Bo Zhao MS, Presenter: Nothing to Disclose

Jun Zhou PhD, Abstract Co-Author: Nothing to Disclose

Wei Zhao PhD, Abstract Co-Author: Nothing to Disclose

Continuous movement of the x-ray tube during exposures has been employed in the latest development of tomosynthesis systems. Moving of the x-ray tube focal spot during exposure adds additional blur. The purpose of our work is to determine the extent of the focal spot blur in tomosynthesis with different imaging geometries and tube output, and investigate its effect on MTF and DQE of a system employing a direct conversion digital mammography detector, so that the imaging geometry and acquisition sequence can be optimized.

Two tomosynthesis imaging geometries, one with stationary and the other with rotating detector, were investigated. Both geometries have a 65 cm source-to-detector distance, a 0.3 mm focal spot size and the angular range for the tube motion is ±25º with respect to the center of rotation. The entire imaging time is ~10 s with 11 views in a tomosynthesis acquisition and full resolution image readout. To achieve a scanning time comparable to that of screening mammography, i.e. 6 s, the detector has to be operated in a binning mode where two pixels along tube motion direction are read out simultaneously, hence with a reduced detector resolution. The focal spot blur with different acquisition geometries and sequences was calculated and its effect on MTF and DQE was determined.

The MTF drop due to focal spot blur results in a decrease in DQE at Nyquist frequency, fNY, of >70%, which is undesirable. The stationary detector system has more significant focal spot blur than the rotating detector system. If we set a threshold DQE drop due to focal spot blur as 50% at fNY, the focal spot travel during exposure has to be decreased through either increased scan time or decreased exposure time. The effects of different tomosynthesis system design, e.g. x-ray spectrum, tube current, acquisition geometry and sequence, on focal spot blur and the overall system imaging performance will be presented.

We investigated the focal spot blur due to continuous movement of the x-ray tube for two practical tomosynthesis systems. Different combinations of system geometry and image acquisition sequence were proposed to keep the focal spot blur at a reasonable level.

Zhao, B, Zhou, J, Zhao, W, Focal Spot Blur in Breast Tomosynthesis Systems.  Radiological Society of North America 2005 Scientific Assembly and Annual Meeting, November 27 - December 2, 2005 ,Chicago IL. http://archive.rsna.org/2005/4418993.html