Development of a training phantom for compression breast elastography-comparison of various elastography systems and numerical simulations.

Single-breath-hold photoacoustic computed tomography of the breast.

Abstract: We have developed a single-breath-hold photoacoustic computed tomography (SBH-PACT) system to reveal detailed angiographic structures in human breasts. SBH-PACT features a deep penetration depth (4 cm in vivo) with high spatial and temporal resolutions (255 µm in-plane resolution and a 10 Hz 2D frame rate). By scanning the entire breast within a single breath hold (~15 s), a volumetric image can be acquired and subsequently reconstructed utilizing 3D back-projection with negligible breathing-induced motion artifacts. SBH-PACT clearly reveals tumors by observing higher blood vessel densities associated with tumors at high spatial resolution, showing early promise for high sensitivity in radiographically dense breasts. In addition to blood vessel imaging, the high imaging speed enables dynamic studies, such as photoacoustic elastography, which identifies tumors by showing less compliance. We imaged breast cancer patients with breast sizes ranging from B cup to DD cup, and skin pigmentations ranging from light to dark. SBH-PACT identified all the tumors without resorting to ionizing radiation or exogenous contrast, posing no health risks.

Compression elastography and endoscopic optical coherence tomography for biomechanical properties evaluation of cerebral arteries walls with aneurysm and their phantoms

Abstract: A new method for obtaining information about the stress-related properties of the cerebral vessel walls in vivo is described. The method is based on compression elastography and endoscopic optical coherence tomography. A pulse wave is used as a deforming force with a minimal risk of the vessel wall rupture under investigation. Evaluation of the object’s deformation is made using test points displacement. New approaches to multilayered tissue like phantoms of blood vessels construction and studies of pulsating flows of biological fluids in them are described. Experimental results of stress-related properties evaluation of the blood vessel walls are presented using tissue like phantoms.

Young's modulus evaluation for blood vessel equivalent phantoms using optical coherence elastography

Abstract: The method of longitudinal elasticity modulus evaluation for the large blood vessel wall is presented. It is based on obtaining and computer analyzing structural images of the same section of the investigated blood vessel wall at the moments correspondent to systole and diastole. Endoscopic optical coherence tomography system with a forward-side probe was used by the structural images raw data acquisition. Digital analysis of structural images includes noise reduction, detection of control points, combination them together and calculation of relative displacements. The Young's modulus was calculated taking into account the surface area of the scanning region, the coherence probing depth and the magnitude of the deformation impact of the pulse wave.

Large field homogeneous illumination in microwave-induced thermoacoustic tomography based on a quasi-conical spiral antenna

Abstract: Conventional helical and horn antennas based on frequency selective surfaces have been used to provide microwave illumination in microwave-induced thermoacoustic tomography (TAT). However, the electromagnetic waves radiated from the conventional antennas are not circularly polarized and thus impair image quality. In addition, conventional antennas can provide uniform radiations only within a relatively small area and thus limit their clinical applications (e.g., breast imaging). To address these problems, we propose a quasi-conical log-spiral antenna for homogenous illumination over a large field. We theoretically and experimentally validated this approach. Tissue-mimicking phantoms were imaged. The antenna produced not only an electric field with a circular polarization but also a homogeneous illumination area with a 10 cm diameter. Accordingly, our method has advanced TAT by improving microwave illumination.

Phantoms of optical and stress-related properties of cerebral arteries with aneurysms for intravascular optical coherence tomography

Abstract: A method for tissue-like phantoms preparation for cerebral arteries with aneurysms is presented. Magnetic resonance angiography (MRA) images are used as a source of structural information about the geometry of the simulated cerebral arteries and surrounding brain tissue. Blood vessels were reconstructed as hollow structures with three-layer walls. The inner layer corresponds to the intima of the real vessel, its middle layer - media, and the outer layer - adventitia. The basis for the reconstruction of the first layer of hollow structures and mold for casting surrounding brain tissue were 3D printed. Hollow structures were reconstructed applying layer-by-layer method with use of two-component transparent silicone gel with a variable mass fraction of two components, A and B. Variation the mass fraction of the components and thickness for each layer allows achieving the necessary stress-related properties. Equivalence to the real structure of the cerebral arteries and optical properties were achieved by variation of mass fraction of the additives for each layer matrix. A powder of titanium dioxide was used as scattering particles and a special gel colourant for silicone was applied as an absorbing agent. Hollow structures were added in the mold for casting surrounding brain tissue simulator, so that their geometrical arrangement corresponds to associated blood vessels. The proximal and distal ends of hollow structures are equipped with forked catheters.

Elastography: A Quantitative Method for Imaging the Elasticity of Biological Tissues

Abstract: We describe a new method for quantitative imaging of strain and elastic modulus distributions in soft tissues. The method is based on external tissue compression, with subsequent computation of the strain profile along the transducer axis, which is derived from cross-correlation analysis of pre- and post-compression A-line pairs. The strain profile can then be converted to an elastic modulus profile by measuring the stresses applied by the compressing device and applying certain corrections for the nonuniform stress field. We report initial results of several phantom and excised animal tissue experiments which demonstrate the ability of this technique to quantitatively image strain and elastic modulus distributions with good resolution, sensitivity and with diminished speckle. We discuss several potential clinical uses of this technique.

Supersonic shear imaging: a new technique for soft tissue elasticity mapping

Abstract: Supersonic shear imaging (SSI) is a new ultrasound-based technique for real-time visualization of soft tissue viscoelastic properties. Using ultrasonic focused beams, it is possible to remotely generate mechanical vibration sources radiating low-frequency, shear waves inside tissues. Relying on this concept, SSI proposes to create such a source and make it move at a supersonic speed. In analogy with the "sonic boom" created by a supersonic aircraft, the resulting shear waves will interfere constructively along a Mach cone, creating two intense plane shear waves. These waves propagate through the medium and are progressively distorted by tissue heterogeneities. An ultrafast scanner prototype is able to both generate this supersonic source and image (5000 frames/s) the propagation of the resulting shear waves. Using inversion algorithms, the shear elasticity of medium can be mapped quantitatively from this propagation movie. The SSI enables tissue elasticity mapping in less than 20 ms, even in strongly viscous medium like breast. Modalities such as shear compounding are implementable by tilting shear waves in different directions and improving the elasticity estimation. Results validating SSI in heterogeneous phantoms are presented. The first in vivo investigations made on healthy volunteers emphasize the potential clinical applicability of SSI for breast cancer detection.

Magnetic resonance elastography by direct visualization of propagating acoustic strain waves

Abstract: A nuclear magnetic resonance imaging (MRI) method is presented for quantitatively mapping the physical response of a material to harmonic mechanical excitation. The resulting images allow calculation of regional mechanical properties. Measurements of shear modulus obtained with the MRI technique in gel materials correlate with independent measurements of static shear modulus. The results indicate that displacement patterns corresponding to cyclic displacements smaller than 200 nanometers can be measured. The findings suggest the feasibility of a medical imaging technique for delineating elasticity and other mechanical properties of tissue.

Solid breast nodules: use of sonography to distinguish between benign and malignant lesions.

Abstract: PURPOSE: To determine whether sonography could help accurately distinguish benign solid breast nodules from indeterminate or malignant nodules and whether this distinction could be definite enough to obviate biopsy. MATERIALS AND METHODS: Seven hundred fifty sonographically solid breast nodules were prospectively classified as benign, indeterminate, or malignant. Benign nodules had no malignant characteristics and had either intense homogeneous hyperechogenicity or a thin echogenic pseudocapsule with an ellipsoid shape or fewer than four gentle lobulations. Sonographic classifications were compared with biopsy results. The sensitivity, specificity, and negative and positive predictive values of the classifications were calculated. RESULTS: Benign histologic features were found in 625 (83%) lesions; malignant histologic features, in 125 (17%). Of benign lesions, 424 had been prospectively classified as benign. Two lesions classified as benign were found to be malignant at biopsy. Thus, the classification s...

Elastic Moduli of Breast and Prostate Tissues under Compression

Abstract: To evaluate the dynamic range of tissue imaged by elastography, the mechanical behavior of breast and prostate tissue samples subject to compression loading has been investigated. A model for the loading was validated and used to guide the experimental design for data collection. The model allowed the use of small samples that could be considered homogeneous; this assumption was confirmed by histological analysis. The samples were tested at three strain rates to evaluate the viscoelastic nature of the material and determine the validity of modeling the tissue as an elastic material for the strain rates of interest. For loading frequencies above 1 Hz, the storage modulus accounted for over 93 percent of the complex modulus. The data show that breast fat tissue has a constant modulus over the strain range tested while the other tissues have a modulus that is dependent on the strain level. The fibrous tissue samples from the breast were found to be 1 to 2 orders of magnitude stiffer than fat tissue. Normal glandular breast tissue was found to have an elastic modulus similar to that of fat at low strain levels, but the modulus of the glandular tissue increased by an order of magnitude above fat at high strain levels. Carcinomas from the breast were stiffer than the other tissues at the higher strain level; intraductal in situ carcinomas were like fat at the low strain level and much stiffer than glandular tissue at the high strain level. Infiltrating ductal carcinomas were much stiffer than any of the other breast tissues. Normal prostate tissue has a modulus that is lower than the modulus of the prostate cancers tested. Tissue from prostate with benign prostatic hyperplasia (BPH) had modulus values significantly lower than normal tissue. There was a constant but not significant difference in the modulus of tissues taken from the anterior and posterior portions of the gland.