In SPECT, noise is one of the major limitations that degrade image quality. To suppress the noisy signals in an image, digital filters are most commonly applied. However, in SPECT image reconstruction, selection of an...In SPECT, noise is one of the major limitations that degrade image quality. To suppress the noisy signals in an image, digital filters are most commonly applied. However, in SPECT image reconstruction, selection of an appropriate filter and its functions has always remained a difficult task. In this work an attempt was made to investigate the effects of varying cut-off frequencies and in keeping the order of Butterworth filter constant on detectability and contrast of hot and cold re-gions images. A new insert simulating hot and cold regions which provides similar views in a reconstructed image was placed in the phantom’s cylindrical source tank and imaged. Tc-99m radionuclide was distributed uniformly in the phantom. SPECT data were collected in a 20% energy window centered at 140 keV by a Philips ADAC Forte dual head gamma camera mounted with a LEHR collimator. Images were generated by using the filtered backprojection technique. A Butterworth filter of order 5 with cut-off frequencies 0.35 and 0.45 cycles·cm<sup>-1</sup> was applied. Images were examined in terms of hot and cold regions, detectability and contrast. Results show that the hot and cold regions’ detectability and contrast vary with the change of cut-off frequency. With a 0.45 cycles·cm<sup>-1</sup> cut-off frequency, a significant enhancement in contrast of cold regions was achieved as compared to a 0.35 cycles·cm<sup>-1</sup> cut-off frequency. Furthermore, the detectability of hot and cold regions improved with the use of a 0.45 cycles·cm<sup>-1</sup> cut-off frequency. In conclusion, image quality of hot and cold regions affected in a different way with a change of cut-off frequency. Thus, care should be taken in selecting the filter cut-off frequency prior to reconstruction of images;particularly, when both types of regions are expected in the reconstructed image.展开更多
In this work, long-period waveguide grating-based tunable wavelength filters using organic–inorganic grafting poly(methyl methacrylate)(PMMA) materials are designed and fabricated by metal-cladding directly defin...In this work, long-period waveguide grating-based tunable wavelength filters using organic–inorganic grafting poly(methyl methacrylate)(PMMA) materials are designed and fabricated by metal-cladding directly defined technique.The thermal stabilities and optical properties of the organic–inorganic grafting PMMA core materials are analyzed. Structures and performance parameters of the waveguide gratings and self-electrode heaters are designed and simulated. The contrast of the filter is about 15 d B and the resonant wavelength can be tuned by different electric powers applied to the metal-cladding self-electrode heaters. The temperature sensitivity is 3.5 nm/℃ and the switching time is about 1 ms. The technique is very suitable for realizing the optoelectronic integrated wavelength-division-multiplexing systems.展开更多
We have proposed and constructed a few-mode fiber(FMF)-based comb filter realized by dislocation splicing a fewmode long-period fiber grating(FM-LPFG) with a single-mode fiber(SMF). From an all-fiber laser with a FMF-...We have proposed and constructed a few-mode fiber(FMF)-based comb filter realized by dislocation splicing a fewmode long-period fiber grating(FM-LPFG) with a single-mode fiber(SMF). From an all-fiber laser with a FMF-based comb filter, the generation of switchable single-, dual-, triple-, and quadruple-wavelength continuous light has been achieved.Moreover, wavelength switchable mode-locked pulses have been obtained with the increased pump power. In the experiment, the output wavelength of the mode-locked fiber laser was changed from 1567.72 nm to 1571.04 nm, while the signal-to-noise(SNR) ratio was maintained above 61 d B. The switchable multiwavelength continuous wave(CW) and mode-locked all-fiber lasers have potentially important applications for fiber sensing, wavelength-division multiplexing(WDM) and signal processing.展开更多
Filter backprojection is an important method of image reconstruction technique in clinical nuclear medicine imaging. Because of noisy images due to less available photon statistics and different factors associated wit...Filter backprojection is an important method of image reconstruction technique in clinical nuclear medicine imaging. Because of noisy images due to less available photon statistics and different factors associated with imaging system in nuclear medicine tomography, using optimal filter to suppress the noise with keeping the proper signal is one of the significant steps in image reconstruction strategy for clinical use. In this paper, we present the effect of implementation of different filters on the hot region of Carlson phantom SPECT image in reconstruction process. By defining some criteria such as image smoothness and contrast, estimation of spatial resolution and location of hot cylindrical sources and their detectability the best filter with specified parameter have been determined and the results have been interpreted. Results show that the perceived image quality of hot region and also their detectability has been improved when Shepp-Logan and Ram-Lak filters with cut-off frequency of 0.4 has been used.展开更多
Complimentary hexagonal-omega structures are used to design compact, low insertion loss (IL), low pass filter with sharp cut-off. It has been designed for improvement of roll-off performance based on both μ and ε ne...Complimentary hexagonal-omega structures are used to design compact, low insertion loss (IL), low pass filter with sharp cut-off. It has been designed for improvement of roll-off performance based on both μ and ε negative property of the complimentary hex-omega structure while maintaining the filter pass-band performance. By properly designing and loading the hexagonal-omega structure in the ground of microstrip line not only improve the roll-off of the low pass filter, but also reduced the filter size. The simulated results indicate that the proposed filter achieves a flat pass band with no ripples as well as selectivity of 19.68 dB/GHz, corresponding to 5-unit cells hex-omega structures. This significantly exceeds the 5.6 dB/GHz selectivity of the conventional low pass filter design, due to sub-lambda dimensions of the hex-omega structure. A prototype filter implementing area is: 0.712λg x 0.263λg, λg being the guided wavelength at 3-dB cut-off frequency (fc). The proposed filter has a size smaller by 36.2%.展开更多
Long-period waveguide grating based filters have attracted attention due to their flexible fabrication,a variety of materials and structures,low back reflection,low insertion loss,and excellent performance in the tuni...Long-period waveguide grating based filters have attracted attention due to their flexible fabrication,a variety of materials and structures,low back reflection,low insertion loss,and excellent performance in the tuning range and temperature sensitivity.To our knowledge,for the first time,a two-segment polymer long-period waveguide grating was cascaded to implement a filter with a narrower bandwidth.Experimental results showed that the device had a maximum extinction ratio of 24 dB at 1577 nm,and the 12 dB bandwidth was 10 nm.The temperature sensitivity of the fabricated device was 1.79 nm/℃.展开更多
文摘In SPECT, noise is one of the major limitations that degrade image quality. To suppress the noisy signals in an image, digital filters are most commonly applied. However, in SPECT image reconstruction, selection of an appropriate filter and its functions has always remained a difficult task. In this work an attempt was made to investigate the effects of varying cut-off frequencies and in keeping the order of Butterworth filter constant on detectability and contrast of hot and cold re-gions images. A new insert simulating hot and cold regions which provides similar views in a reconstructed image was placed in the phantom’s cylindrical source tank and imaged. Tc-99m radionuclide was distributed uniformly in the phantom. SPECT data were collected in a 20% energy window centered at 140 keV by a Philips ADAC Forte dual head gamma camera mounted with a LEHR collimator. Images were generated by using the filtered backprojection technique. A Butterworth filter of order 5 with cut-off frequencies 0.35 and 0.45 cycles·cm<sup>-1</sup> was applied. Images were examined in terms of hot and cold regions, detectability and contrast. Results show that the hot and cold regions’ detectability and contrast vary with the change of cut-off frequency. With a 0.45 cycles·cm<sup>-1</sup> cut-off frequency, a significant enhancement in contrast of cold regions was achieved as compared to a 0.35 cycles·cm<sup>-1</sup> cut-off frequency. Furthermore, the detectability of hot and cold regions improved with the use of a 0.45 cycles·cm<sup>-1</sup> cut-off frequency. In conclusion, image quality of hot and cold regions affected in a different way with a change of cut-off frequency. Thus, care should be taken in selecting the filter cut-off frequency prior to reconstruction of images;particularly, when both types of regions are expected in the reconstructed image.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61575076,61475061,and 61405070)the Fundamental Research Funds for the Central Universities,China(Grant No.JCKY-QKJC08)+1 种基金the Science and Technology Development Plan of Jilin Province,China(Grant Nos.20130522151JH,20140519006JH,and 20160520091JH)the China Postdoctoral Science Foundation(Grant No.2015M571362)
文摘In this work, long-period waveguide grating-based tunable wavelength filters using organic–inorganic grafting poly(methyl methacrylate)(PMMA) materials are designed and fabricated by metal-cladding directly defined technique.The thermal stabilities and optical properties of the organic–inorganic grafting PMMA core materials are analyzed. Structures and performance parameters of the waveguide gratings and self-electrode heaters are designed and simulated. The contrast of the filter is about 15 d B and the resonant wavelength can be tuned by different electric powers applied to the metal-cladding self-electrode heaters. The temperature sensitivity is 3.5 nm/℃ and the switching time is about 1 ms. The technique is very suitable for realizing the optoelectronic integrated wavelength-division-multiplexing systems.
基金supported by the National Natural Science Foundation of China (Grant Nos. 91950105 and 62175116)the 1311 talent plan of Nanjing University of Posts and Telecommunications。
文摘We have proposed and constructed a few-mode fiber(FMF)-based comb filter realized by dislocation splicing a fewmode long-period fiber grating(FM-LPFG) with a single-mode fiber(SMF). From an all-fiber laser with a FMF-based comb filter, the generation of switchable single-, dual-, triple-, and quadruple-wavelength continuous light has been achieved.Moreover, wavelength switchable mode-locked pulses have been obtained with the increased pump power. In the experiment, the output wavelength of the mode-locked fiber laser was changed from 1567.72 nm to 1571.04 nm, while the signal-to-noise(SNR) ratio was maintained above 61 d B. The switchable multiwavelength continuous wave(CW) and mode-locked all-fiber lasers have potentially important applications for fiber sensing, wavelength-division multiplexing(WDM) and signal processing.
文摘Filter backprojection is an important method of image reconstruction technique in clinical nuclear medicine imaging. Because of noisy images due to less available photon statistics and different factors associated with imaging system in nuclear medicine tomography, using optimal filter to suppress the noise with keeping the proper signal is one of the significant steps in image reconstruction strategy for clinical use. In this paper, we present the effect of implementation of different filters on the hot region of Carlson phantom SPECT image in reconstruction process. By defining some criteria such as image smoothness and contrast, estimation of spatial resolution and location of hot cylindrical sources and their detectability the best filter with specified parameter have been determined and the results have been interpreted. Results show that the perceived image quality of hot region and also their detectability has been improved when Shepp-Logan and Ram-Lak filters with cut-off frequency of 0.4 has been used.
文摘Complimentary hexagonal-omega structures are used to design compact, low insertion loss (IL), low pass filter with sharp cut-off. It has been designed for improvement of roll-off performance based on both μ and ε negative property of the complimentary hex-omega structure while maintaining the filter pass-band performance. By properly designing and loading the hexagonal-omega structure in the ground of microstrip line not only improve the roll-off of the low pass filter, but also reduced the filter size. The simulated results indicate that the proposed filter achieves a flat pass band with no ripples as well as selectivity of 19.68 dB/GHz, corresponding to 5-unit cells hex-omega structures. This significantly exceeds the 5.6 dB/GHz selectivity of the conventional low pass filter design, due to sub-lambda dimensions of the hex-omega structure. A prototype filter implementing area is: 0.712λg x 0.263λg, λg being the guided wavelength at 3-dB cut-off frequency (fc). The proposed filter has a size smaller by 36.2%.
文摘Long-period waveguide grating based filters have attracted attention due to their flexible fabrication,a variety of materials and structures,low back reflection,low insertion loss,and excellent performance in the tuning range and temperature sensitivity.To our knowledge,for the first time,a two-segment polymer long-period waveguide grating was cascaded to implement a filter with a narrower bandwidth.Experimental results showed that the device had a maximum extinction ratio of 24 dB at 1577 nm,and the 12 dB bandwidth was 10 nm.The temperature sensitivity of the fabricated device was 1.79 nm/℃.