Optimization of MDCT of the Wrist to Achieve Diagnostic Image Quality with Minimum Radiation Exposure
Harald Marcel Bonel1,
Lorenz Jäger2,
Kathrin Anne Frei3,
Stefan Galiano2,
Sudesh K. Srivastav4,
Thomas Flohr5,
Maximilian F. Reiser2 and
Hans-Peter Dinkel1
1 Institute of Diagnostic, Interventional, and Pediatric Radiology, University
of Berne Inselspital, Freiburgstrasse, Berne CH-3010, Switzerland.
2 Institute of Clinical Radiology, Ludwig-Maximilians-University Munich, Munich,
Germany.
3 Department of Gynecology and Obstetrics, University of Berne Inselspital,
Berne, Switzerland.
4 Department of Biostatistics, Tulane University, New Orleans, LA.
5 Siemens Medical Solutions, Forchheim, Germany.
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Fig. 1 —Summary of average readings. Box-and-whisker plots of average
readings for parameter settings for acquisition and reconstruction slice
thicknesses (a), rotation time and volume pitch (b and c), and voltage and
tube current (d and e). Vertical axes represent 5-point ordinal evaluation
scale of reviewers. Key for presentation is at top right.
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Fig. 2 —85-year-old woman. Influence of acquisition (A) and
reconstruction (R) slice thicknesses on fine anatomic detail in MDCT and MRI
depictions of small bone ganglion in lunate bone. Sclerotic margin is best
shown with smallest acquisition and reconstruction slice thicknesses of 0.5 mm
(top left). Some anatomic detail of ganglion is obscured at acquisition slice
thickness of 1.0 mm. For these scans, a pitch of 2.0 was used. Step artifacts
along table feed are pronounced and decrease with increasing reconstruction
slice thickness. Superb MR image contrast depicts anatomy at high level of
quality even at slice thickness of 3.0 mm. CISS = constructive interference in
steady state, SE = spin echo.
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Fig. 3 —71-year-old man. Effect of tube voltage on bone presentation.
Spongy bone contrast is slightly better with voltage of 80 kV, although noise
in soft tissue is definitely greater. Contrast and noise do not significantly
differ between 120 and 140 kV. Because quality of bone presentation does not
decrease to less than diagnostic quality with smaller voltage, this effect
should be exploited to reduce radiation dosage.
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Fig. 4 —71-year-old man. Influence of rotation time on presentation
of wrist. Slightly more artifacts are found using shorter rotation time of 0.5
sec; on cortical bone of ulna in particular, small step artifacts are
observed. Higher rotation time of 0.75 or 1.0 sec, using jumping focus,
produces images of excellent diagnostic quality.
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Fig. 5A —71-year-old man. Influence of detector pitch on spiral
artifacts. On these three consecutive axial acquisition slices using pitches
of 3.0 and 1.0, wooden identification label is between wrist and
osteodensitometry phantom, which contains hydroxylapatite equivalent (left,
with strong artifacts) and water equivalent (right).
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Fig. 5B —71-year-old man. Influence of detector pitch on spiral
artifacts. Coronal reconstructions with 0.5-mm and 1.0-mm thicknesses show
step artifacts in cortical and spongy bone. If 0.5-mm thickness is used
(B), minor artifacts are evident even at pitch of 2.0, whereas with
reconstruction slice thickness of 1.0 mm (C), artifacts are obscured
and pitch can be as high as 2.0.
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Fig. 5C —71-year-old man. Influence of detector pitch on spiral
artifacts. Coronal reconstructions with 0.5-mm and 1.0-mm thicknesses show
step artifacts in cortical and spongy bone. If 0.5-mm thickness is used
(B), minor artifacts are evident even at pitch of 2.0, whereas with
reconstruction slice thickness of 1.0 mm (C), artifacts are obscured
and pitch can be as high as 2.0.
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Copyright © 2005 by the American Roentgen Ray Society.
