Nowadays, mammography screening is the most effective tool to fight breast cancer. Still, more than 30% of cancers are not detected, in particular in case of dense breast tissue. Today, X-ray detectors for mammography are optimised for resolution but still lack in sensitivity if compared to angiography systems. Reason is the different technology they rely on. Mammography is based merely on direct converters, e.g. amorphous Selenium (a-Se), while angiography on indirect converters like Cesium Iodide (CsI) scintillator coupled with an amorphous silicon (a-Si) photodetector. Furthermore, at comparable detecting area, mammography detectors are up to 5 times more expensive.
Recently, lead halide perovskites, in particular methyl ammonium lead triiodide (MAPI), revealed to be an excellent X-Ray absorber with a 10-fold sensitivity in comparison to a-Se detectors, showing a performance on par with the best available direct conversion technologies, such as HgI2 and Cd(Zn)Te2. We have already realised a small demonstrator based on polycrystalline MAPI and an a-Si thin-film transistor (TFT) backplane with 256 x 256 pixels (resolution of 260 ppi) which is showing the improved sensitivity, a really high resolution (modulation transfer function (MTF) of 0.2 at Nyquist frequency of 5 lp/mm, Figure 3), and this at a fraction of the costs of today’s a-Se detectors.
In this project we will combine the high MAPI sensitivity with a high resolution 500 ppi TFT backplane. This will allow to improve resolution without increasing patient dose. There is a well-known general rule in X-ray imaging that’s says: the higher the dose, the better the image quality. Reducing radiation dose compromises image quality. This is particularly true for small details like micro-calcifications in the breast which have a rather small X-Ray absorption. However, this is only true if the sensitivity of the detectors is somehow limited. In case of increased sensitivity of the detector while maintaining low leakage currents, an improved image quality at lower radiation dose will be possible.
In ESSENCE, TNO will fabricate high resolution 500 ppi TFT backplanes in a size of 640 x 480 pixels (VGA). SHS will process the high sensitivity perovskite frontplane using their soft sintering technology. The readout and driving electronics is already available at TNO and the characterisation under relevant clinical settings will be performed at SHS.
The continuous low-dose discussion challenged us to rethink on what seemed impossible: develop a system that would be the new reference in low-dose mammography, without compromising on image quality.