List- mode tracking and mogon correcgon for PET imaging using low- acgvity fiducial markers

Transcription

1 List- mode tracking and mogon correcgon for PET imaging using low- acgvity fiducial markers Marc Chamberland, MSc (PhD in Spring 2015!) Robert dekemp, PhD Tong Xu, PhD STIR User s MeeGng at IEEE MIC November 13 th, 2014

2 My claim to fame, from the STIR Wiki FAQ: 2

3 Outline Legend Coincidence line (COIL) Distance vector between COIL and marker Marker MoGon tracking and correcgon (Poster M10-5) Use of STIR Results 3

4 MoGon tracking and correcgon 4

5 Positron emission tomography (PET) imaging is rougnely used to assess myocardial perfusion... Walls of the heart insert of a phantom, filled with rubidium- 82 ( 82 Rb) tracer. (Coronal slice) Above: no mogon. 5

6 but respiratory, cardiac, and pagent body mogon create artefacts on the images. Walls of the heart insert of a phantom, filled with rubidium- 82 ( 82 Rb) tracer. (Coronal slice) Above: no mogon; below: mo)on blurring. 6

7 A fiducial point- like positron- emi_ng marker can be localized by finding the posigon in space which minimizes the root mean square distance to its coincidence lines. Legend Coincidence line (COIL) Distance vector between COIL and marker Marker 7

8 EM Clustering Algorithm COIL: COIncidence Lines Estimate marker location We developed an iteragve expectagon- maximizagon (EM) algorithm to track the 3D locagon of fiducial positron- emi_ng markers. Expectation Step Compute probability of each COIL belonging to marker If distance from COIL to marker > 2σ then set probability to zero Some background rejecgon is needed to deal with the tracer acgvity in the pagent s body. (Not shown in figure.) Update parameters and shift marker by the sum of all weighted distance vectors Shift < 0.05 mm? Maximization Step FALSE References T. Xu et al., Med. Phys. 33(7), (2006). M. Chamberland et al., Med. Phys. 38(2), (2011). Terminate TRUE 8

9 We conducted a phantom study with a thorax phantom. 22 Na (92.5 kbq) Heart insert filled with 82 Rb (680 MBq inigally) 9

10 We transformed the phantom into a dynamic one! Phantom resgng on wooden board with wheels Motor with rotagng plate 10

11 The marker was tracked using the raw list- mode data acquired during the PET scan Inferior-superior (IS) motion trace of one sample marker (phantom study) IS (mm) Scan 1 Scan 2 Scan Time (minutes) 11

12 The mogon trace of the marker can be used to apply mogon correcgon to the raw list- mode data. Reference marker position Marker position MoGon correcgon shii according to marker s translagon from reference posigon 12

13 Use of STIR 13

14 To check if the mogon correcgon worked, I had two choices: Use the GE Discovery 690 s console to reconstruct the mogon- corrected list- mode... or use STIR. 14

15 To reconstruct with STIR, I had to rely on projecgon data. Adding GE list- mode support was outside my C++ comfort zone. 15

16 I added (non- validated) support for the GE Discovery 690 scanner in STIR by modifying Scanner.h 16

17 and Scanner.cxx using the published characterisgcs of the scanner (and some detecgve work). EffecGve ring diameter and average depth of interacgon. Number of blocks per module, crystals per module, etc. 17

18 The list_detector_and_bin_info uglity was extremely useful in wrapping my head around STIR and projecgon data convengons. This allowed me to check if the detectors were where I thought they were in Cartesian coordinates. Fun discovery: everybody uses different convengons! (E.g. lei- handed coordinate system instead of right- handed.) 18

19 In order to reconstruct the images, I wrote a uglity that converts GE list- mode to projecgon data. Member of ProjDataInfoCylindricalNoArcCorr class 19

20 In order to reconstruct the images, I wrote a uglity that converts GE list- mode to projecgon data. Only STIR library I needed to link to (I had to include some headers, of course) 20

21 I also did some work on a uglity to convert crystal and geometric efficiency files from the D690 to projecgon data. Member of ProjDataInfoCylindricalNoArcCorr class 21

22 Side note: I found neat stuff that is being worked on for future STIR releases. My tracking and correcgon code implements its own LOR class and methods I implemented a funcgon to get the intersecgons between an N- sided polygon and a LOR 22

23 Results 23

24 QualitaGvely, the images are (relagvely) mogon free. (Several correcgons were not applied!) StaGc scan Fast, irregular mogon Fast, irregular mogon; mogon corrected 24

25 QualitaGvely, the images are (relagvely) mogon free. (Several correcgons were not applied!) No motion correction 0-15 s s s s With motion correction NOTE: Those images were reconstructed from the GE console, not by STIR. 25

26 Take- away message: 1. MoGon tracking using low- acgvity fiducial positron- emi_ng markers and correcgng the raw list- mode data from a GE D690 scanner. 2. Using STIR to convert the list- mode and calibragon files to projecgon data, correct the data, and reconstruct for qualitagve assessment of mogon. 3. It works! (And I have pagent data, but not quite ready to show.) Future work: 1. Beoer correcgons aier applying mogon correcgon. 2. LOR- as- 2- points- based reconstrucgon? 3. Contribute something to STIR! 26

27 Acknowledgements 1. Dr. Rob de Kemp (University of Ooawa Heart InsGtute) 2. All the PET staff involved (University of Ooawa Heart InsGtute) 3. Dr. Charles Stearns for technical discussion of the D690 (GE Healthcare) 4. Dr. Tong Xu (Department of Physics, Carleton University) 5. IEEE NSS/MIC Conference Trainee Grant for travel support 6. Dr. Thielemans and Dr. Tsoumpas for having answered some of my quesgons on the STIR mailing list over the years. 27

28 Thank you for your Gme! 28

29 Position (mm) LR - original AP - original IS - original LR - MC AP - MC IS - MC Time (min) 29

30 30

31 Position (mm) LR AP IS Time (min) 31