Intro to SPECT/CT

Question 1

Benefits of SPECT (and CT)

Answer 1

• increased contrast resolution
• better localization
• improved detection of lesions
• quantitative possibilities
• CT improves anatomic localization and attenuation correction

Question 2

line integrals

Answer 2

• total radioactivity measured along a straight line through the object
• defined by the path of a collimator hole in SPECT, ignoring attenuation and scatter

Question 3

Projection

Answer 3

A full set of line integrals across a detector head

Question 4

SPECT hardware

Answer 4

• collimated detector system
• 360 gantry rotation
• non-attenuating scan table
• computer terminal/console

Question 5

Collimator resolution

Answer 5

• SPECT spatial resolution is poor due to distance from the detector
• rc = [d(a+b)]/a
• c = geometric spatial resolution (FWHM)
• d = septal hole diameter
• a = septal hole length
• b = patient/source to collimator distance

Question 6

Long Bore Collimator

Answer 6

• Increase in “a” spatial resolution formula
• Improved contrast and resolution
• Decreased sensitivity

Question 7

Slant Hole Collimator

Answer 7

• Holes are at a slight angle off perpendicular to the detector face
• Decrease in “b”
• Improved sensitivity and resolution

Question 8

Converging Collimator

Answer 8

• Holes converge to a point in front of the
  collimator
• Variations include fan-beam and cone-
  beam collimators
• Used for small organs (e.g., heart, brain)
• 1.5 to 2 times increase in sensitivity
• Similar resolution to parallel hole

Question 9

Loss of image accuracy

Answer 9

• Attenuation
• Scatter
• Lost counts
• Misplaced counts
• Non-uniformity
• Detector misalignment
• Partial volume effect
• Motion
• Orbit choice
• Truncation

Question 10

Voxel vs. pixel

Answer 10

• voxel: volume element
• pixel: picture element