CT sim/ Imaging Flashcards
cathode is the ____ part of the xray tube
negative
abided us ___ part of the xray tube
positive
what are the portions of the cathode
filament and focusing cup
what is filament made of
its a small coil of tungseten wire with a high melting point
focusing cup
the - charge of thr focusing cup can help direct e towsrds the anode in a or linear path
do e go from anode to cathode or cathode to anode
cathode to anode (- to +)
what are the prts of the anode
line focus principle, composition and target
the target in the anods is aka
focal spot
i am the part of the CT where photons start to fan out in a divergent path
the target of the anode
what is done to overcome extra heat production of a small focal spot
the line focus principle- the target is angled at 7-20 degrees to account for extra heat
anode, cathode, filament, focusing cup, target are components of what machine
CT sim
as FQ + wavelength _
-
as wavelength + FQ_
-
the principal interaction in xray production
bREMSTRAHLUNG
The ideal material for a target of an xray tube is what?
something with high atomic #
mA vs Kvp
mA is th tube current
Kvp is th e tube voltage
predominant interaction in the therapeutic range, is this good or bad?
predominant interaction is compton scattering, this is bad because scattering is not good
what is the only acceptable interaction to create images
photoelectric effect
an incident photon penetrates deep into the atom and ejects an inner shell electron. This process is known as…?
photoelectric effect
an xray photon interacts with an outer shell orbital electron. This process is known as….?
compton scattering
there is a change in photon direction but does not eject an electron. this is known as?
unmodified/ thompsons/ cohernt scattering
photoelectric effect is dependant on what
higher z material, the higher the z the more likely it is to be absorbed by photoelectric effect
the relationship between distance and density
ISL
What does density in imaging refer to
how light or dark an image is
the higher the mA the ____ the density
higher
optimal contrast depnds on whay?
Kvp
computed radiography uses ______ to convert xrays to digital images
photostimable plates
primary method of - scatter
colimating the beam
who would cause more scatter, small pts or larger patients
large patients
what area would cause more scatter: abdomen or pelvis?
pelvis as there is more bone in the pelvis (bone causes more scatter, high Z) abdomen has more soft tissue therefore less scatter
predominant interaction in imaging? kv imaging?
kv- photoelectric effect
mv-compton scatter
which has lower dose to pt? Kv or Mv?
Kv is 100 X less dose than Mv
T1 vs T2 on MRI
T1- longitudinal relaxation time
t2-Transverse relaxation time
MRI uses_____`
pulse sequences
FDG is a _____EMITTER
POSITON
What is used to create US waves
piezoelectrical crystal
how many detectors are /cm and per degree
1-8 detectors/ cm or 1-5 detecros / degree
what do solid state detectors do?
convert radiation to light
what is pitch
the distance that the couch travels through the xray rotation
a higher pitch can cause what?
+ artifacts
whats foltered back projection
an algoritihm used to reconstruct CT image aka convolution method
what image reconstruction is mostly used now
IR iterative reconstruction
what is the pros of IR over FBP
FBP can have significant artifacts and noise, IR corrects for this
CT +1000 is….
dense bone
CT # 0 is…..
water
CT # -1000 is….
air
what is the typical matrix size in CT scan?
512 x 512
voxel is determined by what 3 things?
slice thickness, matrix size and FOV
PIXEL VS VOXEL
picture element vs volume elemnt
n.b. the pixel is 2 d and vixel is 3d
what is isotropic display
this is when all planes of the voxel are = ( therefore equal width, length and depth)
if after imaging you would like to see improved contrast of the image what would you adjust?
window width
if i want to view the lung better what would I adjust?
the window width, in lung the WW # is typically 500
what is tthe effect of a wide WW
- contrast
what is the effect of a narrow WW
+conrast
if I want to - noise of the image what should i do to the mA? kVp?
+ kVP and - mA
to improve tube longevity what kind of mA should you use
LOW if pissible
a ring artifact is an indication of what
detector malfunction
a star artifact is an indication of what
metal in the field
what causes partial volume artifacts
when thick slices are taken
what can be used to - motion artifacts
using fast scanners
a multislice CT systen uses what? A: multiple detector beams b: multi slice beams c: multiple detctor rows d: multi-slice rows e: multiple corn rows
E LOL
C is correct answer
what is the pro of placing pt prone in pelvis tx
it - sm bowel in the field threfore - SE
What is diazorate melgulieum
this is an oral contrast agent that is aqueous
when is aqueous oral contrast used
for patients at risk of GI prforation (ex: UC, diverticulitis) where its dangerous for them to have barium sulfate
contraindications to IV contrast
pt >50
pt with diabetes
pts with impaired kidney fn or cardiovascular disease
or a reaction to contrast in the past
what needs to be done before IV contrast
bloodwork that looks at EGFR (estimated glomoular filtration rate) ad creatinie levels
what EGFR rate is PROBLEM, what happens in this case?
EGFR <60
in this instance the patient will have areduced amount of contrast or will not have contrast at all
IV contrast 2 types
inonic iodine and nonionic contrast
ionic iodine has ____ osmoality
high
what is osmoality
particles in solution / kg of water
what can high osmoality contrast cause
decreased blood pressure
what happens in dehydrated pts if they receive high osmoality contrast, what are these patients given?>
can cause pt to go into shock
these pts are given low osmoality contrast ex nonionic contrast instead
what steps do you take when pt has mild reaction to contrast media
- the injection continues
- reassure the pt
- monitor the pt to ensure rection does NOT progress
- ensure the reaction subsides
what steps do you take when pt has intermediate reaction to contrast media
stop the injection- pt requires careful observation to ensure a severe rection does not occur
what steps do you take when pt has severe reaction to contrast media
stop injection, prompt medical attention is required, pt is often hospitalized
when do most reactions occur from contrast media
70% occur within first 5 mins the rest occurs within half an hour
what subsites need to fast prior to SIM
H&N, lung, brain and PROS
when is contrast admin in H&N and lung
seconds before the scan via power injector
when is contrast admin for brain
10-30 mins before CT via IV push
when to admin contrast for liver
20-40 seconds before scan to visualise hepatic artery, 60-90s to view portal vein
when to admin contrast for pelvis
not all pros patients get contrast- if administered:
15 mins before CT IV injection
Barium can b given orally 30-60 mins before scan to visualize sm bowel
when to admin contrast for GI
Oral contrast is used:
baroum is taken orally 30-60 mins before scan
what sites get IV contrast
lung, H&N, brain, liver, sometimes PROS
contrast media needs _____ in order to -______
needs to have low atomic # to - artifacts
when the scanner is triggered to aquire images/ treat during a certain part of respiration, this is called _____
prospective axial scanning
with PET scanning _____ is used to create the image
A: KV XRAYS
B: 511 kev gamma rays that move in almost opposite directions
C: 6MV gamma rays
D: Magnetic pulses
B
mA is the ____ of the beamand controls ______.
kVp is the ______ of the beam and controls ______.
mA is the quantity of th beam and controls density
kVp is the quality of the beam and controls contrast
VMAT is best used for what type iof tumours ?
central, well defined tumours
Ex: central lung cancer or prostate
