It is therefore suitable for imaging the lung parenchyma but not for detecting, for example, mass lesions. Because of the increased time and radiation required to perform contiguous thin slices, the slices are typically separated along the z axis by an interval of around 10 mm, which minimises total radiation exposure but images only 10 percent of the lung. The high-resolution technique traditionally involves axial or 2-dimensional scanning, i.e., subjects are stationary during a single tube rotation to acquire a single cross-sectional slice. The physical size of the X-ray detectors is therefore one of the determinants of resolution, while scanning technique is the other and more dominant determinant of spatial resolution. High-resolution CT achieves its increased spatial resolution by the use of thinner detectors, which allows the effective thickness of the axial slices to be reduced, usually to around 1 mm. Early scanners used relatively thick, contiguous slices that were obtained along the cranio-caudal (z) axis as the patient was moved stepwise through the scanner. The digitised image slices are comprised of pixels with relative ‘densities’ that are representative of the tissue density in that location. Measuring the attenuation of narrow X-ray beams as they pass through tissues of varying densities allows the construction of a 2-dimensional (x,y) axial ‘slice’ through the body. The technology involves an X-ray beam source with a row of detectors positioned opposite-the source and detectors are assembled in a circular arrangement that rotates around the patient through 180 degrees. X-ray computed tomography (CT) has been in commercial use since 1972 ( 3), and has been revolutionary in providing insight into pulmonary structure and function in vivo. High-resolution computed tomography (HRCT) We will also speculate on the future place of these techniques among the assortment of tools available to clinicians for managing COPD. A large focus will be on their role in furthering our understanding of pathophysiology, clinical phenotyping and response to treatment. In this review, we will describe advanced imaging modalities that are currently in use, either clinically or in a research setting, at varying stages of development. The different modalities vary greatly in terms of temporal and spatial resolution, and each has its own advantages and disadvantages. Depending on the resolution of the images, information can be obtained down to the alveolar level ( 2). In combination, these imaging data expose a remarkable degree of regional variation in lung function. Functional data can also be acquired, often in real-time, and co-registered with the anatomical images. Until recently, these structural and physiological components have been studied in isolation, with inferences made about their relationship.Īdvanced imaging techniques allow detailed anatomical and structural data to be acquired in vivo. The measureable physiological correlate of these changes is airflow obstruction, as indicated by a reduced spirometric ratio. A better understanding of its pathophysiology, early detection and effective treatments is therefore imperative.ĬOPD involves at least two well-defined pathological features, namely parenchymal lung destruction (emphysema) and the loss or narrowing of airways (termed airways disease). Its impact is significant and increasing: COPD is predicted to be the 4 th leading cause of death and the 7 th leading contributor to the global burden of disease by 2030 ( 1). Accepted for publication Nov 10, 2014.Ĭhronic obstructive pulmonary disease (COPD) is a major cause of morbidity and mortality world-wide. Keywords: Chronic obstructive pulmonary disease (COPD) respiratory physiology medical imaging pulmonary ventilation respiratory function tests
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