Constant time imaging

Constant-time imaging of H in solids has been applied in combination with MAS for line narrowing [Cor3, Cor4]. The images were recorded for a dynamically stressed poly(isoprene) phantom and of poly(butadiene) in two poly(butadiene)/poly(styrene) blends. Spectroscopic MAS imaging has also been tested on deuterated polymers to probe differences in molecular moblity from the lineshape of the rotary-echo envelope... 

For short materials the constant time imaging method (also called single point... 

Single point (or constant time) imaging (SPI) is a phase encoding MRI method which uses reasonably large, pulsed magnetic field gradients (up to 0.1 T m ). 2-44 Band-selective radiofrequency pulses are not used and... 

The advantages of constant-time imaging are the easy setup, insensitivity... 

Figure 3 The pulse sequence and /(-vectors for constant-time imaging. Notice that all of the data are collected at a constant time following the excitation pulse and yet the /(-vector is still modulated from point-to-point by systematically varying the strength of the gradient.

Figure 8 Three-dimensional constant-time image of a bovine femur showing both the compact bone and the interior bone marrow. The image resolution is 1.1 x 1.1 x 4.4 mm and the image was acquired over a period of 5 h. Figure reproduced with permission from Balcon BJ (1998) In Blumler P, BIQmich B, Botto B, and Fukushima E (eds) Spatially Resolved Magnetic Resonance. Weinheim Wiley-VCH. p. 84.

The Auto-Reference step that is to solve the Halting solve the Halting Problem proves, only, its own disusability creates just a certain image of what is to be possibly discovered - the infinite cycle in the form of the infinite constant time sequences [when the time expansion (58) for p>l is considered). 

Short-range diffusion (SRD) analysis is the method used to obtain the distribution of diffusion coefficients of target molecules. In this method, short trajectories with constant time duration are successively extracted from one trajectory, and diffusion coefficients are determined for individual short trajectories, producing a time series of diffusion coefficients. This analysis can be used to detect temporal changes in the mobility of individual molecules (14,15). In this section, we suppose that the images were acquired at 33-ms intervals (i.e., 30 frames per second (fps), = 33 ms). 

Adjust illumination and exposure times accordingly and be careful to remain within the Hnear range. Keep settings constant during image acquisition of parallel samples -within an experiment. 

In constant-time methods the line width of the NMR resonance no longer blurs the image and the image resolution is solely determined by the sampling conditions for the coverage of fe-space. The line width does, however, limit the sensitivity, and so... 

With the typical lOOGcm-i gradients available from commercial small scale liquid state imaging equipment, constant-time methods can be used to observe rigid solids, but at very low S/N ratios and at low spatial resolution. 

Constant-time methods are also used in liquid state imaging and in NMR microscopy to avoid distortions from chemical shifts and local variations in the bulk magnetic susceptibility. 

To verify the modelling of the data eolleetion process, calculations of SAT 4, in the entrance window of the XRII was compared to measurements of RNR p oj in stored data as function of tube potential. The images object was a steel cylinder 5-mm) with a glass rod 1-mm) as defect. X-ray spectra were filtered with 0.6-mm copper. Tube current and exposure time were varied so that the signal beside the object. So, was kept constant for all tube potentials. Figure 8 shows measured and simulated SNR oproj, where both point out 100 kV as the tube potential that gives a maximum. Due to overestimation of the noise in calculations the maximum in the simulated values are normalised to the maximum in the measured values. Once the model was verified it was used to calculate optimal choice of filter materials and tube potentials, see figure 9. 

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