Rapid Image Acquisition

The phase-encoding methods are considered to be the most robust and quantitative but, as demonstrated below, TOF and rapid image acquisition can be particularly useful in specific applications. 

An example of the application of RARE for rapid image acquisition is shown in Fig. 19, in which a single frame is shown from a series of 2-D images acquired of an oscillatory chemical reaction occurring within a fixed bed. Relaxation contrast is used to discriminate between the reaction products Mn " and Mn (49). In this example, MR offered the opportunity to map the detailed structure of the fixed bed and the product distribution within it. This pulse sequence has also recently been applied to obtain quantitative images of the evolution of a lysozyme urea separation within a chromatography column (50). 

CTP is a relatively recent development in acute stroke imaging that is already in routine clinical use in many centers. CTP and MRP are similar in that both techniques are based on rapid serial image acquisition during intravenous injection of a bolus of contrast material. In both techniques, measurements of density over time (for CTP) or signal intensity over time (for MRP) are converted to contrast agent-versus-time curves, and these are processed in similar ways to yield the same perfusion measurements (most often CBV, CBF, and MTT). Example CTP images are shown in Figure 2.12. 

The telemedicine-based evaluation of acute stroke is especially challenging. It requires a rapid neurological assessment, CT image acquisition and review, and a detailed history for rt-PA exclusion criteria. Low-cost teleradiology systems are now available for the transmission of compressed CT images viewable on a conventional personal computer (PC) monitor, in accordance with published standards. 

The use of magnetic resonance imaging (MRI) to study flow patterns in reactors as well as to perform spatially resolved spectroscopy is reviewed by Lynn Gladden, Michael Mantle, and Andrew Sederman (University of Cambridge). This method allows even unsteady-state processes to be studied because of the rapid data acquisition pulse sequence methods that can now be used. In addition, MRI can be used to study systems with short nuclear spin relaxation times—e.g., to study coke distribution in catalytic reactors. 

A portion of the exiting stream of the molten blend is diverted into the Flow Cell , where Nomarsky reflection microscopy is carried out in a thin slit, the bottom plate of which is reflective polished steel and the top is a quartz window. The microscope, the rapid image data acquisition device, and analyzer are capable of producing dispersion data down to sizes of one micrometer. The TSMEE is shown schematically for both the (M-M) and DMM) modes in Fig. 11.31 (119-121). 

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