Introduction to Diagnostic Imaging Flashcards
how many radiographic opacities are there?
five
are radiographs sensitive for bone loss?
no
what are mach lines?
when it looks like there is a fracture when there is not
what physical properties are responsible for x-ray attenuation?
atomic number
physical density
thickness
how do we triangulate to deal with squishing 3D into 2D?
two images that are perpendicular
what are iodine and barium usually used to evaluate?
lumens and cavities
how do we describe filling defects?
intraluminal
mural
extramural
where is barium used and when should it not be used?
gastrointestinal tract almost always
do not use in cases of suspected gastrointestinal perforation
where can iodine be given?
almost anywhere
why would you give iodine intravenously for contrast media?
angiogram
intravenous urogram
portogram
what are the positives and negatives of contrast procedures?
improve contrast
help assess function
do not eliminate superimposition
what are the methods of tomographic alternate imaging?
computed tomography
magnetic resonance imaging
ultrasonography
(nuclear medicine)
what are the advantages of multislice computed tomography?
tomographic: no superimposition
better tissue contrast
can do reconstructions
can cover large areas
relatively fast
can do contract procedures
can give IV contrast
CT guided biopsy
can use for radiation therapy planning
great for bones, lung
can computed tomography tell soft tissues apart?
yes
why is it necessary that you can manipulate the CT display to best show the tissue of interest?
human eye can only distinguish a limited number of shades of grey
what do you need in order to get enhancement using IV iodinated contrast?
tissue of interest must have vascular supply
in neural tissue, must have loss of blood-brain barrier
what are the uses of using CT for IV iodinated contrast?
evaluate vessels
assess vascularity of lesion
assess viability of tissue
asses blood-brain barrier
what are the disadvantages of computer tomography?
expensive $1500
lower availability than radiographs
requires anesthesia
use of x-rays still limits tissue contrast resolution
radiation dose higher than radiographs
imaging does not occur in real time
dense bone and metal give artifacts
what are the advantages of magnetic resonance imaging?
tomographic
multiplanar (can image in any plane)
excellent soft tissue contrast
no ionizing radiation
can cover large areas
special sequences (allows better characterization of tissues)
can do angiography without a contrast medium
what is T1W SE magnetic resonance sequence characterized by?
fluid dark
fat bright
what is T2W SE magnetic resonance sequence characterized by?
fluid/fluidy tissues bright
how do lesions often appear on T2-W sequences?
hyperintense or bright
what is signal void/black on all sequences of MRI?
no H+
what does the relative signal strength mean on all sequences?
intensity
hypointense: dark
what do you need for MRI contrast with IV gadolinium?
vascular supply
blood-brain barrier breakdown in CNS
what does IV gadolinium do?
paramagnetic agent
shortens T1 relaxation at low concentrations
what are the disadvantages of MRI?
expensive
lower availability
requires anesthesia
requires radiologist at time of scan
scans take more time
prone to artifact
needs hydrogen protons
magnet is always on
why is MRI not good for lungs?
long scan times lead to motion artifact
too few H+ in aerated lung to generate an image
what are the advantages of ultrasonography?
tomographic
multiplanar
relatively cheap
fairly quick
available
no anesthesia required
good soft tissue contrast
real time imaging
allows guided biopsy
no ionizing radiation
can evaluate vessels
useful artifacts
good for abdominal organs, especially GI
what does hyperechoic mean?
bright
what does isoechoic mean?
equally echogenic
what is the doppler effect in ultrasound?
moving reflectors (red blood cells) generate echoes with a different frequency from the incident beam (doppler shift)
what can the computer calculate using the doppler shift?
direction of flow
velocity of flow
presence or absence of turbulence
what is important about ultrasound artifacts?
sometimes useful
can allow ultrasonographer to make an educated guess about the makeup of the structure
strong or black shadows deep to an object usually mean mineral
dirty or grey shadows often means gass
“fair enhancement” usually means the structure is fluid filled
what are some disadvantages of ultrasonography?
cannot image through gas, intact bone or metal
cannot cover large sections of the patient at once
does not give a global view
cannot do reconstructions
highly user dependent
hard copy difficult for others to understand
can you penetrate aerated lung using ultrasonography?
no
when can you image diseased lung?
only if no aerated lung is between the chest walls and the area of interest
what is nuclear medicine?
radioactive isotope given to the patient
detect emissions from patient to generate image
what are the advantages of nuclear medicine?
relatively inexpensive
gives information on function
global view- can cover whole patient
high sensitivity
what are the disadvantages of nuclear medicine?
radiation dose to patient
patient radioactive following the study
does not give good morphologic information
low specificity
what is the radiation dose in nuclear medicine compared to radiographs?
bone scane 31x 3-view chest radiographs dose
why do we use MRI over radiographs?
better for neural tissue/soft tissues
why do we use CT over radiographs?
better for bone/thorax
why do we use ultrasonography over radiographs?
better for gastrointestinal/abdominal regions
why do we use nuclear medicine over radiographs?
better for function
how does an MRI make an image?
radiofrequency wave absorption and electromagnetic induction
what are the positives of radiography?
relatively cheap
available
gives global view
can do most without anesthesia (not skull or spine)
most people can interpret
what are the disadvantages of radiography?
3D squashed into 2D
limited opacities: only 5, cannot see inside soft tissue organs, insensitive for bone loss
patient receives radiation
why would you give iodine intrathecally?
myelogram
why would you give iodine into the urinary tract?
cystogram
urethrogram
why would you give iodine into joints?
arthrogram
why would you give iodine into the gastrointestinal tract?
if perforation is suspected
why would you give iodine into wounds and fistulas?
to find the extent
what reactions does barium cause outside of the gastrointestinal tract?
granulomatous
what makes up multislice computed tomography?
rotating X-ray tube and electronic detectors
computer represents each slice of a patient as a grid of small units of volume (voxels) and calculates the amount of x-ray attenuation by each voxel
how is a magnetic resonance imaging image generated?
put patient in strong magnetic field
use radiofrequency pulse to cause H protons to precess
this generates a current in a receiving coil
computer forms an image
what is dark in T2*W gradient echo in MRI?
hemorrhage and mineral
what is the FLAIR MRI sequence like?
pure fluid dark, fluidy tissue bright
which sequences do lesions appear hyperintense or bright on?
T2-W
except those with mineralization, bone, hemorrhage, fat, melanin
what color does FAT SAT make fat?
dark
like T1W but fat not bright
on what sequences does IV gadolinium appear bright?
T1-W spin echo and FAT SAT
are the pituitary gland and meninges inside or outside of the blood brain barrier?
outside
what are hydrogen protons bad for?
cortical bone and lung
what do dirty or grey shadows on ultrasound often mean?
gas
what do strong or black shadows on ultrasound often mean?
mineral
what does far enhancement usually mean on ultrasound?
structure is fluid filled
