Radiation Biology and Protection

: X. .

, , 2014, . 1 X X - Projects

22

: The Essential Physics of Medical Imaging, 3rd Edition( Essential physics of medical imaging) ( , , ) = () , , ? , c=., : E=h.=h.c/ ( eV kai nm) ?HM , . FM, . .

, . 3 X4E=h;h=4,135x10 exp{-15} eVDiagnostic X-ray energy spectrum 10-150 keV

=c/(c=2,997925x10exp{8}Diagnostic X-ray wavelengths:0,1 nm(12.4 keV) - 0.01 nm (124 keV)(visible light wavelength spectrum 400 (violet)-650 (red) nm)

X (and ) rays interact with atoms and have the potential toliberate electrons from the atoms that bind them, resulting in ion pairs (negatively charged electrons and positively charged atoms or molecules) (ionizing radiation).

X and rays are the same, but with different spectral characteristics.A X- and - ray of the same energy are the same.

4 ( ) . ( ) . :- (Computed Radiography-CR)- (Digital radiography-DR) -)55 : : - (1%), (99%)

(+) (-) ( e- ) () e-

6 .6

() , ( ).

.7 : -

(ZW 74, Z 42) e-

(34000C)

1. + ,

2. + , -

8 ? : = e V (. V=100kV, E=100keV)

e- :

e-e-() () 910

: X e- ( Coulomb).. 1: 3

( ), X .

( )The intensity of X-rays is defined as the energies of x-rays passing through the unit area with its normal line along the propagating direction of x-rays per unit time.where Ni is the number of photons which have energies of hi. N: :

In order to increase the intensity of x-rays, we need (1) to increase the tube current (more electrons) (2) to increase tube voltage (increasing the energy of each x-ray photon).

1011

X, , , . hE1E2E3n1E1

n2E2n3E3 .1112 ?

:

e- Z ( ( R)

(Z x Emax). ( )

EmaxThe range R of a charged particle in a particular absorbing medium is an experimental concept providing the thickness of the absorber that the particle can just penetrate.

With regard to the range R of electrons with kinetic energy EK in the target material of atomic number Z twotypes of targets are known:

Thin targets with thickness much smaller than R. Thick targets with thickness of the order of R.

, n 1213 , e- X / .

Thin target ( ) X (keV)

( Coulomb) , , e- X . ( e- , Auger e-) .14( e- , Auger e-)14 ? : ( ) ( )

( ) ( L) ( K) (keV)

15The intensity of X-rays is defined as the energies of x-rays passing through the unit area with its normal line along the propagating direction of x-rays per unit time.where Ni is the number of photons which have energies of hi. N: :

In order to increase the intensity of x-rays, we need (1) to increase the tube current (more electrons) (2) to increase tube voltage (increasing the energy of each x-ray photon). 15 ( , E EB, . .

- ( ) (1/E exp{3}) Z (Z exp{3,5})

Z 17

h E = h - EB kVp17 Compton: ( ). Compton. . .

- Compton ( ) >> o . .

h = Ea + Es Ea Es 18 Thomson: (~ 1,022 MeV) . , e , 2 0.511 MeV. ( )

- ( >150 keV) ( ) ( >>)

20 20 ?21 Compton. ( ).

Compton , , .

.

X ().

Grid () -22 (1) . Compton X, , () ( ).

23

Compton (2)

24 ( Compton) , .

(.. ). 24

: / , .

, . (10-150 keV) Compton.25-25 (/)

(,e,) , e- .

/ , .26Energy exceeding twice the rest mass of an electron (1.022MeV)27

X (kVp)

(mA)

3. (s)

X28 X:

max () ( ) .

(-) (kVp)2 ( )

(kVp) , (. 50 kVp). (. 100 kVp). 29 ?29 . () .

( Al) . (Half Value Layer HVL) HVL= 0.693 X: HVLIoI = Io/2

3060 kV - 50 mAs70 kV - 50 mAs80 kV - 50 mAs

E 31Part No...., Module No....Lesson NoModule titleIAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources, , ( ) , ( ), ()

X (mA) ( e- ).

X (ms min).

X (mAs)

, (. ).

, .

X:

32 , .

3270 kV - 25 mAs70 kV - 50 mAs70 kV - 80 mAs

E 33Part No...., Module No....Lesson NoModule titleIAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources .

X35 X: 36

, , (15-35 keV). . 37

2 (25 30 kVp). Mo 2 (25 30 kVp). Mo Rh 30 kVp. Rh Mo/Mo, X: /, 2d-2.5d 38

(1mm) . () (), () , . ( adapted from: Mark A. Helvie, Radiol Clin North Am. 2010 September ; 48(5): 917929) -

3839 X: 2d-2.5d-3d

Adapted from joint AAPM/COMP Meeting August 2011 B. Wolbarst, Physics of Radiology, chapters 2-4, Appleton and Lange 1993, Norwalk, Connecticut, USA.W. Huda and R. M. Slone, Review of Radiologic Physics, chapters 2-5, Williams and Wilkins 1995, Media, PA, USA.Beutel J., Kundel H.L., Van Metter R.L. (eds.), Handbook of Medical Imaging, Volume I: Physics and Psychophysics, chapter 1: X-ray Production, Interaction and Detection in Diagnostic Imaging, J. M. Boone, p3-77, SPIE Press 2000, Bellingham, Washington., USA.Andrew Webb, Introduction to Biomedical Imaging, Chapter 1: X-ray Imaging and Computed Tomography , p1-56, John Wiley & Sons, 2003, Hoboken, NJ, USA.J T Bushberg, J A Siebert, E M Leidholdt, J M Boone The Essential Physics of Medical Imaging, 3rd edition, Chapters 3, 6, 8, Lippincott, Williams & Wilkins, 2012.

40