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Automatic activity measurement and data processing systemusing an imaging analyzer

Takuya.Saze (Radioisotope Research Center, Nagoya University),Masahiro Etoh (Science systems & equipment product Div., Fuji photo film Co.,Ltd),Chizuo Mori (Department of Engineering, Aichi Technological University), andKunihide Nishizawa (Radioisotope Research Center, Nagoya University, Furo-cho, Chikusa-ku,

Nagoya 464-8602, Japan)

1. Introduction An imaging plate (IP) [1,2,7,11], a type of phosphor screen, has been applied in many fields; forradiological diagnosis [13], crystallography [7], electron microscopy [10], personal radiation monitor [17],neutron detector [11], etc., as a two dimensional radiation detector for analyzing radioactivity distribution on asample [4,8,9]. In order to determine the radioactivity of the sample by using an image analyzer with theimaging plate (IP), the count obtained by analyzing an IP image must be properly corrected for three factors:fading, nonuniform sensitivity on the IP, and count-activity characteristics [4,15,16]. A wide area IP of 20 cm x40 cm is used to obtain multiple sample images at a time. Each step, up till now, from reading out sampleimages to calculating the activities has been carried out manually. An automated smear counting and data processing system for a liquid scintillation counter (LSC) anda NaI(Tl) scintillation counter (NSC) was developed at our institution to eliminate human errors and facilitateroutine programs [14]. When the procedure from counting to data processing is automated for the imageanalyzer with the wide area IP, the activity of multiple samples can be determined at the same time. Theautomated IP system may reduce the measurement time to about one tenth less than that required by the manualone.

The IP detects low level activity of high energy beta emitters, e.g. 90Sr [9] and 32P [4]. The IP can

also detect intermediate energy beta emitters such as 147Pm and 14C. A special IP having no protection layer

on the phosphor can detect a low energy beta emitter, 3H without contamination by floating radiography using a

spacer between the IP and samples [3,18]. Thus the IP can be repeatedly used to detect beta emitters fromlow energy to high energy. The IP, however, must be calibrated with a standard source for determining activityof beta emitters. The purpose of this paper is to develop a computerized image analyzer system with a wide area IP that

automatically executes from reading out the latent images of multiple 32P samples to determining their activities

concurrently.

2. Materials and Methods2.1 System An image analysis system consists of the wide area IP (BAS-3 and BAS-SR), an image analyzer(BAS2500Mac) comprised of an image reader and a personal computer, an eraser, an image printer and a laserprinter. The IP was repeatedly used by erasing the residual image. The system performance was tested by

using 32P sources as an example.

2.2 Radioactive sources

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32P-Phosphoric acid solution of 10~100 kBq/ml was dropped on 0.25 mm thick glass wool filter paper

of 2.1 cm in diameter, and dried in a draft chamber. The 32P adsorbed filter paper were measured by the LSC

(Aloka LSC5100). The dried filters after measurement were used as disk sources. The activities weredetermined in accordance with the efficiency tracing method using the LSC [5]. The source activities rangedfrom 40Bq to 605Bq. The dried filters were used as disk sources. Fig.1. shows a surface source S consisting of 18 disk sources fixed by sellotape on a 0.08 mm thick, 40 cmlong and 20 cm wide polyethylene sheet A. Disk sources were arranged on lattice points fixed by lines at 6.1cm intervals. The shortest distance between adjacent two disk borders was 4 cm.

2.3 Measurement Surface source S was placed so that the sheet A was in contact with a cassette base as shown in Fig.2.The IP erased the residual image was covered by another sheet B identical with the sheet A in order to prevent

the contamination, and was shielded against light by the cassette cover. The IP was exposed to 32P beta rays

for 10 min in the cassette. The latent source image were read out by using the image analyzer at 1 min afterexposure for count-activity measurements and were read out at 1, 5, 10, 15, 20, 30, 40, 50 and 60 min afterexposure for fading measurements. The relative sensitivity distribution of IP was measured and corrected.The fading rate, or relative count, was defined by the relative ratio of a count measured at any time afterexposure to a count measured at 1 min after exposure. The room temperature was 25 degrees Celsius . Thebackground (BG) of the IP without the source in the same place was measured three times for the same period of

Glass wool filter (2.1cmφ)

6.1cm3.9cm 6.1cm 3.9cm

6.1cm

6.1cm

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6.1cm

6.1cm

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40cm

20cm

1 2 3

4 5 6

7 8 9

10 11 12

13 14 15

16 17 18

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Fig.1. Schematic diagram of surface source S, consisting of 18 disc sources fixed on a polyethylene sheet.

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time when the source was measured and the mean value was used as BG count. The procedure from setting theIP into the cassette to transferring to the image analyzer was conducted in a dark room, because visible lightfades the latent image.

2.4. Flow Fig.3 shows the flow of the counting and data processing procedure. Measurement conditions such asthe exposure time, the elapsed time, and room temperature, were manually inputted beforehand as a file F1.Attribution of samples, sample number, experimental series number, date, sampler's name, comments, etc., werealso manually inputted as a file F2. After reading out, the counts of 18 disk sources were obtained bysimultaneously superimposing the 18 region of interest (ROI)s on the 18 source images. Those ROIs wereprepared in advance and stored as a file F3 in the image analyzer. The counts along with other sampleidentification data such as sample number, ROI number, ROI area, etc., were saved as a raw data file F4. The net counts of each ROI were obtained by subtracting the BG of each ROI stored in a file F5 fromthe measured counts in the file F4. The net counts were corrected for fading and nonuniformity by using thedata file F5. The activity in Bq was calculated by using the corrected count and the data in a file F6. The finalresult were printed out as a report by using the data in the files F1, F2, and F4, and saved on a hard disk as a fileF7. F5 is the file containing the relative sensitivity of each ROI and fading data. F6 is the file containingexposure time and calibration data on the characteristics of the count-activity.

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Fig.2. Arrangement of IP on surface source S. (1) Surface source S was covered by a polyethylene sheet B. (2) Source S was placed so that the

sheet A was in contact with a cassette base.�

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2.5. Counting procedure Fig.4(1) shows the 18 circular ROIs of 5.9 cm in diameter stored in the analyzer in advance, (2)represents the 18 source images, and (3) is a picture on the monitor showing how the 18 ROIs weresuperimposed on the 18 source images. Each ROI was superimposed on the image so that its center coincidedwith the center of the disk source. The center of disk sources did not necessarily coincide with the center of the

disk source images, because 32P solution could not always be dropped exactly at the center of the filter paper.

The displacement of the image center from the disk center did not affect counting and data processing since thedisks were arranged so that their counts did not interfere each other. Fig.4(4) shows an example of the datacontaining ROI number, counts, ROI area, etc., which were stored as file F4. The procedure from counting todata processing was programmed by using the 'macro' function in the personal computer.

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Fig.3. Flowchart of the counting and data processing procedure.

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File 5 Background Fading data Non uniformity factors

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3. Result3.1 Sensitivity distribution Fig.5(1) shows an example of relative sensitivity distribution and (2) shows the correcteddistribution. The maximum sensitivity difference was reduced to +-2.5% by correction. And the distortedsensitivity distribution became considerably flatter than it was originally. The coefficients for correctingnonuniform characteristic were stored in the file F5.

1 2 3

4 5 6

7 8 9

10 11 12

13 14 15

16 17 18

Source image

Glass wool filter (2.1cmφ)

Region of Interest (5.9cmφ)

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No. PSL Area (mm2) PSL/mm2

1 8377.62 2753.44 3.04

2 8558.15 2753.44 3.11

3 7960.56 2753.44 2.89

4 3230.98 2753.44 1.17

5 3158.95 2753.44 1.15

6 2825.61 2753.44 1.03

7 5923.15 2753.44 2.15

8 6478.25 2753.44 2.35

9 6807.31 2753.44 2.47

10 9123.17 2828.16 3.23

11 9634.45 2753.44 3.50

12 8996.05 2864.96 3.14

13 11611.11 2753.44 4.22

14 13087.57 2753.44 4.75

15 11924.34 2753.44 4.33

16 14237.94 2753.44 5.17

17 16079.06 2753.44 5.84

18 14542.94 2753.44 5.28

Fig.4 Superimposition of ROI on disk source image. (1): 18 ROIs ready to use. (2): 18 source images. (3): ROIs superimposed on source images. (4): Measured results.

(1) (4)(2) (3)

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3.2 Fading Fig.6 shows an example of a fading curve in a short period of time after exposure as a function ofthe elapsed time after exposure. The relative count faded to about 70% in 60 min. The fading curve wasstored as the file F5 and was used to convert the counts read out at any elapsed time to the count at 1 min afterexposure.3.3 Count-activity characteristics Fig.7 shows the count-activity curves for 10 min exposures. The count linearly increased with theincreasing activity. The data was well fitted by the following equations:for IP BAS-3 y = 0.040x - 4.502 (3)for IP BAS-SR y = 0.135x + 0.131 (4)

where x is the count and y is the activity. Two equations (3) and (4) were stored as the file F6. Theactivity of each sample was calculated by inserting the count corrected for fading and nonuniformity to 'x' ofthe equation (3) or (4).

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Fig. 5. An example of a corrected relative sensitivity distribution of BAS2500 obtained with surface source S. (1) Original distribution. (2) Corrected distribution.

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3.4. Reporting Fig.8 shows an example of a report including sample attribution, measurement condition, measuredresults, etc. The activities were calculated by using the fading rate in Fig.6 and the count-activity curve inFig.7 , or eq. (3), that were normalized at 1 min after exposure.

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Fig.7. Relationships between count and activity.Exposure time was 10 min.

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4. Discussion Activity measurement of samples containing beta emitters is commonly carried out by using theLSC. Used liquid scintillator must be considered as a waste organic solvent containing radioactivecontaminants and burned by using a specially designed incinerator approved by regulatory authority [6,14].It is suspected that incinerating waste liquid scintillator including chlorine compounds generates toxic andenvironmentally hazardous dioxin. Developing a new technique replacing the LSC is critical for preventingenvironmental contamination due to incinerating waste scintillator. The count obtained with theradioluminography must be properly corrected for nonuniform sensitivity, fading, and count-activitycharacteristics in order to determine the activity. The counting and correcting procedure was automated byusing the personal computer installed a newly developed program. A database on nonuniform sensitivity,fading and count-activity characteristics was constructed by using data obtained experimentally . Theautomatic IP system executes activity measurement of a number of samples containing beta emitters in aconsiderably short period of time compared with a manual system. The major advantage utilizing the IPsystem is that measurement with the IP system does not produce waste liquid scintillator, that the IP is

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Data

Measurement conditionSample attribution

Name : Takuya Saze

Nuclide : 32PSampling location : Main buildingMeasured date : Nov29,1999Sampling date : Nov15,1999

Elapsed time : 10 min

Exposure time : 10 min

Instrument : BAS2500

IP type : BAS- Ⅲ

Report 　　　　　　　　Radioisotope Reserch Center 　　　　　　　　 Nagoya University Nov. 30, 1999

Fig.8. An example of report including sample attribution, measurement condition, measured results, etc.

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repeatedly usable for various radionuclides including 3H, and that multiple samples can be measured at a time.

The IP system using the wide area IP can measure 18 samples containing 32P at the same time. It

will be possible to measure more samples at a time by improving the sample arrangement. The samples,however, should be separated at intervals of 4 cm or more in order to eliminate mutual interference witheach other when the IP is exposed to multiple samples at a time [12,15]. Furthermore, the IP system can be

applied to radioactivity measurement of other radionuclides, such as 14C, 35S, 125I, etc., providing that

data on the factors; fading, sensitivity distribution, and count-activity characteristics, are prepared for thesenuclides in advance.

5. Conclusions A procedure for determining radioactivity with the IP was clarified. The activity was calculated byusing the count corrected for fading and nonuniform sensitivity, and the count-activity calibration curve. An

automated counting and data processing system for 32P was developed by using an image analyzer, a wide

area IP, and a personal computer. The system can determine the radioactivity of 18 samples at a time andprint out the results as a report.

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an imaging plate system for x-ray diffraction study," Nucl. Instr. and Meth. A. 266;645-653;1988[3] Furuta,E.; Yoshizawa,Y.; Nakane,T.; Takiue,M. "Usefulness of floating radioluminography to tritiated

samples," Appl. Radiat. Isot. 48;1133-1136;1997

[4] Hamada,N.; Nakamura,Y.; kikuchi,K.; Adachi, K.; Nishizawa, K. ﾒ Analysis of 32P surface

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radioactivity distribution of material surfaces with an imaging plate,ﾓ Nucl. Instr. and Meth. A. 353;371-374;1994

[9] Mori,C.; Matsumura,A.; Suzuki,T.; Miyahara,H.; Aoyama,T.; Nishizawa,K. "Detection of extremelylow level radioactivity with imaging plate," Nucl. Instr. and Meth. A. 339;278-281;1994

[10] Mori,N.; Oikawa,T.; Katoh,T. Miyahara,J.; Harada,Y. "Application of the imaging plate to TEM imagerecording," Ultramicroscopy. 25;195-202;1988

[11] Niimura,N.; Karasawa,Y.; Yanaka,I.; Miyahara,J.; Takahashi,K.; Saito,H.; Koizumi,S.; Hidaka,M. "Animaging plate neutron detector," Nucl. Instr. and Meth. A. 349;521-525;1994

[12] Nishizawa,K.; Saze,T. " Application of imaging plate to radiation management. The status quo concerningapplication of imaging plate to radiation protection measurements and problems to be solved,"Hokenbutsuri. 34;29-35;1999

[13] Nohtomi,A.; Terunuma,T.; Kohno,R.; Takada,Y.; Hayakawa,Y.; Maruhashi,A.; Sakae,T. "Responsecharacteristic of an imaging plate to clinical proton beams," Nucl. Instr. and Meth. A. 424;569-574;1999

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[14] Ogata,Y.; Nishizawa,K. ﾒ Automated smear counting and data processing using a notebook computer in abiomedical research facility,ﾓ Health Phys. 69;566-569;1995

[15] Saze,T.; Mori,C.; Nishizawa,K. ﾒ Correction of a nonuniform imaging plate response," Nucl. Instr. andMeth. A. 406;343-349; 1998

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[17] Yamadera,A.; Kim,E.; Miyata,T.; Nakamura,T. "Property test of imaging Plate as X-Ray personaldosimeter," Radioisotopes. 42;676-682;1993

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