Multi-slice technique

In this paper, we review the determination of the shape and the structure of metal particles by electron microscopy as illustrated by examples of Pd clusters epitaxially oriented on oxide single crystals and thin films of MgO and ZnO. The metal-oxide interfaces are characterized by HRTEM profile-view imaging, numerical analysis of the images, and image simulations by the multi-slice technique. 

The HRTEM images of the particles annealed under UHV or in low pressures (10 torr) of O2 show that the junction between the (111) and (100) faces is sharp. Comparison of the experimental images with images simulated by the multi-slice technique shows that this junction is atomically sharp. On annealing at higher pressures (10 torr) progressive rounding occurs at the corners this is completely reversible by reduction in H2. 

The multi-slice technique of H MRI was used to study regional effects of amphetamine on rat brain [49], a two-coil system enabling three-dimensional perfusion imaging. Amphetamine caused a significant increase in perfusion in many areas of the brain, including the cortex, cingulate and caudate putamen. 

Most types of selective excitation can be modified for simultaneous excitation of n slices or volume elements. Such an approach is advantageous when a limited number of slices or volume elements, but not the entire 3D object, needs to be investigated. By suitable coding of the volume information in n experiments an improvement in signal-to-noise ratio of can be gained [Boll, Miill]. Compared to 3D volume imaging, multislice and multi-volume techniques (cf. Section 9.1) suffer from the lack of achieving well-defined boundaries. 

A closely related technique can be used for multi-slice imaging (Fig. 6.2.7) [Fral]. The scheme of Fig. 6.2.5(c) is appended by further slice-selective 90° pulses with different centre frequencies, so that the magnetization of other slices is selected [Fral]. In this way, the otherwise necessary recycle delay can effectively be used for acquisition of additional slices. However, the contrast in each slice is affected by a different Ty weight, because is different for each slice. The technique can readily be adapted to line-scan imaging by applying successive slice-selective pulses in orthogonal gradients [Finl]. 

The other concern about this new technique is related to radiation exposure. From our own measurements, we learned that the radiation exposure of a single-rotation C-arm CT of the liver is approximately the same as for a conventional mono-phase multi-slice CT of the same region (approximately 4 mSv effective dose). Also of concern is the scatter radiation for the investigator. In order to avoid unnecessary scatter radiation exposure, it is mandatory for the investigator to step back as far away as possible or ideally to leave the scan room and to start the whole procedure, including contrast injection and C-arm rotation, from the control... 

Computed tomography (CT) has developed dramatically with the introduction of multi-row detector technology. Especially the abdomen, where motion artifacts due to respiratory motion and bowel peristalsis are disturbing, benefits greatly from this technique. While scanners with 64 or more detector rows are still most common in large community or university hospitals, scanners with between 2 and 16 slices are widely available even in private practice or in small hospitals. With the introduction of multi-detector CT (MDCT) bi- or even tri-phasic examinations of the liver can be combined into a thoraco-abdominal CT examination without compromise with regard to spatial or temporal resolution. The acquisition of the liver with a 64-slice scanner, for example, only requires a few seconds... 

Multi-shce linear interpolation is characterized by a projection-wise linear interpolation between two rays on either side of the image plane to estabhsh a CT data set at the desired image z-position. The interpolation can be performed between the same detector slice at different projection angles (in different rotations) or different detector slices at the same projection angle. In general, scanners relying on this technique provide selected dis-... 

---