Synthesized MR images: comparison with acquired images

Synthesized and directly acquired spin-echo images were compared in order to assess the validity of magnetic resonance (MR) image synthesis as a method enabling retrospective formation of images by interactive manipulation of scan parameters. Synthetic images subjectively compared favorably in both accuracy and precision with acquired images when formed for the same values of echo (TE) and repetition times (TR) and for interpolated and extrapolated values of both TE and TR. Plots of synthetic and acquired signals within the same pixel sectors quantitatively showed comparable values for several regions of interest in the brain. Percent error and noise-normalized differences between acquired and synthetic images were tested as a quantitative measure of accuracy. Percent error was consistently less than 5% for brain parenchyma, and synthetic signals were accurate to within four times the noise level at acquisition. The apparent signal-to-noise ratio of synthetic images was comparable, superior, or inferior to similar acquired images, depending on the values of TE and TR. Total acquisition time required for synthetic formation of images for arbitrary values of TE and TR was equivalent to that of a single direct acquisition with a TR of 2,500 msec.     

小檗碱对培养大鼠神经细胞内游离Ca2+的影响

以Fura-2/AM为细胞内钙离子的荧光指示剂,用AR-CM-MIC阳离子测定系统,直接测定了体外培养的新生大鼠神经细胞内游离钙([Ca²⁺]i)值,并观察了小檗碱(Ber)的影响。结果表明,Ber对神经细胞静息[Ca²⁺]i无明显影响,Ber1～100μmol·L^-1能剂量依赖地抑制去甲肾上腺素和H₂O₂引起的[Ca²⁺]i升高,其IC₅₀分别为39.9和17.9μmol·L^-1。高剂量Ber(10～100μmol·L^-1)能抑制高K+引起的[Ca²⁺]i升高。姐果提示,Ber对去甲肾上腺素,高K⁺及H₂O₂引起的[Ca²⁺]i升高的抑制作用可能是其抗脑缺血作用机制之一。