1. Gamma Camera
Ilker Ozsahin
Oct

2. Questions
Which radiations can be stopped in which medium or material and at what thickness? Why is this important?
What is the mostly used scintillation crystal, and their properties, e.g. NaI(Tl) Thallium-doped Sodium Iodide and its density, atomic number, etc.?
Spatial Resolution & Sensitivity Formula?
Compton Kinematics?
Characteristics of Scintillation Detectors: Energy Resolution, Decay Time, Efficiency, Effective Z, Density, Photon Yield, Relative Light Output, Attenuation Coefficient?

3. Anger Camera

4. Gamma Camera
Invented by Hal Anger, the gamma camera is usually based on the use of a single large area (e.g. 50 cm x 40 cm of NaI(Tl)) phosphor coupled to up to a hundred PMTs. The camera can detect gamma rays emitted by a radiotracer distributed in the body. The lead collimator placed in front of the scintillation counter selects the direction of the gamma rays entering the device and allows an image of the biodistribution of the tracer to be made.

5. Components
The gamma camera, or Anger camera, is the traditional workhorse of nuclear medicine imaging and its components are illustrated here. Gamma camera systems are comprised of four basic elements: the collimator, which defines the lines of response (LORs); the radiation detector, which counts incident gamma photons; the computer system, which uses data from the detector to create 2‑D histogram images of the number of counted photons; and the gantry system, which supports and moves the gamma camera and patient.

6. Components

7. Crystal

8. Bulk Crystal

9. Crystal?

10. Purpose
The overall function of the system is to provide a projection image of the radioactivity distribution in the patient by forming an image of gamma rays exiting the body

11. Collimators
Gamma rays from radioactive source within the body emitted in all directions, so high degree of collimation needed
Operating principle: absorptive collimation
Only gamma rays travelling in certain directions go through and reach the detector, the others are absorbed in the septa where most radiation is absorbed
Made usually from tungsten or lead to provide high absorption probability

12. Collimators
The drawing on the left demonstrates the image of two point sources that would result without the collimator. It provides very little information about the origin of the photons and, thus, no information about the activity distribution in the patient. The drawing on the right illustrates the role of the collimator and how it defines lines of response (LOR) through the patient.

13. Collimators
As mentioned above, the collimator defines LORs. The collimator accomplishes this by preventing photons emitted along directions that do not lie along the LOR from reaching the detector. Thus, collimators consist of a set of holes in a dense material with a high atomic number, typically lead. The holes are parallel to the LORs. Ideally, each point in the object would contribute to only one LOR. This requires the use of collimator holes that are very long and narrow. However, such holes would allow very few photons to pass through the collimator and be detected. Conversely, increasing the diameter or decreasing the length of the holes results in a much larger range of incident angles passing through the collimator.

14. Collimator Size

15. Collimator Size
Illustration of the concept of spatial resolution and how collimator hole length and diameter affect spatial resolution. The lines from the point source through the collimator indicate the furthest apart that two sources could be and still have photons detected at the same point on the image plane (assumed to be the back of the collimator). Thus, sources closer together than this would not be fully resolved (though they might be partially resolved). From this, we see that the resolution decreases as a function of distance. It should also be noted that the resolution improves proportionally with a reduction in the width of the collimator holes and improves (though not proportionally) with the hole length.

16. Multi Hole Collimators
Examples of the three major hole shapes used in multi-hole collimators. They are from left to right: round, hexagonal and square holes. In all cases, black indicates septa and white open space. The diameter is d and the septal thickness is s.

17. Multi Hole Collimators
Multi-hole collimators typically have many thousands of holes. The uniformity of the image critically depends on the holes having uniform sizes and spacing. As a result, high quality fabrication is essential. The septa must be made of a high density, high Z material in order to stop the incident γ rays. Lead is the material of choice for most multi-hole collimators due to its relatively low cost, low melting temperature and malleability

18. Collimator Holes

19. Types of Collimator
Parallel holes are the most commonly used collimators. The LORs are parallel, and there is, thus, a one to one relationship between the size of the object and image.
In converging hole collimators, the LORs converge to a point (focal point) or line (focal line) in front of the collimator, and there is magnification of the image. These two collimator types are referred to as cone-beam and fan-beam collimators, respectively. These are useful for imaging small objects, such as the heart or brain

20. Types of Collimator
In diverging hole collimators, the LORs converge to a point or line behind the collimator. This results in minification of the image. Diverging hole collimators are useful for imaging large objects on a small camera. However, they result in a poor resolution versus noise trade-off, and are, thus, infrequently used.
Pinhole collimators use a single hole to define the LORs. In terms of geometry, they are similar to cone-beam collimators but with the focal point between the image plane and the object being imaged. As a result of this, the image is inverted compared to the object. In addition, the object can be either minified or magnified depending on whether the distance from the image plane to the focal point is less than or greater than the distance from the pinhole to the object plane.

25. Advantages/Disadvantages
3D image
Organ Specific
Exposing to radioactivity
Further discussion will be made after learning about SPECT and PET system

26. Making Slides!!!
No copy&paste, instead, read, understand, write with your own words.
During the presentation, make sure if the audience is listening or reading?
Always have references at the end

27. PMT-Photocathode-Dynode-Anode

28. PMT and PreAmp

29. Scintillation Crystal

30. Scintillation Process
Scintillation is a general term referring to the process of giving off light, it is used both literally and figuratively.
When a gamma ray hits the crystal, it ejects an outer shell electron.
When an excited electron in the scintillator returns to its ground state, it can release a photon in the UV or visible light range.