Calculating parametric BPND or DVR images using BF-SRTM
- BP
- binding potential
- DVR
- distribution volume ratio, BP+1
- BF
- basis function approach (Gunn et al. 1997)
- SRTM
- simplified reference tissue (input) model (Lammertsma and Hume, 1996)
Steps to compute parametric map of BPND or DVR:
- Find the dynamic image file
- Find the SIF file for this image; if SIF file does not exist, then make the SIF file from dynamic image
- Draw ROI on the reference region, calculate its time-activity curve (TAC), and make sure that it is saved alone in a DFT file
- Check the θ3 constraints for this study protocol
- Execute program imgbfbp in MS Windows command prompt or Solaris terminal window. Remember to enter the θ3 constraints using options -min and -max, and preferably also threshold limit 10% using option -T=10
Include also option -DVR, if DVR image is needed instead of
BP image.
Determination of constraints for θ3
Suggested constraints in Turku PET Centre
| PET tracer | Parametric images | Regional TACs | ||
|---|---|---|---|---|
| min | max | min | max | |
| [C-11]FLB | - | - | - | - |
| [F-18]SPA-RQ | 0.03 | 0.6 | 0.01 | 0.6 |
| [C-11]PIB | 0.05 | 0.6 | 0.04 | 0.6 |
| [C-11]raclopride | 0.06 | 0.6 | 0.06 | 0.6 |
Constraints for θ3 may need to be re-evaluated when imaging parameters that affect the noise properties of the PET image are substantially changed (scanner, reconstruction, framing, study length, injected dose, ...).
If your PET tracer is not in the table
Ask Kaisa Liukko (born Sederholm) to determine the constraints for the tracer. For this purpose, you must provide a couple of dynamic images (control subject and patient, basal state and intervention etc), TAC of reference region, and preferably ROI files of all regions that may be of interest in regional or SPM analysis.
Issues to consider when determining the constraints for θ3
- Minimum of θ3 must always be higher that the decay constant (λ) of the isotope that was used to label the tracer; λ for F-18 is 0.0063 min-1 and for C-11 0.034 min-1.
- Regional BF-SRTM (using regbfbp) must fit well all the regional TACs that may be of interest in any analysis
- The results of BF-SRTM are very sensitive to the weights
- The quality of parametric image is usually not very dependent on the θ3max, as long as it is high enough; however, it should not be set to any higher value as necessary, because then more basis functions must be used, which will slow down the calculation.
- The BP or DVR image will look the better (less noisy) the higher value for the θ3min is set. However, it may be that the highest BP or DVR values are subsequently cut off, causing negative bias in regions of high BP or DVR.
- Low θ3min leads to higher noise, which may be skewed and cause positive bias in regions of high BP or DVR.
- Check that regional distribution of BP or DVR pixel values is not extremely skewed
- Parametric BP and DVR images must always be checked to provide similar regional results as the ones calculated from regional average TACs using fit_srtm or lhsrtm
- Initial estimates of suitable constraints for θ3 can be reached from θ3 images produced optionally using imgsrtm or from k2/(1+BP) values (add λ) from lhsrtm
