Lecture_2- Essential Concepts -2.pdf

RMI 213 Principles of medical imaging Lecture 2 Essential Concepts - 2 Slide 1 fchs.ac.ae Learning Outcomes At the conclusion of this lecture, associated tutorial and practical session (if relevant), you will be able to: 1. List the basic concept...

RMI 213 Principles of medical imaging Lecture 2 Essential Concepts - 2 Slide 1 fchs.ac.ae Learning Outcomes At the conclusion of this lecture, associated tutorial and practical session (if relevant), you will be able to: 1. List the basic concepts of radiation protection 2. Explain why different strategies to achieve protection are appropriate in different situations 3. List and define units of radiation and radioactivity Slide 2 fchs.ac.ae Basic Radiation Protection Protection of patients, and of the radiographer, is paramount: Practice the ALARA principle Keeps radiation exposures As Low As Reasonably Achievable Use Filtration Absorbs low energy x-rays that contribute to dose but not to image quality Use collimation Protects adjacent tissue from irradiation Reduces scattered radiation Slide 3 fchs.ac.ae Basic Radiation Protection Use intensifying screens Effectively amplifies the detected radiation Use protective apparel Radiographer wears apron and gloves if necessary Use gonadal shielding Protect groin area of patients of child-bearing age from radiation, if not part of the required exposure region Use protective barriers Stand behind shield to reduce exposure Control from behind lead-glass viewing windows Slide 4 fchs.ac.ae Basic Radiation Protection Read, and be sure to understand, the information in Box 1-2, Bushong page 14; “The Ten Commandments of Radiation Protection” You have a duty of care towards: The patient Any other person assisting Your own health and safety If in doubt, ASK. Slide 5 fchs.ac.ae Slide 6 fchs.ac.ae Units of Measurement Length –1 meter Mass –1 kg Time –1 s Charge, Q , with units of coulomb, C Energy, E, with units of joule, J Slide 7 fchs.ac.ae Units of Measurement in Radiologic Physics Radiographic Special Units International System Quantities (SI) Units Charge Roentgen (R) Exposure, X per unit mass, C/kg coulomb/kg of air (C/kg of air) Absorbed energy Dose Dose, D per unit mass, J/kg Gray, Gy (or Gyt) (t for tissue) Effective dose, E Absorbed energy Sievert, Sv Equivalent dose, H per unit mass, J/kg Sievert, Sv Disintegration Radioactivity, A Becquerel, Bq per second, s-1 Slide 8 fchs.ac.ae Measurement in Radiologic Physics Some dose quantities relate to measurements in air Signified by subscript ‘a’, as in Gya Some dose quantities relate to measurements in tissue Signified by subscript ‘t’, as in Gyt Slide 9 fchs.ac.ae Terminology for Radiologic Science Radiologic science is all about energy Energy can be related to temperature – see opposite Electromagnetic radiation energy can also be related to frequency and wavelength through the expression E = hf = hc/ (we will review this later) Bushong, Figure 1-18, page 21 Slide 10 fchs.ac.ae Terminology for Radiologic Science We have mentioned special units for exposure and dose: Air kerma: for expressing exposure (x-ray tube output) Kerma = kinetic energy released in matter It is measured by the ionization of air (C/kg = Gya) Starting point for determining dose in patients Instrument placed between the x-ray tube and the patient For a given x-ray unit the exposure, X, is normally established for set values of kVp (voltage) and mAs (charge) Old unit of X was the röntgen, R 100 R = 1 C/kg = 1 Gya (subscript ‘a’ means in air) Slide 11 fchs.ac.ae Terminology for Radiologic Science Radioactivity is not associated with x-ray tubes Radioactivity is used for quantifying radioactive output from isotopes (radioactive substances) Modern unit is the becquerel, Bq The old unit was the curie, Ci (the only SI unit ever named after a woman) 1 Bq = 1 nuclear disintegration per second 1 Ci = 3.7  1010 nuclear disintegrations per second Slide 12 fchs.ac.ae Terminology for Radiologic Science Dose also has old units you may come across (particularly in texts from the USA) Old unit of effective dose was rem, 1 rem = 10 mSv Old unit of absorbed dose was rad, 1 rad = 10 mGyt (subscript ‘t’ for tissue) Bushong, Figure 1-20, page 23 Slide 13 fchs.ac.ae Summary Check that you can satisfy the learning outcomes for this lecture Go over calculations/exercises undertaken during the lecture Make sure you can define the following terms: ALARA charge (and its unit) Exposure (and its unit) dose (in its various forms, and the units) Check your understanding of the words shown in the table of units of measurement Check information in Box 1-2, Bushong page 12; “The Ten Commandments of Radiation Protection” Slide 14 fchs.ac.ae