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Why is MRI less useful for imaging air-filled lungs?

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Medical illustration of the human chest showing the lungs, diaphragm, ribs, trachea, bronchus, and bronchioles, with one lung cut away to reveal internal structures. — respiratory disease The bronchioles of the lungs are the site where oxygen is exchanged for carbon dioxide during the process of respiration. Inflammation, infection, or obstruction of the bronchioles is often associated with acute or chronic respiratory disease, including bronchiectasis, pneumonia, and lung abscesses.

Magnetic resonance imaging (MRI) is less useful for imaging air-filled lungs primarily because the technique relies on detecting signals from hydrogen atoms, which are abundant in water-rich tissues but sparse in air-filled spaces. Because air contains very little hydrogen, it produces virtually no signal, making it difficult for MRI to generate detailed images of the lungs' internal structures.12

Furthermore, MRI is highly sensitive to motion artifacts due to its relatively long scanning times. Because the chest is subject to constant movement from breathing and the beating heart, these artifacts significantly degrade image quality in the thoracic region. Consequently, while MRI is valuable for visualizing the heart and blood vessels within the thorax, it remains limited in its ability to examine the air-filled portions of the lungs.12