This paper presents a 90GHz-band waveguide orthomode transducer (OMT) which is composed of a short circuited circular common waveguide and two branching rectangular waveguides dug through a metal block. An analysis and design of the OMT are performed using full wave modematching techniques. A 90GHz-band OMT fabricated with the aid of the analysis and design technique has realized excellent performances.
For more effective Tl-201 imaging, the location and width of the energy window set on the Hg-201 x-rays photopeak was investigated using Monte Carlo simulation and phantom experiments. We calculated energy spectra and investigated the amount of primary and scattered photons within various energy windows set on the x-rays photopeak. The energy resolution (ER) at 71 keV (the peak of the x-rays photopeak) was changed to 10%, 12%, 14% and 16%. The relationships between the energy window and the primary counts rate or the scatter fraction (= scattered counts/primary counts, SF) were obtained. By compromise between the primary counts rate and the SF for ER = 12%, the optimum energy window was determined as a wider off-peak window, 77 keV +/- 14.3% (66-88 keV). This off-peak window increased the primary counts rate by 12.5% and decreased the SF by -17% as compared with the conventional on-peak energy window (71 keV +/- 10%, 64-78 keV). When this off-peak widow acquisition was compared with the conventional on-peak window one on a gamma camera, planar and SPECT images using the off-peak widow clearly showed superior results qualitatively and quantitatively.
SUMMARY
In order to implement the measurement and the evaluation of analog signals in high accuracy, to detect not only amplitude level but also phase information is necessary. For example, measurement of very small phase difference is desired in fields such as electric power and organism‐related. Particularly, in organism‐related field, impedance measurement is important and it is used to measure the urinary bladder volume, the respiratory volume, and so on. For these purposes, portable and real‐time measurement devices with small sized is suitable. In this paper, we propose the urinary bladder volume measurement circuit using a simplified very small phase difference measurement circuit. This circuit is able to infer the changes of urinary bladder volume by measuring bioimpedance and phase difference of urinary bladder noninvasively with four‐terminal method.
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