TTField treatment with optimization of electrode positions based on low frequency (<1MHZ) AC conductivity estimates derived from two MRI images having different repetition times
A 3D model of AC electrical conductivity (at a given frequency) of an anatomic volume can be created by obtaining two MRI images of the anatomic volume, where the two images have different repetition times. Then, for each voxel in the anatomic volume, a ratio IR of the intensity of the corresponding voxels in the two MRI images is calculated. This calculated IR is then mapped into a corresponding voxel of a 3D model of AC electrical conductivity at the given frequency. The given frequency is below 1 MHz (e.g., 200 kHz). In some embodiments, the 3D model of AC electrical conductivity at the given frequency is used to determine the positions for the electrodes in TTFields (Tumor Treating Fields) treatment.
1. A method of creating a 3D model of AC electrical conductivity or resistivity of an anatomic volume at a given frequency, the method comprising the steps of:
obtaining a first MRI image of the anatomic volume, the first MRI image having an associated first frequency and an associated first repetition time;
obtaining a second MRI image of the anatomic volume, the second MRI image having an associated second frequency and an associated second repetition time that is different from the first repetition time;
calculating, for each voxel in the anatomic volume, a ratio IR of an intensity of a corresponding voxel in the first MRI image to an intensity of a corresponding voxel in the second MRI image; and
mapping the calculated IR for each voxel in the anatomic volume into a corresponding voxel of a 3D model of AC electrical conductivity or resistivity at the given frequency, wherein the given frequency is below 1 MHz, wherein the given frequency is different from the first frequency, and wherein the given frequency is different from the second frequency.
2. The method of claim 1 , wherein the given frequency is between 100 and 300 kHz.
3. The method of claim 1 , wherein the given frequency is between 180 and 220 kHz.
4. The method of claim 1 , wherein the first MRI image is a T1 image and the second MRI image is a T1 image.
5. The method of claim 1 , wherein the first MRI image is a T1 image and the second MRI image is a proton density image.
6. The method of claim 1 , wherein the first repetition time is between 400 and 800 ms and the second repetition time is between 2 and 5 seconds.
7. The method of claim 1 , wherein the anatomic volume comprises white matter and grey matter of a brain.
8. The method of claim 1 , wherein the 3D model of AC electrical conductivity or resistivity is a 3D model of AC electrical conductivity.
9. A method of optimizing positions of a plurality of electrodes placed on a subject's body, wherein the electrodes are used to impose an electric field in target tissue within an anatomic volume at a given frequency, the method comprising the steps of:
obtaining a first MRI image of the anatomic volume, the first MRI image having an associated first frequency and an associated first repetition time;
obtaining a second MRI image of the anatomic volume, the second MRI image having an associated second frequency and an associated second repetition time that is different from the first repetition time;
calculating, for each voxel in the anatomic volume, a ratio IR of an intensity of a corresponding voxel in the first MRI image to an intensity of a corresponding voxel in the second MRI image;
mapping the calculated IR for each voxel in the anatomic volume into a corresponding voxel of a 3D model of electrical conductivity or resistivity at the given frequency, wherein the given frequency is below 1 MHz, wherein the given frequency is different from the first frequency, and wherein the given frequency is different from the second frequency;
identifying a location of the target tissue within the anatomic volume; and
determining positions for the electrodes based on the 3D model of electrical conductivity or resistivity at the given frequency generated in the mapping step and the location of the target tissue identified in the identifying step.
10. The method of claim 9 , wherein the given frequency is between 100 and 300 kHz.
11. The method of claim 9 , wherein the given frequency is between 180 and 220 kHz.
12. The method of claim 9 , wherein the first MRI image is a T1 image and the second MRI image is a T1 image.
13. The method of claim 9 , wherein the first MRI image is a T1 image and the second MRI image is a proton density image.
14. The method of claim 9 , wherein the first repetition time is between 400 and 800 ms and the second repetition time is between 2 and 5 seconds.
15. The method of claim 9 , further comprising the steps of:
affixing the electrodes to the subject's body at the positions determined in the determining step; and
applying electrical signals between the electrodes subsequent to the affixing step, so as to impose the electric field in the target tissue.
16. The method of claim 9 , wherein the anatomic volume comprises white matter and grey matter of a brain.
17. The method of claim 9 , wherein the anatomic volume is a brain, and
wherein the determination of positions for the electrodes is based on a composite model in which the 3D model of electrical conductivity or resistivity of the brain is surrounded by a model of at least one shell having a constant conductivity.
18. The method of claim 9 , wherein the anatomic volume is a brain surrounded by cerebrospinal fluid, and
wherein the determination of positions for the electrodes is based on a composite model in which the 3D model of electrical conductivity or resistivity of the brain is surrounded by a model of at least one shell having a constant conductivity.
19. The method of claim 9 , wherein the 3D model of electrical conductivity or resistivity is a 3D model of electrical conductivity.