Lead investigator: Dr. Alla Reznik
Collaborators: Yat-Sen University and XLV Diagnostics
There is a great interest in utilization of non-crystalline photoconductors for direct conversion medical X-ray imaging detectors. Currently, the only direct conversion detectors, available on the market, are amorphous selenium (a-Se) based. Unfortunately, a-Se is a low Z (atomic number) material and suffers from low X-ray stopping power. This limits the application of direct conversion detectors to high dose and low X-ray energy procedures (mammography). For low dose and high energy imaging (fluoroscopy), a-Se must be replaced by high Z material. Potential candidates are: polycrystalline layers of HgI2, PbI2, TlBr, CdZnTe and PbO. Poly-PbO holds a special place in this list: like a-Se, it was previously successfully utilized in optical imaging (Plumbicons pick up tubes) that suggests its appropriate photoconductive properties. Further advantage of PbO over other candidates is the absence of heavy absorption edges up to 88 keV, which inherently offers the higher spatial resolution. In 2005 Simon et al showed a prototype of a PbO-based flat-panel X-ray detector characterized by very high spatial resolution and charge yield sufficient for low dose imaging. However, at that time, poly-PbO layers exhibited the residual signal after the end of X-ray exposure, called lag. Reported signal lag restricts application of PbO to static imaging only and obscures full potential of PbO for medical imaging.
We have developed a practical approach that allows to combat the signal lag. The objective is achieved by advancing the deposition technology and provides a novel type of amorphous lead oxide (a-PbO). The results on temporal response of novel a-PbO samples were found to compare favorably to published results on poly-PbO and a-Se films. Our advances in PbO technology offer a-PbO films, suitable for real time X-ray imaging.