The aim of this study was to propose simultaneous analysis of effective transverse relaxation time (T₂) and biexponential diffusion parameters for breast magnetic resonance imaging (MRI) using conventional sequences available with most clinical MRI scanners. Normal mammary glands and malignant lesions were compared in terms of T₂ value, as well as fast and slow component apparent diffusion coefficients (ADC_fast and ADC_slow) . The study included 98 women who underwent breast MRI and for whom pathological diagnosis was obtained. Diffusion weighted imaging (DWI) was performed at b values of 0, 200, 400, 800, 1500, 2200, and 3000s/mm². The T₂ correction of DW images were performed using diffusion echo-planar imaging-T₂-weighted images with multiple TE because TE increased with increasing b values. Biexponential fitting was performed using the b value range of 0-3000s/mm² for malignant lesions, and 0-1500s/mm² for normal mammary glands, to minimize the influence of noise. Malignant lesions showed significantly higher T₂ values, lower ADC_fast and ADC_slow compared with normal mammary glands. In addition, fast component fraction was significantly higher in malignant lesions than in normal mammary glands. In conclusion, simultaneous T₂ and biexponential diffusion analyses can provide more detailed information on the characteristics of breast lesions.

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【purpose】In order to measure the angular dependence on a personal dosimeter, a new experimental procedure using diagnostic X-ray equipment was proposed. Furthermore, our method was applied to measure the angular dependences of the small-type optically stimulated luminescence (OSL) dosimeter. To evaluate the experimental results, Monte-Carlo simulations of angular dependences were performed.
【methods and materials】We developed a new system consisting of a collimator and a rotation unit. An original design of the collimator was proposed by Takegami et al., and we modified the size of the through hole so as to optimize the irradiation field (diameter of 2cm) on the OSL dosimeter. The rotational unit combined with an originally developed supporting fixture can fix a dosimeter in a free air condition. The OSL dosimeters were irradiated by a diagnostic X-ray with tube voltages of 40-140kV, and angular dependences for every 15 degrees were determined. The source to dosimeter distance was 150 cm, and tube current-time product was 100 mAs. For the simulation, we used a Monte-Carlo simulation code (EGS5) . The published micro-CT data were used as a reference to construct the precise structure of the dosimeter. The X-ray spectra were introduced to the dosimeter and energy depositions calculated.
【results】For X-rays having tube-voltages of 40-140 kV, we determined angular dependence of the OSL dosimeter every 15 degrees with uncertainties of approximately 5%. For these conditions, simulated data was determined with uncertainties of less than 1%. The experimental data were in good agreement with the simulated data.
【conclusion】We concluded that our system was able to measure the angular dependences of the personal dosimeters.

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To measure X-ray spectra with high count rates, we developed a detector consisting of a cerium-doped yttrium aluminum perovskite [YAP (Ce) ] crystal with a decay time of 30 ns and a multipixel photon counter (MPPC) . The photocurrents flowing through the MPPC are converted into voltages and amplified by a high-speed current-voltage amplifier, and 200-ns-width event pulses from the amplifier are sent to a multichannel analyzer (MCA) to measure X-ray spectra. We used three MPPCs of 100, 400 and 1,600pixels/mm², and the MPPCs were driven under pre-Geiger mode at a temperature of 23℃. At a tube voltage of 100kV and a tube current of 5.0μA, the maximum count rate was 6.0 kilo-counts per second using a 400-pixel YAP (Ce) -MPPC detector.

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