Image quality versus TTRS. (a) Plot of TTRS ('time to respiratory signal', which indicates major respiratory damage; see Figure 6) as a function of incident power density for all four species. At least three trials were performed per data point. A power law fit to the data gives: TTRS (s) = 90484 x-1.02, R = 0.97 where × is the incident beam power density in μW/mm2. TTRS measurements as a function of animal mass showed no correlation for the mass range 8.4–53.7 mg and 13.3–1473.5 mg for ants and grasshoppers, respectively. (b) Still images taken from video (16.6 ms exposure) footage of a dead fruit fly (Drosophila melanogaster) as a function of incident beam power density, which are, respectively from i-vi: 4, 8, 16, 36, 80, 103 μW/mm2. X-ray energy is 25 keV. At 80 μW/mm2, the photon density is 2 × 1010 ph/s/mm2. Field of view is 1.0 × 1.3 mm using a 5× objective lens. Head and thoracic air sacs and leg trachea can be clearly seen. These images are taken with our new camera (Cohu 2700), which is twice as sensitive as the camera used in the major part of this study. Although we subjectively consider (iv) to be a high quality image, usable images can be obtained using lower beam intensities.
Socha et al. BMC Biology 2007 5:6 doi:10.1186/1741-7007-5-6