This document discusses different types of CT detectors. It describes how CT detectors work by capturing x-ray radiation from patients and converting it into electrical signals and digital information. It then summarizes the key characteristics of different detector technologies, including high efficiency, fast response time, high dynamic range, and lack of afterglow. Solid state and scintillation detectors are described as the main types that either use semiconductor materials or convert x-rays to light for detection. The advantages of multi-slice detectors over single-slice are also highlighted.

1. Taman kumar
BRIT 4rd sem
190528027

2.  CT detector capture the radiation beam from
the patient and convert it into electrical signal
 which then is converted into binary coded
information
 It measure the intensity of
radiation transmitted
through the patient

3.  High efficiency:- refers to the ability to
capture, and convert x-ray photons to
electrical signal
 Less Response time:- refers to the speed
with which the detector can detect x-rays
 High Dynamic range:- refers to the ratio of
the largest signal to be measured to the
smallest signal.

4.  No After glow:- refers to the persistence of
the image even after the radiation has
been turned off
 Small size :-size should be small but
resolution should be good

5.  Solid state detector (semiconductor
Radiation Detector) –use semiconductor
material as detecting medium.
• Scintillation
Detectors
1
• Gas Ionization
detectors
2

6. 1. Scintillation detectors
 Convert x-ray energy into light then
electrical
signal
2. Gas ionization detector
 Convert x-ray energy directly into electrical
signal

7.  X-rays come in contact with scintillator
 NaI(Erlier) CsI
 Gets converted into light photons
 Light photon falls on photocatode
 Solar cell

9. 1. Photomultiplier tube(not
enough signal)
2. Dinodes
3. Dinode curve shape
4. maintained at diff.
potential(acceleration)
5. Secondary
photoelectrons
6. Leads to the amplification
of photoeletrons

10.  Used in multislice ct scan
 Size 1.0 x 1.5mm
 QDE (quantum detection efficiency)is 90%
 Sensitivity about 90-99%

11.  high pressure ( about 25 atm) non
radioactive xenon gas
 Based on the principle of ionization
 used for 3rd generation scanner only

12.  A series of individual gas chamber,
usually separated by tungsten plate
 Electrodes are positioned to collect
electrons
 Xe is used as gas
 Aprox 1000 chambers
 When x-ray interact with these chamber
 Formation of ions occur
 Run to wards electrodes , lead to moving
charge .(small current)

13.  Not used anymore
 QDE is 50%-60%
 Sensitivity is 50 %

14.  Faster image
 Improve image quality
 Patient dose is less
 Low SNR
 Less afterglow

15.  Problem with single slice is time duration
 Single slice has one detector for imaging
 Introduction of multi-row detector for 360
degree rotation imaging
Collimated Beam
Thickness
Collimated Beam
Thickness
Z-Axis Z-Axis

16. SINGLE SLICE VS. MULTISLICE DETECTOR
Z-Axis
Collimated Beam Thickness
Single slice
detector
Multislice
detector

17.  In 1992, Elscint introduced the first
 solid state detector
 special x-ray tube based on a double dynamic focus system
 Focal spot is switched by a computer controlled electron
optic system
 results in the simultaneous scan of two contiguous slices
with excellent resolution

18.  Acquire 4 to 64 to 320 slices per 360
degree rotation
 Open collimators in “Z” direction
1 2 3 4

19.  Detector signals can be used
 Individually
 In groups
1 2 3 4
Four thin slices
1 2 3 4
Four thicker slices
“z” direction
•Physical Detectors not necessarily
equal to of possible Slices
•Thickness is controlled by
1.Digital Acquisition System (DAS)
channels
2.collimators

20. MULTI-SLICE DETECTOR EXAMPLE
16 DETECTOR ROWS, 4 CHANNELS

21. DETECTORS VS. CHANNELS
4 X 1.25 MM
 Beam collimated to
4 detector rows
 1 detector row per
DAS channel
Effective Detector

22. DETECTORS VS. CHANNELS
4 X 2.5 MM
 Beam collimated to
8 detector rows
 2 detector rows per
DAS channel
Effective Detector

23. DETECTORS VS. CHANNELS
4 X 3.75 MM
 Beam collimated to
12 detector rows
 3 detector rows per
DAS channel
Effective Detector

24. DETECTORS VS. CHANNELS
4 X 5 MM
 Beam collimated to
16 detector rows
 4 detector rows per
DAS channel
Effective Detector

25. A . MATRIX ARRAY DETECTOR(isotropic)
channels or cells that are equal in all dimensions
B . ADAPTIVE ARRAY DETECTORS(anisotropic)
cells have different sizes

26. DISTRIBUTION OF DETECTORS IN AXIAL DIRECTION VARIES
WITH MANUFACTURER
All detectors
same width
“Z”
Direction
Variable
widths

27. MULTI-SLICE CT
“ADAPTIVE ARRAY DETECTORS”
 Some scanners
use detectors of
various widths
 Post-collimators
used to partially
block wider
elements for
thinner slices
“z” direction
1 2 3
Three thicker slices
1 2 4
Four thinner slices
3
Post-
collimators

28.  Currently undergoing testing
 256 slice ct scannerprototype
 flat panel Ct scanner
Philips
256 Slicer
Toshiba
320 Slicer

29. A.The 256-slice CT
912 channels, 256 segments and a beam
width of 128 mm
 Possible to scan entire heart in a single rotation

30. B.Flat panel detectors
•based on the CsI indirect conversion DR

31. •Recently used in
breast CT
•used in DR and
in7th gen