Evaluation method for imaging plate resolution by means of phase contrast transfer function

1995 ◽  
Vol 53 ◽  
pp. 662-663 ◽  
Author(s):  
T. Oikawa ◽  
H. Kosugi ◽  
F. Hosokawa ◽  
D. Shindo ◽  
M. Kersker
Keyword(s):  
Transfer Function ◽  
Phase Contrast ◽  
Evaluation Method ◽  
Amorphous Film ◽  
Imaging Plate ◽  
X Rays ◽  
Special Shape ◽  
Contrast Transfer Function ◽  
Contrast Image ◽  
Specimen Shape

Evaluation of the resolution of the Imaging Plate (IP) has been attempted by some methods. An evaluation method for IP resolution, which is not influenced by hard X-rays at higher accelerating voltages, was proposed previously by the present authors. This method, however, requires truoblesome experimental preperations partly because specially synthesized hematite was used as a specimen, and partly because a special shape of the specimen was used as a standard image. In this paper, a convenient evaluation method which is not infuenced by the specimen shape and image direction, is newly proposed. In this method, phase contrast images of thin amorphous film are used.Several diffraction rings are obtained by the Fourier transformation of a phase contrast image of thin amorphous film, taken at a large under focus. The rings show the spatial-frequency spectrum corresponding to the phase contrast transfer function (PCTF). The envelope function is obtained by connecting the peak intensities of the rings. The evelope function is offten used for evaluation of the instrument, because the function shows the performance of the electron microscope (EM).

Correction of the contrast transfer function to determine the radial density distribution of frozen-hydrated tobacco mosaic virus

1992 ◽  
Vol 50 (1) ◽  
pp. 536-537
Author(s):  
Michael F. Smith ◽  
John P. Langmore
Keyword(s):  
Transfer Function ◽  
Phase Contrast ◽  
Heavy Atom ◽  
Biological Molecules ◽  
Frequency Compensation ◽  
Contrast Transfer Function ◽  
High Background ◽  
Low Contrast ◽  
Radial Density Distribution ◽  
Excellent Preservation

The purpose of image reconstruction is to determine the mass densities within molecules by analysis of the intensities within images. Cryo-EM offers this possibility by virtue of the excellent preservation of internal structure without heavy atom staining. Cryo-EM images, however, have low contrast because of the similarity between the density of biological material and the density of vitreous ice. The images also contain a high background of inelastic scattering. To overcome the low signal and high background, cryo-images are typically recorded 1-3 μm underfocus to maximize phase contrast. Under those conditions the image intensities bear little resemblance to the object, due to the dependence of the contrast transfer function (CTF) upon spatial frequency. Compensation (i.e., correction) for the CTF is theoretically possible, but implementation has been rare. Despite numerous studies of molecules in ice, there has never been a quantitative evaluation of compensated images of biological molecules of known structure.

Measurement of Point-Spread Function of IP-System

1997 ◽  
Vol 3 (S2) ◽  
pp. 1103-1104
Author(s):  
T. Oikawa ◽  
F. Hosokawa ◽  
A. Taniyama ◽  
D. Shindo ◽  
M. Kersker
Keyword(s):  
Transfer Function ◽  
Point Spread Function ◽  
Electron Probe ◽  
Imaging Plate ◽  
Pixel Size ◽  
Modulation Transfer ◽  
Contrast Transfer Function ◽  
Point Spread ◽  
Spread Function ◽  
Resolution Estimation

For the resolution estimation of the Imaging Plate (IP)-system, several methods were carried out. One of them is the measurement of the modulation transfer function (MTF) from the phase contrast transfer function taken with an amorphous Ge film specimen. One of another is the measurement of the point-spread function (PSF) from the auto-correlation of the Poison noise obtained by the IP-system.In this experiment, the PSF of the IP-system were measured from the intensity distribution recorded with a 1.6 μm-diameter electron probe on the IP.When recording the electron intensity with a small enough electron probe as compared with the pixel size of the IP (25 μm × 25 μm), a single pixel detects the electron signal in case of ideal IP-resolution which is limited only by the pixel size. However, practical IP-resolution is limited by the electron diffusion, x-ray emission and the laser beam diffusion in the IP, and so on. Therefore, it is possible to measure the PSF from the intensity distributions of the patterns recorded with a small enough electron probe.

Practical aspects about hollow-cone imaging

1995 ◽  
Vol 53 ◽  
pp. 576-577
Author(s):  
T. Geipel ◽  
W. Mader
Keyword(s):  
Electron Microscope ◽  
Transfer Function ◽  
Phase Contrast ◽  
Hollow Cone ◽  
Low Resolution ◽  
Contrast Transfer Function ◽  
Imaging Parameters ◽  
Specimen Holder ◽  
Optimum Imaging

Hollow-cone imaging (HCI) as a possibility to improve the resolution of a TEM has already been proposed in the late 40ties and besides others, there have been extensive hollow-cone experiments 10 years back using a low resolution TEM with a non-tilt specimen holder. In a recent paper the optimum imaging parameters for HCI were determined leading to an improvement of the resolution by a factor of two. However, there are contrast limitations and experimental problems for HCI which were only partly considered in Ref. and which will be discussed in this paper for a modern electron microscope. Preliminary experiments were performed which are not shown in the abstract.In Fig. 1 ∫ ct f(u)du is plotted versus defocus Δ f for different cone radii Θc and a fixed aperture radius Θo = 1/δ = 5 nm-1 (ct f is the phase contrast transfer function (PCTF) for HCI and δ = 0.2 nm is the resolution of a CM30 supertwin microscope).

Cryoelectron microscopy and image reconstruction of spherical viruses with spot scan and FEG technologies

1995 ◽  
Vol 53 ◽  
pp. 1086-1087
Author(s):  
N. H. Olson ◽  
U. Lücken ◽  
S. B. Walker ◽  
M. T. Otten ◽  
T. S. Baker
Keyword(s):  
Electron Microscope ◽  
Transfer Function ◽  
Field Emission ◽  
Phase Contrast ◽  
Atomic Resolution ◽  
Bright Spot ◽  
Biological Macromolecules ◽  
Contrast Transfer Function ◽  
Transmission Electron ◽  
Chlorotic Mottle

The field emission gun electron microscope (FEG) is a tool that has the potential to achieve near atomic resolution information of biological macromolecules. The FEG provides a beam with higher spatial and temporal coherence and a better phase contrast transfer function than do microscopes with either tungsten or LaB6 filaments. The FEG is also ideal for spot scan imaging applications because it can produce a small, coherent and very bright spot. In spot scan mode the specimen is exposed to an array of nonoverlapping spots rather man a flood beam. This significantly reduces beam-induced specimen drift.Frozen-hydrated samples of cowpea chlorotic mottle (CCMV, Fig. 1A) and cowpea severe mosaic virus (CPSMV, Fig. IB) were examined on a Philips CM12 transmission electron microscope equipped with a standard LaB6 gun and on a Philips CM200 equipped with a field emission gun, respectively. The CM12 was operated at 120kV and was externally controlled by means of a spot scan imaging program which produced a series of 250 nm diameter spots on Kodak SO-163 sheet film.

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