Download RT 255 C Cross Sectional Anatomy

RT 255 C
Cross Sectional Anatomy
Week 1
FINAL
4-13-09
1
Name the Sectional Planes
A
B
C
D
2
Oblique and Transverse
Used for imaging of heart.
Commonly used in MR and sonography
3
Axial (Transverse) Planes
–1
–2
–3
–4
–5
–6
4
Axial Scout
5
6
Axial (cross sectional)
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Sagittal Plane
• 1
• 2
• 3
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Sagittal Scout
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Sagittal
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Coronal Plane
• 1
• 2
• 3
• 4
• 5
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Coronal
12
13
Coronal
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Name the Imaging Plane
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16
17
18
19
20
21
22
23
24
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Both Radiation:
Why CT vs. Radiography
• Superimposition
• Contrast Resolution
– Less scatter
• One exposure
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Similar to Radiography
• Radiopaque are white
– Bone
– Prosthesis
• Lower density images are gray
– Fat
– Muscles
– Organs
• Very low density are black
– Air
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Hounsfield Units
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Fundamentals of CT
Cross sectional
Tube rotates around
patient
Detectors measures
primary data
Primary data sent to computer
Calculated according
to algorithm
Data assembled into a matrix
Each sectional slice is displaced
on cathode ray tube
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Generations of Scanners
• First generation
–
–
–
–
1
2
3
4
• Second generation
–
–
–
–
1
2
3
4
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Third Generation
• Rotate/ rotate
• More than 750
detectors
• 1-10 seconds
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Fourth Generation
• Rotate only
• Fixed detectors
• More detectors
• Higher dose to PT
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Technical Aspects
• Remnant radiation is collected
–1
–2
• Electrical signal digitized
– Each signal assigned a number
• Signals combined to form digital image
– Field of View (FOV) determines amount of data to be
displayed on monitor
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Breakdown of the Digital Image
• Array of numbers
–1
• Pixel
–1
–2
• Voxel
–1
–2
–3
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System Components
• Computer
– Operators console
• Gantry
• Table
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Computer
• Four basic functions
–
–
–
–
1.
2
3
4
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Data Acquisition
• Tech chooses various parameters
–1
–2
–3
–4
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Image Reconstruction
• Digitizes raw data
• Computer performs mathematical
computations on a temporary storage
system
– Host computer has limited storage capacity
• Reconstruction takes a few seconds
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Long term Storage
• After reconstruction it is transferred to
another storage medium
• Those temporary images on the host
computer are archived separately as an
independent study that can be retrieved
later
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Image display
• Can be viewed on a video monitor
• Tech and doctor can communicate with host computer to
view images
• Can manipulate images
– 1
– 2
– Image resolution lost with reconstruction in other planes
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Gantry
• Circular
• Aperture is the hole PT goes in
• Houses
– Detector, slip ring, generator and x-ray tube
• Tube similar to x-ray tube
– Must withstand higher amounts of heat
• Can be tilted 30 degrees forward and back
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Table
• Automated device linked to gantry &
computer
• Moves in increments
– According to protocol
• Made of wood or low density carbon
composite
• Has a weight limit
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Control Console
• Where the tech
controls the scanner
• Has a keyboard,
display monitor &
mouse
• Allows tech to control
–
–
–
–
1.
2
3
4
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Image Manipulation
• Windowing
– 1.
• Window width
–1
–2
–3
• Window level
–1
–2
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Windowing
Window width 400
Window width 2200
Window level 35
Window level 400
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Factors Affecting Image Quality
•
•
•
•
•
•
•
Spatial resolution
Contrast resolution
Noise
Artifacts
Patient factors
Scan times
Scan diameter
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Spatial Resolution
• What happens to resolution with smaller
phosphor crystals in standard film screen
systems?
• Is a function of pixel size
– Smaller: better detail
• Thinner slices: increased detail
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Contrast Resolution and Noise
• Appears as graininess
• Ability to distinguish
adjacent tissue
• In CT it is better than in
conventional x-ray
– Less scatter
• Low noise is smooth to
the eye
• High noise is blotchy and
spotty
• As noise increases
contrast resolution
decreases
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Artifacts
• Streak artifacts
– Metallic objects,
pacemakers, and
prosthesis
• High concentration
barium
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Patient Factors
• Motion
• Size of patient
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Image Quality under Tech Control
• Slice thickness
• Scan time
• Scan diameters
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Diagnostic Applications
• Most common anatomy examined is
– Head, chest and abdomen
• Exam of choice for:
– Head trauma
– CVA
• Also useful for:
–
–
–
–
–
–
–
–
–
Infarctions
Hemorrhage
Disk herniations
Craniofacial fractures and tumors
Cancers
Hydrocephalus
Degenerative diseases
Inflammatory infections
Congenital disorders
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Use of Contrast Media
• Can be administered orally, rectally and
intravenously
• IV usually non-ionic contrast
• BA and Hypaque used for abdomen and
GI studies.
– 2% concentration BA
– Low concentration (hypaque)
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Special Features
•
•
•
•
•
•
Dynamic scanning
CT angiography (CTA)
Spiral/helical CT
Multi-slice Spiral/helical CT
3 D imaging
Radiation therapy treatment
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Dynamic Scanning and CTA
• After contrast administration
• Sequential scanning times as different
structures enhance
• CTA:
–1
–2
–3
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CTA
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CTA
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Spiral / Helical CT and
Multi-slice Spiral/ Helical CT
• Single row of detectors
• Gantry rotates around PT
as table moves
• Multiple rows of detector
arrays
• A four row scanner would
scan 4 times faster
• Scans a volume instead
of slices
• Better detail
• Improced spatial
resolution
• Fast scan times
• LG areas of body can be
done with one breath hold
– For peds and combative
patients
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Spiral and Multi-slice Spiral
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3D Imaging
• Postprocessing
technique
• Takes 2D raw data
and constructs a 3D
image
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3D imaging
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3D Imaging
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Radiation Therapy Planning
• Gives volumetric and depth calculation
ability
• Allows for one CT instead of the 3 they
used to do
• Flat board used instead of curved couch
• Dose to normal tissue is minimized
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RAD Therapy and CT
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RAD Therapy and CT
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CT and Radiation Dose
• CT doses are higher than conventional
radiography
• A lower pitch results in a higher dose
– More overlap
• Thinner slices also result in a higher dose
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CT vs. MRI
• MRI exhibits better
low contrast than CT
• CT demonstrates
bone better than MRI
• Higher cost and takes
longer
• Faster, so preferred
for some PT’s
• Cannot do with metal
– Small gantry
– Wide aperture
• Less costly
67
The Future of CT
• Has significantly increased in the past 5
years
• Higher quality images increase accuracy
of diagnosis and treatment
• Cost effective
• Will continue to be a diagnostic tool
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