Rationale and Objectives Improvements in the diagnosis of early breast cancers depend on a physician’s ability to obtain the information necessary to distinguish nonpalpable malignant and benign tumors. Viscoelastic features that describe mechanical properties of tissues may help to distinguish these types of lesions. Materials and Methods 21 patients with nonpalpable, pathology-confirmed BI-RADS 4 or 5 breast lesions (10 benign, 11 malignant) detected by mammography were studied. Viscoelastic parameters were extracted from a time sequence of ultrasonic strain images and differences in the parameters between malignant and benign tumors were compared. Parametric data were color coded and superimposed on sonograms. Results The strain retardance time parameter, T1, provided the best discrimination between malignant and benign tumors (p<0.01). T1 measures the time required for tissues to fully deform (strain) once compressed, and therefore it describes the time-varying viscous response of tissue to a small deforming force. Compared to the surrounding background tissues, malignant lesions have smaller average T1 values while benign lesions have larger T1 values. This tissue-specific contrast correlates with known changes in the extracellular matrix of breast stroma. Conclusion Characterization of nonpalpable breast lesions is improved by the addition of viscoelastic strain imaging parameters. The differentiation of malignant and benign BI-RADS 4 or 5 tumors is especially evident with the use of the retardation time estimates, T1.

In vivo measurements of the viscoelastic properties of breast tissue are described. Ultrasonic echo frames were recorded from volunteers at 5 fps while applying a uniaxial compressive force (1-20 N) within a 1 s ramp time and holding the force constant for up to 200 s. A time series of strain images was formed from the echo data, spatially averaged viscous creep curves were computed, and viscoelastic strain parameters were estimated by fitting creep curves to a second-order Voigt model. The useful strain bandwidth from this quasi-static ramp stimulus was 10(-2) < or = omega < or = 10(0) rad/s (0.0016-0.16 Hz). The stress-strain curves for normal glandular tissues are linear when the surface force applied is between 2 and 5 N. In this range, the creep response was characteristic of biphasic viscoelastic polymers, settling to a constant strain (arrheodictic) after 100 s. The average model-based retardance time constants for the viscoelastic response were 3.2 +/- 0.8 and 42.0 +/- 28 s. Also, the viscoelastic strain amplitude was approximately equal to that of the elastic strain. Above 5 N of applied force, however, the response of glandular tissue became increasingly nonlinear and rheodictic, i.e., tissue creep never reached a plateau. Contrasting in vivo breast measurements with those in gelatin hydrogels, preliminary ideas regarding the mechanisms for viscoelastic contrast are emerging.

Imaging systems are most effective for detection and classification when they exploit contrast mechanisms specific to particular disease processes. A common example is mammography, where the contrast depends on local changes in cell density and the presence of microcalcifications. Unfortunately the specificity for classifying malignant breast disease is relatively low for many current diagnostic techniques. This paper describes a new ultrasonic technique for imaging the viscoelastic properties of breast tissue. The mechanical properties of glandular breast tissue, like most biopolymers, react to mechanical stimuli in a manner specific to the microenvironment of the tissue. Elastic properties allow noninvasive imaging of desmoplasia while viscous properties describe metabolism-dependent features such as pH. These ultrasonic methods are providing new tools for studying disease mechanisms as well as improving diagnosis.

Techniques are being developed to image viscoelastic features of soft tissues from time-varying strain. A compress-hold-release stress stimulus commonly used in creep-recovery measurements is applied to samples to form images of elastic strain and strain retardance times. While the intended application is diagnostic breast imaging, results in gelatin hydrogels are presented to demonstrate the techniques. The spatiotemporal behaviour of gelatin is described by linear viscoelastic theory formulated for polymeric solids. Measured creep responses of polymers are frequently modelled as sums of exponentials whose time constants describe the delay or retardation of the full strain response. We found the spectrum of retardation times τ to be continuous and bimodal, where the amplitude at each τ represents the relative number of molecular bonds with a given strength and conformation. Such spectra indicate that the molecular weight of the polymer fibres between bonding points is large. Imaging parameters are found by summarizing these complex spectral distributions at each location in the medium with a second-order Voigt rheological model. This simplification reduces the dimensionality of the data for selecting imaging parameters while preserving essential information on how the creeping deformation describes fluid flow and collagen matrix restructuring in the medium. The focus of this paper is on imaging parameter estimation from ultrasonic echo data, and how jitter from hand-held force applicators used for clinical applications propagate through the imaging chain to generate image noise.

Viscoelastic properties of soft tissues and hydropolymers depend on the strength of molecular bonding forces connecting the polymer matrix and surrounding fluids. The basis for diagnostic imaging is that disease processes alter molecular-scale bonding in ways that vary the measurable stiffness and viscosity of the tissues. This paper reviews linear viscoelastic theory as applied to gelatin hydrogels for the purpose of formulating approaches to molecular-scale interpretation of elasticity imaging in soft biological tissues. Comparing measurements acquired under different geometries, we investigate the limitations of viscoelastic parameters acquired under various imaging conditions. Quasistatic (step-and-hold and low-frequency harmonic) stimuli applied to gels during creep and stress relaxation experiments in confined and unconfined geometries reveal continuous, bimodal distributions of respondance times. Within the linear range of responses, gelatin will behave more like a solid or fluid depending on the stimulus magnitude. Gelatin can be described statistically from a few parameters of low-order rheological models that form the basis of viscoelastic imaging. Unbiased estimates of imaging parameters are obtained only if creep data are acquired for greater than twice the highest retardance time constant and any steady-state viscous response has been eliminated. Elastic strain and retardance time images are found to provide the best combination of contrast and signal strength in gelatin. Retardance times indicate average behavior of fast (1-10 s) fluid flows and slow (50-400 s) matrix restructuring in response to the mechanical stimulus. Insofar as gelatin mimics other polymers, such as soft biological tissues, elasticity imaging can provide unique insights into complex structural and biochemical features of connectives tissues affected by disease.

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Ultrasonic elasticity imaging is a promising new tool for breast cancer diagnosis and management. Ultrasound is applied to sense small local tissue deformations noninvasively to image stiffness and thus exploit the large intrinsic stiffness contrast generated during the progression of many diseases in vivo. This paper briefly reviews several related approaches to breast elasticity imaging to explain some of the observed variability in breast imaging results. Preliminary clinical results from a population of 13 patients with small and nonpalpable breast lesions obtained with a low noise elasticity imaging algorithm developed in our group are then reported. All the benign lesions exhibited normal elasticity ranges. About half of the malignant lesions were undetected with elasticity imaging most likely because of their small size (<7mm) or softening from the addition of fatty-replaced tissue. Other malignant lesions were clearly identified as areas with extreme elasticity values compared to their surroundings. We observed that some malignant lesions did not exhibit any desmoplasic stiffening while others showed an uncommon softening. It is clear that by broadening the study population to include small and nonpalpable lesions, we see much variability in elasticity image findings.

Introduction Coronavirus disease 2019 (COVID-19) vaccine hesitancy amongst healthcare workers (HCW) has been reported in varying degrees in different parts of the world. In this study, we investigate the degree of vaccine hesitancy amongst HCWs and factors associated with it during the second wave of the pandemic in our centre. Methods We undertook this single-centre, cross-sectional study in an urban tertiary care hospital, using a modified Oxford COVID-19 vaccine hesitancy scale. We performed descriptive and appropriate univariate analysis. We used the Kruskal Wallis test as appropriate, and Spearman rank correlation to evaluate the relation between general attitude to vaccination and COVID vaccine hesitancy score. Results We obtained 223 responses. The majority of HCWs in our sample (n = 201; 90.1%) had received at least one dose of the vaccine. The mean (SD) Oxford vaccine hesitancy score was 28.54 ± 2.05, with no significant difference observed between doctors (28.45 ± 2.26) and nurses (28.68 ± 1.70), or across different specialities. Of the respondents, 92.7% (n = 216) responded positively to taking the vaccine. The lack of dependents at home was the only significant contributor to vaccine hesitancy. Age, gender, marital status, and COVID-19 infection status did not significantly affect vaccine hesitancy. Conclusion We found a significantly lower degree of hesitancy towards COVID-19 amongst HCWs in our centre during the pandemic’s second wave. A more comprehensive and multi-centric study is required to validate this finding.