Calculated images

Slices of the body are irradiated from one side. X-ray detectors quantify the remaining intensity of the X-rays after passing through the various tissues. The X-ray tube and the detectors are rotating around the body. The data are used to calculate images of the corresponding slice which reflect the absorption of X-rays in a great number of pixels of an individual slice. 

Interpretation of the images is still not straightforward even when there seems to be a simple one-to-one correspondence between black (or white) dots in the image and atom positions. Especially when quantitative data on interatomic distances is to be derived, detailed calculations based on many-beam dynamical theory ( ) must be applied to derive calculated images for comparison with experiment. For this purpose the experimental parameters describing the imaging conditions and the specimen thickness and orientation must be known with high accuracy. 

Figure 27 HREM image and calculated image of a defect...

Fig. 2.29 Structure image of TiNbj Ogj. The inset shows the calculated image, which is in good accordance with the observed one. The marks E - and F - are referred to in Fig. 2.26. For the interpretation of the image, see text.

Figures 2.49 and 2.50 show the high resolution electron micrographs, corresponding to the case of (2)-[l] and (2)-[2], respectively. Although intuitive interpretations for these pictures are not simple, comparing them with those for the shear or block structures, the calculated images are qualitatively in agreement with the observed ones. ...

Figure 3.18 Calculated images for a 14 pm diameter ring-shaped object at X = 6 pm. Left actual object center image for a nonconfocal 32x Schwarzschild objective with NA = 0.65 right image for a confocal 32x Schwarzschild objective with NA = 0.65.

Figure 3.19 Calculated image for a 3 (Jim diameter circular object at a wavelength of 3 xm and at three different locations within the spectrometer s potential viewing area, illustrating diffraction blurring and optical distortion. Left centered on instrument s optic axis middle object located 100 pm from optic axis right object located 283 pm from optic axis.

Fig. 26. A T1 time calculation image showing the prolongation of T1 at the lesion site (right kidney, arrow)... 

Figure 3. An enlargement from approximately the marked area of Figure 2 together with calculated images (Af = -429 A, thickness 80 A) based on (a) the UUDD and (b) UDUD models.

Figure 4. Calculated images for the Cmcm topology of zeolite ZSM-48 for [001] incidence (Af =-29 to -1029 A thickness 20,40,60,80 and 100 A resolution 3.1 A).

Figure 10. Calculated images for the Cmcm topology of zeolite ZSM-48...

Fig. 5. A detailed comparison between STM experimental (a) and calculated constant current (b) images of HBDC molecules. The calculated image was obtained using the elastic scattering quantum chemistry (ESQC) technique with additional molecular mechanics optimization of the conformation on the surface to converge with the experimental image. Different heights in the images of the ferf-butyl lobes are observed experimentally, corresponding to different propeller-like conformations of the HBDC molecules. The intramolecular conformation of each experimentally observed molecule can be accurately extracted using ESQC plus molecular mechanics calculations...

Figure 11. High resolution image and calculated images area corresponding to an oxygen overstoichiometry.

---