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111.
Summary
The introduction of fast gradient systems allows a reliable visualization of the extracranial carotid vessels by the magnetic
resonance angiography (MRA) which meanwhile is implemented into clinical routine. By the mainly applied time-of-flight (TOF)
technique, vessels can be imaged without contrast agent (CA). Due to the application of ultra-fast gradient-echo-sequences,
the first-pass evaluation of an intravenous bolus-injection of Gadolinium in the carotids from the aortic arch up to the skull
base can be performed in less than 30 s. In this study, advantages and disadvantages of both techniques are discussed. For
a qualitatively optimal contrast enhanced MRA (CE-MRA) timing parameters like injection delay, flow rate and the adjustment
of sequence parameters have to be considered in relation to the fast venous return from the sinus to the jugular veins. First,
the optimal time point of the data acquisition have been determined at a model and with a computer simulation in reference
to the presence of CA in the arteries. As a result, 90 % of the contrast contribution is defined by 16 % of the symmetrically
acquired central k-space lines. A measuring protocol for clinical use was obtained by a gradual variation of spacial resolution,
measuring time and CA-injection parameters and was proved in normal volunteers and patients. An exact determination of the
bolus-arrival-time by means of a test-bolus injection was acquired. The best qualitative results were achieved by a double-dose
injection at 2 ml/s injection rate. The temporal reserves of ultra-fast sequences should be invested in the improvement of
the spatial resolution. To date, further investigations related to the problem of optimal CA-application may improve the potentials
of CE-MRA procedures.
相似文献
112.
Nancy P. Caraway Gregg A. Staerkel Christina V. Fanning Datla G. Varma Raphael E. Pollock 《Diagnostic cytopathology》1994,11(3):255-261
The gross and microscopic appearances of aspirates from ten intramuscular myxomas are reported. The specimens were obtained from seven women and three men, ages 43 to 75, who had tumors involving the muscles of the thigh (7), upper arm (2), and forearm (1). Magnetic resonance (MR) imaging performed in six of the ten cases revealed well-defined, sharply demarcated tumors exhibiting low signal intensity relative to muscle on the T1-weighted images. The tumors were hyperintense to muscle on T2-weighted images. All aspirated tissues were clear, tenacious, and viscous. Smears contained few spindled and histiocytoid cells in an abundant mucoid background. Spindle cells demonstrated long cytoplasmic processes that in areas intertwined to form fibrillar tangles. Nuclei were oval to spindled with fine chromatin and inconspicuous nucleoli. Capillaries were sparse with simple (nonplexiform) branching. The differential diagnosis of myxoid lesions of the extremities includes benign entities such as myxoid schwannoma and neurofibroma, mesenchymal repair, and ganglion cyst, as well as malignant neoplasms such as myxoid liposarcoma, fibrosarcoma, malignant fibrous histiocytoma, and extraskeletal chondrosarcoma. The findings of this study revealed that, although the cytologic features were suggestive of intramuscular myxoma, a definitive diagnosis was often difficult, owing to scant cellularity and lack of distinctive cytologic features. The MR imaging findings may be utilized as an adjunct to the cytologic features to more confidently suggest a diagnosis of intramuscular myxoma. Diagn Cytopathol 1994;11:255–261. © 1994 Wiley-Liss, Inc. 相似文献
113.
Florian A Kagerer Jeff J Summers Winston D Byblow Bruce Taylor 《Movement disorders》2003,18(8):919-927
In 6 patients with Parkinson's disease (PD) and 6 age-matched controls, transcranial magnetic stimulation was applied at 56 regions over the motor cortex and premotor cortex of each hemisphere, with the first dorsal interosseous (FDI) muscle of both hands activated at 15% maximum voluntary contraction during stimulation. For each site, motor evoked potential (MEP) landmarks were recovered, including MEP amplitude, MEP onset latency, and silent period duration. Scaled MEP amplitudes were used to construct individual cortical maps of the FDI muscles. The maps revealed an anterior displacement of the muscle representation in PD patients. This anterior shift over motor cortical areas may reflect increased contributions of corticocortical connections between motor cortex and premotor cortical areas, possibly enhanced by the visual feedback aspect of the task. These alterations may reflect adaptations to the impairments in striatocortical circuits in PD. 相似文献
114.
115.
Ronald G. Pratt Jie Zheng Brent K. Stewart Yoseph Shiferaw Anthony J. McGoron Ranasinghage C. Samaratunga Stephen R. Thomas 《Magnetic resonance in medicine》1997,37(2):307-313
A limited flip angle gradient-echo 3D volume acquisition imaging protocol for mapping partial pressure of oxygen (pO2) in perfluorocarbon compounds (PFCs) at low field (0.14 T) is presented. The pO2 measurement method is based on the paramagnetic effect of dissolved molecular oxygen (O2) which reduces the PFC 19F T1? Specific objectives related to imaging of PFCs through use of the protocol include improved image signal-to-noise characteristics and elimination of 19F chemical shift artifacts. A parametric Wiener deconvolution filtering algorithm is used for suppression of 19F chemical shift artifacts. Application of the protocol is illustrated in a series of calculated pO2 maps of a gas equilibrated, multi-chamber phantom containing perfluorotributylamine (FC-43). The utility of the protocol is demonstrated in vivo through images of a commercially available perfluorocarbon based blood substitute emulsion containing FC-43 sequestered in the liver and spleen of a rat. 相似文献
116.
117.
118.
目的探讨MR扩散张量成像(DTI)观察豆状核年龄相关性变化的价值与意义。方法69名健康志愿者纳入本研究。入组对象按年龄分为3组:≤30岁(I)组,22例;31~50岁(Ⅱ)组,24例;〉50岁(Ⅲ)组,23例。利用DTI分别测量受试者大脑左右两侧壳核、苍白球的表观扩散系数(ADC)值、部分各向异性(FA)值及扩散张量特征值λ1、λ2、λ3。分析不同年龄组间ADC、FA、λ1、λ2、λ3值的差异及与年龄的相关性。结果I、Ⅱ、Ⅲ组的壳核ADC值分别为:(6.68±0.40)×10^-4、(6.47±0.36)×10^-4、(6.44±0.34)×10^-4mm^2/s,苍白球ADC值分别为:(6.13±0.50)×10^-4、(6.05±0.33)×10^-4、(6.05±0.52)×10$-4mm^2/s。I、Ⅱ、Ⅲ组的壳核FA值分别为:0.20±0.03、0.23±0.03、0.25±0.03,苍白球FA值分别为:0.35±0.03、0.36±0.03、0.37±0.04。各年龄组内壳核ADC值大于苍白球,而FA值小于苍白球。壳核FA值的组问差异有统计学意义(F=10.082,P=0.000),壳核I、Ⅱ、Ⅲ组入,值分别为(5.35±0.45)×10^-4、(5.04±0.46)×10^-4、(4.90±0.44)×10^-4mm^2/s,差异亦有统计学意义(F=5.675,P=0.005);壳核FA值与年龄呈正相关(r=0.555,P〈0.01),λ3值与年龄呈负相关(r=-0.440,P〈0.01)。结论壳核FA值随年龄的增长而上升,λ3值随年龄的增长而下降。 相似文献
119.
Manolo Piccirilli Jacopo Lenzi Catia Delfinis Guido Trasimeni Maurizio Salvati Antonino Raco 《Child's nervous system》2006,22(10):1332-1337
Case reports The authors report their experience about three children (two girls, one boy; average age 1.6 years) with a spontaneous regression of optic gliomas. All of them had a previous diagnosis of neurofibromatosis type 1 (NF 1). None of them underwent surgery or biopsy nor received chemotherapy or radiotherapy. The complete regression was documented by MRI scans performed during a mean follow-up of 6.3 years.Literature review Moreover, the authors analyze the features of the 16 cases previously reported in English literature of spontaneously regressed optic gliomas with an overview of the different therapeutic strategies. The knowledge that this kind of tumor, particularly in young patients, may regress is important in the decision of the best therapeutic approach. 相似文献
120.
Frank de Vocht Berna van-Wendel-de-Joode Hans Engels Hans Kromhout 《Magnetic resonance in medicine》2003,50(4):670-674
The interactive use of magnetic resonance imaging (MRI) techniques is increasing in operating theaters. A study was performed on 17 male company volunteers to assess the neurobehavioral effects of exposure to magnetic fields from a 1.5 Tesla MRI system. The subjects' neurobehavioral performances on a neurobehavioral test battery were compared in four 1-hr sessions with and without exposure to magnetic fields, and with and without additional movements. Adverse effects were found for hand coordination (-4%, P < 0.05; Pursuit Aiming II) and near visual contrast sensitivity (-16% and -15%, P < 0.10; Vistech 6000). The results from the remaining tests were inconclusive due to a strong learning effect. No additional effect from gradient fields was detected. The results indicate that working near a 1.5 Tesla MRI system may lead to neurobehavioral effects. Further research is recommended, especially in members of operating teams using interactive MRI systems. 相似文献