Image Formation

Question 1

What are the factors which limit image quality

Answer 1

Spatial resolution
Image Noise
Non-uniformities in camera response
Attenuation and scatter
Technical errors or scanning difficulties

Question 2

What is spatial resolution?

Answer 2

The measure of how close together distinguishable objects can be

Question 3

What is the FWHM of a system?

Answer 3

Full width at half maximum response height. Obj separated by the FWHM can be resolved.

Question 4

What is noise?

Answer 4

Variance within regions across an image which makes it harder to distinguish real features (assess via snr and cnr)

noise = stdn = sqrt (avr pixel count)

inc counts -> reduced noise

Question 5

What is the fractional uncertainty on a count rate?

Answer 5

1/sqrt(N)

1% uncertainty = 1 sqrt(10000 counts)

Question 6

What are examples of imaging artefacts (4)?

Answer 6

1) Pharmaceutical
- Labelling problems

2) Equipment
- Image non-uniformity
- Centre of Rotation errors

3) Patient
- Attenuation
- Movement
- Contamination
- Preparation Non-compliance

4) Operator
- Extravasation
- External attenuation
- Acquisition errors
- Display errors

Question 7

What is a CZT system?

Answer 7

Semi-conductor detector – no intermediate visible light stage

Asymmetric peak – incomplete detection due to electron hole recombination, hole trapping charge sharing between pixels and scatter

Continuous cathode on one side, discrete one per pixel anode connections on the other - minimal charge spreading

independence of pixels means a high count can be excepted

Robust and easy to maintain - can swap out sections

Question 8

What is D-SPECT?

Answer 8

9 small detectors rotating about their own axes - non-uniform sampling, high angular

Cardiac specialised / higher ang sample over ROI

List mode, reliant on reconstruction to improve resolution

Cardiac model as OSEM starting point