Temporal subtraction

Two basic CEDM techniques are under development temporal subtraction and dual-energy techniques. Both these techniques use intravenous injection of an iodine-based contrast agent. However, the low-energy exposures used in mammography are not optimal for the visualization of iodine. Indeed, the X-ray beam generated from a molybdenum/rhodium/tungsten anode and a molybdenum /rhodium/silver filter in conventional mammography was developed to maxi-... 

Fig. 12.3. Temporal subtraction CEDM examination. Cranio-caudal mammogram (a) shows two opacities in the upper outer quadrant (arrows). Subtraction image derived from the 1 30 temporal CEDM images (b) and corresponding parametric image of the maximum slope of enhancement (c) show two adjacent areas of enhancement, one with strong and spiculated enhancement (arrow) and the other with moderate and less circumscribed enhancement (arrowheads). Enhancement kinetics curves derived from ROls drawn in the strong area of enhancement (d) show early enhancement followed by a washout whereas the moderate area of enhancement depicts gradual increasing enhancement.

Temporal sequence of OH-LIF measurements captures a localized extinction event in a turbulent nonpremixed CH4/H2/N2 jet flame (Re 20,000) as a vortex perturbs the reaction zone. The time between frames is 125 ps. The velocity field from PIV measurements is superimposed on the second frame and has the mean vertical velocity of 9m/s subtracted. (From Hult, J. et al.. Paper No. 26-2, in 10th International Symposium on Applications of Laser Techniques to Fluid Mechanics, Lisbon, 2000. With permission.)... 

The radial concentration scans obtained from the UV spectrophotometer of the analytical ultracentrifuge can be either converted to a radial derivative of the concentrations at a given instant of time (dc/dr)t or to the time derivative of the concentrations at fixed radial position (dc/dt)r (Stafford, 1992). The dcf dt method, as the name implies, uses the temporal derivative which results in elimination of time independent (random) sources of noise in the data, thereby greatly increasing the precision of sedimentation boundary analysis (Stafford, 1992). Numerically, this process is implemented by subtracting pairs of radial concentration scans obtained at uniformly and closely spaced time intervals c2 — G)/( 2 — h)]. The values are then plotted as a function of radius to obtain (dc/dt) f versus r curves (Stafford, 1994). It can be shown that the apparent sedimentation coefficient s ... 

Fig. 65. Spatiotemporal evolution of the potential at a Pt electrode during the galvanostatic oxidation of H2 in the presence of Cu2+ and Cl- ions after subtraction of the homogeneous oscillating part [64], (b) Temporal evolution of the total current. The first four oscillations correspond to the time interval shown in (a).

The subtracted and enhanced ellipsomicroscopic and microscopic images were stored on a DVD-recorder. Great care was taken to synchronize the video and the current measurements. For this purpose a flashlight was activated which could be easily identified on the videos. Simultaneously, a signal was send to the computer storing the temporal evolution of the current. 

How then does this influence the flow of catalyst particles in the vessel and the liquid -solid mass transfer Figure 2c shows the particle velocities, for a particle density of 1,500 kg/m under identical conditions to Figure 2b. By subtraction of the temporally averaged liquid and particle velocities, the spatially resolved slip velocities can be obtained. Figure 3. This shows that the relative velocity of the liquid and particle (and hence the mass transfer) also varies considerably over the vessel, with the highest values confined to the impeller discharge region. 

The bottom three traces in Fig. 23 depict difference spectra which were generated by subtraction of the HbCO spectrum from that obtained in the dual-pulse experiments. In these experiments a (10 nsec) 532 nm photolysis pulse instantaneously creates the Hb photoproduct. If the approximately 230 nm probe pulse is not temporally delayed with respect to the photolysis pulse (bottom trace), no difference is observed, that is, the photoproduct has an R-state structure. When the probe pulse is delayed... 

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