Chapter 7 - Hyperpolarized Gas MRI of Radiation-Induced Lung Injury

Abstract

Nonsmall cell lung carcinoma is one of the most fatal cancers and is often treated using thoracic radiotherapy (RT). Unfortunately, the lung is a very radiosensitive organ and radiation-induced lung injury (RILI) is a frequent consequence of thoracic RT, affecting about one in three patients. RILI can significantly limit RT and early detection is vital in order to adjust the treatment plan and improve outcomes. Magnetic resonance imaging (MRI) of hyperpolarized gas (3He and 129Xe) presents an unprecedented opportunity to map anatomical and functional changes associated with RILI. In particular, inhaled hyperpolarized 3He and 129Xe gas are exquisitely sensitive to changes in alveolar microanatomy accompanying radiation pneumonitis and fibrosis through changes in the apparent diffusion coefficient (ADC) of alveolar gas. Additionally, 129Xe dissolves in the parenchymal tissue and red blood cells (RBCs) of the lung and reflects changes in sizes and gas exchange associated with these compartments. In this chapter, the application of hyperpolarized gas (3He and 129Xe) MRI to both humans and rat models of RILI is reviewed and results of experiments measuring 129Xe ADC, gas exchange, and tissue and RBC imaging are presented. These results are consistent with conventional functional (e.g., blood gases) and histological (i.e., tissue density) changes, but with the advantage of noninvasive regional information. Hyperpolarized MRI, especially 129Xe, promises to provide new insight into the pathophysiology of RILI and may give an earlier indication of lung injury associated with RT of thoracic tumors, potentially allowing longitudinal monitoring of treatment and adjustment before the onset of severe pneumonitis and irreversible fibrosis.