Various diffusion magnetic resonance imaging techniques for pancreatic cancer

Figure 1 Diffusion weighted imaging sequence. Diffusion weighted imaging (DWI) applies the two motion-probing bipolar gradients on either side of the refocusing 180°pulse. The degree of diffusion weighting depends on the G (the amplitude of the gradients), δ (their duration) and Δ (the interval between gradients). This factor is quantitatively expressed by a parameter b, where b = γ²G²δ² (Δ - δ/3) and γ is a constant of the gyromagnetic ratio. Assuming that the water molecules in tissues are motionless, the effects of the two motion-probing bipolar gradients can cancel each other. Thus, for the free molecular diffusion of water molecules, the displacement can be depicted by the DWI. RF: Radio frequency.