Normalization of the modulation transfer function: The open‐field approach

Friedman, Saul N.; Cunningham, Ian

doi:10.1118/1.2977536

Cited by 32 publications

(33 citation statements)

References 28 publications

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“…15 Several methods have been described for the accurate calculation of sensor resolution via pre-sampled MTF. 16 The MTF of the detector can be obtained by square-shaped stripe patterns ( Figure 1) on the basis of noise response 17 or the Fourier transform of a slanted edge or slit image 18 via its line spread function (LSF). By using the Fourier transform of the LSF, the MTF can be computed.…”

Section: Resolution Of the Two-dimensional Detectormentioning

confidence: 99%

Spatial resolution in CBCT machines for dental/maxillofacial applications—what do we know today?

Brüllmann

Schulze²

2015

Dentomaxillofacial Radiology

170

127

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Spatial resolution is one of the most important parameters objectively defining image quality, particularly in dental imaging, where fine details often have to be depicted. Here, we review the current status on assessment parameters for spatial resolution and on published data regarding spatial resolution in CBCT images. The current concepts of visual [line-pair (lp) measurements] and automated [modulation transfer function (MTF)] assessment of spatial resolution in CBCT images are summarized and reviewed. Published measurement data on spatial resolution in CBCT are evaluated and analysed. Effective (i.e. actual) spatial resolution available in CBCT images is being influenced by the two-dimensional detector, the threedimensional reconstruction process, patient movement during the scan and various other parameters. In the literature, the values range between 0.6 and 2.8 lp mm 21 (visual assessment; median, 1.7 lp mm ). Spatial resolution of CBCT images is approximately one order of magnitude lower than that of intraoral radiographs. Considering movement, scatter effects and other influences in real-world scans of living patients, a realistic spatial resolution of just above 1 lp mm 21 could be expected.

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Section: Resolution Of the Two-dimensional Detectormentioning

confidence: 99%

Spatial resolution in CBCT machines for dental/maxillofacial applications—what do we know today?

Brüllmann

Schulze²

2015

Dentomaxillofacial Radiology

170

127

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“…12,20,22 Difficulties also arise when comparing measurements with published results of other investigators, as slight differences in object, acquisition, and/or processing techniques could easily alter the results. 23,24,[27][28][29][30][31][32] Significant variations have even been shown to occur when different individuals measured the MTF of the same data set. 32 The aim of this work is to develop a new method for measurement of the MTF of digital radiographic systems that is less susceptible to such influences, by using the intrinsic noise response of the detector.…”

Section: Introductionmentioning

confidence: 99%

“…12 However, it is well documented that the edge-response method is also vulnerable to a host of potential problems that could influence the measurement and result in inaccuracies. Inaccuracies may result from errors in the calculated edge angle, 12,22,23 noise, 12,23,24 influences of scattered radiation, 24,25 use of finite-element differentiation, 10,22 profile misregistration and phasing errors, 22,23,26 truncation of the LSF tails and incorrect normalization, 27 and windowing and processing. 12,20,22 Difficulties also arise when comparing measurements with published results of other investigators, as slight differences in object, acquisition, and/or processing techniques could easily alter the results.…”

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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“…Maintenance of the LSF tails is important for estimating the LFD accurately during the presampled MTF analysis [16]. Accordingly, the LSF tails correlate with the low-frequency region of the presampled MTF, and the region near the LSF center inversely correlates with the high-frequency region.…”

Section: Variable Filtering Methodsmentioning

confidence: 99%

“…However, as compared with the slit method, the edge method can provide more accurate MTFs at low spatial frequencies [8, 10, 12, 14], and it is better able to obtain edge images because of its lower sensitivity to X-ray beam alignment errors [8]. Samei et al reduced the ESF noise by using a binning technique during the process of reprojection from a two-dimensional edge image to ESF, and subsequently used a Gaussian-weighted moving polynomial fit for the ESF obtained For presampled MTF measurements of DR systems with glare, long-range ESFs exceeding 8 cm are required for correct evaluation of a low frequency drop (LFD) in the MTF, which is caused by glare [12, 16,17]. In general, the enhanced LSF noise generated in the edge method is noticeable in the LSF tail on the direct exposure (high exposure) side, and the noise therefore causes remarkable errors with fluctuating MTF values over the entire frequency range.…”

Section: Introductionmentioning

confidence: 99%