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.     

2,4-二氨基-5-取代苄基嘧啶类化合物的合成及其抑酶活性

本文设计并合成了18个在苄基上带有不同体积取代基的2,4-二氨基-5-取代苄基嘧啶类化合物。测定了这些化合物对乳酪菌二氢叶酸还原酶及对鸡肝二氢叶酸还原酶的表观50%抑制作用。其中2,4-二氨基-5-(3′-羟基-4′-甲氧基)苄基、2,4-二氨基-5-(3′-甲氧基-4′-甲氧乙氧基)苄基嘧啶对上述二氢叶酸还原酶(DHFR)的选择性较好。     

Complex fractures of the clivus: diagnosis with CT and clinical outcome in 11 patients

During a 20-month period, fractures of the clivus occurring after craniocerebral trauma were diagnosed with computed tomography (CT) in 11 patients. Five patients had longitudinally oriented fractures; these were fatal in four patients due to either vertebral-basilar artery occlusion, brain stem trauma, or both. Six other patients had transversely oriented fractures that extended through the carotid canal and petrous temporal bone. While less frequently contributing directly to mortality, transverse fractures were also associated with cerebrospinal fluid leaks (two patients) and a cavernous sinus-carotid fistula (one patient). They were not as frequently associated with Horner syndrome or cranial nerve deficits as suggested in the current literature. This retrospective evaluation reveals two distinct injury patterns that demonstrate a difference in related morbidity and mortality.     

长鞭红景天化学成分的研究

长鞭红景天化学成分的研究彭江南，葛永潮，李晓晖（军事医学科学院放射医学研究所，北京１００８５０）红景天是滋补强壮药物，目前正引起人们极大的兴趣，现已有一些产品上市。我们曾对数种红景天的化学成分进行过研究［１～４］。长鞭红景天（Ｒｈｏｄｉｏｌａｆａｓｔ...