Submited by Brennan LeRoux, SRT

Computed tomography (CT) imaging is increasingly being employed in the diagnosis of Acute Respiratory Distress Syndrome (ARDS), and for the evaluation of lung aeration. CT imaging has been proven to have superior accuracy in diagnosis to that of a chest X-ray (CXR), and remains the gold standard for lung imaging (Zomparti, Ciccarese & Fasano, 2014). As effective as CT imaging is, concern exists with patient exposure to ionizing radiation during imaging (Ball, Braune, Speith, et al., 2018).

Much current study is focused on reducing the level of radiation produced by CT imaging. Chiumello, Langer, Vecchi, et al. (2014) studied the usage of low dose CT scanning in an attempt to reduce ionizing radiation exposure, and found a 30% reduction in radiation did not significantly impact quantitative or visual image results (p. 699). Similarly, Ball et al. (2017a) studied even lower levels of radiation in CT imaging, an approximate reduction of 97% over conventional scans, and found comparable quantitative results with a longer procedure time (Discussion section, para 1-3).

Competing imaging technologies may offer the answers in patients with contraindications to the use of ionizing radiation. Lung ultrasound (LUS) and electrical impedance tomography (EIT) are relatively simple and non-invasive imaging techniques that can be used both as a supplement to traditional CT scanning, or as a replacement in contraindicated cases (Ball et al., 2017b, emerging imaging techniques at the bedside section, para 1-9). With the usage of competing imaging techniques, a primary focus is on reducing the risk-to-benefit ratio of lung assessments. (Ball et al., 2017a, Discussion section, para 2).

A lesser studied, but potentially promising avenue of lung diagnostic imaging is magnetic resonance imaging (MRI), a technology free of any exposure to ionizing radiation. In 2004, a study conducted by Bankier and colleagues was able to show that equal changes in lung tissue produced equal, corresponding changes in MRI signal intensity (Bankier, O’Donnell, Mai, et al., 2004, Discussion section, para 5). Ball  et al. (2018) studied the usage of Magnetic Resonance Imaging (MRI) in ARDS as to identify a competing imaging strategy for cases with contraindications to ionizing radiation. This was conducted both in ex vivo swine lung to assess the efficacy of MRI in estimating lung aeration, as well as comparable validation in human MRI scans (Methods section, para 1-4). By studying MRI signal intensity, Ball and colleagues (2018) found both a linear relationship between gas content and MRI signal intensity, and were able to determine areas of poor aeration in human MRI films (Conclusion section, para 1).

There are several exciting applications for the use of MRI imaging in cases of respiratory distress. Infant patients are particularly susceptible to ionizing radiation, and concern exists over the usage of CT scanning in infant and pediatric populations, as increasing exposure to ionizing radiation as a child has been associated with certain brain tumours and leukemia (Pearce, Salotti, Little, et al., 2012). MRI scanning by comparison carries no exposure to any ionizing radiation, and can be repeated as required with no risk of cumulative exposure. Effective imaging is key to diagnosing and managing cases of respiratory distress (Ball et al., 2018, Introduction section, para1), and imaging techniques with less contraindications are a welcome tool in the tool belt of radiologists, respiratory therapists and internists.

References

Ball, L., Braune, A., Corradi, F., Brusasco, C., Garlashci, A., Kiss, T., Bluth, T., Simonassi, F., Bergamaschi, A., Kotzerke, J., Schultz, M. J., de Abreu, M. G. & Pelosi, P. (2017a). Ultra-low-dose sequential computed tomography for quantitative lung aeration assessment-a translational study Intensive Care Medicine Experimental, 5(19), 691–699. doi: 110.1186/s40635-017-0133-6

Ball, L., Braune, A., Spieth, P., Herzog, M., Chandrapatham, K., Hietschold, V., Schultz, M., Patroniti, N., Pelosi, P. & Gama D, M. (2018). Magnetic Resonance Imaging for Quantitative Assessment of Lung Aeration: A Pilot Translational Study. Frontiers in Physiology, 9(1120). doi:10.3389/fphys.2018.01120.

Ball, L., Verseci, V., Constantino, F., Chandrapatham, K. & Pelosi, P. (2017b). Lung imaging: how to get better look inside the lung. Annals of Translational Medicine, 5(294). doi: 10.21037/atm.2017.07.20

Bankier, A. A., O’Donnell, C. R., Mai, V. M., Storey, P., De Maertelaer, V., Edelman, R. R. & Chen, Q. (2004). Impact of lung volume on MR signal intensity changes of the lung parenchyma. Journal of Magnetic Resonance Imaging, 20(6), 961–966. doi: 10.1002/jmri.20198

Chiumello, D., Langer, T., Vecchi, V., Luoni, S., Colombo, A., Brioni, M., Froio, S., Cigada, I., Coppola, S., Protti, A., Lazzerini, M. & Gattinoni L. (2014). Low-dose chest computed tomography for quantitative and visual anatomical analysis in patients with acute respiratory distress syndrome. Intensive Care Medicine, 40(5), 691–699. doi: 10.1007/s00134-014-3264-1

Zompatori, M., Ciccarese, F. & Fasano, L. (2014). Overview of current lung imaging in acute respiratory distress syndrome. European Respiratory Review, 2014(23), 519-530. doi: 10.1183/09059180.00001314

Pearce, M. S., Salotti, J. A., Little, M. P., McHugh, K., Lee, C., Kim, K. P., Howe, L., Ronckers, C., Rajaraman, P., Craft, A., Parker, L. & Berrington de González, A. (2012). Radiation exposure from CT scans in childhood and subsequent risk of leukaemia and brain tumours: a retrospective cohort study. Lancet, 380(9840), 499–505. doi:10.1016/S0140-6736(12)60815-0

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