ABSTRACT We hypothesize that an electronic portal imaging device (EPID) consisting of multiple la... more ABSTRACT We hypothesize that an electronic portal imaging device (EPID) consisting of multiple layers, each containing a scintillator coupled to amorphous silicon flat panel imager (AMFPI), increases photon detection efficiency, improving image quality and tracking accuracy of low contrast targets during radiotherapy. The prototype 4-layer imager evaluated in this study contained four individually programmable layers each with a copper-Gd₂O₂S scintillator coupled to an AMFPI with a complete set of readout electronics. The imager was placed on a Varian TrueBeam linac. A Las-Vegas phantom programmed with sinusoidal motion (Peak-to-peak amplitude=20cm, Period=3.5sec) was imaged at a frame rate of 10Hz with one to four layers activated (activation of only the top layer is equivalent to using a conventional EPID). Image quality was assessed by counting the number of visible circles, and computing the contrast-to-noise ratio (CNR) of the least visible circle (depth=0.5mm, diameter=7mm). A previously validated tracking algorithm was employed for auto-tracking. Tracking error was defined as the difference between the programmed and tracked positions of the circle. The Pearson correlation coefficient of the CNR and tracking error was also computed. Motion-induced EPID image blurring significantly reduced circle visibility. During one cycle of phantom motion, the number of visible circles ranged from 11-23, 13-24, 15-25, and 16-26 when imaged with one, two, three and four layer imagers, respectively. Compared with using only a single layer, combining 2, 3, and 4 layers increased the median CNR by factors of 1.19, 1.42, and 1.71, respectively and reduced the average tracking error from 3.32mm to 1.67mm to 1.47mm, and 0.74mm, respectively. Significant correlations (p∼10-(9)) were found between the tracking error and CNR. Combination of four amorphous silicon layers, instead of single layer, significantly improves the EPID image quality and tracking accuracy for a poorly visible object that replicates lung tumor radiotherapy conditions. The project described was supported, in part, by a grant from Varian Medical Systems, Inc., and Award No. R01CA188446-01 from the National Cancer Institute. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Cancer Institute or the National Institutes of Health.
Purpose:Beams‐eye‐view imaging applications such as real‐time soft‐tissue motion estimation are h... more Purpose:Beams‐eye‐view imaging applications such as real‐time soft‐tissue motion estimation are hindered by the inherently low image contrast of electronic portal imaging devices (EPID) currently in clinical use. We introduce and characterize a novel EPID that provides substantially increased detective quantum efficiency (DQE), contrast‐to‐noise ratio (CNR) and dynamic range without degradation in spatial resolution.Methods:The prototype design features a stack of four conventional EPID layers combined with low noise integrated readout electronics. Each layer consists of a copper plate, a scintillator (GdO2S2:Tb) and a photodiode/TFT‐switch (aSi:H). We characterize the prototype in terms of contrast‐to‐noise ratio (CNR), modulation transfer function (MTF) and DQE. CNR is estimated using a Las Vegas contrast phantom, presampled MTF is estimated using a slanted edge technique and the DQE is calculated from measured normalized noise power spectra (NPS) and the MTF. The prototype has be...
Purpose: Vertical stacking of four conventional EPID layers can improve DQE for MV-CBCT applicati... more Purpose: Vertical stacking of four conventional EPID layers can improve DQE for MV-CBCT applications. We hypothesize that shifting each layer laterally by half a pixel relative to the layer above, will improve the contrast-to-noise ratio (CNR) and image resolution. Methods: For CNR assessment, a 20 cm diameter digital phantom with 8 inserts is created. The attenuation coefficient of the phantom is similar to lung at the average energy of a 6 MV photon beam. The inserts have attenuations 1, 2…8 times of lung. One of the inserts is close to soft tissue, resembling the case of a tumor in lung. For resolution assessment, a digital phantom featuring a bar pattern is created. The phantom has an attenuation coefficient similar to soft tissue and the bars have an attenuation coefficient of calcium sulfate. A 2 MeV photon beam is attenuated through these phantoms and hits each of the four stacked detector layers. Each successive layer is shifted by half a pixel in the x only, y only, and x and y (combined) directions, respectively. Blurring and statistical noise are added to the projections. Projections from one, two, three and four layers are used for reconstruction. CNR and image resolution are evaluated and compared. Results: When projections from multiple layers are combined for reconstruction, CNR increases with the number of layers involved. CNR in reconstructions from two, three and four layers are 1.4, 1.7 and 1.99 times that from one layer. The resolution from the shifted four layer detector is also improved from a single layer. In a comparison between one layer versus four layers in this preliminary study, the resolution from four shifted layers is at least 20% better. Conclusion: Layer-shifting in a stacked EPID imager design enhances resolution as well as CNR for half scan MV-CBCT. The project described was supported, in part, by a grant from Varian Medical Systems, Inc., and Award No. R01CA188446-01 from the National Cancer Institute. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Cancer Institute or the National Institutes of Health
L'invention concerne un dispositif d'imagerie par rayons x concu pour communiquer des don... more L'invention concerne un dispositif d'imagerie par rayons x concu pour communiquer des donnees images en temps reel par le biais d'une interface de reseau. Des signaux de donnees images provenant d'un ensemble de detecteur d'imagerie par rayons x issus de la conversion de photons des rayons x incidents correspondant a une image d'un sujet sont, a leur tour, convertis en un ou plusieurs signaux de donnees de reseau correspondants, tels que des signaux de gigabit ethernet.
Purpose-Beams-eye-view imaging applications such as real-time soft-tissue motion estimation are h... more Purpose-Beams-eye-view imaging applications such as real-time soft-tissue motion estimation are hindered by the inherently low image contrast of electronic portal imaging devices (EPID) currently available for clinical use. We introduce and characterize a novel EPID design that provides substantially increased detective quantum efficiency (DQE), contrast-to-noise ratio (CNR) and sensitivity without degradation in spatial resolution. Methods-The prototype design features a stack of four conventional EPID layers combined with low noise integrated readout electronics. Each layer consists of a copper plate, a scintillator (GdO 2 S 2 : T b) and a photodiode/TFT-switch (aSi:H). We characterize the prototype's signal response to a 6 MV photon beam in terms of modulation transfer function (MTF), DQE and contrast-to-noise ratio (CNR). The presampled MTF is estimated using a slanted slit technique, the DQE is calculated from measured normalized noise power spectra (nNPS) and the MTF and CNR is estimated using a Las Vegas contrast phantom. The prototype has been designed and built to be interchangeable with the current clinical EPID on the Varian TrueBeam platform (AS-1200) in terms of size and data output specifications. Performance evaluation is conducted in absolute values as well as in relative terms using the Varian AS-1200 EPID as a reference detector. Results-A fivefold increase of DQE(0) to about 6.7% was observed by using the four-layered design versus the AS-1200 reference detector. No substantial differences are observed between each layer's individual MTF and the one for all four layers operating combined indicating that defocusing due to beam divergence is negligible. Also, using four layers instead of one increases the signal to noise ratio (SNR) by a factor of 1.7. Conclusions-A layered EPID design improves the radiation sensitivity while maintaining the spatial resolution and saturation level of a single layer conventional EPID. Experimental characterization of this first 4-layered prototype demonstrates substantially improved DQE and CNR while maintaining a high resolution. Besides overall improved image quality and dosimetric sensitivity, we anticipate that this novel detector design will enable more accurate soft-tissue motion estimations during radiation therapy procedures.
Medical Imaging 2004: Physics of Medical Imaging, Pts 1 and 2, 2004
The dynamic range of many flat panel imaging systems are fundamentally limited by the dynamic ran... more The dynamic range of many flat panel imaging systems are fundamentally limited by the dynamic range of the charge amplifier and readout signal processing. We developed two new flat panel readout methods that achieve extended dynamic range by changing the read out charge amplifier feedback capacitance dynamically and on a real-time basis. In one method, the feedback capacitor is selected automatically by a level sensing circuit, pixel-by-pixel, based on its exposure level. Alternatively, capacitor selection is driven externally, such that each pixel is read out two (or more) times, each time with increased feedback capacitance. Both methods allow the acquisition of X-ray image data with a dynamic range approaching the fundamental limits of flat panel pixels. Data with an equivalent bit depth of better than 16 bits are made available for further image processing. Successful implementation of these methods requires careful matching of selectable capacitor values and switching thresholds, with the imager noise and sensitivity characteristics, to insure X-ray quantum limited operation over the whole extended dynamic range. Successful implementation also depends on the use of new calibration methods and image reconstruction algorithms, to insure artifact free rebuilding of linear image data by the downstream image processing systems. The multiple gain ranging flat panel readout method extends the utility of flat panel imagers and paves the way to new flat panel applications, such as cone beam CT. We believe that this method will provide a valuable extension to the clinical application of flat panel imagers.
It is known that high dose X-ray irradiation increases the probability of cancer development in h... more It is known that high dose X-ray irradiation increases the probability of cancer development in humans. Therefore, the dose decrease at every X-ray imaging event is a major goal, especially during CT tests, where the applied dose is generally a multiple of a few single ...
Vapor deposited lead iodide films show a wide range of physical attributes dependant upon fabrica... more Vapor deposited lead iodide films show a wide range of physical attributes dependant upon fabrication conditions. High density is most readily achieved with films less than 100 μm. Thicker films, with lessening density, often show lower response (gain) as charge collection ...
2014 IEEE International Conference on Imaging Systems and Techniques (IST) Proceedings, 2014
Contrast agents in CT and MRI investigations have been used for obtaining better diagnosis, inclu... more Contrast agents in CT and MRI investigations have been used for obtaining better diagnosis, including whether a nodule in the breast is benign or malignant. Cone beam CT images of breast cancer nodules have been taken with iodine contrast enhancement using two CT data sets, before and after iodine contrast injection. After the CT reconstructions, by subtracting the pre-contrast HU values from those obtained with iodine contrast at the nodules, the contrast enhancement values of the suspicious nodules were obtained. This article describes a method of determining mean “quantitative imaging biomarker” values such as calibrated mean contrast concentrations of enhancement agents like iodine contrast agents in X-ray CT in segmented nodules identified using X-ray CT image data obtained in a single CT data set acquisitions instead of using two datasets (before and after contrast agent injection). This method can be applied to different organs and/or different contrast agents by using dual energy values optimized for the given cases by carefully calibrating the CT values for each energy pair.
The 2D and 3D modulation transfer functions (MTFs) of a custom made, large 40x30cm2 area, 600- mi... more The 2D and 3D modulation transfer functions (MTFs) of a custom made, large 40x30cm2 area, 600- micron CsI-TFT based flat panel imager having 127-micron pixellation, along with the micro-fiber scintillator structure, were characterized in detail using various techniques. The larger area detector yields a reconstructed FOV of 25cm diameter with an 80cm SID in CT mode. The MTFs were determined with 1x1 (intrinsic) binning. The 2D MTFs were determined using a 50.8 micron tungsten wire and a solid lead edge, and the 3D MTF was measured using a custom made phantom consisting of three nearly orthogonal 50.8 micron tungsten wires suspended in an acrylic cubic frame. The 2D projection data was reconstructed using an iterative OSC algorithm using 16 subsets and 5 iterations. As additional verification of the resolution, along with scatter, the Catphan® phantom was also imaged and reconstructed with identical parameters. The measured 2D MTF was ~4% using the wire technique and ~1% using the ed...
The detection of fire in mines, industrial buildings, ships etc. is an important problem from bot... more The detection of fire in mines, industrial buildings, ships etc. is an important problem from both the economical and life-protecting aspects. The fire could be detected in several ways, e.g. by the measurement of flame-radiation, heat, pressure, temperature, the aerosols, the gases etc. The Department of Electronic Technology has developed a fire sensor which detects the rate of the increase of temperature. The fire sensor consists of two temperature sensitive resistors with different time-constants. If the increase of temperature in consequence of the fire is fast, the difference between the resistance of the temperature sensors is high, while a slow change in temperature causes only small differences. By connecting the temperature sensitive sensors into a bridge, the resistance difference can be easily detected. The temperature sensitive resistors are realized by thin film technology using platinum or nickel film on a thin glass or ceramic substrate. Because of the large surface and small volume of the resistor, its time-constant originally is very low but the time-constant could be easily increased by increasing the volume of the resistor. The present paper gives a detailed description of the analysis and the measurement ofthe temperature sensitive resistors with different time-constants. The technology of the films is also discussed.
A new portal imager consisting of four vertically stacked conventional electronic portal imaging ... more A new portal imager consisting of four vertically stacked conventional electronic portal imaging device (EPID) layers has been constructed in pursuit of improved detective quantum efficiency (DQE). We hypothesize that super-resolution (SR) imaging can also be achieved in such a system by shifting each layer laterally by half a pixel relative to the layer above. Super-resolution imaging will improve resolution and contrast-to-noise ratio (CNR) in megavoltage (MV) planar and cone beam computed tomography (MV-CBCT) applications. Simulations are carried out to test this hypothesis with digital phantoms. To assess planar resolution, 2 mm long iron rods with 0.3 × 0.3 mm(2) square cross-section are arranged in a grid pattern at the center of a 1 cm thick solid water. For measuring CNR in MV-CBCT, a 20 cm diameter digital phantom with 8 inserts of different electron densities is used. For measuring resolution in MV-CBCT, a digital phantom featuring a bar pattern similar to the Gammex™ phan...
We hypothesized that combining multiple amorphous silicon flat panel layers increases photon dete... more We hypothesized that combining multiple amorphous silicon flat panel layers increases photon detection efficiency in an electronic portal imaging device (EPID), improving image quality and tracking accuracy of low contrast targets during radiotherapy METHODS: The prototype imager evaluated in this study contained 4 individually programmable layers each with a copper converter layer, Gd2 O2 S scintillator and active-matrix flat panel imager (AMFPI). The imager was placed on a Varian TrueBeam linac and a Las Vegas phantom programmed with sinusoidal motion (peak-to-peak amplitude=20mm, Period=3.5sec) was imaged at a frame rate of 10Hz with one to four layers activated. Number of visible circles and CNR of least visible circle (depth=0.5mm, diameter=7mm) was computed to assess the image quality of single and multiple layers. A previously validated tracking algorithm was employed for auto-tracking. Tracking error was defined as the difference between the programmed and tracked positions ...
We previously reported on 2"x 2" and 4" x 4" size imagers, direct digital radiography X-ray detec... more We previously reported on 2"x 2" and 4" x 4" size imagers, direct digital radiography X-ray detectors, based on photoconductive polycrystalline mercuric iodide deposited on a flat panel thin film transistor (TFT) array, as having great potential for use in medical imaging, NDE, and security applications. Recently we successfully upgraded our mercuric iodide deposition technique to 20 cm x 25 cm size, the size required in common NDE and security imaging applications. A TFT array with a pixel pitch of 127 microns was used for this imager. The mercuric iodide direct conversion layers were vacuum deposited onto TFT array by Physical Vapor Deposition (PVD). In addition to successful imager scale up, more sophisticated, non-TFT based detectors were developed in order to improve analysis methods of the mercuric iodide photoconductor. Measurements on mercuric iodide photoconductor were performed using a 36 x 6 electrode array on a 10cm x 10cm substrate (total of 216 measurement points). The array is formed by 36 palladium stripes on the glass substrate, upon which the mercuric iodide is deposited, and 6 palladium stripes that are deposited on top of the mercuric iodide layer. These two sets of electrodes are oriented at 90 degrees to each other to create the measurement matrix. These detectors were evaluated in radiographic mode, continuous fluoroscopic mode and pulsed fluoroscopic mode. Mercuric iodide coatings with thickness ranging between 140 microns and 300 microns were tested using beams with energies between 40 kVp and 100 kVp utilizing exposure ranges typical for both fluoroscopic and radiographic imaging. Diagnostic quality radiographic and fluroscopic images at up to 15 pulses per second were demonstrated. We evaluated the dark current, sensitivity and MTF characteristics. The MTF is determined primarily by the aperture and pitch of the TFT array with Nyquist frequency of ~3.93 mm-1 (127 micron pixel pitch). The MTF curve of a good quality HgI 2 imager is very close to the theoretical sinc function. Image lag characteristics of mercuric iodide appear adequate for fluoroscopic rates.
ABSTRACT We hypothesize that an electronic portal imaging device (EPID) consisting of multiple la... more ABSTRACT We hypothesize that an electronic portal imaging device (EPID) consisting of multiple layers, each containing a scintillator coupled to amorphous silicon flat panel imager (AMFPI), increases photon detection efficiency, improving image quality and tracking accuracy of low contrast targets during radiotherapy. The prototype 4-layer imager evaluated in this study contained four individually programmable layers each with a copper-Gd₂O₂S scintillator coupled to an AMFPI with a complete set of readout electronics. The imager was placed on a Varian TrueBeam linac. A Las-Vegas phantom programmed with sinusoidal motion (Peak-to-peak amplitude=20cm, Period=3.5sec) was imaged at a frame rate of 10Hz with one to four layers activated (activation of only the top layer is equivalent to using a conventional EPID). Image quality was assessed by counting the number of visible circles, and computing the contrast-to-noise ratio (CNR) of the least visible circle (depth=0.5mm, diameter=7mm). A previously validated tracking algorithm was employed for auto-tracking. Tracking error was defined as the difference between the programmed and tracked positions of the circle. The Pearson correlation coefficient of the CNR and tracking error was also computed. Motion-induced EPID image blurring significantly reduced circle visibility. During one cycle of phantom motion, the number of visible circles ranged from 11-23, 13-24, 15-25, and 16-26 when imaged with one, two, three and four layer imagers, respectively. Compared with using only a single layer, combining 2, 3, and 4 layers increased the median CNR by factors of 1.19, 1.42, and 1.71, respectively and reduced the average tracking error from 3.32mm to 1.67mm to 1.47mm, and 0.74mm, respectively. Significant correlations (p∼10-(9)) were found between the tracking error and CNR. Combination of four amorphous silicon layers, instead of single layer, significantly improves the EPID image quality and tracking accuracy for a poorly visible object that replicates lung tumor radiotherapy conditions. The project described was supported, in part, by a grant from Varian Medical Systems, Inc., and Award No. R01CA188446-01 from the National Cancer Institute. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Cancer Institute or the National Institutes of Health.
Purpose:Beams‐eye‐view imaging applications such as real‐time soft‐tissue motion estimation are h... more Purpose:Beams‐eye‐view imaging applications such as real‐time soft‐tissue motion estimation are hindered by the inherently low image contrast of electronic portal imaging devices (EPID) currently in clinical use. We introduce and characterize a novel EPID that provides substantially increased detective quantum efficiency (DQE), contrast‐to‐noise ratio (CNR) and dynamic range without degradation in spatial resolution.Methods:The prototype design features a stack of four conventional EPID layers combined with low noise integrated readout electronics. Each layer consists of a copper plate, a scintillator (GdO2S2:Tb) and a photodiode/TFT‐switch (aSi:H). We characterize the prototype in terms of contrast‐to‐noise ratio (CNR), modulation transfer function (MTF) and DQE. CNR is estimated using a Las Vegas contrast phantom, presampled MTF is estimated using a slanted edge technique and the DQE is calculated from measured normalized noise power spectra (NPS) and the MTF. The prototype has be...
Purpose: Vertical stacking of four conventional EPID layers can improve DQE for MV-CBCT applicati... more Purpose: Vertical stacking of four conventional EPID layers can improve DQE for MV-CBCT applications. We hypothesize that shifting each layer laterally by half a pixel relative to the layer above, will improve the contrast-to-noise ratio (CNR) and image resolution. Methods: For CNR assessment, a 20 cm diameter digital phantom with 8 inserts is created. The attenuation coefficient of the phantom is similar to lung at the average energy of a 6 MV photon beam. The inserts have attenuations 1, 2…8 times of lung. One of the inserts is close to soft tissue, resembling the case of a tumor in lung. For resolution assessment, a digital phantom featuring a bar pattern is created. The phantom has an attenuation coefficient similar to soft tissue and the bars have an attenuation coefficient of calcium sulfate. A 2 MeV photon beam is attenuated through these phantoms and hits each of the four stacked detector layers. Each successive layer is shifted by half a pixel in the x only, y only, and x and y (combined) directions, respectively. Blurring and statistical noise are added to the projections. Projections from one, two, three and four layers are used for reconstruction. CNR and image resolution are evaluated and compared. Results: When projections from multiple layers are combined for reconstruction, CNR increases with the number of layers involved. CNR in reconstructions from two, three and four layers are 1.4, 1.7 and 1.99 times that from one layer. The resolution from the shifted four layer detector is also improved from a single layer. In a comparison between one layer versus four layers in this preliminary study, the resolution from four shifted layers is at least 20% better. Conclusion: Layer-shifting in a stacked EPID imager design enhances resolution as well as CNR for half scan MV-CBCT. The project described was supported, in part, by a grant from Varian Medical Systems, Inc., and Award No. R01CA188446-01 from the National Cancer Institute. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Cancer Institute or the National Institutes of Health
L'invention concerne un dispositif d'imagerie par rayons x concu pour communiquer des don... more L'invention concerne un dispositif d'imagerie par rayons x concu pour communiquer des donnees images en temps reel par le biais d'une interface de reseau. Des signaux de donnees images provenant d'un ensemble de detecteur d'imagerie par rayons x issus de la conversion de photons des rayons x incidents correspondant a une image d'un sujet sont, a leur tour, convertis en un ou plusieurs signaux de donnees de reseau correspondants, tels que des signaux de gigabit ethernet.
Purpose-Beams-eye-view imaging applications such as real-time soft-tissue motion estimation are h... more Purpose-Beams-eye-view imaging applications such as real-time soft-tissue motion estimation are hindered by the inherently low image contrast of electronic portal imaging devices (EPID) currently available for clinical use. We introduce and characterize a novel EPID design that provides substantially increased detective quantum efficiency (DQE), contrast-to-noise ratio (CNR) and sensitivity without degradation in spatial resolution. Methods-The prototype design features a stack of four conventional EPID layers combined with low noise integrated readout electronics. Each layer consists of a copper plate, a scintillator (GdO 2 S 2 : T b) and a photodiode/TFT-switch (aSi:H). We characterize the prototype's signal response to a 6 MV photon beam in terms of modulation transfer function (MTF), DQE and contrast-to-noise ratio (CNR). The presampled MTF is estimated using a slanted slit technique, the DQE is calculated from measured normalized noise power spectra (nNPS) and the MTF and CNR is estimated using a Las Vegas contrast phantom. The prototype has been designed and built to be interchangeable with the current clinical EPID on the Varian TrueBeam platform (AS-1200) in terms of size and data output specifications. Performance evaluation is conducted in absolute values as well as in relative terms using the Varian AS-1200 EPID as a reference detector. Results-A fivefold increase of DQE(0) to about 6.7% was observed by using the four-layered design versus the AS-1200 reference detector. No substantial differences are observed between each layer's individual MTF and the one for all four layers operating combined indicating that defocusing due to beam divergence is negligible. Also, using four layers instead of one increases the signal to noise ratio (SNR) by a factor of 1.7. Conclusions-A layered EPID design improves the radiation sensitivity while maintaining the spatial resolution and saturation level of a single layer conventional EPID. Experimental characterization of this first 4-layered prototype demonstrates substantially improved DQE and CNR while maintaining a high resolution. Besides overall improved image quality and dosimetric sensitivity, we anticipate that this novel detector design will enable more accurate soft-tissue motion estimations during radiation therapy procedures.
Medical Imaging 2004: Physics of Medical Imaging, Pts 1 and 2, 2004
The dynamic range of many flat panel imaging systems are fundamentally limited by the dynamic ran... more The dynamic range of many flat panel imaging systems are fundamentally limited by the dynamic range of the charge amplifier and readout signal processing. We developed two new flat panel readout methods that achieve extended dynamic range by changing the read out charge amplifier feedback capacitance dynamically and on a real-time basis. In one method, the feedback capacitor is selected automatically by a level sensing circuit, pixel-by-pixel, based on its exposure level. Alternatively, capacitor selection is driven externally, such that each pixel is read out two (or more) times, each time with increased feedback capacitance. Both methods allow the acquisition of X-ray image data with a dynamic range approaching the fundamental limits of flat panel pixels. Data with an equivalent bit depth of better than 16 bits are made available for further image processing. Successful implementation of these methods requires careful matching of selectable capacitor values and switching thresholds, with the imager noise and sensitivity characteristics, to insure X-ray quantum limited operation over the whole extended dynamic range. Successful implementation also depends on the use of new calibration methods and image reconstruction algorithms, to insure artifact free rebuilding of linear image data by the downstream image processing systems. The multiple gain ranging flat panel readout method extends the utility of flat panel imagers and paves the way to new flat panel applications, such as cone beam CT. We believe that this method will provide a valuable extension to the clinical application of flat panel imagers.
It is known that high dose X-ray irradiation increases the probability of cancer development in h... more It is known that high dose X-ray irradiation increases the probability of cancer development in humans. Therefore, the dose decrease at every X-ray imaging event is a major goal, especially during CT tests, where the applied dose is generally a multiple of a few single ...
Vapor deposited lead iodide films show a wide range of physical attributes dependant upon fabrica... more Vapor deposited lead iodide films show a wide range of physical attributes dependant upon fabrication conditions. High density is most readily achieved with films less than 100 μm. Thicker films, with lessening density, often show lower response (gain) as charge collection ...
2014 IEEE International Conference on Imaging Systems and Techniques (IST) Proceedings, 2014
Contrast agents in CT and MRI investigations have been used for obtaining better diagnosis, inclu... more Contrast agents in CT and MRI investigations have been used for obtaining better diagnosis, including whether a nodule in the breast is benign or malignant. Cone beam CT images of breast cancer nodules have been taken with iodine contrast enhancement using two CT data sets, before and after iodine contrast injection. After the CT reconstructions, by subtracting the pre-contrast HU values from those obtained with iodine contrast at the nodules, the contrast enhancement values of the suspicious nodules were obtained. This article describes a method of determining mean “quantitative imaging biomarker” values such as calibrated mean contrast concentrations of enhancement agents like iodine contrast agents in X-ray CT in segmented nodules identified using X-ray CT image data obtained in a single CT data set acquisitions instead of using two datasets (before and after contrast agent injection). This method can be applied to different organs and/or different contrast agents by using dual energy values optimized for the given cases by carefully calibrating the CT values for each energy pair.
The 2D and 3D modulation transfer functions (MTFs) of a custom made, large 40x30cm2 area, 600- mi... more The 2D and 3D modulation transfer functions (MTFs) of a custom made, large 40x30cm2 area, 600- micron CsI-TFT based flat panel imager having 127-micron pixellation, along with the micro-fiber scintillator structure, were characterized in detail using various techniques. The larger area detector yields a reconstructed FOV of 25cm diameter with an 80cm SID in CT mode. The MTFs were determined with 1x1 (intrinsic) binning. The 2D MTFs were determined using a 50.8 micron tungsten wire and a solid lead edge, and the 3D MTF was measured using a custom made phantom consisting of three nearly orthogonal 50.8 micron tungsten wires suspended in an acrylic cubic frame. The 2D projection data was reconstructed using an iterative OSC algorithm using 16 subsets and 5 iterations. As additional verification of the resolution, along with scatter, the Catphan® phantom was also imaged and reconstructed with identical parameters. The measured 2D MTF was ~4% using the wire technique and ~1% using the ed...
The detection of fire in mines, industrial buildings, ships etc. is an important problem from bot... more The detection of fire in mines, industrial buildings, ships etc. is an important problem from both the economical and life-protecting aspects. The fire could be detected in several ways, e.g. by the measurement of flame-radiation, heat, pressure, temperature, the aerosols, the gases etc. The Department of Electronic Technology has developed a fire sensor which detects the rate of the increase of temperature. The fire sensor consists of two temperature sensitive resistors with different time-constants. If the increase of temperature in consequence of the fire is fast, the difference between the resistance of the temperature sensors is high, while a slow change in temperature causes only small differences. By connecting the temperature sensitive sensors into a bridge, the resistance difference can be easily detected. The temperature sensitive resistors are realized by thin film technology using platinum or nickel film on a thin glass or ceramic substrate. Because of the large surface and small volume of the resistor, its time-constant originally is very low but the time-constant could be easily increased by increasing the volume of the resistor. The present paper gives a detailed description of the analysis and the measurement ofthe temperature sensitive resistors with different time-constants. The technology of the films is also discussed.
A new portal imager consisting of four vertically stacked conventional electronic portal imaging ... more A new portal imager consisting of four vertically stacked conventional electronic portal imaging device (EPID) layers has been constructed in pursuit of improved detective quantum efficiency (DQE). We hypothesize that super-resolution (SR) imaging can also be achieved in such a system by shifting each layer laterally by half a pixel relative to the layer above. Super-resolution imaging will improve resolution and contrast-to-noise ratio (CNR) in megavoltage (MV) planar and cone beam computed tomography (MV-CBCT) applications. Simulations are carried out to test this hypothesis with digital phantoms. To assess planar resolution, 2 mm long iron rods with 0.3 × 0.3 mm(2) square cross-section are arranged in a grid pattern at the center of a 1 cm thick solid water. For measuring CNR in MV-CBCT, a 20 cm diameter digital phantom with 8 inserts of different electron densities is used. For measuring resolution in MV-CBCT, a digital phantom featuring a bar pattern similar to the Gammex™ phan...
We hypothesized that combining multiple amorphous silicon flat panel layers increases photon dete... more We hypothesized that combining multiple amorphous silicon flat panel layers increases photon detection efficiency in an electronic portal imaging device (EPID), improving image quality and tracking accuracy of low contrast targets during radiotherapy METHODS: The prototype imager evaluated in this study contained 4 individually programmable layers each with a copper converter layer, Gd2 O2 S scintillator and active-matrix flat panel imager (AMFPI). The imager was placed on a Varian TrueBeam linac and a Las Vegas phantom programmed with sinusoidal motion (peak-to-peak amplitude=20mm, Period=3.5sec) was imaged at a frame rate of 10Hz with one to four layers activated. Number of visible circles and CNR of least visible circle (depth=0.5mm, diameter=7mm) was computed to assess the image quality of single and multiple layers. A previously validated tracking algorithm was employed for auto-tracking. Tracking error was defined as the difference between the programmed and tracked positions ...
We previously reported on 2"x 2" and 4" x 4" size imagers, direct digital radiography X-ray detec... more We previously reported on 2"x 2" and 4" x 4" size imagers, direct digital radiography X-ray detectors, based on photoconductive polycrystalline mercuric iodide deposited on a flat panel thin film transistor (TFT) array, as having great potential for use in medical imaging, NDE, and security applications. Recently we successfully upgraded our mercuric iodide deposition technique to 20 cm x 25 cm size, the size required in common NDE and security imaging applications. A TFT array with a pixel pitch of 127 microns was used for this imager. The mercuric iodide direct conversion layers were vacuum deposited onto TFT array by Physical Vapor Deposition (PVD). In addition to successful imager scale up, more sophisticated, non-TFT based detectors were developed in order to improve analysis methods of the mercuric iodide photoconductor. Measurements on mercuric iodide photoconductor were performed using a 36 x 6 electrode array on a 10cm x 10cm substrate (total of 216 measurement points). The array is formed by 36 palladium stripes on the glass substrate, upon which the mercuric iodide is deposited, and 6 palladium stripes that are deposited on top of the mercuric iodide layer. These two sets of electrodes are oriented at 90 degrees to each other to create the measurement matrix. These detectors were evaluated in radiographic mode, continuous fluoroscopic mode and pulsed fluoroscopic mode. Mercuric iodide coatings with thickness ranging between 140 microns and 300 microns were tested using beams with energies between 40 kVp and 100 kVp utilizing exposure ranges typical for both fluoroscopic and radiographic imaging. Diagnostic quality radiographic and fluroscopic images at up to 15 pulses per second were demonstrated. We evaluated the dark current, sensitivity and MTF characteristics. The MTF is determined primarily by the aperture and pitch of the TFT array with Nyquist frequency of ~3.93 mm-1 (127 micron pixel pitch). The MTF curve of a good quality HgI 2 imager is very close to the theoretical sinc function. Image lag characteristics of mercuric iodide appear adequate for fluoroscopic rates.
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Papers by George Zentai