AJR
HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
QUICK SEARCH:   [advanced]


     

This Article
Right arrow Abstract Freely available
Right arrow Full Text
Right arrow Full Text (PDF)
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Right arrow Citation Map
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow reprints & permissions
Citing Articles
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Kanal, K. M.
Right arrow Articles by Shuman, W. P.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Kanal, K. M.
Right arrow Articles by Shuman, W. P.
Social Bookmarking
Add to CiteULike   Add to Complore   Add to Connotea   Add to Del.icio.us   Add to Digg   Add to Reddit   Add to Technorati  
What's this?
Hotlight (NEW!)
Right arrow
What's Hotlight?

Impact of Operator-Selected Image Noise Index and Reconstruction Slice Thickness on Patient Radiation Dose in 64-MDCT

Kalpana M. Kanal1, Brent K. Stewart1, Orpheus Kolokythas1 and William P. Shuman1

1 All authors: Department of Radiology, University of Washington Medical Center, 1959 NE Pacific St., Box 357115, Seattle, WA 98195-7115.


Figure 1
View larger version (16K):
[in this window]
[in a new window]
[as a PowerPoint slide]
  		Fig. 1 —Representation of noise index (NI) versus reconstruction slice thickness. CT profile data are acquired using 0.625-mm detector widths and reconstructed to 0.625-, 1.25-, 2.5-, 3.75-, and 5-mm slice thicknesses. Even though reconstruction slice thickness may vary, any slice thickness is generated from acquired 0.625-mm profile data. Thus, NI for any reconstruction slice thickness can be related back to NI for reconstructed 0.625-mm slice. For instance, NI = 40 at 0.625 mm equates nearly to NI = 33.8 at 1.25 mm and NI = 15.3 at 5 mm, each having same noise level ({sigma}) in acquired 0.625-mm profile data, though manifesting as different measured noise levels in reconstructed slices. ROI = region of interest.

 

Figure 2
View larger version (17K):
[in this window]
[in a new window]
[as a PowerPoint slide]
  		Fig. 2A —Graphs of noise index (NI) data from Table 1. NI data plotted versus relative dose for five reconstruction slice thicknesses: 0.625 (black), 1.25 (red), 2.5 (blue), 3.75 (brown), and 5.0 mm (green). NI graph of overall results. NI values are plotted on y-axis and relative radiation dose values are plotted on x-axis as function of varying reconstruction slice thickness values, ranging from 0.625 to 5 mm.

 

Figure 3
View larger version (18K):
[in this window]
[in a new window]
[as a PowerPoint slide]
  		Fig. 2B —Graphs of noise index (NI) data from Table 1. NI data plotted versus relative dose for five reconstruction slice thicknesses: 0.625 (black), 1.25 (red), 2.5 (blue), 3.75 (brown), and 5.0 mm (green). NI graph shows dose penalty if NI is decreased from 40 to 30 for 0.625-mm reconstruction slice thickness. As seen in graph, relative dose at NI of 40 and 0.625-mm reconstruction slice thickness is 1.0 (dotted line). At same reconstruction slice thickness of 0.625 mm, but changing NI to 30, relative radiation dose is 1.8 (solid line), resulting in 80% increase in relative dose.

 

Figure 4
View larger version (18K):
[in this window]
[in a new window]
[as a PowerPoint slide]
  		Fig. 2C —Graphs of noise index (NI) data from Table 1. NI data plotted versus relative dose for five reconstruction slice thicknesses: 0.625 (black), 1.25 (red), 2.5 (blue), 3.75 (brown), and 5.0 mm (green). NI graph shows how to maintain constant radiation dose as reconstruction slice thickness is changed. For operator-selected 5-mm reconstruction slice thickness and NI of 12, how would NI change if reconstruction slice thickness was modified to 0.625 mm while maintaining same radiation dose? It can be seen that for NI of 12 and 5-mm reconstruction slice thickness, maintaining same relative radiation dose of 1.7 (dotted line) when changing to reconstruction slice thickness of 0.625 mm (solid line) requires change in NI from 12 to 31.

 

Figure 5
View larger version (18K):
[in this window]
[in a new window]
[as a PowerPoint slide]
  		Fig. 2D —Graphs of noise index (NI) data from Table 1. NI data plotted versus relative dose for five reconstruction slice thicknesses: 0.625 (black), 1.25 (red), 2.5 (blue), 3.75 (brown), and 5.0 mm (green). NI graph illustrates importance of increase in relative radiation dose when reconstruction slice thickness is changed without changing NI. What happens to dose if same NI of 20 is kept when changing reconstruction slice thickness from 5 to 0.625 mm? At NI of 20 and reconstruction slice thickness of 5 mm, relative radiation dose is 0.6 (dotted line). At same NI of 20 but changing reconstruction slice thickness to 0.625 mm, relative radiation dose changes to 4.0 (solid line), thereby increasing dose by factor of 6.7 times, if maximum mA has not been reached.

 

Add to CiteULike CiteULike   Add to Complore Complore   Add to Connotea Connotea   Add to Del.icio.us Del.icio.us   Add to Digg Digg   Add to Reddit Reddit   Add to Technorati Technorati    What's this?



HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
Copyright © 2007 by the American Roentgen Ray Society.