Transcript IMAGE GENERATION IN CT

IMAGE GENERATION IN CT
CT EXAM
• PROTOCOL AND PARAMETERS
SELECTION
• PATIENT POSITIONING
• SCANNING
• DATA RECONSTRUCTION
• IMAGE DISPLAY
PROTOCOL AND TECHNIQUE
SELECTION
• PROTOCOL
• PARAMETERS
SCANNING MODE
kVp
mA
Time
RECONSTRUCTION
PATIENT POSITION
PATIENT ORIENTATION
SFOV
DFOV
PROTOCOL
• PEDIATRIC OR ADULT
• HEAD, ABDOMEN, EXTREMITIES
• VASCULAR OR REGULAR
SCANNING MODE
• AXIAL (SLICE BY SLICE)
• SPIRAL (HELICAL)
TECHNIQUE
• kVp
• mA
• time
RECONSTRUCTION
• SECTION THICKNESS
• SECTION INDEX
• ALGORITHM
PATIENT POSITION
• SUPINE OR PRONE
• BODY PART UNDER SCRUTINY MUST
BE PLACED IN THE ISOCENTER OF
THE SCANNER
PATIENT ORIENTATION
• HEAD FIRST
• FEET FIRST
SFOV
SCANNING FIELD OF VIEW
(CALLIBRATION FIELD OF VIEW)
• AREA WITHIN THE GANTRY’S
ISOCENTER FROM WHICH THE RAW
DATA IS ACQUIRED DURING THE
SCAN. IT DEPENDS ON THE NUMBER
OF DETECTORS ACTIVATED TO
COLLECT DATA.
LARGE SFOV
SMALL SFOV
SMALL SFOV
SFOV
LARGE SFOV
SFOV
CHOOSE THE SMALLEST
SFOV THAT WOULD
ACCOMMODATE BODY PART
FOR BEST RESOLUTION
IF BODY PART LIES OUTSIDE
SFOV NO DATA WILL BE
COLLECTED FOR THAT PART
THAT EXTEND BEYOND. IT
ALSO CAUSES OUT OF FIELD
ARTIFACT
OUT OF FIELD ARTIFACT
DFOV – DISPLAYED FIELD
OF VIEW
(ZOOM OR TARGET)
• DETRMINES HOW MUCH RAW DATA
FROM WITHIN SFOV WILL BE
UTILIZED TO CREATE AN IMAGE.
SFOV
DFOV
DISPLAYED FOV
vs
SCANNING FOV
• DFOV CAN BE EQUAL OR LESS OF SFOV
DFOV VS PIXEL SIZE
• SMALL DFOV
• SMALL PIXEL
• LARGE FOV
• LARGE PIXEL
LARGE DFOV
LOW SPATIAL RESOLUTION
LOW VISIBILITY OF DETAIL
LARGE DFOV
SMALL DFOV
DFOV
DFOV
PIXEL SIZE
PIXEL SIZE=
DFOV (mm)/ MATRIX SIZE
SAMPLE
SCANNING
• TOPOGRAM
• REGULAR SCAN
TOPOGRAM (SCOUT)
• TUBE DOES NOT REVOLVE AROUND
THE PATIENT
AP SCOUT
TUBE
• TUBE SUSPENDED ABOVE PATIENT
DURING SCOUT GENERATION
LAT SCOUT
• TUBE AT THE 90º ANGLE TO PATIENT
REGULAR SCAN
I, II, AND III GENERATION
• CONTINUOUS DATA ACQUSITION
GEOMETRY
IV GENERATION
• STATIONARY DATA ACQUSITION
GEOMETRY
REGULAR SCAN
• AXIAL (CONVENTIONAL, SLICE-BYSLICE)
• SPIRAL
AXIAL SCAN
• TABLE STOPS AT THE SCANNING
POSITION AND THE TUBE ROTATES
AROUND A PATIENT.
SPIRAL
• PATIENT CONTINUOUSLY MOVES IN
THE Z-AXIS DIRECTION WHILE THE
TUBE ROTATES AROUND.
TOTAL NUMBER OF
TRANMISSION
MEASUREMENT
EQUALS
NUMBER OF VIEWS
X
NUMBER OF RAYS IN EACH
VIEW
ACQUSITION
TERMINOLOGY
• RAY
• VIEW
• PROFILE
RAY
PART OF THE X-RAY BEAM THAT
FALLS ON ONE DETECTOR
VIEW
COLLECTION OF THE RAYS FOR
ONE TRANSLATION ACROSS
THE OBJECT
PROFILE
ANALOG SIGNAL GENERATED
IN A VIEW
RAY
VIEW
PROFILE
RECONSTRUCTION
• DATA THAT HAVE BEEN
BACKPROJECTED INTO THE IMAGE
MATRIX TO CREATE CT IMAGES
DISPLAYED ON THE MONITOR
RECONSTRUCTION
TRANSMISSION MEASUREMENT
(LINEAR ATTENUATION COEFFICIENT)
IS CONVERTED INTO CT NUMBER
(HOUNSFIELD UNIT)
RECONSTRUCTION
Ц
CT #
LINEAR ATTENUATION
COEFFICIENT ( cm-1)
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BONE
BLOOD
G. MATTER
W. MATTER
CSF
WATER
FAT
AIR
0.528
0.208
0.212
0.213
0.207
0.206
0.185
0.0004
CT NUMBER CALCULATION
CT NUMBER SCALE
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CORTICAL BONE
MUSCLE
WHITE MATTER
GRAY MATTER
BLOOD
CSF
FAT
LUNG
• AIR
+1,000
+50
+45
+40
+20
+15
-100
-200
-1,000
WATER – 0
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APPEARS WHITE
GRAY
LIGHT GRAY
GRAY
GRAY
GRAY
DARK GRAY TO BLACK
DARK GRAY TO BLACK
DARK GRAY TO BLACK
BASELINE
CT # vs BRIGHTNESS LEVEL
+ 1000
-1000
CT #
+400
CT #
+500
CT #
+40
CT #
+15
CT #
- 200
CT # OF CYST
0
CT # OF LIPOMA ( FATTY
TUMOR)
-100
CT #
-100