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

Reimann, David A.; Jacobs, Holly A.; Samei, Ehsan

doi:10.1117/12.384546

Cited by 6 publications

(5 citation statements)

References 4 publications

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“…This error was corrected for by dividing the 2D MTF by a normalized 2D first-order Bessel function, which is the Fourier transform of the cylinder function defined by the finite hole diameter of the point source device. 13 Finally, the axial components of the 2D MTF were compared to the 1D MTF measured using a 0.508 mm copper edge device method. 11,22…”

Section: Methodsmentioning

confidence: 99%

“…Recently, methods to measure the 2D MTF using a large circular object and Wiener filtering were proposed. 13 The practical usefulness of this method to measure the sampled 2D MTF of a digital radiography system was recently demonstrated. 14 The purpose of this project was to develop methods to measure the presampled 2D MTF of digital imaging systems.…”

Section: Introductionmentioning

confidence: 99%

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Measurement of the presampled two‐dimensional modulation transfer function of digital imaging systems

et al. 2002

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The purpose of this work was to develop methods to measure the presampled two-dimensional modulation transfer function (2D MTF) of digital imaging systems. A custom x-ray "point source" phantom was created by machining 256 holes with diameter 0.107 mm through a 0.5-mm-thick copper plate. The phantom was imaged several times, resulting in many images of individual x-ray "spots." The center of each spot (with respect to the pixel matrix) was determined to subpixel accuracy by fitting each spot to a 2D Gaussian function. The subpixel spot center locations were used to create a 5 x oversampled system point spread function (PSF), which characterizes the optical and electrical properties of the system and is independent of the pixel sampling of the original image. The modulus of the Fourier transform of the PSF was calculated. Next, the Fourier function was normalized to the zero frequency value. Finally, the Fourier transform function was divided by the first-order Bessel function that defined the frequency content of the holes, resulting in the presampled 2D MTF. The presampled 2D MTF of a 0.1 mm pixel pitch computed radiography system and 0.2 mm pixel pitch flat panel digital imaging system that utilized a cesium iodide scintillator was measured. Comparison of the axial components of the 2D MTF to one-dimensional MTF measurements acquired using an edge device method demonstrated that the two methods produced consistent results.

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Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Measurement of the presampled two‐dimensional modulation transfer function of digital imaging systems

et al. 2002

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“…5,10 Disk-test devices have also been described for use in the assessment of 2D MTF, but reports indicate that they lack accuracy due to signal aliasing. [11][12][13] Recent advances have yielded promising results for extraction of the 2D MTF from NPS data, but the precision and accuracy of these results come at the cost of intensive cascaded systems analysis and fitting of measured data to an assumed functional form of the MTF. 9 By comparison with existing 2D MTF test objects, namely, 2D arrays of pinholes, 5,11 our techniques that estimate the 2D MTF from multiple measurements with 1D devices have certain benefits.…”

Section: Discussionmentioning

confidence: 99%

“…Other authors have proposed the use of a disk test device and Wiener filtering for the measurement of 2D MTF. 12,13 Although this technique requires only a single measurement, reports indicate inaccuracies in 2D MTF assessment due to aliasing at high frequencies resulting from failure to acquire the presampled MTF. 11 Thus, while these efforts at developing 2D test objects for MTF are laudable, there still remain issues of practicality and precision in such direct 2D measurements.…”

Section: Introductionmentioning

confidence: 99%

Estimation of the two‐dimensional presampled modulation transfer function of digital radiography devices using one‐dimensional test objects

Wells

Dobbins

2012

Medical Physics

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Purpose:The modulation transfer function (MTF) of medical imaging devices is commonly reported in the form of orthogonal one-dimensional (1D) measurements made near the vertical and horizontal axes with a slit or edge test device. A more complete description is found by measuring the two-dimensional (2D) MTF. Some 2D test devices have been proposed, but there are some issues associated with their use: (1) they are not generally available; (2) they may require many images; (3) the results may have diminished accuracy; and (4) their implementation may be particularly cumbersome. This current work proposes the application of commonly available 1D test devices for practical and accurate estimation of the 2D presampled MTF of digital imaging systems. Methods: Theory was developed and applied to ensure adequate fine sampling of the system line spread function for 1D test devices at orientations other than approximately vertical and horizontal.Methods were also derived and tested for slit nonuniformity correction at arbitrary angle. Techniques were validated with experimental measurements at ten angles using an edge test object and three angles using a slit test device on an indirect-detection flat-panel system [GE Revolution XQ/i (GE Healthcare, Waukesha, WI)]. The 2D MTF was estimated through a simple surface fit with interpolation based on Delaunay triangulation of the 1D edge-based MTF measurements. Validation by synthesis was also performed with simulated images from a hypothetical direct-detection flat-panel device. Results: The 2D MTF derived from physical measurements yielded an average relative precision error of 0.26% for frequencies below the cutoff (2.5 mm −1 ) and approximate circular symmetry at frequencies below 4 mm −1 . While slit analysis generally agreed with the results of edge analysis, the two showed subtle differences at frequencies above 4 mm −1 . Slit measurement near 45• revealed radial asymmetry in the MTF resulting from the square pixel aperture (0.2 mm × 0.2 mm), a characteristic which was not necessarily appreciated with the orthogonal 1D MTF measurements. In simulation experiments, both slit-and edge-based measurements resolved the radial asymmetries in the 2D MTF. The average absolute relative accuracy error in the 2D MTF between the DC and cutoff (2.5 mm −1 ) frequencies was 0.13% with average relative precision error of 0.11%. Other simulation results were similar to those derived from physical data. Conclusions: Overall, the general availability, acceptance, accuracy, and ease of implementation of 1D test devices for MTF assessment make this a valuable technique for 2D MTF estimation.

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“…A method that directly gives the two-dimensional MTF may be better suited for the task. At present, the authors know of only one publication in which the two-dimensional MTF in digital radiography has been determined directly 11 . However, in the mentioned paper, it is not the presampling MTF that is determined which, in the case of undersampling, leads to an erroneous result.…”

Section: Introductionmentioning

confidence: 99%

Method for determining the two-dimensional presampling modulation transfer function in digital radiography

Båth

Sund

Månsson

2001

Medical Imaging 2001: Physics of Medical Imaging

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In digital radiography, radial asymmetry may be present. The use of a one-dimensional representation of the resolution properties can therefore be questioned. Although measurements are often done in two orthogonal directions, there may be a need for a more detailed description. A method of measuring the two-dimensional presampling modulation transfer function (MTF) has therefore been developed. A finely sampled "disk spread function" is obtained by imaging an aperture mask, consisting of N 2 circular holes arranged in an NxN manner in an opaque material, in such a way that each hole is positioned at a different phase relative to the sampling coordinates of the detector system. This spread function is resampled, extrapolated, Fourier transformed, and finally corrected for the finite hole size in order to obtain the presampling MTF. The method was tested on a computed radiography (CR) system through measurements with a prototype mask, consisting of 100 holes of radius 0.2 mm drilled in a lead alloy. The results were compared with measurements using the slit method, and were found to be consistent. Problems associated with the method, e.g. errors due to incorrect alignment of the holes in the aperture mask with the beam, and limitations due to the finite hole size, are discussed.

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

Cited by 6 publications

References 4 publications

Measurement of the presampled two‐dimensional modulation transfer function of digital imaging systems

Measurement of the presampled two‐dimensional modulation transfer function of digital imaging systems

Estimation of the two‐dimensional presampled modulation transfer function of digital radiography devices using one‐dimensional test objects

Method for determining the two-dimensional presampling modulation transfer function in digital radiography

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