Display and quantitation

Question 1

Partial Volume Effect

Answer 1

• ‘the within-voxel averaging that occurs in any 3D imaging situation due to the finite size of the volume elements used’
• The reduction in contrast resolution when the detail is smaller than the resolution volume of an image
• The counts from the detail are averaged with the counts from surrounding tissue within the resolution volume, reducing contrast and quantitative accuracy

Question 2

2D Slice Display

Answer 2

2D representation of data
* Transverse
* Coronal
* Sagittal
* Oblique
* SA, HLA, VLA
Must visualize 3D relationship between
structures

Question 3

3D Image Display

Answer 3

• Reconstructed data obtain 3D
  representation of RP distribution
  (volume) but no depth information
• 3D rendering displays enable the
  rotation of a set of volumetric images
• Surface Shading
• Volume Rendering

Question 4

Surface shading

Answer 4

• Shows only solid outer surface of organ
  no internal structures
• Threshold used to determine data that
  is expressed
• Useful for thin organs with cold
  abnormalities
• e.g., brain, heart

Question 5

Volume rendering

Answer 5

• Images are generated by reprojecting
  voxel counts from the SPECT data
• Inverse of backprojection
• Produces images with very little noise
• MIP is a common technique used in NM
• Useful for identifying hot abnormalities
• E.g., bone, hemangioma

Question 6

Qualitative analysis

Answer 6

• As with planar imaging, qualitative analysis involves visually assessing for
  defects/lesions
• Quality control to remove any visual artifacts
• Need high contrast, good spatial resolution, low noise
• The ‘absolute value’ (cts/pixel) is not
  important

Question 7

Quantitation

Answer 7

• Quantitation can be thought of as:
• The certainty of detecting a lesion of a certain size in a body of a particular size and shape with a given radioactive distribution
• Determining the volume of a portion of the body
• Mapping of distribution of activity in 3D with accuracy and precision in the quantity of injected radioactivity
• Change with time of any of the above
• The accuracy of quantitation is related to the spatial resolution of the system

Question 8

Relative Quantitation

Answer 8

• Estimate of tracer concentration in target as a function of some other target in the image
• Compare the concentration in one structure to another
• Time activity curves: SPECT removes superimposed structures from the target organ, therefore improving the uptake and distribution measurements over planes
• Myocardium uptake and redistribution (bullseye)

Question 9

Semi-quantitative analysis

Answer 9

• Count density compared to count density in another area or in the same area at a different time
• (ct. density / ct. density) ratio
• Counts/pixel is not important
• Background is not important if consistent
• Ejection fraction, polar plot, bullseye, etc

Question 10

Quantitative analysis

Answer 10

• [activity] in a volume in a patient
• ‘functional analysis’ for physiological functions
• Must know tracer parameters of transport, metabolism, and storage

Question 11

Absolute quantitation

Answer 11

• Measurement of radioactive tracer
  concentrations in MBq/volume element
• Limited by:
• noise, surrounding target background, attenuation, geometry, system performance, filter functions,
  reconstruction artifacts, and target motion
• Method: count syringe prior to injection
  count tracer in target in MBq/pix

Question 12

Quantitative SPECT challenges

Answer 12

• Many factors have an impact on SPECT
  quantitative accuracy:
• Detector response
• Attenuation
• Scatter
• Noise
• Uniformity
• Reconstruction
• Accuracy affected by the backprojection process, filtering parameters, matrix/pixel size, # of projections, QC, etc