Slice width

For a given half width at half maximum in the time domain, Ar,.n =2, /, the slice width A decreases with increasing gradient strength G. ... 

Number - average molecular weight Weight - average molecular weight Number of slices 122 Slice width ... 

Dextran polymers were used to evaluate the utility of the linear, polydisperse calibration method for water-soluble polymer characterization. A blend of T-40 and T-70 dextran standards was used as a polydisperse calibration standard. Table VIII displays the report from the linear calibration method using this standard. Nine Iterations of the search algorithm were required for convergence to the true and Mn values of the standard. As can be seen in the report, the elution volume profile of the standard contained 72 area/time slices upon which calibration calculations were based. The slice width was set at 10 seconds/siIce. Figure 5 shows a plot of the calibration curve generated from the linear calibration method utilizing the dextran standard,... 

Ground water level increase rate (m/day) Strength parameters 0 Slice width (m) Time interval Horizontal residual displacement (m)... 

Effects of the slice width and the time interval of calculation... 

In this paper, based on the parametric studies, effects of the GWL increase rate, the initial value of apparent friction angle, the slice width and the time interval of calculation on the slope displacements were evaluated. Effect of the slice width on the calculation results was found to be insignificant. 

CT detectors must provide different slice widths to adjust the optimum scan speed, longitudinal resolution and image noise for each application. With a singleslice CT detector, different collimated slice widths are obtained by pre-patient collimation of the X-ray beam. For a very elementary model of a two-slice CT detector... 

For M>2, this simple design principle must be replaced by more flexible concepts requiring more than M detector rows to simultaneously acquire M slices. Different manufacturers of MDCT scanners have introduced different detector designs. In order to be able to select different slice widths, all scanners combine several detector rows electronically to a smaller number of slices according to the selected beam collimation and the desired sHce width. 

Both single-sHce and multi-sHce spiral CT require an interpolation of the acquired measurement data in the longitudinal direction to estimate a complete CT data set at the desired plane of reconstruction. As a consequence of this interpolation, the sHce profile changes from the trapezoidal, in some cases almost rectangular shape known from axial scanning to a more beU-shaped curve see Fig. 1.8. The z-axis resolution is no longer determined by the collimated beam width S ji alone (as in axial scanning), but by the effective slice width s, which is established in the spiral interpolation process. Usu-... 

Fig. 1.8. Effective slice width in spiral/helical CT the collimated slice profile, which is a trapezoidal in general, is indicated in red. The slice sensitivity profiles (SSP) after spiral/ helical interpolation are bell-shaped see the green curves for the most commonly used single-slice approach (180-LI) at dif-...

Fig. 1.9. Top FWHM of the SSP as a function of the pitch for the two most commonly used single-slice spiral interpolation approaches, 180 linear interpolation (I80-LI) and 360 linear interpolation (360-LI). For both, the slice significantly widens with increasing pitch as a result of the increasing distance of the interpolation partners. Bottom MPRs of a spiral z-resolution phantom scanned with 2-mm collimation (180-LI) show increased blurring of the 1.5-mm and 2-mm cylinders with increasing pitch as a consequence of the increasing effective slice width...

Fig. 1.10. Adaptive axial interpolation for a four-slice CT system SSP of the 2-mm slice (for 4x1-mm collimation) at selected pitch values. The functional form of the SSP, and hence the effective slice width, are independent of the pitch. Consequently, MPRs of a spiral z-resolution phantom scanned with 2-mm slice width show clear separation of the 1.5-mm and 2-mm cylinders for all pitch values...

Fig. 1.11. Principle of improved z-sampling with the z-flying focal spot technique. Due to a periodic motion of the focal spot in the z-direction, two subsequent M-slice readings are shifted by half a collimated slice width 5 .n /2 at iso-center and can be interleaved to one 2M slice projection...

NY, turned by 90 ) in the isocenter of the scanner as a function of the pitch. Scan data have been acquired with 32x0.6-mm collimation in a 64-slice acquisition mode using the z-flying focal spot and reconstructed with the narrowest slice width (nominal 0.6mm) and a sharp body kernel. Independent of the pitch, all bar patterns up to 16 Ip/cm can be visualized. The bar patterns with 15 Ip/cm are exactly perpendicular to the z-axis, corresponding to 0.33-mm longitudinal resolution... 

In a two phase system of conductive needles embedded in a non conductive matrix the the conductivity should also depend upon the size of the sample with respect to the mesh size of the conductive needle network. When films were cut into slices of decreasing width, a minimum slice width of 100 m was found./5/... 

Table 8.4 Maximum number of image slices for different image slice width...

In single-slice CT,the most important scan parameters can be provided in the form of a triplet including slice collimation (SC, in mm), table feed/rotation (TF, in mm) and reconstruction increment (Rl, in mm). Depending on clinical indications, a compromise has to be reached between z-axis resolution and required scan length. The effective slice thickness or slice width (SW) can be calculated from slice collimation and pitch, P (=TF/SC). The suggested scan parameters for single-slice spiral CT of the liver are 5/8/4 (SC/TF/Rl) and the SW is 6.2 (Uggowitzer 2003). 

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