Diffusion imaging

Luoas A J, Gibbs S J, Jones E W G, Peyron M, Derbyshire J A and Flail L D 1993 Diffusion imaging in the presenoe of statio magnetio-field gradients J. Magn. Reson. A 104 273-82... 

Jan,W., Zimmerman, R. A.,Wang, Z. J., Berry, G. T., Kaplan, P. B. and Kaye, E. M. MR diffusion imaging and MR spectroscopy of maple syrup urine disease during acute metabolic decompensation. Neuroradiology 45 393-399,2003. 

Fig. 20. Spin density, and water diffusion images for a 2.2-inm-diameter, spherical silica catalyst support pellet. In-plane pixel resolution was 45 pm x 45 pm image slice thickness was 0.3 mm. (a) Spin-density map lighter shades indicate higher liquid content, (b) map (150 00 ms) lighter shades indicate longer values of Ti. (c) Diffusivity map ((0-1.5) x 10 m s ) lighter shades indicate higher values of water diffusivity within the pellet.

Comparison of Diffusion Imaging with Changes in Relaxation Times 51... 

Studies by Hossmann et al. have shown that prolonged global ischemia may result in secondary deterioration during the reperfusion phase followed by depletion of energy metabolites, acidosis and a dramatic increase in lactate content (Hossmann et al. 1994). However, in some animals recovery can be observed that is dependent on successful reperfusion. This pathologic condition that imitates cardiac arrest in man, results in a rapid (< 10 min) and marked (68% of control) decrease in the ADC when measured by repeated MR diffusion imaging (Hossmann et al. 1994) (Fig. 4.6). 

Diffusion tensor imaging (DTI) is a sophisticated form of diffusion imaging that is not yet routinely used in clinical stroke. However, it is becoming increasingly popular as a research tool (Sotak 2002), particularly in small lacunar stroke (Gillard et al. 2001 Lie et al. 2004) and in patients with ischemic leukoaraiosis (O Sullivan et al. 2001, 2004), and will, thus, be shortly described here. 

Warach S, Dashe JF, Edelman RR (1996a) Clinical outcome in ischemic stroke predicted by early diffusion-weighted and perfusion magnetic resonance imaging a preliminary analysis. J Cereb Blood Flow Metab 16 53-59 Warach S, Mosley M, Sorensen AG, Koroshetz W (1996b) Time course of diffusion imaging abnormalities in human stroke (letter comment). Stroke 27 1254-1256 Wheatley DN (1985) Mini-review. On the possible importance of an intracellular circulation. Life Sci 36 299-307... 

Hawkins GC, Bonita R, Broad JB et al. (1995). Inadequacy of clinical scoring systems to differentiate stroke subtypes in population-based studies. Stroke 26 1338-1342 Hjort N, Christensen S, Soiling C et al. (2005a). Ischemic injury detected by diffusion imaging 11 minutes after stroke. Annals of Neurology 58 462-465... 

Fig. 14. Radiofrequency and gradient pulse sequence for velocity and diffusion imaging in which the molecular motion is measured in the domain of two spatial dimensions (x, y) of a slice selected normal to the z axis. Note that the PGSE pulse pair (g) provides the third dimension—that of motion—while the phase encode (Gj,) and read gradients (G ) provide the first and second spatial dimensions.

Zawodzinski et al. [64] have reported self-diffusion coefficients of water in Nafion 117 (EW 1100), Membrane C (EW 900), and Dow membranes (EW 800) equilibrated with water vapor at 303 K, and obtained results summarized in Fig. 36. The self-diffusion coefficients were deterinined by pulsed field gradient NMR methods. These studies probe water motion over a distance scale on the order of microns. The general conclusion was the PFSA membranes with similar water contents. A, had similar water self-diffusion coefficients. The measured self-diffusion coefficients in Nafion 117 equilibrated with water vapor decreased by more than an order of magnitude, from roughly 8 x 10 cm /s down to 5 x 10 cm /s as water content in the membrane decreased from A = 14 to A = 2. For a Nafion membrane equilibrated with water vapor at unit activity, the water self-diffusion coefficient drops to a level roughly four times lower than that in bulk liquid water whereas a difference of only a factor of two in local mobility is deduced from NMR relaxation measurements. This is reasonably ascribed to the additional effect of tortuosity of the diffusion path on the value of the macrodiffusion coefficient. For immersed Nafion membranes, NMR diffusion imaging studies showed that water diffusion coefficients similar to those measured in liquid water (2.2 x 10 cm /s) could be attained in a highly hydrated membrane (1.7 x 10 cm /s) [69]. 

The Shroud is a piece of fine linen, approximately 1.1 m wide and 4.3 m long, bearing the faint, diffused image of a crucified male (Figure 1). The linen is in a remarkable state of preservation considering its age (it dates at least from a.d. 1357, when it was first displayed publicly, and possibly dates to the first centrury a.d.) and its function (used to cover a dead body—most shrouds are rather badly decomposed). Its true age may be determined by carbon-14 dating, but this critically important experiment has not yet been performed. 

Reference 28 reports pulsed field gradient NMR studies of water motion in Nafion 1100, yielding intradiffusion coefficients close to 1 x 10-5 cm2 sec-1 for samples in contact with saturated vapor. For liquid-immersed Nafion membranes, other NMR diffusion imaging studies [29]... 

Fig. 7.2.24 (a) Generic scheme for spin-diffusion imaging. Spin diffusion is detected by use of... 

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