Theoretical comparison of energy‐resolved and digital‐subtraction angiography

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BackgroundDual‐energy (DE) x‐ray angiography with photon‐counting detectors (PCDs) may enable single‐exposure DE imaging of coronary vasculature.PurposeTo compare the iodine signal‐difference‐to‐noise ratio (SDNR) of single‐exposure DE angiography with digital subtraction angiography (DSA) and kV‐switching DE angiography for matched patient x‐ray exposure.MethodsIn a phantom study, we determined the technique parameters that maximized the iodine SDNR per root entrance air kerma for DSA, kV‐switching DE angiography and single‐exposure DE angiography. We measured SDNR from images of a phantom consisting of an iodine step‐wedge immersed in a water tank of either 20 or 30 cm in thickness. We also imaged a phantom with simulated vessels embedded in background clutter and measured vessel SDNR. For this second phantom, we also applied anti‐correlated noise reduction (ACNR) and calculated the resulting iodine SDNR. All images were acquired using a cadmium telluride PCD with two energy bins and analog charge summing for charge sharing suppression. The energy‐discrimination capabilities were only used for the single‐exposure DE approach. Optimized techniques were compared in terms of SDNR per root air kerma for two levels of x‐ray scatter.ResultsFor the same patient x‐ray exposure, the SDNR of single‐exposure DE imaging without ACNR was 75% to 85% of that of kV‐switching DE imaging (also without ACNR) and DSA, the latter two of which had nearly equal SDNR. The single‐exposure DE approach required ∼50% of the tube load of the kV‐switching approach to achieve the same SDNR. For matched patient air kermas, the single exposure approach required only ∼25% of the tube load of the kV‐switching approach. ACNR increased SDNR by 2.4 and 3.0 for kV‐switching and single‐exposure DE imaging, respectively.ConclusionsPhoton‐counting, single‐exposure DE angiography can suppress soft tissues and provide iodine SDNR levels comparable to DSA and kV‐switching DE angiography for matched patient radiation exposures. When ACNR is used to reduce DE image noise, the SDNR of single‐exposure DE imaging and kV‐switching DE imaging exceed that of DSA by more than a factor of two. Compared to kV‐switching DE imaging, single‐exposure DE imaging requires substantially lower tube loading to achieve the same SDNR.

Section: Discussioncontrasting

confidence: 54%

Section: Introductionmentioning

confidence: 99%

Signal‐difference‐to‐noise comparison of temporal subtraction, kV‐switching dual‐energy and photon‐counting dual‐energy x‐ray angiography

Aubert,

Tanguay

2023

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“…Larger reductions in image quality are expected for systems that do not implement ACS for charge-sharing correction. For example, in a study of contrast-enhanced vascular imaging, Aubert et al 41 showed that removing ACS degraded iodine SNR by a factor of two. Given that the count rates in mammography are low enough to be able to use ACS with negligible pulse pile-up, that ACS technology is available, and that not using ACS will likely result in substantial image quality reductions,we expect ACS to be implemented if CdTe PCDs become clinically-available.…”

Section: Discussionmentioning

confidence: 99%

Monte‐Carlo study of contrast‐enhanced spectral mammography with cadmium telluride photon‐counting x‐ray detectors

Day,

Tanguay

2023

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BackgroundContrast‐enhanced spectral mammography (CESM) with photon‐counting x‐ray detectors (PCDs) can be used to improve the classification of breast cancers as benign or malignant. Commercially‐available PCD‐based mammography systems use silicon‐based PCDs. Cadmium‐telluride (CdTe) PCDs may provide a practical advantage over silicon‐based PCDs because they can be implemented as large‐area detectors that are more easily adaptable to existing mammography systems.PurposeThe purpose of this work is to optimize CESM implemented with CdTe PCDs and to investigate the influence of the number of energy bins, electronic noise level, pixel size, and anode material on image quality.MethodsWe developed a Monte Carlo model of the energy‐bin‐dependent modulation transfer functions (MTFs) and noise power spectra, including spatioenergetic noise correlations. We validated model predictions using a CdTe PCD with analog charge summing for charge‐sharing suppression. Using the ideal‐observer detectability, we optimized CESM for the task of detecting a 7‐mm‐diameter iodine nodule embedded in a breast with 50% glandularity. We optimized the tube voltage, beam filtration, and the location of energy thresholds for 50 and 100‐μm pixels, tungsten and molybdenum anodes, and two electronic noise levels. One of the electronic noise levels was that of the experimental system; the other was half that of the experimental system. Optimization was performed for CdTe PCDs with two or three energy bins. We also estimated the impact of anatomic noise due to background parenchymal enhancement and computed the minimum detectable iodine area density in the presence of quantum and anatomic noise.ResultsModel predictions of the MTFs and noise power spectra agreed well with experiment. For optimized systems, adding a third energy bin increased quantum noise levels and reduced detectability by ∼55% compared to two‐bin approaches that simply suppress contrast between fibroglandular and adipose tissue. Decreasing the electronic noise standard deviation from 3.4 to 1.7 keV increased iodine detectability by ∼5% and ∼30% for two‐bin imaging and three‐bin imaging, respectively. After optimizing for tube voltage, beam filtration, and the location of energy thresholds, there was ∼a 3% difference in iodine detectability between molybdenum and tungsten anodes for two‐bin imaging, but for three‐bin imaging, molybdenum anodes provided up to 14% increase in detectability relative to tungsten anodes. Anatomic noise decreased iodine detectability by 15% to 40%, with greater impact for lower electronic noise settings and larger pixel sizes.ConclusionsFor CESM implemented with CdTe PCDs, (1) quantitatively‐accurate three‐material decompositions using three energy bins are associated with substantial increases in quantum noise relative to two‐energy‐bin approaches that simply suppress contrast between fibroglandular and adipose tissues; (2) tungsten and molybdenum anodes can provide nearly equal iodine detectability for two‐bin imaging, but molybdenum provides a modest detectability advantage for three‐bin imaging provided that all other technique parameters are optimized; (3) reducing pixel sizes from 100 to 50 μm can reduce detectability by up to 20% due to charge sharing; (4) anatomic noise due to background parenchymal enhancement is estimated to have a substantial impact on lesion visibility, reducing detectability by approximately 30%.

“…We showed that, in theory, ideal photon counting x‐ray detectors can suppress soft‐tissues and produce iodine CNR almost equal to that of DSA and DE kV‐switching approaches for matched patient exposures 15 . More recently, we investigated the effect of charge sharing and other non‐idealities, including electronic noise and non‐unity quantum efficiency, on the image quality of x‐ray angiography implemented with cadmium telluride (CdTe) photon‐counting x‐ray detectors 20,21 . We investigated three‐material decompositions that suppress bone and soft‐tissue but found substantial reductions in image quality relative to DSA, even for ideal photon‐counting detectors.…”

Section: Introductionmentioning

confidence: 99%

“…15 More recently, we investigated the effect of charge sharing and other non-idealities, including electronic noise and non-unity quantum efficiency, on the image quality of x-ray angiography implemented with cadmium telluride (CdTe) photon-counting x-ray detectors. 20,21 We investigated three-material decompositions that suppress bone and soft-tissue but found substantial reductions in image quality relative to DSA,even for ideal photon-counting detectors.…”

Section: Introductionmentioning

confidence: 99%

Experimental optimization of single‐exposure dual‐energy angiography with photon‐counting x‐ray detectors

Aubert

Tanguay

2022

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Background: Photon-counting x-ray detectors may enable single-exposure dual-energy (DE) x-ray angiography. Purpose: The purpose of this paper is to experimentally optimize the energy thresholds and tube voltage for single-exposure DE x-ray angiography. Methods: We optimized single-exposure DE x-ray angiography using the iodine signal-difference-to-noise ratio (SDNR) per root patient air kerma (𝜅) as a figure of merit. We measured the iodine SDNR by imaging an iodine stepwedge immersed in a water tank with a depth of 30 cm in the direction of x-ray propagation. The stepwedge was imaged using tube voltages ranging from 90 to 150 kV and a cadmium telluride (CdTe) x-ray detector with two energy bins and analog charge summing for charge sharing suppression. The energy threshold that separates the two energy bins was varied from approximately 35 keV to approximately 75% of the maximum energy of the x-ray beam. Curve fitting was used to determine the threshold that maximized SDNR∕ √ 𝜅. The effect of scatter was determined from measurements of the scatter-to-primary ratios (SPRs) of the low-energy and high-energy images and a semi-empirical model of the relationship between SDNR and SPR. Using the optimal parameters, we imaged a phantom with vessel-simulating structures and background clutter. Results:The optimal energy thresholds increased monotonically from ∼50 to ∼85 keV over the range of tube voltages considered. For tube voltages greater than 90 kV, the optimal energy thresholds consistently allocated approximately two thirds of all detected primary photons to the low energy bin; this ratio was preserved without scatter. Consistent with prior modeling studies, SDNR∕ √ 𝜅 increased monotonically with tube voltage from 90 to 150 kV; SDNR∕ √ 𝜅 at 150 kV was approximately 38% higher than that at 90 kV for an iodine area density of ∼50 mg/cm 2 . Scatter reduced SDNR by approximately 25% for SPRs of ∼1 and 0.4 in low-energy and high-energy images, respectively. Conclusions: Achieving optimal image quality in single-exposure DE angiography with photon-counting x-ray detectors will require high tube voltages (i.e., >130 kV) and, for thick patients, energy thresholds that allocate approximately two thirds of all primary photons to the low-energy image. Future work will compare the image quality of singe-exposure photon-counting and kV-switching approaches to DE x-ray angiography.