Acoustical impulse responses of the external ear system are measured in order to investigate human three-dimensional auditory localization. A sound source of electric spark discharge is presented in nine directions for each of four vertical planes, 1.5 m from the center of the subject's head. The results show that a human pinna works as a compound sound reflector which produces major reflected components within 350 microseconds. The relationship between the direction of the sound source and the impulse response is clearly shown by the use of an envelope formation technique and radial ray displays.
Two-dimensional digital mammography with synchrotron radiation was developed to obtain highcontrast images. The system consisted of a single-crystal monochromator with an asymmetrically re¯ecting silicon h311i crystal, an avalanche multiplication-type pick-up tube camera with ā uorescent plate and lens-coupling system, and a workstation. The preliminary experiment was carried out with a synchrotron light source at the Photon Factory, KEK, in Tsukuba. Breast phantom and human breast specimen were imaged using 20 keV monochromatic synchrotron X-rays. These images were compared with images obtained by a conventional mammography system. The minimal detectable diameter of microcalci®cation on the breast phantom was 165 mm by the two-dimensional synchrotron radiation imaging system and 196 mm by the conventional mammography system. In the breast specimens, microcalci®cation and soft-tissue masses were clearly imaged and their contrasts improved by about 18% and 38%, respectively, in the two-dimensional synchrotron radiation system. The entrance surface dose of the two-dimensional synchrotron radiation system was about 400 mR, which was almost the same value as the 420 mR delivered by the conventional mammography system. Two-dimensional synchrotron radiation digital mammography is considered to be a powerful imaging modality for diagnosing breast tumors.
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