Why does MRI receive poor signal from lung tissue?

MRI receives poor signal from lung tissue primarily due to low proton density. The lungs contain a significant amount of air, which leads to a decreased concentration of protons available for MR imaging. Proton density is critical in producing a strong MR signal; when the density of protons is low, as it is in lung tissue because of the presence of air, the resulting signal is weak.

This low proton density limits the amount of information that can be obtained from lung scans, making it challenging for MRI to produce clear and informative images of lung structures compared to other tissues that have higher concentrations of protons. Additionally, the air-filled spaces disrupt the uniformity of the magnetic field, further impacting image quality.

In contrast to fat content or magnetic susceptibility, which can affect image contrast and quality in various ways, the primary issue with lung tissue is its inherent low proton density due to its structure and composition. This is why MRI is not typically the preferred imaging modality for lung evaluation, with techniques like CT scanning providing more effective visualization of pulmonary anatomy.