Automatic Patient Centering for MDCT: Effect on Radiation Dose
Jianhai Li1,
Unni K. Udayasankar1,
Thomas L. Toth2,
John Seamans2,
William C. Small1 and
Mannudeep K. Kalra1,3
1 Department of Radiology, Emory University School of Medicine, 1364 Clifton Rd.
NE, Atlanta, GA 30322.
2 GE Healthcare, Waukesha, WI 53188.
3 Present address: Department of Radiology, Massachusetts General Hospital, 55
Fruit St., Boston, MA 02114.
View larger version (11K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 1A —Effect of bow-tie filter (B) on X-ray beam relative to patient (P)
centering (star). T = X-ray tube. Diagram shows that when patient is
centered in gantry isocenter (circle), bow-tie filters allow more
X-rays (X+++) to traverse thicker, central parts and fewer rays (X+, X++) to
pass through thinner, peripheral parts of patient.
|
|
View larger version (11K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 1B —Effect of bow-tie filter (B) on X-ray beam relative to patient (P)
centering (star). T = X-ray tube. Diagram shows that with
off-centering, thicker portion receives fewer X-rays (X+, X++), increasing
image noise and that more X-rays (X+++) pass through peripheral thinner parts,
increasing surface and peripheral radiation doses.
|
|
View larger version (72K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 2B —43-year-old man with suspected appendicitis. Mechanism of automatic
centering technique. Localizer radiograph shows automatic estimate of ideal
patient centering in gantry isocenter within 5-mm range.
|
|
View larger version (70K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 2C —43-year-old man with suspected appendicitis. Mechanism of automatic
centering technique. Localizer radiograph shows that because patient is
off-center relative to gantry isocenter, automatic technique recommends
adjustment factor of off-center distance (white arrow) so that
radiologic technologist can match (gray arrow) patient centering to
gantry isocenter by changing table position.
|
|
View larger version (187K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 3A —Noise field images of CT dose index phantom obtained by subtraction
of two consecutive images. Process removes correlated phantom features and
leaves uncorrelated image of noise. Method allows measurement of noise over
large region without interference of phantom structures. CT scan with optimum
positioning.
|
|
View larger version (187K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 3B —Noise field images of CT dose index phantom obtained by subtraction
of two consecutive images. Process removes correlated phantom features and
leaves uncorrelated image of noise. Method allows measurement of noise over
large region without interference of phantom structures. CT scans with phantom
centered 30 mm (B) and 60 mm (C) below gantry isocenter.
Increase in image noise (inferior aspect of phantom, B and C)
and surface and peripheral CT dose index is evident with off-centering of
phantom.
|
|
View larger version (189K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 3C —Noise field images of CT dose index phantom obtained by subtraction
of two consecutive images. Process removes correlated phantom features and
leaves uncorrelated image of noise. Method allows measurement of noise over
large region without interference of phantom structures. CT scans with phantom
centered 30 mm (B) and 60 mm (C) below gantry isocenter.
Increase in image noise (inferior aspect of phantom, B and C)
and surface and peripheral CT dose index is evident with off-centering of
phantom.
|
|
CiteULike 
Complore 
Connotea 
Del.icio.us 
Digg 
Reddit 
Technorati What's this?
Copyright © 2007 by the American Roentgen Ray Society.
