External Mechanical Vibrations Research Articles

Skeletal Muscle Assessment Using Quantitative Ultrasound: A Narrative Review.

Ultrasound (US) is an important imaging tool for skeletal muscle analysis. The advantages of US include point-of-care access, real-time imaging, cost-effectiveness, and absence of ionizing radiation. However, US can be highly dependent on the operator and/or US system, and a portion of the potentially useful information carried by raw sonographic data is discarded in image formation for routine qualitative US. Quantitative ultrasound (QUS) methods provide analysis of the raw or post-processed data, revealing additional information about normal tissue structure and disease status. There are four QUS categories that can be used on muscle and are important to review. First, quantitative data derived from B-mode images can help determine the macrostructural anatomy and microstructural morphology of muscle tissues. Second, US elastography can provide information about muscle elasticity or stiffness through strain elastography or shear wave elastography (SWE). Strain elastography measures the induced tissue strain caused either by internal or external compression by tracking tissue displacement with detectable speckle in B-mode images of the examined tissue. SWE measures the speed of induced shear waves traveling through the tissue to estimate the tissue elasticity. These shear waves may be produced using external mechanical vibrations or internal "push pulse" ultrasound stimuli. Third, raw radiofrequency signal analyses provide estimates of fundamental tissue parameters, such as the speed of sound, attenuation coefficient, and backscatter coefficient, which correspond to information about muscle tissue microstructure and composition. Lastly, envelope statistical analyses apply various probability distributions to estimate the number density of scatterers and quantify coherent to incoherent signals, thus providing information about microstructural properties of muscle tissue. This review will examine these QUS techniques, published results on QUS evaluation of skeletal muscles, and the strengths and limitations of QUS in skeletal muscle analysis.

Non-local polarization alignment and control in fibers using feedback from correlated measurements of entangled photons.

Quantum measurements that use the entangled photons' polarization to encode quantum information require calibration and alignment of the measurement bases between spatially separate observers. Because of the changing birefringence in optical fibers arising from temperature fluctuations or external mechanical vibrations, the polarization state at the end of a fiber channel is unpredictable and time-varying. Polarization tracking and stabilization methods originally developed for classical optical communications cannot be applied to polarization-entangled photons, where the separately detected photons are statistically unpolarized, yet quantum mechanically correlated. We report here a fast method for automatic alignment and dynamic tracking of the polarization measurement bases between spatially separated detectors. The system uses the Nelder-Mead simplex method to minimize the observed coincidence rate between non-locally measured entangled photon pairs, without relying on classical wavelength-multiplexed pilot tones or temporally interleaved polarized photons. Alignment and control is demonstrated in a 7.1 km deployed fiber loop as well as in a controlled drifting scenario.

SWAVE 2.0 Imaging of Placental Elasticity and Viscosity: Potential Biomarkers for Placenta-Mediated Disease Detection.

Pregnancy complications such as pre-eclampsia (PE) and intrauterine growth restriction (IUGR) are associated with structural and functional changes in the placenta. Different elastography techniques with an ability to assess the mechanical properties of tissue can identify and monitor the pathological state of the placenta. Currently available elastography techniques have been used with promising results to detect placenta abnormalities; however, limitations include inadequate measurement depth and safety concerns from high negative pressure pulses. Previously, we described a shear wave absolute vibro-elastography (SWAVE) method by applying external low-frequency mechanical vibrations to generate shear waves and studied 61 post-delivery clinically normal placentas to explore the feasibility of SWAVE for placental assessment and establish a measurement baseline. This next phase of the study, namely, SWAVE 2.0, improves the previous system and elasticity reconstruction by incorporating a multi-frequency acquisition system and using a 3-D local frequency estimation (LFE) method. Compared with its 2-D counterpart, the proposed system using 3-D LFE was found to reduce the bias and variance in elasticity measurements in tissue-mimicking phantoms. In the aim of investigating the potential of improved SWAVE 2.0 measurements to identify placental abnormalities, we studied 46 post-delivery placentas, including 26 diseased (16 IUGR and 10 PE) and 20 normal control placentas. By use of a 3.33-MHz motorized curved-array transducer, multi-frequency (80,100 and 120 Hz) elasticity measures were obtained with 3-D LFE, and both IUGR (15.30 ± 2.96 kPa, p=3.35e-5) and PE (12.33 ± 4.88 kPa, p=0.017) placentas were found to be significantly stiffer compared with the control placentas (8.32 ± 3.67 kPa). A linear discriminant analysis (LDA) classifier was able to classify between healthy and diseased placentas with a sensitivity, specificity and accuracy of 87%, 78% and 83% and an area under the receiver operating curve of 0.90 (95% confidence interval: 0.8-0.99). Further, the pregnancy outcome in terms of neonatal intensive care unit admission was predicted with a sensitivity, specificity and accuracy of 70%, 71%, 71%, respectively, and area under the receiver operating curve of 0.78 (confidence interval: 0.62-0.93). A viscoelastic characterization of placentas using a fractional rheological model revealed that the viscosity measures in terms of viscosity parameter n were significantly higher in IUGR (2.3 ± 0.21) and PE (2.11 ± 0.52) placentas than in normal placentas (1.45 ± 0.65). This work illustrates the potential relevance of elasticity and viscosity imaging using SWAVE 2.0 as a non-invasive technology for detection of placental abnormalities and the prediction of pregnancy outcomes.

Mechanical vibration effects in the biospeckle laser technique for portable equipment application in agriculture / Efeitos da vibração mecânica na técnica biospeckle laser para aplicação em equipamento portátil na agricultura

The biospeckle laser (BSL) is a technique developed based on the processing of optical interference patterns formed when a laser light strikes a biological surface. This non-destructive image processing technique is used to quantify the activity level of a sample. Since it is not always feasible to move biological samples to a laboratory to be analyzed, on-site application is necessary for the advancement of the technique. There are limitations in the use of the technique in the field, vibration interference is one of them. Aiming to understand the level of this interference as well as to propose ways to mitigate them, in this work it was developed a portable prototype for dynamic laser speckle (DLS) analysis that was subjected to experimental modal analysis and transmissibility tests. The prototype’s natural frequencies were obtained, and it was evaluated how the optical technique behaves when excited at these and other frequencies. It was discovered that BSL is more sensitive to low frequencies, close to 5 Hz. In the transmissibility tests, it was found that the isolator with the lower stiffness presented the best characteristics of vibration isolation for the proposed purposes, making possible the portability of the prototype from the isolation of ordinary external mechanical vibrations.

On the possible mechanism of external infrasonic mechanical stimulating the process of formation of nanocrystals in an amorphous metal film

A kinetic model, a physical reason and a condition for stimulated by external infrasonic mechanical vibrations of the formation of nanocrystals in an amorphous metal film. The nanostructural elements of the amorphous medium are responsible for these processes: locally ordered nanoclusters and nanoregions containing free volume, which contain two-level systems. When glass is deformed, two-level systems are excited, due to which they make a significant contribution to inelastic deformation, structural relaxation, formation of nanoclusters and nanocrystals. The physical mechanism of nanocrystallization of metallic glass during mechanical exposure includes, in addition to the mechanism of local thermal fluctuations, also athermal mechanism of quantum tunneling of atoms or atomic groups stimulated by inelastic deformation. Keywords: Kinetic model, amorphous metal film, nanocrystals, infrasonic mechanical vibrations.

Multifunctional Triboelectric Nanogenerator-enabled Structural Elements for Next Generation Civil Infrastructure Monitoring Systems.

There is a critical shortage in research needed to explore a new class of multifunctional structural components that respond to their environment, empower themselves and self-monitor their condition. Here, we propose the novel concept of triboelectric nanogenerator-enabled structural elements (TENG-SEs) to build the foundation for the next generation civil infrastructure systems with intrinsic sensing and energy harvesting functionalities. In order to validate the proposed concept, we develop proof-of-concept multifunctional composite rebars with built-in triboelectric nanogenerator mechanisms. The developed prototypes function as structural reinforcements, nanogenerators and distributed sensing mediums under external mechanical vibrations. Experiential and theoretical studies are performed to verify the electrical and mechanical performance of the developed self-powering and self-sensing composite structural components. We demonstrate the capability of the embedded structural elements to detect damage patterns in concrete beams at multiscale. Finally, we discuss how this new class of TENG-SEs could revolutionize the large-scale distributed monitoring practices in civil infrastructure and construction fields.

Conductive Porous MXene for Bionic, Wearable, and Precise Gesture Motion Sensors.

Reliable, wide range, and highly sensitive joint movement monitoring is essential for training activities, human behavior analysis, and human-machine interfaces. Yet, most current motion sensors work on the nano/microcracks induced by the tensile deformation on the convex surface of joints during joint movements, which cannot satisfy requirements of ultrawide detectable angle range, high angle sensitivity, conformability, and consistence under cyclic movements. In nature, scorpions sense small vibrations by allowing for compression strain conversion from external mechanical vibrations through crack-shaped slit sensilla. Here, we demonstrated that ultraconformal sensors based on controlled slit structures, inspired by the geometry of a scorpion's slit sensilla, exhibit high sensitivity (0.45%deg−1), ultralow angle detection threshold (~15°), fast response/relaxation times (115/72 ms), wide range (15° ~120°), and durability (over 1000 cycles). Also, a user-friendly, hybrid sign language system has been developed to realize Chinese and American sign language recognition and feedback through video and speech broadcasts, making these conformal motion sensors promising candidates for joint movement monitoring in wearable electronics and robotics technology.

Electrostatic vibrational energy converter with two variable capacitors

The electrostatic two-capacitor vibration-to-electrical energy converter based on the Bennet doubler circuit with a power source in a variable capacitor branch is studied both theoretically and experimentally. The variations of the capacitances both in opposite phase and in-phase with different modulation depths are considered. Analytical expressions evaluating the energy converter main characteristics and enabling to significantly simplify the optimization process during the converter design are derived. It is shown that the theoretical results are in a good agreement with the obtained experimental data, making it possible to use them for the optimal converter parameters choice when developing electromechanical microgenerators or energy harvesters, active vibration and acceleration sensors, as well as threshold devices. The advantage of the investigated interfacing circuit of the two-capacitor vibration-to-electrical energy converter in comparison with the basic Bennet doubler circuit is the versatility and the ability of the converter to operate under the action of small mechanical vibrations (excitations) causing the capacitance modulation depth less than 2. It is also possible to vary the critical capacitance modulation depth within a rather wide range getting the autostabilization mode even for the capacitance modulation depth greater than 2. As a result, it becomes possible to expand both the range of used amplitudes of external mechanical vibrations and the necessary parameters of the used variable capacitors.

ANÁLISE COMPARATIVA DOS MODOS E FREQUENCIAS NATURAIS DE VIBRAÇÃO DE VIGAS ENGASTADA LIVRE E BI-ENGASTADA SUJEITAS À OSCILAÇÕES LIVRES

The objective of this work was the theoretical and computational modeling of free-form and bi-set beams, objectively showing their ways of vibrations and their natural frequencies. The study of the dynamics of rigid or flexible structures, under the action of external forces, such as regular marine waves, winds, external mechanical vibrations of any order, is of extreme importance for the prevention of possible structural problems, for example, displacements, partial or total ruptures of these structures. All the study was carried out Recebido em: 10/08/2018Revisado em: 28/08/2018Aprovado em: 20/09/2018 19Colloquium Exactarum, v. 10, n.4,Out-Dez. 2018, p.18–27. DOI: 10.5747/ce.2018.v10.n4.e252using the methods of Computational Analysis of the Natural Vibration Modes and Frequencies of a Free Beam of Forms for Free Frequencies and Computational Calculation of Lies and Natural Vibration Frequencies of a Beam Without Free Sets of Free Oscillations and the Computational Computation of Lies and Natural Frequencies of Vibration of a Bi Beam established by the Method ofAssumed Modalities. The computational resources used to do the theoretical remodeling of the beams and their functions were Matlab®and Maple®. Employees to implement three-dimensional vibration modes and development of new studies with different bundles and physical properties. This comparative work of the beams provided the mathematical and dynamic knowledge of modeling of the structures, being they, modeling skills through programming.

In-Phase and Quadrature Analysis for Amplitude and Frequency Modulations Due to Vibrations on a Surface-Acoustic-Wave Resonator.

Surface-acoustic-wave resonators (SAWRs) have found widespread usage in various modern consumer radio frequency (RF) communications electronics, such as cellular phones, wireless devices, GPS devices, frequency control, and sensing applications. External mechanical vibrations modify an SAWR relative dimensions and the substrate's elastic properties, which alter the device's acoustic wave propagation velocity and ultimately cause the SAWR RF response to change. Detecting vibrations are desirable for dynamic strain or vibration sensing applications, whereas external mechanical excitations can result in spurious signals which compromise SAW-based filters and oscillators used in RF communication, frequency control, and sensors targeting measurands such as temperature and pressure. Therefore, understanding and characterizing the SAWR's response to external vibration is relevant for establishing device operation, and assisting in device design and packaging to either mitigate the impact of vibrations for RF communications and frequency control or enhance the SAWR response for sensor applications. This paper presents an in-phase and quadrature demodulation technique (I-Q technique) to detect, quantify, and analyze the effect of externally induced mechanical vibrations on an SAWR. The I-Q technique disclosed reveals that the mechanical vibrations cause both frequency and amplitude modulations of the SAWR RF response, which can be separated by this technique. Furthermore, the procedure also allows the direct measurement of vibration frequencies and vibration magnitude. The technique, measured results, and analysis established here provide a better understanding of the impact of external mechanical vibrations on an SAWR response, which is important in contemporary communications, frequency control, and sensing applications.

Flexible Optical Fiber Fabry–Perot Interferometer Based Acoustic and Mechanical Vibration Sensor

We have proposed and demonstrated a novel flexible optical fiber Fabry–Perot interferometer (FPI) based vibration sensor with broadband frequency response. The sensor consists of a flexible FP cavity formed by soft splicing using polydimethylsiloxane (PDMS) material with low Young's Modulus and a compact fiber cantilever of low moment inertia as the vibration receiver. Acoustic or mechanical waves experienced by the fiber cantilever can result in obvious change of the FPI cavity length and finally be transduced to the intensity variation of the sensor signal, which makes the sensor highly sensitive to external acoustic or mechanical vibrations. Taking advantage of the superior elasticity of PDMS and compact structure of cantilever, a broadband frequency response for vibration detection has been achieved together with high sensitivity without extra external vibration receiver. The vibration detection is theoretically analyzed, and acoustic vibrations up to 20 kHz and damped mechanical vibrations from tens of hertz to tens of kilohertz, covering both the sound and part of ultrasound range, have been experimentally detected. Moreover, each event of the ball hitting and rebounding has been accurately identified by our sensor, showing excellent vibration sensing only by a thin optical fiber. We believe such a broadband, compact and cost-effective sensor would be a promising candidate for monitoring both acoustic and mechanical vibrations.

Influence of Tissue Microstructure on Shear Wave Speed Measurements in Plane Shear Wave Elastography: A Computational Study in Lossless Fibrotic Liver Media.

Shear wave elastography (SWE) has been used to measure viscoelastic properties for characterization of fibrotic livers. In this technique, external mechanical vibrations or acoustic radiation forces are first transmitted to the tissue being imaged to induce shear waves. Ultrasonically measured displacement/velocity is then utilized to obtain elastographic measurements related to shear wave propagation. Using an open-source wave simulator, k-Wave, we conducted a case study of the relationship between plane shear wave measurements and the microstructure of fibrotic liver tissues. Particularly, three different virtual tissue models (i.e., a histology-based model, a statistics-based model, and a simple inclusion model) were used to represent underlying microstructures of fibrotic liver tissues. We found underlying microstructures affected the estimated mean group shear wave speed (SWS) under the plane shear wave assumption by as much as 56%. Also, the elastic shear wave scattering resulted in frequency-dependent attenuation coefficients and introduced changes in the estimated group SWS. Similarly, the slope of group SWS changes with respect to the excitation frequency differed as much as 78% among three models investigated. This new finding may motivate further studies examining how elastic scattering may contribute to frequency-dependent shear wave dispersion and attenuation in biological tissues.

Signal integrity in capacitive and piezoresistive single- and multi-axis MEMS gyroscopes under vibrations

The work investigates effects of external mechanical vibrations, with a frequency up to 40kHz, on the operation of micro-electromechanical gyroscopes of different architecture and sensing technology. The analyzed devices differ (i) in the number of sensing axes (one, two or three) per single drive frame, so in the number of resonant modes within the tested vibration range, and (ii) in the used sense transduction technology (parallel-plate capacitances or piezoresistive nano-gauges). After theoretically modeling effects of vibrations occurring around the frequency of in-plane and out-of-plane resonant modes, in presence of process imperfections and nonlinearities, the work benchmarks the predictions through an extensive experimental campaign: using a shaker, vibrations of controlled amplitude and frequency are applied, in operation, to the devices along both in-plane and out-of-plane axes. Results show that, within the tested sensors, the best tolerance to vibrations, quantitatively measured in terms of angle random walk (ARW) worsening, is achieved for single-axis structures based on piezoresistive sensing. Their ARW degrades in the worst case by 1.2 times, compared to a 230-fold degradation observed in 3-axis capacitive sensors.

Granular flows down inclined and vibrated planes: influence of basal friction

We present an experimental study about granular avalanches when external mechanical vibrations are applied. The results of the flow properties highlight the existence of two distinct regimes: (i) a gravity-driven regime at large angles where scaling laws are in agreement with those reported in the literature for non-vibrating granular flows and (ii) a vibration-driven regime at small angles where no flow occurs without applied vibrations. The flow in this regime is well described by a vibrationinduced activated process. We also propose an empirical law to capture the evolution of the thickness of the deposits as a function of the vibration intensity and the inclination angle.

Breakup of free liquid jets influenced by external mechanical vibrations

The breakup of liquid jets has been studied with various test liquids using externally imposed mechanical vibrations. Images of the jets were captured by a high speed camera up to the speed of 1000 frames per second, and analyzed to obtain the profile of the jet and breakup length. The dynamics of the jets have also been studied to understand the effects of additives—a surfactant and polymer—incorporating externally imposed mechanical vibrations. Different types of breakup modes have been explored with respect to the Weber number and Ohnesorge number. The introduction of mechanical vibrations have caused jet breakup with separated droplets at a comparatively lower Weber number. The region of jet breakup by neck formation at constant jet velocities also contracted due to mechanical vibrations.

Research of hand tremor vibrations and interference with external me-chanical oscillations source

This paper presents the research of hand tremor vibrations and interference with external mechanical vibrations source. Photogrammetry were used to capture and analyze hand tremor parameters from 8 patient with essential and Parkinson tremors. Blood perfusion device, that creates mechanical vibrations, was used as an external source of mechanical vibrations and was tested with patients. Device interference with hand tremor showed promising results of hand tremor reduction. The minimum points had 16.5 % lower amplitude of hand tremor. The maximum amplitudes were about 50 % greater and these results show the compatibility of the method but the control algorithm needs to be improved. DOI: http://dx.doi.org/10.5755/j01.mech.22.5.16351

Granular avalanches down inclined and vibrated planes.

In this article, we study granular avalanches when external mechanical vibrations are applied. We identify conditions of flow arrest and compare with the ones classically observed for nonvibrating granular flows down inclines [Phys. Fluids 11, 542 (1999)PHFLE61070-663110.1063/1.869928]. We propose an empirical law to describe the thickness of the deposits with the inclination angle and the vibration intensity. The link between the surface velocity and the depth of the flow highlights a competition between gravity and vibrations induced flows. We identify two distinct regimes: (a) gravity-driven flows at large angles where vibrations do not modify dynamical properties but the deposits (scaling laws in this regime are in agreement with the literature for nonvibrating granular flows) and (b) vibrations-driven flows at small angles where no flow is possible without applied vibrations (in this last regime, the flow behavior can be properly described by a vibration induced activated process). We show, in this study, that granular flows down inclined planes can be finely tuned by external mechanical vibrations.

Temporal artifact minimization in sonoelastography through optimal selection of imaging parameters.

Sonoelastography is an ultrasonic technique that uses Kasai's autocorrelation algorithms to generate qualitative images of tissue elasticity using external mechanical vibrations. In the absence of synchronization between the mechanical vibration device and the ultrasound system, the random initial phase and finite ensemble length of the data packets result in temporal artifacts in the sonoelastography frames and, consequently, in degraded image quality. In this work, the analytic derivation of an optimal selection of acquisition parameters (i.e., pulse repetition frequency, vibration frequency, and ensemble length) is developed in order to minimize these artifacts, thereby eliminating the need for complex device synchronization. The proposed rule was verified through experiments with heterogeneous phantoms, where the use of optimally selected parameters increased the average contrast-to-noise ratio (CNR) by more than 200% and reduced the CNR standard deviation by 400% when compared to the use of arbitrarily selected imaging parameters. Therefore, the results suggest that the rule for specific selection of acquisition parameters becomes an important tool for producing high quality sonoelastography images.

TU‐EF‐207‐01: Introductory Remarks on Recent Advances in Breast Imaging

Breast imaging technology is advancing on several fronts. In digital mammography, the major technological trend has been on optimization of approaches for performing combined mammography and tomosynthesis using the same system. In parallel, photon‐counting slot‐scan mammography is now in clinical use and more efforts are directed towards further development of this approach for spectral imaging. Spectral imaging refers to simultaneous acquisition of two or more energy‐windowed images. Depending on the detector and associated electronics, there are a number of ways this can be accomplished. Spectral mammography using photon‐counting detectors can suppress electronic noise and importantly, it enables decomposition of the image into various material compositions of interest facilitating quantitative imaging. Spectral imaging can be particularly important in intravenously injected contrast mammography and eventually tomosynthesis. The various approaches and applications of spectral mammography are discussed.Digital breast tomosynthesis relies on the mechanical movement of the x‐ray tube to acquire a number of projections in a predefined arc, typically from 9 to 25 projections over a scan angle of +/−7.5 to 25 degrees depending on the particular system. The mechanical x‐ray tube motion requires relatively long acquisition time, typically between 3.7 to 25 seconds depending on the system. Moreover, mechanical scanning may have an effect on the spatial resolution due to internal x‐ray filament or external mechanical vibrations. New x‐ray source arrays have been developed and they are aimed at replacing the scanned x‐ray tube for improved acquisition time and potentially for higher spatial resolution. The potential advantages and challenges of this approach are described.Combination of digital mammography and tomosynthesis in a single system places increased demands on certain functional aspects of the detector and overall performance, particularly in the tomosynthesis mode due to lower photon fluence per projection. This may require fast‐frame acquisition and symmetric or asymmetric pixel binning in some systems. Recent studies investigated the performance of increased conversion layer thickness for contrast‐enhanced imaging of the breast in dual‐energy acquisition mode. In other direct conversion detectors operating in the avalanche mode, sensitivities close to the single photon response are also explored for mammography and breast tomosynthesis. The potential advantages and challenges of this approach are described.Dedicated breast CT brings x‐ray imaging of the breast to true tomographic 3D imaging. It can eliminate the tissue superposition problem and does not require physical compression of the breast. Using cone beam geometry and a flat‐panel detector, several hundred projections are acquired and reconstructed to near isotropic voxels. Multiplanar reconstruction facilitates viewing the breast volume in any desired orientation. Ongoing clinical studies, the current state‐of‐the art, and research to advance the technology are described.Learning Objectives: To understand the ongoing developments in x‐ray imaging of the breast To understand the approaches and applications of spectral mammography To understand the potential advantages of distributed x‐ray source arrays for digital breast tomosynthesis To understand the ongoing developments in detector technology for digital mammography and breast tomosynthesis To understand the current state‐of‐the‐art for dedicated cone‐beam breast CT and research to advance the technology. Research collaboration with Koning Corporation.

TU‐EF‐207‐04: Advances in Detector Technology for Breast Tomosynthesis

Breast imaging technology is advancing on several fronts. In digital mammography, the major technological trend has been on optimization of approaches for performing combined mammography and tomosynthesis using the same system. In parallel, photon‐counting slot‐scan mammography is now in clinical use and more efforts are directed towards further development of this approach for spectral imaging. Spectral imaging refers to simultaneous acquisition of two or more energy‐windowed images. Depending on the detector and associated electronics, there are a number of ways this can be accomplished. Spectral mammography using photon‐counting detectors can suppress electronic noise and importantly, it enables decomposition of the image into various material compositions of interest facilitating quantitative imaging. Spectral imaging can be particularly important in intravenously injected contrast mammography and eventually tomosynthesis. The various approaches and applications of spectral mammography are discussed.Digital breast tomosynthesis relies on the mechanical movement of the x‐ray tube to acquire a number of projections in a predefined arc, typically from 9 to 25 projections over a scan angle of +/−7.5 to 25 degrees depending on the particular system. The mechanical x‐ray tube motion requires relatively long acquisition time, typically between 3.7 to 25 seconds depending on the system. Moreover, mechanical scanning may have an effect on the spatial resolution due to internal x‐ray filament or external mechanical vibrations. New x‐ray source arrays have been developed and they are aimed at replacing the scanned x‐ray tube for improved acquisition time and potentially for higher spatial resolution. The potential advantages and challenges of this approach are described.Combination of digital mammography and tomosynthesis in a single system places increased demands on certain functional aspects of the detector and overall performance, particularly in the tomosynthesis mode due to lower photon fluence per projection. This may require fast‐frame acquisition and symmetric or asymmetric pixel binning in some systems. Recent studies investigated the performance of increased conversion layer thickness for contrast‐enhanced imaging of the breast in dual‐energy acquisition mode. In other direct conversion detectors operating in the avalanche mode, sensitivities close to the single photon response are also explored for mammography and breast tomosynthesis. The potential advantages and challenges of this approach are described.Dedicated breast CT brings x‐ray imaging of the breast to true tomographic 3D imaging. It can eliminate the tissue superposition problem and does not require physical compression of the breast. Using cone beam geometry and a flat‐panel detector, several hundred projections are acquired and reconstructed to near isotropic voxels. Multiplanar reconstruction facilitates viewing the breast volume in any desired orientation. Ongoing clinical studies, the current state‐of‐the art, and research to advance the technology are described.Learning Objectives: To understand the ongoing developments in x‐ray imaging of the breast To understand the approaches and applications of spectral mammography To understand the potential advantages of distributed x‐ray source arrays for digital breast tomosynthesis To understand the ongoing developments in detector technology for digital mammography and breast tomosynthesis To understand the current state‐of‐the‐art for dedicated cone‐beam breast CT and research to advance the technology. Research collaboration with Koning Corporation.