A. Yamadera

Dependence of fading patterns of photo-stimulated luminescence from imaging plates on radiation, energy, and image reader

Abstract We have been investigating the fading characteristics of imaging plates (IPs) as integral type detectors. The dependence on alpha, beta, and gamma ray radiation and their energies of the fading effect was measured using three types of IPs (BAS-UR, BAS-TR, and BAS-MS). The functions to correct the fading were determined by using the method reported in a previous paper. In all types of IPs, we confirmed that the fading effect is independent of the energy of the incident particles of beta and gamma rays and also independent of radiation except for the first component, which fades out in a very short time after irradiation with alpha rays. These results are very useful in the utilization of IPs as integral detectors in practical radiation fields. Empirically, the fading pattern is known to change when the IP is scanned by different types of image readers. The differences in the fading patterns obtained with two types of image readers, the BAS-1000 and the BAS-5000 (Fuji Film Co.), is discussed. Development of an equation for correcting the effects of the differences in the image readers was attempted.

Variations in Cerium X-ray Spectra and Enhanced K-Edge Angiography

A cerium-target X-ray tube is useful in performing cone-beam K-edge angiography because K-series characteristic X-rays from the cerium target are absorbed effectively by iodine-based contrast media. The X-ray generator consists of a main controller and a unit with a high-voltage circuit and a fixed anode X-ray tube. The tube is a 1.0-mm-focus diode with a cerium target and a 0.5-mm-thick beryllium window. The maximum tube voltage and current were 65 kV and 0.4 mA, respectively. Cerium Kα rays were selected out using a barium sulfate filter, and the X-ray intensities without filtering and with a barium sulfate filter were 209 and 16.8 µGy/s, respectively, at 1.0 m from the source with a tube voltage of 60 kV and a current of 0.40 mA. Angiography was performed with an X-ray film using the filter and iodine-based microspheres 15 µm in diameter. In the angiography of nonliving animals, we observed fine blood vessels approximately 100 µm in diameter with high contrasts.

Internal absorbed dose estimation by a TLD method for -FDG and comparison with the dose estimates from whole body PET

The thermoluminescent dosimeter (TLD) method has been proposed as a useful tool for estimating internal radiation absorbed dose in nuclear medicine. An efficient approach to verify the accuracy of the TLD method has been performed in this study. Under the standard protocol for 2-[F-18]fluoro-2-deoxy-D-glucose (18F-FDG), whole body PET experiments and simultaneous body surface dose measurements by TLDs were performed on six normal volunteers. By using the body surface dose measured with TLDs, the cumulated activities of nine source organs were estimated with a mathematical unfolding technique for three different initial guesses. The accuracy of the results obtained by the TLD method was investigated by comparison with the actual cumulated activity of the same source organs measured by whole body PET. The cumulated activities of the source organs obtained by the TLD method and whole body PET show a significant correlation (correlation coefficient, r > 0.98, level of confidence, p < 0.001) with each other. The mean effective doses in this study are 3.2 x 10(-2) mSv MBq(-1) obtained from the TLD method and 2.9 x 10(-2) mSv MBq(-1) obtained from the whole body PET. Good agreement between the results of the TLD method and whole body PET was observed.

Residual long-lived radioactivity distribution in the inner concrete wall of a cyclotron vault.

We measured the depth distribution of residual long-lived radioactivity in the inner concrete wall of a cyclotron vault by assaying concrete cores and we estimated the neutron flux distribution in the inner concrete wall by means of activation detectors. Nine long-lived radioactive nuclides (46Sc, 59Fe, 60Co, 65Zn, 134Cs, 152Eu, 154Eu, 22Na, and 54Mn) were identified from the gamma-ray spectra measured in the concrete samples. It was confirmed that the radionuclides induced by thermal neutrons through the (n, gamma) reaction are dominant, and that the induced activity by thermal neutrons is greatest at a depth of 5 to 10 cm rather than at the surface of the concrete and decreases exponentially beyond a depth of about 20 cm. By comparing the radioactivity and neutron flux distributions, we can estimate the induced long-lived radioactivity in concrete after a long period of operation from the short-term activation measurement.

Development of a functional equation to correct fading in imaging plates

Abstract The time evolution of PSL in certain photo stimulable phosphors has been studied for several storage temperatures ranging from 0°C to 60°C and for time periods from 0.03 to approximately 500 h after irradiation. The experiments were carried out using commercially available BaFBr:Eu 2+ phosphors: BAS-UR and BAS-TR (Fuji Film Co.). The fading curves obtained after irradiation with a 244 Cm source were analyzed by applying Arrhenius’ equation to the experimental results, the same method reported previously ( Ohuchi et al., 2000a ). An improved equation, which is a function of elapsed time ( t ) and absolute temperature ( K ), was proposed. Comparison of the data of the experiment and calculated results based on a model consisting of four components for BAS-UR and five components for BAS-TR showed excellent agreement at all temperatures and over all time periods. The formula was also confirmed as giving the proper calculated photo-stimulated luminescence (PSL) corresponding to the temperature changes between the elapsed times, and showed good consistency with the experimental results.

Fast-neutron profiling with an imaging plate

Abstract A method for taking the fast-neutron profile has been developed using an imaging plate combined with a polypropylene converter. By this method, we can obtain the spatial distribution of fast neutrons without any γ-ray contamination by taking the difference between the data with and without the converter. We have studied properties of this method concerning the neutron energy, converter thickness, fading, dynamic range and spatial resolution. Under appropriate conditions, the method has more than a 102 dynamic range with linearity and less than 1.0 mm spatial resolution for 5 and 15 MeV neutrons. By using this method, we successfully obtained a fast-neutron profile after a collimator and radiography of a 5 cm thick iron block.

In vivo evaluation of a fluorine-acryl-stylene-urethane-silicone antithrombogenic coating material copolymer for intravascular stents

RATIONALE AND OBJECTIVES We evaluated the effectiveness of a fluorine-acryl-styrene-urethane-silicone (FASUS) copolymer as an antithrombogenic coating material for intravascular stents in dogs. METHODS FASUS copolymer-coated stents were placed in the right iliac veins, and uncoated 304 stainless steel stents were placed in the left iliac veins. We examined platelet deposition, microthrombus formation, and neointimal hyperplasia 4 weeks after stent placement by measuring the activity of 111In-labeled platelets, by using scanning electron microscopy, and by measuring neointimal thickness. RESULTS Platelet deposition was significantly decreased on coated than on uncoated stents (p < .05). A less pronounced increase in red blood cell deposition was observed at the sites of the coated than uncoated stents (p < .05). Neointimal thickness 4 weeks after stent placement also was significantly less at the sites of the coated stents (0.27 +/- 0.08 mm versus 0.48 +/- 0.23 mm, p < .05). CONCLUSION FASUS copolymer coating over the vascular stent is effective for preventing thrombus formation and neointimal hyperplasia.

Experimental studies on the neutron emission spectrum and induced radioactivity of the 7Li(d,n) reaction in the 20–40 MeV region

To improve the data accuracy of the neutron emission spectrum of the 7 Li(d,n) reaction and the radioactivity ( 7 Be, 3 H, etc.) accumulated in the 7 Li target in IFMIF, we have measured the neutron emission spectrum and the radioactivity of Be induced in the lithium target for 25 MeV deuterons at the Tohoku University AVF cyclotron (K = 110) facility. Neutron spectra were measured with the time-of-flight (TOF) method at four laboratory angles by using a beam swinger system and a well collimated TOF channel. Induced radioactivity was measured by detecting the gamma-rays from Be with a pure Ge detector. Experimental results are compared with other experimental data. The present result of neutron emission spectra are in qualitative agreement with other experimental data but that of 7 Be production was much larger than expected by the recent codes. Measurement will be extended to several incident energies up to 40 MeV.

Measurements of Differential Thick Target Neutron Yields and 7Be Production in the Li, 9Be (d, n) Reactions for 25 MeV Deuterons

Neutron emission spectra and production rates of radioactive nuclide 7Be in the (d, n) reactions on thick lithium and 9Be targets have been measured for 25 MeV deuterons at the Tohoku University AVF cyclotron (K=110) facility to provide basic data for the design of the intense neutron source, International Fusion Reactor Material Irradiation Test Facility (IFMIF). Neutron spectra were measured with the time-of-flight method at ten laboratory angles between 0° and 90° by using a beam swinger system. Data were obtained down to ~1 MeV from the highest energy, using a two-gain NE213 detector system. Induced radioactivity of 7Be was measured by detecting the 478 keV γ-rays from 7Be with a pure Ge detector. The experimental results of neutron spectra revealed clearly the entire shape of the neutron emission spectrum and the angular dependence including so called “high energy tail” extending up to ~40 MeV. The present data at 0° are in reasonable agreement with corresponding value by Lone et al. at 23 MeV above ~5 MeV, but show large discrepancy in the lower energy region. The results of 7Be production for both nuclei were much larger than expected by the calculation with a recent code IRAC.

Skin dose measurement for patients using imaging plates in interventional radiology procedures.

A method using europium-doped BaFBr imaging plates (IPs) has been developed to estimate and map values of entrance skin doses during interventional radiology (IR). IPs offer many advantages for measuring the entrance skin dose because they have a wide dynamic range (up to 100 Gy), provide high spatial resolution as a detector of two-dimensional images, and can be used repeatedly. The entrance skin dose was measured by fitting a 40 × 40 cm IP sheet around a patients back using a corset in clinical studies involving IR procedures at two hospitals. The corset can minimize a geometric discrepancy in dose estimates between the IP and the patient body. The entrance skin dose was measured by using photoluminescent glass dosimeters simultaneously, and both values were compared. The spatial relative dose profiles from both dose estimates showed generally good agreement; however, the doses obtained with glass dosimeter chips were often lower than those obtained with IPs. This discrepancy comes from a radiation shielding effect for x rays by IPs and a strong angular dependence of the glass dosimeter in low energy x-ray fields. Comprehensive results of this study demonstrated that IPs were able to measure entrance skin dose in even high dose regions with steep dose gradients and to determine the peak skin dose, without missing hot spots, over all ranges used during interventional radiology procedures. Use of the corset minimized variations associated with angular dependence.