chapter 5: ct instrumentation Flashcards
what is the type of radiation used to produce diagnostic xrays?
pair production
compton scattering
characteristic xrays
bremsstrahlung “breaking” radiation
bremsstrahlung “breaking” radiation
what is it called when an atom in the target of the xray tube has been ionized, the inner shell electron is removed, so an outer shell electron drops down to fill this vacancy?
bremsstrahlung radiation
pair production
compton scattering
characteristic xrays
characteristic xrays
the kVp controls
the number of xrays produced
the shape of the xray beam
the energy of the xrays
the type of xrays produced
the energy of the xrays
the mAs controls
the number of xrays produced
the shape of the xray beam
the energy of the xrays
the type of xrays produced
the number of xrays produced
define the equation for pitch
pitch = table movement in one rotation/single-slice thickness
define the partial volume effect
occurs when there is a mixture of tissues within a voxel, so the measurement within that voxel will be inaccurate. typically occurs with small lesions
define the equation for the CT number
CT number = (u tissue - u water)/ u water x 1,000
what are the CT numbers for air, fat, water, muscle, blood, soft tissue, and bone?
-1,000
-100 to -50
0
35-80
20-80
20-80
400-1,000
define the truncation artifact
occurs when the CT is reconstructed with a smaller fov than the PET scan. PET quantitative measurements may be altered at the edge of the scan
what causes a ring artifact on a CT scan?
when the mAs are too low (30 mAs), resulting in low data density
postcollimators on a ct scanner are located in front of, or behind the x ray detectors?
in front of
T/F: the typical slice range of ct scanners used for oncologic pet/ct is 16 to 40 slices
true
good low-contrast resolution is obtained by increasing the…
kvp
scan time
mAs
xray energy
mAs
when an electron undergoes a bremsstrahlung reaction, its energy is
preserved
lost
gained
stays the same
lost
the energy of the characteristic xray is based on
the number of electrons in the vicinity
the energy
the energy of the bremsstrahlung radiation
the total number of ionizations
type of target material that has been ionized
type of target material that has been ionized
on the bremsstrahlung xray spectrum, as energy increases, the number of xrays
increases
decreases
stays the same
is preserved
decreases
as more or less current and voltage are applied to the xray tube, tungsten characteristic xray energy
increases with more current/voltage
decreases with less current/voltage
does not change
is preserved
does not change
the purpose of the xray tube filter is to
shape the xray beam
filter out low energy xrays
A and B
none of the above
A and B
all of the following are true concerning thin collimation for ct xray tubes except
more volume averaging
better spatial resolution
increase in quantum noise
reduction in streak artifacts
more volume averaging
all of the following are materials that may be used to produce xrays in the ct xray tube except
germanium
silicon
tungsten
cadmium
tungsten
in MDCT or MSCT, what defines the number of slices that can be created at the same time?
x axis
y axis
z axis
A and B
z axis
all of the following are considered the 4 Cs of helical CT except
continuous feed of the bed
continuous rotation of the gantry
continuous data reconstruction
continuous data transfer
continuous data reconstruction
generation of high res/high-contrast res for inner ear or eye orbits, or low-res with smoothing properties for the abdomen is called
image recon algorithms
kernel
filtering
chang technique
kernel
a ct for attenuation correction for use with pet must be a
high res scan
low res scan
high res scan with smoothing
low res scan with smoothing
low res scan with smoothing
most body tissues have ct numbers that are close to that of
air
water
soft tissue
blood
blood
a concentric ring artifact may be caused by
patient motion
beam hardening
mA setting is too low
kvp is too low
mA setting is too low; low data density as a result
the CTDI is measured in
mGy
mSv
KBq
MBq
mGy
DLP stands for
dose length procedure
dose length protection
dose length product
dose length probability
dose length product
all of the following are true for accurate calculation of DLP except
it is measured in mGy
scan lengths must be equivalent
it is inversely related to scan length
it is an estimate of absorbed dose
it is inversely related to scan length
the highest fraction of patient radiation exposure comes from
fdg pet scans
chest xrays
ct scans
rb82 rest/stress studies
ct scans
all of the following will reduce the radiation exposure to the patient except
lowering mAs
lowering kvp
using a smaller pitch
decreasing scan time
using a smaller pitch
AEC techniques
are the same across all scanner manufacturers and scanners
may reduce patient exposure by approximately 75%
substantially benefits smaller patients
primarily adjusts the kvp
substantially benefits smaller patients
AEC is adjusted based on
size of the patient
density of the patient
age of the patient
A and B
A and B
the standard deviation of pixel values in a uniform water phantom describes the
standard deviation coefficient
pixel parallax
noise index
houndsfield deviation
noise index
all protocols established for the ct scanner should be reviewed and approved by the
field engineer and physician
ct physicist and physician
ct physicist and field engineer
ct physicist and state licensing agencies
ct physicist and physician
ring artifacts on a ct scan from a failed detector
will be seen on all slices
can be caused by a failed air scan
always requires a service call
causes an artificially high reading
can be caused by a failed air scan
