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6720 Lecture 6_analog imaging

# 6720 Lecture 6_analog imaging - Lecture VI 1 2 3 4 5 6 7...

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2 PHYS 6720 - Lecture VI 7 VI-2 Risk to patients General features of tissue interaction ( σ inc /Z) independent of Z Mass density (g/cm 3 ) Electron density (1/kg) Effective atomic number Z eff p-e interaction for <50keV Incoherent scattering for >30keV Fat 0.92 3.34 × 10 26 5.9~6.3 Weak Strong Soft tissue (water) 1.00 ~ 1.04 3.34 × 10 26 7.42 Strong Strong Bone 1.3~1.8 3.00~3.19 × 10 26 11.6~13.8 Very strong Weak air 1.2 × 10 -3 3.01 × 10 26 7.64 negligible Negligible Ca 1.55 3.01 × 10 26 20 Very strong Negligible ( σ pe /Z) Z (3.0~3.8) PHYS 6720 - Lecture VI 8 VI-2 Risk to patients Example: electron density ρ e of Ca For Ca: Z=20, A=40 so the mass of 1 mole (contains N A atoms) is given by M mole =40g=0.0400(kg). For a system of Ca atoms with a mass M=1.00(kg), the total number of electrons contained in M is given by N e =ZxN A x(M/M mole )=20.0 × 6.022 × 10 23 × (25.0) thus ρ e = N e /M = 3.01 × 10 26 (1/kg) PHYS 6720 - Lecture VI 9 VI-2 Risk to patients Definition of f-factor Æ When absorption of x-ray intensity in tissue is concerned, it is
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