Rationale and Objectives
Diffraction-enhanced imaging (DEI) is a type of phase contrast x-ray imaging that has improved image contrast at a lower dose than conventional radiography for many imaging applications, but no studies have been done to determine if DEI might be useful for diagnosing lung injury. The goals of this study were to determine if DEI could differentiate between healthy and injured lungs for a rat model of gastric aspiration and to compare diffraction-enhanced images with chest radiographs.
Materials and Methods
Radiographs and diffraction-enhanced chest images of adult Sprague Dawley rats were obtained before and 4 hours after the aspiration of 0.4 mL/kg of 0.1 mol/L hydrochloric acid. Lung damage was confirmed with histopathology.
Results
The radiographs and diffraction-enhanced peak images revealed regions of atelectasis in the injured rat lung. The diffraction-enhanced peak images revealed the full extent of the lung with improved clarity relative to the chest radiographs, especially in the portion of the lower lobe that extended behind the diaphragm on the anteroposterior projection.
Conclusions
For a rat model of gastric acid aspiration, DEI is capable of distinguishing between a healthy and an injured lung and more clearly than radiography reveals the full extent of the lung and the lung damage.
Diffraction-enhanced imaging (DEI), sometimes called analyzer-based imaging, is a type of phase contrast x-ray imaging that produces contrast not only from the x-ray attenuation in the subject but also from the refraction and small-angle scattering. It has been shown that DEI has significantly improved contrast resolution relative to radiography for a variety of imaging applications, including mammography , cartilage imaging , and bone and bone implant imaging . To date, the vast majority of DEI studies have been conducted at synchrotron research facilities, but recently, x-ray tube–based DEI systems have been developed by Parham et al and Nesch et al ; these systems provide a realistic pathway to clinical DEI, and thus a new emphasis on determining clinical imaging targets for DEI is warranted. Although several studies have shown DEI’s ability to resolve the lung with high contrast , its ability to distinguish between healthy and injured lung has not yet been fully explored. The goal of this study was to determine if DEI, using realistic imaging parameters for a future clinical DEI system, is capable of resolving differences between healthy and injured lung in a rat model of gastric acid aspiration.
Rat Model of Lung Injury
Aspiration of gastric acid into the lungs and the resulting acute pneumonitis was first described by Mendelson in 1946. Small animal models were used from the outset to develop an understanding of the nature of the lung injury. The temporal response of the rat lung to the aspiration of acids of different volumes and pH values was studied by Kennedy et al . The rat lung was found to have a biphasic response to the acid aspiration, with the maximum lung injury, as measured by permeability index, occurring 4 hours after acid aspiration and accompanied by an acute inflammatory response. During this acute inflammatory phase, one would expect to see radiographic evidence of alveolar atelectasis . The combination of this well-understood animal model and the known radiographic findings for this injury makes this an appropriate model of lung injury to study the applicability of DEI in this setting.
DEI
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Materials and methods
Animal Experimental Protocol
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Image Acquisition
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Histology
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Image Processing
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Results
Histology
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Image Comparison
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Discussion
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Acknowledgments
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