Fig. 2.

Hyperpolarized ³He-MRI coregistered with ¹H-MRI as well as 4DCT acquired within 7 days in a single non-small cell lung cancer patient. Top: axial reconstructions; bottom: coronal slices. Magnetic resonance imaging (MRI) was obtained in the coronal plane during inspiration breath hold, after inhalation of a 1 liter gas mixture of hyperpolarized ³He and ultra-high purity N₂ gas from functional residual capacity. ¹H-MRI preceded ³He-MRI by ∼5 min and the ¹H- and ³He-MRI slices were rigidly coregistered using the carina for fiducial landmarks. To generate the 4DCT ventilation maps, first, thoracic CT images were acquired during a single tidal breathing maneuver (120 kV, 60–120 mA, rotation time of 0.5 s, 360° reconstruction, pitch <0.1). CT images were reconstructed at 10 different respiratory phases and tagged as a percent of full inspiration, with in plane resolution of 1.0 mm. Deformable image registration methods were used to generate a ventilation map. Coregistered ¹H (gray scale)- and ³He-MRI gas distribution images show gas in red, and focal ventilation defects are clearly shown where the ¹H thoracic cavity is exposed (in black) in the absence of gas. 4DCT ventilation maps are color-coded differently such that red, orange, and yellow correspond to regions of greater ventilation; and blue, purple, and black correspond to regions of lower or no ventilation with green representing average values. Note that there is a qualitative regional correspondence between 4DCT regions of decreased ventilation and MRI regions of ventilation defects.