Kenneth Hoyt

Tissue elasticity properties as biomarkers for prostate cancer

In this paper we evaluate tissue elasticity as a longstanding but qualitative biomarker for prostate cancer and sonoelastography as an emerging imaging tool for providing qualitative and quantitative measurements of prostate tissue stiffness. A Kelvin-Voigt Fractional Derivative (KVFD) viscoelastic model was used to characterize mechanical stress relaxation data measured from human prostate tissue samples. Mechanical testing results revealed that the viscosity parameter for cancerous prostate tissue is greater than that derived from normal tissue by a factor of approximately 2.4. It was also determined that a significant difference exists between normal and cancerous prostate tissue stiffness (p < 0.01) yielding an average elastic contrast that increases from 2.1 at 0.1 Hz to 2.5 at 150 Hz. Qualitative sonoelastographic results show promise for cancer detection in prostate and may prove to be an effective adjunct imaging technique for biopsy guidance. Elasticity images obtained with quantitative sonoelastography agree with mechanical testing and histological results. Overall, results indicate tissue elasticity is a promising biomarker for prostate cancer.

Quantitative characterization of viscoelastic properties of human prostate correlated with histology.

Quantification of mechanical properties of human prostate tissue is important for developing sonoelastography for prostate cancer detection. In this study, we characterized the frequency-dependent complex Youngs modulus of normal and cancerous prostate tissues in vitro by using stress relaxation testing and viscoelastic tissue modeling methods. After radical prostatectomy, small cylindrical tissue samples were acquired in the posterior region of each prostate. A total of 17 samples from eight human prostates were obtained and tested. Stress relaxation tests on prostate samples produced repeatable results that fit a viscoelastic Kelvin-Voigt fractional derivative (KVFD) model (r(2)>0.97). For normal (n = 8) and cancerous (n = 9) prostate samples, the average magnitudes of the complex Youngs moduli (|E*|) were 15.9 +/- 5.9 kPa and 40.4 +/- 15.7 kPa at 150 Hz, respectively, giving an elastic contrast of 2.6:1. Nine two-sample t-tests indicated that there are significant differences between stiffness of normal and cancerous prostate tissues in the same gland (p < 0.01). This study contributes to the current limited knowledge on the viscoelastic properties of the human prostate, and the inherent elastic contrast produced by cancer.

Quantitative sonoelastography for the in vivo assessment of skeletal muscle viscoelasticity

A novel quantitative sonoelastography technique for assessing the viscoelastic properties of skeletal muscle tissue was developed. Slowly propagating shear wave interference patterns (termed crawling waves) were generated using a two-source configuration vibrating normal to the surface. Theoretical models predict crawling wave displacement fields, which were validated through phantom studies. In experiments, a viscoelastic model was fit to dispersive shear wave speed sonoelastographic data using nonlinear least-squares techniques to determine frequency-independent shear modulus and viscosity estimates. Shear modulus estimates derived using the viscoelastic model were in agreement with that obtained by mechanical testing on phantom samples. Preliminary sonoelastographic data acquired in healthy human skeletal muscles confirm that high-quality quantitative elasticity data can be acquired in vivo. Studies on relaxed muscle indicate discernible differences in both shear modulus and viscosity estimates between different skeletal muscle groups. Investigations into the dynamic viscoelastic properties of (healthy) human skeletal muscles revealed that voluntarily contracted muscles exhibit considerable increases in both shear modulus and viscosity estimates as compared to the relaxed state. Overall, preliminary results are encouraging and quantitative sonoelastography may prove clinically feasible for in vivo characterization of the dynamic viscoelastic properties of human skeletal muscle.

A Triple-Targeted Ultrasound Contrast Agent Provides Improved Localization to Tumor Vasculature

Actively targeting ultrasound contrast agents to tumor vasculature improves contrast‐enhanced sonography of tumor angiogenesis. This report summarizes an evaluation of multitargeted microbubbles, comparing single‐, dual‐, and triple‐targeted motifs.

Quantitative mapping of tumor vascularity using volumetric contrast-enhanced ultrasound

Objective:The goal of this research project was to develop a volumetric strategy for real-time monitoring and characterization of tumor blood flow using microbubble contrast agents and ultrasound (US) imaging. Materials and Methods:Volumetric contrast-enhanced US (VCEUS) imaging was implemented on a SONIX RP US system (Ultrasonix Medical Corp, Richmond, BC) equipped with a broadband 4DL14–5/38 probe. Using a microbubble-sensitive harmonic imaging mode (transducer transmits at 5 MHz and receives at 10 MHz), acquisition of postscan-converted VCEUS data was achieved at a volume rate of 1 Hz. After microbubble infusion, custom data processing software was used to derive microbubble time-intensity curve-specific parameters, namely, blood volume (IPK), transit time (T1/2PK), flow rate (SPK), and tumor perfusion (AUC). Results:Using a preclinical breast cancer animal model, it is shown that millimeter-sized deviations in transducer positioning can have profound implications on US-based blood flow estimators, with errors ranging from 6.4% to 40.3% and dependent on both degree of misalignment (offset) and particular blood flow estimator. These errors indicate that VCEUS imaging should be considered in tumor analyses, because they incorporate the entire mass and not just a representative planar cross-section. After administration of an antiangiogenic therapeutic drug (bevacizumab), tumor growth was significantly retarded compared with control tumors (P > 0.03) and reflects observed changes in VCEUS-based blood flow measurements. Analysis of immunohistologic data revealed no differences in intratumoral necrosis levels (P = 0.70), but a significant difference was found when comparing microvessel density counts in control with therapy group tumors (P = 0.05). Conclusions:VCEUS imaging was shown to be a promising modality for monitoring changes in tumor blood flow. Preliminary experimental results are encouraging, and this imaging modality may prove clinically feasible for detecting and monitoring the early antitumor effects in response to cancer drug therapy.

Molecular Ultrasound Imaging Using a Targeted Contrast Agent for Assessing Early Tumor Response to Antiangiogenic Therapy

Contrast‐enhanced ultrasound (US) and targeted microbubbles have been shown to be advantageous for angiogenesis evaluation and disease staging in cancer. This study explored molecular US imaging of a multitargeted microbubble for assessing the early tumor response to antiangiogenic therapy.

Real-time sonoelastography of hepatic thermal lesions in a swine model

Sonoelastography has been developed as an ultrasound-based elasticity imaging technique. In this technique, external vibration is induced into the target tissue. In general, tissue stiffness is inversely proportional to the amplitude of tissue vibration. Imaging tissue vibration will provide the elasticity distribution in the target region. This study investigated the feasibility of using real-time sonoelastography to detect and estimate the volume of thermal lesions in porcine livers in vivo. A total of 32 thermal lesions with volumes ranging from 0.2to5.3cm3 were created using radiofrequency ablation (RFA) or high-intensity focused ultrasound (HIFU) technique. Lesions were imaged using sonoelastography and coregistered B-mode ultrasound. Volumes were reconstructed from a sequence of two-dimensional scans. The comparison of sonoelastographic measurements and pathology findings showed good correlation with respect to the area of the lesions (r2=0.8823 for RFA lesions, r2=0.9543 for HIFU lesions). In addition, good correspondence was found between three-dimensional sonoelastography and gross pathology (3.6% underestimate), demonstrating the feasibility of sonoelastography for volume estimation of thermal lesions. These results support that sonoelastography outperforms conventional B-mode ultrasound and could potentially be used for assessment of thermal therapies.

Microbubble-mediated ultrasonic techniques for improved chemotherapeutic delivery in cancer

Background: Ultrasound (US) exposed microbubble (MB) contrast agents have the capability to transiently enhance cell membrane permeability. Using this technique in cancer treatment to increase the efficiency of chemotherapy through passive, localized delivery has been an emerging area of research. Purpose: Investigation of the influence of US parameters on MB-mediated drug delivery in cancer. Methods: The 2LMP breast cancer cells were used for in vitro experiments and 2LMP tumor-bearing mice were used during in vivo experiments. Changes in membrane permeability were investigated after the influence of MB-mediated US therapy parameters (i.e. frequency, mechanical index, pulse repetition period, US duration, and MB dosing and characteristics) on cancer cells. Calcein, a non-permeable fluorescent molecule, and Taxol, chemotherapeutic, were used to evaluate membrane permeability. Tumor response was also assessed histologically. Results: Combination chemotherapy and MB-mediated US therapy with optimized parameters increased cancer cell death by 50% over chemotherapy alone. Discussion: Increased cellular uptake of chemotherapeutic was dependent upon US system parameters. Conclusion: Optimized MB-mediated US therapy has the potential to improve cancer patient response to therapy via increased localized drug uptake, which may lead to a lowering of chemotherapeutic drug dosages and systemic toxicity.

Determination of Breast Cancer Response to Bevacizumab Therapy Using Contrast-Enhanced Ultrasound and Artificial Neural Networks

Objective. The purpose of this study was to evaluate contrast‐enhanced ultrasound and neural network data classification for determining the breast cancer response to bevacizumab therapy in a murine model. Methods. An ultrasound scanner operating in the harmonic mode was used to measure ultrasound contrast agent (UCA) time‐intensity curves in vivo. Twenty‐five nude athymic mice with orthotopic breast cancers received a 30‐μL tail vein bolus of a perflutren microsphere UCA, and baseline tumor imaging was performed using microbubble destruction‐replenishment techniques. Subsequently, 15 animals received a 0.2‐mg injection of bevacizumab, whereas 10 control animals received an equivalent dose of saline. Animals were reimaged on days 1, 2, 3, and 6 before euthanasia. Histologic assessment of excised tumor sections was performed. Time‐intensity curve analysis for a given region of interest was conducted using customized software. Tumor perfusion metrics on days 1, 2, 3, and 6 were modeled using neural network data classification schemes (60% learning and 40% testing) to predict the breast cancer response to therapy. Results. The breast cancer response to a single dose of bevacizumab in a murine model was immediate and transient. Permutations of input to the neural network data classification scheme revealed that tumor perfusion data within 3 days of bevacizumab dosing was sufficient to minimize the prediction error to 10%, whereas measurements of physical tumor size alone did not appear adequate to assess the therapeutic response. Conclusions. Contrast‐enhanced ultrasound may be a useful tool for determining the response to bevacizumab therapy and monitoring the subsequent restoration of blood flow to breast cancer.

Microbubble Therapy Enhances Anti-tumor Properties of Cisplatin and Cetuximab In Vitro and In Vivo

Objective. To determine if microbubble-mediated ultrasound therapy (MB-UST) can improve cisplatin or cetuximab cytotoxicity of head and neck squamous cell carcinoma (HNSCC) in vitro and in vivo by increasing tumor-specific drug delivery by disruption of tumor cell membranes and enhancing vascular permeability. Study Design. In vitro and in vivo study. Setting. University medical center. Subjects. Immunodeficient mice (6 weeks old) and 4 HNSCC cell lines. Methods. Changes to cell permeability were assessed in vitro after MB-UST. Cellular apoptosis resulting from adjuvant MB-UST with subtherapeutic doses of cisplatin or cetuximab was assessed by cell survival assays in vitro. The in vivo effect of adjuvant MB-UST in flank tumors was assessed in vivo with histological analysis and diffusion-weighted magnetic resonance imaging (DW-MRI). Results. In vitro results revealed that MB-UST can increase cell permeability and enhance drug uptake and apoptosis in 4 HNSCC cell lines. In vivo adjuvant MB-UST with cetuximab or cisplatin showed a statistically significant reduction in tumor size when compared with untreated controls. TUNEL analysis yielded a larger number of cells undergoing apoptosis in tumors treated with cetuximab and adjuvant MB-UST than did cetuximab alone but was not significantly greater in tumors treated with cisplatin and adjuvant MB-UST compared with cisplatin alone. DW-MRI analysis showed more free water, which corresponds to increased cell membrane disruption, in tumors treated with MB-UST. Conclusion. MB-UST promotes disruption of cell membranes in tumor cells in vitro, which may be leveraged to selectively improve the uptake of conventional and targeted therapeutics in vivo.