Brain SPECT with short focal-length cone-beam collimation

2005 ◽  
Vol 32 (7Part1) ◽  
pp. 2236-2244 ◽  
Author(s):  
Mi-Ae Park ◽  
Stephen C. Moore ◽  
Marie Foley Kijewski
Keyword(s):  
Focal Length ◽  
Brain Spect ◽  
Cone Beam ◽  
Short Focal Length ◽  
Beam Collimation

scholarly journals Brain SPECT Simulation Using Half-Cone-Beam Collimation and Single-Revolution Helical-Path Acquisition

2007 ◽  
Vol 54 (3) ◽  
pp. 475-479 ◽  
Author(s):  
Ruben Ter-Antonyan ◽  
Ronald J. Jaszczak ◽  
James E. Bowsher ◽  
Kim L. Greer ◽  
Scott D. Metzler
Keyword(s):  
Brain Spect ◽  
Cone Beam ◽  
Half Cone ◽  
Beam Collimation

The Reduction of Chromatic Aberrations Due to Instrumental Instabilities

1971 ◽  
Vol 29 ◽  
pp. 14-15
Author(s):  
J. S. Lally ◽  
R. Evans
Keyword(s):  
Electron Microscope ◽  
High Voltage ◽  
Focal Length ◽  
Chromatic Aberration ◽  
Objective Lens ◽  
Usual Practice ◽  
Voltage Electron ◽  
Short Focal Length ◽  
Chromatic Aberrations ◽  
Electron Microscopes

One of the instrumental factors often limiting the resolution of the electron microscope is image defocussing due to changes in accelerating voltage or objective lens current. This factor is particularly important in high voltage electron microscopes both because of the higher voltages and lens currents required but also because of the inherently longer focal lengths, i.e. 6 mm in contrast to 1.5-2.2 mm for modern short focal length objectives.The usual practice in commercial electron microscopes is to design separately stabilized accelerating voltage and lens supplies. In this case chromatic aberration in the image is caused by the random and independent fluctuations of both the high voltage and objective lens current.

Short focal length Kirkpatrick-Baez mirrors for a hard x-ray nanoprobe

2005 ◽  
Vol 76 (11) ◽  
pp. 113701 ◽  
Author(s):  
Wenjun Liu ◽  
Gene E. Ice ◽  
Jonathan Z. Tischler ◽  
Ali Khounsary ◽  
Chian Liu ◽  
...  
Keyword(s):  
Focal Length ◽  
X Ray ◽  
Short Focal Length

Long focal length, asymmetric fan beam collimation for transmission acquisition with a triple camera SPECT system

1997 ◽  
Vol 44 (3) ◽  
pp. 1191-1196 ◽  
Author(s):  
D.R. Gilland ◽  
H. Wang ◽  
R.E. Coleman ◽  
R.J. Jaszczak
Keyword(s):  
Focal Length ◽  
Spect System ◽  
Beam Collimation

Study on Sound Field of High Intensity Focused Ultrasound with Short Focal Length

2012 ◽  
Vol 195-196 ◽  
pp. 364-369 ◽  
Author(s):  
Jin Hua Zhao ◽  
Li Li Yu ◽  
Chun Hui ◽  
Bin Feng Huang ◽  
Chao Li ◽  
...  
Keyword(s):  
Nonlinear Effect ◽  
Sound Pressure ◽  
Focal Length ◽  
Sound Field ◽  
High Intensity Focused Ultrasound ◽  
Beam Equation ◽  
Focal Region ◽  
Interface Position ◽  
Short Focal Length ◽  
Planar Wave

In this paper, numerical simulation of sound field with short focal length is performed, which is based on spheroidal beam equation (SBE) in frequency-domain for transducer with a wide aperture angle. And we made some experiments on vitro bovine liver to explore the characteristic of sound pressure and-3dB sound focal region at different positions of incident interface. It is found that with a fixed curvature radius if the focal length is shorter under the skin, the amplitude of sound pressure will be higher on the focus and the shape of-3dB sound focal region will be smaller. When the incident interface is in the range of planar wave, nonlinear effect is strong and the focus will change with the interface position. Especially when the position is near to transition location between planar wave and spheroidal wave, the nonlinear effect is lowered. While the focus is closer to the sound source so as to burn the scarfskin easily. When the interface is in the range of spheroidal wave, the focus position changes little but the side lobe effect due to refraction is obvious. And the focusing performance of transducer will be affected. The experimental results validate the accuracy of theoretical results. It is concluded that the position of incident interface should be selected reasonably with short focal length in the treatment of superficial tissue.

Aberration-free short focal length x-ray lenses

2015 ◽  
Vol 40 (23) ◽  
pp. 5586 ◽  
Author(s):  
Lucia Alianelli ◽  
Manuel Sánchez del Rio ◽  
Oliver J. L. Fox ◽  
Katarzyna Korwin-Mikke
Keyword(s):  
Focal Length ◽  
X Ray ◽  
Short Focal Length

scholarly journals A Microlens Super-Surface Film with Regular Graded Circular Hole-Like Subwavelength Structures for Highly Focusing Strength

Coatings ◽  
2019 ◽  
Vol 9 (12) ◽  
pp. 776
Author(s):  
Jinshuang Wu ◽  
Leimengting Zhang ◽  
Yahong Li ◽  
Yixin Zhang ◽  
Bowei Yang ◽  
...  
Keyword(s):  
Circular Hole ◽  
Focal Length ◽  
Surface Film ◽  
Subwavelength Structures ◽  
Lens Array ◽  
Direct Laser ◽  
Short Focal Length ◽  
Micro Lens Array ◽  
Micro Lens ◽  
Sub Wavelength

Using the fact that a sub-wavelength structure exhibits the same thermal expansion coefficient as a micro-lens array, we design a micro-lens super-surface film with regular circular hole-like subwavelength structures to realize the high performances of central highly focusing strength and short focal length. In addition, based on the Fresnel—Kirchhoff diffraction theory, the influences of subwavelength structural period and height on the focusing performance of a micro-lens are analyzed. Furthermore, the finite-difference time-domain method is utilized to optimize the structural parameters. Via direct laser writing and an inductively coupled plasma process, we fabricated a square micro-lens array consisting of a 1000 × 1000 micro-lens unit with a sub-wavelength structure, and the optical focusing performance was measured in the visible light band. Finally, the experimental results indicate that the focal length is decreased to 15 μm, the focal spot central energy is increased by 7.3%, and the light transmission, enhanced via inserting sub-wavelength structures, corresponds to 3%. This proves that the designed micro-lens array with a regular-graded circular hole-like subwavelength structure can achieve central high focusing and a short focal length. This has applications in several fields of wavefront detection and light field imaging systems.

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