Techniques for correcting measurement artifacts in magnetic resonance thermometry
Techniques for correcting measurement artifacts in MR thermometry predict or anticipate movements of objects in or near an MR imaging region that may potentially affect a phase background and then acquire a library of reference phase images corresponding to different phase backgrounds that result from the predicted movements. For each phase image subsequently acquired, one reference phase image is selected from the library of reference phase images to serve as the baseline image for temperature measurement purposes. To avoid measurement artifacts that arise from phase wrapping, the phase shift associated with each phase image is calculated incrementally, that is, by accumulating phase increments from each pair of consecutively scanned phase images.
1. A method of performing proton resonance frequency (PRF) based magnetic resonance (MR) temperature measurement, the method comprising the steps of:
acquiring a plurality of PRF reference images of an MR imaging region, each of the reference images corresponding to a PRF phase background resulting from a different arrangement of one or more devices in or near the MR imaging region;
acquiring a first PRF image of the MR imaging region subsequent to the acquisition of the plurality of PRF reference images;
selecting, from the plurality of PRF reference images, a first PRF reference image most closely corresponding to the first PRF image;
calculating a first PRF phase shift based at least in part on a difference between the first PRF image and the first PRF reference image;
acquiring a second PRF image of the MR imaging region subsequent to the acquisition of the first PRF image;
selecting, from the plurality of PRF reference images, a second PRF reference image most closely corresponding to the second PRF image;
calculating a second PRF phase shift by summing (i) the first PRF phase shift and (ii) an incremental phase shift of a difference between the second PRF image and the first PRF image as compared to a difference between the second PRF reference image and the first PRF reference image; and
determining at least one temperature change based on at least one of the first PRF phase shift and the second PRF phase shift.
2. The method of claim 1 , wherein the plurality of PRF reference images correspond to predicted positionings of at least one treatment device.
3. The method of claim 2 , wherein the treatment device comprises an MR guided focused ultrasound (MRgFUS) transducer.
4. The method of claim 1 , further comprising:
generating a temperature map of the MR imaging region based at least in part on the first PRF image and on the differences.
5. The method of claim 1 , further comprising:
calculating a movement compensation map based on differences between the first PRF reference image and the second PRF reference image.
6. The method of claim 1 , further comprising:
comparing the first PRF image with the plurality of PRF reference images to find matching physical features.
7. The method of claim 1 , further comprising:
acquiring a third PRF image of the MR imaging region subsequent to the acquisition of the second PRF image;
selecting, from the plurality of PRF reference images, a third PRF reference image most closely corresponding to the third PRF image; and
calculating a third PRF phase shift by summing (i) the second PRF phase shift and (ii) an incremental phase shift of a difference between the third PRF image and the second PRF image as compared to a difference between the third PRF reference image and the second PRF reference image.
8. A system for performing proton resonance frequency (PRF) based magnetic resonance (MR) temperature measurement, the system comprising:
an MRI unit;
a control module in communication with the MRI unit, and configured to cause the MRI unit to:
acquire a plurality of PRF reference images of an MR imaging region, each of the reference images corresponding to a PRF phase background resulting from a different arrangement of one or more devices in or near the MR imaging region,
acquire a first PRF image of the MR imaging region subsequent to the acquisition of the plurality of PRF reference images, and
acquire a second PRF image of the MR imaging region subsequent to the acquisition of the first PRF image; and
a processor module having access to image data acquired by the MRI unit, and configured to:
select, from the plurality of PRF reference images, a first PRF reference image most closely corresponding to the first PRF image,
calculate a first PRF phase shift based at least in part on a difference between the first PRF image and the first PRF reference image,
select, from the plurality of PRF reference images, a second PRF reference image most closely corresponding to the second PRF image,
calculate a second PRF phase shift by summing (i) the first PRF phase shift and (ii) an incremental phase shift of a difference between the second PRF image and the first PRF image as compared to a difference between the second PRF reference image and the first PRF reference image, and
determine at least one temperature change based on at least one of the first PRF phase shift and the second PRF phase shift.
9. A method of performing proton resonance frequency (PRF) based magnetic resonance (MR) temperature measurement, the method comprising the steps of:
acquiring a plurality of PRF reference images of an MR imaging region, each of the PRF reference images corresponding to a PRF phase background resulting from one or more predicted anatomical movements of at least a part of a patient's body;
acquiring a first PRF image of the MR imaging region subsequent to the acquisition of the plurality of PRF reference images;
selecting, from the plurality of PRF reference images, a first PRF reference image most closely corresponding to the first PRF image;
calculating a first PRF phase shift based at least in part on a difference between the first PRF image and the first PRF reference image;
acquiring a second PRF image of the MR imaging region subsequent to the acquisition of the first PRF image;
selecting, from the plurality of PRF reference images, a second PRF reference image most closely corresponding to the second PRF image;
calculating a second PRF phase shift by summing (i) the first PRF phase shift and (ii) an incremental phase shift of a difference between the second PRF image and the first PRF image as compared to corresponding pixels of a difference between the first PRF reference image and the second PRF reference image; and
determining at least one temperature change based on at least one of the first PRF phase shift and the second PRF phase shift.
10. The method of claim 9 , further comprising:
predicting a trajectory for the one or more predicted anatomical movements.
11. The method of claim 10 , wherein the predicted trajectory is associated with the patient's respiratory cycles.
12. The method of claim 9 , further comprising:
acquiring a third PRF image of the MR imaging region subsequent to the acquisition of the second PRF image;
selecting, from the plurality of PRF reference images, a third PRF reference image most closely corresponding to the second PRF image; and
calculating a third PRF phase shift by summing (i) the second PRF phase shift and (ii) an incremental phase shift of a difference between the third PRF image and the second PRF image as compared to corresponding pixels of a difference between the third PRF reference image and the second PRF reference image.
13. The method of claim 9 , wherein the plurality of PRF reference images correspond to PRF phase backgrounds resulting from different arrangements of one or more devices in or near the MR imaging region in combination with one or more predicted movements of the patient.
14. A system for performing proton resonance frequency (PRF) based magnetic resonance (MR) temperature measurement, the system comprising:
an MRI unit;
a control module in communication with the MRI unit, and configured to cause the MRI unit to:
acquire a plurality of PRF reference images of an MR imaging region, each of the reference images corresponding to a PRF phase background resulting from one or more predicted anatomical movements of at least a part of a patient's body,
acquire a first PRF image of the MR imaging region subsequent to the acquisition of the plurality of PRF reference images, and
acquire a second PRF image of the MR imaging region subsequent to the acquisition of the first PRF image; and
a processor module having access to image data acquired by the MRI unit, and configured to:
select, from the plurality of PRF reference images, a first PRF reference image most closely corresponding to the first PRF image,
calculate a first PRF phase shift based at least in part on a difference between the first PRF image and the first PRF reference image,
select, from the plurality of PRF reference images, a second PRF reference image most closely corresponding to the second PRF image,
calculate a second PRF phase shift by summing (i) the first PRF phase shift and (ii) an incremental phase shift of a difference between the second PRF image and the first PRF image as compared to corresponding pixels of a difference between the second PRF reference image and the first PRF reference image, and
determine at least one temperature change based on at least one of the first PRF phase shift and the second PRF phase shift.