Imaging Flashcards
What is ionizing radiation?
Ionizing radiation is radiation with enough energy so that during an interaction with an atom, it can remove tightly bound electrons from the orbit of an atom, causing the atom to become charged or “ionized”
What is non-ionizing radiation?
Radiation at the low end of the electromagnetic spectrum DOES NOT cause disruption of atoms when passing through substances and is therefore “nonionizing”.
What are 3 sources of radiation?
- Background radiation is present on earth at all times
- Major sources are radioactive minerals in the earth and cosmic radiation
- Man-made sources of radiation (medical imaging)
There is no such thing as a dose of ionizing radiation so low that it will not have some effect on our body, such as damaging cells.
True/False
True
Combined exposures add up throughout our lifetime and increase our risk of […] over time
cancer
What are the deterministic effects of radiation?
Deterministic effects have a threshold below which the effect does not occur. However, once the threshold has been exceeded, the severity of an effect increases with dose (i.e. cataracts, sterility, hair loss)
What are the stochastic effects of radiation?
Stochastic effects do not involve a threshold and risk increases in a linear-quadratic fashion with dose. (Although the risk increases with dose, the severity of the effects do not; the patient will either develop cancer or they will not).
X-rays represent a form of […]. They are produced by an […], using the high voltage to accelerate the […] produced by the […]. The produced […] interact with the […], thus producing x-rays
ionizing radiation
x-ray tube
electrons
cathode
electrons
anode
Tissue that attenuates (absorbs) x rays appears […]
Calcium in bone absorbs x rays, and appears […]
Air has low absorption of x rays and appears […]
white
white
black
Oral contrast
Used to ID pathology in the GI system
IV contrast
Used to ID pathology in the venous system and tissues that are vascular. Not to be used in patients with nephropathy, diabetes, decreased GFR, CHF, elderly
How are MRI Images generated?
patient put in superconducting magnet (1.5 T) which MRI machine creates a magnetic field around patient. Radiofrequency pulses given and the change in magnetization (largely depends on the presence of H20 molecules) is received as signal. Signals are analyzed by computer to generate images. This is a form of NON IONIZING RADIATION. Can use contrast (Gadolinium, intravenous) for blood vessels and soft tissues.
What are the pros and cons of MRI?
Pros:
- Good for soft tissues
- Excellent detail – shows edema
Cons:
- Takes longer to perform so more sensitive to motion, also not good for patients with claustrophopia
- Expensive
- Gadolinium contrast can be toxic to kidneys (use sparingly in patients with impaired renal function)
- Effect on first trimester pregnancy unknown
What can you not allow in an MRI or in the room with an MRI?
Metal
T1 MRI the fluid is […]
T2 MRI the fluid is […]
Dark
Bright
How is ultrasound imaging generated?
Ultrasound transducer sends high frequency sound wave (above audible range) into patient. Sound waves are reflected back and received by the transducer as an echo. The intensity of the returning echo determines the brightness on the image. Form of NON IONIZING RADIATION.
On an ultrasound, what do the following colors mean?
WHITE
GRAY
BLACK
WHITE: most of the sound waves are reflected back i.e. bone, calcium, gas
GREY: moderate reflection due to tissue interfaces ex: liver, spleen, kidney, uterus
BLACK: sound wave completely passes through and no echo returns i.e. cyst, bladder, gallbladder, blood vessels
What patients are not good candidates for ultrasound?
Obese patients
What are the benefits of ultrasound?
- Non ionizing radiation- great in pediatrics and pregnancy
- Relatively portable equipment
- Fast, non invasive, non painful, inexpensive
2 kinds of ionizing radiation?
2 kinds of non-ionizing radiation?
Xray and CT
MRI and Ultrasound
Bones increase in length by […] growth of epiphyseal plate (area of cartilage)
Interstitial
Bones increase in width by […] growth (osteoblasts lay down matrix in layers parallel to the outer surface)
Appositional
