Figure 4. Example of a 3D FLASH (fast low angle shot) dataset of a normal volunteer measured by the conventional head coil. A. Excellent T- contrast in the original transversal images. B. A strong signal inhomogeneity is obvious

in the reconstructed sagittal images … A very complex signal and texture situation is present in so-called single shot imaging techniques like echo planar imaging (EPI),11 where k-space is filled in one shot with multiple gradient echoes. This is achieved by a gradient scheme in which the upper corner of the k-space is reached by a single gradient pulse followed by a series Inhibitors,research,lifescience,medical of blips resulting in a rectangular movement through the kspace.This technique is very sensitive to local susceptibility artifacts, resulting in image distortions and strong T2* contrast Inhibitors,research,lifescience,medical dependence. Some special imaging techniques like spiral imaging can produce a very complex pattern in the image texture, since this single shot technique moves on a spiral through the k-space, which can be achieved by oscillating gradients with a phase Inhibitors,research,lifescience,medical shift of 90° in the x and y directions. This technique requires data interpolation in k-space to bring the

measured data onto a Cartesian coordinate system before .Fourier transform. This interpolation can produce spurious artifacts with the consequence that the image texture is dependent on k-space interpolation and image reconstruction. In addition, the problem of texture dependence on measuring technique is more complicated Inhibitors,research,lifescience,medical due to the large number of imaging sequences available on modern scanners, as illustrated in (Figure 5) Figure 5. Sketch of the family of imaging techniques available on modern scanners. There are many strategies of mixing spin HDAC inhibitor echoes with gradient echoes to speed up imaging time with the consequence of very complex image contrast and texture. CISS, constructive … Results

and discussion SNR dependence Figure 6 and 6b show Inhibitors,research,lifescience,medical the results of a FLASH experiment, in a normal volunteer for SNR dependence measurement of texture parameters. The measuring parameters of the FLASH experiment were: TR/TE/α = 2 ms/ 9 ms/30°; bandwidth (BW) = 195 Hz/pixel; MA = 512×512; FOV = 280 mm; TH = 2 mm; and acquisitions (AQ) = 1 to 324 resulting in an SNR = 1 to 18. next Texture parameters (SNR, entropy 5×5, correlation 5×5) of white matter, gray matter, and noise are shown as a function of the number of acquisitions (=SNR2). Figure 6c demonstrates that no texture can be measured in white matter using standard image resolution (0.5×0.5×2 mm3) as described above, since the SNR of white matter has the same characteristics as noise. In contrast, the SNR of gray matter reaches a nearly constant value at about 16 acquisitions and no further improvement can be reached due to the true underlying texture of the tissue.