Urban, Matthew W.

Breast biopsy markers have evolved from simple metallic devices to sophisticated multimaterial tools that have become essential for breast cancer care, demonstrating their clinical benefits in surgical planning, radiation targeting, and cost reduction.

Abstract Tissue-mimicking phantoms play a crucial role in evaluating new imaging modalities, simulating clinical scenarios, and ensuring the quality and reliability of imaging systems. Styrene–ethylene/butylene–styrene (SEBS) is an extremely stable and versatile material that has been recently used in ultrasound, elastography, and photoacoustic imaging across diverse applications. Despite its extensive use, a systematic viscoelastic characterization of different SEBS-based formulations reported in the literature, particularly using shear wave elastography (SWE), remains limited. To address this gap, this study investigates the viscoelastic properties of tissue-mimicking phantoms composed of SEBS, glycerol dispersions in SEBS gels, and mixtures of SEBS with low-density polyethylene (LDPE) in mineral oil, using gelatin phantoms as a reference for comparison. Viscoelastic parameters were estimated from shear wave velocity and attenuation dispersion curves using a Kelvin–Voigt model, based on SWE measurements with acoustic radiation force (ARF) excitation, shear plane-wave excitation, and complementary mechanical testing. SEBS-based phantoms exhibited broad, composition-dependent viscoelastic tunability. Increasing SEBS or LDPE content led to stiffer and more viscous responses, while glycerol primarily modulated viscosity and, at higher concentrations, also affected stiffness. Consistent and concordant values were obtained using both ARF and plane wave SWE techniques. The resulting stiffness (2–22 kPa) and viscosity (0.01–1.24 Pa⋅s) overlaps with the mechanical properties of several biological soft tissues, supporting use of these phantoms for SWE validation.

Shear wave elastography generates shear waves with an acoustic radiation force to obtain estimates of the shear wave speed. Shear wave elastography often utilizes time-of-flight calculations that apply cross-correlations or time-to-peak methods to obtain estimates of the shear wave speed in the time-domain. However, these time-domain methods fail to consider the effect of dispersion caused by the shear viscosity, which can introduce substantial errors into estimates of the shear wave speed. To solve this problem, a new viscoelastic method for estimating shear wave parameters in the time-domain is introduced. The performance of the new method, which is applied to shear wave particle velocity waveforms, is established by evaluating a simulated three-dimensional viscoelastic Green's function model for shear waves in the time-domain. Results show that the new viscoelastic time-domain method is applicable to locations outside of the push beam region at the focal depth and throughout a two-dimensional plane. The results also indicate that estimates of the shear wave speed are either comparable to or significantly improved relative to values obtained from cross-correlations while simultaneously providing estimates of the shear viscosity in the time-domain.

Accurate assessment of arterial wall mechanics is essential for detecting vascular pathologies. The technique described herein incorporates a commercially available ultrasound system and applanation tonometry to noninvasively evaluate the local mechanical properties of the common carotid artery (CCA). Pressure waveforms were acquired using a tonometer combined with ultrasound-based diameter of the CCA. The signals were temporally aligned, converted to physical units using brachial systolic and diastolic pressure, and interpolated over uniform strain increments. Hoop stress was estimated using thick-wall assumptions, and hoop strain was derived from mid-wall circumferential stretch. Incremental elastic modulus was computed from local linear fits to the stress–strain data, and the area of the resulting hysteresis loop was used as a surrogate for viscoelastic energy loss, quantified by the energy dissipation ratio (EDR). The method was applied to healthy subjects (HS) and those with cardiovascular risk or confirmed atherosclerosis. In HS, pressure–strain elastic modulus (Ep) ranged from 50–55 kPa and EDR from 2%–6%, while non-healthy subjects showed higher EDR values (10%–20%), reflecting increased arterial viscoelasticity. Results revealed nonlinear pressure–diameter relationships with clear hysteresis, reflecting viscoelastic effects. The technique offers potential as a diagnostic tool for evaluating early, localized vascular alterations.

Color Doppler twinkling improves visibility and ultrasound-guided localization of biopsy markers made of polymethyl methacrylate (PMMA). This study examines the time- and frequency-domain features of twinkling. We performed beamforming on the raw radiofrequency (RF) data collected using a L7-4 transducer, followed by in-phase/quadrature (IQ) demodulation and wall filtering. Frequency content variations were evaluated both within individual Doppler ensembles (pulse-to-pulse) and across multiple frames. Normalized FFT magnitude spectra were computed for both twinkling and non-twinkling (metal) cases using beamformed RF and IQ data. The median of the normalized FFT magnitude (3–10 MHz) was consistently higher for the twinkling case compared to the metal case across RF (–13.75 dB vs –17.29 dB) and the IQ real component (–12.72 dB vs –16.15 dB), indicating broader and more energetic spectral content in twinkling. The frequency spread above the –20 dB threshold was approximately 2.5 times wider (5.38 MHz vs 1.95 MHz) in the twinkling case compared to the metal case. In time domain, the RMS of the standard deviation for the twinkling signal was approximately 28 times higher than that of the metal case across both RF and IQ data. These findings indicate that the ultrasound data from twinkling exhibits a more distributed frequency profile, consistent with observed aperiodic nature.

Color Doppler twinkling is associated with rough-surfaced objects like kidney stones, some clinical breast biopsy markers, and polymethyl methacrylate (PMMA) bone cement. Microbubbles are theorized as the predominant source of twinkling, supported by decreased twinkling under increased pressure. PMMA, metallic breast markers, a low-twinkling PMMA sample, and a non-twinkling metal rod were scanned in a pressure chamber up to 1000 psi using a General Electric Logiq E9 system and C1-6 probe (1.7–3.6 MHz Doppler transmit frequency). Clinical markers maintained distinct twinkling up to 250 psi. PMMA often twinkled at higher pressures, sometimes up to 1000 psi. The controls showed no twinkling. To understand physical structure associations with twinkling, the samples were scanned in a micro-CT system with a pixel resolution of 2 μm. Analysis of PMMA and Cork internal voids showed no correlation with twinkling. However, a correlation between Sa (average difference between the mean surface profile and actual surface profile) values and twinkling was found. This indicates that internal structure is not important for twinkling, and certain surface roughness is critical, possibly providing sites for surface microbubbles to oscillate from incident ultrasound waves.

Ultrasound shear wave elastography is a medical imaging technique where mechanical properties (e.g., shear modulus) of soft tissue are imaged with the goal of diagnosing disease. However, different sources of noise or error often lead to poor images that exacerbate uncertainty of medical diagnosis based on these techniques. Sources of uncertainty include scatterer positions and strengths (e.g., emanating from the cellular structure of tissue), other surrounding tissue not included in the image, and electronic noise, among others. In this work, we are developing Optimal Experimental Design (OED) techniques based on the simulation of the ultrasound imaging process and particle tracking to identify controls that maximize the quality of elastography images. Specifically, we propose a general formulation for OED where the observation error depends on both uncertain quantities and the variables to be inferred (e.g., shear moduli). Furthermore, we pose a nonlinear OED problem where the main design variables are the angles used in plane wave compounding for ultrasound motion tracking of propagating shear waves. The goal of the OED problem is to find the number and values of compounding angles that minimize bias and variance in the estimated shear modulus image. We will demonstrate our approach through various numerical examples.