- Each time the Xray tube and detector make a 360° rotation, an image or slice has been acquired. • The "slice" is collimated (Focused) to a thickness between 1mm - 10mm using lead shutters in Front of the Xray tube and xray detector.

scanning

- The largest component of CT installation - Contains the xray tube and detectors. • maintains the alignment of detectors and the tube while moving along the scan are. • Enables smooth travel of the Xray tube and detectons with slip ring technology. - Able to be tilted iF necessary • The entire gantry can be tipped as angle up to 30º to allow the acquisition of partial coronal images. - Patients are positioned via laser pointers. • Three pasitioning lights or lasers within the gantry assure centering of the patient in the sagittal, coronal, and transverse. lisio

gantry assembly

- shows the reading of parameters the gantry is presently positioned: gantry tilt, table height, position of landmarks, latch status, and scannable range: • Important during positioning of the patient. • Serves as reFerence values used in planning the san. • Some scaners prevent the scan from starting iF set values have exceeded limitations.

display panel

- Incorporates several buttons to mainly control the movements of the gantry table. • Controls for the height adjustment of the Ctable. • Controls for navigating the 2 axis (entry and exit) • Controls For activating the laser pointers. • Controls For setting reference peint of the scan.

control panel

- Ensures proper centering of the patient with the help of three positioning lights : sagital, coronal, and transverse. - Turned on /oFF via the gantry's control panel.

positioning light

- Pressing the ____________ stops all mechanical movement within the gantry and the xray emission oF the xray tube. • should be pressed when the operation endangers the patient or anyone present in the expesure room. • May be present among the gantry controls and lor in the control console.

emergency button

TRUE OR FALSE Components of the Gantry - Being the largest component, the gantry consists of majority of the Fundamental pats of the scanner. • Xray tubc • Detector Array • Collimator Assembly • High voltage Generator • Patient support couch CCT table)

true

TRUE OR FALSE The Xray tube - The complexity of the Xray tube can be noticed in the image display, higher image quality is provided with a more powerful tube. • Uses small Focal spot size Per better spatial resolutions • Txray tubes are of higher heat capacity than radiography Xray tubes.

true

TRUE OR FALSE - Size Does Matter •CT Xray tubes are very large and more powerful. • Factor Selection: 120 KUp 200-500 mA • Thermal capacity: 000, 000 HU - 5 mHu • Anade Cooling Rate: approx • ImHU/min, vees thicker anale disc with a larger diameter.

true

- Receives and coverts the Xray photons into signals to be calculated by the cT computer. • Has a Fixed 510 (110 am) In all angles oF scamning: • A set of factors indicate the detectors's overall efficiency . •Two types of detectors: gas Filled and solid state detectors.

CT detector array

- indicates the overall efficiency of the detector - DDE = CPE + CUE + AE

detector dose efficiency DDE

its ability to receive photons, controlled by detector size and its interspacing.

capture efficiency CpE

its ability to convert xray energy into light (SS) or ions (IC)

absorption efficiency

its ability to convert light or ions into digital signals.

conversion efficiency CvE

- Ability to maintain the quality calibrated state oF the detector, the move stable a detector, the less frequendy it needs to be calibrated, and maintain its sensitivity.

stability

- The speed of the detector to react or recognize on incoming Xray photon then recover the next input.

response time

- The ratio of the largest from the smallest signal the detector is able to recognize, approx 1 million :1.

dynamic range

TRUE OR FALSE Choosing the Right CT Detector - Has a high detector dose efficiency (DDE) to minimize patient radiation dose. - Has high stability to reduce Frequency of calibration and maintain its. sensitivity to incoming xray - Has high tolerance to temperature variations within the gantry to prevent damage.

true

TRUE OR FALSE - previously, gas filled detectors were used. Currently, all scaners use scintillation or solid state detectors.

true

TRUE OR FALSE • Early scintillation detector arrays contained scintillation crystal photodiode assemblies • Photodiode: convert light into an electronic signal. • Scintillation Detector: combination of scintilliation crystals and a light detector.

true

convert light into an electronic signal.

photodiode

combination of scintilliation crystals and a light detector.

scintillation detector

- Pressurized gas Filled (insert gases) ionization dramber + electrode (Tungsten) plate 1.5mm apart • Insert gas: gas that doest't undergo chemical reaction under given conditions. • Gasses used Xenon, krypton. • <50% DDE, >90% CpE, 60-90% AE (Fast response time) • Detectors can be tightly packed together. • Cannot be used in 4th gen and helical scanners.

gas filled detectors

- Scintillation crystals (sodium lodide) + photo multiplier releases light when strucks by Yrays. • >50% DDE, 50% CpE, 100% AE (NAI Has phosphorescence that reduce response time) • Detectors can toe not be tightly packed together • Crystals currently used : Bismuth germanater cesiumiodide, and cadmium tungstate, 90% AE with no afterglow.

solid state detectors

two types of collimation in computed tomography

pre patient collimation,post patient collimator

- Opening depends on Focal size, usvally mounted on the tube housing. - Reduces patient dose by controlling the Field size.

pre patient collimator

- Restricts the Field of view af detectors, reduces scatter radiation reaching the detector array. - Aperture witth helps determine the slice thickness.

post patient collimator

TRUE OR FALSE The CT high Voltage Generator - All CT imaging system operates in three phase or high Frequency power • A high Frequency generator is small because the high voltage stepup trams former is small, thus can be mounted on the rotating gantry. • Tube potential : 80 - 140 KV • Tube current: 20 - 500 mA

true

allows movement into and out of the gantry.

cradle

pressed to latch or unlatch the cradle.

latch button

used to deliver oral instructions to the patient.

speaker

-placed at the foot of a table. - When the operator steps on it, the switch turns on and activates functional buttons on the gantry panel.

mat switch

responsible for processing the displayed program protocols.

operating console

controls the data acquisition process, display and storage oF image data. • A Timaging system zan be equipped with two or three consoles, depending on its Features.

computer

TRUE OR FALSE - The operating console contains: • Display oF parameter (values) of scanner operatio • Controls For technical exposure Factors, moveme of the gantry and cTtable, and positioning teasures . • Assigning patient instructions (manual, automatic) • Commands for inage reconstruction and transfer - usually includes two monitors • One is provided for the operator to annotate partient data on the image. • A second monitor allows the operator to View the resulting image before transFering it to hard copy or to physician's viewing console:

true

the link between the CT technologist to the other components of the imaging system. - PerForms Four basic Functions in thy system: • Data acquisition • Image reconstruction • Image data storage • Image display

CT computer

- Mode by which the patient is scanned. - The technologist selects the scanning parameters before each scan takes place, while the computer is involved in : • Sequencing the generation of xrays • Turning the detectors on /oFF at precise intervals, • TransFerring data • Monitoring the system operation.

data acquisition

- Accomplished using an Array Processor independent From the host computer. • Array processor: aprocessor specially designed to perform computations on large arrays of data. - Control of Scan time and Reconstruction time • Scan time: movement of the Xray tube and detectors • Reconstruction time: processing capacity of the compoter.

image reconstruction

aprocessor specially designed to perform computations on large arrays of data.

array processor

- Control of Scan time and Reconstruction time • __________ movement of the Xray tube and detectors

scan time

processing capacity of the compoter.

reconstruction time

for long term data storage and its retrieval

archiving

- Reconstructed images are displayed on a display monitor. - With the images in the monitor, the technologist: • View speciPic images • Postimages on a scout • Implement images manipulation techniques ceig. zooming, contrast/brightness control, image analysis

display of images

TRUE OR FALSE The Physician's Workstation - Allows the physician to call up amy image and manipulate that image to optimize diagnostic information. • Accepts the reconstructed image from the operator's console and displays it For viewing and diagnosts . • Controls are provided for contrast and bright. ness adjustments, magnification techniques anduse of online computer softuare packages.

true