Abstract
Beyond being a substitute for X-ray, computed tomography, and scintigraphy, magnetic
resonance imaging (MRI) inherently combines morphologic and functional information
more than any other technology. Lung perfusion: The most established method is first-pass contrast-enhanced imaging with bolus injection
of gadolinium chelates and time-resolved gradient-echo (GRE) sequences covering the
whole lung (1 volume/s). Images are evaluated visually or semiquantitatively, while
absolute quantification remains challenging due to the nonlinear relation of T1-shortening
and contrast material concentration. Noncontrast-enhanced perfusion imaging is still
experimental, either based on arterial spin labeling or Fourier decomposition. The
latter is used to separate high- and low-frequency oscillations of lung signal related
to the effects of pulsatile blood flow. Lung ventilation: Using contrast-enhanced first-pass perfusion, lung ventilation deficits are indirectly
identified by hypoxic vasoconstriction. More direct but still experimental approaches
use either inhalation of pure oxygen, an aerosolized contrast agent, or hyperpolarized
noble gases. Fourier decomposition MRI based on the low-frequency lung signal oscillation
allows for visualization of ventilation without any contrast agent. Respiratory mechanics: Time-resolved series with high background signal such as GRE or steady-state free
precession visualize the movement of chest wall, diaphragm, mediastinum, lung tissue,
tracheal wall, and tumor. The assessment of volume changes allows drawing conclusions
on regional ventilation. With this arsenal of functional imaging capabilities at high
spatial and temporal resolution but without radiation burden, MRI will find its role
in regional functional lung analysis and will therefore overcome the sensitivity of
global lung function analysis for repeated short-term treatment monitoring.
Keywords
functional MRI lung - ventilation - perfusion - respiratory mechanics