1. RAD 466-L 8 by Dr. Halima Hawesa
SPECT/CT
TECHNOLOGY & FACILITY DESIGN
RAD 466-L 8 by Dr. Halima Hawesa

2. Objective
To become familiar with basic SPECT/CT technology, and review considerations in establishing a new SPECT/CT facility

3. Content SPECT cameras Image Quality & Camera QA SPECT/CT scanners
Design of SPECT/CT facilities

4. What is SPECT Camera gamma cameras.
The most widely used gamma cameras are the so-called Anger cameras, in which a series of phototubes detects the light emissions of a large single crystal, covering the field of view of the camera.
SPECT imaging systems consist of single- or multiple-head gamma cameras which rotate around the patient, thereby acquiring the projections necessary for reconstruction of axial slices.
SPECT stand for Single Positron Emitting Computing Tomography.

5. SPECT Camera Components
Collimator
NaI(Tl) crystal
Light Guide (optical coupling)
PM-Tube array
Pre-amplifier
Position logic circuits (differential & addition etc.)
Amplifier (gain control etc)
Pulse height analyser
Display (Cathode Ray Tube etc).

6. Scintillators
Density Z
Decay
Light
Atten .
(g/cc)
time
yield
length
(ns)
(% NaI)
(mm)
Na(Tl) I
3.67 51
230
100 30
BGO
7.13 75
300 15 11
LSO
7.4 66 47 75 12
GSO
6.7 59 43 22 15
BGO - Bismuth Gremanate
LSO - Lutetium Oxyorthosilicate
GSO - Gadolinium Oxyorthosilicate
Na(Tl) I works well at 140 keV, and is the most common scintillator used in SPECT cameras

7. Scintillation detector
Amplifier
PHA
It is important to explain why there is a proportionality between the photon energy absorbed in the detector and the pulse height
Scaler

8. Pulse height analyzer Pulse height (V) UL LL Time
The pulse height analyzer allows only pulses of a certain height
(energy) to be counted.
counted
not counted

9. Gamma camera
Used to measure the spatial and temporal distribution of a radiopharmaceutical

10. GAMMA Camera

11. Gamma camera (principle of operation)
Position X
Position Y
Energy Z
PM-tubes
Detector
Collimator
Types of collimator
Pinhole
Parallel hole
Diverging
Converging collimators.

12. GAMMA CAMERA
Photons are selected by a collimator, hits the detector crystal, which produce light flashes that are detected and amplified by the photomultipliers, then send to digitizer, and then to computer processor for image reconstruction, then to display on monitor.

13. PM-tubes
Detect and amplify the light flash produced by the scintillation crystal.

14. GAMMA-ray Scintillation Detector
gamma-ray energy converted to light
Light converted to electrical signal
Photomultiplier Tube
gamma-Rays
Light
Electrical
Signal
Scintillation
Crystal

15. Photomultiplier Tubes
Light incident on Photocathode of PM tube
Photocathode releases electrons + -
gamma-Rays
Light
Scintillation
Crystal
Photocathode PM
Tube
Dynodes

16. Photomultiplier Tubes
Electrons attracted to series of dynodes
each dynode slightly more positive than last one + + + - + +
gamma-Rays
Light
Scintillation
Crystal
Photocathode PM
Tube
Dynodes

17. Gamma camera Data acquisition
Static
Dynamic
ECG-gated
Wholebody scanning
Tomography
ECG-gated tomography
Wholebody tomography

18. Scintigraphy seeks to determine the distribution of a radiopharmaceutical
There are methods to change the radionuclide distribution. In this case (examination of the myocaedium using Tc99 sestamibi) the uptake in the liver and emptying of the gallbladder can be stimulated by giving the patient a fatty meal.

19. SPECT cameras are used to determine the three-dimensional distribution of the radiotracer

20. Tomographic acquisition

21. Tomographic planes
The image can be used to illustrate that gammacamera tomography is imaging of a volume where slices can be displayed in any plane.

22. Myocardial scintigraphy
This is an example of a surface rendered image combined with the information in the coronal slices. The patient has an iscemic heart disease.

23. ECG GATED TOMOGRAPHY
This is an animated image and shows the information in three tomographic planes as well as a surface rendered image to illustrate wall motion.

24. 12.2 Image Quality & Camera QA

25. Factors affecting image formation
Distribution of radiopharmaceutical
Collimator selection and sensitivity
Spatial resolution
Energy resolution
Uniformity
Count rate performance
Spatial positioning at different energies
Center of rotation
Scattered radiation
Attenuation
Noise

26. SPATIAL RESOLUTION
Sum of intrinsic resolution and the collimator resolution
Intrinsic resolution depends on the positioning of the
scintillation events (detector thickness, number of PM-tubes, photon energy)
Collimator resolution depends on the collimator geometry (size, shape and length of the holes)

27. SPATIAL RESOLUTION
Object
Image
Intensity

28. NON-UNIFORMITY (Contamination of collimator)
The image to the right is aquired after cleaning of the collimator
(Contamination of collimator)

29. NON UNIFORMITY RING ARTIFACTS
Good uniformity Bad uniformity
The lower image is the absolute difference between the upper two images. It clearly shows the ring artifacts.
Difference

30. NON-UNIFORMITY Defect collimator
The images in the lower row are acquired using a collimator with 50% lower sensitivity in an 1cm3 area in the center of the field of view. The images in the upper row are from the same patient acquired with a good collimator. It is important to point out the risk of false positive results if the camera is not working perfectly,
Defect collimator

31. Scattered radiation Scattered photon photon electron
Remember that compton scattering is the dominating process in the attenuation of photons in soft tissue.
photon
electron

32. The amount of scattered photons registered
Depends on
1- Patient size
2- Energy resolution of the gammacamera
3- Window setting

33. PATIENT SIZE
In the case of a big patient some of the full energy photons that should have reached the gamma camera will be scattered in the patient. The relation scattered/full energy photons will increase with the volume of the patient.

34. Pulse height distribution
Energy
Counts 20 40 60 80
100
120
140
160
Tc99m
Full energy peak
Scattered
photons
The width of the full energy peak (FWHM) is determined by the energy resolution of the gamma camera. There will be an overlap between the scattered photon distribution and the full energy peak, meaning that some scattered photons will be registered.
FWHM
Overlapping area

35. Window width
20%
40%
10%
The image can be used to discuss the optimum relation between sensitivity and image quality.
Increased window width will result in an increased number of registered scattered photons and hence a decrease in contrast

36. ATTENUATION CORRECTION
Transmission measurements
Sealed source CT

37. ATTENUATION CORRECTION
Ficaro et al Circulation 93: , 1996

38. NOISE
Count density

39. Gamma camera Operational considerations Collimator selection
Collimator mounting
Distance collimator-patient
Uniformity
Energy window setting
Corrections (attenuation, scatter)
Background
Recording system
Type of examination

40. QC GAMMA CAMERA Acceptance Daily Weekly Yearly Uniformity P T T P
Uniformity, tomography P P
Spectrum display P T T P
Energy resolution P P
Sensitivity P T P
Pixel size P T P
Center of rotation P T P
Linearity P P
Resolution P P
Count losses P P
Multiple window pos P P
Total performance phantom P P
P: physicist, T:technician

41. Sensitivity
Expressed as counts/min/MBq and should be measured for each collimator
Important to observe with multi-head systems that variations among heads do not exceed 3%

42. Multiple Window Spatial Registration
Performed to verify that contrast is satisfactory for imaging radionuclides, which emit photons of more than one energy (e.g. Tl-201, Ga-67, In-111, etc.) as well as in dual radionuclides studies

43. Count Rate Performance
Performed to ensure that the time to process an event is sufficient to maintain spatial resolution and uniformity in clinical images acquired at high-count rates

44. Total performance Total performance phantom. Emission or transmission.
Compare result with reference image.

45. Phantoms for QC of gamma cameras
Bar phantom
Slit phantom
Orthogonal hole phantom
Total performance phantom

46. QUALITY CONTROL ANALOGUE IMAGES
Quality control of film processing: base & fog, sensitivity,
contrast

47. QUALITY ASSURANCE COMPUTER EVALUATION
Efficient use of computers can
increase the sensitivity and
specificity of an examination.
* software based on published and
clinically tested methods
* well documented algorithms
* user manuals
* training
* software phantoms

48. SPECT/CT System

49. TYPICAL SPECT/CT CONFIGURATION
The most prevalent form of SPECT/CT scanner involves a dual-detector SPECT camera with a 1-slice or 4-slice CT unit mounted to the rotating gantry; 64-slice CT for SPECT/CT also available

50. SPECT/CT Accurate registration CT data used for attenuation correction
Localization of abnormalities
Parathyroid lesions (especially for ectopic lesions)
Bone vs soft tissue infections
CTCA fused with myocardial perfusion for 64-slice CT scanners

51. The CT Scanner
X ray tube
X ray emission in
all directions
collimators

52. A look inside a rotate/rotate CT
Detector Array
and Collimator
X Ray
Tube

53. A Look Inside a Slip Ring CT
Note:
how most
of the
electronics is
placed on
the rotating
gantry
X Ray
Tube
Detector
Array
Slip Ring

54. What are we measuring in a CT scanner?
We are measuring the average linear attenuation coefficient µ between tube and detectors
The attenuation coefficient reflects how the x ray intensity is reduced by a material

55. Conversion of  to CT number
Distribution of  values initially measured
 values are scaled to that of water to give the CT number

56. Nuclear medicine application according to type of radionuclide
Diagnostics
Therapy
Pure  emitter  ()
e.g. ; Tc99m, In111, Ga67, I123
Positron emitters (ß+)  
e.g. : F-18
, ß- emitters  
e.g. : I131, Sm153
Pure ß- emitters  
e.g. : Sr89, Y90, Er169
 emitters  
e.g. : At211, Bi213

57. RADIOPHARMACEUTICALS
Radiopharmaceuticals used in nuclear medicine can be classified as follows:
ready-to-use radiopharmaceuticals
e.g. 131I- MIBG, 131I-iodide, 201Tl-chloride, 111In- DTPA
instant kits for preparation of products
e.g. 99mTc-MDP, 99mTc-MAA, 99mTc-HIDA, 111In-Octreotide
kits requiring heating
e.g. 99mTc-MAG3, 99mTc-MIBI
products requiring significant manipulation
e.g. labelling of blood cells, synthesis and labelling of radiopharmaceuticals produced in house

58. Radionuclide used with SPECT
99mTc - Technetium

59. 99Mo-99mTc GENERATOR 87.6% 99Mo 99mTc  140 keV T½ = 6.02 h 12.4%
Technetium-99m is a metastable nuclear isomer of technetium-99, symbolized as 99mTc. The "m" indicates that this is a metastable nuclear isomer
87.6%
99Mo
99mTc
Molybdenum 99
 140 keV
T½ = 6.02 h
12.4%
ß- 442 keV
 739 keV
T½ = 2.75 d
99Tc
ß- 292 keV
T½ = 2*105 y
99Ru stable

60. Technetium generator Mo-99 Tc-99m Tc-99 NaCl AlO2 Mo-99 +Tc-99m Tc-99m
66 h h
NaCl
AlO2
Mo-99
+Tc-99m
Tc-99m

61. Technetium generator
Note that there different types of generators. This illustrates a dry type with a separate container of saline solution that is changed every time a new elution will be made. In the wet type of generator there is a built in container with enough volume of saline solution for all elutions

62. Technetium generator
This is a closer look at the top of the generator with the needles where the elution vial and the saline solution vial are placed

63. Radiopharmaceuticals
Radionuclide Pharmaceutical Organ Parameter
+ colloid Liver RES
Tc-99m MAA Lungs Regional
perfusion
+ DTPA Kidneys Kidney
function
The image can be used for a short explanation of a radiopharmaceutical. The same radioactive substance can be used in labeling of different compunds resulting in radiopharmaceuticals with different properties

64. Laboratory work with radionuclides

65. Administration of radiopharmaceuticals

66. SUMMARY OF SPET/CT
SPECT cameras are scintillation cameras, also called gamma cameras, which image one gamma ray at a time, with optimum detection at 140 KeV, ideal for gamma rays emitted by Tc-99m
SPECT cameras rotate about the patient in order to determine the three-dimensional distribution of radiotracer in the patient
SPECT/CT scanners have a CT scanner immediately adjacent to the SPECT camera, enabling accurate registration of the SPECT scan with the CT scan, enabling attenuation correction of the SPECT scan by the CT scan and anatomical localization of areas of unusually high activity revealed by the SPECT scan

67. SPECT/CT CLINICAL ALLPLICATIONS
Refer to the pdf file included with this lecture (spect-appl-L8)