Purpose: This study aims at establishing the optimum x-ray energy for synchrotron acquired propagation-based computed tomography (PB-CT) images to obtain highest radiological image quality of breast mastectomy samples. It also examines the correlation between objective physical measures of image quality with subjective human observer scores to model factors impacting visual determinants of image quality. Approach: Thirty mastectomy samples were scanned at Australian Synchrotron’s Imaging and Medical Beamline. Samples were scanned at energies of 26, 28, 30, 32, 34, and 60 keV at a standard dose of 4mGy. Objective physical measures of image quality were assessed using signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), SNR/resolution (SNR/res), CNR/resolution (CNR/res) and visibility. Additional calculations for each measure were performed against reference absorption-based computer tomography (AB-CT) images scanned at 32 keV and 4mGy. This included differences in SNR (dSNR), CNR (dCNR), SNR/res (dSNR/res), CNR/res (dCNR/res), and visibility (dVis). Physical measures of image quality were also compared with visual grading analysis data to determine a correlation between observer scores and objective metrics. Results: For dSNR, dCNR, dSNR/res, dCNR/res, and dVis, a statistically significant difference was found between the energy levels. The peak x-ray energy for dSNR and dSNR/res was 60 keV. For dCNR and dCNR/res 34 keV produced the highest measure compared to 28 keV for dVis. Visibility and CNR correlate to 56.8% of observer scores. Conclusion: The optimal x-ray energy differs for different objective measures of image quality with 30-34 keV providing optimum image quality for breast PB-CT. Visibility and CNR correlate highest to medical imaging expert scores.
One of the imaging modalities offered by the Imaging and Medical Beamline (IMBL) at the Australian Synchrotron is Xray phase-contrast propagation-based computed tomography (PB-CT). The unique combination of high coherence and high brightness of radiation produced by synchrotron X-ray sources enables phase contrast imaging with excellent sensitivity to small density differences in soft tissues and tumors. The PB-CT images using spatially coherent radiation show high signal-to-noise ratio (SNR) without reducing the spatial resolution. This is due to the combined effect of forward free-space propagation and the advanced step of phase retrieval in the reconstruction processes that allows to accommodate noisier recorded images. This gives an advantage of potentially reducing the radiation dose delivered to the sample whilst preserving the reconstructed image quality. It is expected that the PB-CT technique will be well suited for diagnostic breast imaging in the near future with the advantage that it could provide better tumor detection and characterization/grading than mammography and other breast imaging modalities/techniques in general. The PB-CT technique is expected to reduce false negative and false positive cancer diagnoses that result from overlapping regions of tissue in 2D mammography and avoid patient pain and discomfort that results from breast compression. The present paper demonstrates that PB-CT produces superior results for imaging low-density materials such as breast mastectomy samples, when compared to the conventional absorption-based CT collected at the same radiation dose. The performance was quantified in terms of both the measured objective image characteristics and the subjective scores from radiological assessments. This work is part of the ongoing research project aimed at the introduction of 3D X-ray medical imaging at the IMBL as innovative tomographic methods to improve the detection and diagnosis of breast cancer. Major progress of this project includes the characterization of a large number of mastectomy samples, both normal and cancerous.
Purpose: 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.
Approach: 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.
Results: 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 ( AUCVGC ) of 0.754 (p = 0.009). This was followed by 32 keV (AUCVGC = 0.731, p ≤ 0.001), 34 keV (AUCVGC = 0.723, p ≤ 0.001), and 28 keV (AUCVGC = 0.654, p = 0.015).
Conclusions: 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.
Propagation-based phase-contrast CT (PB-CT) is a novel imaging technique that visualises variations in both X-ray attenuation and refraction. This study aimed to compare the clinical image quality of breast PB-CT using synchrotron radiation with conventional absorption-based CT (AB-CT), at the same radiation dose. Seven breast mastectomy specimens were scanned and evaluated by a group of 14 radiologists and medical imaging experts who assessed the images based on seven radiological image quality criteria. Visual grading characteristics (VGC) were used to analyse the results and the area under the VGC curve was obtained to measure the differences between the two techniques. For six image quality criteria (overall quality, perceptible contrast, lesion sharpness, normal tissue interfaces, calcification visibility and image noise), PB-CT images were superior to AB-CT images of the same dose (AUCVGC: 0.704 to 0.914, P≤.05). For the seventh criteria (artefacts), PB-CT images were also rated better than AB-CT images (AUCVGC: 0.647) but the difference was not significant. The results of this study provide a solid basis for future experimental and clinical protocols of breast PB-CT.
Aim: In recent years Phase Contrast Tomography (PCT) has been rapidly progressing towards clinical translation as an advanced imaging technology for breast cancer diagnosis. Recent optimization of PCT with mastectomy samples has refined imaging protocols and biomedical-engineering prowess is now required to formalize patient table and breast immobilisation requirements. PCT imaging requires women to lie in prone position similar to conventional breast CT, however the imaging couch rotates above the beam allowing exposure of the breast beneath. Motion artefact through involuntary movement of the breast through the rotation cycle has the potential to reduce diagnostic quality of the results. Methods: This paper details the biomedical engineering cycle of breast holder development alongside medical physics considerations. Breast immobilisation via a plastic or silicone supporting material which is sufficiently transparent for X-rays in the targeted energy range is explained, including the two step process of considering single cup versus double cup solutions and how mild-suction to the breast can be implemented in order to maximum breast tissue visualization and assist with dose uniformity. Results: Considering patient comfort, breast positioning and implications upon attenuation and phase shift, a number of models were developed in Australia and Italy. Early prototypes are described here with some preliminary imaging. Considerable work is taking place over the next three months as models undergo imaging with mastectomy samples at the Imaging and Medical Beamline at the Australian Synchrotron and the ELETTRA Synchrotron Italy. Consumer representatives will be rating the immobilisation device for comfort prior to the start of clinical trials in 2020.
X-ray computed tomography (XCT) is an important clinical diagnostic tool which is also used in a range of biological
imaging applications in research. The increasing prevalence of metallic implants in medical and dental radiography and
tomography has driven the demand for new approaches to solving the issue of metal artefacts in XCT. Metal artefacts
occur when a highly absorbing material is imaged which is in boundary contact with one or more weakly absorbing
components, such as soft-tissue. The resulting ‘streaking’ in the reconstructed images creates significant challenges for
X-ray analysis due to the non-linear dependence on the absorption properties of the sample. In this paper we introduce a
new approach to removing metal artefacts which exploits the capabilities of the recently available, photon-counting
PiXirad detector. Our approach works for standard lab-based polychromatic X-ray tubes and does not rely on any postprocessing
of the data. The method is demonstrated using both simulated data from a test phantom and experimental data
collected from a cochlear implant. The results show that by combining the individual images, which are simultaneously
generated for each different energy threshold, artefact -free segmentation of the implant from the surrounding biological
tissue is achieved.
Ross filter pairs have recently been demonstrated as a highly effective means of producing quasi-monoenergetic beams from polychromatic X-ray sources. They have found applications in both X-ray spectroscopy and for elemental separation in X-ray computed tomography (XCT). Here we explore whether they could be applied to the problem of metal artefact reduction (MAR) for applications in medical imaging. Metal artefacts are a common problem in X-ray imaging of metal implants embedded in bone and soft tissue. A number of data post-processing approaches to MAR have been proposed in the literature, however these can be time-consuming and sometimes have limited efficacy. Here we describe and demonstrate an alternative approach based on beam conditioning using Ross filter pairs. This approach obviates the need for any complex post-processing of the data and enables MAR and segmentation from the surrounding tissue by exploiting the absorption edge contrast of the implant.
Determining the specific spatial distributions of elements within compound samples is of critical importance to a range of applied research fields. The usual approaches to obtaining elemental contrast involve measurement of the characteristic peaks associated with x-ray fluorescence or measuring the x-ray transmission as a function of energy. In the laboratory these measurements are challenging due to the polychromaticity and lack of tunability of the source. Here we demonstrate how newly developed, high-resolution, energy-discriminating area detector technology can be exploited to enhance elemental contrast. The detector we employ here is the Pixirad area detector which can simultaneously have up to four separate colour channels. We also discuss the potential of this new technology in the context of tomographic imaging of soft tissue.
X-ray tomography is a workhorse tool of non-destructive imaging. It is used to probe three-dimensional structures across
a wide range of length scales for objects that offer good absorption contrast to x-rays. In recent years extremely high
resolution imaging (on the order of tens of nanometres) has become possible due to technological advances in x-ray
optics. At the same time the requirement for strong absorption contrast has been relaxed thanks to the advent of new
experimental and algorithmic techniques in phase imaging. Advances in both resolution and phase imaging can be
combined to image biological samples at the sub-cellular level. I will report on recent advances in our work including
improvements to the current approaches in extracting phase information at high resolution from measurements of the
diffracted intensity from a sample. I will also discuss our current experimental status.
We have developed a quality function that quantifies how well features are reconstructed in 3D phase contrast tomographic reconstructions for pure phase samples. We consider image formation using the free space propagation method for each projected data-set. A partially coherent radiation field originating from an extended source is also incorporated. This means the model is suitable for a laboratory based micro focus x-ray source. The quality function is useful for optimizing the tomographic reconstruction for given feature sizes in an object. We then use the quality function to develop filters for improving the reconstruction quality for high spatial frequency objects.
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