CT 1-2

the number of x-rays detected by each detector

what is the CT quantum mottle directly related to?

describes the noise resulting from the finite number of x-rays used to make an exposure

what is the quantum mottle in x-ray?

computerized axial tomography

define CAT

computed tomography

define CT

x-rays that pass through patients body

what does CT measure?

computer to perform complex mathematics

what is needed to make CT into images?

x-ray tube produced a thin, focused beam of x-rays (pencil beam) that passed through a single detector, moved across the patient at 1 degree and 5 min/image

describe the first CT scanner

fan beam (x-ray beam shaped like paper fan) with multiple detectors in a straight line, moved across the patient at 5 degree angle and about 20 sec/image

describe 2nd generation scanner

fan beam with multiple detectors along a curve, tube and curved array of detectors rotate around the patient, and 1 sec/image

describe 3rd generation scanner

fan beam with multiple detectors encircle patient, tube rotates around patient, and < 1 sec/image

describe 4th generation scanner

1st generation (parallel beam)

this shows what type of CT scanner?

2nd generation (fan beam)

this shows what type of CT scanner?

3rd generation (fan beam rotate only)

this shows what type of CT scanner?

4th generation (fan beam stationary circular detector)

this shows what type of CT scanner?

reduced time required for exam and increases clinical applications

why were continuous rotation scanners a good development?

allows for continuous rotation of x-ray tube assembly

what is a slip ring?

slip rings

what is the reason for rotation speed?

slip rings

why dont we need power and data cables for 4th generation scanners?

stationary metal contacts through which electrical signals and power are transferred to and from the rotating slip ring

what are electrical brushes?

eletrical brushes

what is in the image?

collects info from multiple anatomical slices in each rotation of the x-ray tube

what is a multi-row scanner?

more anatomical coverage in less time

why are multi-row scanners better than single?

MDCT or MSCT (parallel or 3rd gen)

what detectors can be multi-row?

x-ray beam shape similar to a cone that spreads out like a fan along the table

describe cone beam

cone

what type of beam is now standard?

Electron beam CT; scanner that has no x-ray tube allowing it to have fast scan time

what is EBCT?

cardiac and coronary artery imaging

what is EBCT good for imaging?

when the electron beam strikes the anode

how is an x-ray beam generated on an EBCT?

a fusion of PET and CT image

what is PET/CT

attenuation correction and anatomical clearity

why do we do PET/CT?

size and spacing of detectors

size of focal point

reconstruction filters

what are factors contributing to spatial resolution of a CT?

with small bars of acrylic and then imaged

how is CT spatial resolution checked?

mA

what effects image contrast most?

images slice thickness

spatial resolution

linearity of CT numbers

high and low contrast

what does monthly/quarterly CT phantom do?

verification of tube output and detector response at different kVp and mA settings

what does a CT warm up do?

tube warm-ups

fast calibrations

CT phantom

what QC must be done for CT

1000

what is bone hounsfield unit?

-1000

what is air housfield unit?

0

what is water hounsfield unit?

1000 * (Uij-Uwater/Uwater)

Hu =

tissue attenuation values

what do hounsfield units express?

mA

what increases contrast resolution

slice thickness

rotation speed

table motion

what decreases patient dose?

mA and kVp

what increases patient radiation dose?

kVp, mA, slice thickness, more x-rays per detector, increase beam intensity, decrease pitch

what decreases CT noise?

30-150 kV

what is average kVp range?

50-400 mA

what is average mA range?

helical ro spiral; multislice

what types of CTs have pitch? which have beam pitch?

table moves 2 mm every 1 mm of detector width

what is implied with a collimator pitch of 2

increase number of x-rays at each energy level

what does higher mA values do?

right, more

as kVp gets higher it stretches the energy spectrum to the ______ (left, right) by generating ______ (less, more) higher energy x-rays

energy transferred to x-ray in bremsstrahlung interaction

define kVp

step and shoot for the heart

what is multi-slab axial?

full circle around a small region of interest

what is axial scanning

full circle but scanner moves continuously

what is helical scanning?

ceramic material

cadmium tungstate

bismuth germinate

what can CT detectors be made out of?

50-150 kV

at what kV are electrons accelerated toward the anode?

causes it to release electrons via thermionic emissions

why does the filament circuit need to be heated?

heating the filament wire from electrical resistance

what does the activation of a cathode filament circuit cause?

no, stationary usually

do the brushes move with the slip rings

each ring is electronically conductive and provides circuit path over 360 degrees of rotation and has electrical contact with brushes between the rotating rings

describe the arangement of slip rings

electrical swivel

what is another name for slip ring

measured x-ray photon information that must be processed/ reconstructed to form CT images

what is CT raw data?

by absorption (never leave body) or scattering (interact with structures and change direction)

what are 2 ways x-ray photons are attenuated

reduction in the number of photons in the x-ray beam as it passes throguh the tissues in patients body

define attenuation

bremsstrahlung radiation

how are majority of x-rays produced?

x-ray produced as a result of an electron colliding with or passing near nucleus of an atom

define bremsstrahlung

x-ray produced as a result of an electron in target replacing one ejected by a fast moving incoming electron

define characteristic radiation

electron in target is kicked out, another electron of target atom moves into that location and releases excess energy (x-ray)

what happens if the electron collides with an electron?

directly collide with nucleus

come near nucleus

collides with another electron

what are some ways the electron can interact with the target?

tungsten becasue has high number of electrons (high atomic number) and very high melting point

what is a CT target made out of and why?

electrons are accelerated at very high speeds towards a target

how does a CT work?

traumas and evaluate extent of damage

what are some reasons to CT orthopedic?

kidney stones, blockages, abnormal growths

what are some reasons to CT the urinary tract?

cysts, abscesses, infection, bleeding, tumors, aneurysms, diverticulitis, appendicitis,

what are some reasons to CT the abdomen?

infections, cancer, PE, aneurysms, cardiac, coronary artery

what are some reasons to CT the chest?

see facial bones and sinuses

what are some reasons to CT the head?

there isnt one federally

what is the CT dose limit?

x-rays indirectly produce ion pairs in tissues as they pass through which can interact with chemical systems in the body causing DNA damage

what is x-ray damage?

cause detrimental changes in the atoms and molecular processes

what can ionizing radiation do to the body?

ionizing radiation

what is the disadvantage of CT?

easily stored

accurately reproduced from stored data

electronically transferred to another facility

easily manipulated and processed

what are the advantages of digital information?

information expressed in a continous fashion

define analog

information expressed in terms of discrete numbers

define digital

< 0.5%

what percentage can a CT differentiate density differences?

differentiate tissues in body from each other

what is the greatest advantage of a CT?

axial

all slices are considered

perpendicular to axis which travels from anterior to posterior in patient

what are coronal slices

perpendicular to the axis which travels from left to right in the patient

what are sagittal slices?

perpendicular to the axis which travels from head to foot in patient

what are transverse slices?

sections made by cutting anything at right angles to any axis

what are cross sections?wh

linear accelerator treatment table

what type of table is used for radiation therapy?

oncology to verify patient positioning prior to receiving radiation therapy

what is cone beam most commonly used for?