Chemistry Physics Chapter 13 Radiation Imaging PDF 2023

Radiation/Imaging Chapter 13 Dr. Joseph Curione Objectives Types of Radiation Radiation Physics – – – – Decay Halflife Scatter Ionizing / Non-ionizing Radiation Biology – Somatic / Genetic Radiation Exposure – Measurements – ALARA Medical Uses – Diagnostic – Therapeutic Energy Transmission Energy ca...

Radiation/Imaging Chapter 13 Dr. Joseph Curione Objectives Types of Radiation Radiation Physics – – – – Decay Halflife Scatter Ionizing / Non-ionizing Radiation Biology – Somatic / Genetic Radiation Exposure – Measurements – ALARA Medical Uses – Diagnostic – Therapeutic Energy Transmission Energy can be transferred from one object to another in three ways. – Conduction Direct transfer of energy through physical contact – Convection Indirect transfer of energy through a medium (ex. Heated air) – Radiation Transfer/Emission of energy as electromagnetic waves or moving subatomic particles, especially high-energy particles that cause ionization. Why is it important? Occupational Exposure: C-arm, fluoroscopy used in conventional surgery & interventional procedures Types of Radiation Electromagnetic (EM) - photons – Gamma rays – X-rays – UV Particulate – Alpha (He2+ nucleus) – Beta (electron or positron) Electromagnetic Radiation (EM) Composed of photons Varying amounts of energy depending on wavelength (λ) & frequency (ƒ) Radioactivity Isotopes – two or more forms of the same element with an equal numbers of protons but different numbers of neutrons in their nuclei differ in relative atomic mass but not in chemical properties Unstable, emit subatomic particles to decay down to a stable state – Alpha decay – Beta decay Alpha Radiation Ex. of alpha decay – atom of Uranium 238 – Emits an alpha particle (Helium nucleus) Atomic mass (A) Atomic number (Z) Alpha Radiation in a Cloud Chamber Beta Radiation β− decay (electron emission) – neutron is converted into a proton, an electron, and an antineutrino n → p + e- + oῡe β+ decay (positron emission) – proton is converted into a neutron, a positron, and a neutrino p → n + e+ + υe Electron Capture Decay (“K-capture”) When an inner shell e- is drawn into the nucleus and combines with a proton, forming a neutron and a neutrino. The neutrino is ejected from the atom's nucleus. If the new nucleus is left in an excited state, gamma rays (γ) will also be emitted. p+ + e- → n + υe + γ Half-Life (t1/2) The time it takes for the radioactivity of a specified isotope to decay to half its original value. Example: If we start with N0 atoms, after one half-life ½N0 remain. After two half-lives, ¼ N0 are left. After three half-lives 1/8 N0 are left and so forth. After seven half-lives, only (1/2)7 N0 remain. t1/2 Common Isotopes used in Nuclear Medicine Scatter Radiation Occurs as a result of attenuation of the incident beam to the patient’s body. Three types: Coherent, Compton, Photoelectric Coherent scatter a.k.a. “Thompson scatter” – Occurs when an incident photon collides with an atom. – The atom momentarily absorbs the energy and moves into an excited states. – The atom then releases the same energy as another photon traveling in a different direction as scatter rad. Compton scatter Occurs when incident photon collides with outer orbital e-. The e- is ejected from its orbit. The photon is deflected from its original path and continues with decreased energy in a new direction as a scatter radiation. Photoelectric scatter Occurs when an incident photon collides with an inner shell orbital e-. The e- is ejected. When an outer orbital e- moves to the inner orbit to fill the vacated space, the difference in binding energy between the 2 electron shells is emitted in the form of a new scatter photon. Ionizing vs. Non-ionizing Ionizing radiation carries enough energy to free electrons from atoms or molecules, thereby ionizing them. Ionization of cell structures, organelles and DNA cause severe cellular damage. Penetrating energies are measured in electron volts (eV) - a unit of energy ~ equal to 1.6×10^-19 joules Penetrating Abilities Alpha ~ 5MeV (@ 5% c) Beta particle ~ 1.6 MeV (@ > c) X-rays ~ 100eV – 100KeV (@ c ) Gamma rays ~ 300KeV – 10Mev (@ c ) Non-ionizing Below UV in lower end of EM spectrum. No damage. visible light, infrared, microwaves, and radio waves are all considered non-ionizing radiation. The boundary between ionizing and non-ionizing EM radiation that occurs in the UV range is not sharply defined, since different molecules and atoms ionize at different energies. Boundary of ionizing photon energy is between 10eV and 33 eV in the UV range. Non-ionizing Ionizing Cherenkov Radiation Radiation Biology 2 types of cell interactions from ionizing radiation: – Direct hit – Indirect hit Direct hit: breakage of a DNA molecule as a result of being struck directly by EM or Particulate radiation. Indirect hit: H2O breakage into H+ + OH- free radicals, which then chemically damage DNA. Cells then die or mutate. Biologic Effects Somatic effects – Short-term – Long-term (“latent”) Genetic effects Short-term Effects Further categorized according to body system affected: – Hematologic (dysplastic anemia) – GI (“radiation sickness” damaged mucosal lining w/ infx) – CNS (seizures, coma, death) Observed within 3 months of exposure Involve very high doses (unlike medical imaging) Long-term Effects Observed at 5 – 30 years, avg. at 10 – 15 years Latent effects of long term low dose ionizing radiation – Cataracts (with extensive fluoroscopy) – Cancer (skin, thyroid, breast & leukemia) – Shortened Life span Genetic effects Occurs with radiation exposure to reproductive organs (testes & ovaries) Involve mutations to the genes of the reproductive cells Mutations carried over to progeny Occupational Exposure Two systems used to measure radiation dose: Conventional Units Roentgen Rad Rem SI Units Coulombs/kg (C/kg) Gray (Gy) Sievert (Sv) Measurements Roentgen (R) is a unit of Exposure Determined by photon exposure under standard temp. & pressure that produces a total positive or negative ion charge of 2.58 x 10^-4 coulombs per kilogram of dry air. (not used to calc. tissue dose) Corresponding SI unit is C/kg 1 R = 2.58 x 10^-4 C/kg Measurements Rad (rad) is a unit of Absorbed Dose (D) Absorbed Dose = the amt. of energy per unit mass absorbed by tissue. Rad stands for “Radiation absorbed dose” Equal to 100 erg (unit of msr. = 10^-7 joules) 1 roentgen ~ 1Rad of absorbed dose in muscle tissue Corresponding SI unit is the Gray (Gy) 1 Gy = 100 rad 1 rad = 0.01 Gy Measurements Rem (rem) is a unit of Equivalent Dose (EqD) Biologic effects of radiation vary according to the type of radiation involved. Rem stands for “radiation equivalent man” Corresponding SI unit is the Sievert (Sv) To calc. occupational dose, a radiation weighting factor (WR) is assigned to each type of radiation. WR values are based on variation of biologic damaged produced by each type of radiation. Radiation Weighting Factors (WR) Equivalent dose (EqD) is calculated by multiplying absorbed dose by WR D x WR = EqD Ex. Worker receives 10rads alpha particles and 5rads x-rays. EqD = 205 rem. (10rads x 20 = 200) + (5rads x 1 = 5) Measurements Corresponding SI unit of a rem is the Sievert (Sv) 1 Sv = 100 rem 1 rem = 0.01 Sv How many Sv did the worker in the previous problem receive? Sv = rem * 0.01 Sv = (205)(0.01) Sv = 2.05 Measurements Doses from diagnostic radiology are small ∴ 1/1000 of the common units are typically used Ex. mrem or mSv Note: Doses are cumulative in occupational exposure, ∴ devices (dosimeters) are worn to monitor doses received. Dosimeters “film badges” Common types include thermoluminescent-type (TLD) and optically stimulated luminescence-type (OSL) ALARA In addition to monitoring doses, radiation safety practices are employed. ALARA -acronym: As Low As Reasonably Achievable 3 Factors of ALARA: – Time – Distance – Shielding Shielding Equipment Lead aprons Thyroid shields Pb gloves Leaded glasses Medical Imaging Medical uses of radiation: diagnostic & therapeutic Results in radiation dose to the patient “Benefit outweighs the risk” Ionizing Tests: x-rays, CT, nuclear scans Non-ionizing Tests: US, MRI X-rays CXR most common ordered imaging study (second to dental films) CT Computed Tomography (A: conventional B: spiral) Nuclear Medicine Scans PET – Positron Emission Tomography Pt. injected with beta emitter FDG (fluorodeoxyglucose) Fluorine-18 tagged to glucose Sensors detect emissions from pt. PET/CT Combines both tests in one machine, provides highly detail information of anatomy and cell physiology in one test. SPECT scan Single-photon emission computed tomography Unlike PET/CT, Spect uses gamma emitting radioisotope (ex. Galium111) 3D images for neurologic and cardiac studies MRI Non-ionizing. Magnetic field aligns H2O molecules RF disturbs H2O, molecules reorient, sensors record as image T1: anatomy T2: pathology Echo TEE vs. TTE TEE Advantages: – Heart rests on esophagus, only a few mm of tissue vs. chest wall (skin, fat, muscle, bone, lung tissues) – Better visualization of structures Disadvantages: – Pt. must be NPO – Takes longer than TTE – Requires sedation or Gen. anesthesia Ultrasound Non-ionizing. Uses sound waves to image. Transducer contains piezoelectric crystal that vibrates to generate high freq. sound waves. Waves reflect off internal structures. Receiver senses reflected signal echo. Used in regional anesthesia. Ultrasound For optimal visualization of structures, transducer must be manipulated. A. sliding B. tilting C,D. rocking E,F. rotating G. compression Short & Long Axis planes Ultrasound Guided Nerve Block Video Echogenic Needles Common needles used for regional blocks Smooth needles (A.) reflect sound energy away from transducer.