Hence, current therapy is guided largely by patients’ symptoms and survival 5– 7. Additionally, these metrics largely rely on subject effort, causing significant measurement uncertainty and variability. This insensitivity of PFTs to the functioning of the distal lung ( Fig 1) has led these regions to be referred to as the ‘silent zone’ 4. However, by assessing the lung only on a global basis, PFT metrics generally lack the ability to detect functional changes associated with the small airways and gas exchange regions. The current gold standard for diagnosis and monitoring treatment of pulmonary diseases is spirometric pulmonary function testing (PFTs). However, equally problematic is the lack of sensitive biomarkers that can be used to diagnose these diseases earlier, better monitor progression and show early therapeutic response. This is partially attributable to a lack of viable therapeutic options to treat the underlying diseases 3. Furthermore, interstitial lung diseases (ILD), while less prevalent than COPD or asthma, also have a high morbidity. Similarly, airway diseases such as asthma have a high prevalence and a large economic impact with $56 billion in associated healthcare costs 2. After cardiovascular diseases and cancer, COPD is predicted to be the third leading cause of death in the US 1. Chronic obstructive pulmonary disease (COPD), for example, is an umbrella term for progressive and irreversible obstructive diseases that affect the airways as well as the parenchyma. As a result, they have a high impact on patients’ morbidity, and quality of life. Lung diseases affect the conducting airways, the gas exchange parenchyma or both. With a plethora of contrast mechanisms, hyperpolarized gases and 129Xe in particular, stands to be an excellent probe of pulmonary structure and function, and provide sensitive and non-invasive biomarkers for a wide variety of pulmonary diseases.
The added advantage of 129Xe is its solubility in pulmonary tissue, which allows exploring specific lung function characteristics involved in gas exchange and alveolar oxygenation. Xenon is well tolerated and recent technical advances have ensured that the 129Xe image quality is on par with that of 3He. With the recent scarcity in the supply of 3He the field of hyperpolarized gas imaging shifted to the use of cheaper and naturally available 129Xe. Hyperpolarized helium ( 3He) and xenon ( 129Xe) MR imaging of the lungs provided new sensitive contrast mechanisms to probe changes in pulmonary ventilation, microstructure and gas exchange. Functional imaging today offers a rich world of information that is more sensitive to changes in lung structure and function than traditionally obtained pulmonary function tests.
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