Med Imaging Flashcards
Specificity
the ability of a test to obtain a true negative
–> if it shows up then its definitely there, & you can rule it IN; but can get high false negative tests
SPIN
i.e. X-rays & home pregnancy tests
Sensitivity
the ability of a test to obtain a true positive
–> the test is sensitive so if its there it will definitely show up so if its not then you can rule it OUT; but can get high false positive tests
i.e. MRI & HIV tests
Attenuation
reduced strength &/or density of the x-ray beam as it passes through the subject (forms the image)
Objects that have high attenuation make up the “white” area; such as bone, heavy metals (radioopaque)
Objects that have low attenuation make up the “black” area; the beam passes all the way through; such as air, water, fat (radiolucent)
Permeability (radiology)
how much of the x-ray beam passes through a substance to reach the film plate;
AKA the “exposed film”
Radiodensity (radiology)
x-ray absorption capacity, based on substance composition, density & thickness
- -> amount of radiodensity linear w/ amount of attenuation of substance
- -> INVERSE relationship between radiodensity of an object & radiodensity on a film
- aka high object radiodensity = decreased radiodensity on the film = object appears white (image)
ABC’s of Radiology
A = alignment B = bone density C = cartilage S = soft tissue
MRI’s
-how it works, T1 vs. T2
external magnet & pulses of radiofrequency generate electromagnetic field
- -> atomic nuclei align to the field (resonance)
- -> field is removed and nuclei realign to resting state & signal is captured
T1 = time it takes for the protons to realign to resting state
- ideal for viewing bone, fat & hemorrhage (1ong bone is bright)
T2 = time that the protons stay in resonance before returning to resting state
-ideal for viewing fluid & fluid filled structures; soft tissues & acute trauma (H20 is Bright)
Pittsburg Decision Rule for Knee Trauma
History of blunt trauma or fall AND
- 50 and/or
- cannot WB more than 4 steps
Ottowa Knee Rule
- Age >55
- Tenderness at fibular head
- Isolated tenderness of patella
- Inability to flex knee to 90
- Inability to walk 4 weight bearing steps
Ottowa Ankle Rule
pain in the malleolar area AND
- Tenderness at posterior aspect or tip of lateral or medial malleolus OR
- inability to WB immediately in ER
Ottowa Foot Rule
Pain in the midfoot area AND
- Tenderness at base of 5th MT or navicular bone OR
- Inability to WB immediately in ER
Guidelines for Low Back Pain
- Adults 50 w/ suggestive findings of systemic disease = x-ray and lab test (to rule out)
- Advanced imaging suggested for those w/ systemic disease and considering surgery
Radiology
- ADV/DISADV
- specific or sensitive?
2D picture of a 3D object; image based on high attenuation and radiodensity
ADV: time & cost efficient, non-invasive, low risk & good for screening
DISADV: not super sensitive (may look normal when pathology exists; high false negatives), radiation exposure
Specific for fractures
CT
- ADV/DISADV
- Specific or sensitive?
x-ray attenuation to produce a cross-sectional, 3D image
ADV: visualize complex anatomy, sensitive & specific for fractures, rapid assessment of brain/neurological injury
DISADV: radiation exposure, limited in precise histologic differences
Specific & sensitive for fractures
MRI
- ADV/DISADV
- Specific or sensitive
image captured using electromagnetic field and protons
ADV: sensitive for soft tissue structures, no radiation, little distortion b/c images obtained in 1 plane
DISADV: low specificity, expensive, & contraindicated if pt has metal implant or pacemaker
Sensitive to soft tissue
