Image acquisition

The classical scheme of sample scanning with a single-point probe is flexible in applicable methodology and both spectral and spatial resolution. In practice, 

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Certain neutral technetium complexes can be used to image cerebral perfusion (Fig. 4). Those in Figure 4a and 4b have been approved for clinical use. Two other complexes (Fig. 4c and 4d) were tested in early clinical trials, but were not developed further. An effective cerebral perfusion agent must first cross the blood brain barrier and then be retained for the period necessary for image acquisition. Tc-bicisate is retained owing to a stereospecific hydrolysis in brain tissue of one of the ester groups to form the anionic complex TcO(ECD) , which does not cross the barrier. This mechanism of retention is termed metaboHc trapping. 

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. 

Pomerantz SR, Harris GJ, Desai HJ, Lev MH. Computed tomography angiograph and computed tomography perfusion in ischemic stroke a step-hy-step approach to image acquisition and three-dimensional postprocessing. Semin Ultrasound CT MR 2006 27 243-270. 

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. 

Fig. 1.20 Gradient-echo based pulse sequences based on low flip angles. When low flip angles and short image repetition times are employed at the expense of transverse magnetization during the course of the complete image acquisition, this represents a FLASH sequence (without ). The combination of flip angle and repetition time can be adjusted in...

Figure 2.2.3 shows a typical block diagram for a compact MRI system. The square box surrounded by the dotted lines shows the electrical sub-system, which is stored in a single portable rack as shown in Figure 2.2.2. The electrical sub-system is thus often called the (portable) MRI console. In accord with Figure 2.2.3, an MR image acquisition process is described as follows.

The PC system runs under a Windows95/98/2000 operating system and is capable of real-time image acquisition, reconstruction and display (16, 17). 

Rudenauer FG (1989) Multidimensional image acquisition and processing in surface analysis. Fresenius Z Anal Chem 333 308... 

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