Detection of regional radiation-induced lung injury using hyperpolarized 129 Xe chemical shift imaging in a rat model involving partial lung irradiation: Proof-of-concept demonstration

Abstract

PurposeThe purpose of this work was to use magnetic resonance imaging (MRI) of hyperpolarized (HP) 129Xe dissolved in pulmonary tissue (PT) and red blood cells (RBCs) to detect regional changes to PT structure and perfusion in a partial-lung rat model of radiation-induced lung injury and compare with histology.Methods and materialsThe right medial region of the lungs of 6 Sprague-Dawley rats was irradiated (20 Gy, single-fraction). A second nonirradiated cohort served as the control group. Imaging was performed 4 weeks after irradiation to quantify intensity and heterogeneity of PT and RBC 129Xe signals. Imaging findings were correlated with measures of PT and RBC distribution.ResultsAsymmetric (right vs left) changes in 129Xe signal intensity and heterogeneity were observed in the irradiated cohort but were not seen in the control group. PT signal was observed to increase in intensity and heterogeneity and RBC signal was observed to increase in heterogeneity in the irradiated right lungs, consistent with histology.ConclusionRegional changes to PT and RBC 129Xe signals are detectable 4 weeks following partial-lung irradiation in rats.

Physiological gas exchange mapping of hyperpolarized 129Xe using spiral‐IDEAL and MOXE in a model of regional radiation‐induced lung injury

“…One cohort was used as nonirradiated controls. The other cohort was irradiated with 20 Gy using a 1 × 1 cm 2 collimated beam targeting the right‐medial lung as previously described . Figure illustrates a representative treatment plan.…”

“…The calculated right‐ and left‐medial PTA, PRA, c v,PTA, and c v,PRA for all analyzed rats were then compared within and between groups. Histology preparation and micrograph segmentation have been previously described in detail …”

“…A recent study by our group introduced a new partial‐lung irradiation rat model that was imaged at 4 weeks postirradiation . The model involved focal irradiation of the right‐medial lung only, thereby localizing injury to a specific known region using on‐board image guidance.…”

“…This irradiation scheme more closely mimics a clinical distribution of dose than whole or hemithoracic irradiations and limits compounding of damage and systemic pulmonary dysfunction due to the small volume of tissue irradiated. In our previous study, RILI was detected using two‐dimensional chemical shift imaging (2DCSI) . Asymmetric changes in tissue signal intensity, tissue signal heterogeneity, and RBC signal heterogeneity were observed between the right and left lungs.…”

“…To improve upon these shortcomings, we analyze HP 129 Xe spiral‐IDEAL images acquired in the same rat cohort using the same partial‐lung model of RILI, to extend the work to physiological gas exchange mapping based on fully spatial, spectral, and temporally resolved imaging. Gas exchange modeling of the spiral‐IDEAL images is performed on a voxel‐by‐voxel basis using the Model of Xenon Exchange (MOXE) and regional lung parameter estimates which govern gas exchange are extracted.…”