1. www.le.ac.uk
Evaluation of a CdTe detector for
medical imaging
Layal K. Jambi
Bioimaging Unit
Space Research Centre
Supervisor: Dr John Lees and Professor Alan Perkins
3. Radiation detectors
• Radiation detectors are the sensing element in
nuclear measurement systems.
• Detection of radiation is related to the absorption of
radiation and how it interacts with matter.
• There are several types of radiation detectors.
4. Scintillation detectors
• The main purpose of scintillation in detectors is that
the scintillator material converts higher energy
incident photons into several lower energy photons.
Figure - taken from the Idaho state university Radiation Information Network.
5. Scintillation detectors
• There are two types of solid state scintillators:
– Inorganic scintillators
e.g. NaI and CsI.
NaI(TI) is the most frequently used scintillation
crystal.
– Organic scintillators
e.g. Plastics composed of aromatic hydrocarbons.
6. Semiconductor detectors
• Semiconductors are based
on a more direct approach
which converts photons
directly into an electronic
signal.
Figure - taken from NSEP Nuclear Safeguards Education Portal.
8. Small field of view (SFOV) cameras in
medical imaging
• Pinhole collimator has been used with SFOV offering
high spatial resolution.
• In medical imaging SFOV used for a small organ
dedicated system.
11. CdTe X-ray and 𝜸-ray detectors for
imaging system
• Hybrid CdTe pixel detector arrays for breast
screening to replace mammography.
• CdTe MediProbe for sentinel lymph nodes (SLNs) to
replace the gamma probe.
12. Main research area
• Evaluate the performance of the XRI-UNO CdTe
detector in comparison with CGC.
13. XRI-UNO system
Physical specification
Dimensions (W x L x
H)
138mm x 172mm x
34mm
Active area 14.08mm x 14.08mm
Pixel size / # Pixels 55 µm x 55 µm /
65.536 pixels
Semicoducting
material
1mm Cadmium
Telluride
14. Initial investigation
• A 0.45mm diameter cannula tube, 18mm length
filled with 0.63 MBq 99mTc solution.
A. With high resolution
parallel hole
collimator (1mm ∅)
B. With low resolution
parallel hole
collimator (2mm ∅)
C. Without collimator
No. of frames 999 frame, each frames 100ms
16. 1. Intrinsic spatial resolution
• It is the full width at half maximum (FWHM) of a line
spread function (LSF) or of a point spread function
(PSF) without a collimator.
17. 1. Intrinsic spatial resolution
345MBq of Cd-109 at 112mm
distance from the 3mm width slit
26. 3. Intrinsic spatial uniformity
Flood image of a 2 MBq Co-57 placed 107mm
away from the detector
27. 3. Intrinsic spatial uniformity
Intrinsic spatial uniformity
Co-efficient of variation XRI-UNO CdTe 0.38
CGC 1.58
Differential uniformity XRI-UNO CdTe 5.17
CGC 0.6
XRI-UNO is less uniform
28. 4. Intrinsic sensitivity
• The proportion of photon flux incident on the
detector that is recorded within the photopeak
energy window being used.
• Tested by placing various width of scattering
medium (Perspex) between the source and the
detector.
29. 4. Intrinsic sensitivity
0 10 20 30 40 50 60 70
0.020
0.025
0.030
0.035
0.040
0.045
Countspersecondperincidentcounts
Perspex Thickness (cm)
Cd-109 placed at 420mm away from the
detector with increasing layers of Perspex
35. Conclusion
• The XRI-UNO CdTe detector exceeds the CGC in
areas such as intrinsic resolution and count rate
capability.
• The XRI-UNO CdTe detector would not be able to
replace the CGC due to low sensitivity.
36. Further work
• No more semiconductors.
• Try to use different type of scintillators such as
Gadolinium Oxysulfide (GOS) ceramic scintillator.
37. Acknowledgement
• University of Leicester
Dr. John Lees, Sarah Bugby, Mohammed Alqahtani, Dr. Simon Lindsay,
Bahadar Bhatia and William R McKnight
• University of Liverpool
Sean Tipper
• University Hospitals Nottingham
Prof. Alan Perkins and A K Ng
• Leicester Royal Infirmary
Helen Hill and David Monk
38.
39. Further information
• Bugby, S.L., J.E. Lees, B.S. Bhatia, and A.C. Perkins, Characterisation of a
high resolution small field of view portable gamma camera. Phys Med,
2014. 30(3): p. 331-9.
• Bhatia, B.S., S.L. Bugby, J.E. Lees, and A.C. Perkins, A scheme for assessing
the performance characteristics of small field-of-view gamma cameras.
Phys Med, 2015. 31(1): p. 98-103.
40. Radioactive Sources used
Source Activity (MBq) Energy (keV) Diameter (mm)
Cadmium-109 345 22 8
Cobalt-57 2 122 6
Technetium-99m 229 140 NA
41. Comparison Table
Detector CGC CdTe
Field of view (mm) 40 x 40 14.08 x
14.08
Intrinsic spatial resolution FWHM (mm) 0.63 0.4555
FWTM (mm) 1.06 0.7985
System spatial resolution FWHM (mm) 1.28 1.61
FWTM (mm) 2.35 8.00
Intrinsic spatial uniformity Integral uniformity (%) 8.5 100
Spread of differential uniformity (%) 0.6 5.174
Co-efficient of variation (%) 1.58 0.38
Intrinsic Sensitivity Counts per second 62300 28839
Count rate capability Maximum counts (incident counts per
MBq)
1200 1668
Contrast to noise ratio CNR No data 12
43. GOS Advantages
• High sensitivity, short decay time, short afterglow.
• Eco-friendly with no hazardous materials contained.
• Resistant to humidity.
• High x-ray shielding capability to protect light
receiving element.
• Toshiba also has line-up of green and red light
emitting high sensitivity scintillators, although with
inferior decay time, afterglow characteristics.
http://www.toshiba-tmat.co.jp/eng/list/sc_cera.htm
Editor's Notes
They are considered as a device that converts radiation energy into an electronic signal.
There are several types of radiation detectors which are categorised according to the general mode of interaction mechanisms and process of recording the acquired data.
Scintillation detectors and semiconductor detectors are the most commonly radiation detectors used in nuclear measurement systems.
For traditional gamma imaging the scintillating material is coupled to photomultiplier tubes or photodiodes which amplify and convert the lower energy photons into electronic signals which can then be read out.
- Instead of converting high energy particles into lower energy photons and then into an electronic signal
Nuclear diagnostic imaging allows clinicians to look at processes within the body. In nuclear diagnostics, a patient is given a radioactive tracer which produces gamma radiation and circulates around the body to areas of interest. This gamma radiation can pass through the body and be imaged with an external gamma camera.
This gamma camera is housed in specialised rooms. Patients need to travel to the camera rather than the other way round.
Converging multi-hole collimator have been used with large field of view (LFOV) cameras to improve sensitivity and spatial resolution.
sentinel lymph node in breast, parathyroid gland surgery, malignant melanoma and radiopharmaceutical guided surgery.
An example of semiconductor detector is a CdTe X-ray and 𝛾-ray detectors which have been used in imaging system with a great potential to take place of the most commonly used scintillating materials such as I mentioned previously CsI(TI) and NaI(TI) in gamma camera. There are two types of semiconductor detectors used
Five images of Cd-109 were obtained with different Perspex thicknesses ranging from 9.5mm increasing up to 47.5mm.
An example of these images illustrated in the figure
- So to conclude the performance of the XRI-UNO CdTe detector has successfully been quantified although it is difficult to make a full comparison between the XRI-UNO CdTe detector and the CGC due to the limitations of the using of the XRI-UNO
As the XRI-UNO CdTe detector was made available by X-Ray Imatek Company for only a short period of time, no further tests on this system will be carried out.
The next stage of this research is to try using different types of scintillators such as Gadolinium Oxysulfide (GOS) ceramic scintillator and to make a comparison between the GOS and the currently used CsI(TI) in the hybrid compact gamma camera.
