Dual-energy digital subtraction chest radiography: technical considerations

Our plain-English summary of Dual-energy digital subtraction chest radiography: technical considerations, by G.J. Whitman, L.T. Niklason, M. Pandit, et al (Current Problems in Diagnostic Radiology, 2002).

The study

• Authors: G.J. Whitman, L.T. Niklason, M. Pandit, L.C. Oliver, E.H. Atkins, O. Kinnard, A.H. Alexander, M.K. Weiss, K. Sunku, E.S. Schulze, R.E. Greene
• Journal: Current Problems in Diagnostic Radiology
• Published: 2002;31(2):48-62
• Cited by: 22 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

In the evaluation of asbestos-related pulmonary and pleural abnormalities, conventional chest radiography has been shown to have a low sensitivity for the detection of lung nodules and subtle interstitial disease. Pleural plaques may simulate pulmonary nodules, and interstitial processes can be masked by adjacent pleural abnormalities. Dual-energy digital subtraction chest radiography may enable investigators to characterize asbestos-related pulmonary and pleural abnormalities with greater accuracy. "Soft-tissue" images, designed to remove pleural calcifications, may allow for better evaluation of the lung parenchyma. "Bone" images, designed to remove soft-tissue structures, may enhance the detection of pleural calcifications. In this pictorial essay we illustrate the methods, technical considerations, and limitations of dual-energy digital subtraction chest radiography performed with global subtraction weighting factors.

In plain English

This article was a pictorial essay, an illustrated technical description, of dual-energy digital subtraction chest radiography (DSR) using global subtraction weighting factors. The authors performed DSR on 18 men, average age 59, with a history of occupational exposure to asbestos. A single x-ray exposure captured two digital images, using two storage phosphor plates with a thin copper filter between them. A workstation combined these into "soft-tissue" images, designed to remove pleural calcifications, and "bone" images, designed to remove soft tissue. In one illustrated case, the soft-tissue image removed some pleural calcifications from the middle of the chest, but thick calcifications along the diaphragms remained. The authors reported that factors chosen for the midthorax were not appropriate for the mediastinal, paraspinal, cardiac and diaphragmatic regions. They also reported that alignment of the two images was uneven in some cases. The essay showed illustrated examples, not counts or measures of diagnostic accuracy. The authors concluded that the technique may prove useful in patients with asbestos-related pleural disease or pulmonary fibrosis, and that pixel-by-pixel subtraction may ease the limits of global factors.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Pictorial essay (illustrated technical description of an imaging method), with DSR performed on a small group of men
• Who was studied: 18 men, average age 59 years, with a history of occupational exposure to asbestos; project originated at Massachusetts General Hospital; dates not given
• Exposure: History of occupational exposure to asbestos (fiber types, jobs and doses not given). The imaging method was single-exposure dual-energy digital subtraction chest radiography, phototimed at 141 kVp, with a copper filter between two storage phosphor plates.
• Main results:
  • In a 62-year-old man with extensive pleural calcifications, the global factors designed to subtract calcium from the midthorax did not remove the thick calcifications from the diaphragmatic region.
  • In the same man, the frontal digital radiograph gave better delineation of the mediastinum than the conventional radiograph obtained with the same dose.
  • Because both images came from a single exposure, there was no misregistration caused by patient motion.
  • In some cases, spatial registration of the low- and high-energy images was not uniform, with adequate and suboptimal regions on the same subtraction image.
  • The x-ray dose reaching the back imaging plate was reduced to one fifth to one tenth of the dose at the front plate, which increased quantum noise.
• The authors' conclusion: The authors concluded that the technique may prove useful in evaluating patients with asbestos-related pleural disease, pulmonary fibrosis, or both, or other complex pleuroparenchymal disease. They stated that DSR depends on proper spatial registration and appropriate weighting factors, and that pixel-by-pixel subtraction algorithms may alleviate the limitations of global factors.
• Limitations the authors state:
  • The subtraction techniques used had limited value for evaluating the mediastinal and subdiaphragmatic structures, because global weighting factors may not apply to all areas of the chest.
  • Beam-hardening corrections and noise-suppression algorithms were not used.
  • Magnification differences between imaging plates may cause incomplete signal cancellation at the edges of the image.

Topics

Medical terms in this study, explained in our Lexicon: Interstitial, Pleural Plaques, Pleural Calcification, Parenchyma.

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