Generalizing the MTF and DQE to include x-ray scatter and focal spot unsharpness: Application to a new microangiographic system

Kyprianou, Iacovos S.; Rudin, Stephen; Bednarek, Daniel R.; Hoffmann, Kenneth R.

doi:10.1118/1.1844151

Cited by 76 publications

(91 citation statements)

References 37 publications

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“…We define q o (X, m) = m 2 q in (X) = m 2 Xϕ in which is the photon fluence at a given magnification, for a given scatter fraction ρ, at a detector entrance exposure X. The GDQE can be defined by dividing the GNEQ with q o (ρ, X, m) (8) The zero frequency of the GDQE(0) is the same as the detector DQE D (0), therefore the GDQE is consistent with the definition of the detector DQE D . As the scatter fraction ρ goes to zero, only the primary radiation enters the detector, and as magnification m goes to 1, there are no effects from the focal spot, hence the detection efficiency is determined solely by the detector.…”

Section: The Generalized System Quantitiesmentioning

confidence: 99%

“…Here we also focus on the theoretical definitions of the generalized functions, as well as presenting the results obtained from the detectability simulations. The experimental methodology for obtaining and analyzing the data is rigorously presented in reference (8). Other factors such as patient motion blur and image lag are not investigated here.…”

Section: Introductionmentioning

confidence: 99%

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Study of the generalized MTF and DQE for a new microangiographic system

et al. 2004

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We study the properties of a new microangiographic system, consisting of a Region of Interest (ROI) microangiographic detector, x-ray source, and patient. The study was performed under conditions intended for clinical procedures such as neurological diagnostic angiograms as well as treatments of intracranial aneurysms, and vessel-stenoses. The study was performed in two steps; first a uniform head equivalent phantom was used as a "filter". This allowed us to study the properties of the detector alone, under clinically relevant x-ray spectra. We report the detector MTF, NPS, NEQ, and DQE for beam energies ranging from 60-100kVp and for different detector entrance exposures. For the second step, the phantom was placed adjacent to the detector, allowing scatter to enter the detector and new measurements were obtained for the same beam energies and detector entrance exposures. Different radiation field sizes were studied, and the effects of different scatter amounts were investigated. The spatial distribution of scatter was studied using the edge-spread method and a generalized system MTF was obtained by combining the scatter MTF weighted by the scatter fraction with the detector MTF and focal spot unsharpness due to magnification. The NPS combined with the generalized MTF gave the generalized system NEQ and DQE. The generalized NEQ and the ideal object detectability were used to calculate the Dose Area Product to the patient for 75% object detection probability. This was used as a system optimization method.

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Section: The Generalized System Quantitiesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Study of the generalized MTF and DQE for a new microangiographic system

et al. 2004

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“…10 It is 12 inch × 12 inch square and consists of 3.2mm thick Al and 6 inches thick PMMA; the phantom was clinically verified to be nearly equivalent to an average human head. 11 A focal spot of 0.6 mm was used for this simulated study of neurovascular angiography. An antiscatter grid with grid ratio 10:1 (line rate 44 l/cm, focus distance 100 cm, absorption material 0.036 mm Pb and fiber inter-space material) was employed with the image intensifier to reduce the amount of scatter reaching the detector.…”

Section: X-ray System and Experimental Set Upmentioning

confidence: 99%

Generalized performance evaluation of x-ray image intensifier compared with a microangiographic system

Yadava

Kyprianou

Rudin

et al. 2005

Medical Imaging 2005: Physics of Medical Imaging

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Standard objective parameters such as MTF, NPS, NEQ and DQE do not reflect complete system performance, because they do not account for geometric unsharpness due to finite focal spot size and scatter due to the patient. The inclusion of these factors led to the generalization of the objective quantities, termed GMTF, GNNPS, GNEQ and GDQE defined at the object plane. In this study, a commercial x-ray image intensifier (II) is evaluated under this generalized approach and compared with a high-resolution, ROI microangiographic system previously developed and evaluated by our group. The study was performed using clinically relevant spectra and simulated conditions for neurovascular angiography specific for each system. A head-equivalent phantom was used, and images were acquired from 60 to 100 kVp. A source to image distance of 100 cm (75 cm for the microangiographic system) and a focal spot of 0.6 mm were used. Effects of varying the irradiation field-size, the air-gaps, and the magnifications (1.1 to 1.3) were compared. A detailed comparison of all of the generalized parameters is presented for the two systems. The detector MTF for the microangiographic system is in general better than that for the II system. For the total x-ray imaging system, the GMTF and GDQE for the II are better at low spatial frequencies, whereas the microangiographic system performs substantially better at higher spatial frequencies. This generalized approach can be used to more realistically evaluate and compare total system performance leading to improved system designs tailored to the imaging task.

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“…The transfer function related to the finite width of the x-ray focal spot (T 0 ) is a source of blur for systems with geometric magnification. 57,59,60 Although T 0 degrades the system MTF [and therefore the NEQ based on Eq. (2.8)], it does not influence the noise characteristics.…”

Section: Iiia Cascaded System Model For Dpc-ct and Act Acquisitionsmentioning

confidence: 99%

“…23 These include the transfer functions associated with the spread of secondary quanta in the scintillator (T 3 ), the integration of secondary quanta within the finite pixel aperture (T 5 ), the apodization filter during the reconstruction (T 11 ), and the interpolation during the reconstruction (T 12 ). In addition, there is a transfer function T 0 associated with the system magnification M and the focal spot MTF T spot by 57,60 …”

Section: Iiic Characterizing the Performance Of The Dpc-ct And Act mentioning

confidence: 99%

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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Generalizing the MTF and DQE to include x-ray scatter and focal spot unsharpness: Application to a new microangiographic system

Cited by 76 publications

References 37 publications

Study of the generalized MTF and DQE for a new microangiographic system

Study of the generalized MTF and DQE for a new microangiographic system

Generalized performance evaluation of x-ray image intensifier compared with a microangiographic system

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

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