IMAGE GENERATION IN CT

CT EXAM PROTOCOL AND PARAMETERS SELECTION PATIENT POSITIONING SCANNING DATA RECONSTRUCTION IMAGE DISPLAY

PROTOCOL AND TECHNIQUE SELECTION 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 LARGE FOV SMALL PIXEL LARGE PIXEL LARGE DFOV LOW SPATIAL RESOLUTION LOW VISIBILITY OF DETAIL

LARGE DFOV

SMALL DFOV

DFOV

DFOV

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-BY-SLICE) 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

PART OF THE X-RAY BEAM THAT FALLS ON ONE DETECTOR

COLLECTION OF THE RAYS FOR ONE TRANSLATION ACROSS THE OBJECT VIEW COLLECTION OF THE RAYS FOR ONE TRANSLATION ACROSS THE OBJECT

ANALOG SIGNAL GENERATED IN A VIEW 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) Ц CT # RECONSTRUCTION

LINEAR ATTENUATION COEFFICIENT ( cm-1) BONE 0.528 BLOOD 0.208 G. MATTER 0.212 W. MATTER 0.213 CSF 0.207 WATER 0.206 FAT 0.185 AIR 0.0004

CT NUMBER CALCULATION

CT NUMBER SCALE WATER – 0 BASELINE CORTICAL BONE +1,000 MUSCLE +50 WHITE MATTER +45 GRAY MATTER +40 BLOOD +20 CSF +15 FAT -100 LUNG -200 AIR -1,000 APPEARS WHITE GRAY LIGHT GRAY DARK GRAY TO BLACK WATER – 0 BASELINE

CT # vs BRIGHTNESS LEVEL + 1000 -1000

CT # +400

CT # +500

CT # +40

CT # +15

CT # - 200

CT # OF CYST

CT # OF LIPOMA ( FATTY TUMOR)                                                                                                                          -100

CT # -100