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OP 13
Title
THE TRIAL OF REDuCING DOSE OF MDCT FOR IMPLANT PLANNING
Authors
y. yOTSuI 1 , y. NAKASHIMA 1 , K. SHIMIzuTANI 1 , T.A. LARHEIM 2
Affiliations
1 Department of Oral Radiology, Osaka Dental University, Osaka, Japan, 2 Department of Oral
Radiology, Faculty of Dentistry, University of Oslo, Oslo, Norway
Body
Recently, Computed tomography is used for planning of the dental implantation. In these
cases, dentists hope to observe the outline of alveolar bone and suppose the direction and
depth of the planting implants. From the view point of only displaying outline of alveolar
bone, the X-ray tube currency should be minimized and should be tried minimizing X-ray dose.
But in such condition, the signal-noise rate would be increase in CT images. And the accuracy
of the measurement would not be realized on CT images.
Purpose: We should evaluate how images are affected by changing raw numbers and pitch to
minimize the radiation dose of implant planning CT. We will investigate the correlation
between the accuracy of the measurement, Table feeding speed and the X-ray tube currency
with the image kernels.
Materials and method: A lower jaw of skull was used for the examination as a model.
The model put into a case filled with water under fixed with Oasis and be taken CT several
times with changing X-ray tube currency, Row numbers and table feeding.
1) About SNR : ROI measurement was performed with CT images in changing the condition of
exposure. In the data, we used Standard divisions as Signal-Noise Ratio (SNR).
2) Reliability in the measurement: Putting 11 markers on the Skull mandibule as a model, the
skull was taken CT images for measuring dimension each other points.
3) Evaluating the CT images that were taken under several exposure conditions by observers
with ROC analysis, from the view point of observing outline of the bone.
Results: 1) Relationship between Dose and SNR: 4 Row and table feed speed1.5:1 is the most
effective for nose and dose reduction.
2) In the almost of series, the length difference between the venire calipers and images
measurement are within 1%.
3) With the low dose exposure such as 20mA or 30mA tube currency, the outline of the bone
could be observed same as images of high dose exposure such as 60mA or 80mA tube currency.
Conclusion: In occasion to limit the implantation planning, we recognized that CT images
could be taken in low currency and high table feeding rate. By this fact, we will be able to
reduce exposure dose largely in MDCT.
Keywords
MDCT,CT number, Digittal image
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