CT systems components

what is the top arrow

gantry

what does the gantry house

qSlip rings

qX-ray tube

qHigh voltage generator

qDetectors

qDAS (data acquisition system)

what is the aperture size range of the gantry (diameter)

70-90 cm

what feature do the modern CT scanners have

automatic instructions for the patient and automated communication systems

what is used to align the patient in the gantry

x and y axis

in what scenario would we angle the gantry

kyphotic patients

what is the gantrys range of angle

+/ - 30 degrees

what is the point of angling the gantry

to be perpendicular to the anatomy

in what instance can we NOT angle the gantry

helical scanning

Gantry – Recoiling System Cables

• earlier generation tech

• would rotate 360 and then reverse 360

• step and shoot scanning method

• it is not a continuous rotation, cables are invovled

• longer wait times

• interscan delay = time it takes to reset into the next 360 shot

Gantry – Slip Ring Technology

• newer tech

• helical scanning method

• uses electromechanical device to rotate the gantry without cables

• there is no interscan delay, constant power supply

• constant xray output

how does the Gantry – Slip Ring Technology work

there circular electronic conductive rings and brushes.

1. power goes to the tube and supplies it with motion to the brushes

2. brushes are continuously moving in the slip ring

3. constant xray output

what are the 2 functions in the gantry control panel

1. light alignment

2. gantry tilt

what prevents arcing in the CT scanners

metal envelope

what is the metal envelope

metal envelope tube have a thicker anode disk than conventional tubes. it is designed with tungsten-rhenium focal track fused with a graphite base making the thermal capacity 10x higher

what kind of tubes do helical scanners have to prevent arcing

brazed graphite anode disk

•Conventional x-ray tube has x

ball technology

•CT tube has x technology

liquid bearing

how does liquid bearing technology work in CT

•Anode shaft has grooves that receive the gallium based liquid metal alloy during rotation. •Provides cooling of anode; also rids vibrations and noise

how many hours of work can a CT scanner do before we hear the gravelling sounds

10-40 hours

what is a focal spot

the collimation of the view you wanna see

what are the 2 most common sizes of focal spots in CT

1. 0.5mm

2. 1.0mm

what are the advantages of a small focal spot

1. reduced penumbra

2. sharper images

•Pre-patient

controls x-ray beam width (slice thickness); determines patient radiation dose & dose profile – pre patient

•Pre-detector

•shapes the beam (ensures width) and prevents scatter radiation reaching detectors – post patient.

explain how the solid state crystal detector works again

what defines the solid state crystal detector

ability to capture photos and alter elxtronic signal to create a good image

what is the criteria for a solid state cyrstal detector

• High detector efficiency

• no afterglow = there should be persistent flow of subtraction

• High scatter suppression

• High stability = meaning that after some use, it will be fine on its own and does not require too much maintenance

§Ideally detectors should be x so that all of the x-rays emitted are converted to data and used for the image

closely packed

in a solid state cyrstal detector, how can we avoid scatter radiation in relation to the detector

deep narrow detector . Smaller detectors also provide good spatial resolution and scatter rejection

what is special about the photon counting detectors

instead of photons > crystal > light > electrical signal

it is

photons > electrical signal.

volume averaging

Photoiodide is removed

photon counting detectors are advantages because it…

excludes noise thus increasing resolution

what materials are used in a photon counting detector

CdTe or silicon

what is DAS

stands for data acquisition system, it converts photon signals from the detector to digital signal to be sent to teh computer for processing.

DAS is coupled to x by switches

multi-detector array

The multi-row detector allows for various selections of x to meet the needs of the examination

slice thicknesses

what characteristics of scatter

1. size

2. shape

3. placement

what is the table made of?

carbon fiber composite

what is special about the carbon fiber composite

low attenuation of the beam and is strong enough to hold bariatric patients

what happens if the motor drive is damaged because of heavy weight stress on the table?

• alters pitch of the table because the speed of the table movement during rotation is affected

• section intervals are affected

•Incrementation, feed, step or index refers to the x

process of moving the table by a specified measure

•Helical CT table incrementation is quantified in x because of continuous table movement throughout the scan

millimeters per second

Scannable range is the

range that the table can be moved horizontally; determines the extent a patient can be scanned without being repositioned

What is included in the control console

1. keyboard

2. monitors for image display

3. window width and level manipulation

4. archive controls

define what the computer is

both hardware and software

what are the controls in the computer

1. data acquisition

2. processing

3. image display

4. storage (PACS)

what is the brain of the computer

CPU

what table mechanics provide exact section interval positioning

motor drive