Breast cancer is the most common cancer in women worldwide. Two million women are diagnosed annually, resulting in 685,000 annual deaths. Early diagnosis is critical to reducing mortality. Although screening with mammography has been shown to have reduced breast cancer-related mortality through early detection, dense breast tissues reduce mammographic sensitivity, potentially delaying diagnoses, and contributing to poorer outcomes. Therefore, there is a need for more accessible and cost-effective supplemental screening technologies, especially for high-risk populations, especially women with dense breasts. To address these challenges, a promising approach involves combining widely available, cost-effective, and accessible ultrasound-based technologies with economical hardware, software modules, and automated techniques. Among these technologies, Doppler imaging plays a crucial role in the clinical evaluation of breast abnormalities, as intratumoural blood flow has been shown to correlate with the aggressiveness and histological grade of the tumour. The development of a novel automated, portable, and a patient-dedicated 3D automated breast ultrasound (ABUS) system for point-of-care breast cancer supplemental screening holds significant promise. The proposed system has previously demonstrated the capability to generate accurate whole-breast B-mode images, which can aid in the early detection of breast cancer in women with dense breasts. Additionally, it offers the advantage of incorporating Doppler imaging for the assessment of blood flow within suspicious lesions, a capability not commonly available with commercial ABUS systems. By leveraging Doppler imaging in conjunction with 3D Bmode ABUS, this innovative approach could improve breast cancer-related health outcomes and equity in access to healthcare, especially for underserved and vulnerable populations.
Fabrication of arterial phantoms is enabled through specially developed additive manufacturing techniques in the Organic Mechatronics and Smart Materials Laboratory to produce high resolution 3D conjugated polymer structures. These techniques have been modified to enable fabrication of arterial phantoms through the direct ink writing of polydimethylsiloxane (PDMS) into a microgel support bath. This support bath behaves as a Bingham plastic, deforming under shear stress during extrusion but quickly returning to solid-state, thus supporting the PDMS and allowing the desired structure to be maintained, producing high-resolution complex geometries. Following curing and removal of the PDMS phantom from the support bath, PEDOT:PSS thin films are selectively deposited on the phantom surface. These films have demonstrated significant hygroscopic actuation under an applied electric field. These phantoms may be imaged with Particle image velocimetry (PIV) to characterize the effect of actively changing vessel geometry. PIV can provide the instantaneous full-field velocity profile and is a well-established technique to characterize flow through phantoms fabricated by conventional casting techniques to provide a standard of comparison. To effectively image the device via PIV, the optical properties of the components must be considered. To this end, PDMS and PEDOT:PSS have been employed due to their favourable transmission properties in the visible spectrum. Additionally, PDMS provides a compliant passive structure to be deformed with relatively low force, easing the performance requirements of the actuators. While this device focuses on the actuation of phantom vessel geometry, this technique may be extended to other applications in microfluidics to create onboard peristaltic pumping action and vascular networks.
New high-frame-rate ultrasound imaging techniques are being developed to image tissue motion and blood flow with high sensitivity and at high temporal resolution. An emerging application for these new techniques is diagnosing inutero and neonatal cardiac disease. We have developed a morphologically and hemodynamically accurate neonatal heart phantom to provide a high-fidelity physical model for laboratory testing of ultrafast color Doppler echocardiography methods. This paper summarizes the design and functionality of the simulator by measuring pressure gradients across the mitral valve at a physiologic heart-rate range and stroke volume and by evaluating valve function using 2D transesophageal echocardiography (TEE) and Doppler images. The phantom achieved normal physiological pressures across the mitral valve ranging from 42 to 87 mmHg in systole and 2.4 to 4.2 mmHg in diastole at heartrates of 100, 125 and 150 beats per minute (bpm), with a realistic neonatal stroke volume of 7 ml. 2D ultrasound images were obtained at 60 bpm.
KEYWORDS: Tissues, Ultrasonography, Signal attenuation, Medical imaging, Medical research, Diagnostics, Acoustics, Liquids, Transducers, Manufacturing, Silicon
Tissue mimicking materials are physical constructs exhibiting certain desired properties, which are used in machine
calibration, medical imaging research, surgical planning, training, and simulation. For medical ultrasound,
those specific properties include acoustic propagation speed and attenuation coefficient over the diagnostic frequency
range. We investigated the acoustic characteristics of polyvinyl chloride (PVC) plastisol, polydimethylsiloxane
(PDMS), and isopropanol using a time-of-light technique, where a pulse was passed through a sample
of known thickness contained in a water bath. The propagation speed in PVC is approximately 1400ms-1
depending on the exact chemical composition, with the attenuation coefficient ranging from 0:35 dB cm-1 at
1MHz to 10:57 dB cm-1 at 9 MHz. The propagation speed in PDMS is in the range of 1100ms-1, with an
attenuation coefficient of 1:28 dB cm-1 at 1MHz to 21:22 dB cm-1 at 9 MHz. At room temperature (22 °C), a
mixture of water-isopropanol (7:25% isopropanol by volume) exhibits a propagation speed of 1540ms-1, making
it an excellent and inexpensive tissue-mimicking liquid for medical ultrasound imaging.
Plane wave imaging is desirable for its ability to achieve high frame rates, allowing the capture of fast dynamic events, and continuous Doppler data. In most implementations of plane-wave imaging, multiple low resolution image (LRI) frames from different plane wave tilt angles are compounded to form a single high resolution image (HRI) frame, thereby reducing the frame rate. Compounding is a low-pass mean filter that causes attenuation and aliasing to signals with high Doppler shifts. On the other hand, the lateral beam profile and hence the quality of the HRI frames is improved by increasing the number of compounded frames. Therefore, a tradeoff exists between the Doppler limits and beam profile. In this paper, we present a method that eliminates this tradeoff and produces high resolution images without the use of compounding. The method suppresses the off-focus (clutter) signal by spreading its spectrum, while keeping the spectrum of the in-focus signal intact. The spreading is achieved by using a random sequence of tilt angles, as opposed to a linear sweep. Experiments performed using a carotid vessel phantom with constant flow demonstrate that the spread-spectrum method more accurately measures the parabolic flow profile of the vessel and in particular outperforms conventional plane-wave Doppler at higher flow velocities. The spread-spectrum method is expected to be valuable for Doppler applications that require measurement of high velocities at high frame rates.
KEYWORDS: Data modeling, Statistical modeling, Simulation of CCA and DLA aggregates, Doppler effect, Ultrasonography, In vitro testing, Arteries, Modeling, Independent component analysis, Turbulence
An in vitro flow system has been used to assess the flow disturbances downstream of the stenosis in a family of seven
carotid bifurcation phantoms modelling varying plaque build-up both axially symmetrically (concentrically) and
asymmetrically (eccentrically). Radio frequency data were collected for 10 s at each of over 1000 sites within each
model, and a sliding 1024-point FFT is applied to the data to extract the Doppler spectrum every 12 ms. From this, the
ensemble average over 10 cardiac cycles of the spectral mean velocity, and the root mean square over these same 10
cardiac cycles - the turbulence intensity (TI), can be obtained as a function of an ensemble averaged cardiac cycle at
each spatial point in all phantoms. TI was investigated by looking at the average over a 25 mm2 square region of interest
in the ICA centered 2 cm distal to the apex of the bifurcation.
TI in the region of interest increased with stenosis severity; at 23ms following peak systole, the time point when TI was
maximal for the majority of models, this ranged from 2.4±0.1 cm/s in the non-diseased model to 6.6±0.3, 16.0±1.4 and
26.1±1.3 cm/s in the 30, 50 and 70% concentrically stenosed (by NASCET criteria) models, respectively. Similarly, TI
was 8.3±0.7, 19.9±1.1, and 26.2±1.2 cm/s in the 30, 50 and 70% eccentrically stenosed models, respectively. Differences
in TI between models, both in increasing stenosis severity and between eccentricities, were statistically different except
between the 70% concentric and eccentric models.
KEYWORDS: Turbulence, Arteries, Doppler effect, Independent component analysis, Linear filtering, Ultrasonography, Simulation of CCA and DLA aggregates, In vivo imaging, Doppler tomography, Electronic filtering
The most widely performed test for patients suspected of having carotid atherosclerosis is Doppler ultrasound (DUS).
Unfortunately, limitations in sensitivity and specificity prevent DUS from being the sole diagnostic tool. Novel DUS
velocity-derived parameters, such as turbulence intensity (TI), may provide enhanced hemodynamic information within
the carotid artery, increasing diagnostic accuracy. In this study, we evaluate a new technique for recording, storing and
analyzing DUS in a clinical environment, and determine the correlation between TI and conventional DUS
measurements. We have recruited 32 patients with a mean age of 69±11 yrs. An MP3 recorder was used to digitally
record Doppler audio signals three times at three sites: the common carotid artery, peak stenosis and region of maximum
turbulence. A Fourier-based technique was used to calculate TI, facilitating clinical application without additional ECGgating
data. TI was calculated as the standard deviation of Fourier-filtered mean velocity data. We found that TI and
clinical PSV were linearly dependent (P<0.001) within the region of maximum turbulence and the precision of all TI
measurements was found to be 14%. We have demonstrated the ability to record Doppler waveform data during a
conventional carotid exam, and apply off-line custom analysis to Doppler velocity data to produce measurements of TI.
KEYWORDS: Particles, 3D modeling, Arteries, Motion models, Independent component analysis, Hemodynamics, Computational fluid dynamics, Turbulence, Data modeling, Simulation of CCA and DLA aggregates
The presence of ulceration in carotid artery plaque is an independent risk factor for thromboembolic stroke. However,
the associated pathophysiological mechanisms - in particular the mechanisms related to the local hemodynamics in the
carotid artery bifurcation - are not well understood. We investigated the effect of carotid plaque ulceration on the local
time-varying three-dimensional flow field using computational fluid dynamics (CFD) models of a stenosed carotid
bifurcation geometry, with and without the presence of ulceration. CFD analysis of each model was performed with a
spatial finite element discretization of over 150,000 quadratic tetrahedral elements and a temporal discretization of 4800
timesteps per cardiac cycle, to adequately resolve the flow field and pulsatile flow, respectively. Pulsatile flow
simulations were iterated for five cardiac cycles to allow for cycle-to-cycle analysis following the damping of initial
transients in the solution. Comparison between models revealed differences in flow patterns induced by flow exiting
from the region of the ulcer cavity, in particular, to the shape, orientation and helicity of the high velocity jet through the
stenosis. The stenotic jet in both models exhibited oscillatory motion, but produced higher levels of phase-ensembled
turbulence intensity in the ulcerated model. In addition, enhanced out-of-plane recirculation and helical flow was
observed in the ulcerated model. These preliminary results suggest that local fluid behaviour may contribute to the
thrombogenic risk associated with plaque ulcerations in the stenotic carotid artery bifurcation.
Doppler ultrasound (DUS) is widely used to diagnose and plan treatments for vascular diseases, but the relationship between complex blood flow dynamics and the observed DUS signal is not completely understood. In this paper, we demonstrate that Doppler ultrasound can be realistically simulated in a real-time manner via the coupling of a known, previously computed velocity field with a simple model of the ultrasound physics. In the present case a 3D computational fluid dynamics (CFD) model of physiologically pulsatile flow a stenosed carotid bifurcation was interrogated using a sample volume of known geometry and power distribution. Velocity vectors at points within the sample volume were interpolated using a fast geometric search algorithm and, using the specified US probe characteristics and orientation, converted into Doppler shifts for subsequent display as a Doppler spectrogram or color DUS image. The important effect of the intrinsic spectral broadening was simulated by convolving the velocity at each point within the sample volume by a triangle function whose width was proportional to velocity. A spherical sample volume with a Gaussian power distribution was found to be adequate for producing realistic Doppler spectrogram in regions of uniform, jet, and recirculation flow. Fewer than 1000 points seeded uniformly within a radius comprising more than 99% of the total power were required, allowing spectra to be generated from high resolution CFD data at 100Hz frame rates on an inexpensive desktop workstation.
KEYWORDS: Turbulence, Doppler effect, In vitro testing, Arteries, Blood, Ultrasonography, Simulation of CCA and DLA aggregates, Independent component analysis, Data acquisition, Computer simulations
Turbulence is ubiquitous to many systems in nature, except the human vasculature. Development of turbulence in the human vasculature is an indication of abnormalities and disease. A severely stenosed vessel is one such example. In vitro modeling of common vascular diseases, such as a stenosis, is necessary to develop a better understanding of the fluid dynamics for a characteristic geometry. Doppler ultrasound (DUS) is the only available non-invasive technique for in vivo applications. Using Doppler velocity-derived data, turbulence intensity (TI) can be calculated. We investigate a realistic 70% stenosed bifurcation model in pulsatile flow and the performance of this model for turbulent flow. Blood-mimicking fluid (BMF) was pumped through the model using a flow simulator, which generated pulsatile flow with a mean flow rate of 6 ml/s. Twenty-five cycles of gated DUS data were acquired within regions of laminar and turbulent flow. The data was digitized at 44.1 kHz and analyzed at 79 time-points/cardiac cycle with a 1024-point FFT, producing a 1.33 cm/s velocity resolution. We found BMF to exhibit DUS characteristics similar to blood. We demonstrated the capabilities to generate velocities comparable to that found in the human carotid artery and calculated TI in the case of repetitive pulsatile flow.
KEYWORDS: Doppler effect, Ultrasonography, Turbulence, Arteries, Simulation of CCA and DLA aggregates, Data acquisition, Independent component analysis, In vitro testing, Visualization, Signal processing
A unique in-vitro system has been developed that incorporates both realistic phantoms and flow. The anthropomorphic carotid phantoms are fabricated in agar with stenosis severity of 30% or 70% (by NASCET standards) and one of two geometric configurations- concentric or eccentric. The phantoms are perfused with a flow waveform that simulates normal common carotid flow. Pulsed Doppler ultrasound data are acquired at a 1 mm grid spacing throughout the lumen of the carotid bifurcation. To obtain a half-lumen volume, symmetric about the mid plane, requires a 13 hour acquisition over 3238 interrogation sites, producing 5.6 Gbytes of data. The spectral analysis produces estimates of parameters such as the peak velocity, mean velocity, spectral-broadening index, and turbulence intensity. Color-encoded or grayscale-encoded maps of these spectral parameters show distinctly different flow patterns resulting from stenoses of equal severity but different eccentricity. The most noticeable differences are seen in the volumes of the recirculation zones and the paths of the high-velocity jets. Elevated levels of turbulence intensity are also seen distal to the stenosis in the 70%-stenosed models.
KEYWORDS: Doppler effect, Ultrasonography, Signal processing, Computer programming, Data acquisition, Image compression, Digital signal processing, Data modeling, Analytical research, In vitro testing
The effect of lossy, MP3 (MPEG-Layer 3) compression on clinically important Doppler parameters - derived from spectral analysis of Doppler ultrasound signals - was investigated. Ten, 10-second acquisitions of gated Doppler ultrasound signal were collected in a phantom perfused with a pulsatile flow waveform. Doppler data were collected using two sample volume lengths - 1.5 mm and 10 mm. The in- phase and quadrature Doppler signals were digitized at 44.1 kHz and compressed using four grades of signal compression (with corresponding compression ratios given in brackets): uncompressed, 128 kbits/s (11:1), 64 kbits/s (44:1). The digital audio signals were identically processed with a Fourier analysis program that provided an estimate of the instantaneous Doppler frequency (velocity) spectrum and derived parameters such as peak velocity, mean velocity, spectral width, total integrated power, and ratio of spectral power from negative and positive velocities. Analysis of variance indicated there were no significant differences (p>0.05) observed in the peak or mean velocities, spectral width, or the power ratio derived from 128 kbits/s and 64 kbits/s audio signals when compared to the uncompressed audio signals (both sample volume lengths) and the 128 kbits/s audio signals (10 mm sample volume length). However, for the 32 kbits/s audio signals, significant differences (p<0.001) were found in all of the studied parameters.
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