Introduction to Medical Imaging - eLearning

Question 1

Ionizing radiation

Answer 1

dislodge electrons

x-ray, gamma ray, alpha particle, beta particle, positrons, neutrons

Question 2

Non-ionizing radiation

Answer 2

no electron ionization

radio, microwave, infrared, visible light, ultraviolet

Question 3

spatial resolution

Answer 3

sharpness, clarity

able to differentiate between two closely located objects

Question 4

contrast

Answer 4

ability to detect differences in light and dark

Question 5

relationship of contrast to resolution

Answer 5

as object contrast increases, spatial resolution required to distinguish a target decreases

Question 6

Radiography

Answer 6

x-ray to tissue, 2D, contrast related to tissue attenuation, four basic contrast values - bone, soft tissue (water), fat, and air

Question 7

strengths and weaknesses of radiography

Answer 7

S - large area, low x-ray exposure, low cost, widely available
W - low contrast, overlapping anatomic structures, exposure to ionizing radiation

Question 8

clinical indications of radiography

Answer 8

Chest - pain, SOB, trauma, cough, pneumonia, CHF, lung mass

Question 9

computed tomography

Answer 9

x-ray to tissue, multiple projections in plane attenuation measured, cross-sectional image constructed, eliminates superimposition, sensitivity to changes in tissue contrast at least 10x that of radiography

Question 10

High resolution CT

Answer 10

thin section and high res reconstruction algorithms
indications - diffuse infiltrative lung disease or dyspnea with normal CXR
special techniques - prone imaging for evaluation of peripheral basilar lung disease, expiratory imaging for evaluation of distal airways disease

Question 11

strengths and weaknesses of CT

Answer 11

S - cross-sectional images, 3D rendering, excellent contrast and spatial res, wide availability
W - moderate radiation exposure, concern for pediatric population, concern about induced cancers, moderate to high cost

Question 12

clinical indications of CT

Answer 12

Chest - trauma, lung mass, mediastinal mass, pulmonary embolism, aortic aneurysm, COPD/Emphysema, interstitial lung disease, coronary artery disease

Question 13

Magnetic resonance imaging

Answer 13

radio waves with magnetic nuclei (hydrogen/protons), image formed as energized nuclei “relax” into alignment with external magnetic field, 2D cross sectional image with NO superimposition, image contrast depends on tissue characteristics and acquisition protocol

Question 14

strengths and weaknesses of MRI

Answer 14

S - cross-section, high soft tissue contrast, potential for 3D rendering, no ionizing radiation
W - limited clinical applications, long exam times, claustrophobia, high cost, relatively limited availability, cannot do certain implants - pacemakers, cochlear, neural stimulators, heart valves, mechanical hazard

Question 15

clinical indications for MRI

Answer 15

Chest - Imaging of heart and great vessels - congenital heart disease, coronary artery disease, distinction of vascular structures from adjacent soft tissues (+/- IV contrast) - aortic aneurysm, evaluation of the mediastinum and hila, evaluation of the chest wall and diaphragm

Question 16

Ultrasound (sonography)

Answer 16

high frequency sound waves with tissues, based on strength of scattered and reflected acoustic energy, 2D cross-sectional image, real-time, 3D imaging possible, eliminates superimposition

Question 17

Ultrasound characteristics

Answer 17

range for human hearing 20-20,000 Hz
frequencies for medical imaging between 3 and 15 mHz
as frequency increases, resolution increases
as frequency increases, ability to penetrate tissue decreases

Question 18

strengths and weaknesses of ultrasound

Answer 18

S - cross-sectional images in real-time, high soft tissue contrast, potential for 3D rendering, NO ionizing radiation, cheap and widely available
W - highly operator dependent, limited clinical applications (cannot image certain things like aerated lung or bone)

Question 19

clinical indications of ultrasound

Answer 19

Thoracic imaging - echocardiography - congenital heart disease or acquired heart disease; pleural abnormalities - effusions, thoracentesis planning, masses

Question 20

Biologic effects of electromagnetic radiation

Answer 20

non-ionizing: thermal injury, cataract formation, carcinogenesis with ultraviolet
ionizing: thermal injury, somatic cell mutation that can be lethal or non-lethal (carcinogenesis), germ line mutations

Question 21

Risk of imaging

Answer 21

The small but finite risk of medical imaging must be less than the risk of not having the information provided by imaging
Keep all exposures “as low as reasonably achievable” (ALARA)