• Progress in Medical Physics
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• v.12 no.2
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• pp.113-124
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• 2001

For veterinary imaging diagnosis, we obtained MR images of the canine brain, spine, kidney and pelvis from 3T MRI system which was equipped with the world first 3T active shield magnet. Spin echo (SE) and fast Spin Echo (FSE) images were obtained from the canine brain, spine, kidney and pelvis of normal and sick dogs using a homemade birdcage and transverse electromagnetic (TEM) resonators operating in quadrature and tuned to 128 MHz. In addition, we employed a homemade saddle shaped RF coil. Typical common acquisition parameters were as follows: matrix=512$\times$512, field of view (FOV)=20cm, slice thickness=3 w, number of excitations (NEX)=1. For T1-weighted MR images, we used TR=500 ms, TE=10 or 17.4 ms. For T2-weighted MR images, we used TR=4000 ms, TE=108 ms. Signal to noise ratio (SNR) of 3T system was measured 2.7 times greater than that of prevalent 1.57 system. The high resolution images acquired in this study represent more than a 4-fold increase in in-plane resolution relative to conventional images obtained with a 20 cm field of view and a 5 mm slice thickness. MR images obtained from 3T system revealed numerous small venous structures throughout the image plane and provided reasonable delineation between gray and white matter The present results demonstrate that the MR images from 3T system could provide better diagnostic quality of resolution and sensitivity than those of 1.5T system. The elevated SNR observed in the 3T high field magnetic resonance imaging can be utilized to acquire images with a level of resolution approaching the microscopic structural level under in vivo conditions. These images represent a significant advance in our ability to examine small anatomical features with noninvasive imaging methods. Moreover, MRI technique could begin to apply for veterinary medicine in Korea.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.40 no.11
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• pp.9-18
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• 2003

Two configurations of Film Bulk Acoustic Wave Resonators with acoustic quater-wave bragg reflector layers are theoretically analyzed using equivalent circuits and the difference of their characteristics are discussed. We compare the characteristics of λ/2 mode to those of ideal FBAR with top and bottom electrode contacting air and the characteristics of λ/4 mode to those of ideal FBAR with top electrode contacting air and bottom electrode clamped. We assume that the piezoelectric film is ZnO, the electrode is A1 and the substrate is Si, ABCD parameters are extracted and input impedance is calculated by converting the equivalent circuit from Mason equivalent circuits to the simplified equivalent circuits that ABCD parameters are extracted possible, From the variation of resonance frequency due to the change of thickness of reflector layers and the variation of electrical Q due to the change of mechanical Q of reflector layers, it is confirmed that the reflector layer just under the bottom electrode have the greatest effect on the varation of resonance frequency and electrical Q. It is shown that the number of reflector layers required for the saturation of electrical Q decreases with the increase of the impedance ratio of reflector layers and electrical Q of λ/2 mode is larger than that of λ/4 mode, Electromechanical coupling factor is independent of the number of layers, The impedance ratio of reflector layers becomes larger as the electromechanical coupling factor becomes larger, The electromechanical coupling factor of the two mode are smaller than those of ideal FBARs because of the trapping of acoustic energy in the reflector layers, The insertion loss of the ladder filter decreases with the increase of the number of reflector layers but the bandwidth is not affected much by the number of reflector layers, As the impedance ratio of reflector layers becomes larger the insertion loss becomes smaller and the bandwidth becomes wider, In our analysis of the two mode, characteristics of λ/2 mode appear to be slightly more favorable than that of λ/4 mode