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정상적인 노화 과정에서 국소뇌포도당대사의 변화 : FDG PET 연구
윤준기(Joon Kee Yoon),김상은(sang Eun Kim),이경한(Kyung Han Lee),최용(Yong Choi),최연성(Yearn Seong Choe),김병태(Byung Tae Kim) 대한핵의학회 2001 핵의학 분자영상 Vol.35 No.4
N/A Purpose: Normal aging results in detectable changes in the brain structure and function. We evaluated the changes of regional cerebral glucose metabolism in the normal aging process with FDG PET. Materials and Methods: Brain PET images were obtained in 44 healthy volunteers (age range 20-69 ‘y’: M:F = 29:15) who had no history of neuropsychiatric disorders. On 6 representative transaxial images, Rols were drawn in the cortical and subcortical areas. Regional FDG uptake was normalized using whole brain uptake to adjust for the injection dose and correct for nonspecific declines of glucose metabolism affecting all brain areas equally. Results: In the prefrontal, temporoparietal and primary sensorimotor cortex, the normalized FDG uptake (NFU) reached a peak in subjects in their 30s. The NFU in the prefrontal and primary sensorimotor cortex declined with age after 30s at a rate of 3.15%/decade and 1.93%/decade, I'6Spectively. However, the NFU in the temporoparietal cortex did not change significantly with age after 30s. The anterior (prefrontal) posterior (temporoparietal) gradient peaked in subjects in their 30s and declined with age thereafter at a rate of 2.35%/decade. The NFU in the caudate nucleus was decreased with age after 20s at a rate of 2.39%/decade. In the primary visual cortex, putamen, and thalamus, the NFU values did not change significantly throughout the ages covered. These patterns were not significantly different between right and left cerebral hemispheres. Of interest was that the NFU in the left cerebellar cortex was increased with age after 20s at a rate of 2.86%/decade. Conclusion: These data demonstrate regional variation of the age-related changes in the cerebral glucose metabolism, with the most prominent age-related decline of metabolism in the prefrontal cortex. The increase in the cerebellar metabolism with age might reflect a process of neuronal plasticity associated with aging. (Korean J Nucl Med 2001;35:231-240)
윤준기(Jun-Ki Youn),오형철(Hyeong-Cheol Oh) 한국정보과학회 2004 한국정보과학회 학술발표논문집 Vol.31 No.2Ⅰ
O.18um 표준 셀 라이브러리로 구현할 때 2.69 ns의 임계 경로 지연을 가지는 SIMD 구조의 포화 덧셈기를 설계하였다. 기존의 설계에서 임계 경로를 구성하는 CLA를, 8비트 까지만 자리올림 (Carry)이 전파될 때 정확한 계산을 보장하는 근사 덧셈기의 형태로 설계한 결과, 임계 경로 시간 지연을 약 22% 감소시킬 수 있었다. 파이프라인 구조 프로세서에서 사용될 포화 덧셈기의 근사계산이 실패하는 경우에는, 추가적인 2개의 클록주기 동안 재계산을 수행하게 된다.