Effect of x-ray energy on the radiological image quality in propagation-based phase-contrast computed tomography of the breast

Abstract

<p><b>Purpose:</b> Breast cancer is the most common cancer in women in developing and developed countries and is responsible for 15% of women’s cancer deaths worldwide. Conventional absorption-based breast imaging techniques lack sufficient contrast for comprehensive diagnosis. Propagation-based phase-contrast computed tomography (PB-CT) is a developing technique that exploits a more contrast-sensitive property of x-rays: x-ray refraction. X-ray absorption, refraction, and contrast-to-noise in the corresponding images depend on the x-ray energy used, for the same/fixed radiation dose. The aim of this paper is to explore the relationship between x-ray energy and radiological image quality in PB-CT imaging.</p> <p><b>Approach:</b> Thirty-nine mastectomy samples were scanned at the imaging and medical beamline at the Australian Synchrotron. Samples were scanned at various x-ray energies of 26, 28, 30, 32, 34, and 60 keV using a Hamamatsu Flat Panel detector at the same object-to-detector distance of 6 m and mean glandular dose of 4 mGy. A total of 132 image sets were produced for analysis. Seven observers rated PB-CT images against absorption-based CT (AB-CT) images of the same samples on a five-point scale. A visual grading characteristics (VGC) study was used to determine the difference in image quality.</p> <p><b>Results:</b> PB-CT images produced at 28, 30, 32, and 34 keV x-ray energies demonstrated statistically significant higher image quality than reference AB-CT images. The optimum x-ray energy, 30 keV, displayed the largest area under the curve(AUC_VGC) of 0.754 (<i>p</i> = 0.009). This was followed by 32 keV (AUC_VGC = 0.731, <i>p</i> ≤ 0.001), 34 keV (AUC_VGC = 0.723, <i>p</i> ≤ 0.001), and 28 keV (AUC_VGC = 0.654, <i>p</i> = 0.015).</p> <p><b>Conclusions:</b> An optimum energy range (around 30 keV) in the PB-CT technique allows for higher image quality at a dose comparable to conventional mammographic techniques. This results in improved radiological image quality compared with conventional techniques, which may ultimately lead to higher diagnostic efficacy and a reduction in breast cancer mortalities.</p>