Magnification Differences Research Articles

Extending the bandwidth of speckle interferometry

In speckle interferometry, the scale of the speckle array is wavelength dependent, and this limits the spectral bandwidth that can be used. A simple optical system is described to correct this effect, over a wide spectral range, by introducing a chromatic difference of magnification of opposite sign to the speckle dispersion, and variable in magnitude.

Linewidth measurement with an optical microscope: the effect of operating conditions on the image profile

A theoretical model of the optical microscope based on the theory of partial coherence is used to predict the image profiles of lines on IC photomasks and assess factors contributing to measurement errors for different conditions of microscope operation. A comparison of experimental and theoretical image profiles is given, showing good agreement with theory for a 0.9 N.A. and linewidths as small as 0.5 microm. The primary sources of differences appear to be edge quality and accuracy of focus. The theory indicates that for well-corrected microscope optical systems, spectrally filtered to eliminate longitudinal chromatic aberration and chromatic difference of magnification, accurate determinations of linewidth may be made from the image profile using a threshold of 25% of maximum intensity (corrected for finite background transmittance in the opaque region). The correspondence between the edge location and the 25% threshold appears to be nearly invariant with small amounts of defocus and spherical aberration as well as variation in the numerical aperture of the condenser.

Displaying distortion in ophthalmic lenses.

A procedure is outlined for generating and displaying information about distortion in an ophthalmic lens. It involves a direct comparison of an object and its image as viewed at the entrance pupil of the eye. The same procedure may also be used to assess chromatic dispersion produced by the chromatic differences in magnification.

Improved Methods for Quantitative Radiographic Evaluation with Particular Reference to Total-Hip Arthroplasty

The range of magnification factors in 40'' and 72'' radiographs were calibrated using three simple mathods. The relationship between X-ray source to cassette distance, object to cassette distance and magnification factors was determined experimentally for both 40'' and 72'' radiographs. The resulting nomogram showed that: (1) there was no significant magnification difference between centered (AP-hip) and offset (AP-pelvis) radiographs; (2) magnification factors of 40'' films were twice those of 72'' films for the same object to cassette distances; and (3) due to the smaller magnification range of 72'' films (1 to 13%) compared to 40'' films (1 to 26%) there was less chance of error in determining magnification factors for the larger film distances. The skin radiation dosage for the patient was similar in both procedures. Magnification factors were also calculated from 414 A-P radiogrphs of total-hip prosthesis, using the femoral ball as a calibration standard. This provided magnifications of 20 per cent +/- 6(2SD) for 40'' films and by extrapolation on the nomogram gave corresponding values of 10 per cent +/- 3 for the 72'' films. The associated hip to cassette distances (L), also obtained from the nomogram, varied from 125 to 205 mm, average 165 mm. In subsequent clinical trials using 72'' films, it was possible to represent the patients as either small (L less than 145 mm) medium (145 less than or equal to L less than or equal to 185 mm) or large (L greater than 185 mm) with corresponding magnification factors of 8, 10 and 12 per cent, respectively. The error with this simplification was still within +/-21/2 per cent. For 40'' films the corresponding magnification factors for small, medium or large patient categories were 16, 20 and 24 per cent respectively with likely errors within +/-5 per cent. Magnification factors were also calculated from the radiographic image of a 100 mm long rod which had been attached to the patien's thigh. The overall accuracy with this method was comparable to the techniques described above and had the advantage that every radiograph featured its own scale, a particularly important feature for preoperative films which have no implant for calibration purposes. As a result of such simple calibration procedures, it was possible to identify the overall magnification variations and specify particular magnification factors within +/-21/2 per cent (72'' films) or +/-5 per cent (40'' films).

Calculating magnification differences in monocular aphakia.

The calculation of magnification differences is treated well in a number of texts, 1, 3, 4, 5, 7 but the formulas are not always presented in their most convenient form. Because of this, many complex schemes have been illustrated 2 and many different versions have been published. 3, 4, 5. The purpose of this paper is to present the pertinent equations in a simplified manner and to illustrate them by a specific example, namely, the case of monocular aphakia.

New method of anatomic localization of scintigram of various organs by simultaneous combination of emission scanning and transmission scanning

When the photoscintillo-roentgenography is used for relating the scintigram of internal organs to the anatomic structures, this method is found to have some defects--the difference of magnification between the emission scan and the roentgenogram, the inaccuracy due to the geometric distortion of the X-ray image, the impossibility of the simultaneous photographing of the scan and the X-rays, etc. Then, to diminish the influence of these defects we improved on the photographic recording system of a dual-heal scanner, and made use of the transmission scanning method. That is, we combined the recording parts, Ch1 and Ch2, into one system, using Ch1 for the light source of transmission scan and Ch2 for that of emission scan. In this way, we managed to make the two incident rays from those light sources converge into a focus upon a film. Thus we could perform a simultaneous emission-transmission scanning, by moving, at the same time in the same direction, the scanning detector over the patient and the small radioactive source (241Am) under him. This method can be applied to any radioactive nuclide to be used in transmission scanning and emission scanning. As the result of applying this method clinically in our department, the method has proved to be very useful for anatomic localization.

Splenic irradiation portals.

Measurements from splenic scans and celiac arteriograms were used to determine the topography of the spleen with reference to a fixed point, the xiphoid. It was observed that the spleen is more medially placed than generally thought and that the supine position used in radiotherapy produces important changes in the position of the spleen. Due consideration must be given to differences in geometry and magnification when transposing position and size of the spleen as determined by scanning and arteriography to the therapy beam arrangement. Guidelines for more accurate portal placement in splenic irradiation are suggested.

Growth in width of the maxilla studied by the implant method.

The transverse growth of the maxilla was studied radiographically by means of the metallic implant method. The sample consisted of 9 boys without malocclusion of the teeth. They had never received orthodontic treatment and were followed longitudinally by annual registrations from 4 years of age. Sutural growth in width of the maxilla was determined from frontal radiographs as the increase in the distance between metallic implants inserted at the lower aspect of the maxillary zygomatic process on each side. The shape of distance and velocity curves representing transverse growth in the median suture was similar to the shape of the curve representing the growth in body height, both showing a distinct puberal growth maximum. The individual time of puberal maximum for the transverse sutural growth coincides with the time of puberal maximum of facial growth, measured from implants on profile radiographs. The individual time of growth completion in these sutures also coincided, occurring on an average of 17 years of age. The development in width of the maxillary dental arch, measured between the first molars, showed a small puberal growth spurt, but the total increase in width was only about one fourth of the sutural growth in width of the maxilla in this area. To assess whether growth in the median suture was of the same amount throughout its length, metallic implants were also inserted anteriorly into the maxilla on each side of the median suture, on a level with the apices of the central incisors. With correction for differences in magnification on the frontal radiographs, the increase in distance between the laterally placed implants was three times greater than between the anterior implants for a corresponding period of time. This demonstrates that the sutural separation of the two maxillae was greater posteriorly than anteriorly, and consequently they rotate in the transverse plan in relation to each other. The influence of the transverse rotation of the two maxillae on the development of the maxillary dental arch is discussed.

Validation of the role of retrograde urethrogram in the management of urethral strictures

Introduction: Urethral stricture is a common cause of lower urinary tract symptoms in the middle aged and elderly men in our environment. Its diagnosis and management is hinged mainly on a retrograde urethrogram (RUG) that is associated with variable lengths and sites with that found intraoperatively due to difference in magnification (source patient as well as source image distance), penile stretch, and positioning during the procedure. We hereby sort to validate this tool in defining urethral strictures. Materials and Methods: Adult patients with lower urinary tract symptoms suspected to be due to urethral strictures who presented to the outpatient department and emergency departments of the hospital between January 2016 to December 2016 were recruited into the study. This was followed by obtaining an informed consent from the patient and ethical clearance from the institution. Patients who were not fit or not willing to have a urethroplasty were excluded from the study. The recruited patients had RUG to characterize the strictures. The intraoperative findings at urethroplasty were compared with that found on RUG. Data were collected and analyzed using SPSS version 23 to determine sensitivity specificity of the test. Results: A total of 84 patients were studied during the period. The mean age of the patients was 44.1 years. Bulbar strictures accounted for 65% of the strictures. Most of the strictures were single (72%) and long segment (52%). Sensitivity and specificity of RUG in determination of the length of stricture were 76.9% and 74.6%, respectively, whereas the sensitivity and specificity of RUG in determination of site of stricture were 92.9% and 96.4%, respectively. The determination of number of stricture on RUG has a sensitivity of 94.2% and specificity of 90.8%. Conclusion: RUG is a valuable tool in the management of urethral strictures with a higher sensitivity and specificity for the determination of site and number of strictures as compared to length of stricture that is more affected by magnification and techniques in contrast administration. This should be considered during procedure as well as during interpretation of images.

Aniseikonia and magnification in ophthalmic lenses. Problems and solutions.

Aniseikonia is frequently induced or aggravated by lens magnification when it is associated with anisometropia. Because of this factor, magnification properties of lenses and problems which may arise because of these properties are of interest. Quantitative data describe the relationship of anisometropia and aniseikonia. Tables are included which give the magnification differences in various lenses and provide assistance to min imize difficulties due to these differences.

Aggregate Structure in Thin Nickel Films

IT is recognized that in the initial stages of metal film growth by vacuum deposition the incident atoms may possess sufficient mobility on the substrate to form aggregates (clusters of crystallites)1,2. The degree of aggregation is chiefly a function of the substrate temperature and rate of deposition, and is conveniently thought of as a film thickness above which the films have a continuous structure. Various investigators have obtained electron microscopic evidence of the aggregated structure in thin films of a number of metals prepared under various conditions3–6. In addition, precise density measurements have indicated that aggregation in the initial portion of the film formation may result in a decrease in the observed density7. Severe aggregation may also be detected by electrical resistivity measurements. In contrast to the foregoing procedures, a simple chemical etching technique has been successfully used to observe metallographically the aggregate structure in thin nickel films. Despite the difference in magnification, such photomicrographs bear a striking resemblance to the published electron micrographs indicating aggregated structures in thin metal films.

The chromatic field aberrations and their correction in a three lens reflexion electron microscope

The coefficient of the chromatic difference in magnification for a three lens reflexion electron microscope is found to be a function of the focal length of the intermediate lens and the axial position of the objective aperture. A condition is shown to exist for which the coefficient vanishes and the aberration is then corrected. The coefficient of the chromatic difference in rotation is proportional to the overall rotation of the image and can be minimized by exciting lenses in opposition. The effect on the image of a misalinement of the objective aperture is also dealt with. Tolerances in the settings of the correction conditions for the aberrations and in the alinement of the objective aperture are calculated for typical values of the energy spread in the electron beam at low and high angles of beam deviation.

On the Chromatic Field Aberration of the Magnetic Electron Lens in the Electron Microscope

The chromatic field aberration of the magnetic lens in the electron microscope is theoretically studied. Good results are obtained for the coefficient of the chromatic difference in magnification of the objective, taking into account the inclination of the principal illuminating rays. The same coefficient of the intermediate lens increases rapidly as the magnification is reduced by the intermediate lens. The calculated results agree well with experimental results. Calculated results are given for the coefficients of chromatic difference in rotation of all lenses as well as for the coefficient of chromatic difference in magnification of the projection lens.

The Formation of the Diffraction Image with Electrons in the Gabor Diffraction Microscope

The projection and transmission methods of diffraction image formation with electrons are discussed in relation to their practical application.The significance of the two methods as limiting cases of one general method is shown. Analysis shows that the projection method is limited in a practical sense by the combination of a chromatic variation in magnification and path difference. This effect leads either to a severely limited field or a much more stringent electrical stability requirement. Analysis of the transmission method shows it to be free from the above effect, besides having other practical advantages. Some initial results of the application of this method are shown.

Micro-stimulation of the Human Retina

BY correcting the chromatic difference of magnification of the lens system of the eye, and by using very small test objects as stimuli, it has been found possible to construct a plan showing the approximate positions of some of the photo-receptors of my own left retina. Four methods have been employed and their results correlated.

Problems in Selective Reception

In this paper we are comparing from a theoretical standpoint the methods of attainment of the highest degree of selectivity required by present broadcasting conditions, and investigating the distortions introduced by receivers employing such methods in practice. The equations for magnification and phase differences introduced by one or more simple tuned circuits are first obtained in a convenient form: corresponding expressions are obtained for the band-pass circuit, and a note is appended upon circuits with reaction. We then investigate the effect of the detector by determining the audio output from a square law rectifier when an amplitude modulated wave of general form is applied to it: the effective selectivity of, and audio distortion initroduced by, the tuners previously discussed are thus obtained. The whole process is then repeated for the more difficult case of the linear detector and the harmonic distortion here calculated; the "demodulation" effect which occurs when two transmissions are received simultaneously is considered in theory and practice. The two rival systems of selective tuning-viz., the band-pass and the simple sharp tuner with audio tone correction-are compared as regards their ability to deal with the direct and also the heterodyne interference from unwanted neighboring transmissions: the probability of frequency and harmonic distortion in the resulting reception under practical operating conditions is also discussed, and it is shown in particular that the band-pass system is inferior on at least two of these four heads.