LOW-DOSE PHASE-CONTRAST X-RAY MEDICAL IMAGING

Phase contrast x-ray imaging is a powerful technique for the detection of low-contrast details in weakly absorbing objects. This method is o f possible relevance in the field of diagnostic radiology. In fact, im aging low-contrast details within soft tissue does not give satisfacto ry results in conventional x-ray absorption radiology, mammography bei ng a typical example. Nevertheless, up to now all applications of the phase contrast technique, carried out on thin samples, have required r adiation doses substantially higher than those delivered in convention al radiological examinations. To demonstrate the applicability of the method to mammography we produced phase contrast images of objects a f ew centimetres thick while delivering radiation doses lower than or co mparable to doses needed in standard mammographic examinations (typica lly similar to 1 mGy mean glandular dose (MGD)). We show images of a c ustom mammographic phantom and of two specimens of human breast tissue obtained at the SYRMEP bending magnet beamline at Elettra, the Triest e synchrotron radiation facility. The introduction of an intensifier s creen enabled us to obtain phase contrast images of these thick sample s with radiation doses comparable to those used in mammography. Low ab sorbing details such as 50 mu m thick nylon wires or thin calcium depo sits (similar to 50 mu m) within breast tissue, invisible with convent ional techniques, are detected by means of the proposed method. We als o find that the use of a bending magnet radiation source relaxes the p reviously reported requirements on source size for phase contrast imag ing. Finally, the consistency of the results has been checked by theor etical simulations carried out for the purposes of this experiment.