Invited. Ultrafast MR imaging of the abdomen: Echo planar imaging and diffusion-weighted imaging

Ultrafast MRI technique has become available with the introduction of new generation MR scanners for abdominal imaging. However, there is no consensus about the optimal imaging acquisition at the present time. Because single shot echo planar imaging (EPI) technique is based on high technology and had just applied in clinical imaging, further clinical investigation will be needed. Currently, the hypersensitivity to magnetic inhomogeneity and local magnetic susceptibility and the low spatial resolution may limit the widespread application of EPI technique. In addition to providing information for morphologic diagnosis, EPI will be more widely used for functional and qualitative diagnosis. Diffusion-weighted imaging can be used for differentiation of solid tumors according to their different cellular construction, evaluation of cystic lesions based on the different viscosity of their contents, and assessment of diffused pathologic changes in the parenchyma of solid organs. In addition to the previous parameters such as proton density and T1 and T2 values, diffusion factors may provide important information for the qualitative and dynamic evaluation of abdominal pathologic changes. Even though there are many difficulties that must be solved for diffusion-weighted imaging, a more wide application of this technique is expected through technologic improvement.     

海口市流动儿童家长计划免疫认知现状调查分析

目的 了解流动人口儿童家庭对计划免疫的认知状况，为当地制定计划免疫规化提供依据。方法采取横断面调查的方法，对全市流动人口聚居地的流动儿童家庭进行了普查。蛄果全市137个流动人口聚居点1-7岁的流动人口儿童家庭共有5035户，对应接种的疫苗0PV、MV、DPT、BCG、HBV等五种疫苗认知率分别为：54．9％、52.7％、46.0％、42．9％和57.4％。认为免疫接种重要的占93．9％，不重要占1．5％，表示不知道占4．7％；有97．2％的家庭能获取预防接种信息；获取信息的的渠道以医生为主占65．1％、其次为当地干部占22.2％。其认知率分布的特点是：(1)市区人群、农村较低；(2)随文化层次递增而增高；(3)任职于政府机关或合资企业者较高，农民较低；(4)随人口数递增而降低；(5)居住时间4年以内认知率逐步升高，5年以后表现为下降；(6)汉族明显高于其他民族。蛄论海口市流动儿童家长对计划免疫的认知状况堪忧，应在卫生部门宣教的基础上，采取多种形式加强社会宣传。     

Diffusion-weighted multiple shot echo planar imaging of humans without navigation

A new method is proposed for reducing the artifacts produced in diffusion-weighted imaging. When data are acquired using multiple shot echo planar acquisitions, conventional reconstruction methods produce artifactual images as a consequence of diffusion weighting and small amounts of bulk motion of the subject. If the amount of motion can be determined, it is possible to correct the data before reconstruction, which removes the artifact. A method for estimating the motion from the acquired data has been developed and evaluated. This method assumes that ghost image effects will be minimized when motion has been correctly compensated. By considering the amount of signal in the background of the image, appropriate corrections to the data can be made, and the accuracy of the motion compensation may be estimated. This technique has been evaluated by computer simulation, and its performance has been demonstrated in a phantom and humans with both two- and four-shot echo planar acquisitions and using both “mosaic” and “interleaved” sampling schemes.     

北京市1985～1995年计划免疫接种率监测分析

本文对北京市1985～1995年间计划免疫接种率监测资料与相应传染病发生情况进行比较分析,结果显示免疫接种率达到一定高度的水平时,相应传染病发生率呈急剧下降;免疫接种率与相应传染病呈高度负相关;政府参与、领导重视、报告系统完善、各部门协调和家长对计划免疫的态度等是保持合格免疫接种率高水平的重要影响因素。     

北京市海淀区1955～1994年脊髓灰质炎流行病学综合分析

本文对北京市海淀区１９５５～１９９４年脊髓灰质炎的流行和防治工作情况进行了分析，１９５５～１９８３年共报告脊髓灰质炎１０４７例，１９８４年后无脊髓灰质炎报告。１９５５～１９６２年发病率在３．１～３５．０／１０万，１９６３～１９７５年发病率０．１～１０．９／１０万，１９７６～１９９３年仅１９８３年报告１例。自６０年代开展脊髓灰质炎疫苗预防接种以来，该病发病率大幅度下降直至零。并对脊髓灰质炎抗体监测、接种率、ＡＦＰ监测进行探讨。提示常规免疫的高接种率，不能阻断野毒株的侵袭，必须采取全市或全国统一的强化服苗，在儿童肠道中形成疫苗株的优势苗群，才能阻断脊髓灰质炎野病毒的循环。     

A comparison of fast MR scan techniques for cerebral activation studies at 1.5 Tesla

To evaluate the sensitivity of fast, gradient-echo MR scan techniques in their ability to detect blood oxygenation level dependent (BOLD) signal changes in task activation studies, three dedicated fast scan techniques, each with whole-brain coverage, were compared during a 3-min finger tapping paradigm on nine normal volunteers on a clinical 1.5 T scanner. Multislice (2D) single-shot spiral, 3D spiral, and multislice (2D) single-shot EPI scan techniques were done with similar temporal and spatial resolutions on each of the volunteers in random order. After image registration and statistical analysis, the sensitivity to detect activation was evaluated for the techniques by calculating t scores and number of activated voxels in predetermined regions of interest, including the contralateral primary sensorimotor cortex, the premotor region, the parietal region, the supplementary motor area, and the ipsilateral cerebellum. Baseline images acquired with the three techniques were qualitatively comparable and had a similar effective spatial resolution of around 5 × 5 × 5 mm³, as determined from autocorrelation analysis. The anatomical coverage was somewhat reduced (4 less slices per volume) with EPI at the identical temporal resolution of 1.76 s for all techniques. The use of multislice 2D spiral scan for motor cortex fMRI experiments provided for a superior overall temporal stability, and an increased sensitivity compared with multislice 2D EPI, and 3D spiral scan. The difference in sensitivity between multislice 2D spiral and EPI scans was small, in particular in the case of a ramp-sampled version of EPI. The difference in performance is attributed mainly to the difference in scan-to-scan stability.     

Calculation of signal intensities in hybrid sequences for fast NMR imaging

A number of techniques that recently have been used for fast NMR-imaging are based on a hybrid sequence of echo planar imaging (EPI) and FLASH imaging: after each NMR excitation several k-space lines are measured. The complete k-space is covered by performance of several excitations. It has been observed that there is usually an optimal hybrid sequence that maximizes the signal-to-noise ratio. In this work, a method is presented that allows a determination of the optimal sequence as a function of the relaxation times T₁ and T₂^*.     

Active Acoustic Screening: Reduction of Noise in Gradient Coils by Lorentz Force Balancing

We have designed and constructed a quiet gradient set with restricted access for the combined purposes of evaluating the principles of active acoustic screening, recently introduced by Mansfield, Glover, and Bowtell, and for EPI studies of the head at 3.0 T. The design utilizes the return paths of the conductors in a closed arc loop arrangement to eliminate net Lorentz forces thereby attenuating acoustic noise especially at low frequency. This design should significantly reduce the dangers to patients of high noise levels, especially in high field magnetic resonance imaging systems.     

Receptor binding sites for beta-adrenergic ligands on human erythrocytes

Affinity, specificity and kinetics for [3H]-DHA binding to human red cell ghost were determined by ultra-filtration. At 2 degree an apparent dissociation constant of 0.96 nM was found with maximum specific binding of 29 fmoles per mg protein. The low dissociation constant was confirmed by kinetic studies with a value of 0.86 nM. Propranolol and isoproterenol inhibited [3H]-DHA binding stereo specifically. Agonist potency (IPR greater than EPI greater than NE) indicated that human erythrocytes had an adrenergic receptor of beta-2 subtype. Isoproterenol in the presence of theophylline resulted in a concentration-dependent increase of intracellular cAMP levels in intact cells. Basal and maximal levels were 2.3 and 7.5 pmoles/108 cells respectively after 2.5 min stimulation. EC50 for isoproterenol was 0.27 microM. Propranolol shifted the isoproterenol concentration response curve to the right. The present results show that human erythrocytes possess recognition sites for beta-adrenergic ligands with binding characteristics similar to that of adrenergic receptors of beta-2 subtype. At least a small number of these binding sites are functionally coupled to adenylate cyclase.     

Proton imaging of siloxanes to map tissue oxygenation levels (PISTOL): a tool for quantitative tissue oximetry

Hexamethyldisiloxane (HMDSO) has been identified as a sensitive proton NMR indicator of tissue oxygenation (pO(2)) based on spectroscopic spin-lattice relaxometry. A rapid MRI approach has now been designed, implemented, and tested. The technique, proton imaging of siloxanes to map tissue oxygenation levels (PISTOL), utilizes frequency-selective excitation of the HMDSO resonance and chemical-shift selective suppression of residual water signal to effectively eliminate water and fat signals and pulse-burst saturation recovery (1)H echo planar imaging to map T(1) of HMDSO and hence pO(2). PISTOL was used here to obtain maps of pO(2) in rat thigh muscle and Dunning prostate R3327 MAT-Lu tumor-implanted rats. Measurements were repeated to assess baseline stability and response to breathing of hyperoxic gas. Each pO(2) map was obtained in 3(1/2) min, facilitating dynamic measurements of response to oxygen intervention. Altering the inhaled gas to oxygen produced a significant increase in mean pO(2) from 55 Torr to 238 Torr in thigh muscle and a smaller, but significant, increase in mean pO(2) from 17 Torr to 78 Torr in MAT-Lu tumors. Thus, PISTOL enabled mapping of tissue pO(2) at multiple locations and dynamic changes in pO(2) in response to intervention. This new method offers a potentially valuable new tool to image pO(2) in vivo for any healthy or diseased state by (1)H MRI. Copyright (c) 2008 John Wiley & Sons, Ltd.