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51.
A new technique to avoid the initial signal fluctuations in steady-state free precession (SSFP)-sequences, such as trueFISP, FIESTA, and refocused FFE, is presented. The "transition into driven equilibrium" (TIDE) sequence uses modified flip angles over the initialization phase of a SSFP experiment, which not only avoids image artifacts but also improves the signal-to-noise ratio (SNR) and contrast behavior compared to conventional approaches. TIDE is demonstrated to be robust against variations of T(1) and T(2), and leads to a monotonous signal evolution for off-resonance spins. The basic principles can also be applied repetitively to optimize continuous 3D acquisitions. 相似文献
52.
Sonnet S Buitrago-Téllez CH Scheffler K Strecker R Bongartz G Bremerich J 《AJR. American journal of roentgenology》2002,179(1):159-165
OBJECTIVE: Time-resolved pulmonary two-dimensional MR projection angiography is a fast acquisition technique that allows the generation of dynamic projection angiograms by a method similar to that used to generate digital subtraction angiograms. MR images are obtained after subtracting the mask defined at the beginning of the sequence from later images, thus generating time-resolved continuous projection angiograms that depict the passage of a bolus through the pulmonary circulation. This article describes the application of this novel technique in three patients with pathologic conditions not previously described with this modality and two control subjects. CONCLUSION: The analysis of the findings on dynamic time-resolved contrast-enhanced two-dimensional MR projection angiography shows that this technique is useful not only in revealing morphologic changes associated with pulmonary disorders but also in following the passage of the bolus through the cardiopulmonary circulation. The latter capability allows qualitative detection of normal or abnormal pathways and thus is potentially of value in the assessment of several pulmonary disorders. 相似文献
53.
54.
Schulz T Schneider JP Bootz F Keiner S Scheffler B Weidenbach H Dietrich J Schirmer T Schmidt F Kahn T 《Journal of magnetic resonance imaging : JMRI》2001,13(1):3-11
Magnetic resonance imaging (MRI) allows excellent tissue characterization in the area of the petroclival region and can depict lesions not visualized with ultrasound or computed tomography (CT). The aim of this study was to demonstrate the clinical feasibility and utility of an interactive MR-guidance system to target and biopsy tumors in the petroclival region. MRI-guided biopsies of 10 patients with tumors in the clivus and petrous apex were performed in an open 0.5-T MR system. Lesions were targeted through a transsphenoidal or transnasal approach. Imaging during biopsies was achieved by a combination of standard and interactive mode. T1-weighted spin-echo, T2-weighted fast spin-echo (FSE), and three-dimensional T1-weighted gradient-echo (GRE) scans (standard mode) were selected to provide optimal tissue characterization for both the lesion and surrounding structures and varied according to the anatomic site. For interactive imaging, T1-weighted GRE and T2-weighted FSE sequences were used. We performed MRI-guided transsphenoidal biopsies in 10 patients who had lesions identified by CT (n = 5) and/or MRI (n = 10). The indications for biopsies were to differentiate between suspected malignant processes (n = 4 ) and benign processes (n = 6). Lesions adjacent to structures like the internal carotid artery were accurately targeted in particular. All biopsies were performed successfully and were the basis for selection of further treatment. No complications occurred during the procedures. An open MR system allows interactive control of biopsies in the area of the petroclival region, providing maximum patient safety and diagnostic accuracy not possible in other systems. The advantages of MRI tissue characterization are combined with an interactive, one-step method of localization and targeting, as well as tissue sampling. J. Magn. Reson. Imaging 2001;13:3-11. 相似文献
55.
Two children with acute lymphoblastic leukaemia (ALL) taking daily 6-mercaptopurine as part of a national UK therapeutic trial repeatedly developed profound myelosuppression on 25% of the standard protocol dose. Both were found to have undetectable intracellular activity of thiopurine methyltransferase (TPMT), an enzyme controlling one of the major alternative catabolic pathways of 6-mercaptopurine, and both produced higher concentrations of cytotoxic drug metabolites at 10-25% of the protocol dose than other patients taking 100%. It is supposed that these patients represent the 0.33% of the normal population constitutionally lacking TPMT. It is important to recognise such individuals both to avoid fatal bone marrow failure through inadvertent overdosage, and to be reassured that an adequate drug effect can be achieved at around 10% of the standard dose. 相似文献
56.
57.
Photochemical inactivation of duck hepatitis B virus in human platelet concentrates: a model of surrogate human hepatitis B virus infectivity 总被引:1,自引:0,他引:1
BACKGROUND: Photochemical decontamination of platelet concentrates (PCs) has been demonstrated by the use of 8-methoxypsoralen and ultraviolet A light. Systems for studying the inactivation of blood- borne viruses facilitate the evaluation of photochemical decontamination protocols. STUDY DESIGN AND METHODS: Duck hepatitis B virus (HBV), a model for human HBV, was adapted for the study of hepadnavirus inactivation. A highly specific in vitro infectivity assay used primary duck hepatocyte cultures and was followed by the detection of replicated duck HBV sequences. RESULTS: Duck HBV-infected primary duck hepatocyte cultures produced authentic infectious virus. High- titer (> 10(9) virus genome equivalents/mL) duck HBV-infected sera were completely inactivated in serum or PCs by the use of 100 micrograms per mL of 8-methoxypsoralen and 70 J per cm2 of ultraviolet A light. Intracellular duck HBV (> 4.2 log10) in PCs was also inactivated. Culture results were confirmed by a sensitive duckling infectivity assay that indicated that 6.3 log10 of infectious duck HBV had been inactivated by photochemical decontamination. CONCLUSION: The sensitivity of the culture assay was comparable to that of the duckling assay using polymerase chain reaction gene amplification to detect duck HBV. Duck HBV inactivation in PCs was dependent on the dose of ultraviolet A light and independent of 8-methoxypsoralen concentrations of 100 to 300 micrograms per mL: 100 micrograms per mL 8- methoxypsoralen inactivated 4 to 5 log10 of virus in conjunction with 20 to 40 J per cm2 of ultraviolet A light. The polymerase chain reaction-enhanced duck HBV culture system has utility in optimizing photochemical decontamination protocols. 相似文献
58.
Auditory cortical responses in hearing subjects and unilateral deaf patients as detected by functional magnetic resonance imaging 总被引:9,自引:4,他引:5
Scheffler K; Bilecen D; Schmid N; Tschopp K; Seelig J 《Cerebral cortex (New York, N.Y. : 1991)》1998,8(2):156-163
Functional magnetic resonance imaging is a non-invasive method for the
detection of focal brain activity at high spatial resolution. Acoustic
stimulation leads to a blood oxygenation level dependent signal change in
the plane of the superior temporal gyrus. The dependence of this response
in the auditory cortex on binaural, monaural left and monaural right
acoustic stimulation for 10 healthy subjects and five monaural deaf
patients is described. Acoustic stimulation consists of 1000 Hz pulsed sine
tones at a pulse rate of 6 Hz and a sound pressure level of 95 dB. For
monaural stimulation, normal-hearing subjects revealed a strong
lateralization of cortical response towards the contralateral hemisphere.
The lateralization ratios between left and right hemispheric response areas
were 3.4-5.2 for monaural stimulation and nearly balanced for binaural
stimulation. Additionally, the sum of cortical activation volumes induced
by monaural left and right stimulation was approximately 30% smaller than
for binaural stimulation, indicating either inhibitory mechanisms or
neuronal facilitation within the auditory pathways. For monaural deaf
subjects the lateralization ratio between left to right response was just
1.3 towards the contralateral hemisphere of the healthy ear, which is
comparable to binaural responses of normal-hearing subjects. This
observation seems to indicate a plasticity or a reorganization of auditory
pathways of monaural deaf patients.
相似文献
59.