The PA upright chest x-ray (CXR) gives an overview of the thorax for plaquing, interstitial/parenchymal changes, nodules and/or other masses, pleural effusions and diffuse pleural thickening. It is what the ILO (International Labor Organization) form codification and grading is based upon. However the chest wall, pleura, hila, mediastinum and lung parenchyma are superimposed and thus, findings may be overlapping and difficult to separate out from one another; missed and underestimated; or overcalled and overestimated. Oblique views of the chest allow for additional analysis of the lateral chest walls and diaphragms. The lateral view shows the spine in more detail; can improve visualization of diaphragmatic plaquing and can help better localize a nodule/mass or infiltrate.
Supine Spiral CT & Supine HRCT:
The supine computerized tomographic scan of the chest, without iodinated contrast (supine spiral CT scan aka routine CAT scan) when using the smoothed, chest wall/mediastinum image processing, is designed to screen for pleural plaquing and differentiate extra-pleural fat from pleural plaques. It also looks for pulmonary nodules suggestive for carcinoma, pleural effusions, rounded atelectasis and mesotheliomas. Compared with plain radiographs, it is better able to separate out the chest wall, pleura, hila, mediastinum and lung parenchyma for improved delineation of individual findings. It is superior to plain radiographs for the detection of calcification within plaques. When also using the high resolution lung image processing, it shows emphysema in most cases and moderate to severe asbestosis well. Should mild interstitial fibrosis of asbestosis be a concern, then prone HRCT will be necessary because the spiral CT scan is a) performed with relatively thick slices (3 to 10 mm (commonly 5 mm) thick slices; 3 to 10 mm (commonly 5 mm) apart) and b) in the supine position, where localized lung collapse/atelectasis and blood pooling in the posterior aspects of the lungs, causes increased dependent density, the area most often the location of interstitial fibrosis caused by mild asbestosis. The supine, high resolution, thin slice, computerized tomographic scan of the chest, without iodinated contrast (supine HRCT), eliminates the slice thickness issue due to its thin slices (0.0625 to 2.5 mm [commonly 1.0 to 1.25 mm] thick, 0.0625 to 2.5 mm [commonly 1.0 to 1.25 mm] apart), enhancing identification of plaquing, their calcifications, small pulmonary nodules and emphysema, but still has the problem of dependent density interfering with the identification of mild asbestosis, requiring prone HRCT.
The prone high resolution, thin slice, computerized tomographic scan of the chest (prone HRCT), without iodinated contrast, when used with the high resolution lung image processing) is designed to evaluate the lungs for interstitial fibrosis, given its thin slices (0.0625 to 2.5 mm [commonly 1.0 to 1.25 mm] thick slices; 5, 10 or 15 mm apart) and lack of dependent density – lack of gravitational atelectasis and/or blood pooling. There is also improved visualization of emphysema and improved pulmonary nodule characterization, should the slices include such nodules. Improved resolution for pleural plaque formation and their calcifications (provided the additional use of the smoothed, chest wall/mediastinal image processing), but lesser screening for plaques as well nodules occur, due to the skipped spaces between slices, to reduce radiation exposure to the individual scanned.
This article is provided as a public service by Daniel Powers, M.D.: B-Reader and Board-Certified Diagnostic Radiologist, Certified by the American Board of Radiology.
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