Wolfgang Haerer

Optimizing filtered backprojection reconstruction for a breast tomosynthesis prototype device

Digital breast tomosynthesis is a new technique intended to overcome the limitations of conventional projection mammography by reconstructing slices through the breast from projection views acquired from different angles with respect to the breast. We formulate a general theory of filtered backprojection reconstruction for linear tomosynthesis. The filtering step consists of an MTF inversion filter, a spectral filter, and a slice thickness filter. In this paper the method is applied first to simulated data to understand the basic effects of the various filtering steps. We then demonstrate the impact of the filter functions with simulated projections and with clinical data acquired with a research breast tomosynthesis system.** With this reconstruction method the image quality can be controlled regarding noise and spatial resolution. In a wide range of spatial frequencies the slice thickness can be kept constant and artifacts caused by the incompleteness of the data can be suppressed.

Method and apparatus for adaptive focusing in a medical ultrasound imaging apparatus

A sectional plane of the examination subject is first scanned by focused ultrasound transmission beams in an adaptation phase. Disturbing effects from the reflected echo signals which are caused by the inhomogenities in the tissue are thereby measured. In this adaptation phase, correction values for the delay time of the signals of the elemental transducers of the ultrasound array in comparison to the standard focusing are also derived from the measured values. In a following B-image imaging phase, the delay times of the active aperture are then varied dependent on the correction values during the emission and/or during reception. The disturbing effects are thereby compensated. A method and apparatus are disclosed which are especially well-suited for linear array systems and for patients having inhomogeneous tissues.

Adaptation of image quality using various filter setups in the filtered backprojection approach for digital breast tomosynthesis

The main limitations of conventional projection mammography consist in tissue overlap and missing depth information. These deficiencies are intended to be reduced by the new technique of digital breast tomosynthesis. From a set of radiographic projections, acquired at different view angles in a linear tomosynthesis research system setup, 3-D slices of the scanned breast region are reconstructed. As the method of choice for the reconstruction we use filtered backprojection. By applying different filters with task-adapted parameters this method allows to control the image quality regarding noise, spatial resolution and artifacts. In order to investigate the basic effects of the various settings in the filtering step the method is first applied to simulated data. The impact of the selected filter functions is then demonstrated with clinical data.