Glancing Angle Interferometer Tomosynthesis System (GAI-TS) for High Energy, Fast and Low Dose X-ray Phase-contrast Imaging

Unmet Need
Current clinical imaging methods include conventional X-ray computed tomography (CT), and magnetic resonance imaging (MRI). Conventional X-ray CT, also known as attenuation-based X-ray CT, has excellent spatial resolution but poor soft tissue contrast, so it is not suited for imaging internal organs. Meanwhile, MRI has good soft tissue contrast but suffers from poor spatial resolution and long scan intervals that result in motion blur. A new form of CT scanning known as Differential Phase Contrast CT (DPC-CT) combines good spatial resolution and soft tissue contrast and can effectively detect small lesions and tumors in internal organs. Unlike the conventional attenuation-based CT, DPC-CT is refraction-based, so it offers enhanced detection of soft tissues. However, DPC-CT experiences poor refraction at the high X-ray energies that are required to penetrate the torso or head, so it requires a large radiation dosage to image organs. Also, conventional DPC-CT uses multiple images per angle, which leads to long exposures and scan time. Moreover, it is difficult and expensive to build a DPC-CT scanner with a large enough field of view (FOV) to cover the width of the human body. Hence, there is a need for a practical and affordable DPC-CT imaging method that is compatible with the high X-ray energies needed to penetrate the torso, has efficient scan times, and delivers better soft tissue contrast and spatial resolution of internal organs than MRI and conventional CT, while using similar or lower radiation dosages. Development of this imaging method can yield potential applications in many fields, including clinical applications like high resolution 3D imaging of internal organs for lesions or plastic medical implants, industrial applications like detecting internal damage in composites used by the aerospace or defense industries, and security applications such as low dose screening against implanted explosive devices or drugs.

Technology Overview
Current DPC-CT experiences poor refraction at high X-ray energies because the absorption gratings in conventional interferometers cannot be made thicker than ~150 micrometers, which is insufficient to absorb X-rays above ~45 keV. Inclining the gratings at a glancing angle of 15 degrees increases their ‘effective’ thickness by a factor of 4, which allows the interferometer to absorb more high-energy X-rays, thus increasing refraction. This novel inclined design is named Glancing Angle Interferometer (GAI) and enables enhanced soft tissue contrast and resolution at high-energy X-rays compared to conventional CT and MRI. GAI is used in conjunction with existing techniques including single image phase retrieval, Region-of-Interest (ROI) scanning, and limited angle tomosynthesis CT reconstruction to improve cost-effectiveness and reduce scan time and radiation dosage. The integration of these approaches is referred to as GAI-Tomosynthesis (GAI-TS). Limited angle tomosynthesis reconstruction enables imaging with less scan angles compared to traditional full coverage scans, and single image phase retrieval only uses one picture per scan angle, both of which decrease scan time and reduce radiation exposure. ROI scanning restricts the scan boundaries, which enables precise, high resolution imaging focused on a smaller field of view (FOV) and offers improved image quality when compared to conventional CT and MRI. Because the GAI scanner’s FOV is restricted to only several inches in either direction, it is more practical and less costly to build compared to a traditional full body CT scanner or MRI scanner. Additionally, the smaller FOV results in less radiation exposure, reducing the radiation dosage compared to conventional attenuation-CT.

Stage of Development
The inventors have developed a prototype of the GAI-TS system and conducted in vitro studies on an anthropomorphic CT phantom with embedded vials containing fresh or preserved organ tissues from humans and animals to optimize radiation dosage and scan time. The preliminary results indicate that high resolution imaging of the internal organs with a scanner having a field of view of a few inches is feasible when combined with an organ radiation dose of several milligrays and a scan time of about 10 seconds. Studies at low X-ray energies with a peak kilovoltage smaller than 90kV show that GAI-TS enables improved 3D imaging of lesions and tumors in human and animal soft tissues.

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