A method to measure the MTF of digital x-ray systems

Sones, R. A.; Barnes, Gary T.

doi:10.1118/1.595493

Cited by 33 publications

(17 citation statements)

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“…[1][2][3][4] Although the methods used to measure the MTF have changed slightly over the past several decades, [5][6][7][8][9][10][11][12][13][14] the underlying premise has remained a constant: A precisely machined object or test device is imaged and the subsequent response of the detector is used to obtain the MTF using several steps, which generally include determination of the line spread function ͑LSF͒, taking the Fourier transform of the LSF, and use of various noise reduction and fitting techniques. 6,11,12,[15][16][17][18][19][20] The slit 11 and edge 12 response methods are the two most commonly used and accepted techniques for measurement of the MTF, with the edge-response method being preferred ͑with adoption by the IEC͒ ͑Ref.…”

Section: Introductionmentioning

confidence: 99%

Accurate MTF measurement in digital radiography using noise response

et al. 2010

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Purpose:The authors describe a new technique to determine the system presampled modulation transfer function ͑MTF͒ in digital radiography using only the detector noise response. Methods: A cascaded-linear systems analysis was used to develop an exact relationship between the two-dimensional noise power spectrum ͑NPS͒ and the presampled MTF for a generalized detector system. This relationship was then utilized to determine the two-dimensional presampled MTF. For simplicity, aliasing of the correlated noise component of the NPS was assumed to be negligible. Accuracy of this method was investigated using simulated images from a simple detector model in which the "true" MTF was known exactly. Measurements were also performed on three detector technologies ͑an x-ray image intensifier, an indirect flat panel detector, and a solid state x-ray image intensifier͒, and the results were compared using the standard edge-response method. Flat-field and edge images were acquired and analyzed according to guidelines set forth by the International Electrotechnical Commission, using the RQA 5 spectrum. Results: The presampled MTF determined using the noise-response method for the simulated detector system was in close agreement with the true MTF with an averaged percent difference of 0.3% and a maximum difference of 1.1% observed at the Nyquist frequency ͑f N ͒. The edgeresponse method of the simulated detector system also showed very good agreement at lower spatial frequencies ͑less than 0.5 f N ͒ with an averaged percent difference of 1.6% but showed significant discrepancies at higher spatial frequencies ͑greater than 0.5 f N ͒ with an averaged percent difference of 17%. Discrepancies were in part a result of noise in the edge image and phasing errors. For all three detector systems, the MTFs obtained using the two methods were found to be in good agreement at spatial frequencies less than 0.5 f N with an averaged percent difference of 3.4%. Above 0.5 f N , differences increased to an average of 20%. Deviations of the experimental results largely followed the trend seen in the simulation results, suggesting that differences between the two methods could be explained as resulting from the inherent inaccuracies of the edgeresponse measurement technique used in this study. Aliasing of the correlated noise component was shown to have a minimal effect on the measured MTF for the three detectors studied. Systems with significant aliasing of the correlated noise component ͑e.g., a-Se based detectors͒ would likely require a more sophisticated fitting scheme to provide accurate results. Conclusions: Results indicate that the noise-response method, a simple technique, can be used to accurately measure the MTF of digital x-ray detectors, while alleviating the problems and inaccuracies associated with use of precision test objects, such as a slit or an edge.

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Section: Introductionmentioning

confidence: 99%

Accurate MTF measurement in digital radiography using noise response

et al. 2010

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“…Other methods that have also been used to measure the MTF one-dimensionally include the bar phantom method [5] and the line response method [6J . The narrow slit method focuses on measuring the line spread function from a narrow slit.…”

Section: Introductionmentioning

confidence: 99%

Use of Wiener filtering in the measurement of the two-dimensional modulation transfer function

2000

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This paper presents a new method for the measurement of modulation transfer function (MTF) using Wiener filtering. The method, unlike conventional methods using slit or edge devices, allows the direct determination of the MTF in all directions at one step. An image containing a precise circular region is acquired and its Fourier transform is calculated. In the absence of any blurring, the Fourier transform yields a simple Bessel function. Because of the symmetry in the convolution theorem, the roles of the blurring function and object can be interchanged, allowing the blurring function to be recovered using a Wiener filter. We simulated this process to understand the effects of attenuation, signal-to-noise ratio, and circle size. Images were simulated containing a circular region and degraded by spatial domain blurring with a Gaussian convolution kernel and by additive Poisson noise. The determined MTF matches the expected MTF except for a slight high frequency overestimate due to noise aliasing, which can be compensated. This method allows one to easily measure the two-dimensional MTF, particularly in systems which have an asymmetrical point spread function such as computed radiography. The method can be used as a tool for quality assurance and for comparing the resolution characteristics of various digital radiography systems.

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“…A similar technique is the edge-spread-function method, which is easier to use [2]. Both these methods need precisely constructed tools and can introduce systematic errors if operating techniques are imperfect [1][2][3][4][5][6]; moreover, different methods can be used for the same equipment to estimate systematic errors [3,5]. The other source of systematic errors that should be mentioned is aliasing, which cannot be estimated easily [4].…”

Section: Introductionmentioning

confidence: 99%

“…The two-dimensional presampled point-spread function (PSF ) measurements, obtained using a round-hole collimator [6] or cylindrical absorber, have similar technical difficulties. 0 An alternative to these methods is to evaluate the system response in a periodic pattern [4,5]. Using this method, the aliasing problem can be solved, but precise technical execution is still required.…”

Section: Introductionmentioning

confidence: 99%

Simultaneous pixel detection probabilities and spatial resolution estimation of pixelized detectors by means of correlation measurements

Grabski

2008

Nuclear Instruments and Methods in Physics Research Section A:

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On the basis of the determination of statistical correlations between neighboring detector pixels, a novel method of estimating the simultaneous detection probability of pixels and the spatial resolution of pixelized detectors is proposed. The correlations are determined using noise variance measurement for isolated pixels and for the difference between neighboring pixels. The method is validated using images from two image-acquisition devices, a General Electric Senographe 2000D and a SD mammographic unit. The pixelized detector is irradiated with X-rays over its entire surface. It is shown that the simultaneous pixel detection probabilities can be estimated with an accuracy of 0.001-0.003, with an estimated systematic error of less than 0.005. The two-dimensional presampled point-spread function (PSF ) 0 is determined using a single Gaussian approximation and a sum of two Gaussian approximations. The results obtained for the presampled PSF 0 show that the single Gaussian approximation is not appropriate, and the sum of two Gaussian approximations providing the best fit predicts the existence of a large (~50%) narrow component. Support for this observation can be found in the recent simulation study of columnar indirect digital detectors by Badano et al. The sampled two-dimensional PSF is determined using Monte Carlo simulation for the L-shaped, uniformly distributed acceptance function for different fill-factor values. The calculation of the presampled modulation transfer function based on the estimated PSF 0 shows that the observed data can be reproduced only by the single Gaussian approximation, and that when the sum of two Gaussians is used, significantly larger values are apparent in the higher-frequency region for images from both detection devices. The proposed method does not require a precisely, constructed tool. It is insensitive to beam collimation and to system physical size and may be indispensable in cases where thin absorption slits or edges are difficult to use. It could therefore be very useful for regular detector verification.

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A method to measure the MTF of digital x-ray systems

Cited by 33 publications

References 0 publications

Accurate MTF measurement in digital radiography using noise response

Accurate MTF measurement in digital radiography using noise response

Use of Wiener filtering in the measurement of the two-dimensional modulation transfer function

Simultaneous pixel detection probabilities and spatial resolution estimation of pixelized detectors by means of correlation measurements

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