Pulsed 17O2 Inhalation Ventilation for MRI Metabolism Imaging
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Solution Overview
Problem
Current methods for delivering 17O2 for MRI imaging face challenges in interpreting regional cerebral metabolic rate of oxygen consumption (CMRO2) due to diffusion and convection of metabolically produced H217O, which complicates the interpretation of MRI signals and require expensive and inefficient gas recovery systems.
Innovation Solution
A system for mechanical ventilation that enables a brief pulse of 17O2 inhalation with a step increase in concentration, allowing for simpler interpretation of MR imaging signals by minimizing the impact of H217O diffusion and convection, and incorporates a mechanism for recovering enriched exhaled gas.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If 17O2 is delivered as a continuous or long-duration inhalation, then sufficient 17O is delivered to tissues for detection, but H217O diffuses out of local tissue and convects through venous circulation, complicating MRI signal interpretation
Solution Approach 1:
The patent applies periodic action by delivering 17O2 in brief pulsed inhalations (typically 1-3 seconds) rather than continuous inhalation. This pulsed delivery creates discrete temporal windows for H217O production that can be distinguished from recirculated water, simplifying the interpretation of MRI signals while maintaining sufficient signal accumulation for accurate CMRO2 measurement.
Solution Approach 2:
The patent uses preliminary action by pre-delivering a breath-hold of 17O2-enriched gas before the imaging sequence. This preliminary delivery ensures that 17O is already present in the tissues when imaging begins, allowing for accurate measurement without requiring complex continuous delivery systems during the imaging process.
2Quantity of substance
If 17O2 inhalation duration is extended to ensure sufficient signal, then more H217O is produced for detection, but recirculation of H217O from other tissues increases, complicating regional CMRO2 interpretation
Solution Approach 1:
By using brief pulsed inhalation of 17O2, the patent creates a temporal pattern where H217O is produced in discrete bursts. The imaging sequence is synchronized to capture signals during specific time windows after pulse delivery, allowing quantification of locally produced H217O before significant recirculation occurs, thus preserving regional information while accumulating sufficient signal.
Solution Approach 2:
The patent employs feedback by using the measured MRI signal to calculate CMRO2 values, which then inform adjustments in subsequent 17O2 delivery. The system monitors the accumulated signal and can adjust the number or intensity of pulses to achieve optimal signal-to-noise ratio while minimizing recirculation effects.
3Ease of operation
If conventional mechanical ventilation systems are used for 17O2 delivery, then gas delivery is simplified, but rapid step changes in gas concentration cannot be achieved, reducing imaging accuracy
Solution Approach 1:
The patent segments the gas delivery process into distinct phases: a brief 17O2-enriched inhalation pulse followed by a return to baseline gas composition. This segmentation creates sharp temporal transitions in gas concentration that improve the precision of H217O production timing, enabling more accurate CMRO2 measurement while using standard ventilation equipment.
Solution Approach 2:
The patent changes the concentration parameter of delivered gas over time by introducing brief pulses of 17O2-enriched gas (e.g., 20-100% enrichment) against a background of normal or hyperoxic gas. This temporal variation in gas concentration parameters enables precise timing of H217O production events while maintaining compatibility with conventional ventilation systems.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach simplifies the interpretation of MR imaging signals by focusing on locally produced H217O, reduces the need for complex input function measurement, and efficiently recovers expensive 17O2 gas, enhancing the accuracy and cost-effectiveness of CMRO2 imaging.
Implementation Method 1
17O is delivered to all tissues and metabolized in the mitochondria to produce H217O
Implementation Method 2
measuring the changes in T2 or T1ρ weighted proton NMR signal caused by 17O—1H scalar coupling and proton chemical exchange
Implementation Method 3
17O—1H scalar coupling
Implementation Method 4
proton chemical exchange
Implementation Method 5
H217O produced in the mitochondria, but also diffuses out of the local tissue to the venous circulation
Implementation Method 6
convectively transported to arterial blood
Data Source
AI summary
Prior approaches have delivered 17O2 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.