Jasmina Orman

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.

3D soft tissue imaging with a mobile C-arm

We introduce a clinical prototype for 3D soft tissue imaging to support surgical or interventional procedures based on a mobile C-arm. An overview of required methods and materials is followed by first clinical images of animals and human patients including dosimetry. The mobility and flexibility of 3D C-arms gives free access to the patient and therefore avoids relocation of the patient between imaging and surgical intervention. Image fusion with diagnostic data (MRI, CT, PET) is demonstrated and promising applications for brachytherapy, RFTT and others are discussed.

Optimization of detector operation and imaging geometry for breast tomosynthesis

In breast tomosynthesis there are tradeoffs between resolution, noise and acquisition speed for a given glandular dose. The purpose of the present work is to investigate the dependence of tomosynthesis imaging performance on system configuration, which includes detector operational modes and image acquisition geometry. A prototype Siemens breast tomosynthesis system with maximum angular range of +/- 25 degrees was used in our investigation. The system was equipped with an amorphous selenium (a-Se) full field digital mammography detector with pixel size of 85µm. The detector can be read out with full resolution or 2x1 binning (binning in the tube travel direction), which increases the image readout rate and decreases the degradation effect of electronic noise. The total number of views can be varied from 11 to 49, and filtered back projection (FBP) method was used to reconstruct the tomosynthesis images. We investigated the effects of detector operational modes (binning) and imaging geometry (view angle and number) on temporal performance and spatial resolution of the projection images. The focal spot blur due to continuous tube travel was measured for different acquisition geometry, and its effect on in-plane presampling modulation transfer function (MTF) was compared to that due to pixel binning. A three-dimensional cascaded linear system model was developed for tomosynthesis to predict the 3D MTF, NPS and DQE. The results were compared with experimental measurements, and reasonable agreement was achieved. The understanding of the relationship between the 3D and projection image quality will lead to optimization of the x-ray spectrum, imaging geometry and reconstruction filters for digital breast tomosynthesis.

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.