Methods for imaging pulmonary and cardiac vasculature and evaluating blood flow using dissolved polarized 129 Xe

• US 20010000727A1
• Filed: 12/15/2000
• Published: 05/03/2001
• Est. Priority Date: 03/18/1998
• Status: Active Grant

• Current Assignee: Polarean, Inc. (Polarean Imaging Plc)
• Original Assignee: Bastiaan Driehuys, Kenton Christopher Hasson, Paul Lev Bogorad
• Inventors: Bogorad, Paul Lev, Hasson, Kenton Christopher, Driehuys, Bastiaan
• Granted Patent: US 6,491,895 B2
• Time in Patent Office: Days
• US Class Current: 424/9.36
• CPC Class Codes: A61B 5/0263 using NMR
• CPC Class Codes: A61B 5/02755 Radioactive tracers
• CPC Class Codes: A61B 5/055 involving electronic [EMR] or nuclear [NMR] magnetic resonance, e.g. magnetic resonance imaging
• CPC Class Codes: A61K 49/1815 compo-inhalant, e.g. breath tests
• CPC Class Codes: G01R 33/5601 involving use of a contrast agent for contrast manipulation, e.g. a paramagnetic, super-paramagnetic, ferromagnetic or hyperpolarised contrast agent
• CPC Class Codes: G01R 33/563 of moving material, e.g. flow contrast angiography

Abstract

MR spectroscopy and imaging methods for imaging pulmonary and cardiac vasculature and the cardiac region and evaluating blood flow or circulatory deficits use dissolved phase polarized ¹²⁹Xe gas and large flip angle excitation pulses. Pulmonary and cardiac vasculature MRI images are obtained by delivering gas to a patient via inhalation such as with a breath-hold delivery -procedure, exciting the dissolved phase gas with a large flip angle pulse, and generating a corresponding image. Preferably, the image is obtained using multi-echo imaging techniques. Blood flow is quantified using low field MR spectroscopy and an RF excitation pulse with a frequency which corresponds to the resonance of the dissolved phase ¹²⁹Xe.

Claims

1. A method for MRI imaging the pulmonary and/or cardiac vasculature using dissolved-phase polarized ¹²⁹Xe, comprising the steps of:

positioning a patient in an MRI apparatus having a magnetic field associated therewith;

delivering polarized ¹²⁹Xe gas to a predetermined region of the patient'"'"'s body, the polarized gas having a dissolved imaging phase associated therewith;

exciting a predetermined region of the patient'"'"'s body having a portion of the dissolved phase polarized gas therein with at least one large flip angle RF excitation pulse; and

acquiring at least one MR image associated with the dissolved phase polarized gas after said exciting step.

2. A method according to

claim 1

, wherein said exciting step is repeated within a predetermined repetition time, the predetermined repetition time being less than the time it takes for a given volume of blood to move from the lungs to the heart.

3. A method according to

claim 1

, wherein the large flip angle excitation pulse is about a 90 degree excitation pulse.

4. A method according to

claim 1

, wherein the RF excitation pulse has a pulse frequency, and wherein the pulse frequency is selected such that it corresponds to the dissolved phase polarized gas resonance.

5. A method according to

claim 3

, wherein the repetition time is less than about 3 seconds.

6. A method according to

claim 1

, wherein the large angle pulse selectively excites substantially only the dissolved phase of the ¹²⁹Xe.

7. A method according to

claim 1

, wherein the excitation pulse has a duration which is less than about 2.5 milliseconds.

8. A method according to

claim 1

, wherein the predetermined region is the patient'"'"'s blood volume in the vasculature between and/or within the lungs and the heart.

9. A method according to

claim 1

, wherein said delivering step includes having the patient inhale the polarized ¹²⁹Xe gas into the lungs, the ¹²⁹Xe having a gas phase resonance which is higher than the dissolved-phase resonance, and wherein at least a portion of the ¹²⁹Xe gas enters into the pulmonary vasculature in a dissolved-phase, and wherein at least a portion of the dissolved-phase ¹²⁹Xe then enters the blood stream with an associated perfusion rate.

10. A method according to

claim 9

, wherein a differential-MRI image is obtained which includes information corresponding to both the ¹²⁹Xe gas and dissolved-gas phase, and wherein said differential image is obtained by exciting the ¹²⁹Xe gas phase with an RF pulse having an excitation pulse frequency which corresponds to the resonance of the gas phase and exciting the dissolved phase with an RF pulse having an excitation frequency which corresponds to the resonance of the dissolved phase, and wherein the gas phase RF excitation pulse is a small flip angle pulse and the dissolved phase RF excitation pulse is a large flip angle pulse.

11. A method according to

claim 9

, wherein said method further comprises the step of delivering via inhalation a quantity of polarized ³He gas, and wherein a MRI differential image is obtained which includes information corresponding to the polarized gas ³He in the lungs in addition to the information corresponding to the dissolved phase polarized ¹²⁹Xe.

12. A method according to

claim 9

, wherein said inhalation delivering step includes a breath-hold delivery period.

13. A method according to

claim 12

, wherein the breath-hold period is at least 10 seconds.

14. A method according to

claim 9

, wherein the at least one image is a multi-echo image.

15. A method according to

claim 14

, wherein the multi-echo image is one of a slice selective and volume selective image pattern.

16. A method according to

claim 2

, wherein the repetition time is decreased to emphasize a signal associated with capillaries in the pulmonary region.

17. A method according to

claim 2

, wherein the repetition time is increased to include distal vasculature relative to the pulmonary capillaries.

18. A method according to

claim 1

, wherein dissolved-phase ¹²⁹Xe has an associated decay time constant (T1) corresponding to its polarization life and a transverse relaxation time in blood (T₂*), and wherein for T₂* greater than about 100 ms, said acquiring step employs one of EPI and RARE multi-echo imaging methods.

19. A method according to

claim 1

, wherein said acquiring step acquires at least 32 echoes per each excitation pulse.

20. A method according to

claim 9

, wherein cardiac gating is used so that said acquiring step is timed such that it is performed during slow blood flow periods.

21. A method according to

claim 14

, wherein the multi-echo imaging uses one of gradient recalled and RF recalled echoes.

24. A method according to

claim 21

, wherein said evaluating step includes a measuring step which quantifies the subject'"'"'s blood flow rate.

25. A method according to

claim 24

, wherein said measuring step uses the heart rate of the subject to normalize the measured blood flow rate.

22. A method for evaluating the blood flow of a patient, comprising the steps of:

positioning a subject in a MR spectroscopy system capable of detecting spectroscopic signals in a subject having a pulmonary vasculature;

delivering gaseous polarized ¹²⁹Xe to the subject;

dissolving a portion of the gaseous polarized ¹²⁹Xe into the pulmonary vasculature having an associated blood flow path;

exciting the dissolved portion of the ¹²⁹Xe with an MR spectroscopy RF excitation pulse; and

evaluating blood flow of the patient based on a spectroscopic signal corresponding to the dissolved polarized ¹²⁹Xe.

23. A method according to

claim 22

, farther comprising the step of identifying one or more of:

(a) perfusion deficits in the pulmonary vasculature or the cardiac vasculature, (b) pulmonary vasculature emboli, (c) blood flow related circulatory system deficits, and (d) restrictions and obstructions in the blood flow path of the subject based on said evaluating step.

26. A method according to

claim 22

, wherein said evaluating step includes the steps of exciting the dissolved ¹²⁹Xe with a large angle RF excitation pulse.

27. A method according to

claim 26

, wherein said large angle pulse is above about a 90 degree flip angle pulse, and wherein said delivering step is performed by the subject inhaling a quantity of gaseous polarized ¹²⁹Xe.

28. A method according to

claim 27

, wherein said exciting step is performed selectively to excite the dissolved ¹²⁹Xe and leave the gaseous ¹²⁹Xe substantially undisturbed.

29. A method according to

claim 22

, wherein said evaluating step includes the step of comparing the blood flow rates of healthy subjects with the measured blood flow rate.

30. A method according to

claim 26

, wherein the MR Spectroscopy System includes a magnetic field operably associated therewith, and wherein the magnetic field is less than about 0.5 T.

31. A method according to

claim 30

, wherein said evaluating step is performed to provide real-time blood flow information.

32. A cardiac imaging method, comprising the steps of:

positioning a subject having a cardiac blood flow path in an MRI system;

delivering polarized ¹²⁹Xe to the subject;

dissolving at least a portion of the polarized ¹²⁹Xe into the subject'"'"'s cardiac blood flow path;

exciting dissolved polarized ¹²⁹Xe in a target region along the blood flow path with at least one large angle RF excitation pulse; and

generating a MR image associated with the excited dissolved polarized ¹²⁹Xe.

33. A method according to

claim 32

, wherein said delivering step is performed by the subject inhaling a quantity of gaseous ¹²⁹Xe.

34. A method according to

claim 33

, wherein said positioning step includes positioning the patient in close proximity to a cardiac coil configured to spatially limit the excitation pulses transmitted to the subject.

35. A method according to

claim 34

, wherein said generating step uses a volume selective pulse-gradient combination.

36. A method according to

claim 32

, wherein said exciting step is directed to the target imaging region such that said exciting step is selectively delivered to spatially limit the depolarizing effect of the excitation pulse on the polarized gas outside the selected imaging region.

37. A method according to

claim 33

, wherein said excitation pulse has a frequency which corresponds to the resonance of the dissolved polarized ¹²⁹Xe, and wherein the excitation frequency is selected such that it has a narrow frequency bandwidth.