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KMID : 0357520130360040290
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Journal of Radiological Science and Technology
2013 Volume.36 No. 4 p.290 ~ p.297
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The Study of Error for Analysis in Dynamic Image from the Error of Count Rates in NaI (Tl) Scintillation Camera
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Oh Joo-Young
Kang Chun-Goo
Kim Jung-Yul
Oh Ki-Baek
Park Hoon-Hee
Kim Jae-Sam
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Abstract
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This study is aimed to evaluate the effect of T1/2 upon count rates in the analysis of dynamic scan using NaI (Tl) scintillation camera, and suggest a new quality control method with this effects.
We producted a point source with 99mTcO₄- of 18.5 to 185 MBq in the 2 mL syringes, and acquired 30frames of dynamic images with 10 to 60 seconds each using Infinia gamma camera (GE, USA). In the second experiment, 90 frames of dynamic images were acquired from 74 MBq point source by 5 gamma cameras(Infinia 2, Forte 2, Argus 1).
There were not significant differences in average count rates of the sources with 18.5 to 92.5 MBq in the
analysis of 10 to 60 seconds/frame with 10 seconds interval in the first experiment (p>0.05). But there were
significantly low average count rates with the sources over 111 MBq activity at 60 seconds/frame (p<0.01).
According to the second analysis results of linear regression by count rates of 5 gamma cameras those were
acquired during 90 minutes, counting efficiency of fourth gamma camera was most low as 0.0064%, and
gradient and coefficient of variation was high as 0.0042 and 0.229 each. We could not find abnormal fluctuation
in χ²test with count rates (p>0.02), and we could find the homogeneity of variance in Levene’s F-test among the gamma cameras (p>0.05). At the correlation analysis, there was only correlation between counting efficiency and gradient as significant negative correlation (r=-0.90, p<0.05). Lastly, according to the results of calculation of T1/2 error from change of gradient with -0.25% to +0.25%, if T1/2/ is relatively long, or gradient is high, the error increase relationally. When estimate the value of 4th camera which has highest gradient from the above mentioned result, we could not see T1/2 error within 60 minutes at that value.
In conclusion, it is necessary for the scintillation gamma camera in medical field to manage hard for the quality of radiation measurement. Especially, we found a tendency that count rate changes over time at this study, and we proved that it can effect T1/2. And also, there is need of appropriate phantoms and the method of quality management like this study, because there are not any advice or limitation degrees for domestic medical purpose scintillation camera.
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KEYWORD
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Point source , Count rate , Quality control , T1/2 , Gradient
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