No abstract

Two parameters in high-frequency ultrasound (20-80 MHz) have been found to be sensitive to a range of pathologies in resected margins from breast conservation surgery: The number of peaks (the peak density) in the waveform spectrum and the slope of the Fourier transform of the waveform spectrum. Previous studies have indicated that peak density and slope may correlate to microscopic heterogeneity in tissue structure, which is modified by atypical and malignant processes. To test this hypothesis, through-transmission and pulse-echo measurements were acquired from gelatin-based phantoms containing polyethylene microspheres and nylon fibers (2.5-10% volume concentration). Multipole methods were also used to model through-transmission measurements of tumor progression in lobular carcinoma in situ. The simulated breast tissue contained 1000-2000 nucleated cells with random lobular cavities. The peak densities of the heterogeneous phantoms were significantly greater than those of the homogeneous control samples, whereas the slopes were less. Similarly, the models produced spectra with peak densities that increased with malignant cell proliferation. The results are consistent with breast tissue data, and provide a physical mechanism for the use of peak density and slope in the imaging of breast tissues with atypical and malignant pathologies. This work was supported by Utah Valley University.

Recent work indicates that Alzheimer's disease (AD) affects the cytoskeleton and cellular structure through mutations that alter structural proteins, and that dysfunction of the cytoskeleton may play a pivotal role in AD and other neurodegenerative diseases. The goal of our research is to determine if high-frequency ultrasound can detect cytoskeletal dysfunction in AD. Research on the molecular subtypes of breast cancer indicate that mutations specific to each subtype may change the characteristics of the cytoskeleton and resulting properties of the cell such as size, shape, and stiffness. Both computer simulation and experiment have demonstrated that high-frequency ultrasound in the 10–100 MHz range is sensitive to these properties. For this study, ultrasonic tests were conducted on monolayer cell cultures of breast cancer cell lines of different subtypes. The ultrasonic spectra were compared and correlated to model results using a pattern recognition algorithm. Preliminary results indicate that cell stiffness and size can be determined from the measurements. The cytoskeletal properties of the cells were additionally modified by chemical and physical agents such as the introduction of colchicine and electric fields to mimic the effects of AD. Results from these and future studies with neuron cell cultures will be discussed.

Breast cancer can be divided into molecular subtypes which are defined by their genetic and protein expression profiles. Current methods aimed at testing these biochemical signatures are effective classifiers but are not easily transferable to real-time clinical applications. The rapid, cost-effective determination of molecular subtype by other means would be a significant advancement in cancer detection and treatment. Our studies suggest that high-frequency ultrasound (10–100 MHz) may be sensitive to variations among breast cancer subtypes through their cytoskeletal structures, which have distinct biomechanical signatures. To further test this hypothesis, four breast cancer cell lines of different subtypes were cultured and ultrasonically tested. Direct pulse-echo measurements were collected from the cell layers using a 50-MHz transducer immersed in the growth media of the culture plates. Cell reflections in the waveforms were isolated and spectrally analyzed using computationally modeled spectra and principal component analysis (PCA). Cell phenotypes were profiled by using heat maps to display the relative distances between the PCA scores of the experimental and model spectra. The results indicate the phenotype and thus molecular subtype of cancer cells could potentially be determined by comparing their measured spectra to model spectra using a feature classification program such as PCA.

The molecular subtypes of breast cancer correlate more strongly to prognosis, treatment response, and local recurrence than the traditional classifications based on histopathology. The ability to determine the subtype of breast tumors during surgery or biopsy in real time would provide physicians with new diagnostic capabilities to screen suspicious lesions, to perform high-precision surgery on malignant and premalignant lesions, and to personalize treatment for patients. This work studied the potential of using the molecular subtypes as natural biomarkers for characterizing breast cancer with high-frequency ultrasound (10–100 MHz). We hypothesized that high-frequency ultrasound would be able to detect variations in cell biomechanical properties due to mutations found in aggressive subtypes (e.g., basal-like and Her2 +). These mutations alter the expression levels of proteins that regulate the actin cytoskeleton, thereby modifying the biomechanical and thus ultrasonic properties of the cells. Pulse-echo measurements were acquired in vitro from breast cancer cell lines with different subtypes. The results showed that each cell line produced a unique ultrasonic spectral signature. One of the cell lines additionally exhibited changes over time, possibly due to dedifferentiation. Correlation of the results to other cell characterization methods will also be presented. [This work was supported by Utah Valley University.]