claim 4 wherein the computer system is further configured to acquire the one or more spin echo signals when applying the gradient G3 during the acquisition time period.

6. The MRI system of claim 1 wherein the computer system is further programmed to select the one or more voxels by applying a Point-RESolved Spectroscopy (PRESS) pulse sequence.

7. The MRI system of claim 6 wherein the computer system is further programmed to select the one or more voxels by applying a STimulated Echo Acquisition Mode (STEAM) pulse sequence.

8. The MRI system of claim 1 wherein the computer system is further programmed to reconstruct a plurality of images from the CEST medical imaging data set, wherein each of the plurality of images corresponds to one of the one or more spin echo signals.

9. The MRI system of claim 1, wherein the computer system is programmed to acquire the one or more spin echo signals with a repetition time chosen based on properties of an underlying CEST system of interest;

and

wherein the computer system is programmed to choose the saturation time period based on properties of an underlying CEST system of interest.

10. The MRI system of claim 1 wherein the computer system is further programmed to perform spatial encoding with at least one of phase and frequency encoding.

11. The MRI system of claim 1 wherein the ROI comprises one of the following:

brain, breast, prostate, muscle, liver, kidney, placenta, and heart.

12. A method for producing an image of a subject with a magnetic resonance imaging (MRI) system, the method comprising:

applying, with the MRI system, a saturation radiofrequency (RF) irradiation during a saturation time period at a reference frequency that saturates a selected labile spin species of a subject;

encoding, with the MRI system, frequency offsets by applying a gradient G1, along the slice selection direction or a preset direction, at least during the saturation time period;

applying a plurality of slice selection gradients accompanied by a train of RF pulses during a voxel selection time period, wherein a padding gradient G2 is applied for formation of a spin echo;

applying a third gradient G3 during an acquisition time period;

acquiring, with the MRI system, one or more spin echo signals having information pertaining to at least one of metabolites and metabolite byproducts within the ROI to form a chemical exchange saturation transfer (CEST) medical imaging data set during the acquisition time period; and

reconstructing, with the MRI system, the CEST medical imaging data set to form a CEST image of the subject including information about the at least one of metabolites and metabolite byproducts within the subject.

13. The method of claim 12 further comprising at least one of:

calculating a quantitative CEST map using ratiometric analysis by taking amplitude ration at different frequency offsets; and

performing line decoupling to derive CEST effect from one or more compounds.

14. The method of claim 12 further comprising selecting one or more voxels by applying a plurality of slice selection gradients accompanied by a train of RF pulses during a voxel selection time period.

15. The method of claim 12 further comprising applying a plurality of slice selection gradients accompanied by a train of RF pulses during a voxel selection time period, wherein a magnitude and polarity of the padding gradient G2 is calculated based on the signal formation during G3.

16. The method of claim 12 further comprising acquiring the one or more spin echo signals when applying the third gradient G3 during the acquisition time period.

17. The method of claim 12 further comprising choosing the saturation time period based on properties of an underlying CEST system of interest.

18. The method of claim 12 further comprising acquiring the one or more spin echo signals with a repetition time that is chosen based on properties of an underlying CEST system of interest.

19. A method for producing a report regarding a subject with a magnetic resonance imaging (MRI) system, the method comprising:

applying, with the MRI system, a saturation radiofrequency (RF) irradiation during a saturation time period at a reference frequency that saturates a selected labile spin species of a subject;

encoding, with the MRI system, frequency offsets by applying a gradient G1 at least during the saturation time period;

acquiring, with the MRI system, one or more spin echo signals having information pertaining to at least one of metabolites and metabolite byproducts within the ROI to form a chemical exchange saturation transfer (CEST) data set with spatial encoding; and

generating a spectroscopy report from the CEST data set including information about the at least one of metabolites and metabolite byproducts within the subject.

20. The method of claim 19 further comprising:

applying a plurality of slice selection gradients accompanied by a train of RF pulses during a voxel selection time period;

applying a padding gradient G2 for formation of spin echo; and

applying a gradient G3 during an acquisition time period.