Exploring silver as a contrast agent for contrast-enhanced dual-energy X-ray breast imaging

Abstract

Cite this article as: Karunamuni R, Tsourkas A, Maidment ADA. Exploring silver as a contrast agent for contrast-enhanced dual-energy X-ray breast imaging. Br J Radiol 2014;87:20140081. FULL PAPER Exploring silver as a contrast agent for contrast-enhanced dual-energy X-ray breast imaging Objective: Through prior monoenergetic modelling, we have identified silver as a potential alternative to iodine in dual-energy (DE) X-ray breast imaging. The purpose of this study was to compare the performance of silver and iodine contrast agents in a commercially available DE imaging system through a quantitative analysis of signal difference-to-noise ratio (SDNR). Methods: A polyenergetic simulation algorithm was developed to model the signal intensity and noise. The model identified the influence of various technique parameters on SDNR. The model was also used to identify the optimal imaging techniques for silver and iodine, so that the two contrast materials could be objectively compared. Results: The major influences on the SDNR were the lowenergy dose fraction and breast thickness. An increase in the value of either of these parameters resulted in a decrease in SDNR. The SDNR for silver was on average 43% higher than that for iodine when imaged at their respective optimal conditions, and 40% higher when both were imaged at the optimal conditions for iodine. Conclusion: A silver contrast agent should provide benefit over iodine, even when translated to the clinic without modification of imaging system or protocol. If the system were slightly modified to reflect the lower k-edge of silver, the difference in SDNR between the two materials would be increased. Advances in knowledge: These data are the first to demonstrate the suitability of silver as a contrast material in a clinical contrast-enhanced DE image acquisition system.Contrast-enhanced (CE) dual-energy (DE) X-ray breast imaging provides quantitative functional information with high-resolution anatomical data in a single imaging procedure. DE images can be used to identify tumour neovasculature and morphology, and consequently aid in the detection and diagnosis of breast cancer. [1][2][3][4][5][6][7] The most widely used approach for DE imaging is k-edge imaging. In this technique, two distinct energy spectra [low energy (LE) and high energy (HE)] are placed on either side of the kedge of the contrast material. Through a weighted subtraction of the LE and HE images, it is possible to suppress the anatomical background signal and enhance the visualization of the contrast agent. The total dose of the two images is judiciously allocated so as to maximize the visibility of the contrast agent while providing an anatomical image of diagnostic quality. DE X-ray breast imaging has been shown to aid visualization of lesions that are otherwise mammographically occult as well as to provide functional blood flow information consistent with MRIthe current gold standard in functional breast imaging.

Gold silver alloy nanoparticles (GSAN): an imaging probe for breast cancer screening with dual-energy mammography or computed tomography

“…3,4 While all soft tissues have similar ratios of attenuation between the low and high energy x-ray images, the contrast agents used have higher attenuation in the high energy window, due to their k-edge. 8 A logarithmically weighted image subtraction is done to create a DE image. The signal from the breast tissue is suppressed and that from the contrast agent is enhanced.…”

“…8 It has been shown via experiments that silver nanoparticles produce 40% more contrast than iodine in DEM phantom imaging. 8 Proof of concept imaging was done in mice with silica-coated silver nanoparticles. The results confirmed that silver nanoparticles produce strong DEM contrast in vivo .…”

Development of silica-encapsulated silver nanoparticles as contrast agents intended for dual-energy mammography

“…A weighting factor, W , was applied to the LE image in order to remove the background structures (bone, soft tissue) in the DE image. W was calculated to be analogous to previous formulations [14], using the average signal intensities ( SI ) of the bone and soft tissue regions: $$W=\frac{\text{ln}false(S{I}_b^{HE}false)-\text{ln}false(S{I}_s^{HE}false)}{\text{ln}false(S{I}_b^{LE}false)-\text{ln}false(S{I}_s^{LE}false)}.$$ …”

“…Silver (Ag) has been identified as a new candidate agent for DE mammography that can provide more contrast than iodine at clinically utilized imaging parameters [14–16]. The lower k-edge energy of silver (25.5 keV) provides two key benefits.…”

“…Second, there is greater flexibility in the choice of the HE spectrum, allowing for optimal selection. Analytic modelling together with experimental validation in phantoms [14; 16] demonstrate that if the established technique parameters currently utilized in the clinic are considered, silver provides higher values of signal difference-to-noise ratio (SDNR) than iodine. In particular, the SDNR of silver was found to be 43% higher than that of iodine when using the optimal DE imaging parameters for each contrast agent [15].…”