Dr. John A. Rowlands Profile

Dr. John A. Rowlands

Founding Scientist

SPIE Involvement:

Author

Publications (60)

Proceedings Article | 19 March 2014 Paper

Investigation of spatial resolution and temporal performance of SAPHIRE (scintillator avalanche photoconductor with high resolution emitter readout) with integrated electrostatic focusing

David Scaduto, Anthony Lubinsky, John Rowlands, Hidenori Kenmotsu, Norihito Nishimoto, Takeshi Nishino, Kenkichi Tanioka, Wei Zhao

Proceedings Volume 9033, 90333S (2014) https://doi.org/10.1117/12.2043187

KEYWORDS: Sensors, Spatial resolution, Modulation transfer functions, Electrodes, Finite element methods, X-rays, Scintillators, Photoresistors, Imaging systems, X-ray imaging

Read Abstract +

Proceedings Article | 24 February 2012 Paper

Order of magnitude reduction of fluoroscopic x-ray dose

Abhinav Bal, Normand Robert, Lindsay Machan, Meir Deutsch, David Kisselgoff, Paul Babyn, John Rowlands

Proceedings Volume 8313, 831356 (2012) https://doi.org/10.1117/12.912760

KEYWORDS: X-rays, Fluoroscopy, Attenuators, Image processing, Sensors, Camera shutters, Image quality, X-ray imaging, Cancer, Radiation effects

Read Abstract +

Proceedings Article | 22 March 2010 Paper

Investigation of gain non-uniformities in the two TFT current programmed amorphous silicon active pixel sensor for fluoroscopy, chest radiography, and mammography tomosynthesis applications

Nader Safavian, M. Yazdandoost, D. Wu, M. Izadi, K. Karim, J. Rowlands

Proceedings Volume 7622, 76221N (2010) https://doi.org/10.1117/12.845592

KEYWORDS: Amplifiers, Fluoroscopy, Sensors, X-rays, Amorphous silicon, Active sensors, Temperature metrology, Mammography, Computer programming, Chest

Read Abstract +

Proceedings Article | 22 March 2010 Paper

Effect of scintillator crystal geometry and surface finishing on depth of interaction resolution in PET detectors: Monte Carlo simulation and experimental results using silicon photomultipliers

Sarah Cuddy, Alla Reznik, John Rowlands, Farhad Taghibakhsh

Proceedings Volume 7622, 76221O (2010) https://doi.org/10.1117/12.845065

KEYWORDS: Crystals, Sensors, Waveguides, Photodetectors, Scintillators, Surface finishing, Monte Carlo methods, Positron emission tomography, Photons, Scintillation

Read Abstract +

SPIE Journal Paper | 1 March 2010 Open Access

Nonlinear multicontrast microscopy of hematoxylin-and-eosin-stained histological sections

Adam Tuer, Danielle Tokarz, Nicole Prent, Richard Cisek, Jennifer Alami, Daniel Dumont, Ludmilla Bakueva, John Rowlands, Virginijus Barzda

JBO, Vol. 15, Issue 02, 026018, (March 2010) https://doi.org/10.1117/12.10.1117/1.3382908

KEYWORDS: Tissues, Luminescence, Absorption, Microscopy, Nonlinear optics, Microscopes, Tissue optics, Second-harmonic generation, Picosecond phenomena, Aluminum

Read Abstract +

DOWNLOAD PAPER

Proceedings Article | 16 March 2009 Paper

Characterization of bias induced metastability of amorphous silicon thin film transistor based passive pixel sensor switch and its impact on biomedical x-ray imaging application

Afrin Sultana, N. Safavian, M. Izadi, K. Karim, J. Rowlands

Proceedings Volume 7258, 72583Q (2009) https://doi.org/10.1117/12.812282

KEYWORDS: Imaging systems, Sensors, Switches, Biomedical optics, Amorphous silicon, X-ray imaging, Proteins, Thin films, Transistors, Crystallography

Read Abstract +

Proceedings Article | 14 March 2009 Paper

A counting and integrating pixel readout chip for amorphous selenium direct radiation detectors for medical imaging applications

A. Goldan, Bahman Hadji, K. Karim, G. DeCrescenzo, J. Rowlands, O. Tousignant, L. Laperrière

Proceedings Volume 7258, 72583K (2009) https://doi.org/10.1117/12.813730

KEYWORDS: Sensors, Imaging systems, Selenium, Clocks, Spectroscopy, X-rays, Mammography, Photodetectors, Surgery, Switches

Read Abstract +

Proceedings Article | 13 March 2009 Paper

Characterization of current programmed amorphous silicon active pixel sensor readout circuit for dual mode diagnostic digital x-ray imaging

Nader Safavian, M. Yazdandoost, D. Wu, A. Sultana, M. Izadi, K. Karim, A. Nathan, J. Rowlands

Proceedings Volume 7258, 725815 (2009) https://doi.org/10.1117/12.813886

KEYWORDS: Computer programming, X-rays, Sensors, Amorphous silicon, Imaging systems, Capacitors, Capacitance, Active sensors, Transistors, Signal to noise ratio

Read Abstract +

Proceedings Article | 28 February 2009 Paper

Development of a targeted CT contrast agent: assessment of cellular interactions using novel integrated optical labels

Naomi Matsuura, Melissa Hill, Ivan Gorelikov, Siqi Zhu, Kelvin Wan, James Mainprize, Martin Yaffe, J. Rowlands

Proceedings Volume 7262, 72622A (2009) https://doi.org/10.1117/12.812048

KEYWORDS: In vivo imaging, X-ray computed tomography, Computed tomography, Luminescence, In vitro testing, Nanoparticles, Integrated optics, Toxicity, Tissues, Flow cytometry

Read Abstract +

Proceedings Article | 18 March 2008 Paper

An indirect flat-panel detector with avalanche gain for low dose x-ray imaging: SAPHIRE (scintillator avalanche photoconductor with high resolution emitter readout)

Wei Zhao, Dan Li, J. Rowlands, N. Egami, Y. Takiguchi, M. Nanba, Y. Honda, Y. Ohkawa, M. Kubota, K. Tanioka, K. Suzuki, T. Kawai

Proceedings Volume 6913, 69130M (2008) https://doi.org/10.1117/12.772774

KEYWORDS: Finite element methods, X-rays, X-ray imaging, Image sensors, Sensors, Modulation transfer functions, Electrodes, Electron beams, Photoresistors, Scintillators

Read Abstract +

Proceedings Article | 18 March 2008 Paper

Photon counting readout pixel array in 0.18-µm CMOS technology for on-line gamma-ray imaging of 103-palladium seeds for permanent breast seed implant (PBSI) brachytherapy

A. Goldan, K. Karim, A. Reznik, C. Caldwell, J. Rowlands

Proceedings Volume 6913, 69130S (2008) https://doi.org/10.1117/12.770766

KEYWORDS: Sensors, Signal to noise ratio, Photon counting, Picosecond phenomena, Breast, Imaging systems, CMOS technology, Clocks, CMOS sensors, Electrodes

Read Abstract +

Proceedings Article | 18 March 2008 Paper

Development of an MR compatible rotating anode x-ray tube

Prasheel Lillaney, John Bracken, Arun Ganguly, John Rowlands, Rebecca Fahrig

Proceedings Volume 6913, 691347 (2008) https://doi.org/10.1117/12.773911

KEYWORDS: X-rays, Electron beams, Magnetism, Finite element methods, X-ray imaging, Magnetic resonance imaging, Computer simulations, Sensors, 3D modeling, Surgery

Read Abstract +

Proceedings Article | 12 March 2008 Paper

Enhancement of third harmonic contrast with harmonophores in multimodal non-linear microscopy of histological sections

Adam Tuer, Ludmila Bakueva, Richard Cisek, Jennifer Alami, Daniel Dumont, John Rowlands, Virginijus Barzda

Proceedings Volume 6860, 686005 (2008) https://doi.org/10.1117/12.763509

KEYWORDS: Tissues, Luminescence, Second-harmonic generation, Microscopy, Microscopes, Harmonic generation, Collagen, Prostate, Cancer, Multiphoton microscopy

Read Abstract +

Proceedings Article | 19 March 2007 Paper

Photon counting pixel architecture for x-ray and gamma-ray imaging applications

Amir Goldan, Li Ng, J. Rowlands, Karim Karim

Proceedings Volume 6510, 65103V (2007) https://doi.org/10.1117/12.710358

KEYWORDS: Photon counting, Sensors, X-rays, PIN photodiodes, Amplifiers, Silicon, Analog electronics, Microcontrollers, Intelligence systems, Gamma ray imaging

Read Abstract +

Proceedings Article | 16 March 2007 Paper

The x-ray light valve: a low-cost, digital radiographic imaging system-spatial resolution

Robert MacDougall, Ivaylo Koprinarov, Christie Webster, J. Rowlands

Proceedings Volume 6510, 651018 (2007) https://doi.org/10.1117/12.713659

KEYWORDS: X-rays, Modulation transfer functions, Liquid crystals, X-ray imaging, Sensors, Scanners, Radiography, Optical scanning, Digital x-ray imaging, Imaging systems

Read Abstract +

Proceedings Article | 6 March 2006 Paper

Selective photon counter for digital x-ray mammography tomosynthesis

Amir Goldan, Karim Karim, J. Rowlands

Proceedings Volume 6142, 61425B (2006) https://doi.org/10.1117/12.653764

KEYWORDS: Photon counting, Sensors, Amplifiers, Digital mammography, Mammography, Interference (communication), X-rays, Electrons, Imaging systems, CMOS technology

Read Abstract +

Proceedings Article | 2 March 2006 Paper

Light induced degradation in amorphous silicon photodiodes and implication for diagnostic medical imaging application

I. Khodami, M.M. Adachi, M. Malhotra, F. Taghibakhsh, J.A. Rowlands, K.S. Karim, K.L. Kavanagh

Proceedings Volume 6142, 61422U (2006) https://doi.org/10.1117/12.653862

KEYWORDS: Plasma enhanced chemical vapor deposition, Diodes, Quantum efficiency, Amorphous silicon, Sensors, Photons, Photodiodes, Medical imaging applications, Diagnostics, Aluminum

Read Abstract +

Proceedings Article | 2 March 2006 Paper

Low cost digital radiographic imaging systems: the x-ray light valve

J. Rowlands, Christie Webster, Ivaylo Koprinarov, Peter Oakham, Kelly Schad, Timothy Szeto, Stephen Germann

Proceedings Volume 6142, 614203 (2006) https://doi.org/10.1117/12.650195

KEYWORDS: X-rays, X-ray imaging, Imaging systems, Radiography, Sensors, Image quality, Liquid crystals, Digital x-ray imaging, Reflectivity, X-ray optics

Read Abstract +

Proceedings Article | 2 March 2006 Paper

Effect of ghosting on the modulation transfer function of amorphous selenium based flat panel detectors

Lamia Chowdhury, Olivier Tousignant, Giovanni DeCrescenzo, P. Gauthier, J. Leboeuf, J. Rowlands

Proceedings Volume 6142, 61421S (2006) https://doi.org/10.1117/12.650204

KEYWORDS: Modulation transfer functions, Electrons, Sensors, Electrodes, Photoresistors, X-rays, Selenium, Spatial frequencies, Data modeling, Metals

Read Abstract +

Proceedings Article | 2 March 2006 Paper

Low-noise pixel architecture for advanced diagnostic medical x-ray imaging applications

M. Izadi, K. Karim, A. Nathan, J. Rowlands

Proceedings Volume 6142, 61420T (2006) https://doi.org/10.1117/12.654900

KEYWORDS: Amplifiers, Sensors, Amorphous silicon, Electrons, Transistors, Capacitance, Imaging systems, X-ray imaging, Fluoroscopy, Data modeling

Read Abstract +

Proceedings Article | 28 February 2006 Paper

Composite metal-semiconductor nanodots for medical imaging

Ludmila Bakueva, Elena Bogdanovich, Ivan Gorelikov, Daniel Dumont, John Rowlands, Harry Ruda, Alexander Shik

Proceedings Volume 6095, 60950H (2006) https://doi.org/10.1117/12.644801

KEYWORDS: Gold, Semiconductors, Luminescence, Plasmons, Nanostructures, Composites, Zinc, Absorption, Toxicity, Nanolithography

Read Abstract +

Proceedings Article | 14 October 2005 Paper

Amorphous silicon based direct x-ray conversion detector for protein structure analysis

Afrin Sultana, Arokia Nathan, J. Rowlands

Proceedings Volume 5969, 596928 (2005) https://doi.org/10.1117/12.629543

KEYWORDS: Sensors, X-rays, Proteins, X-ray detectors, Signal detection, Photons, Crystals, Crystallography, X-ray diffraction, Diffraction

Read Abstract +

Proceedings Article | 14 October 2005 Paper

TFT active image sensor with current-mode readout circuit for digital x-ray fluoroscopy

Nader Safavian, G. R. Chaji, A. Nathan, J. A. Rowlands

Proceedings Volume 5969, 596929 (2005) https://doi.org/10.1117/12.629811

KEYWORDS: Amplifiers, Computer programming, X-rays, Fluoroscopy, X-ray imaging, Image sensors, Digital electronics, Error analysis, Sensors, Interference (communication)

Read Abstract +

Proceedings Article | 13 October 2005 Paper

Photoluminescence-based detection of human chronic total occlusion in peripheral vessels

Ludmila Bakueva, Lukasz Brzozowski, Brian Courtney, Nikita Reznik, Stephen Fremes, J. Rowlands

Proceedings Volume 5969, 596918 (2005) https://doi.org/10.1117/12.628153

KEYWORDS: Luminescence, Arteries, Angiography, Collagen, Statistical analysis, Chemical vapor deposition, X-rays, Fiber optics, Tissues, Visualization

Read Abstract +

Proceedings Article | 12 October 2005 Paper

Luminescence investigation of endothelial cells using metallic and semiconductor nanocrystals

Elena Bogdanovic, Ludmila Bakueva, Lukasz Brzozowski, Ivan Gorelikov, Nikita Reznik, Daniel Dumont, J. A. Rowlands

Proceedings Volume 5969, 596906 (2005) https://doi.org/10.1117/12.628234

KEYWORDS: Nanocrystals, Luminescence, Gold, Receptors, Semiconductors, Confocal microscopy, In vitro testing, Zinc, Cell biology, In vivo imaging

Read Abstract +

Proceedings Article | 20 April 2005 Paper

Indirect flat-panel detector with avalanche gain: design and operation of the avalanche photoconductor

Wei Zhao, Dan Li, Alla Reznik, Brian Lui, D. Hunt, Kenkichi Tanioka, J. Rowlands

Proceedings Volume 5745, (2005) https://doi.org/10.1117/12.597295

KEYWORDS: Selenium, Sensors, X-rays, Quantum efficiency, X-ray imaging, Fluoroscopy, Photons, X-ray detectors, Photoresistors, Radiography

Read Abstract +

Proceedings Article | 20 April 2005 Paper

Investigation of high quantum efficiency megavoltage CT detectors for use in rotational tomotherapy utilizing amorphous selenium conversion layers: dose dependent sensitivity

Andreas Rau, Guang Fang, Ludmila Bakueva, John Rowlands

Proceedings Volume 5745, (2005) https://doi.org/10.1117/12.605847

KEYWORDS: X-rays, Sensors, Electrons, Selenium, Radiotherapy, Electrodes, Quantum efficiency, Imaging systems, X-ray detectors, X-ray imaging

Read Abstract +

Proceedings Article | 20 April 2005 Paper

Effect of flare on computed radiography systems

John Rowlands, Stephen Kengyelics, Andrew Davies, Winston Ji, Kuo Yan

Proceedings Volume 5745, (2005) https://doi.org/10.1117/12.597382

KEYWORDS: Chromium, X-rays, Radiography, Modulation transfer functions, Light scattering, Computing systems, Waveguides, Scanners, X-ray imaging, Photons

Read Abstract +

Proceedings Article | 6 May 2004 Paper

Development of a new generation of area detectors for portal imaging: high-quantum-efficiency direct-conversion MV flat-panel imagers

Geordi Pang, John Rowlands

Proceedings Volume 5368, (2004) https://doi.org/10.1117/12.531921

KEYWORDS: Sensors, Quantum efficiency, X-rays, X-ray detectors, Metals, Spatial resolution, Electrodes, Electrons, Prostate, Radiotherapy

Read Abstract +

Proceedings Article | 6 May 2004 Paper

Indirect flat-panel detector with avalanche gain

Wei Zhao, Dylan Hunt, Kenkichi Tanioka, John Rowlands

Proceedings Volume 5368, (2004) https://doi.org/10.1117/12.536863

KEYWORDS: Sensors, X-rays, Selenium, Imaging systems, X-ray imaging, Modulation transfer functions, Photoresistors, Systems modeling, Electrodes, Quantum efficiency

Read Abstract +

Proceedings Article | 6 May 2004 Paper

Inherent imaging performance of cesium iodide scintillators

Wei Zhao, Goran Ristic, John Rowlands

Proceedings Volume 5368, (2004) https://doi.org/10.1117/12.536865

KEYWORDS: Modulation transfer functions, X-rays, X-ray imaging, Sensors, Spatial frequencies, Cesium, Scintillators, Photons, Imaging systems, CMOS sensors

Read Abstract +

Columnar structured cesium iodide (CsI) scintillators doped with Thallium (Tl) have been used extensively for indirect x-ray imaging detectors. The purpose of this paper is to develop a methodology for systematic investigation of the inherent imaging performance of CsI as a function of thickness and design type. The results will facilitate the optimization of CsI design for different x-ray imaging applications, and allow validation of physical models developed for the light channeling process in columnar CsI layers. CsI samples of different types and thicknesses were obtained from the same manufacturer. They were optimized either for light output (HL) or image resolution (HR), and the thickness ranged between 150 and 600 microns. During experimental measurements, the CsI samples were placed in direct contact with a high resolution CMOS optical sensor with a pixel pitch of 48 microns. The modulation transfer function (MTF), noise power spectrum (NPS) and detective quantum efficiency (DQE) of the detector with different CsI configurations were measured experimentally. The aperture function of the CMOS sensor was determined separately, which allows estimation of the MTF of CsI alone. We also measured the pulse height distribution of the light output from both the HL and HR CsI at different x-ray energies, from which the x-ray quantum efficiency, Swank factor and x-ray conversion gain were determined. Our results showed that the MTF at 5 cycles/mm for the HR type is 50 % higher than for the HL, however at a cost of ~ 36 % reduction in light output. The Swank factor below K-edges of Cs and I is 0.91 and 0.93 for the HR and HL types, respectively, which means that their DQE(0) are essentially identical for the same thickness. The presampling MTF decreases as a function of thickness, and the rate of decrease drops as the thickness increases. This indicates that the light channeling process in CsI improves the MTF of thicker layers more significantly than it does for the thinner ones.

Proceedings Article | 6 May 2004 Paper

High-dynamic-range pixel architectures for diagnostic medical imaging

Karim S. Karim, Sherman Yin, Arokia Nathan, John Rowlands

Proceedings Volume 5368, (2004) https://doi.org/10.1117/12.537404

KEYWORDS: Amplifiers, Sensors, Amorphous silicon, Signal to noise ratio, Capacitance, High dynamic range imaging, Switches, Resistance, X-rays, Fluoroscopy

Read Abstract +

Proceedings Article | 6 May 2004 Paper

High-resolution (20 cycles/mm) digital x-ray mammography using amorphous selenium directly coupled to CCD readout devices

David Hunter, Gueorgui Belev, Giovanni DeCresenzo, Safa Kasap, James Mainprize, Gordon Mawdsley, John Rowlands, Charles Smith, Tumay Tumer, Vladimir Verpakhovski, Shi Yin, Martin Yaffe

Proceedings Volume 5368, (2004) https://doi.org/10.1117/12.536001

KEYWORDS: Charge-coupled devices, X-rays, Sensors, Modulation transfer functions, Selenium, Electrodes, X-ray detectors, Digital mammography, CCD image sensors, Aluminum

Read Abstract +

Proceedings Article | 5 June 2003 Paper

Active pixel image sensor for large-area medical imaging

Karim Karim, Yurii Vygranenko, Alfredo Avila-Munoz, Denis Striakhilev, Arokia Nathan, Stephen Germann, John Rowlands, George Belev, Cyril Koughia, Robert Johanson, Safa Kasap

Proceedings Volume 5030, (2003) https://doi.org/10.1117/12.480254

KEYWORDS: X-rays, Sensors, Amplifiers, Amorphous silicon, X-ray detectors, Electrons, Capacitance, Aluminum, Medical imaging, Selenium

Read Abstract +

Proceedings Article | 5 June 2003 Paper

Imaging performance of an amorphous selenium flat-panel detector for digital fluoroscopy

Dylan Hunt, Olivier Tousignant, Yves Demers, Luc Laperriere, John Rowlands

Proceedings Volume 5030, (2003) https://doi.org/10.1117/12.480131

KEYWORDS: Modulation transfer functions, X-rays, Spatial frequencies, Sensors, Quantum efficiency, Selenium, Fluoroscopy, Electrons, Aluminum, X-ray imaging

Read Abstract +

Proceedings Article | 30 August 2002 Paper

Resolution enhancement and performance characteristics of large-area a-Si:H x-ray imager with a high-aspect-ratio SU-8 micromold

Ye Zhou, Alfredo Avila-Munoz, Sheng Tao, Zhihua Gu, Arokia Nathan, John Rowlands

Proceedings Volume 4925, (2002) https://doi.org/10.1117/12.481582

KEYWORDS: X-rays, X-ray imaging, Modulation transfer functions, Absorption, Coating, Visible radiation, Photons, Glasses, Image resolution, Spatial resolution

Read Abstract +

Proceedings Article | 3 May 2002 Paper

Investigation of lag and ghosting in amorphous selenium flat-panel x-ray detectors

Wei Zhao, Giovanni DeCrescenzo, John Rowlands

Proceedings Volume 4682, (2002) https://doi.org/10.1117/12.465557

KEYWORDS: X-rays, Sensors, Electrodes, Selenium, X-ray detectors, X-ray imaging, Amplifiers, Dielectrics, Breast, Image sensors

Read Abstract +

Proceedings Article | 28 June 2001 Paper

Investigation of imaging performance of amorphous selenium flat-panel detectors for digital mammography

Wei Zhao, W. Ji, John Rowlands, Anne Debrie

Proceedings Volume 4320, (2001) https://doi.org/10.1117/12.430876

KEYWORDS: Sensors, Modulation transfer functions, X-rays, Prototyping, Spatial frequencies, X-ray detectors, Systems modeling, X-ray imaging, Digital mammography, Electrodes

Read Abstract +

Proceedings Article | 28 June 2001 Paper

Effect of depth-dependent modulation transfer function and K-fluorescence reabsorption on the detective quantum efficiency of indirect-conversion flat-panel x-ray imaging systems using CsI

John Rowlands, Winston Ji, Wei Zhao

Proceedings Volume 4320, (2001) https://doi.org/10.1117/12.430931

KEYWORDS: Modulation transfer functions, Sensors, X-rays, Imaging systems, X-ray imaging, Scattering, Data modeling, Quantum efficiency, Light scattering, X-ray detectors

Read Abstract +

Proceedings Article | 28 June 2001 Paper

Alternate pixel architectures for large-area medical imaging

Karim Karim, Arokia Nathan, John Rowlands

Proceedings Volume 4320, (2001) https://doi.org/10.1117/12.430903

KEYWORDS: Amplifiers, Sensors, Capacitance, Interference (communication), Switches, Fluoroscopy, Electrons, Resistance, Capacitors, Imaging systems

Read Abstract +

Proceedings Article | 25 April 2000 Paper

Direct-conversion flat-panel x-ray imaging: reduction of noise by presampling filtration

John Rowlands, Winston Ji, Wei Zhao, Denny Lee

Proceedings Volume 3977, (2000) https://doi.org/10.1117/12.384519

KEYWORDS: Sensors, Modulation transfer functions, X-rays, Imaging systems, X-ray imaging, Spatial frequencies, Electrodes, Prototyping, Photoresistors, Interference (communication)

Read Abstract +

Proceedings Article | 25 April 2000 Paper

Experimentally validated theoretical model of avalanche multiplication x-ray noise in amorphous selenium

Dylan Hunt, Brian Lui, John Rowlands

Proceedings Volume 3977, (2000) https://doi.org/10.1117/12.384483

KEYWORDS: X-rays, Sensors, Amplifiers, Interference (communication), Quantum efficiency, Electrodes, Signal to noise ratio, X-ray imaging, Photoresistors, Cameras

Read Abstract +

Proceedings Article | 28 May 1999 Paper

Optimization of the presampling modulation transfer function of flat-panel detectors for digital radiology

John Rowlands, Winston Ji

Proceedings Volume 3659, (1999) https://doi.org/10.1117/12.349536

KEYWORDS: Modulation transfer functions, Sensors, X-ray imaging, X-rays, Spatial frequencies, Photoresistors, Imaging systems, Electrodes, Radiography, X-ray detectors

Read Abstract +

Large area, flat panel solid state detectors are being investigated for digital radiography and fluoroscopy. These detectors employ an x-ray imaging layer of either photoconductor ('direct' conversion method) or phosphor ('indirect' conversion method) to detect x-rays. In both cases the image formed at the surface of the layer is read out in situ using an active matrix array. Depending upon the resolution of the layer compared to the pixel size, undersampling of the image and hence aliasing may occur. Aliasing is always present regardless of the pixel size in direct detectors based on amorphous selenium because of its high intrinsic resolution. Aliasing gives rise to increased noise which results in reduction of detective quantum efficiency DQE at high spatial frequencies. The aliasing can be reduced or even eliminated by blurring prior to pixel sampling (e.g., by scattering in a phosphor layer). However, blurring, which may be quantified by the spatial frequency f dependent modulation transfer function MTF(f), also has a deleterious effect: the imaging system becomes much more susceptible to noise for example that arising in the charge amplifiers or secondary quantum statistics. Note that in principle, the system MTF can be corrected to any desired values in a digital system thus MTF has no predictive value for the quality of an imaging system, rather it is the DQE(f) which determines the overall signal to noise ratio independently of the MTF enhancement chosen. Nevertheless, determining the ideal level of presampling blurring (i.e., the Presampling Modulation Transfer function) is not straightforward. A problem caused by blurring is that the degree of blurring often depends on the depth of absorption of the x-ray in the imaging layer. In such cases (as pointed out by Lubberts) additional noise is transferred to the image. The predictions of a Lubberts model will be compared with published measurements of DQE for both direct and indirect detectors. A preliminary conclusion, is that blurring by CsI phosphor layers is non-ideal and leads to a significant loss of DQE at high spatial frequencies while no such loss is occurring in (alpha) -Se layers due to the equal MTF (in this case MTF(f) approximately equals 1) at all depths. Thus the only method which appears practical to cause blurring so as to avoid noise aliasing while avoiding the Lubberts depth dependent effect is to have a perfect MTF in the imaging layer and then blur before sampling. Such an approach has been proposed for the direct method based on the use of a partially conducting layer. Theoretical estimates of the final DQE(f) to be expected using this variation of the direct conversion method are produced.

Proceedings Article | 28 May 1999 Paper

Signal and noise analysis using transmission line model for larger-area flat-panel x-ray imaging sensors

Zhong Shou Huang, Giovanni DeCrescenzo, John Rowlands

Proceedings Volume 3659, (1999) https://doi.org/10.1117/12.349546

KEYWORDS: Amplifiers, Resistance, Interference (communication), Capacitance, Switches, Data modeling, Sensors, Signal processing, X-ray imaging, Capacitors

Read Abstract +

Proceedings Article | 24 July 1998 Paper

Detective quantum efficiency of direct flat-panel x-ray imaging detectors for fluoroscopy

Dylan Hunt, Wei Zhao, John Rowlands

Proceedings Volume 3336, (1998) https://doi.org/10.1117/12.317041

KEYWORDS: Photoresistors, Sensors, Quantum efficiency, X-rays, Fluoroscopy, X-ray imaging, X-ray detectors, Systems modeling, Spatial frequencies, Electrodes

Read Abstract +

Proceedings Article | 24 July 1998 Paper

Digital radiology using amorphous selenium and active-matrix flat-panel readout: photoconductive gain and gain fluctuations

Ira Blevis, Dylan Hunt, John Rowlands

Proceedings Volume 3336, (1998) https://doi.org/10.1117/12.317050

KEYWORDS: X-rays, Radiology, Imaging systems, Selenium, X-ray imaging, Sensors, Radiography, Surgery, Photoresistors, Fluoroscopy

Read Abstract +

Proceedings Article | 24 July 1998 Paper

Electronic portal imaging device (EPID) based on a novel camera with avalanche multiplication

Gendi Pang, Wei Zhao, Randy Luhta, John Rowlands

Proceedings Volume 3336, (1998) https://doi.org/10.1117/12.317018

KEYWORDS: Cameras, X-rays, Video, Imaging systems, Electronic components, Electronic imaging, Imaging devices, Modulation transfer functions, X-ray detectors, Photons

Read Abstract +

Proceedings Article | 2 May 1997 Paper

Large-area x-ray sensitive video camera: design of electron optics

Gendi Pang, Randy Luhta, John Rowlands

Proceedings Volume 3032, (1997) https://doi.org/10.1117/12.274028

KEYWORDS: X-rays, Photoresistors, Lens design, Electron beams, Electrodes, X-ray imaging, Video, X-ray optics, Cameras, Optical design

Read Abstract +

Proceedings Article | 2 May 1997 Paper

Large area x-ray sensitive video camera: overall feasibility

Randy Luhta, John Rowlands

Proceedings Volume 3032, (1997) https://doi.org/10.1117/12.274027

KEYWORDS: X-rays, Photoresistors, X-ray imaging, Electron beams, Televisions, Prototyping, Cameras, Capacitance, Zoom lenses, Interference (communication)

Read Abstract +

Proceedings Article | 2 May 1997 Paper

Flat panel detector for digital radiology using active matrix readout of amorphous selenium

John Rowlands, Wei Zhao, Ira Blevis, Gendi Pang, Winston Ji, Stephen Germann, Safa Kasap, David Waechter, Zhong Shou Huang

Proceedings Volume 3032, (1997) https://doi.org/10.1117/12.273974

KEYWORDS: Sensors, X-rays, X-ray imaging, Electrodes, Direct methods, Imaging systems, Radiography, Selenium, Photoresistors, Fluoroscopy

Read Abstract +

Proceedings Article | 11 April 1996 Paper

Flat panel detector for digital radiology using active matrix readout of amorphous selenium

Wei Zhao, Ira Blevis, Stephen Germann, John Rowlands, David Waechter, Zhong Huang

Proceedings Volume 2708, (1996) https://doi.org/10.1117/12.237814

KEYWORDS: Sensors, X-rays, Prototyping, X-ray imaging, Modulation transfer functions, Radiography, Electrodes, X-ray detectors, Amplifiers, Selenium

Read Abstract +

Proceedings Article | 8 May 1995 Paper

Amorphous selenium liquid crystal light valve for x-ray imaging

Pia Rieppo, Birendra Bahadur, John Rowlands

Proceedings Volume 2432, (1995) https://doi.org/10.1117/12.208341

KEYWORDS: X-rays, X-ray imaging, Imaging systems, Charge-coupled devices, X-ray detectors, Sensors, Interference (communication), Liquid crystals, Signal to noise ratio, Image resolution

Read Abstract +

Proceedings Article | 8 May 1995 Paper

Digital radiology using self-scanned readout of amorphous selenium: design considerations for mammography

Wei Zhao, John Rowlands, Stephen Germann, David Waechter, Zhong Huang

Proceedings Volume 2432, (1995) https://doi.org/10.1117/12.208343

KEYWORDS: Sensors, X-rays, Digital mammography, Selenium, X-ray detectors, Mammography, Electrodes, Molybdenum, Amplifiers, X-ray imaging

Read Abstract +

Proceedings Article | 1 May 1994 Paper

Preliminary experience with acquisition of 2048 2 fluorographic images

David Hynes, Larry Mazurkewich, John Rowlands, Klaus Schulenburg, Ernest Edmonds

Proceedings Volume 2163, (1994) https://doi.org/10.1117/12.174251

KEYWORDS: Cameras, X-rays, Imaging systems, Video, Radiography, Image resolution, X-ray imaging, Image processing, Image acquisition, Digital x-ray imaging

Read Abstract +

Proceedings Article | 14 September 1993 Paper

Digital radiology using self-scanned readout of amorphous selenium

Wei Zhao, John Rowlands

Proceedings Volume 1896, (1993) https://doi.org/10.1117/12.154581

KEYWORDS: X-rays, X-ray imaging, Sensors, Photoresistors, Selenium, X-ray detectors, Radiology, Radiography, Fluoroscopy, Electrodes

Read Abstract +

Proceedings Article | 14 September 1993 Paper

X-ray sensitive video camera

Randy Luhta, John Rowlands

Proceedings Volume 1896, (1993) https://doi.org/10.1117/12.154617

KEYWORDS: X-rays, Video, X-ray imaging, Medical imaging, Cameras, Electron beams, Surgery, Photoresistors, Physics, Quantum efficiency

Read Abstract +

Proceedings Article | 1 June 1992 Paper

Real-time digital processing of video image sequences for videofluoroscopy

John Rowlands

Proceedings Volume 1652, (1992) https://doi.org/10.1117/12.59437

KEYWORDS: Image processing, Video, Digital filtering, Cameras, Digital image processing, Medical imaging, X-rays, Video processing, Imaging systems, Motion detection

Read Abstract +

Proceedings Article | 1 June 1992 Paper

Large-area solid state detector for radiology using amorphous selenium

Wei Zhao, John Rowlands

Proceedings Volume 1651, (1992) https://doi.org/10.1117/12.59391

KEYWORDS: X-rays, Sensors, X-ray imaging, Imaging systems, Radiography, Fluoroscopy, Radiology, Field effect transistors, Solid state electronics, Switches

Read Abstract +