The objective of this study was to demonstrate the potential benefits of using high energy x-rays for phase sensitive breast imaging through a comparison with conventional mammography imaging. We compared images of a contrast-detail (CD) phantom acquired on a prototype phase sensitive x-ray imaging system with images acquired on a commercial flat panel digital mammography unit. The phase contrast images were acquired using a micro-focus x-ray source with a 50 μm focal spot at 120 kVp and 4.5 mAs, with a magnification factor of 2.46 and a 50 μm pixel pitch. A phase attenuation duality (PAD)-based phase retrieval algorithm that requires only a single phase contrast image was applied. Conventional digital mammography images were acquired at 27 kVp, 131 mAs and 28 kVp, 54 mAs. For the same radiation dose, both the observer study and SNR/FOM comparisons indicated a large improvement by the phase retrieved image as compared to the clinical system for the larger disk sizes, but the improvement was not enough to detect the smallest disks. Compared to the double dose image acquired with the clinical system, the observer study also indicated that the phase retrieved image provided improved detection capabilities for all disk sizes except the smallest disks. Thus the SNR improvement provided by phase contrast imaging is not yet enough to offset the noise reduction provided by the clinical system at the doubled dose level. However, the potential demonstrated by this study for high energy phase sensitive x-ray imaging to improve lesion detection and reduce radiation dose in mammography warrants further investigation of this technique.

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The ability of microbubbles to benefit the imaging quality of high-energy in-line phase contrast as compared with conventional low-energy contact mode radiography was investigated. The study was conducted by comparing in-line phase contrast imaging with conventional contact-mode projection imaging under the same dose delivered to a phantom. A custom-designed phantom was employed to simulate a segment of human blood vessel injected with microbubble suspensions. The microbubbles were suspended in deionized water to obtain different volume concentrations. The area contrast-to-noise ratio (CNR) values corresponding to both imaging methods were measured for different microbubble volume concentrations. The phase contrast images were processed by phase-attenuation duality phase retrieval to preserve the imaging quality. Comparison of the resultant CNR values indicates that the microbubble suspension images deliver a higher CNR than the water-only image, with monotonically increasing trends between the CNR values and microbubble concentrations. Compared to low-energy conventional images of the microbubble suspensions, high-energy in-line phase contrast CNRs are lower at high concentrations and are comparable, even better than, at low concentrations. This result suggests that 1) the performance of copolymer-shell microbubble employed in this study as x-ray contrast agent is constrained by the detective quantum efficiency of the system and the attenuation properties of the shell materials, 2) the phase-attenuation duality phase retrieval method has the potential to preserve image quality for areas with low concentration of microbubbles, and 3) the selection of microbubble products as a phase contrast agent may follow criteria of minimizing the impact of absorption attenuation properties of the shells and maximizing the difference factor of electron densities.

This research successfully demonstrated a high-energy in-line phase contrast tomosynthesis prototype. In addition, the PAD-based method of phase retrieval was combined with tomosynthesis imaging for the first time, which demonstrated its capability in significantly improving the contrast-to-noise ratios in the images.

The objective of this study was to demonstrate the potential benefits of using high energy x-rays in comparison with the conventional mammography imaging systems for phase sensitive imaging of breast tissues with varying glandular-adipose ratios. This study employed two modular phantoms simulating the glandular (G) and adipose (A) breast tissue composition in 50G-50A and 70G-30A percentage densities. Each phantom had a thickness of 5 cm with a contrast detail (CD) test pattern embedded in the middle. For both phantoms, the phase contrast images were acquired using a micro-focus x-ray source operated at 120 kVp and 4.5 mAs, with a magnification factor (M) of 2.5 and a detector with a 50 μm pixel pitch. The mean glandular dose delivered to the 50G-50A and 70G-30A phantom sets were 1.33 and 1.3 mGy, respectively. A phase retrieval algorithm based on the phase attenuation duality (PAD) that required only a single phase contrast image was applied. Conventional low energy mammography images were acquired using GE Senographe DS and Hologic Selenia systems utilizing their automatic exposure control (AEC) settings. In addition, the automatic contrast mode (CNT) was also used for the acquisition with the GE system. The AEC mode applied higher dose settings for the 70G-30A phantom set. As compared to the phase contrast images, the dose levels for the AEC mode acquired images were similar while the dose levels for the CNT mode were almost double. The observer study, contrast-to-noise ratio (CNR) and figure of merit (FOM) comparisons indicated a large improvement with the phase retrieved images in comparison to the AEC mode images acquired with the clinical systems for both density levels. As the glandular composition increased, the detectability of smaller discs decreased with the clinical systems, particularly with the GE system, even at higher dose settings. As compared to the CNT mode (double dose) images, the observer study also indicated that the phase retrieved images provided similar or improved detection for all disc sizes except for the disk diameters of 2 mm and 1 mm for the 50G-50A phantom and 3 mm and 0.5 mm for the 70G-30A phantom. This study demonstrated the potential of utilizing a high energy phase sensitive x-ray imaging system to improve lesion detection and reduce radiation dose when imaging breast tissues with varying glandular compositions.

The spatial resolution characteristics of an in vivo micro computed tomography (CT) system was investigated in the in-plane (x-y), cross plane (z) and projection imaging modes. The micro CT system utilized in this study employs a flat panel detector with a 127 μm pixel pitch, a micro focus x-ray tube with a focal spot size ranging from 5-30 μm, and accommodates three geometric magnifications (M) of 1.72, 2.54 and 5.10. The in-plane modulation transfer function (MTF) curves were measured as a function of the number of projections, geometric magnification (M), detector binning and reconstruction magnification (MRecon). The in plane cutoff frequency (10% MTF) ranged from 2.31 lp/mm (M=1.72, 2×2 binning) to 12.56 lp/mm (M=5.10, 1×1 binning) and a bar pattern phantom validated those measurements. A slight degradation in the spatial resolution was observed when comparing the image reconstruction with 511 and 918 projections, whose effect was visible at the lower frequencies. Small value of MRecon has little or no impact on the in-plane spatial resolution owning to a stable system. Large value of MRecon has implications on the spatial resolution and it was evident when comparing the bar pattern images reconstructed with MRecon=1.25 and 2.5. The cross plane MTF curves showed that the spatial resolution increased as the slice thickness decreased. The cutoff frequencies in the projection imaging mode yielded slightly higher values as compared to the in-plane and cross plane modes at all the geometric magnifications (M). At M=5.10, the cutoff resolution of the projection and cross plane on an ultra-high contrast resolution bar chip phantom were 14.9 lp/mm and 13-13.5 lp/mm. Due to the finite focal spot size of the x-ray tube, the detector blur and the reconstruction kernel functions, the system's spatial resolution does not reach the limiting spatial resolution as defined by the Nyquist's detector criteria with an ideal point source. The geometric magnification employed in the micro CTs provide a tradeoff between field of view and spatial resolution for a wide range of applications.

The rapid and dramatic increase in confirmed cases of COVID-19 has led to a global pandemic. Early detection and containment are currently the most effective methods for controlling the outbreak. A positive diagnosis is determined by laboratory real-time reverse transcriptase polymerase chain reaction (rRT-PCR) testing, but the use of chest computed tomography (CT) has also been indicated as an important tool for detection and management of the disease. Numerous studies reviewed in this paper largely concur in their findings that the early hallmarks of COVID-19 infection are ground-glass opacities (GGOs), often with a bilateral and peripheral lung distribution. In addition, most studies demonstrated similar CT findings related to the progression of the disease, starting with GGOs in early disease, followed by the development of crazy paving in middle stages and finally increasing consolidation in the later stages of the disease. Studies have reported a low rate of misdiagnosis by chest CT, as well as a high rate of misdiagnosis by the rRT-PCR tests. Specifically, chest CT provides more accurate results in the early stages of COVID-19, when it is critical to begin treatment as well as isolate the patient to avoid the spread of the virus. While rRT-PCR will probably remain the definitive final test for COVID-19, until it is more readily available and can consistently provide higher sensitivity, the use of chest CT for early stage detection has proven valuable in avoiding misdiagnosis as well as monitoring the progression of the disease. With the understanding of the role of chest CT, researchers are beginning to apply deep learning and other algorithms to differentiate between COVID-19 and non-COVID-19 CT scans, determine the severity of the disease to guide the course of treatment, and investigate numerous additional COVID-19 applications. Impact statement The impact of the COVID-19 pandemic has been worldwide, and clinicians and researchers around the world have been working to develop effective and efficient methods for early detection as well as monitoring of the disease progression. This minireview compiles the various agency and expert recommendations, along with results from studies published in numerous countries, in an effort to facilitate the research in imaging technology development to benefit the detection and monitoring of COVID-19. To the best of our knowledge, this is the first review paper on the topic, and it provides a brief, yet comprehensive analysis.

The investigation demonstrated the potential of imaging gold nanoparticles quantitatively in vivo for in-tissue studies, but future studies will be needed to investigate the ability to apply this method to clinical applications.