Experimental Setup


Preliminary Results (Feb. 2001)

We studied the performance of our apparatus by irradiating a breast phantom with a standard mammographic unit at 28 kVp and 60 cm focus-to-phantom distance.
The phantom consisted of a 10 cm diameter, 4 cm thick Lucite cylinder with (12 mm diameter, 3 mm thick) holes containing Al disks of known thickness d (25 to 125 micron) immersed in Wax.

The picture on the right is a digital radiography, taken by our apparatus, of one of the Al disks (yellow disk at the centre). The darker circular area around is the Wax surrounded by Lucite (yellow). The pixel contents are displayed in false colours.

Space resolution

We measured the Line Spread Function (LSF) of the system by imaging the sharp edge of a Tungsten bar which was positioned slightly tilted w.r.t. the pixels axis

The Modulation Transfer Function (MTF) of the system was then extracted using the Fast Fourier Transform (FFT)

The resolution is 15 lp / mm @ 10 % MTF. It is found to be dominated by the structured scintillator contribution.

Due to Compton scattering in the body, image contrast C is expected to be degraded by a factor 1/(1+R) where R is the Secondary (S) to Primary (P) ratio. :

We have measured image contrasts with and without the two anti-scattering grids using a mammography phantom.

An enhancement in image contrast using the anti-scattering grids has been observed as expected. The amount of scattering rejection is close to 84% .
Details on the analysis can be found in our paper "Experimental test of a new technique of background suppression in digital mammography" [Proc. Int. Conf. VCI 2001 - Wien - to be published on Nucl.Instr & Methods]

We have also compared the measurements with the predictions of our Monte Carlo simulation. Data are found in agreement with expectations within errors.

Conclusions :

The proposed scattering suppression method has been experimentally tested : a significant enhancement in image contrast has been observed using the anti-scattering grids.
Comparison of measured contrast with and without grids shows a quantitative agreement with MC predictions.
No significant image artifacts were found in the digital images taken at 10 cm phantom-detector distance.