applied magnetic field and enabling blood and bone to be distinguished a non limiting example of the orders of magnitude involved follows given that a sample of blood has a susceptibility of 10 u2212 3 units and the applied magnetic field strength is 2 u00d7 10 5 a m then b u2212 u03bc r u03bc 0 h where u03bc r 1 10 u2212 3 1 001 in the absence of blood b 1 u00d7 4 u03c010 u2212 2 u00d7 2 u00d7 10 5 251 3 mt hence the magnetic flux density within the blood when introduced into the external field u03b4b 0 3 mt next assume that the introduction of blood into the excitation field of density 2 u00d7 10 5 a m leads to a variation of 10 of u03b4b i e 0 03 mt moreover the sensitivity of a hall device of the detector array is 1300 v a t then assuming a current drive of 1 ma a hall output voltage relating to an induction of 0 03 mt will give an output voltage of 1300 u00d7 1 u00d7 0 03 u00d7 10 u2212 3 mv or 30 u03bcv a voltage of this magnitude is easily measured it should be noted that 1 the assumed perturbation of the excitation field represents a percentage change of 0 012 and 2 in the absence of blood the normal hall voltage would be 1300 u00d7 1 u00d7 251 3 u00d7 10 u2212 3 mv.