Characterization of imaging performance in differential phase contrast CT compared with the conventional CT—Noise power spectrum NPS(<i>k</i>)

Tang, Xiangyang; Yang, Yi; Tang, Shaojie

doi:10.1118/1.3602071

Cited by 47 publications

(65 citation statements)

References 44 publications

(107 reference statements)

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“…In contrast, DPC-CT does not need additional image smoothing due to the low-frequency nature of its NPS. 25,27,28,30 In fact, a recent study showed that detectability in DPC-CT may actually benefit from a carefully chosen high-pass filter. 65 Therefore, the transfer functions in this stage are generally different for ACT and DPC-CT and are denoted as T a 11 and T dpc 11 , respectively.…”

Section: Iiib3 Stage 11: Apodization Windowmentioning

confidence: 99%

“…It was demonstrated 15,25 that for some materials under certain experimental conditions, DPC-CT may have superior contrast to noise ratio (CNR) compared to ACT, and the CNR for both DPC-CT and ACT is inversely proportional to the square root of exposure level. It was also discovered both theoretically [25][26][27][28] and experimentally 26 that the noise variance of DPC-CT system scales with the spatial resolution with an exponent of −1, rather than the value of −3 for twodimensional (2D) ACT. 29 To compare the spatial correlation of noise in DPC-CT with that of ACT, the noise power spectrum (NPS) of DPC-CT was theoretically studied 25,27,28 and experimentally measured 30 in the 2D case.…”

Section: Introductionmentioning

confidence: 98%

“…It was also discovered both theoretically [25][26][27][28] and experimentally 26 that the noise variance of DPC-CT system scales with the spatial resolution with an exponent of −1, rather than the value of −3 for twodimensional (2D) ACT. 29 To compare the spatial correlation of noise in DPC-CT with that of ACT, the noise power spectrum (NPS) of DPC-CT was theoretically studied 25,27,28 and experimentally measured 30 in the 2D case. The effect of the DPC-CT noise texture on low contrast detectability was studied using human observers.…”

Section: Introductionmentioning

confidence: 98%

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Fundamental relationship between the noise properties of grating-based differential phase contrast CT and absorption CT: Theoretical framework using a cascaded system model and experimental validation

Bevins

Zambelli

et al. 2013

Med. Phys.

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Purpose: Using a grating interferometer, a conventional x-ray cone beam computed tomography (CT) data acquisition system can be used to simultaneously generate both conventional absorption CT (ACT) and differential phase contrast CT (DPC-CT) images from a single data acquisition. Since the two CT images were extracted from the same set of x-ray projections, it is expected that intrinsic relationships exist between the noise properties of the two contrast mechanisms. The purpose of this paper is to investigate these relationships. Methods: First, a theoretical framework was developed using a cascaded system model analysis to investigate the relationship between the noise power spectra (NPS) of DPC-CT and ACT. Based on the derived analytical expressions of the NPS, the relationship between the spatial-frequencydependent noise equivalent quanta (NEQ) of DPC-CT and ACT was derived. From these fundamental relationships, the NPS and NEQ of the DPC-CT system can be derived from the corresponding ACT system or vice versa. To validate these theoretical relationships, a benchtop cone beam DPC-CT/ACT system was used to experimentally measure the modulation transfer function (MTF) and NPS of both DPC-CT and ACT. The measured three-dimensional (3D) MTF and NPS were then combined to generate the corresponding 3D NEQ. Results: Two fundamental relationships have been theoretically derived and experimentally validated for the NPS and NEQ of DPC-CT and ACT: (1) the 3D NPS of DPC-CT is quantitatively related to the corresponding 3D NPS of ACT by an inplane-only spatial-frequency-dependent factor 1/f 2 , the ratio of window functions applied to DPC-CT and ACT, and a numerical factor C g determined by the geometry and efficiency of the grating interferometer. Note that the frequency-dependent factor is independent of the frequency component f z perpendicular to the axial plane. (2) The 3D NEQ of DPC-CT is related to the corresponding 3D NEQ of ACT by an f 2 scaling factor and numerical factors that depend on both the attenuation and refraction properties of the image object, as well as C g and the MTF of the grating interferometer. Conclusions: The performance of a DPC-CT system is intrinsically related to the corresponding ACT system. As long as the NPS and NEQ of an ACT system is known, the corresponding NPS and NEQ of the DPC-CT system can be readily estimated using additional characteristics of the grating interferometer.

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Section: Iiib3 Stage 11: Apodization Windowmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 98%

Section: Introductionmentioning

confidence: 98%

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Fundamental relationship between the noise properties of grating-based differential phase contrast CT and absorption CT: Theoretical framework using a cascaded system model and experimental validation

Bevins

Zambelli

et al. 2013

Med. Phys.

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“…It is a fundamental understanding that the subject contrast of soft tissues in an imaging system is intrinsically determined by their interaction with the x-ray beam, [14][15][16] while the system's performance is determined by its signal and noise transfer properties. 11,[17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35] In principle, the signal transfer property of an imaging system is dependent on its modulation transfer function MTF(k), [17][18][19][20][21][22][23][24][25][26][27][28][29][30] while the noise transfer property can only be thoroughly characterized by its noise power spectrum NPS(k), i.e., the variation of noise intensity as a function over spatial frequency k. [17][18][19][20][21][22][23][24][25]…”

Section: Introductionmentioning

confidence: 99%

Characterization of imaging performance in differential phase contrast CT compared with the conventional CT: Spectrum of noise equivalent quanta NEQ( k )

2012

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Purpose: Differential phase contrast CT (DPC-CT) is emerging as a new technology to improve the contrast sensitivity of conventional attenuation-based CT. The noise equivalent quanta as a function over spatial frequency, i.e., the spectrum of noise equivalent quanta NEQ(k), is a decisive indicator of the signal and noise transfer properties of an imaging system. In this work, we derive the functional form of NEQ(k) in DPC-CT. Via system modeling, analysis, and computer simulation, we evaluate and verify the derived NEQ(k) and compare it with that of the conventional attenuation-based CT. Methods: The DPC-CT is implemented with x-ray tube and gratings. The x-ray propagation and data acquisition are modeled and simulated through Fresnel and Fourier analysis. A monochromatic x-ray source (30 keV) is assumed to exclude any system imperfection and interference caused by scatter and beam hardening, while a 360• full scan is carried out in data acquisition to avoid any weighting scheme that may disrupt noise randomness. Adequate upsampling is implemented to simulate the x-ray beam's propagation through the gratings G 1 and G 2 with periods 8 and 4 μm, respectively, while the intergrating distance is 193.6 mm (1/16 of the Talbot distance). The dimensions of the detector cell for data acquisition are 32 × 32, 64 × 64, 96 × 96, and 128 × 128 μm 2 , respectively, corresponding to a 40.96 × 40.96 mm 2 field of view in data acquisition. An air phantom is employed to obtain the noise power spectrum NPS(k), spectrum of noise equivalent quanta NEQ(k), and detective quantum efficiency DQE(k). A cylindrical water phantom at 5.1 mm diameter and complex refraction coefficient n = 1 − δ + iβ = 1 −2.5604 × 10 −7 + i1.2353 × 10 −10 is placed in air to measure the edge transfer function, line spread function and then modulation transfer function MTF(k), of both DPC-CT and the conventional attenuation-based CT. The x-ray flux is set at 5 × 10 6 photon/cm 2 per projection and observes the Poisson distribution, which is consistent with that of a micro-CT for preclinical applications. Approximately 360 regions, each at 128 × 128 matrix, are used to calculate the NPS(k) via 2D Fourier transform, in which adequate zero padding is carried out to avoid aliasing in noise. Results:The preliminary data show that the DPC-CT possesses a signal transfer property [MTF(k)] comparable to that of the conventional attenuation-based CT. Meanwhile, though there exists a radical difference in their noise power spectrum NPS(k) (trait 1/|k| in DPC-CT but |k| in the conventional attenuation-based CT) the NEQ(k) and DQE(k) of DPC-CT and the conventional attenuation-based CT are in principle identical. Conclusions: Under the framework of ideal observer study, the joint signal and noise transfer property NEQ(k) and detective quantum efficiency DQE(k) of DPC-CT are essentially the same as those of the conventional attenuation-based CT. The findings reported in this paper may provide insightful guidelines on the research, development, and performance optimization o...

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“…Recently, an x-ray grating interferometric technique was developed to extract high quality differential phase images and dark-field images using a phase-stepping scan method [11]. In the x-ray grating-based tomographic imaging, the noise variance is inversely proportional to the third power of in-plane spatial resolution, and phase imaging may enable higher spatial resolution than absorption CT for the same noise variance level [12][13]. Dark-field images of biological specimens present significantly better contrast resolution than conventional attenuation-based images.…”

Section: Introductionmentioning

confidence: 99%

X-ray dark-field imaging modeling

et al. 2012

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Dark-field images are formed from x-ray small-angle scattering signals. The small-angle scattering signals are particularly sensitive to structural variation and density fluctuation on a length scale of several tens to hundreds of nanometers, offering a unique contrast mechanism to reveal subtle structural features of an object. In this study, based on the principle of energy conservation, we develop a physical model to describe the relationship between x-ray small-angle scattering coefficients of an object and dark-field intensity images. This model can be used to reconstruct volumetric x-ray small-angle scattering images of an object using classical tomographic algorithms. We also establish a relationship between the small-angle scattering intensity and the visibility function measured with x-ray grating imaging. The numerical simulations and phantom experiments have demonstrated the accuracy and practicability of the proposed model.

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Characterization of imaging performance in differential phase contrast CT compared with the conventional CT—Noise power spectrum NPS(k)

Abstract: The differential phase contrast CT detects the projection of refractive coefficient's derivative and uses the Hilbert filter for image reconstruction, which leads to the radical difference in its NPS and the advantage in noise in comparison to that of the conventional CT.

Cited by 47 publications

References 44 publications

Fundamental relationship between the noise properties of grating-based differential phase contrast CT and absorption CT: Theoretical framework using a cascaded system model and experimental validation

Fundamental relationship between the noise properties of grating-based differential phase contrast CT and absorption CT: Theoretical framework using a cascaded system model and experimental validation

Characterization of imaging performance in differential phase contrast CT compared with the conventional CT: Spectrum of noise equivalent quanta NEQ( k )

X-ray dark-field imaging modeling

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