Method to measure tissue texture using NMR spectroscopy to identify the chemical species of component textural elements in a targeted region of tissue
A method for identifying the chemical species of various textural elements in a targeted region of tissue wherein a volume of interest (VOI) is selectively excited and a k-encode gradient pulse is applied to induce phase wrap to create a spatial encode for a specific k-value and orientation. The specific k-value is selected based on anticipated texture within the VOI. Multiple sequential samples of the NMR RF signal encoded with the specific k-value are recorded as signal data. The Fourier Transform of the acquired signal data is then taken, wherein for each k-encode, the signal recorded is indicative of the spatial frequency power density at that point in k-space. Each peak in the NMR spectrum is then evaluated, whereby the relative contribution to the texture of tissue in the VOI at a k-value for each chemical species is determined.
1. A method for identifying the related texture and chemical species in a targeted region of tissue, the method comprising:
selectively exciting a volume of interest (VOI) and applying a k encode gradient pulse to induce phase wrap to create a spatial encode for a specific k-value and orientation, the specific k-value selected based on anticipated texture within the VOI;
recording multiple samples of the NMR RF signal encoded with the specific k-value as signal data;
taking the Fourier Transform of the acquired signal data, wherein for each k-encode, wherein the signal data recorded is indicative of the spatial power density at that point in k-space; and,
evaluating each peak in the NMR spectrum whereby the relative contribution to texture of tissue in the VOI at a k-value for each chemical species is determined.
2. The method as defined in claim 1 wherein the step of recording multiple sequential samples further comprises:
initiating a time varying gradient to produce time varying k-value encodes, a resulting k-value set being a subset of that required to produce an image of the VOI;
simultaneously recording multiple sequential samples of the NMR RF signal encoded with the k-value set as signal data.
3. The method as defined in claim 1 further comprising:
acquiring signal data across a series of TRs, with a k-encode at each excitation sequence, the k-encode being varied from one excitation sequence to the next creating a k-value set;
and wherein the step of taking the Fourier Transform of the acquired signal data comprises taking the Fourier Transform of the acquired signal data for each excitation sequence, the signal recorded in that excitation sequence including the spatial frequency density of each chemical species at that point in k-space.
4. The method as defined in claim 1 wherein the step of evaluating each peak comprises integrating the area under each peak.
5. The method as defined in claim 1 wherein the step of evaluating each peak comprises determining signal magnitude of the peak.
6. The method as defined in claim 1 wherein the step of evaluating each peak comprises determining a relative width of each peak.
7. The method as defined in claim 4 further comprising ratioing the integrated areas.
8. The method as defined in claim 3 further comprising:
applying multiple 180 refocusing pulses within each TR systematically varying the phases of exciting and refocusing RF pulses to acquire multiple measurements of a spin echo signal within each TR; and
combining signal outputs with common k-value for reduction of artifacts.
9. The method as defined in claim 8 further comprising reapplying the k-value selection gradients for the selected k-values after each refocusing pulse.
10. The method as defined in claim 1 further comprising:
generating a k-encoded excitation with wavelength λ to produce signal data with low to zero magnitude if the magnitude of the chemical species are equal, or higher magnitude if the magnitudes of the chemical species are unequal;
separating the signal data by NMR frequency by Fourier transforming the received signal data and separately measuring individual NMR signals by calculating the area under the spectral peak or by measuring the maximum signal to increase sensitivity to the texture at the encoded k-value.
11. The method as defined in claim 1 further comprising:
generating k-encoded excitation at a particular wavelength λ for a target species to suppress signals from textures of different wavelength from the target species in one or more of the chemical species;
using NMR frequency to identify and remove signal from other chemical species that may have some signal at the specific k-value but are not related to a targeted texture exhibited by the target species.
12. The method as defined in claim 3 further comprising:
post processing the signal data to produce a data set of signal vs k-values for k-values in the k-value set, to characterize textural features of tissue in the VOI.
13. The method as defined in claim 12 further comprising:
correlating the textural features and chemical species with other patient metrics and outcomes;
inputting the correlated textural features and chemical species as biomarkers to provide disease diagnosis, prognosis and therapy planning.
14. The method as defined in claim 12 further comprising inputting the textural features and chemical species to provide information of chemical composition in conjunction with variation in microstructural tissue changes.
15. The method as defined in claim 12 further comprising:
using AI/machine learning analytics to extract features and develop biomarkers from changes in microstructure and changes in the chemical composition of the various phases of that microstructure present in the measured textural features of the tissue for diagnostic purposes; and
correlating the developed biomarkers with other diagnostic metrics, and other measures of tissue texture for use as a surrogate measure of the other diagnostic metrics.
16. The method as defined in claim 12 further comprising:
using AI/machine learning analytics to extract features and develop biomarkers from changes in microstructure and changes in the chemical composition of the various phases of that microstructure present in the measured textural features of the tissue for diagnostic purposes; and
correlating the developed biomarkers with genomic data for use as a surrogate measure of genomic fingerprinting in the targeted tissue.
17. The method as defined in claim 12 further comprising:
using AI/machine learning analytics to extract features and develop biomarkers from changes in microstructure and changes in the chemical composition of the various phases of that microstructure present in the measured textural features of the tissue and correlating a multiplicity of tissue parameters; and
using the features and biomarkers as a surrogate marker for the tissue parameters.