• The Korean Journal of Nuclear Medicine Technology
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• v.18 no.1
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• pp.62-68
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• 2014

Purpose: After I-131 therapy, SPECT/CT is useful in identifying location of thyroid remnants and metastasis of thyroid cancers. An excessive uptake of thyroid leads to a ringing artifact in the SPECT images. The aim of this study is to investigate and suggest a proper post filters to remove ringing artifact and produce better image quality. Materials and Methods: A low-cost, customized thyroid-mimicking phantom, consisting of an acrylic bottle and a hollow sphere was used for SPECT/CT Discovery (GE Healthcare, USA). It was filled with I-131 solution. The ratio of hollow sphere to background were varied as 50:1, 200:1, 1000:1 and 4000:1. Acquired images were reconstructed by OSEM (2 iterations, 10 subsets) with and without Evolution (resolution recovery correction, GE). Three different post-filters were applied; Butterworth (cut off: 0.38 to 0.58 with intervals of 0.05), Hanning (cut off: 0.8 to 1 with intervals of 0.05) and Gaussian (FWHM: 3 to 5 with intervals of 0.5) filters. Contrast, background variability, air area variability, and full width half maximum (FWHM) were compared. Results: Higher contrasts were obtained from the SPECT images with Evolution than without Evolution. In the case of images without Evolution, image distortion such as star artifact was generated. For all sphere-to-background ratio, the Butterworth filter showed better constrasts and FWHMs than other two filters, but the ringing artifact was still generated in all studies except 50:1 and it was decreased as cutoff value was increased. The ringing artifact didn't appear with Hanning and Gaussian filters at all studies, however constrats and FWHMs with Gaussian was worse than Hanning filter. For the images having ringing artifacts, the background variability and air area variability were increased. Conclusion: In this study, we suggested that it is desirable to use Hanning filter when the ringing artifact is generated and to use Butterworth filter when ringing artifact is not generated in I-131 SPECT.

• International journal of advanced smart convergence
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• v.4 no.2
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• pp.138-144
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• 2015

Digital filters are extensively used in the world of communication. In order to design a digital finite impulse response (FIR) filter that satisfies all the required conditions is challenging. In this paper, design techniques of digital low pass FIR filters using Rectangular window method, Hamming window, Hanning window, and Optimal Parks McClellan method are presented. The stability, number of components required and filter coefficients are demonstrated for different design techniques. It is demonstrated that filter design using hamming window is comparatively better than rectangular and hanning window though the components required for all of the windowing technique are same, hamming shows higher stability. The stability is shown with the help of magnitude and phase spectrum of each window. Simulation is carried out using MATLAB and comparisons are made entirely based on the output of the simulation.

• The Journal of the Korea Contents Association
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• v.9 no.12
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• pp.322-331
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• 2009

In clinical SPECT, FWHM provides quality information of the images obtained under different observing conditions. Therefore, the purpose of this study was to determine the optimum cut off level with comparison of FWHM according to cut off levels in each filter - Band limited, Sheep-Logan, Hanning, Hamming, Low pass cosine, Parazen and Butterworth filter in a SPECT camera. I recorded images along the X, Y, Z-axis with 99mTcO4 point source and measured FWHM with profile curves. In conclusion, all filters showed the longest figures of FWHM with cut off level 0.4, which has the worst image resolution. The images with cut off level 0.7 showed best image resolution. The shortest average of FWHM in MS2 was $11.07\pm0.07mm$ using the Butterworth filter, in MS3 it was $8.44\pm0.19mm$ through using the Hanning filter.

• Journal of the Institute of Convergence Signal Processing
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• v.4 no.1
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• pp.49-55
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• 2003

The use of digital filters in the signal process field is increasing rapidly with development of the modern industrial society. Especially, detail processors, Y/C separators, ghost removing filters, standard converters (NTSC to PAL or PAL to NTSC) and noise reducers, all of which use digital filters, tend to be used in digital video and audio processing, CATV and various communication fields. Generally, there are two different digital filters, the Rf (infinite impulse response) filter and the FIR (finite impulse response) filter in digital filter. In this paper, we have designed FIR filter which has the phase linearity and the easiness of creation. In the design of the FIR digital filter, the window function is used to alleviate the ripples caused by Gibbs Phenomenon around the cut off frequency of the band pass. But there're some problems to choose proper window function for the design destination due to its fixed values. Therefore, in this paper, we designed a modified Hanning window with new parameter which is adaptively chosen corresponding to design objectives. The digital filter was simulated to prove the validity of the model and it was compared with the Hamming, the Manning, the Blacknan and the Kaiser window function. And we have used peak side-lobe and transient characteristics as standard of judgement.

• Journal of Radiopharmaceuticals and Molecular Probes
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• v.3 no.2
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• pp.65-71
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• 2017

To assess the effects of filter and reconstruction of Cu-64 PET data on Siemens scanner, the various reconstruction algorithm with various filters were assessed in terms of spatial resolution, non-uniformity (NU), recovery coefficient (RC), and spillover ratio (SOR). Image reconstruction was performed using filtered backprojection (FBP), 2D ordered subset expectation maximization (OSEM), 3D reprojection algorithm (3DRP), and maximum a posteriori algorithms (MAP). For the FBP reconstruction, ramp, butterworth, hamming, hanning, or parzen filters were used. Attenuation or scatter correction were performed to assess the effect of attenuation and scatter correction. Regarding spatial resolution, highest achievable volumetric resolution was $3.08mm^3$ at the center of FOV when MAP (${\beta}=0.1$) reconstruction method was used. SOR was below 4% for FBP when ramp, Hamming, Hanning, or Shepp-logan filter were used. The lowest NU (highest uniform) after attenuation & scatter correction was 5.39% when FBP (parzen filter) was used. Regarding RC, 0.9 < RC < 1.1 was obtained when OSEM (iteration: 10) was used when attenuation and scatter correction were applied. In this study, image quality of Cu-64 on Siemens Inveon PET was investigated. This data will helpful for the quantification of Cu-64 PET data.

• Journal of Power Electronics
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• v.12 no.3
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• pp.509-517
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• 2012

This paper presents control strategies for cascaded H-bridge multilevel active power filters (APFs). A current loop controller is implemented using a proportional-resonant (PR) regulator, which achieves zero steady-state error at target frequencies. The power balancing mechanism for the dc-link capacitor voltages is analyzed and a voltage balancing controller is presented. To mitigate the picket-fence effect of the conventional FFT algorithm under asynchronous sampling conditions, the Hanning Windowed-FFT algorithm is proposed for reference current generation (RCG). This calculates the frequency, amplitude and phase of individual harmonic components accurately and as a result, selective harmonic compensation (SHC) is achieved. Simulation and experimental results are presented, which verify the validity and effectiveness of the devised control algorithms.

• Journal of radiological science and technology
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• v.26 no.2
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• pp.63-69
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• 2003

Filtering is necessary to reduce statistical noise and to increase image quality in SPECT images. Noises controled by low-pass filter designed to suppress high spatial frequency in SPECT image. Most SPECT filter function control the degree of high frequency supression by chosing a cut of frequency. The location of cut off frequency determines the affect image noise and spatial resolution. If select the low cut off frequency, its provide good noise suppression but insufficient image quantity and high cut off frequencies increase the image resolution but insufficient noise suppression. The purpose of this study was to determines the optimam cut off level with comparison of FWHM according to cut off level in each kiters-Band-limited, Sheep-logan, Sheep-logan Hanning, Generalized Hamming, Low pass cosine, Parazen and Butterworth filter in SPECT camera. We recorded image along the X, Y, Z-axis with $^{99m}TcO_4$ point source and measured FWHM by use profile curve. We find averaged length is $9.16\;mm{\sim}18.14\;mm$ of FWHM in X, Y, and Z-axis, and Band-limited and Generalized Hamming filters measures 9.16 mm at 0.7 cycle/pixel cut off frequency.

• Speech Sciences
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• v.14 no.4
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• pp.131-144
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• 2007

In an effort to improve the performance of mel frequency cepstral coefficients (MFCC), we investigate the effects of varying the parameters for the filter banks and their associated windows on speech recognition rates. Specifically, the mel and bark scales are combined with various types of filter bank windows. Comparison and evaluation of the suggested methods are performed by two independent ways of speech recognition and the Fisher discriminant objective function. It is shown that the Hanning window based on the bark scale yields 28.1% relative performance improvements over the triangular window with the mel scale in speech recognition error rate. Further work on incorporating PCA and/or LDA would be desirable as a postprocessor to MFCC extraction.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2004.05b
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• pp.68-74
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• 2004

The use of digital filters in the signal processing field is increasing rapidly with development of the modem industrial society, and generally digital filter is classified into FIR (infinite impulse response) fillers and FIR (finite impulse response) filters. The FIR digital filter has the phase linearity and the easiness of creation. In the design of the FIR digital filter, the window function is used to alleviate ripples caused by Gibbs Phenomenon around the cut-off frequency of the passband. In this paper, we designed a new window function and compared with existing Manning, Hamming and Blackman window functions. And we used peak side-lobe and transient characteristics as standard of judgement.

• Proceedings of the KIPE Conference
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• 2007.07a
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• pp.409-411
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• 2007

This paper deals with an automatic tuning method of the notch filter to suppress oscillations in a permanent magnet linear synchronous motor(PMLSM) drive. First, it saves automatically the reference torque-component current when oscillations are detected. Then the oscillation frequency of the saved data is calculated by using the fast Fourier transform(FFT) algorithm. And also the Hanning function is used to reduce the leakage components due to the aperiodic measurement data. Finally, the proposed method tunes the notch filter to suppress oscillations. Experimental results on the test rig show the validity of the proposed method.