MRI offers improved soft-tissue contrast, with advanced sequences able to identify soft-tissue characteristics to the cellular level (ie, diffusion-weighted imaging and spectroscopy). Advanced techniques allow for calculation of total lung water density, which has been shown to correlate with disease severity in adult patients with cystic fibrosis [45]. With the addition of intravenous (IV) contrast, the vascular nature of an abnormality is exquisitely imaged and has been shown to be as accurate as contrast-enhanced CT for the evaluation for pulmonary embolism [35]. IV contrast also offers the evaluation of pulmonary perfusion [46]. Limitations of pulmonary MRI include low signal-to-noise ratio (especially with a normally aerated lung), low spatial resolution, and need for adequate breath-hold technique or respiratory gating [46]. Parenchymal lung abnormalities naturally increase cellular proton density and/or water content while displacing low signal gas, providing contrast for visualization [35]. Despite limitations, pulmonary MRI has been shown to have noninferior diagnostic quality when compared with CT [46,47]. Ohno et al [47] analyzed 85 consecutive patients with high-resolution pulmonary MR using ultrashort time to echo and compared findings with both standard CT and LDCT. The authors found equivalent diagnostic efficacy for all observed findings, noting decreased sensitivity and image quality when evaluating for emphysema, bronchiectasis, and reticular opacity. The authors concluded that based on their assessment, ultrashort time to echo pulmonary MR is equivalent to LDCT imaging [47]. There is no relevant literature evaluating IV contrast versus noncontrast MRI in the setting of chronic cough, and decisions may need to be made on a case-by-case basis. Investigational contrast agents may prove useful in the future. Hyperpolarized gas MRI is an example, which is currently FDA approved for investigational use [44,48].
Chronic Cough. MRI offers improved soft-tissue contrast, with advanced sequences able to identify soft-tissue characteristics to the cellular level (ie, diffusion-weighted imaging and spectroscopy). Advanced techniques allow for calculation of total lung water density, which has been shown to correlate with disease severity in adult patients with cystic fibrosis [45]. With the addition of intravenous (IV) contrast, the vascular nature of an abnormality is exquisitely imaged and has been shown to be as accurate as contrast-enhanced CT for the evaluation for pulmonary embolism [35]. IV contrast also offers the evaluation of pulmonary perfusion [46]. Limitations of pulmonary MRI include low signal-to-noise ratio (especially with a normally aerated lung), low spatial resolution, and need for adequate breath-hold technique or respiratory gating [46]. Parenchymal lung abnormalities naturally increase cellular proton density and/or water content while displacing low signal gas, providing contrast for visualization [35]. Despite limitations, pulmonary MRI has been shown to have noninferior diagnostic quality when compared with CT [46,47]. Ohno et al [47] analyzed 85 consecutive patients with high-resolution pulmonary MR using ultrashort time to echo and compared findings with both standard CT and LDCT. The authors found equivalent diagnostic efficacy for all observed findings, noting decreased sensitivity and image quality when evaluating for emphysema, bronchiectasis, and reticular opacity. The authors concluded that based on their assessment, ultrashort time to echo pulmonary MR is equivalent to LDCT imaging [47]. There is no relevant literature evaluating IV contrast versus noncontrast MRI in the setting of chronic cough, and decisions may need to be made on a case-by-case basis. Investigational contrast agents may prove useful in the future. Hyperpolarized gas MRI is an example, which is currently FDA approved for investigational use [44,48].