Test 2 - CT
voxel size formular =
(dfov x 10) / matrix x slice thickenss or DFOVmm / matrix x slice thiccness or pixel size mm x section width
ho long must patient fast for PET
(pt must fast 4-6hrs)`
min tech-based requirements for Coronary calcium measurement?
0.5 sec gantry rotation time 4 detector rows dose is HI
x-ray can detect differences if contrast varies at least 5%. CT on the other hand can detect at
0.5% contrast variation
positron is beta plus charged particle that travels until it collides with a electron and annihilates releasing
0.511 eV gamma rays in 180 degree of each other
in practice pitch may vary ___ to 2. 2 being ________
1 worse
During a spiral or helical CT examination, the scanner acquires data:
1. Continuously as the patient travels through the gantry 2. in a volumetric set
Which of the following technical factors exhibit an effect upon longitudinal spatial resolution?
1. Detector collimation 2. Detector pitch 3. Interpolation algorithm
1% contrast corresponds to _____ HU in CT
10 HU
how greater is the CT number of the liver than the spleen (normally)?
10 HU greater
exposure from a chest, ab, or pelvis CT is
10 mSv
surface dose is ___________times higher in CT and absorbed dose is ___________ times higher than x-ray
10 times 100 times
nonequilibrium phase/venous has a AVID of
10-30 HU
normal width and level for brain?
100-160 WW 30-40 WL
what is lung window settings?
1000 to 1500 WW -600 to -700 WL
isodense center surrounded by areas of hypodense tissue from ______ days to _________ months
11; 6
what is trade off with ATCM?
15-40% reduction of dose but lower image quality only adjusts mA atm
what are half scans?
180 degree of arc of fan angle
how do you achieve higher temporal resolution in ct?
2 tubes 90 deg of each multi detector rows
how long does PET CT take?
20-40 mins
avg annual dose of background rad
3 mSv
axial brain uses ________mm slice for posterior fossa, and _________ slices for remainder of the brain
3-5mm; 7-10mm (5mm in workbook)
injection rates for CTA?
3-6ml/sec injection 10-30 sec prior to scanning
bolus phase/arterial phase has a AVID of?
30 or more HU
untreated what is the death rate of PE?
30 percent 3rd most common death in hospitalized patients
Modern CT scanners use large matrices for image reconstruction and display. Typical sizes include:
320x320, 512x512, and 1024x1024.
what is common scan geometry?
360 degrees for each slice
what is 3d reformation/rendering?
3D Reformations seek to represent the entire scan volume in only one image 3D techniques manipulate or combine CT values to display an image the original CT value information is not included
helical mode is mostly used for studies that require
3d reformations, quicker studies
paranasal sinus protocol
3mm coronal plane bone or soft tissue algorithims
ICH hyperdense center surrounded by concentric areas of hyperdense and hypodense tissue from _________ days
4-10
avg dose of scan to head?
4.0-4.5 rad or 0.04 gray to 0.045 gray
liver HU
40-70 HU
what are overscans and what are they used for?
400 degree used in 4th gen scanners to reduce motion
In a modern CT system, the total number of possible Hounsfield values that may be assigned to any one pixel is approximately:
4096.
cardiac scoring
45-60 images looks 4 areas of calcification in 5 major branches of coronary arteries score based on density and area values adjusted for age/sex
mediastinal/soft tissue window settings?
450 to 500 WW 20-40 WL
avg dose for CT exam in rads
5 rads 0.05 gray tissue
On an ECG of the complete cardiac cycle, at which portion of the R-R interval is the heart muscle in diastole?
55% to 75% one cardiac cycle R-R acquire images here because lowest cardiac motion
hypodense tissue to normal tissue after ________ months
6
equilibrium phase/delayed phased has a AVID of?
>10 HU
ROI for CTA in cardiac study is in the?
AA but at St. Luke's DA to prevent ROI trigger from streaking
what is 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/seen smaller pixels = better image resolution random chance plays role in whether small object will be seen on recon
effective dose
Attempts to account for the effects particular to the patient's tissue that has absorbed the radiation dose The dose to patients is reported in rads or centigray (cGy)
What is a subarachnoid hemorrhage?
Blood escapes from defective or injured vasculature into the subarachnoid space increased density in cisterns and ventricles CT is approximately 85 percent accurate in demonstrating this if within 24 hrs
number one cause of disease in americans?
Coronary artery disease
Parameters that can be change retrospectively are
DFOV Image center Reconstruction algorithm Slice incrementation (on helical data only) Image thickness (on MDCT systems only)
To reformat a CT study all the source images must have identical
DFOV, image center, gantry tilt, no gaps (DING!)
normal concentration barium used in GI Exams?
Dilute Barium solution of 1-3%
Roentgen Equivalent Man (REM)
Dosage in rads that will cause same amount of biological injury as 1 rad of x-rays takes radiation type and radiosenstivity in account 100 rems = 1 sV
Glucose is usually not excreted by the kidneys while
FDG is excreted by the kidneys
Temporal resolution is determined by?
Frame rate or how rapidly data is acquired controlled by rotation speed, num of detectors, speed of systems
to improve contrast
Higher mAs Thicker slices Smaller patients Larger pixels (large FOV and small matrix) Smoothing filters aka things that reduce spat resolution
MSAD=
MSAD = CTDI x (slice thickness / table movement or incrementation) ratio of slice width to slice spacing multiplied by CTDI
are body scans higher dose than head scans?
NO central dose of body scans are 1/3rd to 1/2 of that peripheral dose while head dose are pretty much uniform i.e. center of brain gets as much as outer skin dose 4.0 rad (brain) vs 1.2 rad (spine)
what are stochastic effects?
No threshold. As dose increases, probability of occurrence increases but the severity does not. no risk free dose.Think about cancer risk with radiation
in CT noise is?
Noise is the undesirable fluctuation of pixel values in an image of homogeneous material "salt-and-pepper" look The presence of noise on an image degrades its quality things that increase spat resolution will make noise more apparent, things that improve contrast will decrease noise.
volume averaging? how to reduce this effect
Process by which different tissue attenuation values are averaged to produce one less accurate pixel reading. Also referred to as partial volume effect. decrease slice thickness
What does a positive D-Dimer mean?
Pt must be ruled out for PE; there is a blood clot somewhere. Pt must receive a CTA Chest or VQ scan
describe liver cysts
ROi for density, cyst has clear borders
Factors Affecting Dose
Radiation beam geometry Filtration Detector efficiency Slice width and spacing Pitch Scan field diameter (SFOV) Radiographic technique (i.e., mAs and kVp) Patient size and body part thickness Repeat scans Collimation
what is CTDI?
Radiation dose that is normalized to the width of the beam. Based on a phantom for single slice dose. report to FDA
which exams do not need IV contrast, why?
Renal Stone Study • Spine workups including C, T and L‐spine • Extremity work (i.e. ankles, knees, wrists, etc.) • Patients who are in renal failure* (and are not on dialysis) • Chest High Resolution (i.e. interstitial lung disease, pulmonary fibrosis, bronchiectasis‐‐typically ordered by pulmonologist) • General brain screening • General sinus, orbit or maxillofacial imaging * patients where renal function is in question need a referral for BUN/ creatinine, within last 30 days, please! appendicitis
what is surface rendering?
SR includes only information from the surface of an object
T or F: Many parameters can be changed in retrospective reconstruction, but the images that result are always in the same plane and the same orientation as were the original images
TRUE
what is spatial resolution?
The ability to distinguish two separate objects close together
What is the isocenter?
The intersection of the axis of rotation of ... - gantry - collimator - couch best is place patient here
what is a partial volume artifact?
The result of averaging the linear attenuation coefficient in a voxel that is heterogeneous in composition tl;dr more than one type of tissue/density contained within voxel
what are deterministic effects/threshold?
The severity (not probability) of the effects increase with the increase in dose kind of guarantee effect at certain thresholds cataracts, SE, epilation, pericarditis
what is partial volume averaging? why does it happen? how is it reduced?
Two or more tissue types contained in one pixel can give ROI reading of (average) pixel values (wrong CT numbers) scanner can't tell difference between similar density objects/tissue the computer tries to average out the two densities and information is lost ex: you know there is the claustrum is there but CT just shows one similar grey blob USE THINNER SLICES
endoluminal imaging/VR imaging?
VR, perspecting volume rendering or virtual endoscopy, look at lumens gr8 4 virtual colonoscopy or colonography, air fills inside colon, evaluate airways with bronchoscope can also eval bile duct or pancreas or inner ear
DLP formula?
Volume CTDI * Scan length scan length = slice thickness x number of slices
best window level and width for abd pel soft tissue?
W:400 L:50
Roentgen
a measure of radiation in air
give a cupping artifact example?
a skull shows lighter at edge and darker center. dark bands or streaks between dense objects in the image
Quality Factor
accounts for diff types of ionizing radiation xray = 1
reduce dose in CT
add filtration, low mAs high kv, long slices, not doing smalls scans or smaller body parts, smaller pitch, repeats
what is tube arcing?
aka high voltage arcing it is an unwanted surge of electrical current (ie a short circuit)
avid uses which two things to measure differneces?
aorta and vena cava
what are edge enhancement artifacts?
appear as bright streaks caused by too different density structures with irregularly shaped structures errors in recon process most commonly seen where bone and soft tissue and air meet fix: reposition patient and obtain thinner slices or use water a contrast
SFOV determines? dfov...
area where raw data acquired dfov only determines how much raw data used for an image
what is ATCM?
auto tube current modulation adjust mAs to fit the specific anatomy region like AEC
spine protocols
axial 3mm or less parallel to disk space 12-15 cm dfov
what do you use to lower heart rate for CTAs?
b blockers (lower rate to 65-70 BPM) may use nitro to improve by dilation of vessels
Phantom measurement of the uniformity of a CT system is performed primarily to assess the negative effects of:
beam hardening aka cupping
most common issue with biospy overall vs lung biospy?
bleeding; pneumo
What is a epidural hematoma?
blood between the dura and the skull. a brisk epidural hematoma may almost develop instantly and show symptoms. convex football shape
inner ear bones would need a ________________ filter to be clearer
bone
best window level and width for bone?
bone W:1800 L:400
Normal increased accumulation of FDG occurs in:
brain, muscles, salivary glands, myocardium, GI tract, urinary tract, brown adipose tissue, thyroid gland, and gonadal tissues
water may be used to define the _________ and head of pancreas
c loop
what is the spiral artifacts?
caused by interpolation and recon results in inaccurate CT number and can lead to misdiagnoses LOWER PITCH BITC
describe cirrhosis?
characterized by the persistent scarring of liver tissue, you can't recover, occurs in 10-20% of heavy drinkers that drink for a long time, you will only survive if you have a liver transplant, interferes with all functions of the liver ascites is common
why use saline in CTA?
chases contrast and reduces SVC streaking
thymus uptake is
children's uptake is higher than adults, in adults its higher post chemo or rad therapy
what is a good avg CT number of water?
closest to 0 +- 3 or max of +-5 test said +-4
large pixels in recon have a tendency of...
combining finer details, lowering quality overall smaller pixels can display two distinct shapes adjacent to each other better
neck is most commonly done with?
contrast demonstrates, AV, submandibular glands, parotid glands, etc
how is one way to measure low contrast resolution?
contrast phantom it contains objects of varying sizes and with a small difference in density from the background.
phases of kidney
corticomedullary - 30-40 sec nephrogram - 100-120 sec excretory - 3-5 mins
what makes the F-18 radionuclide?
cyclotron
how often are water number tests performed?
daily
describe metastatic liver disease?
dark spots on liver, MOST COMMONLY FROM COLON migration
how do you change image thickness?
data from parallel rows of detectors can combine to create thicker slices for viewing or storing
reducing noise will improve contrast but may ______________ spatial resolution
decrease
pixel size (mm) formular
dfov/matrix size
what is a good contrast resolution amount in phantom testing? how often tested?
different mAs settings used to determine different density but distinct objects. the more seen, the better. min: 0.5% min difference in 5mm object OR LESS than 1% diff (easy to remember) monthly
pitch formular
distance traveled in rotation divided by slice thickness/beam collimation
If table movement is greater than slice thickness,
dose DECREASES
what is DLP?
dose of entire scan length
liver phases
early arterial (15-25 sec) venous (60-70 sec) equilibrium (2-3 min) delayed hemangioma(10-20 min)
how does food or water affect F-18-FDG
eating food before exam can increase insulin (insulin must be taken as far away from test) water can promote excretion of radionuclide
what is caused mainly from fx at temporal bone of middle meningeal artery, looks bright convex blister shape? do not pass suture lines either
epidural hematoma
which phase is worse for liver?
equilibrium phase
larygneal uptake can vary based on
excessive talking
what induces uptake into skeletal muscles
exercise, stress/tension of muscles, hyperventilation normal = symmetric
what is sagittal head scans for?
facial images, temporal bones, sinuses, midline structures
area of rad exposure in CT?
figure 8 shaped lowest is plane of gantry and oustide donut
how does CT combat beam hardening?
filtration, calibration, software algos, water phantom testing
what trimester is most vulnerable for fetus
first they developing organs and neural stuff
what do you need for rad therapy in CT planning?
flat table, larger gantry, immobile devices
thicker slices need more...
flattening, produce less sharp images
what is head coronal scans for?
floor, roof of orbit, skull base, ossicles, medial wall of middle ear oval window, and lateral semi canal, surgical planning
abcess appearance on CT?
fluid collection with debris, definable walls, air fluid/air bubbles
what captures the gamma rays? what happens to the gamma?
gamma cameras converted in light energy by crystals both 511 kEv must be collected at same time, called COINCIDENCE DETECTION
quality of reformations depend on
good high quality thin slices of axial cuts
overlapping recons can be changed on ______________ data from either SDCT or MDCT
helical
what is most common primary mass in the eye's orbit?
hemangioma it look gray
liver blood supply proportion (in %)
hepatic artery and hepatic portal vein 25 percent arterial. 75 percent venous
reproductive uptake
higher in ovulation, menstruation, postmenopausal (means malignancy),
how does mAs affect quality of scans?
higher mAs allows for shorter scans, shorter scans = less chance of motion also higher mAs means less image noise/grainy-ness
ICH (intracerebral hemmorhage) will look ______________ to normal brain tissue for the first 3 days
hyperdense
what kind of data is used to generate images in different plane or orientation?
image data
when voxels of images are isotrophic (same in x,y, and z plane) there is no loss of
image quality in the new plane
what are ring artifacts, what creates it?
imperfect detector elements, commonly seen in 3rd gen scanners
how to increase elimination go FDG
increase hydration, dieuretics
bone marrow uptake
increased after chemo
breast uptake
increased in nipples, dense breasts, on hormones, lactating women
gray air
international unit for air
gray tissue
international unit for tissue 100 rad = 1 Gy
what is mostly from CVAs and aneurysms that bleed into ventricles or tissue?
intracerebral hemorrhage
what are edge gradient artifacts in the liver?
irregular shading in left lobe caused by edge gradient and beam hardening arise from differing densities in nearby stomach
SNR is
is an expression of the desired signal to the background higher = better 100000000000:1 for ex.
total dose
is from the radiation to the selected slice and from scatter radiation, or "tails," from neighboring slices tails will contribute approximately 25-40 percent of total dose
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 lets see thru both internal and surface structions, uses all data from 3d
best detail image =
largest matrix + SMALLEST fov
What improves signal-to-noise ratio?
less grainy ness on image increasing section width/bigger aperture, increasing mAs, smaller patients, bigger pixels/smaller matrix size aka things that improves contrast
what is the physical way of measuring spatial resolution
line pair phantom scanned, then visible strips counted
what are 2 ways of measuring spatial resolution?
line pairs phantom MTF in data analysis - graphically represents system's performance
overexposure has ______________ in digital imaging (due to software correction) but not __________________ which leads to quantum noise
little affect ; underexposure
organs doses are higher for ___________ people than __________________ people
little; larger
best window level and width for liver?
liver W:150 L:30
greater pitch results in
loss of quality
when sequential CT or CTF is used, set mAs to
lowest possible
what is HRCT needed for?
lung parenchyma, high detailed lung prone supine
radiation dose is most affected by...
mAs mAs more flexible, and affect on image quality more visible/predictable
normal increased uptake occurs in
main 4 for test though: cecum, left ventricle, bladder, stomach BLS+C
what is the point of using thin slices for scanning and reconning thicker slices?
maintain high resolution thin slice imaging and create image files that are manager and more easily reviewed by radiologists
factors that affect spatial resolution
matrix size, dfov, pixel size, slice thicc, recon algorithims, focal spot size, pitch, motion
what is MIP?
maximum intensity projection selects voxels with highest value to display best for bone and contrast filled studies
what is temporal resolution in cardiac imaging?
measure of data acquisition for one image
who measures dose and how is it done in CT?
medical physicist used standard head and body CTDI phantoms and pencil ionizing chamber
what is most common benign intracranial tumors? they also arise from dura adjacent to inner table of skull?
meningiomas
what does the combo of PET and Ct give you?
metabolic detail and anatomic detail
what is minIP?
min intensity projection lowest value voxels to display, good for bronchial tree
how often are line pair phantoms used to test spatial resolution? what is a good minimum resolution
monthly up to manufacturer
higher accumulation of FDG means?
more aggro tumors
what is MSAD?
multiple scan average dose, uses CTDI to calculate an average dose in middle o series of CT scans ratio of slice width to slice spacing multiplied by CTDI
use _____________ window widths for the brain and liver
narrow typically 150 WW 50 WL
does kV affect CT as much as xray?
no there are more limited selections 120 is common
normal aorta diameter (cm)?
no more than 3 cm in diameter
normal appendix
not be detected, fill with oral contrast/air, <6 mm in diameter, no associated inflammation acute appendicitis will show as a dilated non opacified appendix
where do cone beam effects occur?
only in MDCT helical MDCT may experience windmill artifacts, caused by cone beams, aka streaks or bright shades near area of large density differences, worse in outer detectors - fixed with cone beam algos
what artifact is SIMILAR to metallic but is caused by anatomy that shouldn't be in the SFOV but is in it?
out of field artifacts
thicker the slice the better the ___________ recons
overlapping recons
how should slices be for head to reduce exposure to the lens?
parallel to supraorbital meatal line aka ABOVE upper eye border
who can do PET CT?
people who have ARRT or NMTCB license
how are the lasers calibrated? how often is it done
phantom used laser to match radiation field within 2mm done semi annally
mSAD is equal to CTDI if
pitch is equal to 1
MSAD is less that CTDI if
pitch is greater than 1
MSAD is greater than CTDI if
pitch is less than 1
matrix and dfov determine
pixel size
positioning needed for virtual colonoscopy?
prone and supine
cardiac scanning is made possible by?
rapid scanning, thin slices, ECG, 5th gen EBCT
how does MTF work?
ratio of the accuracy of the image compared to actual object scanned scale: 0-1 1 being perfect, curve father to right has higher resolution
Algorithm is only applied to
raw data
ways to reduce image noise
reduce scatter, increase slice thickness, increase pixel size, more mAs, smaller matrix aka things that lower spat resolution/quality
describe fatty liver disease?
reduced attentuation (10 HU less than spleen), best seen on noncontrast
what is cupping? where is it best tested?
reduction in CT number toward middle of a uniform test object water phantoms
what is the linearity test?
relationship between CT num and linear attenuation values of scanned object at certain kVps test look similar to water number test except known density of objects (like bone or fat or muscle) are placed throughout the phantom daily calibrations to help avoid changes done semiannally
what is Region of Interest editing?
removes obscuring structures from 3d image can be auto or involve drawing around structure to be saved or discarded
most exams except for finding _________ stones need IV contrast
renal
when you use drip infusion for iv?
routine brain scans, metastasis, brain tumors but not super useful due to images looking like delayed phase
how to obtain pancreas when regular scans fail?
rt decube, oral CM
Which of the following technical factor(s) play(s) a role in the production of an isotropic data set?
section width, dfov
what does Pulmonary emboli look like?
seen as filling defects in pulmonary arteries
contrast resolution is aka
sensitivity
The smaller the focal spot, the ___ the image.
sharper
hemangiomas on CT?
sharply defined masses on same density as vessels on non contrast and contrast images. extra growth of blood vessels ie enhancement as bright as aorta in arterial phase
how does slice thickness affect image quality?
short thicknesses produce higher quality images
thin slices may improve resolution but derease...
signal to noise ratio and more noise = lower contrast
narrow, or high contrast, can more easily distinguish _______ density lesions
similar density lesions
The ability of a CT scanner to image a small high-density object is controlled by the __________ of the scanner
spatial resolution
what is benign tumors with thickening and sclerosis of sphenoid wing?
sphenoid wing meningioma it looks white
barium for stomach, abd, abd/pel
stomach: 300ml prior abd: 300ml 2 hours prior and 300 at exam abd/pel: 300 ml night before or at least 6 hrs 300 ml 2 hours prior and 300 ml at exam (TEST said only 600 needed???) rectal: 150-200 ml
what do metallic artifacts look like?
streaks or bands of light or lines
what is bleeding between dura and brain tissue that is cause more from chronic symptoms than fx? may cross a suture line but not more than one hemisphere? its more linear shaped
subdural hematoma
who shares responsibility for QA?
tech and medical physicists
what does isotropic mean in relation to voxels?
the image is the same in x,y,z plane. there is no loss of quality in the new plane
what is peaking?
the increasing of CT number toward the middle of a uniform test
absorbed dose
the radiation energy absorbed per unit mass of an organ or tissue and is used in studies of the damage to a particular organ or tissue
protocol for temporal bones?
thin 1-2mm bone axial and coronal
orbit protocols
thin 3mm axial, cor, sag
best way to diagnose appendicitis?
thin sections >5mm can use oral, rectal, IV, OR EVEN NO contrast material
what is aliasing?
too great of pitch makes inadequate number of projections. inadequate amount of data/info from projections fixed with reducing pitch and slowing gantry speed
if you are looking for metastatic disease in a chest scan, start _______ and end?
top of apices to adrenals
pelvis scans start where and end?
top of crest to pubic symphysis
why use glucose with F-18-FDG radionuclide?
tumors take up glucose at 10x
as SFOV and patient thickness increase
uniformity of dose decreases Less dose for pt/area
what is an issue with mip?
unless depth cues are given, 3d not exactly on point generates bead string artifax
to view inner ear ____________________ plane
use coronal
how to reduce beam hardening effects in the skull?
use thinner slices
what is best way to get correct CT number?
use z-sensitivity that is equal or smaller than features in scan
what is MPR?
using image data to create a view in different body plane
how is slice thickness tested? how often is it done?
using ramp, spiral, or step wedge that contained marked measurements along it it should match the slice of scanner, with no more -+1 difference with 5mm thickness for example if >5mm it should be +- 0.5 mm deviation semi annally
face and neck uptake of radionuclides can be
variable due to surgery, rad therapy, look variable, chewing, teeth clenching,
myocardium uptake is
variable from patient to patient left ventricle most common increased in uptake
GI uptake
variable, but higher in larger bowel (cecum), patients with IBS, under 60 YO
how are noise and cross uniformity tested? how often?
water phantom ROI deviation should not exceed 10 uniformity tests ensure each area of phantom's perimeter (north south east west) matches with no more than +- 2 from the center daily?
why use SUV?
when you cant use qualitive measures (areas look the same) use SUV to measure relative number of radionuclides in tissue
