Intrapulmonary 3He Gas Distribution Depending on Bolus Size and Temporal Bolus Placement

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Abstract

Objective:

Dynamic ventilation 3He-MRI is a new method to assess pulmonary gas inflow. As differing airway diameters throughout the ventilatory cycle can influence gas inflow this study intends to investigate the influence of volume and timing of a 3He gas bolus with respect to the beginning of the tidal volume on inspiratory gas distribution.

Materials and Methods:

An ultrafast 2-dimensional spoiled gradient echo sequence (temporal resolution 100 milliseconds) was used for dynamic ventilation 3He-MRI of 11 anesthetized and mechanically ventilated pigs. The applied 3He gas bolus was varied in volume between 100 and 200 mL. A 150-mL bolus was varied in its application time after the beginning of the tidal volume between 0 and 1200 milliseconds. Signal kinetics were evaluated using an in-house developed software after definition of parameters for the quantitative description of 3He gas inflow.

Results:

The signal rise time (time interval between signal in the parenchyma reaches 10% and 90% of its maximum) was prolonged with increasing bolus volume. The parameter was shortened with increasing delay of 3He application after the beginning of the tidal volume. Timing variation as well as volume variation showed no clear interrelation to the signal delay time 10 (time interval between signal in the trachea reaches 50% of its maximum and signal in the parenchyma reaches 10% of its maximum).

Conclusions:

Dynamic ventilation 3He-MRI is able to detect differences in bolus geometry performed by volume variation. Pulmonary gas inflow as investigated by dynamic ventilation 3He-MRI tends to be accelerated by an increasing application delay of a 3He gas bolus after the beginning of the tidal volume.

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