We report advances in the development of a robust, laser-driven X-ray source. An ultrafast, high-average-power laser driver (1 kHz, 25 mJ, 1.5 ps) allows us to reach sufficient X-ray photon flux to demonstrate the source performance in a realistic imaging application by realizing a complete tomographic sequence in under-15min exposure time, edging toward clinical imaging relevance. This kind of compact, high-brilliance, hard X-ray source holds promise to unlock the development of practical phase-contrast medical imaging.
X-ray absorption imaging is used in the medical field since a long time, but recent advance in phase-contrast imaging made it feasible in a clinical setup. X-ray Phase-contrast imaging technique using a Hartmann sensor allows extracting the absorption and phase information in a single acquisition, allowing to extract a phase-shift information with a minimal exposition and deposited dose. An iterative wavefront reconstruction (IR-WF) algorithm is necessary to extract the phase and absorption values from an acquired image. Our method consists of merging the wavefront reconstruction with a computed tomographic iterative reconstruction (IR-CT) to ensure that all images converge to the same result, improving the final 3D volume.
Needs of improved medical diagnostics, specially for early and reliable breast cancer detection, lead us to consider developments in scintillation crystals and position sensitive photomultiplier tubes (PSPMT) in order to develop a high resolution medium field g-ray imaging device. However, gamma rays detector need to find a compromise between many conflicting requirements. In order to optimize different parameters involved in the detection process, we have developed a Monte Carlo simulation software. Its aims were to optimize a gamma ray imaging system based on pixellated scintillation crystal coupled to a PSPMT array. Several crystal properties were taken into account as well as the measured intrinsic response of PSPMTs. Images obtained by simulations are compared with experimental results. Agreement between simulation and experimental results validate our simulation model.
Although gamma cameras have emerged in the sixties, their spatial resolution is still not sufficient to detect small tracer concentration abnormalities. Examinations like scintimammography requires high spatial resolution and then the possibility to position the detector as close to the explored organ as possible . The emergence of the new position sensitive photomultipliers tubes(PSPMT), from HAMAMATSU, permitted us to develop a compact gamma ray imaging probe which fulfils these requirements. The major interest of the new R8520-00-C12 PSPMT generation is their very low height (27mm) which allows to build a very compact and relatively light gamma ray detector. Their square shape (25.7x25.7mm2) and their very thin dead edges (1.85mm) authorize their juxtaposition in order to obtain a large detection area. In this study we investigate the characteristics of a prototype using a square 2x2 array of HAMAMATSU R8520 position sensitive photomultiplier tubes coupled to a pixelated NaI(Tl) crystal array containing 24x24 pixels each made of 2 x 2 x 5 mm3 crystals with 2.2 mm centre to centre spacing. We present the first results regarding intrinsic spatial resolution, energy resolution and homogeneity . Illuminating the detector, without scintillating crystal, with a light source simulating a scintillation at 140kev, we obtain an intrinsic spatial resolution better than 1mm on the whole field of view also including dead areas between PSPMTs. By coupling this detector to the crystal scintillator previously described, an energy resolution better than 10% FWHM at 140kev is obtained in PSPMT centers. These performances and the inherent scalability of detectors built using arrays of square tubes, make it an attractive choice for use in dedicated nuclear medicine instruments, including small animal imaging.
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