CT SCAN EQUIPMENTS ARE DESCRIBED IN DETAIL. CONTENT TAKEN FROM MUTIPLE BOOKS AND GENERALS.

1. CT SCAN EQUIPMENT
MR. ROHIT BANSAL
ASISTANT PROFESSOR
MAMC (AGROHA)

3. A. CONSOLE ROOM
a). Graphic Monitors.
b). Keyboard & Mouse.
c). Computers.
B. EXAMINATION ROOM
a). PatientTable.
b). Gantry.
I. X-RayTube.
II. Generators.
III. Detector Array.
IV. Data Acquisition System (DAS).
V. Slip Rings.
C. CONTROL ROOM
a). AC Plants.
b). UPS.
CT SCAN SYSTEM COMPONENTS

4. A. GRAPHIC MONITORS
 DILOUGE MONITORS: Use for data entry and scan. Now
a days being obsolete.
 VIEWING MONITORS:
o Used to view reconstructed image in 2D and 3D .
o Zoom /Planning.
o Control contrast and brightness.
o Image analysis technique.
 INTERACTIVE MONITORS: Which do works of both
dialogue and viewing monitors.
CONSOLE ROOM

5. Help to enter patient data quick and quick reference guide.
COMPUTERS:
Provides the link between CT technologist to other components
of the imaging system.
It helps to reconstruct an CT image from the microns of
mathematical operations required to digitize & reconstruct the raw
data.
Ct imaging system requires a large computing capacity.
The microprocessor and the primary memory are the heart of
computer (These determine the reconstruction time).
Image can be stored on magnetic tapes, discs, CD and record
when required.
Keyboard and Mouse

6. The patient couch, or patient table, provides a platform on which
the patient lies during the examination .
The couch should be strong and rigid to support the weight of the
patient.
The couch top is usually made of carbon fiber composites because
they have low absorption.
Gantry:
It is a ring that comprised core components of a ct system.
It contains a rotating scan frame onto which the x-ray generator, x-
ray tube, and other components are mounted.
It houses imaging components such as the slip rings, x-ray tube,
high-voltage generator, collimators, detectors, and the DAS.
Can be tilted +/- 30 degree vertical to the couch.
Gantry and couch should be positioned such that the technologist
can observe the patient in gantry from operating table.
Patient Table

7. Ideally, the radiation source for CT would supply a monochromatic x-ray
beam (i.e., one made up of photons all having the same wavelength). With
a monochromatic beam, image reconstruction is simpler and more
accurate.
CT requires larger exposure time at higher kVp then needed for general
radiography.
In early generation CT scanners were used oil cooled, stationary anode
relatively large (2*16mm) focal spot operated at 120 kVp to 140 kVp & 30
mAs heavily filtered x-ray tube (6mm Al equivalent) which help to reduce
beam hardening artifact.
Now a days CT tubes are heavy duty rotating anode with high atomic
capacity & smaller focal spot (0.6-1.2mm) which are air cooled with current
value up to 400-800 mA & heat loading capacity of 3.5 MHU.
Borosilicate glass envelope has been replaced with a metallic envelope
(Alloy of Chromium and Iodine(I)) & Ceramic insulator (Al-Oxide).
X-Ray tube

8. Anode disc is made up of compound materials consisting of
Tungsten- Rhenium focal spot and graphite base with disc
diameter of 200nm compared to 75-160 mm.
Anode speed is increased upto 10000-12000 RPM by having
liquid bearing technology for smooth rotation of disc. E.g.
gadolinium based liquid metal alloy.
A Teflon filter is used to match with the contour of body to
reduce attenuation unsharpness. (Bow-tie filter).
Tube Housing:
 Material- Borosilicate & metal ceramic.
 Heat storage capacity- 1.3-1.8 MHU.
 Oil- Distilled oil.

9. Anode:
Diameter- 200nm
Weight- 200gm
Heat dissipation rate- 1 MHU/MIN
Anode angle- 10-12 degree
Focal spot- 0.6-1.6 mm
Rotation- 10000-12000 RPM/MIN
Material-Tungsten+ Rhenium+ Molybdenum+ Graphite
Cathode:
Material-Tungsten
Types- Dual Focus

10. The x-ray beam is collimated at two points, one close to the x-ray tube
and the other at the detector(s). Perfect alignment between the two is
essential.
The collimator at the x-ray tube (Pre patient collimator) is used to shape
the x-ray beam and limit patient dose.
The collimator at the detector (Post patient collimator) is the sole means
of controlling scatter radiation. Each detector has its own collimator.
The collimators also regulate the thickness of the tomographic slice (i.e.,
the voxel length).
Most scanners have collimators that can be varied to produce different
slice thicknesses, typically from 1 to 10 or 15 mm. Choice of slice thickness
is usually limited to one of several predetermined values, with choices of 1,
2, 5, or 10 mm being typical examples.
Pixel size is determined by the computer program and not by the
collimator.
Collimators

12. Detectors
Detectors are the device used to measure the amount of
electromagnetic radiation emitted by the object.
Detectors detect the X-Rays passing through the patient body.
Detector collects information regarding the degree to which
each anatomical structure attenuate the beam during a scan.
The requirements of CT detectors are:-
Should be small with good resolution.
Should have high detection efficiency.
Should have fast response.
Negligible after glow effect.
Stable noise free response.

13. Two types of detectors are in use nowadays.
(a) Xenon gas detector.
(b) Solid state detector.
Types of Detectors

14. Gas filled ionization detector consist of the Xenon gas and krypton gas
chambers (1000 chambers) under high pressure around 25 to 30 atm to
increase the number of gas molecules available for ionization which
improves their x-ray detection efficiency.
These chambers individually separated by tungsten plates known as
metal septal enclosed by a thick ceramic substrate material.
Each chambers (1000) share the same gas volume to minimizing
variation in sensitivity between the chambers.
As x-rays interact with the xenon gas atoms, ionization takes place then
the electric field between the plates cause the charge ions to move
towards the electrodes where the electronic charge is collected as electric
current.
Then the electric signal is amplified and then digitized which numerical
value is directly proportional to the x-ray intensity striking the detectors.
Gas Ionization Detector

15. Used mainly in rotate-rotate system because use of long
linear structures.
Chambers size- wide:1-2 mm, height: 10 mm, depth: 10 cm.
Gas- Mixture of Xenon and Krypton.
Anode- Made up of copper.
Cathode- Made up of Tantalum (Ta).
Pressure- 25-30 atm.
No afterglow.
Very fast Response.

16. Cheap and easily available.
It has constant sensitivity at long and short term.
Provides in-built collimation.
Rapid response with no afterglow effect.
Have better thermal stability.
Advantages

17. Quantum detection efficiency is less than 50 which is about
50% of solid state detectors.
The xenon has to be maintain high pressure to increase
detection efficiency and higher response to exposure.
Must be set in a fixed positioned orientation to the x-ray
source.
Reception of x-rays from a moving source is not efficient.
For the above two reason gas detectors are not suitable for
fourth generation and helical scanners.
Disadvantages

19. It is composed of a “scintillator” coupled tightly with a ‘photodiode’ or
‘PM-tubes’.
The ‘Scintillator’ emits visible light when it is stuck with x-rays.
The light emitted by the Scintillator reaches either ‘PM-tubes’ or
‘photodiodes’ which is an electronic device that converts light photons into
an electrical signal.
Now a days commonly Scintillation coupled with solid state photodiodes.
Scintillation material used with photodiodes are ceramic material made
of high purity ‘rare earth oxides’ based on dopped rare earth compounds as
‘Yettrium & Gadolinium oxysulphides (Gd2O2S) ultra fast ceramic (UFC)
detectors.
In early CT-scanners (1st and 2nd generation) Sodium Iodide (NaI) were
used withThallium (Nai:Ti) crystals coupled with PM-Tubes as x-ray
detector.
Solid State (Scintillation Crystal Detector)

20. The PM Tubes could not provide packing density that was
necessary with fan shaped beam geometry and required
power supply for each PM Tube makes bulky detector
assembly, so because of poor packing density higher
afterglow problems are seen that’s why it was quickly
replaced by silicon photodiodes.
Detector element converts the absorbed x-rays into light.
The light is then detected by si-photodiodes.
The resulting electric current is then amplified and convert
into a digital signal.

21. NaI:Ti
• Used in 1st generation CT scan, 100% efficient in diagnostic
range.
•Not suitable for rapid sequential exposure.
•CsI:Ti
•Crystal structure variation affect the efficiency.
CdWO4
•Low afterglow but toxic.
BGO [Bismuth Germinate Oxide] (Bi4Ge3O4)
•Difficult in matching.
Modern Detectors
•Ceramic rare earth phosphors like Gd2O2S,Y2O2GdO2:Eu.

22. Photodiodes are smaller in size, greater stability and cheap.
Do not require a power supply and are equally efficient.
Solid state detectors have better x-ray absorption efficiency
then xenon gas detectors.
Increase efficiency can result in less x-ray tube loading
(reduce image noise and reduce patient dose).
The top surface of solid state detectors are essentially flat
and therefore it is capable of x-ray detection over a wide
range of angels unlike the xenon detector.
Advantages

23. Relatively long afterglow.
Stable output signals depends upon a very high voltage
supply.
Multi-detector uniformility of response is difficult to
maintain.
It may be less stable in long term, they require time to
time calibration.
Disadvantages

25. Good sensitivity (detection efficiency is good).
Fast response time.
Stable (could not easily affected by varying temperature, humidity,
voltage etc.)
High conversion efficiency.
Small afterglow.
Cost effective.
Image quality must be good.
High packing density.
Wide dynamic range (able to detect wide number of x-ray)
Properties of a Ideal Detector

26. It generates high voltage potential between cathode and anode
of the x-ray tube.
All CT-Imaging systems operates on high frequency power.
A high frequency generator is small in size, so it can be mounted
on the rotating gantry.
kVp selection (Tube Potential)- 80-140
mAs selection (Tube current)- 20-500
All multislice spiral CT scanner operates on high frequency power.
CT scanner uses three phase power for efficient production of x-
rays.
In CT scanner generators low voltage low frequency is converted
into high voltage and high frequency (500-2500 Hz) direct current of
almost constant potential is supplied to the x-ray tube.
High Voltage Generator

27. Slip rings are electromechanical device that conduct electricity and
electrical signal through rings and brushes from a rotating surface on
to fixed surface.
One surface is smooth ring (stationary) and other is a ring with
brushes (rotating) that sweep the smooth ring.
Spiral ct is made possible by the use of slip ring technology, which
allows the gantry to rotate without interruption.
Composite brushes are made up to conductive materials (e.g. silver
graphite alloy)are used.
The brushes have to be replaced every year for preventive
maintenance.
Slip Rings

28. Data acquisition is a process of sampling signals that means real world
physical signals converting into digital numerical values that can be
manipulated by computers.
DAS typically convert analog waveform into digital value for easy
processing.
PROCESS OF DAS:
Physical signal: input of DAS can be represented in digital form are like
temperature, pressure, light, force etc.
Transducer/Sensor: convert physical signal into electrical waveform.
(Noisy)
DAS (Data Acquisition System)

29. Signal Conditioning: filter and amplifies noisy electrical
waveforms.
ADC: Convert analog signal into digital signal.
Pre- Processing: Image reconstruction (Back projection, Iterative
reconstruction, Filter back projection).
DAC: convert digital signal into analog signal. (Video/Picture)
Image Display: image displayed on computer.
Post Processing: 3D, angiographic image etc.
Image Archiving: Image Archive through PACS.

30. Power loss and power surges are good reasons to have back-
up power, like a UPS, hooked up to your medical equipment.
Say a power loss occurs in your facility, the UPS
(uninterruptible power supply) seamlessly kicks in to keep the
equipment from shutting down for a short period of time, so
that you are able to save what you are working on and safely
shut the system down.
AC PLANTS:
AC plants helps in controlling the temperature, humidity in
the CT Scan room.
UPS