An example for oak is given in Fig. 3. Spatial and temporal resolution As Wortmannin datasheet stated above spatial resolution depends on the discrimination of the unique frequencies for each position. The differences in frequencies are only dependent on the magnetic field gradient (Δν = γ × G × Δr), and not on the main frequency of the spins in the homogeneous magnetic field. In order to be sure that each frequency interval Δν contains unique position information, Δν must be bigger or at least

equal to the line width at half maximum of the resonance line in the homogeneous magnetic field without field gradient, which is dictated by 1/T 2 *. Plant tissue can include intercellular air spaces, resulting in susceptibility artifacts manifest as local magnetic field gradients, < g z 2  > , which shortens the effective T 2: $$ 1/T_2 BV-6 in vitro * = 1/T_2\;+\;\textf\left( < g_\textz^ 2 > \right) $$ (7) These artifacts increase with increasing field strength: < g z 2  > ~ B 0 2 . Shorter T 2 * values increase the necessary Δν for a fixed value of Δr. Applying a strong enough

magnetic field gradient G can regulate Δν. Doing so, there seems to be no limit on spatial resolution. However, an increase in Δν results in a decrease of the signal-to-noise ratio (S/N), since the signal per Δr this website is proportional to the number of spins at that position interval, which is fixed. As a result, the signal per Δr is smeared out over a larger frequency range Δν at increasing G, resulting in a decrease in S/N. The S/N is defined by the magnetic field strength, B 0 , the radius of the rf measuring coil (detector), r, and details

of the experiment, including the measurement time (Homan et al. 2007): $$ S/N \sim (V/r) \times B_0^ 7/ 4 \times (N_\textav \times N_\textecho /\Updelta f) \, ^ 1/ 2 $$ (8) Here V is the pixel volume, and is defined by the number of pixels N within the Field-of-View (FOV), the dimension (in e.g., cm) of the image. N av is the number of averages, N echo the number of echoes used to construct or calculate the image. Δf is the spectral width, representing the frequency range over the given FOV. It is inversely related Niclosamide to the dwell time, the time between successive sampled data points. The dwell time times N is the time needed to detect the signal, T acq, and determines the minimal echo time TE. Δf divided by the FOV defines G. T acq on its turn is inversely proportional to G during acquisition. The product of G and T acq defines Δr. A number of different approaches can be followed to increase the spatial resolution (minimal V) at a certain S/N, at the same time trying to avoid increasing the measurement time. The S/N of a pixel in an NMR image depends on the amount of water in that pixel.