Phase contrast allows for qualitative blood flow analysis in large blood vessels. (a) Describe MR sequences required and how such analysis could be done to calculate blood flow. (b) What is VENC? What MRI pulse sequence parameters affect VENC value? (c) Suppose very low flows were under investigation; what modifications should be made and why? Suppose very large flows were under investigation; what modifications should be made and why?
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Sri K.
please go into depth with this question and explain formulas used.
Andreas P.
Measuring blood flow. Blood contains positive and negative ions and therefore is a conductor. A blood vessel, therefore, can be viewed as an electrical wire. We can even picture the flowing blood as a series of parallel conducting slabs whose thickness is the diameter $d$ of the vessel moving with speed $v$ .(See Figure $21.62 . )$ (a) If the blood vessel is placed in a magnetic field $B$ perpendicular to the vessel, as in the figure, show that the motional potential difference induced across it is $\mathcal{E}=v B d .$ (b) If you expect that the blood will be flowing at 15 $\mathrm{cm} / \mathrm{s}$ for a vessel 5.0 $\mathrm{mm}$ in diameter, what strength of magnetic field will you need to produce a potential difference of 1.0 $\mathrm{mV} ?$ (c) Show that the volume rate of flow $(R)$ of theblood is equal to $R=\pi \mathcal{E} d / 4 B .$ (Note: Although the method developed here is useful in measuring the rate of blood flow in a vessel, it is limited to use in surgery because measurement of the potential $\mathcal{E}$ must be made directly across the vessel.)
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