**4.3 Need for other data acquisition schemes to improve statistics**

Another important consideration in the context of biomarkers is speed. X-ray fluorescence imaging is currently quite slow. Samples are raster-scanned through an X-ray beam with dwell times of 1s or more per pixel. With potentially hours of scan time required for imaging a single cell, good statistical sampling is difficult to achieve. What is needed for this? Some current areas of development may help, particularly the development of fast fly-scanning data acquisition, where samples are raster scanned continuously and fluorescence information is recorded 'on-the-fly'. Another area with promise for speed is the development of microfluidic devices that will enable X-ray fluorescence spectra of whole cells to be individually captured while flowing in a stream, thus allowing measurement of at least the total metals in individual cells over populations of hundreds of cells. As techniques like these emerge, the promise of Xray fluorescence imaging for diagnostics comes closer to a reality.
