Metal artifact reduction by dual energy CT using monoenergetic extrapolation
Objective
The aim of the study was to assess the performance and diagnostic value of a dual energy CT approach to reduce metal artefacts in subjects with metallic implants.
Methods
31 patients were examined in the area of their metallic implants using a dual energy CT protocol (filtered 140 kVp and 100 kVp spectrum, tube current relation: 3:1). Specific post-processing was applied to generate energies of standard 120 and 140 kVp spectra as well as a filtered 140 kVp spectrum with mean photon energies of 64, 69 and 88 keV, respectively, and an optimized hard spectrum of 95-150 keV. Image quality and diagnostic value were subjectively and objectively determined.
Results
Image quality was rated superior to the standard image in 29/31 high energy reconstructions; the diagnostic value was rated superior in 27 patients. Image quality and diagnostic value scores improved significantly from 3.5 to 2.1 and from 3.6 to 1.9, respectively. In several exams decisive diagnostic features were only discernible in the high energy reconstructions. The density of the artefacts decreased from -882 to -341 HU.
Conclusions
Dual Energy CT with specific postprocessing can reduce metal artefacts and may significantly enhance diagnostic value in the evaluation of metallic implants.
Authors: Bamberg F, Dierks A, Nikolaou K, Reiser MF, Becker CR, Johnson TR.
Full text: Eur Radiol. 2011 Jan 20. [Epub ahead of print]
Dr.Johnson,
How does the DE per se, play a role in this study.Since most of the action is taking place in the High KeV range, and the contribution from the 80/100KVp tube to the high KeV range may not be very significant,in this case?
Of course it is helpful that the Sn140kVp spectrum is quite hard, because it just penetrates metal better. However, the monoenergetic reconstruction is based on an extrapolation of density from the images that have been acquired. In order to extrapolate what the image would look like at even higher energies, an image obtained at a lower photon energy is required additional to the high energy image. It’s basically like drawing the graph of a linear equation: you need two points (i.e. density values at 80 and Sn140 kVp) in order to find a third point (i.e. the density at the extrapolated monoenergetic energy).
Dr. Johnson,
Hi, I’m very much interested in your study and I’d like to go into this technique. May I ask for a white paper of this study?
This initial study has been published in European Radiology (Eur Radiol. 2011 Jul;21(7):1424-9), so you can read the full paper there. I am also sending you a white paper directly by email.
A further, systematic study is under review; we optimized the protocol to achieve best-possible artifact reduction. It will take a few more weeks until this is published.
Thank you so much, Dr. Johnson.