Biomedical subjects
D Sayre
Publications and source records attributed to D Sayre.
Contact x-ray microscopy. A new technique for imaging cellular fine structure.
Contact x-ray microscopy potentially allows living, wet cells to be visualized at a resolution of up to 100 A. Furthermore, differential absorption by specific elements permits the study of the distribution of those elements in biological specimens. In contact x-ray microscopy, soft x-rays (10 A to 100 A) pass through a biological sample and expose an underlying x-ray sensitive polymer (resist), producing an image that reflects the photon absorbance within the specimen. The high penetrating power of soft x-ray enables images to be obtained from specimens up to several microns thick. In this paper, the technique is described, some of the areas currently under study are considered, and biological examples of the use of contact x-ray microscopy are given.
Direct imaging of live human platelets by flash x-ray microscopy.
A 100-nanosecond pulse of long-wavelength x-rays was used to produce high-resolution stop-motion images of living human platelets. Although some aspects of the structure conform to those seen in dehydrated specimens, novel features are apparent. The technique should permit detailed stop-motion examination of the interaction of platelets with their surrounding medium as well as exploration of the phagocytic and secretory activities of a wide variety of other cells.
Potential operating region for ultrasoft x-ray microscopy of biological materials.
Calculations are presented which indicate an extensive suboptical region in the microscopy of biological materials in their natural state which is accessible to ultrasoft x-ray transmission microscopy. Throughout most of the region, radiation dosage levels to the specimen are lower than in electron microscopy.
Transmission microscropy of unmodified biological materials: comparative radiation dosages with electrons and ultrasoft x-ray photons.
The minimum radiation dosage in a specimen consistent with transmission microscopy at resolution d and specimen thickness t is calculated for model specimens resembling biological materials in their natural state. The calculations cover 10(4)-10(7) eV electrons and 1.3-90 A photons in a number of microscopy modes. The results indicate that over a considerable part of the (t,d)-plane transmission microscopy on such specimens can be carried out at lower dosage with photons than with electrons. Estimates of the maximum resolutions obtainable with electrons and photons, consistent with structural survival of the specimen, are obtained, as are data on optimal operating conditions for microscopy with the two particles.
X-ray microscopy of biological objects with carbon kappa and with synchrotron radiation.
X-ray micrographs of biological objects have been obtained with a resolution better than 1000 angstroms by using poly(methyl methacrylate) x-ray resist and carbon Kalpha or synchrotron radiation. Synchrotron radiation allows short exposure times; storage rings especially designed as radiation sources and improved x-ray resists would make exposure times under 1 second possible.