A Study of Grid Artifacts Formation and Elimination in Computed Radiographic Images

Lin, Chen‐Yuan; Lee, Wei-Jei; Chen, Shyh-Jye; Tsai, Ching Hwa; Lee, Jei Han; Chang, C.; Ching, Yu-Tai

doi:10.1007/s10278-006-0630-8

Cited by 35 publications

(46 citation statements)

References 11 publications

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“…Grid structure noise is generally not an issue for the large detector elements of the FPD. 25 The MAF and FPD have previously been compared in imaging a stent and an aneurysm coil under the same conditions and the much better quality of the MAF images was clearly evident. 11,26 In this study, we demonstrate the effect of the focal spot size on image quality by imaging a stent with the MAF with identical techniques for three different focal spots.…”

Section: Discussionmentioning

confidence: 99%

Evaluation of the microangiographic fluoroscope (MAF) using generalized system performance metrics

2013

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Purpose:The performance of a newly developed, high resolution, microangiographic fluoroscope (MAF) (35 μm pixel pitch and 300 μm thick CsI phosphor) was evaluated using a generalized linear system analysis and compared with that of a standard amorphous Si thin film transistor flat panel detector (FPD) (194 μm pixel pitch and 600 μm thick CsI phosphor). The linear system metrics such as modulation transfer function (MTF), noise power spectrum, and detection quantum efficiency (DQE) are commonly used to gauge the intrinsic detector performance in the detector plane. However, these linear system metrics do not provide information about the image receptor performance in a real system since they do not include the effects of other parameters such as focal spot distribution, scatter radiation, and geometric unsharpness, which may compromise detector performance characteristics. Use of generalized linear system metrics [generalized modulation transfer function (GMTF), generalized normalized noise power spectrum (GNNPS), and generalized detection quantum efficiency (GDQE)] that include these effects gives a more meaningful, complete, and appropriate evaluation of detector performance as part of the imaging system. Methods: A uniform head equivalent phantom was used to simulate realistic clinical parameters and x-ray spectra. The detector MTFs were measured using the slanted edge method and the focal spot MTFs were measured using a pinhole assembly. The scatter MTF was simulated and the scatter fraction was measured for a head-equivalent phantom. The generalized system metrics were calculated for different combinations of three choices of focal spots and three different magnifications with two different air-gaps. The performance of the MAF was also illustrated using stent images obtained with different focal spots under similar conditions. Results: Results for the generalized metrics provide a quantitative description of the performance of the imaging system for both detectors. This generalized analysis demonstrated that both detectors have similar imaging capabilities at lower spatial frequencies, but that the MAF has superior performance over the FPD at higher frequencies even when considering focal spot blurring and scatter. Conclusions: This generalized performance analysis demonstrates the significance of focal spot size, magnification, and scatter on the system performance metrics (GMTF, GNNPS, and GDQE). Although the ideal detector performance characteristics of the MAF are not fully realized due to these other system factors, it still retains an advantage in DQE at high spatial frequencies over the FPD. Similar studies based on the generalized linear system metrics can serve as an efficient tool to evaluate total system capabilities under different realistic conditions to enable optimal design for specific imaging tasks.

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Section: Discussionmentioning

confidence: 99%

Evaluation of the microangiographic fluoroscope (MAF) using generalized system performance metrics

2013

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“…In Fig. 4, the proposed algorithm is compared to a traditional scheme, which is based on using BRFs [3] for the φ = 0 • case. Since this image has the Fourier transform of Fig.…”

Section: Rotated Gridsmentioning

confidence: 99%

“…To overcome the weakness of the 1-D filtering, Sasada et al [2] implemented two-dimensional (2-D) filters in the spatial and wavelet domains. Since the grid and sampling frequencies are usually known, Lin et al [3] calculated the aliased frequencies. However, for practical cases, the calculated frequencies are inaccurate because of the imperfections of grids.…”

Section: Introductionmentioning

confidence: 99%

Grid artifact reduction in radiography with arctan(1/2)-degree rotated grid

Kim

Lee²

2010

2010 IEEE International Conference on Image Processing

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In order to reduce the grid artifacts in the digital radiography with stationary antiscatter grids, artifact frequency detection schemes should be adopted and appropriate band-rejection filters should be applied. However, by rotating the grid angle for certain grid densities and sampling frequencies, the artifact frequencies can be placed near the boundary of the frequency domain, and then the grid artifacts can be easily alleviated by applying a simple low-pass filter without any estimates of the artifact frequencies. In this paper, we propose a grid artifact reduction algorithm, which is based on rotating the grid and applying a low-pass filter. For the sampling frequency 7.194 lines/mm, an optimal rotate angle is arctan(1/2) ≈ 26.57 • and the grid density is 102.2 lines/inch. Better performances are obtained for real x-ray images.

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“…Even though we use the moving grids, the grid artifact is still visible as shown in Fig. 1(a), and thus it should be removed from the obtained x-ray image by applying filters in the spatial [1] or frequency domain [2]. In the frequency domain, the grid artifacts can be described as amplitude-modulated terms [3], and thus the band-rejection filters (BRFs) should be applied to remove the grid artifacts.…”

Section: Introductionmentioning

confidence: 98%

Slope detector for determination of the ringing artifact in filtering x-ray images

Kim

Lee²

2012

2012 IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP)

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In order to reduce the grid artifacts, which are caused by using the antiscatter grid in obtaining x-ray digital images, we analyze the effect of applying band-rejection filters (BRFs) in the frequency domain. The property of the grid artifacts is quite different depending on the shape of the object to be recovered in the spatial domain. Furthermore, if the frequency component of the grid artifact is relatively close to that of the object, then simply applying a BRF may seriously distort the object and cause the ringing artifact. In this paper, we propose a hybrid filtering scheme, which can cooperate such different properties in the spatial domain. In order to perform a robust detection of the position of the ringing artifact, we propose the frequency-modulation (FM) model for the extracted signal, which corresponds to a specific grid artifact. An estimation of the position image for the ringing artifact is then conducted based on the slope detection algorithm, which is commonly used as an FM discriminator in the communication area. Numerical result for real x-ray images shows that applying BRFs in the frequency domain in conjunction with the spatial property of the ringing artifact can successfully remove the grid artifact, distorting the object less.

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A Study of Grid Artifacts Formation and Elimination in Computed Radiographic Images

Cited by 35 publications

References 11 publications

Evaluation of the microangiographic fluoroscope (MAF) using generalized system performance metrics

Evaluation of the microangiographic fluoroscope (MAF) using generalized system performance metrics

Grid artifact reduction in radiography with arctan(1/2)-degree rotated grid

Slope detector for determination of the ringing artifact in filtering x-ray images

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