Investigating the potential for super-resolution in digital breast tomosynthesis

In tomosynthesis, super-resolution has been demonstrated using reconstruction planes parallel to the detector. Super-resolution allows for subpixel resolution relative to the detector. The purpose of this work is to develop an analytical model that generalizes super-resolution to oblique reconstruction planes. In a digital tomosynthesis system, a sinusoidal test object is modeled along oblique angles (i.e., "pitches") relative to the plane of the detector in a 3D divergent-beam acquisition geometry. To investigate the potential for super-resolution, the input frequency is specified to be greater than the alias frequency of the detector. Reconstructions are evaluated in an oblique plane along the extent of the object using simple backprojection (SBP) and filtered backprojection (FBP). By comparing the amplitude of the reconstruction against the attenuation coefficient of the object at various frequencies, the modulation transfer function (MTF) is calculated to determine whether modulation is within detectable limits for super-resolution. For experimental validation of super-resolution, a goniometry stand was used to orient a bar pattern phantom along various pitches relative to the breast support in a commercial digital breast tomosynthesis system. Using theoretical modeling, it is shown that a single projection image cannot resolve a sine input whose frequency exceeds the detector alias frequency. The high frequency input is correctly visualized in SBP or FBP reconstruction using a slice along the pitch of the object. The Fourier transform of this reconstructed slice is maximized at the input frequency as proof that the object is resolved. Consistent with the theoretical results, experimental images of a bar pattern phantom showed super-resolution in oblique reconstructions. At various pitches, the highest frequency with detectable modulation was determined by visual inspection of the bar patterns. The dependency of the highest detectable frequency on pitch followed the same trend as the analytical model. It was demonstrated that super-resolution is not achievable if the pitch of the object approaches 90°, corresponding to the case in which the test frequency is perpendicular to the breast support. Only low frequency objects are detectable at pitches close to 90°. This work provides a platform for investigating super-resolution in oblique reconstructions for tomosynthesis. In breast imaging, this study should have applications in visualizing microcalcifications and other subtle signs of cancer.

Mammographic breast density is a known breast cancer risk factor. Studies have shown the potential to automate breast density estimation by using computerized texture-based segmentation of the dense tissue in mammograms. Digital breast tomosynthesis (DBT) is a tomographic x-ray breast imaging modality that could allow volumetric breast density estimation. We evaluated the feasibility of distinguishing between dense and fatty breast regions in DBT using computer-extracted texture features. Our long-term hypothesis is that DBT texture analysis can be used to develop 3D dense tissue segmentation algorithms for estimating volumetric breast density. DBT images from 40 women were analyzed. The dense tissue area was delineated within each central source projection (CSP) image using a thresholding technique (Cumulus, Univ. Toronto). Two (2.5cm) 2 ROIs were manually selected: one within the dense tissue region and another within the fatty region. Corresponding (2.5cm) 3 ROIs were placed within the reconstructed DBT images. Texture features, previously used for mammographic dense tissue segmentation, were computed. Receiver operating characteristic (ROC) curve analysis was performed to evaluate feature classification performance. Different texture features appeared to perform best in the 3D reconstructed DBT compared to the 2D CSP images. Fractal dimension was superior in DBT (AUC=0.90), while contrast was best in CSP images (AUC=0.92). We attribute these differences to the effects of tissue superimposition in CSP and the volumetric visualization of the breast tissue in DBT. Our results suggest that novel approaches, different than those conventionally used in projection mammography, need to be investigated in order to develop DBT dense tissue segmentation algorithms for estimating volumetric breast density.

Digital breast tomosynthesis (DBT) is becoming an important part of breast cancer screening and diagnosis. Compared to two-dimensional mammography, tomosynthesis introduces limited three-dimensional (3D) resolution, but maintains high in-plane resolution, low dose, and allows for similar clinical protocols. The scanning motion and oblique projections of tomosynthesis acquisitions introduce shift-variance to the image quality, in addition to effects such as source blurring and geometric magnification. Shift-variant detector response caused by oblique incidence has been extensively studied previously and is most easily mitigated by letting the source and detector move in sync. In addition, conical reconstruction grids, that is, a grid aligned with the central tomosynthesis projection, have been proposed to compensate for magnification effects. This paper introduces a shift-variant cascaded systems model for tomosynthesis and validates it against measurements. As an example, the model was used to investigate the shift-variance of a tomosynthesis system. The shift-variant cascaded systems model was validated on a slit-scanning photon-counting DBT system, with synchronous source-detector movement, using simple back-projection in a conical reconstruction volume. The modulation transfer function (MTF), normalized noise-power spectrum (NNPS), and detective quantum efficiency (DQE) were used as figures of merit. Simulations were performed for single points while measurements were done over a finite volume, assuming local shift invariance. To investigate the full extent of shift-variance, 80 locations across the volume were simulated, and the MTF and DQE at 2.5lp/mm were calculated as a function of position. The simulated metrics generally agreed well with their corresponding measurements. The frequency at 50% MTF along the scan direction showed a relatively small variation, ranging from 2.1 to 2.4lp/mm for the different locations. The frequency at 50% MTF along the chest-mammilla direction showed a larger variation, ranging from 2.9 to 3.8lp/mm. All points exhibited a similarly shaped NNPS but the noise magnitude varied with slice height. The zero-frequency DQE in reconstructed slices was lower than that of the projections, an effect likely caused by noise-aliasing increasing the zero-frequency noise. A shift-variant cascaded systems model has been developed for slit-scanning tomosynthesis using simple back-projection. The model was successfully validated against measurements. Even though the study was performed on a slit-scanning system, several parts of the framework can be applied and extended to other tomosynthesis geometries. The conical reconstruction grid has low variation in image quality in the scan direction where the 3D information is acquired, but source and geometric magnification still dominate in the slit direction, causing a larger variation in image quality. We conclude that image quality is close to shift-invariant in the scan direction, but not in the height and chest-mammilla directions, and we recommend that small measurement volumes are used when measuring image quality in these directions to minimize the effects of shift variance.

The purpose of this study is to develop a new method for generating synthesized mammogram (SM) from digital breast tomosynthesis (DBT) and to assess its potential as an adjunct to DBT. We first applied multiscale bilateral filtering to the reconstructed DBT slices to enhance the high-frequency features and reduce noise. A maximum intensity projection (MIP) image was then obtained from the high-frequency components of the DBT slices. A multiscale image fusion method was designed to combine the MIP image and the central DBT projection view into an SM and further enhance the high-frequency features. We conducted a pilot reader study to visually assess the image quality of SM in comparison to full field digital mammograms (FFDM). For each DBT craniocaudal or mediolateral view, a clinical FFDM of the corresponding view was retrospectively collected. Three MQSA radiologists, blinded to the pathological and other clinical information, independently interpreted the SM and the corresponding FFDM side by side marked with the lesion locations. The differences in the BI-RADS assessments of both MCs and masses between SM and FFDM did not achieve statistical significance for all three readers. The conspicuity of MCs on SM was superior to that on FFDM and the BI-RADS assessments of MCs were comparable while the conspicuity of masses on SM was degraded and interpretation on SM was less accurate than that on FFDM. The SM may be useful for efficient prescreening of MCs in DBT but the DBT should be used for detection and characterization of masses.

In this article the authors evaluate a recently proposed variable dose (VD)-digital breast tomosynthesis (DBT) acquisition technique in terms of the detection accuracy for breast masses and microcalcification (MC) clusters. With this technique, approximately half of the total dose is used for one center projection and the remaining dose is split among the other tomosynthesis projection views. This acquisition method would yield both a projection view and a reconstruction view. One of the aims of this study was to evaluate whether the center projection alone of the VD acquisition can provide equal or superior MC detection in comparison to the 3D images from uniform dose (UD)-DBT. Another aim was to compare the mass-detection capabilities of 3D reconstructions from VD-DBT and UD-DBT. In a localization receiver operating characteristic (LROC) observer study of MC detection, the authors compared the center projection of a VD acquisitioh scheme (at 2 mGy dose) with detector pixel size of 100 microm with the UD-DBT reconstruction (at 4 mGy dose) obtained with a voxel size of 100 microm. MCs with sizes of 150 and 180 microm were used in the study, with each cluster consisting of seven MCs distributed randomly within a small volume. Reconstructed images in UD-DBT were obtained from a projection set that had a total of 4 mGy dose. The current study shows that for MC detection, using the center projection alone of VD acquisition scheme performs worse with area under the LROC curve (AL) of 0.76 than when using the 3D reconstructed image using the UD acquisition scheme (AL=0.84). A 2D ANOVA found a statistically significant difference (p=0.038) at a significance level of 0.05. In the current study, although a reconstructed image was also available using the VD acquisition scheme, it was not used to assist the MC detection task which was done using the center projection alone. In the case of evaluation of detection accuracy of masses, the reconstruction with VD-DBT (AL=0.71) was compared to that obtained from the UD-DBT (AL=0.78). The authors found no statistically significant difference between the two (p-value=0.22), although all the observers performed better for UD-DBT.

Accurate detection of microcalcifications ( ) is crucial for the early detection of breast cancer. Some clinical studies have indicated that digital breast tomosynthesis (DBT) systems with a wide angular range have inferior detectability compared with those with a narrow angular range. This study aims to (1)provide guidance for optimizing wide-angle (WA) DBT for improving detectability and (2)prioritize key optimization factors. An in-silico DBT pipeline was constructed to evaluate detectability of a WA DBT system under various imaging conditions: focal spot motion (FSM), angular dose distribution (ADS), detector pixel pitch, and detector electronic noise (EN). Images were simulated using a digital anthropomorphic breast phantom inserted with clusters. Evaluation metrics included the signal-to-noise ratio (SNR) of the filtered channel observer and the area under the receiver operator curve (AUC) of multiple-reader multiple-case analysis. Results showed that FSM degraded sharpness and decreased the SNR and AUC by 5.2% and 1.8%, respectively. Non-uniform ADS increased the SNR by 62.8% and the AUC by 10.2% for filtered backprojection reconstruction with a typical clinical filter setting. When EN decreased from 2000 to 200 electrons, the SNR and AUC increased by 21.6% and 5.0%, respectively. Decreasing the detector pixel pitch from 85 to improved the SNR and AUC by 55.6% and 7.5%, respectively. The combined improvement of a pixel pitch and EN200 was 89.2% in the SNR and 12.8% in the AUC. Based on the magnitude of impact, the priority for enhancing detectability in WA DBT is as follows: (1)utilizing detectors with a small pixel pitch and low EN level, (2)allocating a higher dose to central projections, and (3)reducing FSM. The results from this study can potentially provide guidance for DBT system optimization in the future.

We have constructed a prototype next-generation tomosynthesis (NGT) system that supports a non-isocentric acquisition geometry for digital breast tomosynthesis (DBT). In this geometry, the detector gradually descends in the superior-to-inferior direction. The aim of this work is to demonstrate that this geometry offers isotropic super-resolution (SR), unlike clinical DBT systems which are characterized by anisotropies in SR. To this end, a theoretical model of a sinusoidal test object was developed with frequency exceeding the alias frequency of the detector. We simulated two geometries: (1) a conventional geometry with a stationary detector, and (2) a non-isocentric geometry. The input frequency was varied over the full 360° range of angles in the plane of the object. To investigate whether SR was achieved, we calculated the Fourier transform of the reconstruction. The amplitude of the tallest peak below the alias frequency was measured relative to the peak at the input frequency. This ratio (termed the r-factor) should approach zero to achieve high-quality SR. In the conventional geometry, the r-factor was minimized (approaching zero) if the orientation of the frequency was parallel with the source motion, yet exceeded unity (prohibiting SR) in the orientation perpendicular to the source motion. However, in the non-isocentric geometry, the r-factor was minimized (approaching zero) for all orientations of the frequency, meaning SR was achieved isotropically. In summary, isotropic SR in DBT can be achieved using the non-isocentric acquisition geometry supported by the NGT system.

To the Editor, I have a concern regarding a recently published article in European Radiology entitled 'Diagnostic accuracy of digital breast tomosynthesis versus digital mammography for benign and malignant lesions in breasts: a meta-analysis' [1]. The authors claim to investigate one-view digital breast tomosynthesis (DBT) versus digital mammography (DM) in a meta-analysis based on seven studies [2–8], but in fact, only four of the studies [2,3,7,8] investigate these particular imaging techniques. Out of these four studies, only one study showed significant improvement using one-view DBT in comparison with regular mammography (DM). That study material was enriched with subtle cases, more difficult than typically encountered in the clinical practice, with a relatively low frequency of DCIS. These factors may have increased the effect sizes. However, when the studies are stratified and analysed according to projection views, the pooled sensitivity and specificity may not correlate with the conclusions drawn, e.g. ‘the present study revealed that one-view DBT had higher sensitivity and specificity for the diagnosis of benign and malignant lesions in the breasts. These results illustrated the superior diagnostic accuracy of DBT relative to DM using meta-analysis’. Readers of the article might get the impression that one-view DBT alone is superior to DM in a general population of women, which may not be true. The following studies [4–6] did not investigate DBT in one view, but used other DBT techniques:

In the attack of the encryption algorithm ARCFOUR(RC4), new method of machine learning based on Wavelet Transform(WT) and Principal Component Analysis(PCA)is proposed. WT is used to reconstruct the new signals to extract information from the original signals effectively. Components in low and high frequency and reconstructed signals are made by WT. In order to analyze the impact of the signals on the success rate of prediction, four kinds of signals are adapted respectively for dimensionality reduction, which contains initial signals, reconstructed signals, and the signals in low and high frequency. By the classification of Support Vector Machine (SVM), the results show that the effect of the reconstructed signals is the best one. The reconstructed signals reduce the noise influence. In the range of 500 dimensions, the classification effect of the reconstructed signals is obviously better than others. As the dimension increases, the effect becomes small. The effect of signals in low frequency is more effective than that of the original in most of dimensions. The classification success rate is still high with fewer dimensions. In the four kinds of signals, the effect of the signals in high frequency is the worst. The results show that WT combined with PCA is a good method to handle with classification.

Analysis of geophone recordings from an OBS survey offshore Norway shows that excellent long-offset signals may be measured for frequencies below 2 Hz, and as low as 0.25 Hz. This observation is in contrast to the hydrophone recordings that do not show such excellent long-offset low frequency signals. We think that there are at least two factors that cause this: First, the fact that the receiver ghost spectrum is non-zero for the geophone component while the hydrophone ghost spectrum approaches zero for low frequencies, respectively. Second, the hydrophone component is more affected by noise created by (long wave length) ocean water waves compared to the vertical geophone component. Furthermore, a critical factor is the intrinsic low frequency response of the geophone and the hydrophone, which is a critical factor that controls what frequencies we may record. In our case, we find that the low frequency geophone response is sufficient to measure signals that are above the background noise level. We think that this opens a new possibility for low frequency seismic acquisition: Use seabed geophones that are specifically designed to measure low frequency (0.1-5 Hz) signals. If successful, this might open new possibilities for imaging below complex salt structures, below basalt and for full waveform inversion.

The response of the global ionosphere to solar flares is an important topic in the field of space weather. The global ionospheric response to solar flares is comprehensively analyzed from the perspectives of total electron content (TEC) and very low frequency (VLF) signals by using solar flare data on the eruption days of X-class flares from 2006 to 2019, including flare level, flare duration, geographical location, and local time. In addition, the relationship between X-ray flux and VLF phase variation is studied through correlation analysis. The concepts of disturbance intensity (DI) and disturbance angle are defined, and a DI evaluation model is established to help detect the difference in sensitivity to solar flares between TEC and VLF signals. Results show the following. (1) The higher the flare level and the longer the duration, the greater the disturbance to the ionosphere. Simultaneously, a phenomenon exists in which the disturbance caused by low-level and long-lasting flares is greater than that caused by high-level flares. (2) VLF phase variation and flare level exhibit a good correlation, and they are also closely related to geographical location and local time. The disturbance degree of a station facing the sun is more evident than that of a station facing away from the sun. The TEC disturbance of stations in the morning (local time) is more obvious than that in the afternoon, and disturbance increases along the direction of Earth’s rotation. (3) When DI is at the same level, the lowest flare level that causes TEC response is higher than the lowest flare level that causes VLF signal response. The disturbance angle of TEC is unevenly distributed within the interval [0°, 90°], and that of VLF signals is more than 85°. The sensitivity of VLF signals to flare response is considerably higher than that of TEC, and the difference between the two even stride across DI level.

Very low frequency (VLF) (2 to 20 Hz) and low frequency (LF) (20 to 200 Hz) physical noise models and previous measurements are discussed and compared to low frequency, high resolution noise measurements. These data show long-term persistent directional characteristics associated with distant shipping lanes and density patterns. Short-term averages show a temporally dynamic field composed of resolved distant shipping and uncorrelated background noise. Calibrated low frequency transmission loss and signal coherence length estimates are presented for down-slope to deep ocean and bottom-limited sound channels. The transmission results compare favorably with previous measurements and computations performed with range-dependent water column and sediment characteristics. These results emphasize the importance of the coherent contribution from coastal shipping to the mid-ocean noise field. Vertical directionality measurements by Anderson et. al. (1972) show a broad angular distribution of noise intensity near the horizontal at low frequencies and a peaked distribution about the horizontal at high frequencies. This broad angular distribution near the horizontal is consistent with sound propagating down-slope via a bottom reflectivity which favors lower frequencies. The frequency variation near the horizontal was found smooth and indicates that in addition to surface ships, environmental noise influences the vertical directionality.

Cochlear implant (CI) recipients with residual hearing show improved performance with the addition of low-frequency acoustic stimulation (electro-acoustic stimulation, EAS). The present study sought to determine whether a synthesized first formant (F1) signal provided benefit to speech recognition in simulated EAS hearing and to compare such benefit with that from other low-frequency signals. A further aim was to determine if F1 amplitude or frequency was more important in determining benefit and if F1 benefit varied with formant bandwidth. In two experiments, sentence recordings from a male speaker were processed via a simulation of a partial insertion CI, and presented to normal hearing listeners in combination with various low-frequency signals, including a tone tracking fundamental frequency (F0), low-pass filtered speech, and signals based on F1 estimation. A simulated EAS benefit was found with F1 signals, and was similar to the benefit from F0 or low-pass filtered speech. The benefit did not differ significantly with the narrowing or widening of the F1 bandwidth. The benefit from low-frequency envelope signals was significantly less than the benefit from any low-frequency signal containing fine frequency information. Results indicate that F1 provides a benefit in simulated EAS hearing but low frequency envelope information is less important than low frequency fine structure in determining such benefit.

A low frequency living beings electrotherapy instrument is designed which is based on the transcutaneous electrical nerve stimulation. This system uses ATmega32 (MCU) to control its output and display. The hardware part includes the keyboard, the LCD, the alarm circuit and output circuit .The other part is software, which includes keyboard module, LCD module, pulse creating module and so on. The human-computer interaction can be realized well by the keyboard and LCD module. The pulse creating module controls the frequency, the duty-ratio and time of treatment. Introduction In the area of treatment, physical therapy is a common method of treatment. It is wide application because of the course of treatment without pain, little side effects and significant effect on certain diseases. Investigation shows that the fixed frequency signal is long applied to the stimulation of the human body, the signal will weaken the effect of the human body treatment . Therefore, it is significant for the stimulation of the body that the output signal frequency is independent, which can be well adapted to overcome the ability of human tissue, make the patient obtain the optimal therapeutic effect. The output signal of traditional physical therapy instrument has a certain regularity, which can make the body produce the adaptability and reduce the effect. The core of living beings electrotherapy instrument is the output signal waveform generation module, which relies on Atmega32 to achieve. The PWM module of Atmega32 can control the shape, frequency and amplitude of the output signal, and the output waveform can be generated randomly, applicable symptoms. The system can well solve the shortage of traditional electrotherapy instrument system, such as the treatment of adaptability of output signal, polarization voltage smaller, patient comfort and simple operation etc.. Therefore, it has a certain practical value to research and development of living beings electrotherapy. Electrotherapy principle The human body is a good conductor of electricity, has certain conductivity. During the treatment, the pulse current is applied to the deep body tissues and stimulate tissue to produce a variety of regular and irregular shrinkage . Such action by the organization can reduce the pain sensation, promote parts of the organization metabolism, but also has anti-inflammatory, removing blood stasis, adjusting the endocrine and metabolic disorders, improving local tissue blood circulation, eliminating excess fat, dredging the channel and other effects [3] . The pulse signal frequency is lower than 1000Hz is defined as the low frequency signal in medicine. The use of low frequency electrical stimulation of tissue to recuperate the body way is referred to as low frequency electrotherapy. Low frequency electrical signals applied to human tissue, stimulates the human tissue, which can accelerate the blood flow of partial tissue and alleviate the pain. Treatment principle of the system is based on transcutaneous electrical nerve stimulation therapy .The low frequency electrical signal is inputted to the human body by the skin and plays a role in healing and alleviate pain, which is known as TENS. TENS is widely used clinically, which can promote the local blood circulation, alleviate the pain and promote the development of bones. International Conference on Materials, Environmental and Biological Engineering (MEBE 2015) © 2015. The authors Published by Atlantis Press 448 People know about more the pain mechanism along with the progress of electronic and medical knowledge and the improving of people living conditions. Firstly the meridian theory thinks that the disease occurrence and development are related the acupoints of main and collateral channels. Later, the research indicates that the main and collateral channels and acupoints have the characteristic of potential high and low impedance and the impedance can change when the electrical signal effects them, which can make the human body appear acid, hemp, pain, swelling and other physiological phenomena. Therefore, the meridian and points which can reflect the function of muscle tissue, organ or physical condition should be chosen, the potential of the body can quickly restore balance, the meridian smooth, and the body is healthy by imposing its corresponding pulse signal. The overall design of the system The structure diagram of the system is shown in figure 1. It mainly consists of two parts: based on the ATmega32 control circuit and PWM interface circuit. The core of the control circuit is ATmega32, which has abundant resources and general equipment interface and includes key module, LCD module, PWM output module, sampling module, alarm module. The PWM Interface circuit includes filter circuit and power amplifier circuit. Atmage32 ADC LCD interface Keyboard interface PWM output display module Keyboard module alarm module signal sampling output circuit electrode

The ipsilateral comparison paradigm (ICP) uses a monaurally presented base tone punctuated by referent tones of greater or less intensity to reveal magnitude-estimated loudness adaptation. Research with this technique has demonstrated adaptation across a broad spectrum of base-tone intensities [Dange etal., J. Gen. Psychol. 120, 217–274 (1993)]. Given evidence for different coding mechanisms at high and low signal frequencies and ear differences in adaptation [Ivry and Libby, Psychol. Sci. 4, 41–45 (1993); Davis and Weiler, Br. J. Audiol. 12, 59–60 (1978)], the present study examined the generality of ICP-determined loudness adaptation for the two ears at frequencies of 250, 1000, and 4000 Hz. Base tone intensity in all conditions was 50 dBA. Three referent conditions (+10 dB referent, −10 dB referent, and a no referent control) were also employed. The generality of ICP-determined adaptation was demonstrated by similar declines in loudness over time in all ear/frequency combinations when referent tones were present. Adaptation effects were noted for the base and for the referent tones. In addition, adaptation was stronger for the base tone in comparison to the +10 dB referent and for the −10 dB referent in comparison to the base, a result consistent with Hood’s model of loudness adaptation [Weiler and Hood, Audiology 16, 499–506 (1977)].