事件相关功能磁共振成像

事件相关设计是功能磁共振成像的一种新的实验范式,与传统的组块设计相比,其主要特点有三：（1）任务刺激和刺激间隔时间的随机化;（2）可基于任务类型和被试反应类型进行选择性处理;（3）提供更加细致的脑的局部信息。     

Surface coil magnetic resonance imaging

Detection of MR signals with surface coils provides increased signal-to-noise ratio for superficial structures relative to detection by circumferential coils, permitting improved spatial resolution. Different geometries of surface coils can be used for different regions. Coils that are flat or curved to fit body contours are good for general imaging, with a range of coil sizes useful for structures of different size or depth. Solenoidal coils are useful for imaging protruding structures such as breasts, while smaller versions of conventional circumferential coils that can be slipped over limbs are useful for imaging extremities.     

Quantifying mixing using magnetic resonance imaging

Mixing is a unit operation that combines two or more components into a homogeneous mixture. This work involves mixing two viscous liquid streams using an in-line static mixer. The mixer is a split-and-recombine design that employs shear and extensional flow to increase the interfacial contact between the components. A prototype split-and-recombine (SAR) mixer was constructed by aligning a series of thin laser-cut Poly (methyl methacrylate) (PMMA) plates held in place in a PVC pipe. Mixing in this device is illustrated in the photograph in Fig. 1. Red dye was added to a portion of the test fluid and used as the minor component being mixed into the major (undyed) component. At the inlet of the mixer, the injected layer of tracer fluid is split into two layers as it flows through the mixing section. On each subsequent mixing section, the number of horizontal layers is duplicated. Ultimately, the single stream of dye is uniformly dispersed throughout the cross section of the device. Using a non-Newtonian test fluid of 0.2% Carbopol and a doped tracer fluid of similar composition, mixing in the unit is visualized using magnetic resonance imaging (MRI). MRI is a very powerful experimental probe of molecular chemical and physical environment as well as sample structure on the length scales from microns to centimeters. This sensitivity has resulted in broad application of these techniques to characterize physical, chemical and/or biological properties of materials ranging from humans to foods to porous media (1, 2). The equipment and conditions used here are suitable for imaging liquids containing substantial amounts of NMR mobile (1)H such as ordinary water and organic liquids including oils. Traditionally MRI has utilized super conducting magnets which are not suitable for industrial environments and not portable within a laboratory (Fig. 2). Recent advances in magnet technology have permitted the construction of large volume industrially compatible magnets suitable for imaging process flows. Here, MRI provides spatially resolved component concentrations at different axial locations during the mixing process. This work documents real-time mixing of highly viscous fluids via distributive mixing with an application to personal care products.     

Real-time functional magnetic resonance imaging.

Magnetic resonance imaging (MRI) has been shown to be useful in the detection of brain activity via the relatively indirect coupling of neural activity to cerebral blood flow and subsequently to magnetic resonance signal intensity. Recent technical advances have made possible the continuous collection of successive images at a rate rapid compared with such signal changes and in the statistical processing of these image time series to produce tomographic maps of brain activity in real time, with updates of 10 frames/s or better. We describe here our preferred method of real-time functional MRI and some of the early results we have obtained with its use.     

Technical artifacts in magnetic resonance imaging

Various artifacts of Magnetic Resonance Imaging (MRI) typically associated with currently available imaging techniques such as projection reconstruction and two-dimensional fourier transform (2D-FT) are described and illustrated. Examples of MRI artifacts were obtained with an imaging unit with a super conducting magnet operated at .15 Tesla and .27 Tesla with corresponding proton resonance frequency of 6.4 MHz and 11.25 MHz. The .15 Tesla images were obtained using projection reconstruction and the .27 Tesla using the 2D-FT method. Instrument related artifacts include those due to direct current (DC), projection, gradient offset, active shimming, phase encoding, and pulse sequencing. Other often encountered artifacts are related to the patient. These include those due to motion, ferromagnetic effect, and tissue contents. The cause of these artifacts and how (if possible) they may be eliminated or minimized is discussed.     

Paramagnetic pharmaceuticals for magnetic resonance imaging

Complexes of paramagnetic ions that are tissue-, organ- or tumor-specific will supplement routine magnetic resonance imaging, help assess organ perfusion, and in some cases assess specific organ function. Studies are described in animals and man and the results suggest that dilute iron solutions may be useful for contrast-enhancement of the gastrointestinal tract; that ferrioxamine B, a stable ferric iron complex, appears to permit identification of focal blood-brain-barrier defects and to assess renal excretory function; and that gadolinium-DTPA can produce contrast-enhancement of a variety of lesions. In addition, gadolinium-DTPA can detect a breakdown in the blood-brain-barrier and can delineate functioning myocardium in the setting of acute ischemia.     

Application of magnetic resonance imaging in zoology

Magnetic resonance imaging (MRI) is a noninvasive imaging technique that today constitutes one of the main pillars of preclinical and clinical imaging. MRI’s capacity to depict soft tissue in whole specimens ex vivo as well as in vivo, achievable voxel resolutions well below (100 μm)³, and the absence of ionizing radiation have resulted in the broad application of this technique both in human diagnostics and studies involving small animal model organisms. Unfortunately, MRI systems are expensive devices and have so far only sporadically been used to resolve questions in zoology and in particular in zoomorphology. However, the results from two recent studies involving systematic scanning of representative species from a vertebrate group (fishes) as well as an invertebrate taxon (sea urchins) suggest that MRI could in fact be used more widely in zoology. Using novel image data derived from representative species of numerous higher metazoan clades in combination with a comprehensive literature survey, we review and evaluate the potential of MRI for systematic taxon scanning. According to our results, numerous animal groups are suitable for systematic MRI scanning, among them various cnidarian and arthropod taxa, brachiopods, various molluscan taxa, echinoderms, as well as all vertebrate clades. However, various phyla in their entirety cannot be considered suitable for this approach mainly due to their small size (e.g., Kinorhyncha) or their unfavorable shape (e.g., Nematomorpha), while other taxa are prone to produce artifacts associated either with their biology (e.g., Echiura) or their anatomy (e.g., Polyplacophora). In order to initiate further uses of MRI in zoology, we outline the principles underlying various applications of this technique such as the use of contrast agents, in vivo MRI, functional MRI, as well as magnetic resonance spectroscopy. Finally, we discuss how future technical developments might shape the use of MRI for the study of zoological specimens.     

Methodological features of magnetic resonance imaging mammography

By studying 211 females by currently available radiation techniques, such as X-ray study, ultrasonography, and magnetic resonance imaging mammography (MRIM), the authors consider that the specificity of contrast-enhanced MRIM (CE MRIM) is greater than that of MRIM without administering magnetic resonance contrast agents (MRCA). CE MRIM reveals clinically suspicious early-stage breast lesions and defines the stage of a tumorous process, the patients being unexposed to ionizing irradiation. CE MRIM as an auxiliary technique becomes one of the most informative ones, particularly in girls, early reproductive-age females with developed glandular tissue, and pregnant females. In the authors' opinion, the total algorithm of a breast study in this group of patients in specialized medical centers where trained physicians work should differ from the generally accepted algorithm: instead of applying X-ray mammography (XRM) as a basic method of primary diagnosis, ultrasound mammography using Doppler color mapping, followed by MRIM or XRM should be employed.     

Nuclear magnetic resonance imaging of mummified corpses

Clinical applications of nuclear magnetic resonance (NMR) imaging have demonstrated its great potential for noninvasive examinations of soft tissues. Here preliminary experiments are reported on mummified human tissue by means of NMR cross-sectional and transmission imaging. For this purpose the natural viscosity of the tissues has been lowered by rehydration with an aqueous solution of 20% acetone.     

Contrast agents for nuclear magnetic resonance imaging

Nuclear magnetic resonance imaging relies upon differences in relaxation times for much of its ability to resolve anatomical structures and to detect changes in tissue. The natural differences can be changed by the administration of paramagnetic substances, such as metal complexes and stable organic free radicals, and ferromagnetic materials, such as small particles of magnetite. Detailed studies of the chemistry and biophysics of such substances in the body are required if they are to become safe and effective contrast agents for use in medical NMR imaging.     

Muscle cross-section measurement by magnetic resonance imaging

Muscle cross-section areas were measured by magnetic resonance imaging (MRI) in the thigh of a human cadaver, the results being compared with those obtained by photography of corresponding anatomic macroslices. A close correlation was found between MRI and photographic evaluation, differences between the methods ranging from nil to 9.5%, depending on the scan position and the muscle groups. In vivo MRI measurements were performed on 12 female and 16 male students, the objectivity, the test-retest reliability and the variability of the MRI measurements being studied by fixing the scan position either manually or by coronary scan. The latter method appeared to be more objective and reliable. The coefficients of variation for muscle cross-section areas measured by MRI were in the range of those for the planimetry of given cross-section areas. Allowing for differentiation between several small muscle bundles in a given area, MRI proved to be a suitable method to quantify muscle cross-sections for intra- and interindividual analysis of muscle size.