Acquisition time imaging

Figure 4 Chemical images of a nickei TEM grid. Fieid of view is approximateiy 25 x 15 im, 50 X 50 pixeis. Analyticai conditions Ga sputtering, spot size about 0.2 pm, 24S-nm radiation, acquisition time 33 minutes.

To date, the usual way of recording the LEED pattern is a light-sensitive video camera with a suitable image-processing system. In older systems movable Earaday cups (EC) were used which detected the electron current directly. Because of long data acquisition times and the problems of transferring motion into UHV, these systems are mostly out of use nowadays. 

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

Figure 2.2.14 shows cross-sections of salmon acquired with a gradient echo sequence (TR = 30 ms, TE = 15 ms, slice thickness = 4 cm, image matrix = 128 x 128, total acquisition time = 3.84 s). For the female salmon, roe were clearly visualized as dark regions because the T2 is shorter than that of the surrounding tissues. For the male salmon, milt was observed instead of roe. However, the image intensity of the milt was similar to that of the surrounding tissues. 

Phase encoding of higher order terms (locally time dependent accelerations) is feasible in principle with pulse trains such as the example shown in Figure 2.9.4(d). However, the relatively long acquisition times of NMR parameter maps conflict with snapshot records that would be needed for such maps. In any case, in Ref. [27] fast imaging techniques are described and discussed that could be employed for moderate versions of snapshot experiments. 

Fig. 3.4.12 Three-dimensional rendered spin-echo image of water filled cracks in a cement paste specimen [13]. Three cracks are visible in the image a large triangular crack in the forefront, a smaller crack in the bottom left corner and a sheet-like structure at the top of the image. Water droplets can also be observed condensing on the cement paste surfaces. The measurement parameters were FOV 20 x 20 x 20 mm, acquisition points 128 x 128 x 64, nominal resolution 156 x 156 x 312 pm, echo time 2.7 ms, repetition time 500 ms and acquisition time 270 min.

Our very first experiments with the reactor depicted in Figure 5.4.1 were carried out with a 15% Pt-Y-Al203 single cylindrical catalyst pellet [10-12], The acquisition time of 2D images of an axial slice at that time was about 260 s. Despite this, the first direct MRI visualization of the operation of a model gas-liquid-solid reactor has revealed the existence of large gradients of the liquid phase content within the catalyst pellet upon imbibition of liquid a-methylstyrene (AMS) under conditions... 

The theoretical lateral spatial resolution achievable with Raman imaging using the optical arrangements of our system (50 x objective with NA = 0.75, 633 nm HeNe laser) should be about 1 pm. In this investigation the resolution is worse than predicted. In practice, sample drift during long acquisition times, uneven surface structures and penetration of laser light into the material worsen the lateral spatial resolution to a value of about 2 pm (estimated). 

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