JAEA-Review-2010-065.pdf:15.99MB - 日本原子力研究開発機構

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Uniformity Measurement of Newly Installed Camera
Heads of Positron-emitting Tracer Imaging System
N. Kawachi a) , N. Suzui a) , S. Ishii a) , H. Yamazaki a), b) and S. Fujimaki a)
a) Radiation-Applied Biology Division, QuBS, JAEA,
b) Faculty of Science and Technology, Tokyo University of Science
A positron-emitting tracer imaging system (PETIS) is the
most promising device that can be used for radiotracer
imaging in plant studies. Elucidation of nutrient dynamics
in a plant is important from an agricultural viewpoint in
terms of the growth and development of a plant body; this
helps in understanding the mechanisms underlying nutrient
kinetics using the PETIS. Here, we have performed
phantom experiments for the quarterly maintenance of the
uniformity and sensitivity correction of the PETIS to assess
the performance of its newly installed detector head and
maintain a sufficiently high image quality for plant study.
In order to quantitatively acquire the analyzable dynamic
data of PETIS images, it is mandatory to begin a scheduled
work for constant quality control.
We prepared a flat uniform phantom containing a
radioactive solution of Na-22 (half-life; 2.6 years), and the
radioactivity of the solution was 16.3 kBq/mL. The
phantom had a thickness of 3 mm, a width of 90 mm, and a
height of 90 mm. We have operated three types of the
PETIS detector head (Hamamatsu Photonics Co. [1]).
Newly installed PETS No. 4 and elderly PETIS No. 2,
which has a large field of view, and No. 3, which has fine
detector module, acquired for 5 min to image the phantom in
this maintenance experiment. All images were corrected
for detector geometry and counting rate losses. To analyze
the image quality of the phantom data, we estimated the
mean value (MEAN), standard deviation (SD), and the root
mean square uncertainty (RMSU) of a selected region of
interest (ROI) in the images. %RMSU is defied as follows,
100
%RMSU
where is the standard deviation, and x is the mean value
of the count in ROI.
Figure 1 shows the imaging results of the phantom
experiments performed with PETIS No. 3 and No. 4. The
phantom image acquired with PETIS No. 3 has a sharper
pattern than those acquired with PETIS No. 4; on the other
hand, the phantom image obtained with PETIS No. 4 has
more uniformity than that obtained with PETIS No. 3. The
crosshatching pattern on the image of PETIS No. 3 indicates
that the errors of geometry correction and sensitivity
dispersions are caused by the aged deterioration of the
detector modules. Results of uniformity analysis of
MEAN, SD, and %RMSU for an active image area are
summarized in Table 1. The analyzed data support the
impression of the visualized phantom images. PETIS No. 4
exhibited excellent uniformity performance for plant study.
x
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(PETIS No. 3) (PETIS No. 4)
Fig. 1 Images of radioactive flat phantom ( 22 Na;
390 kBq) acquired for 5 minutes with PETIS No. 3
(left) and PETIS No. 4 (right).
Table 1 Analyzed performance of MEAN, SD,
and %RMSU for the active image area of the PETIS
detector head of No. 2, No. 3, and No. 4.
MEAN
S. D.
%RMSU
PETIS
No. 2
6.89 × 10-4
7.63 ×10 -5
PETIS
No. 3
PETIS
No. 4
7.14 × 10-4 3.56 × 10-4
1.23 × 10-4 1.46 × 10-5
11.1 17.2 4.11
The %RMSU is expected to increase in the activity of the
images; therefore, the measurements of %RMSU
dependence on the counting rate in each detector head are
now in progress. These works on the maintenance of
PETIS quality control ensure quantitative kinetic analysis
and support many other plant physiological experiments of
PETIS studies.
Reference
1) H. Uchida et al., Nucl. Instrum. Meth. A 516 (2004)
564.