Published on February 20, 2014
HISTORY • X-rays accidentally discovered by Wilhelm Conrad Roentgen in 1895 • Why the name? • But he knew they could penetrate the body
HISTORY • Roentgen’s discovery was a bomb shell • News papers and magazines provided interesting stories. • Advertisers associated their products with the term “x-ray” • Headache medicines, stove polish, golf balls, razors….
AD FROM 1896
PRODUCTION OF X-RAYS • X-rays are produced when rapidly moving electrons that have been accelerated through a potential difference of order 1 kV to 1 MV strikes a metal target. Evacuated glass tube Target Filament
NATURAL BACKGROUND RADIATION • • • • • Average 2.4msv per year Cosmic radiation from sun Terrestrial: soil, buildings, granite Body activity: potassium Radon gas is naturally occuring decay product of uranium and thorium • Skiing at high altitudes and airline flights • Return flight from Sydney to LA: dose 0.16msv
The Electromagnetic Spectrum Waveform of Radiation NONIONIZING IONIZING Radio Infrared Microwaves Ultraviolet Visible light Gamma rays X-rays 7
Difference between ionizing and nonionizing radiation • Energy levels: – Ionizing radiation has enough energy to break apart (ionize) material with which it comes in contact (knock off e-) – Non ionizing radiation does not 8
Types of Ionizing Radiation • Important in healthcare: • Diagnosing - X-Rays, PET Scans, Nuclear Medicine • Therapy - Radiation Treatment, Nuclear Medicine 9
Biological Effects of Radiation • Somatic – Affects cells originally exposed (cancer) – Affects blood, tissues, organs, possibly entire body – Effects range from slight skin reddening to death (acute radiation poisoning) • Genetic – Affects cells of future generations – Reproductive cells most sensitive 10
EFFECTS • Effects of low level radiation in diagnostic imaging is presumptive and continue to be debated • No large clinical trials • Data collected from the atomic bomb survivors
RISKS • Based on linear/no lower threshold model and extrapolated • Indicates that no dose, however small, is entirely without risk • Average lifetime risk of induction of fatal cancer from exposure to 5msv is 1 in 4000 and to 20msv is 1 in 1000 • Risk is considerably great in children and young adults • Hence, all imaging procedures should be justified
TISSUE WEIGHTING FACTOR Gonads Red Bone Marrow Colon Lung Stomach Bladder Breast Liver Oesophagus Thyroid Skin Bone Surface 0.20 0.12 0.12 0.12 0.12 0.05 0.05 0.05 0.05 0.05 0.01 0.01
PLAIN RADIOGRAPHY INVESTIGATION DOSE(msv) EQUIVALENT NATURAL BACKGROUND RADIATION Extremities 0.01 1.5 days Chest 0.02 3 days Skull 0.07 11 days C spine 0.1 15 days T spine 0.7 4 months L spine 1.3 7 months Hip 0.3 7 weeks Pelvis 0.7 4 months Abdomen 1.0 6 months
CT and NM Head 2.3 1 year C spine 1.5 8 months T spine 6.0 2.5 years Chest 8.0 3.6 years L spine 3.3 1.4 years Abdomen 10.0 4.5 years Pelvis 10.0 4.5 years Bone scan 4.0 1.6 years V/Q 1.3 7 months
RISKS • Risk is a defered risk that may occur 5 to 15 years after exposure • Use of medical imaging is rising • Population exposure to ionizing radiation is increasing and majority of them is from CT scans • Risk is cumulative
• Radium was discovered in Marie Curie and Pierre Curie in 1898 • Highly radioactive and its decay product radon gas is also radioactive • Marie Curie died secondary to aplastic anaemia, believed to be induced by the long term exposure to radiation • Carried test tubes with radioactive isotopes in her pocket and stored them in her desk drawer
APPROPRIATE REQUESTING • Cannot ignore the increasing use of ionizing radiation • All requests should be subject to Justification and Optimisation • Radiologist has the knowledge and experience to determine the radiation risks and consider alternative investigations • Referring doctor who has seen the patient can best assess the potential benefits • Justification should be a joint responsibility • Optimisation is to achieve diagnostic quality images by using low radiation dose
RESPONSIBILITIES OF REFERRING DOCTOR • Avoid unnecessary duplication of tests • Ensure that test could potentially change management • Provide adequate clinical details • Be aware that many imaging tests have risks • Consult with imaging colleagues if appropriate • Consider the use of US or MRI (non ionizing) when appropriate
PREGNANCY AND LACTATION • Raising the awareness of patients for the need to inform the possibility of pregnancy • 28 day rule. In a young patient who has missed a period, pregnancy should be excluded • If appropriate employ tests that do not use ionizing radiation • Foetus more sensitive during 3 to 8 weeks and 1st trimester
EFFECTS ON FOETUS • • • • Miscarriage and foetal death in the first few weeks Malformations within first 8 weeks of implantation CNS abnormalities during weeks 8 to 25 Carcinogenesis • IV contrast can be used in exceptional circumstances • Contrast induced foetal hypothyroidism is not validated • Current guidelines recommend neonatal thyroid function testing
PE IN PREGNANCY • Risks of missing PE in pregnancy far outweighs the risks of exposing the foetus to radiation • CXR is useful to exclude conditions that mimic PE • D-Dimer is less useful in pregnancy, however low probability and negative D-Dimer excludes PE • Doppler of both lower limbs should be considered first and treatment commenced if positive
PE IN PREGNANCY • CTPA and V/Q scan have equal diagnostic quality • CTPA recommended in first 2 trimesters • Phantom studies have shown less foetal dose with CTPA in first two trimesters • MRI is a promising new option but availability and expertise are the main limitations
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