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A novel balanced SSFP technique for the separation or suppression of different resonance frequencies (e.g., fat suppression) is presented. The method is based on applying two alternating and different repetition times, TR(1) and TR(2). This RF scheme manipulates the sensitivity of balanced SSFP to off-resonance effects by a modification of the frequency response profile. Starting from a general approach, an optimally broadened stopband within the frequency response function is designed. This is achieved with a TR(2) being one third of TR(1) and an RF-pulse phase increment of 90 degrees . With this approach TR(2) is too short ( approximately 1 ms) to switch imaging gradients and is only used to change the frequency sensitivity. Without a significant change of the spectral position of the stopband, TR(1) can be varied over a range of values ( approximately 2.5-4.5 ms) while TR(2) and phase cycling is kept constant. On-resonance spins show a magnetization behavior similar to balanced SSFP, but with maximal magnetization at flip angles about 10 degrees lower than in balanced SSFP. The total scan time is increased by about 30% compared to conventional balanced SSFP. The new technique was applied on phantoms and volunteers to produce rapid, fat suppressed images. 相似文献
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Teng-Yi Huang Hsiao-Wen Chung Fu-Nien Wang Cheng-Wen Ko Cheng-Yu Chen 《Magnetic resonance in medicine》2004,51(2):243-247
In this work the feasibility of separating fat and water signals using the balanced steady-state free precession (SSFP) technique is demonstrated. The technique is based on the observation (Scheffler and Hennig, Magnetic Resonance in Medicine 2003;49:395-397) that at the nominal values of TE = TR/2 in SSFP imaging, phase coherence can be achieved at essentially only two orientations (0 degrees and 180 degrees ) relative to the RF pulses in the rotating frame, under the assumption of TR < T2, and independently of the SSFP angle. This property allows in-phase and out-of-phase SSFP images to be obtained by proper choices of the center frequency offset, and thus allows the Dixon subtraction method to be utilized for effective fat-water separation. The TR and frequency offset for optimal fat-water separation are derived from theories. Experimental results from healthy subjects, using a 3.0 Tesla system, show that nearly complete fat suppression can be accomplished. 相似文献
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比较了几种拆分剂分离猪血红细胞中血红蛋白的效果,其中羧甲基淀粉(CMS)得到最佳效果。脱色球蛋白的功能性实验证实其有良好的起泡和乳化性能,氨基酸分析显示其赖氨酸和组氨酸的含量较高,适合作为婴儿的营养强化剂。 相似文献
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TAMÁS HENICS & DENYS N. WHEATLEY 《International journal of experimental pathology》1997,78(5):343-354
Hep-2, human epithelial carcinoma cells, and human foreskin fibroblasts (FF9 and FF13) were exposed to either an ultrafiltrate (< 50 kD) of human sera or the weak base, procaine hydrochloride, to induce reversible cytoplasmic vacuolization. The formation of vacuoles was shown not to be due to imbibition of medium. Ultrastructural details obtained from various stages of vacuole formation were compared. In both cases of induction vacuoles were irregular and often appeared membraneless, with little in the way of electron-dense content. They started to form in the perinuclear cytoplasm and progressed towards the periphery. Osmotic stress was not involved since mitochondria remained normal throughout a vacuolization episode.
Vacuoles were often seen in close contact with filamentous structures, and this association remained detectable at late stages of the phenomenon. Fluorescent visualization of F-actin confirmed that the vacuoles were frequently bordered by microfilaments. No major metabolic impairment was apparent in vacuolized cells as judged by protein synthesis measurements, but nuclear fluorescence (DNA content) and forward light scatter (nuclear volume) by flow cytometric analysis suggested late S phase and G2 retardation.1 H-nmr relaxation measurements indicated intracellular water restricted in motional characteristics in vacuolized cells. The possibility of a restricted cytoplasmic phase separation as part of a transient adaptation response is raised, and a hypothesis to explain the findings is discussed. 相似文献
Vacuoles were often seen in close contact with filamentous structures, and this association remained detectable at late stages of the phenomenon. Fluorescent visualization of F-actin confirmed that the vacuoles were frequently bordered by microfilaments. No major metabolic impairment was apparent in vacuolized cells as judged by protein synthesis measurements, but nuclear fluorescence (DNA content) and forward light scatter (nuclear volume) by flow cytometric analysis suggested late S phase and G2 retardation.
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Treatment of complete acromioclavicular joint disruption remains controversial and ranges from rehabilitation to extensive surgical reconstruction. However, high-grade injuries (type IV, V, and VI) are typically treated surgically. Most reconstruction techniques addressing these injuries selectively focus on coracoclavicular ligament augmentation because it has been shown to be the primary stabilizer of the acromioclavicular joint. The conventional coracoclavicular polydioxanone (PDS) loop, which is widely performed, has been detected to have some pivotal disadvantages, including anterior subluxation of the clavicle, extensive preparation of the coracoid, and bony avulsion of the clavicle as a result of rotational clavicle movement. Therefore we present an augmentation technique that reduces these complications by replicating the orientation of the native coracoclavicular ligament complex and providing a minimally invasive subcoracoid and clavicular fixation of a double PDS loop by use of 2 flip buttons, typically used for extracortical anterior cruciate ligament graft fixation. The key step of the procedure includes the anatomic, secure, and stable placement of the double PDS cerclage under the coracoid base transferring a flip button through a coracoid bone tunnel. Our clinical experience shows that the presented technique is easy to perform and has a comparable invasiveness to recently presented arthroscopic techniques. 相似文献