Signal-to-noise optimization of medical imaging systems

Cunningham, Ian; Shaw, Rodney

doi:10.1364/josaa.16.000621

Cited by 167 publications

(121 citation statements)

References 47 publications

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“…Ongoing developments in the spatial domain methods include means of reducing the bias in estimates of d when the sample size is small. [73][74][75] In various previous studies aimed at system development and optimization (including this work), [76][77][78][79] the Fourier approach has been employed for reasons of practicality, computational speed, and the ability to estimate the MTF, NPS, and d with a small sample of realizations. The performance of the Fourier approach was found to be reasonable when only a small sample size is available, for example, d calculated from 10 samples (in a 49 × 49 ROI) was within 12.0% of that calculated using 30 000 samples (0.5 cm sphere detection task in location 1 of the Thorax phantom).…”

Section: Appendix: Assessment Of Spatial Localitymentioning

confidence: 99%

Task‐based detectability in CT image reconstruction by filtered backprojection and penalized likelihood estimation

et al. 2014

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Purpose: Nonstationarity is an important aspect of imaging performance in CT and cone-beam CT (CBCT), especially for systems employing iterative reconstruction. This work presents a theoretical framework for both filtered-backprojection (FBP) and penalized-likelihood (PL) reconstruction that includes explicit descriptions of nonstationary noise, spatial resolution, and task-based detectability index. Potential utility of the model was demonstrated in the optimal selection of regularization parameters in PL reconstruction. Methods: Analytical models for local modulation transfer function (MTF) and noise-power spectrum (NPS) were investigated for both FBP and PL reconstruction, including explicit dependence on the object and spatial location. For FBP, a cascaded systems analysis framework was adapted to account for nonstationarity by separately calculating fluence and system gains for each ray passing through any given voxel. For PL, the point-spread function and covariance were derived using the implicit function theorem and first-order Taylor expansion according to Fessler ["Mean and variance of implicitly defined biased estimators (such as penalized maximum likelihood): Applications to tomography," IEEE Trans. Image Process. 5(3), 493-506 (1996)]. Detectability index was calculated for a variety of simple tasks. The model for PL was used in selecting the regularization strength parameter to optimize task-based performance, with both a constant and a spatially varying regularization map. Results: Theoretical models of FBP and PL were validated in 2D simulated fan-beam data and found to yield accurate predictions of local MTF and NPS as a function of the object and the spatial location. The NPS for both FBP and PL exhibit similar anisotropic nature depending on the pathlength (and therefore, the object and spatial location within the object) traversed by each ray, with the PL NPS experiencing greater smoothing along directions with higher noise. The MTF of FBP is isotropic and independent of location to a first order approximation, whereas the MTF of PL is anisotropic in a manner complementary to the NPS. Task-based detectability demonstrates dependence on the task, object, spatial location, and smoothing parameters. A spatially varying regularization "map" designed from locally optimal regularization can improve overall detectability beyond that achievable with the commonly used constant regularization parameter. Conclusions: Analytical models for task-based FBP and PL reconstruction are predictive of nonstationary noise and resolution characteristics, providing a valuable framework for understanding and optimizing system performance in CT and CBCT.

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Section: Appendix: Assessment Of Spatial Localitymentioning

confidence: 99%

Task‐based detectability in CT image reconstruction by filtered backprojection and penalized likelihood estimation

et al. 2014

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“…(2.7), the units of the NPS depend on the units of the image signal and thus are different between ACT and DPC-CT. By expressing the image noise in terms of the number of Poisson-distributed photons per unit length/area at each spatial frequency, an absolute scale of noise, the NEQ, can be introduced. 45 The frequency-dependent NEQ of a 2D axial CT is given by 42,43 …”

Section: Iic Noise Equivalent Quantamentioning

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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“…The rotation thus prevents damage to the anode and permits large tube currents to be used so that sufficient x-ray photons can be generated to produce high-quality images. 25 The images are of high quality because producing more photons enables high signal-to-noise ratio images to be produced over short exposure times, which is critical for typical cineangiography needed in percutaneous aortic valve replacement procedures.…”

Section: Principle Of X-ray Tube Motor Operationmentioning

confidence: 99%

Closed bore XMR (CBXMR) systems for aortic valve replacement: Investigation of rotating‐anode x‐ray tube heat loadability

et al. 2008

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In order to improve the safety and efficacy of percutaneous aortic valve replacement procedures, a closed bore hybrid x-ray/MRI ͑CBXMR͒ system is proposed in which an x-ray C-arm will be positioned with its isocenter Ϸ1 m from the entrance of a clinical MRI scanner. This system will harness the complementary strengths of both modalities to improve clinical outcome. A key component of the CBXMR system will be a rotating anode x-ray tube to produce high-quality x-ray images. There are challenges in positioning an x-ray tube in the magnetic fringe field of the MRI magnet. Here, the effects of an external magnetic field on x-ray tube induction motors of radiography x-ray tubes and the corresponding reduction of x-ray tube heat loadability are investigated. Anode rotation frequency f anode was unaffected when the external magnetic field B b was parallel to the axis of rotation of the anode but decreased when B b was perpendicular to the axis of rotation. The experimental f anode values agreed with predicted values to within Ϯ3% over a B b range of 0 -30 mT. The MRI fringe field at the proposed location of the x-ray tube mounted on the C-arm ͑Ϸ4 mT͒ reduced f anode by only 1%, so x-ray tube heat loadability will not be compromised when using CBXMR systems for percutaneous aortic valve replacement procedures. Eddy current heating power in the rotor due to an MRI fringe field was found to be two orders of magnitude weaker than the heating power produced on the anode due to a fluoroscopic exposure, so eddy current heating had no effect on x-ray tube heat loadability.

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Signal-to-noise optimization of medical imaging systems

Cited by 167 publications

References 47 publications

Task‐based detectability in CT image reconstruction by filtered backprojection and penalized likelihood estimation

Task‐based detectability in CT image reconstruction by filtered backprojection and penalized likelihood estimation

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

Closed bore XMR (CBXMR) systems for aortic valve replacement: Investigation of rotating‐anode x‐ray tube heat loadability

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