Klaus-Ruediger Peters

Grebe syndrome: Clinical and radiographic findings in affected individuals and heterozygous carriers

Grebe syndrome is a recessively inherited acromesomelic dysplasia. We studied, clinically and radiographically, 10 affected individuals, originating from Bahia, Brazil. The phenotype is characterized by a normal axial skeleton and severely shortened and deformed limbs, with a proximo-distal gradient of severity. The humeri and femora were relatively normal, the radii/ulnae and tibiae/fibulae were short and deformed, carpal and tarsal bones were fused, and several metacarpal and metatarsal bones were absent. The proximal and middle phalanges of the fingers and toes were invariably absent, while the distal phalanges were present. Postaxial polydactyly was found in several affected individuals. Several joints of the carpus, tarsus, hand, and foot were absent. Heterozygotes presented with a variety of skeletal manifestations including polydactyly, brachydactyly, hallux valgus, and metatarsus adductus. Grebe syndrome is caused by a missense mutation in the gene encoding cartilage-derived morphogenetic protein-1.

Rationale for the application of thin, continuous metal films in high magnification electron microscopy

Various metal films of different thicknesses were deposited on to a particle test specimen and their effects on topographic contrast generation and specimen preservation were determined. Tobacco mosaic virus adsorbed on to thin carbon supports or silicon chips was imaged in TEM or high resolution SE‐I SEM at a magnification of 350,000×. Tantalum films of 1–2 nm (average mass) thickness produced best contrasts and prevented volume loss of the particles from electron beam damage. Excessively thick films of 5–10 nm thickness blanketed fine structures and caused severe volume losses. Discontinuous 2 nm thick films of gold or platinum decorated the surfaces, caused a loss in topographic contrasts and induced very high volume losses. Thin continuous metal films were necessary to generate high topographic contrast and to prevent volume loss from beam damage by providing sufficient mechanical stability for small topographic features and increased thermal conductivity of the specimen surface.

Electron Energy Loss Spectrometry

The aim of this laboratory session is to demonstrate the use of a magnetic prism electron spectrometer to perform electron energy loss spectrometry (EELS). The main characteristics of the energy loss spectrum will be discussed as well as the effect of instrumental and specimen parameters on the spectrum. Quantitative elemental analysis will be demonstrated and if time permits an example of EELS imaging will be shown. More details can be found in PAEM, Chapters 7 and 8.

Electron Channeling Contrast

The objective is to acquaint the microscopist with the crystallographic and contrast effects of electron channeling. The initial emphasis is on channeling experiments which can be performed on any conventional scanning electron microscope: large area channeling patterns of single crystals and channeling contrast images to reveal the crystalline microstructure of polycrystalline materials. The optional advanced experiments on covering area electron channeling patterns can only be carried out on an SEM which is equipped with special scanning and/or electron optical modifications. More detail on this topic may be found in ASEMXM, Chapter 3.

Perceptually standardized imaging of digitized film for comparative ROC measurements

Primary diagnostic reading of digitized film, displayed on a CRT, requires a quality assurance (QA) that all of the perceptual information, which is accessible from the film when displayed on a light table, can be reproduced on the CRT display. Some of the CRT display parameters are already defined. The DICOM standard 3.14 introduces a contrast transfer function (grayscale display function standard) for minimum contrasts which are defined as single just-noticeable- differences (JND) in luminance. It establishes, throughout the entire intensity range of the data, contrast recognition of single JND resolution and implies linearity of contrast perception. Conventionally, the CRT QA utilizes a SMPTE contrast test pattern of 5% contrast ]13 digital driving levels (DDLs)[ resolution. We developed for the QA of the new standard a perceptual contrast pattern with single DDL resolution (perceptual contrast pattern equals P-pattern). It allows the visual assessment and measurement of perceived contrast linearity at a minimum level 1.2% contrast (3 DDLs). We analyzed, at various room light conditions (0 - 300 cdm-2) and on DICOM 3.14-standardized CRTs of various maximum luminance (110 - 400 cdm-2), the minimum luminance of the CRT that is required for establishing perceptual contrast linearity. We compared the use of the SMPTE pattern and the P-pattern for QA of linearity. The SMPTE pattern was not effective for a statistically significant correlation of contrast linearity with room light and monitor luminance. However, the P-pattern furnished an effective tool for the assessment, measurement or adjustment of contrast linearity. We found that perception of linearity for 3 JND contrasts at low room light conditions (0 - 6 cdm-2) requires a minimum luminance of 10 cdm-2 which is not directly derived from the background luminance of the light reflected from the monitor but may indicate a perceptual threshold value for task performance.

Image Contrast and Quality

This laboratory demonstrates: (1) the two major types of contrast in SEM images, known as atomic number contrast and topographic contrast, (2) the factors affecting the quality of the image and how they ultimately limit the image resolution, and (3) the effects of electronic signal processing on the visibility of features in the image. More details and references may be found in SEMXM, Chapters 3 and 4.

Bulk Specimens for SEM and X-Ray Microanalysis

The purpose of this laboratory is to prepare samples of metallic, ceramic, polymeric, and biological specimens for examination and analysis in the SEM. The organization is such that under each type of material sample preparations are discussed for surface topography (e.g., fracture surface), microstructural analysis (e.g., phase morphology), and x-ray microanalysis. Special procedures for semiconductor devices, polymers, and biological samples are also considered. The objective is to provide a brief outline and enough general references to enable the reader to produce all of the specimens used in this workbook. The outlined methods should not be considered comprehensive, however, and the reader is strongly urged to consult the references listed. For further discussion, see SEMXM, Chapters 9–12.

Backscattered Electron Imaging

Experiment 8.1: E-T Detector Collection Efficiency. The solid angle and efficiency of a specific E-T detector for direct collection of BSEs is: (a) Area, A, of scintillator (cm2) = 1.5 cm2. (b) Distance, r, from specimen to scintillator (cm) = 4 cm. (c) Solid angle, Ω = A/r2 = 1.5/16 = 0.094 steradians. (e) For a specimen set normal to the beam (0° tilt), approximate take-off angle = 45°.

Electron Beam Parameters

This laboratory demonstrates: (1) election gun saturation and alignment; (2) the measurement of beam current, beam size, and beam convergence; (3) the concept of electron gun brightness; and (4) the effects of these parameters on depth-of-field and resolution. More details and references can be found in SEMXM, Chapter 2.

Basic SEM Imaging

This first laboratory is designed to acquaint the beginning SEM operator with the steps for taking a micrograph. The steps are described without reference to a particular instrument. Please consult the manufacturer’s operation manual or an instructor before proceeding.