Turku PET Centre04/12/14Jarkko Johansson

HRRT Reconstruction Cluster Validation Report – Status at December 2004

Timeline:- cluster set-up project started by Petri Numminen in autumn 2003- project management delegated to Jarkko Johansson in July 2004- first reasonable HRRT images reconstructed at the cluster in August 2004 after solving the problems with the CTI software (lmhistogram, GMINI etc.)- first release candidate of the cluster validation report, containing the parameter optimisation results, released in August 2004- the specific problem with the varying plane efficiencies in the homogeneity phantom reconstructions has been studied since September 2004

Status:- HRRT reconstruction workstation Powerslave and reconstruction cluster Saturn have been cross-mounted so that Powerslave (Clairvoyant) d-drive is read-accessible and Saturn disk array is read-write-accessible- the problem with the varying plane efficiencies in the homogeneity phantom reconstructions was discovered in the software validation- numerous test reconstructions with different phantoms (mostly homogeneity) have been made at the cluster and analysed- artifacts have been reported to Byars and Bloomfield, and supporting results have been re-produced by Bloomfield- conclusion is that the artifacts are due to the structure of the reconstruction algorithm- decision of whether to continue exclusively with zosem3d or with zosem3d together with the CTI Windows software is not made...

1. Test Material and Methods

The varying plane efficiencies are illustrated by plotting the mean values inside ROIs of different sizes asa function of plane number. The mean values are obtained from the reconstructions of homogeneity phantoms.

Homogeneity phantom I: Ge-68-phantom for daily QC- 10 hours acquisition with the HRRT of TPC

Homogeneity phantom II: Fluor-18 phantom for calibration- 2 hours acquisition with the HRRT of TPC

Homogeneity phantom III: synthetic phantom- oval shaped cylinder forward projected with zosem3d

Homogeneity phantom IV: Ge-68 phantom for daily QC- ? hours acquisition with the HRRT of Toronto

2. Results

Regions of interest are drawn with YaIT 0.5.3 inside the active region. Mean values inside the ROIs are obtained with img2dft and plotted with gnuplot as a function of plane number.

2.1 Homogeneity phantom IThe plane efficiencies are illustrated in Figures 1- 4.

2.2 Homogeneity phantom IIThe plane efficiencies are illustrated in Figure 5.

2.3 Homogeneity phantom IIIThe plane efficiencies are illustrated in Figure 6.

2.4 Homogeneity phantom IVThe plane efficiencies are illustrated in Figure 7.

Figure 1: notice the shift of the ladder when the feather parameter is changed from five (default) to 25

Figure 2: correlation between the variance and the segment borders in span 3

Figure 3: 2-D (seg 0), partial 3-D (seg 0,+-1,+-2,+-3) and full 3-D reconstructions with zosem3d; notice the flatness of the 2-D profile and the greatest difference in the region of the highest sensitivity,note also the concurrence of the partial 3-D and full 3-D reconstructions in the area of lower sensitivity

Figure 4: an example of a test reconstruction made with zosem3d; a line profile through a transaxial cut shows a greatoverestimation towards the center of the FOV (no scatter correction)

Figure 5: CTI s/w reconstruction compared to zosem3d reconstruction

Figure 6: 2-D (seg 0) and 3-D reconstructions of a small F-18 homogeneity phantom; notice the similarity withthe corresponding Ge-68 plot (Figure 3)

Figure 7: 3-D reconstruction of synthetic data; an artificial weight file containing a “0/1” mask of the scan datais utilised in the reconstruction

Figure 8: plane efficiencies obtained by Bloomfield in Toronto from the zosem3d reconstruction

3. Conclusion

Figures 1-8 show a correlation between the plane efficiencies and the segment borders. According to figures shown here and test runs with various different parameter combinations the problem seems to be due the acceleration scheme utilised in thezosem3d reconstruction.

4. Discussion

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