Ultrahigh resolution and brilliance laser wakefield accelerator betatron x-ray source for rapidin vivotomographic microvasculature imaging in small animal models

Abstract

We are developing ultrahigh spatial resolution (FWHM < 2 μm) high-brilliance x-ray source for rapid in vivo tomographic microvasculature imaging micro-CT angiography (μCTA) in small animal models using optimized contrast agent. It exploits Laser Wakefield Accelerator (LWFA) betatron x-ray emission phenomenon. Ultrashort high-intensity laser pulse interacting with a supersonic gas jet produces an ion cavity (“bubble”) in the plasma in the wake of the laser pulse. Electrons that are injected into this bubble gain energy, perform wiggler-like oscillations and generate burst of incoherent x-rays with characteristic duration time comparable to the laser pulse duration, continuous synchrotron-like spectral distribution that might extend to hundreds keV, very high brilliance, very small focal spot and highly directional emission in the cone-beam geometry. Such LWFA betatron x-ray source created in our lab produced 1021 –1023 photons⋅ shot-1⋅mrad-2⋅mm-2/0.1%bw with mean critical energy in the12–30 keV range. X-ray source size for a single laser shot was FWHM=1.7 μm; x-ray beam divergence 20–30 mrad, and effective focal spot size for multiple shots FWHM= ~2 μm. Projection images of simple phantoms and complex biological objects including insects and mice were obtained in single laser shots. We conclude that ultrahigh spatial resolution μCTA (FWHM ~2 μm) requiring thousands of projection images could be accomplished using LWFA betatron x-ray radiation in approximately 40 s with our existing 220 TW laser and sub seconds with next generation of ultrafast lasers and x-ray detectors, as opposed to several hours required using conventional microfocal x-ray tubes. Thus, sub second ultrahigh resolution in vivo microtomographic microvasculature imaging (in both absorption and phase contrast mode) in small animal models of cancer and vascular diseases will be feasible with LWFA betatron x-ray source.