S1_L2_MSKI - 1-4 Flashcards by Andre Neri Valencia

who discovered CT

Godfrey Hounsfield

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godfrey hounsfield’s CT was based on _

Work was based on Alan Cornack’s mathematical formulas for reconstruction of images for digital signals

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t or f First scanners were dedicated to scanning the head

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Primary purpose of CT was for _

imaging of the brain

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what year when godfrey divocered CT

1972

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Whole body scan was possible. in what year

1976

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Hounsfield was awarded Nobel Prize in Medicine in _

1979

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Hounsfield was awarded_in 1979

Nobel Prize in Medicine

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t or f CT scan has different imaging principles as conventional radiography

f, Same imaging principles as conventional radiography

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X-rays are _ by body tissues

attenuated

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Radiodensities of the body tissues are represented in the image as shades of _

gray

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_ of the body tissues are represented in the image as shades of gray

Radiodensities

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CT creates images based on _(axial) slices, created by up to
_ projections
from different angles, unlike X-rays

cross-sectional, 1000 projections

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3 ELEMENTS OF CT SCAN

GANTRY
OPERATOR’S CONSOLE
COMPUTERS

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Into which the patient slides during the examination

GANTRY

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gantry parts:

X-ray tube and the high-voltage generator
● Collimator Assembly
Detector Array
Data Acquisition

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employs a high-intensity x-ray tube in order to provide uniform penetration of
the tissues and reduce attenuation

X-ray tube and the high-voltage generato

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Aperture through which xrays pass

● Collimator Assembly

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Controls radiation center

Collimator Assembly

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Creates a narrow fan-shaped beam of
x-rays

Collimator Assembly

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collimator assembly creates __ beam of xrays

narrow fan shaped

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Measures the remnant radiation

● Detector Array

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what determines the slice thickness

Collimator Assembly

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Opposite X-Ray tube

● Detector Array

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Up to how many detectors are arranged in an array, encircling the patient

1000

Amplifies signal from the detectors in the form of varying electrical current = analog signal

● Data Acquisition

varying electrical current is called

analog signal

Will later on be converted into digital for an image to be seen in the computer

● Data Acquisition

Converts analog to digital form

computer (data acquisition)

CT tech controls scanning process, selects slice thickness, reconstruction algorithms (post-processing), and other specs

OPERATOR’S CONSOLE

Transforms radiant energy to something we are able to see

COMPUTERS

computers transform __ to somewthing we are able to see

radiant energy

MAKING THE CT IMAGE (2)

SCREENING PROCESS DATA CONVERSION

Where transduction occurs

SCREENING PROCESS

2 Dimensional digital radiograph

SCOUT IMAGE

X-ray tube moves circumferentially around patient to get a “slice”

CT SCANNING

Will revolve _ degrees in the gantry

360

● Table moved for a new “slice” in what cuts for ct scanning

axial

movement of the tabletop is referred to in terms of _

pitch

○ CT scan will revolve, stop, move, and go.

● Stop-and-go action

t or f For modern scanners they move continuously during the exam process

Modern scanners move continuously during the examination process -> what slices

helical

While the x-ray beam is moving around, _continuously goes on

scanning process

DATA CONVERSION (3)

matrix image post processing

Radiodensities are converting by the computer into a _

matrix

Each cell of the matrix is a _ (picture element).

pixel

Each pixel is assigned a shade of _, which represents the _ of that cell of the matrix, expressed in terms of _ units.

gray, radiodensity, hounsfiel

Matrix becomes an _ using a mathematical process called

image, “back projection”

the image of ct scan will perform what cuts

sagittal or coronal cuts

Image can be manipulated in the computer’s software

POST PROCESSSING

Improving contrast in __

post porcessing

Modifying the window can be done in _

post processing

DIFFERENT FORMS OF CT

THREE-DIMENSIONAL CT CT MYELOGRAM CONE BEAM CT

Multiplanar reconstruction

THREE-DIMENSIONAL CT

Imaged part can be rotated “in space” on the computer screen

THREE-DIMENSIONAL CT

Invasive in nature -> inject a contrast

ct myelogram

Media into the subarachnoid space

ct myelogram

_ is better able to distinguish between osteophytes, ligament infolding, and annular material than is MRI.

CT myelography

ct myelography is better able to distinguish between _, _, and _ than is MRI.

osteophytes, ligament infolding, annular material

Best viewed in digital format than on printed forma

THREE-DIMENSIONAL CT

t or f You can print out 3d images, but can’t be manipulated

in ct myelgram, where will you inject the media

subarachnoid space

Acquires all the data in a single sweep of the scanner

CONE BEAM CT

is not constructed from a large number of slices but rather based on one volume of data.

CBCT scanner

cone beam ct is used mostly in _

drentistry

Uses a large, cone-shaped x-ray beam matched with a flat-panel detector

cone beam ct

cone beam ct is for imaging of the _

breast

○ For breast cancer detection ○ To check for malignant cells

cone beam ct

Tissues will have differing _ represented by different shades of _

radiodensities, gray

Dense structure in CT = what color

white or light shade of gray

Less dense in CT, what color

dark

tracheas and epiglottis will appear what color in CT

black

t or f Cortical bone is more dense than cancellous bone

cancellous bone sanwiched between cortical is called

flat bone

For axial cuts/images, images are viewed in a __

caudo-cephalad manner

For sagittal cuts, images are viewed from _

left to right

t or f Viewing adjacent slices may help orient you with the anatomy

in viewing ct images, concentrate only on 1 area t or f

CT scan slices are identified in terms of _ that correspond to _

slice numbers, scout images

_ appears as a small locator image inserted into the image for each slice (left uppermost corner)

Scout image

Selecting the range of radiodensities displayed in an image

WINDOWING

t or f CT is inable to choose the range of radiodensities displayed

f, CT has the ability to choose the range of radiodensities displayed

a CT image made for the purpose of viewing musculature, soft tissues, or viscera

Soft tissue window

CT image for viewing of the bone

Bone window

Slice thickness for _ CT can vary from 0.5 to 2 mm (for small joints) to 2 to 3 mm (for the pelvis)

musculoskeltal CT

Slice thickness for musculoskeletal CT can vary from _(for small joints) to _ (for the pelvis)

0.5 to 2 mm, 2 to 3 mm

0.5 to 2 mm is for _

small joints

2 to 3 mm is for

pelvis

Thinner slices are typically used in areas of_

rapidly changing anatomy

Smaller bones or joints can be missed in _ slices

thicker

CLINICAL USES OF CT SCAN

● Subtle fractures and/or complex fractures Degenerative changes (spinal arthritic changes), spinal stenosis especially with CT myelography Serious trauma since multiple injuries to both osseous and soft tissue structures can be determined IV disc conditions when combined with diskograms Best for evaluation of loose bodies in a joint Less time-consuming than MRI or UTZ Accurate measurement of osseous alignment Less expensive than MRI Less problematic for claustrophobic patients

Comminuted fx: better seen with _

CT Scan

_ are like myelograms, you inject the contrast to the disc.

Diskograms

ct scan is best for evaluation of __

loose bodies in a joint

UTZ is also fast, but it is _

operator-dependent.

MRI only takes _

45 mins - 1 hr long

At present, CT is the modality of choice for detailed imaging of _ _

cortical and trabecular bone.

Limited capability for determining the histological makeup of tissues for _

ct scan

Different tissues may have the similar _ = difficult to differentiate tissues

radiodensity

High radiation exposure (1000 projections) for MRI t or f

f, ct