The conventional x-ray tube is characterized by low output, low brightness, a large focal spot and a polychromatic photon energy distribution. The large focal spot problem is especially problematic in magnification work. The low output mandates undersirable long exposure times. The polychromatic spectral distribution, with very limited mean photon energy control, impedes effective application of DSA and makes DESA impractical. The applicants proposed a new x-ray source that is created by focusing a high energy laser pulse on the surface of solids. This laser-based source is very bright and delivers radiation in the form of very short pulses (below 1 us) from a very small focal spot area (as low as 10 um). The estimated cost of a clinical system is comparable to the rotating anode-based units. An additional advantage of this new laser-based source rests on the fact that it has a disposable target which is replaced after each laser pulse. The target's elemental composition can be thus rapidly (tens of Hz) changed between subsequent laser pulses. This allows tailoring (including optimized K-edge filters) of the spectral position of characteristic emission lines to the specific imaging tast (e.g. patient thickness in magnification studies or the K-edge of a contrast agent in DSA studies). Due to the high brightness of the laser-based x-ray source, a spherically bent crystal monochromator can be inserted between the target and the patient allowing utilization of near-monoenergetic x-rays for true digital energy subtraction angiography studies. The polychromatic structure of the x-ray beam generated by an electron-impact tube does not allow precise matching to the K-edge of the object of interest and is always mismatched with the optimal energy response of the typical x-ray detectors used in radiology. Therefore, one could expect that the application of the near-monoenergetic x-ray source will result in lowering the integral dose by precisely tuning the x-ray energy according to the subject's composition and thickness and by better matching the x-ray energy with the optimized detector. In this proposed project, the applicants proposed to study, develop, evaluate, and optimize a laser-based ultra-microfocused and very short pulsed laser-based x-ray source for application in magnification and DSA studies and monochromatic x-ray system LAMOX (LAser-based Monochromatic X-rays) for application in digital energy subtraction angiography (DESA). This project will be realized with close collaboration among x-ray physicists (monochromator), laser physicists (laser x-ray source), medical physicists, a physiologist and radiologists (evaluation and optimization of the system through phantom studies). The specific goals of this project are to optimize image quality and dose utilization and to demonstrate the economic feasibility of the laser-based x-ray systems as a viable clinical, hospital based, alternative to traditional magnification, DSA and DESA systems.
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