Active scanning time

This problem can be illustrated by the data given in a paper by Hinsmann et al. [ 1], who used a Bruker Equinox 55 interferometer (see Figure 5.17) for stopped-flow measurements (see Section 19.2). The mirror velocity on this instrument was set so that data were acquired with a HeNe laser frequency of 280 kHz. For a spectral resolution of 32 cm , the time for each 1000-point interferogram was, therefore, 1024/ (280 X 10 ) s, or 3.66 ms. The time between successive spectra was reported as 45 ms, so that the duty-cycle efficiency was 8.1%. Clearly, the time resolution for this measurement was limited by the turnaround time and not the active scanning time. 

The catalyst pellets showed stable activity with time. Conversion and selectivity remained essentially constant over the duration of the experiment, which for each pellet lasted several days. Furthermore, by scanning the temperature range several times, in both increasing and decreasing order, it was determined that the reproducibility was very good and that multiple steady states were not present. 

Figure 8.4. Main window of Gepasi. The main window of Gepasi consists of menus (File, Options, and Help), icons, and four tabs (Model definition, Tasks, Scan, and Time course). Activation of any of the tab opens an indexed page. At the start of Gepasi, the Model definition page is opened. Enter name of the metabolic pathway to the Title box. Click Reactions button to define enzymatic reactions (e.g., E + A+B = EAB for R1, EAB = EPQ for R2, and EPQ = E + P + Q for R3 shows 3 reactions and 7 metabolites), and then click Kinetics button to select kinetic type. Activate Tasks tab to assign Time course (end time, points, simufile.dyn), Steady state (simufile.ss) and Report request. Activate Scan tab to select scan parameters. Activate Time course tab to select data to be recorded and then initiate the time course run.

The wideband holographic imaging technique is very sensitive because of the active, coherent, heterodyne detection that is employed in typical systems [15-17], Therefore, the primary limitation on image acquisition is the time required to mechanically scan the transceiver. Two-dimensional raster scans are often used for laboratory experiments, and these typically require scan times on the order of 1-30 min. Practical systems employing linear switched antenna arrays and mechanical scanning reduce this time to 1-10 seconds [15-17],... 

Classical simulations are used to examine the transport of di-oxygen across to the active site of the heme protein. An expansion was not used, and dilferent scanning times and agreement of the profiles were used to assess the convergence of the results. Vemparala et alP use the JE and methods based on the JE to examine the transport of a halothane molecule across a lipid/water interface. 

These are extremely fast with the highest possible resolution, although the scan-averaging required for adequate signal-to-noise may provide ultimate scan times that are similar to other instrumentation. They are the best bet for analyzing gasses or materials where resolution is critical (due to a sharp Xmax). Many active pharmaceutical ingredients (APIs) are crystalline and have sharp peaks, even in the NIR. In such cases, the resolution of a FT instrument is a plus. 

The detection efficiency of a detector is another important property in PET technology. Since it is desirable to have shorter scan times and low tracer activity for administration, the detector must detect as many of the emitted photons as possible. The 511-keV photons interact with detector material by either photoelectric absorption or Compton scattering, as discussed in Chap. 1. Thus, the photons are attenuated (absorbed and scattered) by these two processes in the detector, and the fraction of incident 7 rays that are attenuated is determined by the linear attenuation coefficient (/x) given in Chap. 1 and gives the detection efficiency. At 511 keV, /x = 0.92 cm-1 for bismuth germanate (BGO), 0.87 cur1 for lutetium oxyorthosilicate (LSO), and 0.34 cm-1 for Nal(Tl) (Melcher, 2000). Consequently, to have similar detection efficiency, Nal(Tl) detectors must be more than twice as thick as BGO and LSO detectors. 

One of the inherent problems in the production of short-lived radiopharmaceuticals is the (X)nsistent delivery of usable amounts of labeled product. In a clinical cardiac study using the PETT system and relabeled palmitic acid, 20-25 mCi is normally injected into a patient. The amount of activity injected depends on the patient s physical characteristics and the desired scan time. The lower limit of usable amount of activity is 15-17 mCi however, this amount of riC-palmitate often produces borderline statistical information and makes determination of the infarct size diflBcult. Animal studies usually require lower amoxmts of labeled product however, in the case of some dog studies, the amount of activity required is the same as for a human preparation. In our experience covering over 220 syntheses for patient and animal studies during the past two years, C-palmitic acid has been prepared in usable amounts in over 85% of the cases. Several modifications and additional quality control tests have been added to the previously described synthesis to increase the reliability of the procedure (32-34). 

C = fraction of time occupied by active scanning after subtracting vertical and horizontal blanking periods... 

Total measurement time for data acquisition If signal-averaging has been performed time per active scan... 

It is important to know that if the activity administered to the patient is greater, the scanning time is shorter. Another important feature of the technique is that if the patient moves during the imaging, the picture will be blurred and then it should be repeated. If the channel is not on the photo-peak, the image will have poor geometrical resolution with low diagnostic value. 

---