SPECT Imaging Brain

Question 1

Advantages of SPECT over planar imaging

Answer 1

Localisation

Increased contrast - you can visualise a slice without all the overlying anatomy

Question 2

FBP

What filters do we need?

What possible disadvantages?

Answer 2

Measure projections from object in many planes. Backproject the signal across the image, NB// you need to filters to smooth out the image

• Back projection itself smoothes the image with a 1/f (spatial frequency) filter
• The image is recorved by multiplying with a ramp filter. But this adds noise so you also need to modify with a:
• Smoothing filter (Butterworth) with cut-off and order

NB// ramp filter can introduce star artefacts

Question 3

Iterative Reconstruction

describe

Answer 3

Estimating the activity distribution, forward project to generate a set of planar images, compare with the estimate of activity distribution and adjust

Question 4

Attenuation Correction

Why do you need it?

How do you do it?

Answer 4

Gamma rays that come from surface of object are attenuated less and look brighter on the image (hot-ring). Need to correct.

• Chang Method - assume uniform attenuation, multiply each pixel by calculated attenuation factor
• Attnenuation map froo m transmission source or CTh data
• Iterative methods, incorporate them into the forward prejection

Question 5

ScatterCorrection

Why do you need it?

How do you do it?

Answer 5

140kev photons are scattered more than they are absorbed. Best method is to combine CT image in iterative recosntruction process.

Question 6

Clinical example:

Brain imaging in dimentia HMPAO

Answer 6

structural and chemical changes in rbain leads to deapth of brain tissue e.g. Alzheimers, dimentia. NICE guidance - MR or CT for structural, if in doubt perfusion SPECT whould be sued to differentiate

• RP - 99m-Tc HMPAO crosses blood brain barrier and binds in proportion to amount of perfusion. Need to reference to an uneffected area.
• 500MBq
• Image for 2 min, 3 hours after injection
• 60 128*128 projections
• FBP

Question 7

Clinical example:

DATSCAN

Answer 7

Used to distinguis tremor and parkinsons, dimentia

• 185MBq
• Thyroid blocking 1hr and 12 hours. Ioflupane has high binding affinity for presynaptic dopamine transporters (DAT). Introducing RP to bind to the DATs, in order to get an idea of how many there are. reduced = disease
• Image 3 hours after injection for 30 mins
• LEHR collimators
• FBP

NB// there are plenty more clinical examples in the slides (might be best to print)