NMR methods for monitoring blood clot formation
The invention features a method of monitoring a clotting process by measuring a signal characteristic of the NMR relaxation of water in a sample undergoing clotting to produce NMR relaxation data and determining from the NMR relaxation data a magnetic resonance parameter of water in the sample characteristic of the clots being formed.
1. A method of monitoring a clotting process comprising:
(i) adding to whole blood obtained from a subject a clotting initiator to initiate a clotting process;
(ii) during the clotting process making a plurality of T 2 relaxation rate measurements on the whole blood sample at a series of time points during said process to produce a plurality of T 2 relaxation rate decay curves,
(iii) transforming the T 2 relaxation rate measurements using an algorithm that distinguishes two or more separate water populations within the whole blood sample at one or more of said time points, wherein the two or more water populations comprise a water population having a serum-associated T 2 signal and a water population having a clot-associated T 2 signal, and the serum-associated T 2 signal and the clot-associated T 2 signal are separately characterized by one or more magnetic resonance parameters;
(iv) obtaining values of the one or more magnetic resonance parameters for the water population having a serum-associated T 2 signal and a water population having a clot-associated T 2 signal; and
(v) on the basis of the results of step (iv), monitoring said clotting process.
2. The method of claim 1 , further comprising (a) calculating the difference between the value of the serum-associated T 2 signal and the value of the clot-associated T 2 signal; and (b) on the basis of the difference, determining the activity of the platelets in the whole blood.
3. The method of claim 1 , further comprising (a) following step (i), measuring the period of time prior to the initial detection of the clot-associated T 2 signal; and (b) on the basis of the period of time, determining the clotting time for the whole blood.
4. The method of claim 1 , further comprising (a) following step (i), calculating a T 2 time curve for a first water population; (b) calculating the maximum value of the second derivative of the T 2 time curve; and (c) on the basis of the result of step (c), calculating a value characteristic of clotting time.
5. The method of claim 1 , further comprising calculating the T 2 value for the whole blood prior to initiating clot formation, and on the basis of the T 2 value, determining the hematocrit of the whole blood.
6. The method of claim 1 , wherein prior to step (ii), fibrinogen is added to the whole blood sample.
7. The method of claim 1 , wherein the clotting initiator is an intrinsic pathway activator.
8. The method of claim 1 , wherein the clotting initiator is an extrinsic pathway activator.
9. The method of claim 8 , wherein the clotting initiator is tissue factor.
10. The method of claim 1 , further comprising determining whether the whole blood is hypercoagulable, hypocoagulable, or normal.
11. The method of claim 10 , further comprising, prior to step (i), (a) administering an anticoagulation therapy to the subject; and (b) if the subject is found to be hypercoagulable, identifying the subject as a non-responder to the anticoagulation therapy.
12. The method of claim 1 , wherein the whole blood sample has a volume between 2 microliters and 400 microliters.
13. The method of claim 12 , wherein the whole blood sample has a volume between 2 microliters and 250 microliters.
14. The method of claim 13 , wherein the whole blood sample has a volume between 2 microliters and 50 microliters.
15. The method of claim 1 , wherein the whole blood sample has a volume between 200 microliters and 500 microliters.
16. The method of claim 1 , wherein step (i) comprises adding the whole blood to a tube containing one or more clotting initiators, and mixing the contents to initiate a clotting process.
17. The method of claim 1 , wherein said algorithm comprises an algorithm selected from the group consisting of a multi-exponential algorithm, a bi-exponential algorithm, a tri-exponential algorithm, a decaying exponential algorithm, a Laplace transform, a goodness-of-fit algorithm, an SSE algorithm, a least squares algorithm, and a non-negative least squares algorithm.
18. The method of claim 17 , wherein said algorithm is an inverse Laplace transform.
19. The method of claim 18 , wherein said inverse Laplace transform includes a lower bound for the T 2 time constants of from 1 to 50 ms and an upper bound for the T 2 time constants of from 1000 to 4000 ms.
20. The method of claim 19 , wherein said blood sample is plasma, platelet poor plasma, or platelet rich plasma, and said upper bound for the T 2 time constants is from 2500 to 4000 ms.
21. The method of claim 19 , wherein said blood sample is a whole blood sample and said upper bound for the T 2 time constants is from 1000 to 2000 ms.
22. The method of claim 19 , wherein each of the two or more water populations has a distinct relaxation rate at one or more time points during the clotting process.
23. The method of claim 19 , wherein each of the two or more water populations has a distinct T 2 signal intensity at one or more time points during the clotting process.