term test 2 imaging Flashcards
what does PET stand for
positron emission tomography
what are the standard measures for image quality in PET
- spatial resolution
- sensitivity / contrast
= noise
what are the units of FDG
- KBQ / mL
- SUVs
what is SUV ?
- standardized uptake value
- tracer in tissue (Bq/ml) / inj. dose (Bq) / weight (g)
what are the applications of PET in radiation oncology
- staging
- treatment planning / tumour targeting
- monitoring treatment response
how is PET-CT used in treatment planning / tumour targeting
- tumour delineation
- planning target volume
- research
what does RECIST stand for (structural)
response
evaluation
criteria
in
solid
tumours
what does EROTIC stand for (functional)
European Organization for Research and Treatment of Cancer
what does PERECIST stand for
Positron Emission Reponse Criteria In Solid Tumours
what is complete response
complete resolution of FDG uptake within tumour volume
what is Partial response
reduction of a minimum of 15-25% in tumour SUV
what is stable disease
increase in SUV less than 25% or a decrease of less than 15%
what is progressive disease
increase of SUV more than 25% or a decreawse of less than 15%
what is the definition of sonography
use of reflected sound waves to describe the position and shape of an object
what is the definition of ultrasonography
= sonography that uses sound waves that are above the frequency that is audible to humans
how are ultrasounds made
- transducer made of peizoelectrical crystal
- so is the scanhead where echos are recieved
what frequency waves can thinner and thicker crystals make
thinner: higher frequency waves (5-10MHz)
thicker: lower frequency waves ) 2-3.5 Mhz
what is the difference in resolution and penetration in thinner and thicker piezoelectric crystals
thinner: greater resolution but less penetration
thicker: lower resolution but better penetration
how are images produced in ultrasounds (brightness of dots and location of dots)
- brightness: proportional to the strengths of echos returning from there
- location: due to the transit time of the sound waves
what is the constant velocity for recon
1540m/s
how do structures show up in ultrasound images
due to differences in acoustic impedance between different tissues
what is acoustic impedance
the product of a tissues density and propagation velocity
what happens at boundaries between tissues with acoustic impedance
sound is reflected back
what determines return echo
- reflection (specular or diffuse)
- refraction (u/s assumes return echo is a straight line, scan perpendicular to surface)
- tranmission
- attenuation
what is echogenicity
- amount of energy reflected back from tissue interface
what are the three types of echogenicity
hyperechoic (greatest intensity, white)
hypoechoic (intermediate, grey)
anechoic (no reflection , black)
isoechoic (same intensity)
what structures are hyperechoic
- diaphragm, tendons, bones
what structures are hypoechoic
- most solid organs, thick fluids
what structures are anechoic
- fluids in cyst, urine, blood
what are the types of positive agents
barium
iodine
what are the types of negative agents
air
carbon dioxide
what is the difference between ionic and non ionic compounds
ionic compounds dissociates in water
non ionic - covalently bounded compound
what is the osmolality of blood
280 - 300 mOs/kg
fill in blanks
____ agents typically have higher osmolaity
high osmoality agents have higher risk of ______
ionic
adverse evetns
what are some examples of IV ionic contrast agents
- hypaque
- isopaque
- hexabrix
what are some examples of IV NON ionic contrast agents
ultravist, omnipaque, visipaque note: all except visi have higher osmo than blood
what contrasts are taken orally
barium iodine water
what contrasts are taken rectally
water, barium, iodine, air, CO2,
what contrasts are taken intravenous or intra arterial
iodine
what contrasts are taken intrathecally
iodine
which vein do we inject contrast into
cubital fossa, cephalic vein
what are the 4 general phases of AVID
- pre contrast
- bolus phase (arterial phase)
- non equilibrium phase (venous phase)
- equilibrium phase (delayed phase)
what does AVID stand for
arteriovenous iodine difference
what phases are compared
HU taken within aorta measurement taken within IVC
the bolus phase immediately follows the _________
it is characterized by attenuation differences of ________ or more HU between ____ and _____.
can see _____ filled. also
known as _____ phase
- IV bolus injection
- 30
- aorta and IVC
- arterial vessels
- arterial phase
how long after the injection does the non equilibrium venous phase begin ? how long does it last
1 minute for both
what is the HU difference in the non equilibrium / venous phase
10 - 30
which phase is good at looking at liver lesions
venous phase
when does the equilibrium delayed phase occur
- 2 minutes after bolus
what is the HU difference in the equilibrium / delayed phase
< 10 HU
which phase is the worst to look at structures
- equilibrium delayed phase
what do time density curves predict
- contrast media dose
- injection flow rate
- scan delay
- scan duration
what are the premedications for patients with a high risk reaction
prednisone : 50mg po 13 hours and 1 hour before
benadryl: 50mg 1 hour prior
What do the following drugs do
Chlorpheniramine (Chlor-Tripolon)
* Diphenhydramine (Benadryl) -
* Diazepam (Valium) –
* Epinephrine (Adrenalin)
IV adrenalin
* Hydrocortisone (Solu Corlef)
* Salbutamol (Ventolin)
* Phentolamine (Rogatine)
* Sodium Chloride 0.9%
- antihistamine vial/pill
- antihistamine vial
- controls convulsions
– for anaphylaxis
– rapid increase in BP, stimulates heart, increases HR,
relaxes smooth muscle to alleviate bronchospasm/asthma attack - acute allergic anaphylactic rxns
– bronchial dilator
– vasodilator - keep veins open
for the site, name
site: rectum / anal canal
see:
type
delay
- lower small bowel
- telebrix and water
- 1 hour prior
for the site, name
site: esophagus
see:
type
delay
GE stomach
telebrix and water
just after scout
for the site, name
site: pancreas liver cholangio
see:
type
delay
duodenum
telebrix and water
20 minutes prior
for the site, name
site: upper GI
see:
type
delay
lower small bowel
telebrix and water
1 hour prior
for the site, name
site: Lower GI
see:
type
delay
lower small bowel
telebrix and water
1 hour prior
what does x ray image quality depend on
- x ray source (energy, spot size)
- SSD
patient thickness and the part to be imaged
detector to patient distance (Airgap_
amount of exposure or dose
quality of detector
what are the advantages of portal films
- high resolution
- fair contrast
- low maintenance and set up costs
what are the disadvantages of portal films
time consuming
high cost per film
not online or digital
what are the advantages of EPIDs
- fair resolution
- images at any angle
- fast efficient
- online digital
what are the disadvantages of portal films
- poor contrast
- high cost
- image database maintenance
- image quality operator dependant
what are the advantages of flat panel technology
- much better image quality
- excellent spatial resolution
- online digital
-transit dose measurements
what are the disadvantages of flat panel technology
- limited to bony or fiducial markers
- 2D information only
- image quality can be poor
limitations to flat panel detectors
- lower efficiency (lower x ray cross section)
- higher noise characteristcis
- slower readout per frame
signal memory (lag or ghosting)
describe each for linac acquisition
frames / s
min / rotation
projections
exposures
5
2
600
120 kVp, 100mA, 10-20ms
describe the process to project data
300 projections
gain anad offset
exposure normalization
pixel defect correction
what are sources of image artifacts
- truncation (detector FOC)
motion artifacts
metal artifacts
scatter
lag/ghosting
what does the bowtie filter do in CBCTs
- compensate for anticipates thickness of patient along beam length to achieve a fluence of photons that is uniform
- filters our lower energy photons at periphery
in varians a full fan is a _____ bowtie filter
and a half fan is a ____ bowtie filter
half and full
what is Precession in relation to MRIs and hydrogen
axial spin of the H proton
independent of the alignment of axis of the atom
the wobble of the axial spin of the H proton
how is precessional frequency determined
- type of atom and is the magnetic field strength
what is the rate of precession determined by
magnetic field
what do gradient coils do
superimpose magnetic fields over the main magnetic field to create a gradient of magnetic field strength down the bore of the machine
- how the location of signal is determined
what is the energy exchange between two systems called
resonance
how is the slice selection and data origin location determined
RF pulse
what is the T1 and T2 stage
T1: recovery of net magnetization
t2: spin spin relaxation
- loss of phase coherence
what is time of echo
- time from RF pulse and the time where we measure the signal of the lateral magnetization
what is time of repetition
-time between one pulse and another
can be used to see which tissues are losing and gaining their perpendicular magnetization faster
how do you increase slice thickness on MRI
increase bandwidth of the RF pulse
decrease the gradient of the main magnetic field
move patient slower
how does shadowing occur
(ultrasound)
due to a dense object attenuating most of the sound energy leaving little to travel beyond this creating a shadow, can be used diagnostically
how are most signals located in MRI (plane)
cartesian
what are the 3 dose metrics and how are they calculated
- CTDI (computed tomography dose)
- DLP ( dose length product)
- effective dose ED
what are some factors affecting dose in CT
- intensity
- noise
- spatial resolution
- slice thickness
how does edge shadowing occur
(ultrasound)-
sound refracting at tissue boundaries
how does the enhancing artifact occur
(ultrasound)-
sound does through a structure that does not attenuate well
- fluid filled
- reflections of the other side of the object are enhanced
how does the duplication artifact occur
(ultrasound)-
due to refraction
- system assumes reflections come back along line of transmitted sound waves at constant speed
- refraction at the boundary therefore makes a false duplicate of the real structure
how does the mirroring artifact occur
(ultrasound)-
pulse can properly reflect off an object in front of a reflective boundary (diaphragm)
- pulse can transmit through object and reflect off boundary again properly displaying boundary on image
how does the reverbation artifact occur
(ultrasound)
result of a strong reflector
sound waves bounce off the reflector properly placing it in space
- creates lines on the other side of the strong reflector
how does the ring down/ comet tail artifact occur
(ultrasound)
similar to reverberation artifact
- ring down can be caused by fluid wedged between microbubbles and that results in reverberations
- comet tail can be caused by two small but strong reflectors close to each other that result in reverberations
how does the ring side lobe or grating artifact occur
(ultrasound) energy directed outside the field of view reflects and the system incorrectly indicates that a stricture is there in the FOV when it isnt
how does a speed artifact occur
(ultrasound)
object in path slows down sound waves
how does a ambiguity artifact occur
(ultrasound)
- closer than it seems
how does a chemical shift artifact occur
MRI
frequency encoding gets messed up where fat would be and moved to the left
how does an aliasing artifact occur
- also known as a wrap around
- frequent
- FOV is smaller than what is being imaged
- due to misrepresentation in frequency and phase coding
3 main types of CT artifacts
streak
shading
ring
how do streak artifacts occur
CT
- improper sampling of data
- beam hardening
- metal
- noise
- partial volume averaging
- patient motion
- spiral helical scanning
- mechanical failure
how do shading artifacts occur
CT
partial volume averaging
beam hardening
patient motion
spiral helical scanning
scatter radiation
off focal radiation
incomplete projections
how do ring artifacts occur
bad detector channels in 3rd generation CTs
when detector is not calibrated
what are the origins of artifacts categories
- physics based
- patient based
- scanner based
- helical and multisection
what are examples of physics based artifacts
beam hardening
partial volume
photon starvation
undersampling
how does a cupping artifact occur
- from beam hardening
what are examples of patient based artifacts
metallic materials
patient motions
incomplete patient projections
what are examples of helical and multisection CT artifacts
helical artifacts in the axial plane : single section scanning
helical artifacts in the multisection scanning
cone beam effect
what are examples of multiplanar and 3D reformation artifacts
stair step artifact
zebra artifact
what should typical scanners be able to display
spatial resolution
contrast resolution
uniformity
linearity
0.3mm
0.5% for a 5mm object
deviation of less than 8CT numbers (SD)
coefficient of correlation of 0.96%
what is noise / quantum mottle artifact
PET CT artifact
- not enough time to overcome the signal to noise
what is respiration artifact
PET CT
white band due to misalignment between breath hold CT and breathing PET with its relatively long acquisition time
what is injection site artifact
stems from extravasation of injected PET tracers
what is a truncation artifact
- when PET FOV does not match CT FOV
