Imaging tissue deformation using strain encoded MRI
Disclosed is a system and method for imaging strain of tissue, such as the heart, in a quantitative manner. The present invention provides images of strain, which corresponds to heart function, by tagging a tissue region of interest, and acquiring multiple images by tuning an MRI RF receiver to frequencies above and below the tagging frequency. Depending on the tagging spatial frequency, and the spread between the high- and low-tuning frequencies, linear measurements of strain may be made on a pixel by pixel basis. By selectively tagging the tissue of interest by use of selective excitation, images may be acquired sufficiently fast to provide anatomical and functional imagery within a single heartbeat. By acquiring additional images, dead tissue may be differentiated from contracting tissue as well as blood.
1. A method for acquiring strain images of tissue, comprising:
transmitting a tagging pulse having a tagging spatial frequency;
receiving a first RF signal corresponding to a first receive spatial frequency that is below the tagging spatial frequency;
receiving a second RF signal corresponding to a second receive spatial frequency that is above the tagging spatial frequency; and
computing a strain value corresponding to the received first RF signal and the received second RF signal.
2. The method of claim 1 , wherein transmitting a tagging pulse comprises transmitting a slice-selection encoded gradient signal.
3. The method of claim 1 , further comprising assembling a strain image based on the computed strain value.
4. The method of claim 1 , wherein computing the strain value comprises:
computing a first intensity corresponding to the received first RF signal;
computing a second intensity corresponding to the received second RF signal;
computing an estimated strain frequency based on the first intensity and the second intensity; and
computing the strain value based on the strain frequency.
5. The method of claim 1 , further comprising:
computing a first plurality of pixel values corresponding to the received first RF signal;
computing a second plurality of pixel values corresponding to the received second RF signal;
computing a first plurality of intensity values based on the first plurality of pixel values;
computing a second plurality of intensity values based on the second plurality of pixel values; and
computing a plurality of strain values based on the first plurality of intensity values and the second plurality of intensity values.
6. The method of claim 5 , wherein computing a plurality of strain values comprises computing a strain frequency based on the first plurality of intensity values and the second plurality of intensity values.
7. The method of claim 5 , further comprising:
combining the first plurality of pixel values and the second plurality of pixel values into an anatomical image.
8. The method of claim 7 , further comprising combining the anatomical image with the plurality of strain values to form a colored functional image.
9. The method of claim 8 , further comprising:
receiving a third RF signal corresponding to a zero tuning;
computing a third plurality of pixel values corresponding to the third RF signal; and
combining the third plurality of pixel values with the colored functional image.
10. The method of claim 9 , further comprising differentiating a plurality of tissue types, after combining the third plurality of pixel values with the colored functional image.
11. The method of claim 8 , wherein differentiating the plurality of tissue types comprises differentiating blood, dead tissue, contracting tissue, and background.
12. The method of claim 1 , wherein transmitting the tagging pulse comprises transmitting a 1D-1 SPAMM pulse sequence.
13. The method of claim 1 , wherein transmitting the tagging pulse comprises transmitting a 1D-1D SPAMM pulse sequence.
14. The method of claim 1 , wherein transmitting the tagging pulse comprises transmitting a 12D-1 SPAMM pulse sequence.
15. The method of claim 1 , wherein transmitting the tagging pulse comprises transmitting a 1-SF SPAMM pulse sequence.
16. The method of claim 1 , wherein transmitting the tagging pulse comprises transmitting a 1D-SF SPAMM pulse sequence.
17. The method of claim 1 , wherein transmitting the tagging pulse comprises transmitting a 2D-SF SPAMM pulse sequence.
18. A system for acquiring strain imaging of a tissue, comprising:
a gradient coil;
an RF coil;
an RF demodulator; and
a processor having a computer readable medium encoded with a program for transmitting a tagging pulse having a tagging spatial frequency; receiving a first RF signal corresponding to a first receive spatial frequency that is below the tagging spatial frequency; receiving a second RF signal corresponding to a second receive spatial frequency that is above the tagging spatial frequency; and computing a strain value corresponding to the received first RF signal and the received second RF signal.
19. The system of claim 18 , wherein the program for receiving a first RF signal corresponding to a first receive spatial frequency includes providing the first receive spatial frequency to the RF demodulator.
20. The system of claim 18 , wherein the program comprises a program for assembling a strain image based on the computed strain.
21. The method of claim 18 , wherein the program for computing the strain value comprises:
a program for computing a first intensity corresponding to the received first RF signal;
a program for computing a second intensity corresponding to the received second RF signal;
a program for computing an estimated strain frequency based on the first intensity and the second intensity; and
a program for computing the strain based on the strain frequency.