Brett Spivey

Doppler imaging device

A device and method for producing an image of a fluid moving through a medium. An acoustic wave insonifies the medium to produce Doppler shifted scattering from randomly located scatterers in the moving fluid. At least eight channels of acoustic detectors detect signals reflected from the medium and the amplitudes of the scattered signal is determined at each channel for at least one Doppler shifted frequency. Time averaged channel-to-channel amplitude correlations are produced using the Doppler shifted amplitude data from which the image of the moving fluid is calculated.

A New Consideration of Diffraction Computed Tomography for Breast Imaging: Studies in Phantoms and Patients

Previous medical applications of ultrasound computed tomography showed promise of increased resolution over conventional pulse-echo imaging and exhibited potential for quantitative tissue characterization. 1-4 This research was limited by significant technical difficulties due in part to inadequate beam sampling and, in some cases, the assumptions associated with the straight-line ray-optical approach to pulse propagation. Nonetheless, experimental systems were constructed and credible clinical results were obtained in the breast where the range of tissue properties is less than in other parts of the body. Theoretical research has continued but few experimental systems have been built and there has been limited new work in tissue.5,6

Optimization of tungsten x-ray spectra for digital mammography: a comparison of model to experiment

Tungsten (W) target x-rays tubes are being studied for use in digital mammography to improve x-ray flux, reduce noise and increase tube heat capacity. A parametric model was developed for digital mammography to evaluate optimization of x-ray spectra for a particular sensor. The model computes spectra and mean glandular doses (MGD) for combinations of W target, beam filters, kVp, breast type and thickness. Two figures of merit were defined: (signal/noise)2/MGD and spectral quantum efficiency; these were computed as a means to approach optimization of object contrast. The model is derived from a combination of classic equations, XCOM from NBS, and published data. X-ray spectra were calculated and measured for filters of Al, Sn, Rh, Mo and Ag on a Eureka tube. (Signal/noise)2/MGD was measured for a filtered W target tube and a digital camera employing CsI scintillator optically coupled to a CCD for which the detective quantum efficiency (DQE) was known. A 3-mm thick acrylic disk was imaged on thickness of 3-8 cm of acrylic and the results were compared to the predictions of the model. The relative error between predicted and measured spectra was +/- 2 percent from 24 to 34 kVp. Calculated MGD as a function of breast thickness, half-value layer and beam filter compares very well to published data. Best performance was found for the following combinations: Mo filter with 30 mm breast, Ag filter with 45 mm, Sn filter for 60 mm, and Al filter for 75 mm thick breast. The parametric model agrees well with measurement and provides a means to explore optimum combinations of kVp and beam filter. For a particular detector, this data may be used with the DQE to estimate total system signal-to-noise ratio for a particular imaging task.

Simultaneous Spatial and Velocity Vector Mapping with Diffraction Tomography

Current Doppler ultrasound technology privides only two-dimensional projections of vessels or velocity patterns, is highly operator-dependent and is unable to accomplish accurate maps of the vessel lumen and flow velocity at the same time. Doppler techniques are limited in their ability to detect or measure small or deep vessels especially in the presence of slow flow, although new contrast media may enhance sensitivity. Even in superficial vessels such as the corotid artery, a very small number of pixels defines the flow channel. The aim of this study was to explore a novel diffraction tomography technique for producing quantitative, high- resolution cross-sectional Doppler images. Using this approach, a flow channel or vessel may be mapped in sequential tomograms providing a unique representation of the three- dimensional patterns of complex, curvilinear, multi-phasic or turbulent flows. The method is based on instrumentation initially developed for breast imaging1 where the value of Doppler flow data is proving valuable for breast cancer diagnosis.