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