1. Dosimetry Sanja Dolanski Babić March, 2010. Ultrasound interaction with tissue

2. Dosimetry

3. Radiation - the process of emitting energy as waves or particles, and the radiated energy Radioactivity - the property of radionuclides of spontaneously emitting ionizing radiation Dosimetry – assessment of radiation dose by measuring or calculating and assessment of biological damages What’s the difference between radiation and radioactivity? Sources of radiation – natural and artificial

4. Types of ionizing radiation

5. The half-life is the time taken for half of the atoms of a radioactive substance to decay. [A]= Bq Bq = 27 x 10 -12 Ci

6. Standard warning sign for a possible radioactive hazard Pie chart for background radiations

8. Basic principle of devices for detecting and measuring of radiation Effective volume of detector Basic detector gass liquid solid Measuring effects of radiation Fragments of fission  particles X,  - radiation Electrical: el.current or impulse Optical Calorimetric Chemical Biological

9. Devices for detecting and measuring of radiation: 1. Devices for track visualisation of radioactive particles – radiographic track and Wilson cloud chamber 3. Dosimeter is a small portable instrument for measuring and recording the total accumulated dose of ionizing radiation a person receives – such as a film badge, thermoluminescent or pocket dosimeter 2. Counters (detectors) – Geiger counter, scintillation detector, semiconductor detector, gamma-camera etc. Radiation detectors are used in: nuclear physics, medicine, particle physics, astronomy and industry

10. 4.1 Slide 1 Radiographic film Diagnostics Radiotherapy Protection from radiation

11. Ionization Chamber (1898. Marie Curie) - device used for two major purposes: detecting charged particles in the air (as in a smoke detector) and for detecting or measuring of ionizing radiation - device measures the electric current generated when radiation ionizes the gas in the chamber and therefore makes it electrically conductive - electric currents are very low: around 10 -15 A - dosimetry in medicine measures very low doses X and  radiation Principle of an ionization chamber

12. Simplified diagram of a smoke alarm

13. – higher voltage at the source of current Geiger-Müller Counter – imediate “chain” ionization of the gas – electric current is 10 10 times higher than primary electric current - detects a single particle of ionizing radiation and produce an audible click for each GM tube – simply gas detector – GM counter is used to detect usually alpha and beta radiation

14. Scintillation counter - measures ionizing radiation - sensor fluoresces when struck by ionizing radiation - a sensitive photomultiplier tube measures the light from crystal - sodium iodide scintillation counter detects gamma rays

15. That’s how it used to be... Chest X ray examination

16. EXPOSURE (X)– measure for ionization of the air mass of 1kg X =  Q/  m [X]=C/kg 1 R = 2.58 x 10 -4 C/kg - defined only for electromagnetic radiations which energies are smaller than 3 MeV

17. RADIATION ABSORBED DOSE (D)– measure of increasing internal energy (  U) in a mass of 1 kg tissue (  U) caused by absorption of ionizing radiations D = U/m [D]=Gy=J/kg 1Gy = 100 rad D = U/m [D]=Gy=J/kg 1Gy = 100 rad - defined for all ionizing radiations - measuring of absorbed doses are not possible in living tissues

18. dose in sivert

19. D eq = D x H ; - EQUIVALENT DOSE is calculated: D eq = D x H ; H is radiation quality factor [D eq ]= Sv 1 Sv = 100 rem H is radiation quality factor [D eq ]= Sv ; 1 Sv = 100 rem

20. D eq x f EFFECTIVE EQUIVALENT DOSE: D eq x f - each body part has its own weight factor, f Whole body1 (100%) Ovaries, testes 0.25 (25%) Bone marrow0.12 (12%) Bone surface0.03 (3%) Thyroid0.03 (3%) Lungs0.15 (15%) Breasts0.12 (12%) Other tissues0.30 (30%)

21. --- DOSE SPEED – radiation doses during 1sec - very important to biological damages Upper limit for Radiation Workers50 mSv per year Upper limit for general population5 mSv per year Visible blood changes0.5 mSv per year Lethal dose for 50% of individuals500 mSv Lethal dose for all1 500 mSv Radiation dose by one chest X ray examination 0.2 mSv Radiation dose by one head CT scanning11 mSv Natural radiation in Croatia2 mSv per year Smoking13 mSv per year Radiation levels and their effects

23. 0.02- 0.05 mSv 0.03 mSv X ray examination

24. Hard technique Soft technique Effective dose (mSv) (ICRP 25)0,030,14 Effective equivalent dose(mSv) (ICRP 60)0,040,22 Chest X ray examination Marija Surić, Institut za medicinska istraživanja, Zagreb

25. Interactions between Ultrasound and Tissue

26. Conditions of ultrasound scanning  Diagnostic -frequency range: 0,5 MHz - 20 MHz -the time of puls: 0,2 - 2,0 s -intensity: 1 - 100 mW/cm 2 - amplitudes of vibrating: do 10 nm  Therapy -frequency range : 0,8 MHz - 1 MHz - constant wave -intensity : 100 - 1000mW/cm 2 - amplitudes of vibrating: 10 - 25 nm

27.  have the depth of penetration at the f=0,88 MHZ around 5 cm for muscle tissue, 10 cm for fat tissue and 0,3 cm for bone  have very low apsorbtion in fat tissues (use for diagnostic), higher in muscles and the highest in bones (use for therapy) Ultrasound waves

28.  The sideeffects in diagnostic usage almost do not exist because the pulses are short, intensities are low and frequencies are very high.  Scanning of small structures (embrio, eye) requires higher frequencies because of the better resolution. But higher frequencies mean fast changes in local pressure what presents risk for breaking of macromolecules. Intensity must be lower. Ultrasound waves

29. Ultrasound effects: 1. thermical 2. mechanical 3. appereance of caviation 4. chemical 5. biological

30. 1. Thermical effects – are used in therapy; thermical stress possible 2. Mechanical effects – bonds in macromolecules break when amplitude of the oscillation is higher than 10 nm and the change of local pressure is few atmospheres

31. 3. Cavitation – the appereance of air bubbles inside the tissue that is treated by ultrasound of high intensity - molecular bonds are breaking and free radicals are occuring 4. Chemical effects – breaking of chemical bonds and producing free radicals 5. Biological effects – ultrasound is fatal for bacteria, viruses and fungies