Lecture notes on SPECT technology for nuclear medicine technologists

1. SPECT
Single Photon Emission Computed Tomography
David S. Graff PhD

2. • Tomography
• Filtered Back Projection
• Iterative Reconstruction
• Quality Control

3. Tomography
τομοσ: a cut or a slice
atom: cannot be cut
anatomy: a cutting (of the patient)

4. A Gamma Camera measures the
total activity along a line of sight*
*Ignoring scatter, attenuation, noise, blurring

5. We want to know the activity at every point in space, but
we measure the sum total attenuation along the line of sight
All these systems will look the same

6. To get more information: measure
sums along rays at different angles

7. To get full information,
measure at all angles
In order to see a sharp edge,
we must have rays parallel to the edge

10. A sinogram shows all
the angles in one slice
0º
Head Angle
180º360º
Position on detector

11. • Tomography requires lines of sight through
180º
• Filtered Back Projection
• Iterative Reconstruction
• Quality Control

12. Collect
projections
(data) at wide
range of angles

13. Backproject from
all projections
Edges are
lost. Image
is fuzzy

14. Enhance edges
of projections
(filter)
Backproject
filtered
projections

15. Filter increases high spatial frequencies
and decreases low frequencies

16. A ramp filter would increase noise too much
The filter is modified to reduce high frequencies

17. Filters combine blurring
and ramp to reduce noise
a mp Hann
R
lp/mm

18. Filtered Back Projection

20. Object

21. Projections

22. Filtered

23. Backprojected

25. • Tomography requires lines of sight through
180º
• Filtered Back Projection enhances edges and
backprojects to reconstruct images
• Iterative Reconstruction
• Quality Control

26. Filtered Back Projection assumes
• No noise
• No attenuation
• Perfect resolution
• No scatter
These assumptions are much worse for SPECT than for CT
Iterative algorithms don’t make these assumptions

27. Collect
projections
(data) at wide
range of angles

28. Collect projections (data)
at wide range of angles

29. Assume a simple smooth model of patient

30. Collect projections (data)
at wide range of angles
Assume a simple smooth
model of patient

31. Project
model of
patient
Include attenuation,
resolution, scatter in
projection

32. Collect projections (data)
at wide range of angles
Assume a simple smooth
model of patient
Project model of patient
(including physics)

33. Compare projections of
model with actual projections
Derive a correction for each
projection
÷ =

34. Backproject
corrections

35. Collect projections (data)
at wide range of angles
Assume a simple smooth
model of patient
Project model of patient
(including physics)

36. Collect projections (data)
at wide range of angles
Assume a simple smooth
model of patient
Project model of patient
(including physics)
Compare model projections
to measured projections
Backproject correction to
update model

37. • proper reconstruction requires attenuation
and scatter.
• How do we know how much attenuation?

38. SPECT-CT

39. • Create projections from model of patient
• Compare projections with data from patient
• Improve model

41. • Tomography requires lines of sight through
180º
• Filtered Back Projection enhances edges and
backprojects to reconstruct images
• Iterative Reconstruction accounts for noise,
attenuation, scatter, resolution. Compare
model of patient with data to improve
model.
• Quality Control

44. Bullseye artifact results
from poor homogeneity

50. • Tomography requires lines of sight through
180º
• Filtered Back Projection enhances edges and
backprojects to reconstruct images
• Iterative Reconstruction accounts for noise,
attenuation, scatter, resolution. Compare
model of patient with data to improve
model.
• Quality Control to verify center of rotation,
uniformity, ability to pick up cold spheres
and rods

52. rat heart