METHOD AND APPARATUS FOR PROVIDING PULSES INHALATION OF 17O2 FOR MAGNETIC RESONANCE IMAGING OF CEREBRAL METABOLISM

• US 20100282258A1
• Filed: 07/18/2008
• Published: 11/11/2010
• Est. Priority Date: 07/20/2007
• Status: Active Grant

• Current Assignee: Trustees Of The University Of Pennsylvania (University of Pennsylvania)
• Original Assignee: Trustees Of The University Of Pennsylvania (University of Pennsylvania)
• Inventors: Tailor, Dharmesh R., Baumgardner, James E., Reddy, Ravinder
• Granted Patent: US 8,554,305 B2
• Time in Patent Office: Days
• US Class Current: 128/204.23
• CPC Class Codes: A61B 5/0033 Features or image-related aspects of imaging apparatus classified in A61B5/00, e.g. for MRI, optical tomography or impedance tomography apparatus; arrangements of imaging apparatus in a room image data processing or generation G06T
• CPC Class Codes: A61B 5/055 involving electronic [EMR] or nuclear [NMR] magnetic resonance, e.g. magnetic resonance imaging
• CPC Class Codes: A61B 5/0833 Measuring rate of oxygen consumption
• CPC Class Codes: A61B 5/0836 Measuring rate of CO2 production
• CPC Class Codes: A61B 5/7207 of noise induced by motion artifacts
• 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 33/56366 Perfusion imaging

Abstract

Prior approaches have delivered O₂ to a subject by inhalation, but the relationship between local signal changes and metabolism has been complicated by H₂¹⁷O created in non-cerebral tissues. During a brief pulse of ¹⁷O₂ inhalation, this arterial input function for H₂¹⁷O is negligible due to convective transport delays. Additional delays in the arterial input function due to restricted diffusion of water makes pulsed inhalation of ¹⁷O₂ even more effective. Accordingly, ventilator system are provided to deliver ¹⁷O₂ as a brief pulse to a subject. Subsequent MR imaging demonstrates delayed appearance of H₂¹⁷O in the cerebral ventricles, suggesting that the arterial input function of H₂¹⁷O is delayed by restricted water diffusion in addition to convective transit delays. Delivery as a brief pulse therefore offers significant advantages in relating MR signal changes directly to metabolism.

Claims

1. A method of administering ¹⁷O₂ to a patient for magnetic resonance imaging a region of interest, comprising:

providing ¹⁶O₂ to the patient by inhalation; and

applying a pulse of ¹⁷O₂ by inhalation comprising an approximately step increase in ¹⁷O₂, a duration of said pulse selected so as to be shorter than a diffusion time of metabolized H₂¹⁷O in the patient from the lungs to the region of interest.

2. The method of claim 1, wherein the pulse of ¹⁷O₂ has a duration in a range of from about 30 seconds to about 60 seconds.

3. The method of claim 1, comprising the further step of imaging during the duration of said pulse.

4. The method of claim 3, wherein the region of interest is the brain, comprising the further step of calculating cerebral metabolic rate of oxygen consumption (CMRO₂) from the amount of ¹⁷O₂ measured in an image taken during the imaging step by calculating:

CMRO₂=k₁(dC_b(t)/dt)/C_a(t)

where C_a(t) and C_b(t) are the ¹⁷O₂ concentrations in arterial blood as a function of time at times a and b, and k₁ is a conversion constant.

5. The method of claim 1, further comprising recovering unused ¹⁷O₂ exhaled by the patient.

6. The method of claim 1, comprising the further step of assisting exhalation by the patient using a pump.

7. The method of claim 6, comprising the further step of monitoring the pressure of exhaled gases and adjusting an exhalation speed of said pump so as to adjust the exhalation pressure to a target exhalation pressure.

8. A ventilation apparatus, comprising:

means for selecting either a source of ¹⁶O₂ or ¹⁷O₂ ;

an inhalation pump for pumping the selected source to a patient at a first pressure;

an exhalation pump for pumping exhaled gases at a second pressure; and

means for controlling said selecting means so as to apply a pulse of ¹⁷O₂ to the patient, said pulse comprising an approximately step increase in ¹⁷O₂ for a duration selected so as to be shorter than a diffusion time of metabolized H₂¹⁷O in the patient from the lungs to a region of interest in the patient'"'"'s body.

9. The apparatus of claim 8, wherein the pulse of ¹⁷O₂ has a duration in a range of from about 30 seconds to about 60 seconds.

10. The apparatus of claim 8, wherein the selecting means comprises a valve.

11. The apparatus of claim 8, further comprising means for recovering unused ¹⁷O₂ exhaled by the patient.

12. The apparatus of claim 11, wherein said recovering means comprises a sampling bag that receives exhaled gases output by said exhalation pump and a CO₂ absorber that removes CO₂ from the exhaled gases before the exhaled gases reach said sampling bag.

13. The apparatus of claim 8, wherein the region of interest is the brain, wherein said processor calculates cerebral metabolic rate of oxygen consumption (CMRO₂) from the amount of ¹⁷O₂ measured during said duration by calculating:

CMRO₂=k₁(dC_b(t)/dt)/C_a(t)

where C_a(t) and C_b(t) are the ¹⁷O₂ concentrations in arterial blood as a function of time at times a and b, and k₁ is a conversion constant.

14. The apparatus of claim 8, further comprising a pressure transducer that monitors the second pressure and adjusts an exhalation speed of said exhalation pump so as to adjust the second pressure to a target exhalation pressure.