Method for nuclear magnetic resonance diffusion measurements

Abstract

A method and system for determining a property of a substance using nuclear magnetic resonance (NMR) is described herein. The method includes applying a NMR pulse sequence to the substance. The NMR pulse sequence includes a first set of pulses and a second set of pulses. The first set of pulses and the second set of pulses encode for overlapping diffusion times. By overlapping diffusion times, the NMR pulse sequence can be used to measure a diffusion coefficient for a first diffusion time, a diffusion coefficient for a second diffusion time, and a correlation between the two overlapping diffusion times. This information, in turn, can be used to differentiate between intrinsic bulk diffusivity of the substance and the reduced diffusivity of the substance caused by restricted diffusion.

1 . A method comprising:
 applying a nuclear magnetic resonance (NMR) pulse sequence comprising a first set of pulses and a second set of pulses to a substance, wherein the first set of pulses encode for a first diffusion time and the second set of pulses encode for a second diffusion time, the first diffusion time overlapping the second diffusion time, and wherein (i) the first set of pulses comprises two pulses that are each defined by a first area parameter and separated by a time period, and (ii) the second set of pulses comprises two pulses that are each defined by a second area parameter and separated by the time period;   detecting an NMR signal produced by the NMR pulse sequence to obtain NMR signal data;   applying to the substance a modified NMR pulse sequence generated by changing at least one of (a) the first diffusion time and (b) the second diffusion time;   detecting an NMR signal produced by the modified NMR pulse sequence to obtain NMR signal data; and   determining a property of the substance using at least the NMR signal data over each of the overlapping diffusion times for the NMR pulse sequence and the modified NMR pulse sequence.   
     
     
         2 . The method of  claim 1 , further comprising:
 applying the NMR pulse sequence to the substance a plurality of times using different values for the first area parameter and the second area parameter;   detecting NMR signals produced by the NMR pulse sequence for the different values of the first area parameter and the second area parameter to obtain NMR signal data.   
     
     
         3 . The method of  claim 1 , wherein the values of the first area parameter and the second area parameter are varied according to the following relationships:
     q   s   =q   1   +q   2 ,       q   d   =q   2   −q   1 ,   
       where q 1  is the first area parameter, q 2  is the second area parameter, q s  is an area parameter for the portion of pulses that correspond to the first diffusion time, and q d  is an area parameter for the complimentary portion of pulses that correspond to the second diffusion time. 
     
     
         4 . The method of  claim 3 , further comprising:
 performing a Laplace inversion on the NMR signal data to obtain diffusion coefficients for the first diffusion time and the second diffusion time.   
     
     
         5 . The method of  claim 1 , wherein:
 (i) the two pulses within the first set of pulses include pulse areas that cancel, and   (ii) the two pulses within the second set of pulses include pulse areas that cancel.   
     
     
         6 . A method comprising:
 generating decoupled gradient waveforms;   applying a nuclear magnetic resonance (NMR) pulse sequence comprising the decoupled gradient waveforms to a substance;   detecting an NMR signal produced by the NMR pulse sequence to obtain NMR signal data;   determining a property of the substance using the NMR signal data.   
     
     
         7 . The method of  claim 6 , wherein the generating the decoupled gradient waveform includes decoupling diffusion encoding based on at least one of symmetry, blurring, spectral separation, phase decoherence, and orthogonalization.