- 标题
- 摘要
- 关键词
- 实验方案
- 产品
-
Characterizing a novel scintillating glass for application to megavoltage cone-beam computed tomography
摘要： Purpose: The purpose of the present study was to evaluate the performance of a prototype electric portal imaging device (EPID) with a high detective quantum efficiency (DQE) scintillator, LKH-5. Specifically, image quality in context of both planar and megavoltage (MV) cone-beam computed tomography (CBCT) is analyzed. Methods: Planar image quality in terms of modulation transfer function (MTF), noise power spectrum (NPS), and detective quantum efficiency (DQE) are measured and compared to an existing EPID (AS-1200) using the 6 MV beamline for a Varian TrueBeam linac. Imager performance is contextualized for three-dimensional (3D), MV-CBCT performance by measuring imager lag and analyzing the expected degradation of the DQE as a function of dose. Finally, comparisons between reconstructed images of the Catphan phantom in terms of qualitative quality and signal-difference-to-noise ratio (SDNR) are made for 6 MV images using both conventional and LKH-5 EPIDs as well as for the kilovoltage (kV) on-board imager (OBI). Results: Analysis of the NPS reveals linearity at all measured doses using the prototype LKH-5 detector. While the first zero of the MTF is much lower for the LKH-5 detector than the conventional EPID (0.6 cycles/mm vs. 1.6 cycles/mm), the normalized NPS (NNPS) multiplied by total quanta (qNNPS) of the LKH-5 detector is roughly a factor of 7-8 times lower, yielding a DQE(0) of approximately 8%. First, second, and third frame lag was measured at approximately 23%, 5%, and 1% respectively, although no noticeable image artifacts were apparent in reconstructed volumes. Analysis of low dose performance reveals that DQE(0) remains at 80% of its maximum value at a dose as low as 7.5x10-6 MU. For a 400 projection technique, this represents a total scan dose of 0.0030 MU, suggesting that if imaging doses are increased to a value typical of kV-CBCT scans (~2.7 cGy), the LKH-5 detector will retain quantum noise limited performance. Finally, comparing Catphan scans, the prototype detector exhibits much lower image noise than the conventional EPID, resulting in improved small object representation. Further, SDNR of H2O and polystyrene cylinders improved from -1.95 and 2.94 to -15 and 18.7, respectively. Conclusions: Imaging performance of the prototype LKH-5 detector was measured and analyzed for both planar and 3D contexts. Improving noise transfer of the detector results in concurrent improvement of DQE(0). For 3D imaging, temporal characteristics were adequate for artifact-free performance and at relevant doses, the detector retained quantum-noise limited performance. Although quantitative MTF measurements suggest poorer resolution, small object representation of the prototype imager is qualitatively improved over the conventional detector due to the measured reduction in noise.
关键词： EPID,NPS,scintillator,MV-CBCT,DQE,MTF,Portal imaging
更新于2025-09-23 15:23:52
-
Towards the Experimental Assessment of the DQE in SPECT Scanners
摘要： The purpose of this work was to introduce the Detective Quantum Efficiency (DQE) in single photon emission computed tomography (SPECT) systems using a flood source. A Tc-99m-based flood source (Eγ=140 keV) consisting of a radiopharmaceutical solution of dithiothreitol (DTT, 10-3 M)/Tc-99m(III)-DMSA, 40 mCi/40 ml bound to the grains of an Agfa MammoRay HDR Medical X-ray film) was prepared in laboratory. The source was placed between two PMMA blocks and images were obtained by using the brain tomographic acquisition protocol (DatScan-brain). The Modulation Transfer Function (MTF) was evaluated using the Iterative 2D algorithm. All imaging experiments were performed in a Siemens e-Cam gamma camera. The Normalized Noise Power spectra (NNPS) were obtained from the sagittal views of the source. The higher MTF values were obtained for the Flash Iterative 2D with 24 iterations and 20 subsets. The noise levels of the SPECT reconstructed images, in terms of the NNPS, were found to increase as the number of iterations increase. The behavior of the DQE was influenced by both MTF and NNPS. As the number of iterations was increased, higher MTF values were obtained, however with a parallel, increase of magnitude in image noise, as depicted from the NNPS results. DQE values, which were influenced by both MTF and NNPS, were found higher when the number of iterations results in resolution saturation. The method presented here is novel and easy to implement, requiring materials commonly found in clinical practice and can be useful in the quality control of SPECT scanners.
关键词： film,NNPS,flood source,MTF,DQE,LSF,SPECT
更新于2025-09-23 15:22:29
-
A Modified Local Binary Pattern Descriptor for SAR Image Matching
摘要： Image matching is an important step which is taken in most applications of synthetic aperture radar (SAR) images. In this letter, a method is proposed for SAR image matching which introduces a modified local binary pattern (LBP) as a descriptor. Multitextural feature LBP (MTF-LBP) uses the gray-level cooccurrence matrix to increase image texture information. MTF-LBP creates bit plane for each point candidate for matching. Then, using hamming distance, true matches are determined. Experiments are conducted on four spaceborne SAR image pairs including Radarsat-2, TerraSAR-X, ALOS-PALSAR, and Sentinel-1. The proposed method is compared with five common LBP approaches. The results indicate that the proposed method has a better performance in terms of the number of true matches.
关键词： Image texture analysis,LBP (MTF-LBP),synthetic aperture radar (SAR),multitextural feature,matching
更新于2025-09-23 15:21:01
-
Study of the MTF of a MWIR T2SL focal plane array in IDDCA configuration
摘要： Type-II InAs/GaSb superlattice (T2SL) has recently matured into a commercially available technology addressing both MWIR and LWIR spectral domains. As the prerequisites such as Quantum Efficiency (QE) and dark current were met, more advanced figures of merits related to the ElectroOptic (EO) system as a whole can now be studied to position this technology. In this paper, we focus on modulation transfer function (MTF) measurements. Knowing the MTF of a detector is indeed of primary importance for the EO system designers, since spatial filtering affects the system range. We realized MTF measurements on a 320 × 256 MWIR T2SL FPA provided by IRnova, using a Continuously Self Imaging Grating (CSIG). The advantage of this experimental configuration is that no high performance projection optics is required thanks to the self-imaging property (known as Talbot effect) to project a pattern with known spatial frequencies on the photodetector. Besides, the pattern being propagation invariant, alignment is easier and the bench does not require exact knowledge of the focal plane distance to operate, opening measurement in Integrated Detector Dewar Cooler Assembly (IDDCA) configuration. Extracted from measurements, the pixel size is 26 μm for a pitch of 30 μm.
关键词： MWIR,MTF,CSIG,T2SL,IDDCA,FPA
更新于2025-09-19 17:15:36
-
Comparison of optical quality and distinct macular thickness in femtosecond laser-assisted versus phacoemulsification cataract surgery
摘要： Background: Optical quality and macular thickness changing optical quality is rarely reported after femtosecond laser-assisted cataract surgery (FLACS). In current research, we evaluated optical quality recovery and distinct macular thickness changes after FLACS and phacoemulsification cataract surgery (PCS). Methods: A total of 100 cataract patients (100 eyes) were included (50 eyes for the FLACS group and 50 eyes for the PCS group). Modulation transfer function (MTF), point spread function (PSF) and dysfunctional lens index (DLI) were measured by a ray-tracing aberrometer (iTrace). Uncorrected distance visual acuity (UDVA) and corrected distance visual acuity (CDVA) were also assessed pre-operation,1 week and 1 month after surgery. The MTF values at spatial frequencies of 5, 10, 15, 20, 25 and 30 cycles/degree (c/d) were selected. We used optical coherence tomography (OCT) to assess the macular thickness of different regions pre-operatively and1month after the surgery. Results: In PCS group, we found the statistically significant differences between pre-operation and post-operation in DLI (p < 0.0001), PSF (strehl ratio, SR) (p = 0.027) and MTF (p = 0.028), but not intraocular pressure (IOP) (p = 0.857). The differences between pre-operation and post-operation for DLI (p = 0.031), SR (p = 0.01) and IOP (p = 0.03), but not MTF (p = 0.128) were also found in FLACS group. The differences were statistically significant when the spatial frequencies were at 5, 10 and 25 (p = 0.013, 0.031 and 0.048) between pre-operation and post-operation in PCS group but not FLACS group at 1 month. In PCS group, we found the differences between pre-operation and post-operation in nasal inter macular ring thickness (NIMRT) (p = 0.03), foveal volume (FV) (p = 0.034) and average retinal thickness (ART) (p = 0.025) but not FLACS group at 1 month. Conclusion: FLACS is safe that did not cause significant increase of macular thickness in current study. However, it also cannot produce better optical quality. In contrast, PCS can produce macular thickness changes, but better optical quality recovery. The slightly retinal change may not affect optical quality.
关键词： Macular thickness,Femtosecond laser-assisted cataract surgery (FLACS),Point spread function (PSF),Modulation transfer function (MTF),Phacoemulsification cataract surgery (PCS),Dysfunctional lens index (DLI),Optical quality
更新于2025-09-19 17:13:59
-
The MTF & DQE of Annular Dark Field STEM: Implications for Low-dose Imaging and Compressed Sensing
摘要： Annular dark-field imaging in the scanning transmission electron microscope (ADF-STEM) is a hugely useful incoherent imaging mode, yielding monotonically increasing mass / thickness contrast facilitating quantitative compositional mapping, atom-counting, structure-solving and even unstained biological-imaging. With increasing interest in beam-sensitive materials, many people would like to perform ultra-low-dose imaging or compressed-sensing (CS). Unfortunately, some CS implementations require complex blankers/mask/shutters and may require expensive instrument modification; fast-scanning on the other hand should in principle be available to everyone. Nearly all installed ADF detectors follow the same basic design comprising; a scintillator, light-pipe, PMT, amplifier and a digitiser outputting in arbitrary uncalibrated units. While the scintillator material itself may have an afterglow of only some tens of nanoseconds, the combined assembly has a decay constant of the order of 1.7-3μs which becomes significant in some cases. Scanning with dwell-times faster than this decay introduces issues such as increased background and loss of contrast, streaking in real-space and a diffuse noise band in Fourier-space. In spite of these problems, previous literature has shown that PMT based detectors are in fact sensitive to even single electron signals, unfortunately they are also highly inhomogeneous in their collection efficiency. One solution to this is to as whether we can form an image using these signals using a pulse read-out? Such an image would record the arriving electron as a single impact-event rather than a streak (perfect MTF), the results would be digital rather than analogue, and all electrons would be recorded with equal sensitivity (perfect DQE). The integer nature of the resulting image signal would also directly benefit quantitative contrast (fractional-beam) studies, statistical image analysis, and compressed-sensing / image-inpainting. In this presentation, we will present a new tool to generate realistic noise realisations from ADF image-simulations. This tool registers each electron of a finite dose passing through the sample, to the detector (incorporating afterglow), and onward to amplifiers with realistic thermal and electronic noise. This tool is verified against previous experimental observations of the behaviour of fast-scanned images, and is used to explore the modulation transfer function (MTF) of ADF-STEM for various dwell-times. We then propose, and demonstrate using both simulations and experiment, a new method for operating an ADF detector in a pulse read-out mode (which we call ADFpro) using dwell-times of 0.5μs and 0.2μs. The detector’s quantum efficiency is evaluated indirectly through the evaluation of image pixel-value histograms but also directly using ADF-detector sensitivity maps. The limitations of this approach will be presented, as well as the implications for ultra-low-dose imaging and for compressed-sensing / image-inpainting using such fully digital data.
关键词： ADF-STEM,MTF,DQE,compressed sensing,low-dose imaging
更新于2025-09-10 09:29:36
-
Objective Clinical Evaluation of Ocular Optical Instrument According to the Type of Lens Opacity
摘要： To investigate the results using the OQAS and the Pentacam in cataract patients classified according to the type of lens opacity. Methods: The present study included 124 eyes of 92 patients who had cataract surgery at Seoul St. Mary’s Hospital from December 2011 to January 2012 and were classified into nuclear, cortical, and posterior subcapsular cataract patients. The lens opacity was determined with OSI, MTF, Strehl ratio, width 10%, width 50% and the opacity of Scheimpflug image by the OQAS and the Pentacam. Additionally, the correlation between subjective cataract classification and objective opacity value was analyzed. Results: The nuclear cataract group showed a 6.40 ± 2.41 OSI value and had high opacity. The cortical cataract group showed the highest MTF cut-off value (12.02 ± 6.19 C/deg). When evaluating Pentacam results, the posterior subcapsular cataract group had the lowest average level of lens opacity (9.12 ± 1.08) followed by in increasing order, the cortical cataract group (9.79 ± 1.67) and the nuclear cataract group (11.08 ± 1.84). The results were statistically significant (p < 0.001). The OSI value of the OQAS was significantly correlated with nuclear and posterior opacity (p = 0.049, p = 0.039, respectively) except cortical opacity (p = 0.781). MTF and nuclear opacity showed statistically significant correlation and the lens opacity of Pentacam was correlated with nuclear and posterior opacities. In cortical cataract with severe peripheral opacity, the cortical opacity showed significant correlation with Maximum. Conclusions: The OQAS and Pentacam results showed high correlation with the nuclear and posterior opacities which can be useful for cataract surgery.
关键词： OQAS,MTF,Cataract,Pentacam,OSI
更新于2025-09-04 15:30:14