Phys 102: Photomultiplier Tubes

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What is the primary function of the photocathode in a photomultiplier tube?

To focus the electrons

To produce photoelectrons (correct)

To amplify the electrons

To collect the electrons at the anode

What happens when the primary electrons collide with the first dynode surface?

The electrons are reflected back to the photocathode

The electrons are amplified by the dynode

The electrons liberate more electrons (correct)

The electrons are absorbed by the dynode

What is the final stage of the electron amplification process in a photomultiplier tube?

The production of photoelectrons by the photocathode

The collision with the first dynode surface

The focusing of electrons by the focusing electrode

The collection of electrons at the anode (correct)

What is the purpose of a pixelated grid in a conventional gamma camera?

To form a gamma image by recording the number of detected gamma photons Signup and view all the answers

Why is it important to minimize scattered gamma photons in gamma ray collimation?

To reduce image noise Signup and view all the answers

What does the gamma image produced by a conventional gamma camera represent?

A true mapping of the radioactive agents in the targeted region of interest Signup and view all the answers

What is the role of the focusing electrode in a photomultiplier tube?

To direct the photoelectrons towards the first dynode Signup and view all the answers

What is the result of the cascade procedure in a photomultiplier tube?

The liberation of multiple electrons Signup and view all the answers

What is the main drawback of the current gamma camera collimators?

Only gamma photons passing through the collimator's holes can be registered. Signup and view all the answers

What is the primary function of a gamma camera collimator?

To map gamma rays emitted from the examined region onto the scintillator. Signup and view all the answers

What type of material is commonly used in the high-density plate of a parallel hole collimator?

Lead Signup and view all the answers

Why is the hexagonal structured hole arrangement used in parallel hole collimators?

To maximise the exposed area of the gamma camera detector. Signup and view all the answers

What determines the appropriate type of collimator for gamma ray detection?

The FOV dimension, targeted areas' dimensions, and the desired level of sensitivity and spatial resolution. Signup and view all the answers

What is the purpose of gamma ray collimation?

To improve the sensitivity of the gamma camera. Signup and view all the answers

What is the most common type of collimator used in gamma image formation?

Parallel hole collimator Signup and view all the answers

What would improve the gamma imaging outcome?

Improving the ability of the gamma camera to maximise the detection of primary gamma photons. Signup and view all the answers

What is the primary concern when designing a collimator body?

Minimising scattered gamma photon penetration Signup and view all the answers

What is the main difference between diverging and converging collimators?

Field of view Signup and view all the answers

What type of collimator is used for scanning small targeted areas?

Converging collimator Signup and view all the answers

What is the purpose of a pinhole collimator?

To satisfy the needs of nuclear medicine clinics with small organ imaging procedures Signup and view all the answers

What is the typical diameter range of a pinhole collimator's aperture?

2-6 mm Signup and view all the answers

What type of material is often used to make pinhole collimators?

Metals like tungsten, lead or platinum Signup and view all the answers

In which applications is the pinhole collimator particularly effective?

Paediatric scans and skeletal extremities nuclear scanning Signup and view all the answers

What do converging and diverging collimators have in common?

Exit plane dimensions Signup and view all the answers

What is the required pinhole diameter for small targeted structures in small animal gamma imaging systems?

1-2 mm or even lower Signup and view all the answers

What is the characteristic of a low-energy collimator?

Thin septa and can be used with gamma rays of up to 150 keV Signup and view all the answers

What is the purpose of a high-resolution collimator?

To achieve high resolution where required Signup and view all the answers

What is the characteristic of a general purpose collimator?

20000 holes each 2.5 mm diameter, a resolution of 9 mm, and sensitivity 150 cps MBq-1 Signup and view all the answers

What is the trade-off of a high-sensitivity collimator?

Poorer resolution Signup and view all the answers

Why is higher spatial resolution required in small animal gamma imaging systems?

To image smaller targeted structures Signup and view all the answers

What is the characteristic of a high-resolution collimator compared to a general purpose collimator?

More and smaller holes Signup and view all the answers

What is the purpose of using a collimator with smaller holes?

To achieve higher spatial resolution Signup and view all the answers

What is the purpose of using medium-energy collimators?

To accept poorer resolution for shorter exposure times Signup and view all the answers

What is the limitation of conventional planar gamma imaging?

It loses depth information and reduces contrast Signup and view all the answers

How many types of emission tomography are mentioned in the text?

Two Signup and view all the answers

What occurs every 6° during a SPECT scan?

The camera halts for 20-30 seconds Signup and view all the answers

How many views are taken from different directions in a SPECT scan?

60 views Signup and view all the answers

What is the approximate total scanning time for a SPECT scan?

30 minutes Signup and view all the answers

What is the consequence of using a parallel hole collimator in SPECT?

Fewer counts in each view Signup and view all the answers

What is the purpose of emission tomography?

To address the limitations of conventional planar gamma imaging Signup and view all the answers

What is the benefit of using SPECT over conventional static imaging?

Better depth information in images Signup and view all the answers