RADIATION PROTECTION AND MRI SAFETY.pptx

Radiology

1. RADIATION PROTECTION AND MRI SAFETY DR. GADHA B DNB RESIDENT

2. ELECTROMAGNETIC SPECTRUM Increasing frequency

3. RADIATION Radiation describes any process in which energy emitted by one body travels through a medium or through space, ultimately to be absorbed by another body.  IONISING Cosmic rays X rays Gamma rays Alpha rays( He² ) Beta rays(beam of electrons) NON IONISING radiant heat radio waves microwaves infrared light visible light ultraviolet light. photons particle

4. MEDICAL APPLICATIONS OF RADIATION Leading diagnostic tool : > 5 billion medical imaging studies are carried out each year, out of which 2/3 rds involve ionising radiation. About 40 million nuclear medicine procedures are carried out using medical isotopes. > 5 million patients requiring cancer treatment receive radiotherapy.

5. INVESTIGATIONS USING RADIATIONS IONISING NON IONISING Bone scan Thyroid scan DTPA Thallium Tc based scan PET GAMMA RAYS (Nuclear scans) X RAYS (Radiological scans)

6. RADIATION UNITS Unit of radiation exposure is Roentgen (R) Defined as amount of xrays or gamma rays that will liberate a charge of 2.58 x c / kg under standard temperature and pressure. SI unit of radiation exposure is coulombs/kg  

7. RADIATION ABSORBED DOSE Unit is Rad Defined as the energy absorbed per unit mass. SI unit is GRAY (J/Kg) 1 gray = 100 rad

8. EQUIVALENT DOSE Unit is Rem. Equivalent dose = absorbed dose x radiation weighting factor Represents the biological impact of various types of radiations. SI unit of equivalent radiation is Sievert. 1 sievert = 100 rem TYPE OF RADIATION QUALITY FACTOR XRAY , GAMMA RAY , BETA RAY 1 NEUTRONS 10 HIGH ENERGY PROTONS 10 ALPHA PARTICLES 20 More the quality factor , more the damaging power.

9. EFFECTIVE DOSE It assigns the various organs / tissues the proportional risk of stochastic effect to radiation , compared to the uniform whole body radiation by same equivalent dose Effective dose = sum of dose equivalent of each tissue x appropriate tissue weighting factor. Expressed in Sievert

10. TISSUE TWF (new) GONADS 0.08 ( ICRP – 0.2) ACTIVE BONE MARROW, COLON , LUNGS , STOMACH 0.12 BLADDER , ESOPHAGUS, LIVER , THYROID 0.04 BREAST 0.12 BONE SURFACE , SKIN , BRAIN , SALIVARY GLANDS 0.01

11. LAW OF BERGONIE & TRIBONDEAU Radiosensitivity increases as proliferation rate of cells and growth rate of tissues increases. When the level of metabolic activity is high , the radiosensitivity is also high. Stem calls are more radiosensitive than mature cells. Younger tissues and organs are more radiosensitive.

12. DOSE CONVENTIONAL UNIT SI UNIT EXPOSURE DOSE ROENTGEN COULUMBS/KG ABSORBED DOSE RAD GRAY EQUIVALENT DOSE REM SIEVERT EFFECTIVE DOSE SIEVERT RADIOACTIVITY CURIE BECQUEREL

13. EFFECTS OF RADIATION BIOLOGICALLY SOMATIC GENETIC RADIATION PROTECTION STOCHASTIC DETERMINISTIC

14. SOMATIC EFFECTS Appears in exposed individual during lifetime. Prompt effects : Appear shortly after exposure. eg : hair loss after exposure to scalp Delayed effects : Appears years after exposure. eg : cancer , cataract

15. Dose (rad) effect 0-25 no detectable symptoms 25-100 changes in blood 100-300 nausea, anorexia 300-600 diarrhea , hemorrhage,possible death LD50/60 : dose of radiation expected to cause death Within 60 days to 50% of those exposed. For humans, it is 350 rads.

16. GENETIC EFFECTS Abnormalities that may occur in future generations of exposed individuals. i.e ; it affects the unexposed individuals as well.

17. STOCHASTIC EFFECTS Random / chance events Dose independent No dose threshold Eg : cancer genetic side effects teratogenicity Linear quadratic no threshold theory :Even though risk increases in linear quadratic fashion with dose, the severity of the effect will not. i.e ; the patient will either develop cancer or not.

18. DETERMINISTIC EFFECTS Has specific threshold for radiation, beyond which only the effects are seen. Severity of effect increases with increase in dose( dose dependent ). Lethal mutations affecting large number of cells. eg : cataract (50 – 200 rads) permanent sterility(350 – 600 rads) alopecia Only observed in lengthy fluoroscopically guided interventional procedures

19. RADIATION PROTECTION Radiation protection  is based on the three fundamental principles of justification of exposure keeping doses (of ionizing radiation) as low as reasonably achievable ( optimisation ) A pplication of dose limits . The  International Commission on Radiological Protection (ICRP)  is responsible for the development of these principles.

20. 1)JUSTIFICATION The justification principle is anecdotally known as the benefit vs risk principle; that is, an individual's exposure to medical radiation should always have a greater benefit to the patient as to outweigh the negative consequences of the proposed examination. 

21. 2)OPTIMISATION Optimisation is also known at the   as low as reasonably achievable (ALARA)  principle. That is, medical radiation exposures should always be kept as low as achievable to ensure it is employed optimally. There is a particular focus on the term achievable, as medical radiation exposure lower than achievable can result in non-diagnostic examinations .

22. ALARA Cardinal principle of radiation protection Basic protective actions to minimise external dose include : Minimising time in radiation areas. Maximising distance from source of radiation. Using shielding whenever possible.

23. a)TIME Exposure from radiation source is directly proportional to time Reduce period of exposure to radiation to reduce the dose received from source

24. b)DISTANCE Increase distance from source to decrease exposure rate. I 1  d 1 2  = I 2  d  2 2  (Inverse square law) Double the distance from the source; dose-rate falls to ¼ the original value.

25. c)SHIELDING Use an appropriate shielding material or protection devices Shielding reduces exposure rate:                        I = I     e   - µt                      µ- linear attenuation coefficient of shielding material                      t – Thickness of shielding material                      I  – Initial exposure rate                      I – Exposure rate after transmission from shielding material Use large shielding thickness (High Z materials eg Lead, Steel, Concrete, etc ) - reduce the exposure rate of gamma/X-ray radiation.

26. XRAY TUBE SHIELDING ROOM SHIELDING Primary protective barrier (1.6 mm lead) Secondary protective barrier(0.8mm lead) Viewing window(lead glass – 1.5 mm LE) PERSONNEL SHIELDING Lead apron Gonadal shielding Thyroid shielding Lead glass goggles Lead rubber glove LEAD EQUIVALENT is the thickness of lead required to achieve the same shielding effect against radiation under specified conditions as provided by a given material.

27. 3)DOSE LIMITS Dose limits are recommended by the International Commission on Radiological Protection T hey are in place to ensure that the individuals are not exposed to an unnecessarily high amount of ionising radiation. The limits are split into two groups T he public Occupationally-exposed workers. These limits do not apply to patients, however, the aforementioned principles do. 

28. Dose Limitations   Part of the body Occupational Exposure Public Exposure Whole body (Effective dose) 20 mSv/year averaged over 5 consecutive years; 30 mSv in any single year 1 mSv/y Lens of eyes (Equivalent dose) 150 mSv in a year 15 mSv/y Skin (Equivalent dose) 500 mSv in a year 50 mSv/y Extremities (Hands and Feet) Equivalent dose 500 mSv in a year - For pregnant radiation workers, after declaration of pregnancy 1 mSv on the embryo/fetus should not exceed.

29. PERSONNEL MONITORING Monitoring is necessary when there is a chance that the personnel may receive about 1/10 th of the dose limit. PERSONNEL MONITORING DEVICES : Film badge (100 µ Sv ) Thermoluminescent dosimeter(10 µ Sv ) passive OSL dosimeter(10 µ Sv ) Pocket dosimeter (1 µ Sv ) - active

30. Devices should be worn at the level of waist or collar or under lead apron. In case of high work load as in interventional radiology , additional dosimeter outside apron should be considered: one under apron at waist level and another over the apron at collar level. Effective dose E = 0.5Hw + 0.25Hn Hw = dose at waist lvel under apron Hn = dose at neck level over apron

31. WAYS TO PROTECT – PATIENT Maintain a lower current and therefore a higher kv Tight collimation to the area of interest. Patient positioning : protective gonadal shields. Do not use grid for smaller patients – when there is a substantial gap between the patient and the detector , remove the grid as this utilises the air gap technique.

32. WAYS TO PROTECT – GENERAL PUBLIC Information boards Restricted entry inside radiation area Regular radiation survey Radiation warning lamps and signs Xray room design

33. RADIATION AND PREGNANCY Radiation related risk are related to the stage of pregnancy and absorbed dose. Least hazardous during first 2 weeks of pregnancy while most significant during organogenesis; somewhat less in 2 nd trimester and least during 3 rd trimester. Radiation induced malformations have a threshold of 100 – 200 mGy or higher and are mostly CNS related.

34. MRI SAFETY

35. MRI Magnetic Resonance Imaging (MRI) is one of the most powerful medical diagnostic technologies, combining strong magnetic fields with powerful computer image processing. The core of an MRI machine is a very high-strength magnet arranged to surround most of the patient's body. This magnet is usually wrapped with coils of copper wire, and when electricity flows through the wire a powerful magnetic field is produced. Most clinical scanners are 1.5 - 3 Tesla scanners 3 Tesla = 30,000 gauss Earths magnetic field ~ 0.5 gauss

36. In normal MRI machines, the magnets are superconducting - their wires have zero resistance to the flow of electric current. The only way to achieve superconductivity is to make the magnets ultra-cold by submerging them in liquid helium: at about -453 °F, the magnet assembly is barely 5°F above absolute zero. Often, this liquid helium is surrounded by an insulating blanket of liquid nitrogen. Because superconducting wires continually conduct and recalculate the electric current without resistance, the magnetic field is present 24 hours a day; whether the MRI machine is being used or not.

37. Safe operation of an MRI machine requires managing three main categories of potential safety issues, all addressed by MRI safety training programs: 1. Medical/biological effects of high-strength magnets 2. Area/vicinity effects of high-strength magnets 3. Cryogenic (ultra-cold) gases.

38. BIOLOGICAL EFFECTS Include : Thermal injuries by heating of tissues Acoustic noise Peripheral nerve stimulation Even though there is no evidence indicating biological side effects from the magnetic fields of an MRI scan, and MRI machines don't utilize any ionizing radiation that can damage cells or DNA, pregnant patients and technicians are generally advised to avoid MRI during the early months of pregnancy, due to a lack of research on potential magnetic effects on the developing fetus.

39. THERMAL SAFETY OF SUBJECTS Radiofrequency energy deposited in the body during an MR examination will be converted into heat. This heat gain is countered by heat loss through sweat glands and cutaneous blood vessels ‘ Specific Absorption Rate’ (SAR) is defined as the average energy dissipated in the body per unit mass and time. Resonant circuitry can result in heating of the tips of wires or leads to temperature in excess of 90 deg C within a few seconds. To prevent this : All unnecessary electrically conductive materials should be removed before imaging. All attached leads should be covered with cold compress or ice pack. Avoid any large conductive loops, including limbs(do not cross arms or legs in the MR, this forms a loop as well). Care should be taken to place thermal insulation between the subject and electrically conductive material.

40. HEARING PROTECTION A characteristic of the switching gradient fields is the production of acoustic noise. When the alternating low-frequency currents flow through the gradient coils, which are immersed in the high static magnetic field , forces are exerted on the gradient coils that move like a loudspeaker coil and generate sound waves. The level of this acoustic noise at the location of the subject or volunteer can reach an unacceptable and even dangerous level. All personnel (MRI Technician, research group member, volunteer subject, family member, etc.) are required to wear hearing protection in the magnet room while the scanning procedure is being performed.

41. AREA EFFECTS The main potential danger from MRI machines comes from the interaction of the strong magnetic field with metallic objects or particles. Metallic objects in the vicinity of an MRI room can be attracted by the "fringe" magnetic field-causing them to be sucked into the MRI machine at high speed, posing a severe danger to patients. Also,any metal inside the patient (such as medical devices like pacemakers or dental implants) can cause severe injuries.

42. All non-MR personnel & study subjects entering the MRI scanner room must be screened. ACR recommends that non-emergent patients should be screened by two separate individuals. Consider using plain-film radiographic study to confirm the absence of metal fragments in critical parts of the body. Zones : Zone 1 : Reception area Zone 2 : Screening interview area Zone 3 : Control area, access restricted with key locks, passkey systems etc. Zone 4: MR scanner room N on-MR personnel should not have independent access to Zone 3 or 4.

43. CRYOGENIC GASES In the event of a rapid boil-off of the liquid nitrogen or liquid helium surrounding the magnet (a "quench"), a failure of the emergency venting system can cause a life-threatening oxygen shortage in the MRI room.

44. ADDITIONAL TRAINING ISSUES Operators may also be trained in responding to medical emergencies during an MRI scan; fire and evacuation procedures; and hearing protection and communication during the often-noisy scanning process.

45. MAGNET ROOM ACCEPTIBILITY LABELS MR SAFE : an item which poses no known hazards in all MR environments MR UNSAFE : an item which is known to pose hazards in all MR environments. MR CONDITIONAL : an item which has been demonstrated to pose no known hazards in a specified MR environment with specified conditions of use. Field conditions that define the specified MR environment include field strength, spatial gradient, dB/dt (time rate of change of the magnetic field), radio frequency (RF) fields, and specific absorption rate (SAR). Additional conditions, including specific configurations of the item, may be required.

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