Quantification of scattered radiation in projection mammography: Four practical methods compared

Salvagnini, Elena; Bosmans, Hilde; Struelens, Lara; Marshall, Nicholas

doi:10.1118/1.4711754

Cited by 37 publications

(39 citation statements)

References 40 publications

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“…The primary and scatter transmissions, T p and T s , used for the scatter removal were estimated from the simulation as a function of PMMA thickness, shown in Table 3. The average scatter and primary transmissions over different PMMA thicknesses are 0.137 and 0.756, respectively, which agree well with the results of 0.13 and 0.75 measured by Salvagnini et al, 21 with the same grid and anode-filter combination. Figure 5(c) is the corrected image I c obtained by subtracting the scatter field from the original image.…”

Section: Theoretical Resultssupporting

confidence: 81%

“…3, the dose reduction factor D as a function of PMMA thickness, based on the theoretical model and the data published by Salvagnini et al, 21 is compared with the results by Åslund et al, 17 which were derived from the screen-film data. The breast thicknesses in Åslund et al's study were converted into the equivalent PMMA thicknesses using the conversion factors described by Dance et al 27 The dose reduction factor D was fitted as a linear function of PMMA thickness.…”

Section: Theoretical Resultsmentioning

confidence: 99%

“…The grid in the system is the same one used in Salvagnini et al's study. 21 PMMA layers 2 to 8 cm thick in 1-cm steps simulated breasts of different thicknesses. The SDNR values were determined by a 4 × 8 cm 2 , 0.2 mm Al filter placed on top of the PMMA with its left edge superimposed on the center line of the PMMA layers (Fig.…”

Section: Phantom Studymentioning

confidence: 99%

“…If the photons exited from the bottom of the PMMA layers, their positions on the detector plane were recorded as they passed through the air gap. We assumed that the deposited energy of each photon Table 1 The scatter-to-primary ratios with and without a grid (SPR grid and SPR) and the primary transmission T p , measured as a function of PMMA thickness by Salvagnini et al 21 on a full-field digital system. These values are the average results over the different tube potentials of 26, 28, 30, and 32 kV.…”

Section: Monte Carlo Simulationmentioning

confidence: 99%

“…We calculated the factor K with the values of SPR, SPR grid , and T p measured by Salvagnini et al 21 as a function of poly (methyl methacrylate) (PMMA) thickness using the beamstop method on a digital mammography system, Siemens MAMMOMAT Inspiration. The system has a common linear grid, with a lead septa of 5:1 ratio and strip density of 31 lines∕cm.…”

Section: Theoretical Modelmentioning

confidence: 99%

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On image quality metrics and the usefulness of grids in digital mammography

et al. 2015

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Abstract. Antiscatter grids are used in digital mammography to reduce the scattered radiation from the breast and improve image contrast. They are, however, imperfect and lead to partial absorption of primary radiation, as well as failing to absorb all scattered radiation. Nevertheless, the general consensus has been that antiscatter grids improve image quality for the majority of breast types and sizes. There is, however, inconsistency in the literature, and recent results show that a substantial image quality improvement can be achieved even for thick breasts if the grid is disposed of. The purpose of this study was to investigate if differences in the considered imaging task and experimental setup could explain the different outcomes. We estimated the dose reduction that can be achieved if the grid were to be removed as a function of breast thickness with varying geometries and experimental conditions. Image quality was quantified by the signal-difference-to-noise ratio (SDNR) measured using an aluminum (Al) filter on blocks of poly(methyl methacrylate) (PMMA), and images were acquired with and without grid at a constant exposure. We also used a theoretical model validated with Monte Carlo simulations. Both theoretically and experimentally, the main finding was that when a large 4 × 8 cm 2 Al filter was used, the SDNR values for the gridless images were overestimated up to 25% compared to the values for the small 1 × 1 cm 2 filter, and gridless imaging was superior for any PMMA thickness. For the small Al filter, gridless imaging was only superior for PMMAs thinner than 4 cm. This discrepancy can be explained by a different sensitivity to and sampling of the angular scatter spread function, depending on the size of the contrast object. The experimental differences were eliminated either by using a smaller region of interest close to the edge of the large filter or by applying a technique of scatter correction by subtracting the estimated scatter image. These results explain the different conclusions reported in the literature and show the importance of the selection of measurement methods. Since the interesting structures in mammography are below the 1-cm scale, we advocate the use of smaller contrast objects for assessment of antiscatter grid performance.

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Section: Theoretical Resultssupporting

confidence: 81%

Section: Theoretical Resultsmentioning

confidence: 99%

Section: Phantom Studymentioning

confidence: 99%

Section: Monte Carlo Simulationmentioning

confidence: 99%

Section: Theoretical Modelmentioning

confidence: 99%

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On image quality metrics and the usefulness of grids in digital mammography

et al. 2015

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A novel method for quantification of beam's‐eye‐view tumor tracking performance

Myronakis

Rottmann

et al. 2017

Medical Physics

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Purpose In-treatment imaging using an electronic portal imaging device (EPID) can be used to confirm patient and tumor positioning. Real-time tumor tracking performance using current digital megavolt (MV) imagers is hindered by poor image quality. Novel EPID designs may help to improve quantum noise response, while also preserving the high spatial resolution of the current clinical detector. Recently investigated EPID design improvements include but are not limited to multi-layer imager (MLI) architecture, thick crystalline and amorphous scintillators, and phosphor pixilation and focusing. The goal of the present study was to provide a method of quantifying improvement in tracking performance as well as to reveal the physical underpinnings of detector design that impact tracking quality. The study employs a generalizable ideal observer methodology for the quantification of tumor tracking performance. The analysis is applied to study both the effect of increasing scintillator thickness on a standard, single-layer imager (SLI) design as well as the effect of MLI architecture on tracking performance. Methods The present study uses the ideal observer signal-to-noise ratio (d′) as a surrogate for tracking performance. We employ functions which model clinically relevant tasks and generalized frequency-domain imaging metrics to connect image quality with tumor tracking. A detection task for relevant Cartesian shapes (i.e. spheres and cylinders) was used to quantify trackability of cases employing fiducial markers. Automated lung tumor tracking algorithms often leverage the differences in benign and malignant lung tissue textures. These types of algorithms (e.g. soft tissue localization – STiL) were simulated by designing a discrimination task, which quantifies the differentiation of tissue textures, measured experimentally and fit as a power-law in trend (with exponent β) using a cohort of MV images of patient lungs. The modeled MTF and NPS were used to investigate the effect of scintillator thickness and MLI architecture on tumor tracking performance. Results Quantification of MV images of lung tissue as an inverse power-law with respect to frequency yields exponent values of β = 3.11 and 3.29 for benign and malignant tissues, respectively. Tracking performance with and without fiducials was found to be generally limited by quantum noise, a factor dominated by quantum detective efficiency (QDE). For generic SLI construction, increasing the scintillator thickness (gadolinium oxysulfide – GOS) from a standard 290 μm to 1720 μm reduces noise to about 10%. However, 81% of this reduction is appreciated between 290 and 1000 μm. In comparing MLI and SLI detectors of equivalent individual GOS layer thickness, the improvement in noise is equal to the number of layers in the detector (i.e. 4) with almost no difference in MTF. Further, improvement in tracking performance was slightly less than the square-root of the reduction in noise, approximately 84–90%. In comparing an MLI detector with an SLI with a GOS scintillator of...

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

Day,

Tanguay

2023

Medical Physics

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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%.

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Quantification of scattered radiation in projection mammography: Four practical methods compared

Cited by 37 publications

References 40 publications

On image quality metrics and the usefulness of grids in digital mammography

On image quality metrics and the usefulness of grids in digital mammography

A novel method for quantification of beam's‐eye‐view tumor tracking performance

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

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