Varian Associates

About: Varian Associates is a based out in . It is known for research contribution in the topics: Beam (structure) & Wafer. The organization has 2160 authors who have published 2591 publications receiving 46002 citations.

Method for increasing the accuracy of a radiation therapy apparatus

Abstract: Disclosed is a method for increasing the accuracy of images obtained in radiation therapy apparatus, such as computer tomography simulator which employs an image intensifier (40) and a photodiode detector (44) for converting light from the image intensifier to electrical signals for further processing. The method recognizes that a significant amount of crosstalk can exist in the image intensifier and photodiode detector chain and provides a series of steps for adjusting the electrical signals obtained from the photodiode detector to compensate for the crosstalk.

The quantitative measurement of rotational motion of the subfragment-1 region of myosin by saturation transfer epr spectroscopy.

Abstract: According to current models of muscle contraction (Huxley, H. E., Science 164: 1356-1366 [1969]), motion of flexible myosin crossbridges is essential to the contractile cycle. Using a spin-label analog of iodoacetamide bound to the subfragment No. 1 (S1) region of myosin, we have obtained rotational correlation times (tau 2) for this region of the molecule with the ultimate goal of making quantitative measurements of the motion of the crossbridges under conditions comparable to those in living, contracting muscle. We used the newly developed technique of saturation transfer electron paramagnetic resonance spectroscopy (Hyde, J.S., and Thomas, D.D., Ann. N.Y. Acad Sci. 22:680-692 [1973]), which is uniquely sensitive to rotational motion in the range of 10(-7)-10(-3) sec. Our results indicate that the spin label is rigidly bound to S1 (tau 2 for isolated S1 is 2 X 10(-7) sec) and that the motion of the label reflects the motion of the S1 region of myosin. the value of tau 2 for the S1 segment of myosin is less than twice that for isolated S1, while the molecular weights differ by a factor of 4, indicating flexibility of myosin in agreement with the conclusions of Mendelson et al. (Biochemistry 12:2250-2255 [1973]). Adding F-actin increses tau 2 in either myosin or isolated S1 by a factor of mearly 103, indicating rigid immobilization of S1 by actin. Formation of myosin filaments (at an ionic strength of 0.15 or less) increses tau 2 by a factor of 10-30, depending on the ionic strength, indicating a decrease of the rotational mobility of S1 in these agregates. The remaining motion is at least a factor of 10 faster than would be expected for the filament itself, suggesting motion of the S1 region independent of the filament backbone but slower than in a single molecule. F-actin has a strong immobilizing effect on labeled S1 in myosin filaments (in 0.137 M KC1), but the immobilization is less complete than that observed when F-actin is added to labeled myosin monomers (in 0.5 M KC1). A spin-label analog of maleimide, attached to the SH-2 thiol groups of S1, is immobilized to a much lesser extent by F-actin than is the label on SH-1 groups. The maleimide label also was attached directly to F-actin and was sufficiently immobilized to suggest rigid binding to actin.

Automatic steering of a high velocity beam of charged particles

Abstract: In a high energy X-ray therapy machine, an accelerator accelerates a beam of electrons to energies of several MEV. The electron beam is directed, generally via a beam deflector, onto an X-ray target to produce X-rays for treating a patient. The accelerator and beam deflector are often carried within a rotatable gantry structure, movable for radiating the patient through a series of angular positions or ports. A plurality of ionization chamber radiation detectors are disposed in the radiation field surrounding the beam path of the accelerated electron beam. Ionization current signals are compared from a plurality of the detectors to derive an error signal determinative of a deviation of the beam from an intended beam path. The error signal is utilized to energize beam steering coils for steering the beam along the predetermined beam path. A sample and hold circuit is provided for sampling and holding the error signal to allow interruption of the beam for extended periods of time as may be encountered in the prescribed therapy treatment, while maintaining the proper beam steering conditions.

Electronically enhanced x-ray detector apparatus

Abstract: The detector of the present invention is suitable for use in a radiation therapy simulator machine. The detector comprises an X-ray image intensifier tube to convert X-rays into photons, a linear array of photodiodes to convert the photons to electrical signals, optical means for coupling the photons to the linear array of photodiodes, and electronic signal processing means for conditioning the signals from the photodiodes. The conditioning includes the use of low noise, phaselocked sampling electronics, implementation of a dual sampling technique for increasing dynamic range, implementation of a linearizing technique for increasing the accuracy of the measurements, and implementation of techniques for adjusting the measurements for point spread and background noise effects.