Regional Blood Flow Measurement with Non-Radioactive Microspheres by X-ray Fluorescence Spectrometry

Summary

X-ray fluorescence spectrometry has now become available for measuring regional blood flow with microspheres loaded with heavy nonradioactive elements. Drawbacks in previous studies were leaching of elements from the nonradioactive microspheres, and insufficient sensitivity for detecting small amounts of elements. We developed 9 sets of new nonradioactive microspheres (Ti, Br, Y, Zr, Nb, In, I, Ba, Ce) with a mean diameter of about 15 μm, and 1 set of Br-microspheres with a diameter of 60 μm which did not leach tracer elements even in strongly alkaline solution. We used a wavelength dispersive X-ray fluorescence spectrometer, which is characterized by great sensitivity and is commercially available (PW 1480 Philips Almelo, The Netherlands). We validated the method by comparing duplicate flows measured with radioactive and nonradioactive microspheres in acute dog experiments, expanded the application of the method into long term experiments in dogs up to 6–12 months, and into systemic and pulmonary blood flow distributions in rats. By applying a monochromatic synchrotron radiation as a primary X-ray source, we increased the signal-to-background ratios of X-ray fluorescence spectra 50 dB or more above those with the wavelength dispersive system. This system allowed us to measure accurately blood flow distributions in contiguous small regions of 10–20 mg or less.