Computed Tomography for Technologists P2 (p 64 - 176)
for a slice thickness of less than 5mm, how much can the thickness vary?
+/- 0.5mm
for a slice thickness of 5mm or greater, how much can the thickness vary?
+/- 1 mm
for uniformity measurements, there should be no more than a _______ HU variation
+/- 2 HU
what is the general normal range for a serum creatinine?
0.6-1.7mg/dL
100 RAD = _________Gy
1 Gy
what is the quality factor for the diagnostic xrays used in CT?
1 Q
1CGy = _____________ RAD
1 RAD
100 REM = __________ Sv
1 Sv
what 3 features do CT scanners use to minimize beam hardening
1) filtration (bow tie filters, etc) 2) calibration correction 3) beam hardening correction software
what are the factors that affect contrast resolution?
1) mAs / dose 2) pixel size 3) slice thickness 4) reconstruction algorithm 5) patient size 6) subject (inherent) contrast
why is dose more uniform in CT than in conventional x-ray?
1) the beam us heavily filtered as it exits the x-ray tube 2) the CT exposure comes from all directions, creating a more uniform exposure
quality assurance programs should be built around 3x principles, what are those?
1) the test should be performed on a regular basis 2) the results should all be documented in a consistent format 3) the test results should indicate that they are within acceptable standards
how can we reduce the incidence of CIN in high-risk patients?
1) using LOCM or IOCM 2) hydrating the patient before and after contrast administration 3) using the smallest dose possible 4) allowing 48 hours to elapse between contrast enhanced studies
how many nephrons are in each kidney?
1-2 million
for noise measurements, the standard deviation should not exceed what?
10
a 1% contrast difference corresponds to a difference of how many hounsfield units?
10 HU
two tissues must be different by _______ HU's to be visibly different on CT
10 HU's
what is the average infant pulse?
100-160bpm
1keV = ________________eV
1000eV
what is the general normal range for a prothrombin time (PT)?
11-14 seconds
what is the minimum, maximum, and mean energy values of the CT x-ray beam?
120-140keV, mean 70keV
what is the average adult respiration rate?
14-20 pm
most organs have exclusively arterial blood supply, and their peak enhancement is at how many seconds?
15-22 seconds after injection
what is the general normal range for blood platelet count?
150,000 - 400,000 mm^3
what is the average adolescent respiration rate?
18-22 pm
when were the first DICOM standards created?
1985
what is the half-life of most CT contrast media?
2 hours
how long does the drip infusion method take to fully infuse all contrast media?
2-3 minutes
for flow rates over 3mL/s, what gauge needle should you use?
20 gauge or higher
what are the ACR reference numbers for the CTDIvol for a pediatric abdomen?
20mGy
what is the average child respiration rate?
22-28 pm
what is the general normal range for a partial thromboplastin time (PTT)?
25-35 seconds
what are the ACR reference numbers for CTDIvol for an adult abdomen?
25mGy
what is the osmolality of blood plasma?
290 mOsm/kg water
what is a common formula for dosing of contrast to an individual?
2mg of contrast per 1kg, up to usually 200mL in one 24-hour period
the radiation field should coincide with the radiationfield by within how much?
2mm
what is the average infant respiration rate?
30+ pm
what is the average american background radiation exposure?
3mSv per year
which generation of scanners has ring artifacts?
3rd generation scanners
doubling the mAs increases the SNR by how much?
40% increase in SNR
when the radiation doses used in adult protocols are used in neonates or young children, the effective dose is up to _______% higher
50% higher this is why we have pediatric protocols!!
what is the atomic number of iodine?
53
when is the portal-venous phase?
60 seconds after a bolus injection
what is the average adult pulse rate?
60-100bpm
CT exams represent 11% of all diagnostic radiologic procedures but account for _____________% of the effective dose
67% of the effective dose
what is the general normal range for a BUN?
7-25mg/dL
what are the ACR reference numbers for the CTDIvol for an adult head?
75mGy
when is the nephrogenic phase?
80-120 seconds after a bolus injection
what percent of the meaning that we derive from communication comes from nonverbal cues?
90%
how efficient are solid-state detectors?
90-100%
what is the average child pulse?
95-110bpm
what is a normal adult axillary temperature range?
95.8-99.4 (35.4-37.4)
what is a normal adult oral body temperature range?
96.8-100.4 (36.0-38.0)
what is a normal adult rectal body temperature range?
97.2-100.8 (36.7-38.7)
define subject contrast
AKA "inherent contrast" this relates to the inherent properties of the object being scanned.
define contrast resolution
AKA "sensitivity" the ability to differentiate a structure that varies only slightly from surrounding tissues
what is the sampling theorem?
AKA the "Nyquist Theorem" basically, because an object may not lie entirely within a single pixel, the pixel dimension should be half the size of the object to increase the likelihood of that object being resolved smaller pixels = better image resolution
which has better contrast resoution, CT or conventional radiography?
CT contrast resolution is what truly sets these two modalities apart
what does CTDI stand for?
CT dose index
in a helical scanner, how do you get the CTDIvol?
CTDIw / pitch
DLP formula
DLP = (CTDIvol * scan length)
true or false: children are less radiosensitive than adults
FALSE
what is an example of a LOCM that is ionic?
Hexabrix
when was the ACR's reference for CTDIvol created?
January 1, 2008
are idiosyncratic reactions dose dependent?
NO
can you use the drip infusion method for angiography?
NO
can you use tunneled catheters that are for dialysis for power injecting contrast?
NO
will iodinated contrast cross an intact blood-brain barrier?
NO
is a seafood allergy a good indicator for if the patient will have a reaction?
NO DIFFERENT TYPE OF IODINE! THIS THOUGHT IS UNFOUNDED!
what does the acronym PACS stand for?
Picture Archive and Communication System
what is the REM?
Roentgen Equivalent in Man unit for dose equivalent
what is surface rendering?
SR includes only information from the surface of an object
true or false: girls are more radiosensitive than boys
TRUE
true or false: smaller patients absorb more than larger patients
TRUE
what was the first Isomolar contrast agent?
Visipaque, introduced by GE in 1992
what is volume rendering?
a 3D rendering technique similar to surface rendering
what is an isotropic voxel?
a cube shaped voxel, the X,Y, and Z axis are althe same isotropic voxels are achieved with MDCT
define a network
a group of 2 or more computers linked together
define a local area network
a group of linked computers that are geographically close together AKA "LAN"
What kind of phantom do you use to test spatial resolution?
a line-pair per millimeter phantom
what is an isotonic liquid?
a liquid having nearly the same numbers of particles in solution per unit of liquid
what is the most important indicator of if a patient will have a reaction to the contrast media?
a prior reaction
what is the bolus triggering method of administering IV contrast?
a single, axial slice is taken in an ROI and the injection is started. Low dose scans follow. Once the desired HU's or enhancement is reached, the table moves and the scan begins. This can be an automatic trigger or a manual one.
what is tube arcing?
aka high voltage arcing it is an unwanted surge of electrical current (ie a short circuit)
what is z-axis dose distribution
aka radiation profile variations along the z axis of the pt an ideal profile includes no scatter, but IRL scatter is included in the radiation profile
what is region of interest editing?
aka segmentation it is the process of selectively removing or isolating information from the data set
what is Contrast-induced nephropathy? (CIN)
an acute impairment of renal function that occurs after the IV administration of contrast media some pt's with CIN may go temporarily on dialysis
what is Health Level Seven (HL7)?
an organization that works to develop universal standards for clinical and administrative data
what does the renal fasciae do?
anchors the kidneys to surrounding structures
define nephropathy
any condition or disease affecting the kidneys is used synonymous with renal impairment
what phantom can be used to test noise?
any phantom with a uniform density, but, we more commonly call it the "water phantom"
define artifacts
anything appearing on the image that is not present in the object scanned
as flow rate of contrast increases, there is a decrease in time to peak ___________ enhancement
aortic enhancement
The ACR has a CT accreditation phantom that is 4cm deep and 20cm in diameter. What does the third module test for?
assess CT number uniformity and the accuracy of in-plane distance measurements
reconstruction is when raw data is assigned into what?
assigned into pixels
what are some common risk factors for a contrast media reaction?
asthma, food and drug allergies, the use of beta-blockers
why are the temperatures taken orally, rectally, and tympanically usually higher than temperatures taken in axillary areas?
because the thermometer is in contact with mucous membranes
Creatinine, PT, PTT, and platelet count levels are indicators for what?
blood coagulation ability
the enhancement of most brain lesions is caused by what?
blood-brain barrier disruption
visual communication is also known as what?
body language
what are the 3 general phases of tissue enhancement?
bolus phase, non-equilibrium phase, equilibrium phase
bolus triggering is also known as?
bolus tracking, automated triggering, smart prep
which is more efficient, test bolus or bolus triggering?
bolus triggering
MIP's are good for displaying what?
bone and contrast-filled structures
how do you measure noise?
by obtaining the standard deviation within an ROI
how do you combat aliasing artifacts?
by slowing gantry rotation or reducing the helical pitch
contrast viscosity can be halved by simply doing what?
by warming it to body temperature
how can we reduce pulsation artifacts?
cardiac gating
what does a large focal spot size cause?
causes geometric unsharpness and reduced spatial resolution
who has a lower frequency of a reaction to contrast, adults or children?
children
what are some pharmacokinetic factors?
contrast media characteristics, contrast media volume, flow rate, flow duration, scan delay time, total scan time
what is Isomolar Contrast Media (IOCM)?
contrast media that is close to the osmolality of blood
what is the 3rd leading cause of acute renal failure (ARF) in hospitalized patients?
contrast media-induced nephropathy (CIN)
as pixel size decreases, then number of detected x-ray photons per pixel will decrease, which means a decrease in _______________________
contrast resolution
which has better spatial resolution, CT or conventional radiography?
conventional radiography
as patient weight increases, the magnitude of contrast enhancement does what?
diminishes
when should the kidneys be scanned?
during the nephrogenic phase
when should the lover be scanned?
during the portal-venous phase
define peer-to-peer
each party has the same capabilities and any party can initiate communication aka P2P
what is the non-equilibrium phase?
follows the bolus phase (approx 1 min after injection) AKA venous phase venous structures are enhanced
what is the equilibrium phase?
follows the non-equilibrium/venous phase begins 2 mins after injection intravascular and interstitial structures are enhanced
when would you lower the mAs?
for imaging soft tissue (such as a soft tissue neck or chest)
when is the fetus most radiosensitive?
from conception to 3months gestation this is because their organs and neural crest is developing at this time
what controls temporal resolution?
gantry rotation speed, the number of detector channels in the system, and the speed with which the system can record changing signals
what are some generic names for the drug METFORMIN?
glucophage, rhiomet, fortamet, glumetza, diabex, diaformin
shaded surface display / surface rendering is good for looking at what?
good for looking inside the surfaces of airways, the colon, blood vessels, and bony structures
which has a higher does, head or body CT's?
head, always smaller objects always absorb the highest doses, and the difference is at least a factor of 2x
define temporal resolution
how rapidly data are acquired
for the test bolus method, how often are the test scans done?
in 2-second intervals
when were LOCM's first introduced?
in the 1980's they were very expensive when they were first introduced
when you _______ DFOV, you ________ pixel size
increase, increase they are directly proportional
as the number of x-ray photons used to create an image decreases, image noise ___________________
increases
for any given level of desired enhancement, that level is maintained longer as contrast volume: increases or decreases?
increases
the uniformity of the dose decreases as the SFOV and patient size ________________
increases
how do you overcome an out-of-field artifact?
increasing the SFOV
define intraarticular injection
injecting directly into a joint space
define intrathecal injection
injecting directly into the subarachnoid space
what causes a edge gradient effect?
it arises from irregularly shaped object that have a pronounced difference in density from surrounding tissues
why can you NOT give contrast media to any patient who is currently taking METFORMIN or a METFORMIN-containing drug?
it can cause lactic acidosis and CIN
what does the DFOV determine when it comes to image reconstruction?
it determines how much RAW data will be used to reconstruct the image
how do we get the effective dose / effective dose equivalent?
it extrapolates the risk of partial body exposure to patients from data obtained from whole body doses to Japanese atomic bomb survivors it is a weighted average of organ doses
what is a High Osmolality Contrast Media (HOCM)?
it has 1,300-2,140 mOsm/kg water is 4-7x that of blood very thick
what is a Low Osmolality Contrast Media?
it has 600-850 mOsm/kg water is 2-3x that of blood thinner contrast than HOCM
what is volume rendering?
it is a 3D semi-transparent representation of an imaged structure all voxels contribute to this image, which allows VR's to display multiple tissues at once
what is endoluminal imaging?
it is a form of VR designed to reveal the inside of the lumen of a structure
define osmolality
it is a property of IV contrast that refers to the number of particles in solution per unit liquid as compared to blood measured in: mOsm/kg water
what is a CVAD (central venous access device)?
it is a venous catheter that is designed to deliver medication and fluids directly into the SVC, IVC, and RA
what is the radiation weighing factor?
it is analogous to the Q (quality factor)
what causes ring artifacts?
it is caused by imperfect detector elements
what is the variable sliding slab method?
it is creating a MIP from only a portion of the data set
using the test bolus method, how do they determine the optimal scan delay?
it is presumed to be equal to the time that elapsed from the start of the injection to that of the image showing maximum enhancement
what is a pencil ionization chamber used for?
it is what medical physicists use to measure the CTDI it is a 100mm long cylindrical device
what is barium peritonitis?
it is when barium leaks into the peritoneal cavity
the beam attenuation abilities of a given amount of contrast media are directly related to what?
its' iodine concentration
what are some barriers to communication?
language, power struggles, misreading nonverbal cues, inconsistency, distortion, assumptions, preconceptions, past experiences, cultural differences
the relationship between mAs and dose is ___________
linear
what are implanted ports used for?
long term access to a vein
what determines pixel size?
matrix size and DFOV
99% of contrast reactions are classified as what: mild, moderate, or severe?
mild
how can you overcome metallic artifacts if you cannot just remove the metal (ie dental work)?
minimize the amount of metal in the SFOV, increasing kVp
ionic contrast agent are made up of what?
molecules that will dissociate into ions when in a solution
less efficient detectors require ____________ radiation exposure to produce adequate images
more
what are the two most common sources for artifacts?
motion and metal
what are banding artifacts?
motion artifacts on a cardiac CT image
what are common, non-harmful side effects to the contrast media?
nausea, vomiting, metallic taste, perspiration, warmth, flushing, anxiety
should you give contrast to patients with hyperthyroidism (such as grave's disease)?
no - it can cause thyroid toxicosis, and lead to thyroid storm
when you halve the mAs, noise increases by _________
noise increase 41%
the relationship between kVp and dose is ________________
non linear
when does most routine (non angiographic) imaging with contrast take place?
non-equilibrium phase
what are some ways to overcome motion artifacts?
over-scanning, partial scans, software correction, and cardiac gating
what is systolic pressure?
peak blood pressure
what's the formula for pixel size
pixel size = (DFOV /Matrix Size)
The ACR has a CT accreditation phantom that is 4cm deep and 20cm in diameter. What does the first module test for?
positioning, alignment, CT accuracy and slice thickness
what is diastolic pressure?
pressure when resting
what is the RAD?
radiation absorbed dose the amount of energy per unit mass
what do smoothing algorithms do?
reduce the difference between adjacent pixels at the cost of reduced spatial resolution smoothing algorithms help reduce metal artifacts as well
BUN and creatinine levels are indicators for what?
renal funciton
increasing pitch reduces ___________________
resolution
define in-plane resolution
resolution in the XY direction
define longitudinal resolution
resolution in the Z direction
effective radiation dose is directly proportional to what?
scan volume
what does the matrix do?
segments the RAW data into pixels these pixels are always squares
what is the best strategy to avoid beam hardening artifacts?
selecting the appropriate SFOV
what is the fastest, and least expensive way to measure GFR?
serum creatinine serum creatinine is a byproduct of muscle protein metabolism and is generated and excreted by the body at a steady rate
surface rendering is AKA what?
shaded surface display (SSD)
how do you calculate the dose from a single axial slice?
single-slice does + amount scattered
The ACR has a CT accreditation phantom that is 4cm deep and 20cm in diameter. What does the fourth module test for?
spatial resolution
how does the edge gradient effect appear on an image?
streaking and shading can be caused by a barium filled stomach
injecting saline at the same time as contrast can help reduce what type of artifact?
streaking artifacts
how does an out-of-field artifact appear on an image?
streaks most commonly caused by patient's arms being at their sides
how is blood pressure written?
systolic pressure over diastolic pressure
what are the most common locations to find a pulse?
temporal pulse, facial pulse, carotid pulse, radial pulse, brachial pulse, femoral pulse, popliteal pulse, pedal pulse
what is the Sievert (Sv)?
the SI unit for dose equivalent
what is the Gray (Gy)?
the SI unit of absorbed dose
larger slice thicknesses have better SNR but lose spatial resolution in which axis?
the Z axis
slice thickness can also be referred to as which axis?
the Z axis
define uniformity
the ability of the scanner to yield the same CT numbers regardless of the location of an ROI within a homogeneous object
define low contrast sensitivity
the ability to distinguish an object that is nearly the same density as the background
what are "tails" in terms of dose?
the areas of scatter that fall into adjacent slices. these can contribute 25-40% additional dose to the patient
what are minIP's good for displaying?
the bronchial tree
what is the multiple scan average dose (MSAD)?
the central slice radiation dose plus the scatter overlap (tails). this increases if slices overlap, and decreases with gap imaging
define informatics
the collection, classification, storage, retrieval, and dissemination of recorded information
how do we get a maximum intensity projection (MIP)?
the computer examines each voxel along a line through the data set and selects only the voxels with the highest values for inclusion
how do we get minimum intensity projections (minIP)?
the computer selects the voxel with the minimum value from the line to display
why do metallic artifacts occur? (aside from the fact that the metal is there in the first place)
the density of the metal is beyond the HU's that the machine is designed to handle
which contrast phase is the WORST to scan in?
the equilibrium phase
define topology
the geometric arrangement of a computer system
define lossless compression
the image that is decompressed is an exact replica of the original
when using the lp/mm phantom, spatial resolution is given as what?
the maximum number of visible line pairs per millimeter line pair is lead strip and space next to it, NOT 2x lead strips
what is the basic functional unit of the kidney?
the nephron
where in the body does beam hardening frequently occur?
the petrous bones
define blood pressure
the pressure exerted by circulating blood on the walls of the vessels
define communication
the process of creating meaning
what is the equivalent dose (H)?
the product of the absorbed dose (RAD/Gy) and a radiation weighing factor (Wr)
define linearity
the relationship between CT numbers and the linear attenuation values of the scanned object at a designated kVp value daily calibrations help avoid fluctuations
what is the Roentgen (R)?
the unit of xray exposure in air
define clearance
the volume of plasma that is cleared of a specific substance in a given time
why are isotropic voxels better than the rectangular voxels we saw with SDCT?
there is no loss of data when isotropic voxels are reformatted into different planes with rectangular voxels, data can be lost in the reformatting process also, isotropic voxels are preferred when imaging very small vessels
what is an idiosyncratic reaction to contrast media?
these are all other reaction types that are not covered by chemotoxic reactions. they are unpredictable and normally occur within 1 hour of injection.
how do helical and cone beam effects arise?
these are mostly caused by interpolation issues
what is a chemotoxic reaction to contrast media?
these result from the physiochemical properties of the contrast media itself, the dose, and the speed of injection
what causes out-of-field artifacts?
they are caused by anatomy that extends outside of the selected SFOV, and this anatomy attenuates the x-ray beam and hardens it. this is ignored by the scanner during the reconstruction process
what are quality control programs designed to do?
they are designed to ensure that they CT system is producing the best possible image quality using the smallest dose possible to the patient
why do windmill artifacts occur?
they occur because the beam is cone shaped occurs in MDCT
with higher concentrations of iodine, contrast media become what?
thicker
how do you overcome partial volume artifact?
thinner slices
what is the quality factor (Q)?
this accounts for the different biologic effects produced from different types of ionizing radiation
what is the CTDIw?
this adjusts for periphery being a higher dose than the central dose, and provides a weighted average of measurements at the center and periphery (x and y dimensions)
what is the effective dose / effective dose equivalent?
this attempts to account for the effects particular to the pt's tissue that has absorbed the radiation dose measured in Sv / REM
what is the Hospital Information System (HIS)?
this focuses on administrative issues, such as demographic data and financial data
what is the Computed Tomography Dose Index (CTDI)?
this is another dose measurement, and is what is reported to the FDA the CTDI can only be calculated with contiguous slices (ie NO GAPS)
what is the Radiology Information System (RIS)?
this is designed to schedule pt's, store reports, track pt's, protocoling exams and billing
define lossy compression
this is used to transmit images that do not need to be diagnostic the decompressed image is not the same as the original image, it is of a lower quality
what is the Clinical Information System (CIS)?
this keeps track of clinical data
what is the test bolus method of administering IV contrast?
this method consists of administering 10-20mL by IV bolus injection and performing several scans to determine the length of time from injection to peak enhancement in a target region
What is the bolus phase?
this phase occurs immediately after IV injection of contrast AKA arterial phase arterial structures are enhanced
what is the CTDIvol?
this takes into account the exposure variance in the z axis. It is a measure of exposure per slice and is independent of scan length it is the preferred expression of radiation dose in CT dosimetry
what causes aliasing?
undersampling
define image noise
undesirable fluctuations of pixel values in an image of a homogeneous material
The ACR has a CT accreditation phantom that is 4cm deep and 20cm in diameter. What does the second module test for?
used to asses low-contrast resolution
what is the most important method of reducing idiosyncratic reactions to contrast media?
using LOCM
how is contrast expelled from the body?
via the glomerular filtration of the kidneys, exclusively
endoluminal imaging is AKA what?
virtual endoscopy, virtual bronchoscopy, and virtual colonoscopy
what are the five ways that non-verbal communication can be categorized?
visual, tactile, vocal, the use of time space and images, objects or values
what are come common anticoagulants?
warfarin (coumadin), heparin, plavix, aspirin
define partial volume artifact
when a dense object lies to the edge of the FOV, resulting in the object only showing up in a few views, which can cause shading
define aliasing
when fine stripes appear to be radiating from a dense structure
define beam hardening
when lower energy x-ray photons are absorbed, leaving behind only the high energy beams
what is a multiphasic injection?
when more than 2 flow rates are used for contrast injection
when does the partial volume effect occur?
when more than one type of tissue is contained in a voxel
what is a ghosting artifact
when objects appear to have a shadow
what is the Dose Length Product (DLP)?
when the irradiated length of the scan is to be accounted for
what is a cupping artifact?
when the periphery of the image is lighter; the appearance of dark bands; streaks between dense objects this is a beam hardening artifact
how do we get the "dose equivalent"?
when the quality factor (Q) has been applied to the radiation absorbed dose (RAD/Gy)
what is manual segmentation?
when the user identifies an selects data to be saved or removed when creating 3D imaging and MPR's
when does quantum mottle occur?
when there are insufficient numbers of protons detected by the detectors
what is a biphasic injection?
when two flow rates are used for contrast injection
define renal failure
when urine volume is less than 50mL in 24 hours aka Anuric
what causes a stair-step artifact?
when wide slices are used as source images to create MPR's
when is having a high temporal resolution most important?
when you are imaging moving structures and dynamic flow of vessels
define overbeaming
when you open the collimators more to allow prenumbra to fall outside the active detectors this contributed to pt dose but NOT to image quality this allows for the sane intensity at each of the detectors
when do most adverse reactions to contrast occur?
within minutes of injection (usually 20 mins for the most severe reactions)
can helical data be reformatted to create overlapping slices?
yes
does contrast media cross the placental barrier?
yes
why does having smaller pixel sizes produce better spatial resoultion?
you are less likely to have volume averaging occur with smaller pixel sizes
