Mixing oxygen with hyperpolarized (3)He for small-animal lung studies

Area of Science:

• Medical Imaging
• Pulmonary Medicine
• Biophysics

Background:

• Hyperpolarized helium (HP (3)He) MRI enables direct imaging of gas spaces in small animal lungs.
• Traditional methods alternate HP (3)He with air, limiting efficiency for extensive imaging or disease studies.
• Oxygen (O(2)) can depolarize HP (3)He, reducing signal quality.

Purpose of the Study:

• To develop and validate a method for simultaneously delivering O(2) and HP (3)He during mechanical ventilation for small animal lung MRI.
• To assess the impact of O(2) co-delivery on HP (3)He polarization and signal loss.
• To evaluate the benefits of simultaneous O(2)/HP (3)He delivery for imaging efficiency and physiological stability.

Main Methods:

• A computer-controlled ventilator was modified with a custom breathing valve to mix O(2) and HP (3)He before each breath.
• The HP (3)He T(1) relaxation time was measured in guinea pig lungs during simultaneous O(2)/HP (3)He ventilation.
• Signal loss due to O(2) depolarization was calculated based on imaging time and T(1) relaxation.

Main Results:

• Simultaneous O(2)/HP (3)He ventilation resulted in an HP (3)He T(1) relaxation time of approximately 20 seconds in guinea pig lungs.
• This is comparable to the 30-second T(1) observed with alternate air/HP (3)He breathing.
• Signal loss due to O(2) contact during short (500 ms) imaging breaths was calculated to be less than 5%.

Conclusions:

• Mixing HP (3)He with O(2) during ventilation is feasible for small animal lung MRI.
• This method offers advantages including shorter imaging times and improved physiological stability.
• The minimal signal loss is outweighed by the practical benefits for high-resolution and disease-specific pulmonary imaging.