This lecture discusses the development of nuclear imaging techniques. It begins with an overview of nuclear imaging and its use of gamma rays and x-rays to form images. The earliest device was the rectilinear scanner, which used a single moving detector. The Anger gamma camera was a significant improvement as it allowed simultaneous detection over a large area. Modern gamma cameras use NaI(Tl) scintillator crystals coupled to PMTs to convert gamma ray interactions to light and then electrical signals. Digital processing is used to determine interaction locations and form images. Collimators are used to selectively detect gamma rays from a desired direction.

1. Lecture 9: Nuclear Imaging-I
Shahid Younas
NUCLEAR IMAGING
The Scintillation Camera- Design Performance

2. INTRODUCTION
Lecture 9: Nuclear Imaging-I
 Nuclear imaging produces images of the
isotropicaly distributed of radionuclides in
patients.
 Uses gamma rays, characteristic x-rays, or
annihilation photons to form images

3. INTRODUCTION
Lecture 9: Nuclear Imaging-I
 An imaging system must determine,
 Photon flux Density
 Direction of the detected photon

4. INTRODUCTION
Lecture 9: Nuclear Imaging-I
 Instruments designed to image gamma
ray and x-ray emitting radionuclides
use collimators.
 Vast majority (over 99.95%) of emitted
photons is wasted.

5. Development- Rectilinear Scanner
Lecture 9: Nuclear Imaging-I
 Earliest successful imaging device
was the rectilinear scanner
 A single moving radiation detector
sampled the photon fluence at a
small region at a time

6. Development- Rectilinear Scanner
Lecture 9: Nuclear Imaging-I
 The output was recorded on white
paper with a series of black marks.
 Intensity of exposure or depth of
color, corresponded to the
concentration of radioisotope.

7. Development- Rectilinear Scanner
Lecture 9: Nuclear Imaging-I
Benedict Cassen invented the rectilinear scanner.
Do you know which was the first organ scanned
on this scanner?
Thyroid

8. Development- Rectilinear Scanner
Lecture 9: Nuclear Imaging-I
 Improved upon by use of a large-area positron-sensitive detector
(indicating the location of each interaction) to sample
simultaneously the photon fluence over the entire image plane.
 More expensive; permits more rapid image acquisition

9. Development- Anger Gamma Camera
Lecture 9: Nuclear Imaging-I
 Developed by Hal Anger from 1952 to 1958
 Significantly replace rectilinear scanners in the late 1960s
 Spatial resolution became comparable to that of rectilinear scanners.
 Tc-99m-labeled radiopharmaceuticals became commonly used
 Replacing I-131 and Hg-203

10. Development- Anger Gamma Camera
Lecture 9: Nuclear Imaging-I
Do you know what was the main
short-coming of Anger Gamma
Camera?
Continuous motion.

11. Development- Anger Gamma Camera
Lecture 9: Nuclear Imaging-I
 Simultaneous collection of data over
large area.
 Permits more rapid acquisition of images
and enables dynamic studies.
 More flexible in its positioning,
permitting images to be obtained from
almost any angle

12. Development- Anger Gamma Camera
Lecture 9: Nuclear Imaging-I
 Scintillation camera wastes fewer
photons.
 Images have less quantum mottle
(statistical noise).
 Can be used with higher resolution
collimators, producing images of better
spatial resolution

13. Development- Anger Gamma Camera
Lecture 9: Nuclear Imaging-I
What is the suitable photon energy range of usage of
gamma camera?
100 to 200 keV

14. Gamma Camera Design
Lecture 9: Nuclear Imaging-I
 Scintillation camera contains a disk-shaped or
rectangular NaI(Tl) crystal,
 ~ 0.95 cm thick, optically coupled to
 ~37 to 91 PMTs
 5.1- to 7.6-cm diameter

15. Gamma Camera Design
Lecture 9: Nuclear Imaging-I
 Some designs incorporate a Lucite light-pipe between the glass
cover of the crystal and the PMTs; in others, the PMTs are directly
coupled to the glass cover.
 In most cameras, a preamp is connected to the output of each PMT

16. Nuclear Stability Tests
Lecture 9: Nuclear Imaging-I

17. Gamma Camera Design
Lecture 9: Nuclear Imaging-I
 Front side of Gamma
Camera Head without
collimator. A

18. Gamma Camera Design
Lecture 9: Nuclear Imaging-I
 Between the patient and the crystal is a
collimator, usually made of lead.
 A scintillation camera without a collimator
does not generate meaningful images

19. Gamma Camera -Design
Lecture 9: Nuclear Imaging-I
 Septa absorbs most of the photons ( 99.95%).
 Photons approaching the collimator from a nearly perpendicular
direction pass through the holes.
 Those absorbed in NaI(Tl) causes emission of visible and
ultraviolet light.

20. Gamma Camera -Design
Lecture 9: Nuclear Imaging-I
 Lights photons are converted into electrical signals.
 Amplification by PMTs.
 Further amplified by pre-amplifiers (preamps).
 Amplitude of the amplified pulse ~ amount of interaction light

21. Gamma Camera -Design
Lecture 9: Nuclear Imaging-I
 The pattern of photon interactions in the crystal forms a 2D
projection of the 3D activity distribution in the patient.
 The PMTs closest to each photon interaction in the crystal receive
more light producing larger voltage pulses

22. Gamma Camera -Design
Lecture 9: Nuclear Imaging-I
 Relative amplitude of the pulses from the PMTs contain sufficient
information to determine the location of the interaction in the
plane of the crystal.

23. Gamma Camera -Design
Lecture 9: Nuclear Imaging-I
Why Sodium Iodide is doped with Thallium?
Pure NaI is scintillator only at Liquid Nitrogen temperature. Thallium
(0.1-0.4 mole %) is added to create activity centers to scintillate at room
temperature.

24. Gamma Camera –Analogue Design
Lecture 9: Nuclear Imaging-I
Electronic circuits of a fully analog scintillation camera.

25. Gamma Camera -Design
Lecture 9: Nuclear Imaging-I
 Single Channel Analyzer produced a logic pulse (a voltage pulse
of fixed amplitude) only if the Z pulse received was within a
preset range of energies.
 Different Energy Setting ranges for different radionuclides.

26. Gamma Camera –Analogue Design
Lecture 9: Nuclear Imaging-I
Have you heard that in old cameras there used to be a manual dial
which is changed by technologist?
That was actually SCA Shift

27. Gamma Camera –NaI(Tl) Crystal
Lecture 9: Nuclear Imaging-I
 Scintillator is a transparent material that converts the energy lost by
ionization into pulse of light.
 Higher conversion efficiency
 Short decay time of excited state
 Transparent to its own emissions
 High Detection Efficiencies
 Rugged, hygroscopic free, inexpensive

28. Gamma Camera –NaI(Tl) Crystal
Lecture 9: Nuclear Imaging-I
Property NaI (Tl) BGO LSO (Ce) CsI (Tl) BaF2
Density 3.67 7.13 7.4 4.15 4.89
Effecitve No. 50 74 66 54 54
Decay time
(nsec)
230 300 40 1000 0.8
Photon Yield
Per KeV
38 8 20-30 52 10
Hygroscopic Yes No No Slightly No

29. Gamma Camera –NaI(Tl) Crystal
Lecture 9: Nuclear Imaging-I
 Good absorber and Efficient Detector due to ,
 Relative Density 3.67 g /cm3
 Higher Z of Iodine ( 53)
 Sensitivity > 85 % at 140 keV
 Moderate Energy Resolution 9-10 %
 Well matched in λ to peak response to PMT.

30. Gamma Camera –NaI(Tl) Crystal
Lecture 9: Nuclear Imaging-I
 At higher gamma ray energies (>300 KeV) needs larger volume
for better detection.
 Fragile
 Hygroscopic
 Temperature Range

31. Gamma Camera –Analogue Design
Lecture 9: Nuclear Imaging-I
Do you know the desirable Temerature and humidity range for
efficient camera working?
18-24 ± 1.5 oC
30-60 ± 5%

32. Gamma Camera –NaI(Tl) Crystal
Lecture 9: Nuclear Imaging-I
 NaI is doped with 0.1-0.4 mole % Thallium to scintillate.
 Single, Large area usually, 6-12.5 mm ( ~ 9.5 mm) thick
 Increased Sensitivity but Resolution decreases.
 25-50 cm diameter or 60 x 40 cm dimensions if rectangular.
 Surrounded by highly reflective material TiO2 or Mag-Oxide to
maximize light output.

33. Gamma Camera –hybrid Design
Lecture 9: Nuclear Imaging-I
 Late 1970s hybrid analog-digital scintillation cameras introduced
 Analog X, Y, and Z pulses converted to digital signals by analog-
to-digital converters (ADCs)
 Digital signals sent to digital correction circuits

34. Gamma Camera –hybrid Design
Lecture 9: Nuclear Imaging-I
 Corrected digital X, Y, and Z signals converted back to analog
voltage pulses.
 Energy discrimination done in the analog domain by SCAs.
 Output to CRT as with display on a computer monitor.

35. Gamma Camera –hybrid Design
Lecture 9: Nuclear Imaging-I
Electronic circuits of a hybrid analog-digital scintillation camera.

36. Gamma Camera –Model Digital Design
Lecture 9: Nuclear Imaging-I
 Corrected digital X, Y, and Z signals converted back to analog
voltage pulses.
 Energy discrimination done in the analog domain by SCAs.
 Output to CRT as with display on a computer monitor.

37. Gamma Camera –Model Digital Design
Lecture 9: Nuclear Imaging-I
Electronic circuits of a modern digital scintillation camera.

38. Gamma Camera –Model Digital Design
Lecture 9: Nuclear Imaging-I
Even if the cameras are digital but you have to identify
radionuclide.

39. Gamma Camera –Collimators
Lecture 9: Nuclear Imaging-I
 Collimator forms the projection image by permitting gamma ray
photons to reach the crystal while absorbing most of the other
photons.
 Most common collimator is the parallel-hole collimator

40. Gamma Camera –Collimators
Lecture 9: Nuclear Imaging-I
 Holes may be round, square, or triangular.
 Most state-of-the-art collimators have hexagonal holes and are
usually made from lead foil.
 Septa must be thick enough to absorb most of the photons
incident upon them

41. Gamma Camera –Collimators
Lecture 9: Nuclear Imaging-I
 Inherent compromise between spatial resolution and efficiency
(sensitivity) of collimators.
 Reducing size of holes or lengthening collimator to improve
spatial resolution reduces efficiency.

42. Gamma Camera –Collimators
Lecture 9: Nuclear Imaging-I
 Most scintillation cameras are provided with a selection of
parallel-hole collimators:
 “low-energy, high-sensitivity”
 “low-energy, all-purpose” (LEAP)
 “low-energy, high-resolution” (LEHR)

43. NUCLEAR IMAGING-I
Lecture 9: Nuclear Imaging-I
Curie was the passion and Becquerel was the passion however
radiation are still at large.
(SY)