CT Scan
Ct can distinguish between density differences of less than
.5 %
CT can distinguish between density differences of less than
0.5%
Ct demonstrates bone better than
MRI
pt with metal in their bodies can not be scanned in
MRI
water is reference bc
abundant in body and has uniform density
computer uses to compile and calculate data
algorithm
xray tube --> detector assembly--> primary data-->
algorithm-->matrix-->axial image on CRT
values are converted to
an electrical signal
in the body the point of reference is
anatomical position
opening in the center of the gantry
aperture
pt table advances through
aperture
Dental fillings or a pacemaker can cause
artifact
computer assembles data into matrix to form
axial image
name the different planes
axial/horizontal/transverse, sagittal, coronal
the most frequently used section in imaging modalities
axial/transverse/horizontal plane
volume ct can image
entire body sections on single breathe holding
amount of data displayed on a monitor
field of view
spatial resolution is affected by
focal spot size, slice thickness, FOV, matrix
circular device that houses the xray tube
gantry
circular device that houses the xray tube,data axquisition system and detector array
gantry
CT was first categorized as
generations, now their by tube and detector movement
who developed CT
godfrey Hounsfield and allan Cormack in 1970
CT is examination of choice for
head trauma
2 types of strokes
hemmorhagic and ischemic stroke
hemorrhagic stroke =
hemorrhage/ blood leaks into the brain
water is a reference bc
it is abundant in the body and has uniform density
+ noise =
less contrast resolution
this describes the amount of blurring on an image and how accurately objects can be differentiated
spatial resolution
name the four main quality factors
spatial resolution, contrast resolution, noise and artifact
CT angiography is an application of
spiral CT
dental fillings, pace makers and artificial joints can cause
streak artifact
automated device linked to computer and gantry
table
Negative Ct numbers
tissue with less density than water
positive CT numbers
tissues that are denser than water
t or f A pt with a pacemaker can have a CT scan
true
in 1973
united states first Ct in mayo clinic
latest technology is
volume CT
voxel is
volume element of the matrix, product of pixel area abd slice thickness
volume of tissue, product of pixel area and slice thickness
voxel
greater shades of gray, longer scale contrast
wide window
midpoint of the gray range ,controls image brightness
window level
A range of CT numbers used to map signals into shades of gray
window width
establishes the number of gray levels displayed
window width
range of CT numbers used to map signals into shades of gray
window width
technique that allows the contrast of image to be altered
windowing
CT numbers are a relative comparison of
xray attenuation of a voxel of tissue with an equal volume of water
ct number of water
zero
t or f An arterial puncture is made for CT
False
t or f First units were dedicated head scanners
TRue
scale ranges from
-1000 air and + 3000 dense bone
value of each number is directly proportional to
signal strength
CT dose is _____ dependent
size (child/adult:brain/abdomen)
four main quality factors
spatial res, contrast res, noise and artifact
t or f Both 3rd and 4th designs used today
True
first generation had how many detectors
1 to 3, limited to brain, 3 to 5 min per slice
conventional radiography needs how much difference between densities
10%
fourth generation
1000 detector, 1 to 10 sec per slice
1st brain tissue scanner was in
1971
the whole body CT was developed in
1974
aperature is about how wide
28 inches
second generation had how many detectors
30 detectors, 20 sec per slice
table weight limits very from
300 to 600 lbs ( 136 to 272 kilograms)
volume ct has rows of elemts in the detector arrays
64
third generation scanner
750 to 950 detectors, 1 to 10 sec per slice
useful for diagnosing
CNS disorders
MRI demonstrates soft tissue better than
CT
allows visualization of vascular system in three dimensions
CT angiography
does not require arterial puncture and eliminates overlying anatomy
CT angiography
this Ct obtains lg amount of data in a short time and scans volume of tissue not individual
Spiral/Helical CT
cradle is used for
brain CT
VCT rapidly growing for
cardiac imaging
the process of creating a cross sectional tomographic plane of the body
computed tomography
3 major components of CT
computer and operating console, gantry and patient table
contraindications to CT
contrast allergies,pregnancy,diabetes,renal failure and multiple myeloma
ability to differentiate between small density differences
contrast resolution
the ability to differentiate between small density differences
contrast resolution
holds the head still and a positioning aide
cradle
the assigned number that is related to the linear attenuation coefficient of the tissue within each voxel
ct number
this sends information, or primary data to computer
detector assembly
measures exit radiation, converts it to electrical signal and sends to computer
detectors
measures the amount of radiation transmitted through the body and also converts this into proportional electrical signal
detectors
measures the radiation that exits the patient
detectors
where is CT image viewed in a gray scale image
display monitor
based on principal that structures enhance at different rates after contrast administration
dynamic scanning
based on the principle that structures enhance at different rates after contrast administration
dynamic scanning
amount of blurring detail and sharpness
spatial resolution
an array of numbers in a grid of rows and colums
matrix
digital image is displayed in a
matrix
specific sagittal plane that passes through the midline is
midsagittal ( all others are parasagittal)
advantages of spiral/helical CT
motion minimized,detects small lesions,useful for uncooperative patients and decrease amount of contrast
fewer shades of gray or high contrast
narrow window
caused most common by quantum noise
noise
this gives an image a grainy quality or mottle appearance
noise
point from which the tech controls the scanner
operators console
single square or picture element within a matrix
pixel
noisy CT scan is
pixely
2 forms of dynamic scanning
rapid sequential and incremental dynamic
incremental dynamic is
rapid serial scanning at consecutive levels
measured xray transmission values
raw data
rapid sequential is at
same level