Phantom study to evaluate contrast-medium-enhanced digital subtraction mammography with a full-field indirect-detection system
ABSTRACT This phantom study simulates contrast-medium-enhanced digital subtraction mammography (CEDM) and compares subtracted image quality and total mean glandular dose for two alternative spectral combinations available in a GE Senographe DS mammography unit. The first choice takes advantage of large iodine attenuation at low photon energies and uses traditionally available spectra (anode/filter combinations Mo/Mo at 25 kV and Rh/Rh at 40 kV, "Mo25-Rh40"). The second choice, selected from a previous analytical optimization, includes harder spectra obtained by adding external filtration to traditional beams (Rh/Rh at 34 kV and Rh/Rh+5 mm of Al at 45 kV, "Rh34-Rh45H"). Individual images of a custom-made phantom containing tubes of various diameters filled with water- or iodine-based contrast agent were acquired with both spectral combinations. The total breast entrance air kerma, considering subtraction of two images, was limited to 8.76 mGy (1 R). The results were compared to predictions obtained through an analytical formalism that assumes noise of stochastic origin. Individual images were evaluated and subtracted under five combinations of temporal and dual-energy modalities. Signal variance analysis in individual raw images showed important contributions of nonstochastic origin, associated with the software applied to raw images, the curved geometry, and strong attenuation of the phantom cylindrical iodine-filled tubes, causing experimental SNR to vary from 2.2 to 0.8 times the predictions from low to high values of SNR. Iodine contrast in the subtracted images was found to be mainly defined by the spectra, independent of exposure, and linearly dependent on the iodine mass thickness. The highest contrast was obtained with the combined dual-energy temporal subtraction with Rh34-Rh45H, its value was 7% larger than the highest value measured with Mo25-Rh40. As expected, temporal modalities (single and dual energy, any spectral choice) led to higher contrast-over-noise ratio (CNR) than nontemporal dual-energy subtraction, the latter being negligibly small with Mo25-Rh40. CNR for 4 mg iodine/cm2 imaged temporally in a dual-energy fashion with Rh34-Rh45H (iodine imaged at high energy) is about 1.7 times the optimum for Mo25-Rh40 (iodine imaged at low energy). Iodine thicknesses needed to fulfill Rose's criterion were 0.78 +/- 0.02 mg iodine/cm2 for Mo25-Rh40 and 0.54 +/- 0.17 mg iodine/cm2 for Rh34-Rh45H, both lower than the proposed biological concentration of iodine in breast tumors after contrast medium administration. Although similar dose levels were obtained with both spectral choices under dual-energy (temporal and nontemporal) subtraction, the dose obtained in single-energy temporal subtraction with the Mo25 spectrum was 1.2 mGy lower than the dose from the modality offering the highest CNR. In all results considered, the spectral choice Mo25-Rh40 was found to represent an interesting alternative to the use of high-energy hardened spectra for CEDM, particularly when performing dynamic studies of the contrast-agent uptake in breast lesions.
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ABSTRACT: Phantoms containing iodine details with clinically relevant iodine concentrations are required to systematically study dose requirements, for quality assurance and optimizing exposure parameters and protocols for contrast enhanced dual energy mammography (CEDEM) applications. Most such phantoms use liquid iodine solutions, challenging the user with air inclusions, evaporation or the necessity for changing the iodine concentration through refilling. A prototype phantom with an array of sintered solid iodine-containing platelets with iodine area weights of 0, 0.25, 0.5, 1, 1.5 and 2 mg cm(-2) is described. Disks containing various iodine concentrations were produced using polymer sintering of Iopamidol embedded into a polystyrene/graphite matrix. Iopamidol-containing platelets with a diameter of 0.5 cm and thickness of 550 µm forming an array with gradually increasing iodine area weight, were embedded in PMMA to allow statistical analysis of contrast and contrast-to-noise ratio (CNR). The homogeneity of the plates was tested and images of the phantom were acquired to assess the iodine area density progression and to evaluate phantom accuracy. The phantom was imaged on a mammography system applying low and high energy spectra as used for CEDEM. The disks show good homogeneity. Uncertainties in absolute iodine area weight were estimated ±5%. The iodine CNR showed a linear correlation with R(2) > 0.99. Polymer powder sintering works well for producing stable iodine contrast phantoms without the necessity to handle liquid iodine solutions. Thus, it is a promising approach to construct phantoms not only for CEDEM but also angiography or other contrast enhanced methods with iodine details for quality control or research purposes and optimization.Physics in Medicine and Biology 01/2013; 58(3):N25-N35. DOI:10.1088/0031-9155/58/3/N25 · 2.92 Impact Factor
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ABSTRACT: An easily implementable tissue cancellation method for dual energy mammography is proposed to reduce anatomical noise and enhance lesion visibility. For dual energy calibration, the images of an imaging object are directly mapped onto the images of a customized calibration phantom. Each pixel pair of the low and high energy images of the imaging object was compared to pixel pairs of the low and high energy images of the calibration phantom. The correspondence was measured by absolute difference between the pixel values of imaged object and those of the calibration phantom. Then the closest pixel pair of the calibration phantom images is marked and selected. After the calibration using direct mapping, the regions with lesion yielded different thickness from the background tissues. Taking advantage of the different thickness, the visibility of cancerous lesions was enhanced with increased CNR, depending on the size of lesion and breast thickness. However, some tissues near the edge of imaged object still remained after tissue cancellation. These remaining residuals seem to occur due to the heel effect, scattering, non-parallel Xray beam geometry and Poisson distribution of photons. To improve its performance further, scattering and the heel effect should be compensated.09/2013; 33(1). DOI:10.1109/TMI.2013.2280901
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ABSTRACT: The degree of vascularization in breast lesions is related to their malignancy. For this reason, functional diagnostic imaging techniques have become important in recent years. Dual-energy contrast-enhanced mammography is a new, apparently promising technique in breast cancer that provides information about the degree of vascularization of the lesion in addition to the morphological information provided by conventional mammography. This article describes the state of the art for dual-energy contrast-enhanced mammography. Based on 15 months' clinical experience, we illustrate this review with clinical cases that allow us to discuss the advantages and limitations of this technique.07/2014; 56(5). DOI:10.1016/j.rxeng.2014.05.007