Collimation Techniques Research Articles

Pinhole radionuclide ventriculography in small infants

Radionuclide equilibrium gated ventriculograms were performed in 23 infants before and after surgery for congenital heart disease using standard parallel hole general purpose collimation followed by a pinhole collimation technique to magnify images and improve spatial resolution. A second group of nine infants had pinhole collimated gated ventriculography during cardiac catheterization for comparison with cineangiographic ejection fraction. In group I, pinhole collimation gave improved ventricular and atrial separation over general purpose parallel collimation for determination of left ventricular ejection fraction (42 of 42 studies calculable vs 37 of 42) and for right ventricular ejection fraction (36 of 37 studies calculable vs 20 of 37). In patients with transposition, pinhole technique allowed right ventricular ejection determination in nine of nine studies but in only one of nine was right ventricular ejection fraction possible by standard parallel collimation. In group II, the correlation between left ventricular ejection fraction by cineangiography and pinhole radionuclide ventriculography was excellent ( r = 0.95). The correlation for right ventricular ejection fraction between cineangiography and pinhole radionuclide ventriculography was 0.82. Pinhole radionuclide ventriculography is a useful, practical clinical tool that can be used to assess ventricular function in small infants in an intensive care or outpatient setting.

Improvements in SPECT technology for cerebral imaging

Advancement in three major areas of SPECT (single photon emission computed tomography) technology have resulted in improved image quality for cerebral studies. In the first area, single-crystal camera electronics, extensive use of microprocessors, custom digital circuitry, an data bus architecture have allowed precise external control of all gantry motions and improved signal processing. The new digital circuitry permits energy, uniformity, and linearity corrections to be an integral part of the processing electronics. Calibration of these correlations is controlled by algorithms stored in the camera's memory. In addition, digital signals can be routed directly to interface circuitry of auxiliary computer systems without analog-to-digital conversion. Look-up tables, downloaded to the interface from the central processing unit (CPU), permit computer-controlled real-time processing of coordinate signals, including truncation, magnification, and spatial calibration. The second area of improved SPECT technology is camera collimation and related imaging techniques. In this area, system resolution has been improved without loss of sensitivity by decreasing the air gap between patient and collimator surface. Rotating the detector in close apposition to the head has required various stratagems to avoid detector-shoulder contact: the selective reduction of camera shielding, the use of long bore collimators, and the 30 degrees angulation of the camera head for slant hole collimation. Since cerebral studies characteristically image high-contrast regions less than 1 cm in size, image quality has been improved by increasing collimator resolution even at the expense of sensitivity. Increased resolution also improved image contrast for studies using 123I-labeled pharmaceuticals with 3% to 4% 124I contamination. Such studied acquired with low energy or medium energy collimation and a window centered on the 159 keV 123I photopeak contain appreciable septal breakthrough signals originating from Compton scatter of high energy photons primarily from 124I. The third area of advancements in technology, multidetector instrumentation, offers the promise of increased sensitivity and resolution. For the dynamic computer-assisted tomograph (DCAT) system, which was especially designed for regional blood flow studies with 133Xe or 127Xe, a count rate of 170,000 counts per microCi/cc for three slices has been achieved. This system consists of four detector banks each with 16 rectangular NaI crystals. An alternative system at Harvard uses an array of 12 moving detectors with focused collimators to acquire a single slice.(ABSTRACT TRUNCATED AT 400 WORDS)

Non-destructive collimation technique for measuring glass constants using a Ronchi grating shearing interferometer

A non-destructive liquid immersion collimation technique in combination with a Ronchi grating shearing interferometer has been used for determining the constants of a transparent glass material, especially when it is in the form of a lens. Due to its simplicity and the fact that it will work equally well at any wavelength, the technique is superior to existing methods for determining the various glass constants (refractive index, Abbe number or v-value, partial dispersion factor etc). The shearing fringes appearing inside a Ronchi-gram are adequate to locate the exact position of the point source which has been treated as the target in the present communication. The fringe-free space in the overlapping region between the two laterally displaced spherical wavefronts indicates the sharply focused position of the target which corresponds to zero defocusing. In this way the target displacements with different liquids are determined.

Small‐angle x‐ray scattering measurements on dilute solutions of polyisobutene by use of kratky cone collimation

AbstractSAXS measurements on dilute solutions of polyisobutene inn‐hexane (Mν= 25,600−3.55 × 106,c< 53 g/liter) were carried out by combining conventional slit collimation with the new cone collimation technique. With a fractionated sample (Mν= 25,600;U< 0.2) the radius of gyration (R= 48 Å), the cross‐sectional radius of gyration (Rq= 3.9 Å), the molecular weight per unit length (M/L= 22.8 Å−1), and the Porod persistence length (a*= 8.1 Å) are found. The persistence length appears to be dependent on the molecular weight. The partial specific volumeνof polyisobutene inn‐hexane also depends on the molecular weight according toν= 1.025 + 105/Mν(cm3/g).

Beam deflection and isolation in laser amplifiers

A new beam deflection and collimation technique is described which utilizes transverse gain variations in laser amplifiers. This method may be used to achieve beam mixing or optical isolation between the stages of an amplifier chain. Results with a CO 2 amplifier are decribed.

Letters to the Editor A Multi-Aperture Collimation Technique

A pair of identical multi-aperture templates is described that enable beam collimation to be rapidly evaluated at discrete points over the beam aperture. The technique is independent of the accuracy of other optical components and is inexpensive to implement. A method for fabricating the two templates is indicated, and an application to rapid evaluation of a lens used as a collimator is described.

Studies of the surface type gamma-ray backscatter soil density gauges using collimation and spectrometry techniques

A prototype gauge was constructed which allowed evaluation of the effects of energy discrimination and source and detector collimation and collimation angles on gauge performance. A NaI (T1) scintillation detector and a multichannel analyzer were used to provide the energy discrimination capability and rotatable lead collimators were constructed for collimation purposes. In addition, source-detector separation was varied over a small range. Because of possible competing effects, the different design parameters were varied simultaneously and both single- and dual-gauge results evaluated. The purpose was to monitor and interpret the effects of energy discrimination and of collimation more than to obtain the best possible design for field applications. The effects on individual errors and on quality factor are displayed and discussed for single gauges, and the best dual gauges obtained are reported. A triple-gauge concept is introduced which would eliminate errors due both to composition variations and to surface roughness.

Decay Curves and Half-lives of Gamma-Emitting States from a Study of Prompt Fission Gamma Radiation

Measurements were made on the time distributions of the prompt gamma radiation emitted from fragments in the thermal-neutron induced fission of 235U. The gamma radiation emitted during different time intervals after the fission event was studied with the help of a collimator, the position of which was changed along the path of the fragments. In this way decay curves were obtained from which half-lives could be estimated. Time components with half-lives of 7.5, 18 and 60 ps were found and their relative intensities were calculated. Half-lives and associated intensities are in good agreement with earlier data from uranium and californium fission. Problems involved in this type of study are discussed. The collimator technique has proved to be effective for determination of half-lives down to less than 10 ps.

A New Technique for Measurements of Radial Distributions of Excited Species in Plasmas and Its Application to Capillary Discharges in Argon

This paper describes a novel technique for obtaining the radial profiles of individual emission lines from a plasma directly in the form of a recorded trace of intensity vs radial position. The method employs an ``end-on'' collimation technique which eliminates the complicated data reduction treatment required by conventional ``side-light'' methods. Spatial resolution and instrumental distortion effects are discussed. The method is applied in an experimental study of the capillary discharge in argon, and the relevance of the results to the excitation mechanisms of the cw AII laser is indicated. In particular, it is found that populations of excited AI states are substantially independent of the local electron density over wide ranges of plasma parameters, an effect which is attributed to the predominance of electron-impact-induced transfers over radiative transfers for the AI states. The populations of excited states of AII are found to have profiles which are in agreement with those predicted by a plasma model in which (a) the ion loss is controlled by ambipolar diffusion at higher pressures with a steady approach towards an essentially collisionless ``free-fall'' motion occurring as the pressure is decreased, and (b) excitation to the AII excited levels proceeds stepwise via the AII ground state. The method is of general applicability to problems involving spatial variations in plasmas, and has been coupled with high-resolution interferometric techniques to provide direct measurements of spatial dependence of spectral line-broadening parameters.