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An Event-Driven Motion Correction Method for Neurological PET Studies of Awake Laboratory Animals

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Abstract

Purpose

The purpose of the study is to investigate the feasibility of an event driven motion correction method for neurological microPET imaging of small laboratory animals in the fully awake state.

Procedures

A motion tracking technique was developed using an optical motion tracking system and light (<1g) printed targets. This was interfaced to a microPET scanner. Recorded spatial transformations were applied in software to list mode events to create a motion-corrected sinogram. Motion correction was evaluated in microPET studies, in which a conscious animal was simulated by a phantom that was moved during data acquisition.

Results

The motion-affected scan was severely distorted compared with a reference scan of the stationary phantom. Motion correction yielded a nearly distortion-free reconstruction and a marked reduction in mean squared error.

Conclusions

This work is an important step towards motion tracking and motion correction in neurological studies of awake animals in the small animal PET imaging environment.

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Acknowledgments

We thank Danny Newport, Stefan Siegel, Aaron McFarland, and Anne Smith of Siemens Medical Solutions for kindly providing details of the global dead time correction and the microPET list mode and sinogram formats. This work was supported by Australian Research Council Discovery Project 0663519.

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Authors and Affiliations

  1. School of Physics, University of Sydney, NSW 2006, Sydney, Australia

    Victor W Zhou, Andre Z Kyme & Roger Fulton

  2. Ramaciotti Imaging Centre, Brain and Mind Research Institute, University of Sydney, NSW 2006, Sydney, Australia

    Victor W Zhou, Andre Z Kyme, Steven R Meikle & Roger Fulton

  3. Discipline of Medical Radiation Sciences, University of Sydney, NSW 2006, Sydney, Australia

    Steven R Meikle & Roger Fulton

  4. Department of Medical Physics, Westmead Hospital, NSW 2145, Westmead, Australia

    Roger Fulton

Authors
  1. Victor W Zhou
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  2. Andre Z Kyme
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  3. Steven R Meikle
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  4. Roger Fulton
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Corresponding author

Correspondence to Roger Fulton.

Appendix 1: Focus 220 List Mode Data Format

Appendix 1: Focus 220 List Mode Data Format

This appendix describes the microPET Focus 220 list mode data packets that were used in this work. Data are transported from the tomograph to the host PC via a Firewire interface and stored on disk in 48-bit list mode packets. The most significant byte and the lower four bits of the fifth byte of each packet are always 0 and 4, respectively, to provide a synchronization pattern in the list mode stream. Figure 9 shows the generalized list mode data packet format.

Fig. 9
figure 9

The microPET F220 list mode data packet. T represents the tag bit (1 for tag and 0 for event), P is the prompt bit for a coincidence event (1 for prompt and 0 for delay). The sixth byte is not shown since it is always zero. The data word occupies bits 0–31.

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There are two classes of list mode data packets, event and tag packets, identified by bit 39 (0 for event and 1 for tag). The event packets cater for coincidence, singles, and double singles events as identified by bits 36–37. The format of a coincidence event packet is shown in Table 3.

Table 3 Coincidence event data packet
Full size table

Tag packets consist of time mark packets, prompt/delay count packets, block singles count packets and user-defined pose packets. Time mark packets contain elapsed time (in bits 0–28 as shown in Table 4) and are inserted into the list mode data stream every millisecond. Users can also insert their own time mark packets into the list mode data stream via DOS commands. In the present work, bit 28 of the time mark packet is dedicated to distinguishing between system and user-inserted time mark packets. This leaves bits 0–27 available in a system time mark to represent elapsed time in milliseconds or the identification number of a pose measurement in a user-inserted time mark (see Table 4).

Table 4 Time mark packet
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Prompt/delay count packets report the number of prompt or delayed events detected by the coincidence controller every 40ms as shown in Table 5. Bits 0–23 report the number of coincidence events (prompt or delayed as indicated by the sense of bit 26) in the preceding 40ms period.

Table 5 Prompt/delay count packet
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Block singles count packets, in bits 0–17, report the number of singles counts recorded in a block in the preceding 200ms, as shown in Table 6. Bit 26 is the valid bit (0 for valid singles counts and 1 for CFD singles counts). CFD singles counts are singles counts received by the constant fraction discriminator (CFD). Valid singles counts are singles counts that have been validated in terms of energy and position.

Table 6 Block singles count packet
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In the post-processing of the list mode data, synchronized pose data (R x (yaw), R v (pitch), R z (roll), x, y and z) are inserted into the list mode data in user-defined pose packets (Table 7).

Table 7 Pose packet (user-defined tag)
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Zhou, V.W., Kyme, A.Z., Meikle, S.R. et al. An Event-Driven Motion Correction Method for Neurological PET Studies of Awake Laboratory Animals. Mol Imaging Biol 10, 315–324 (2008). https://doi.org/10.1007/s11307-008-0157-0

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  • DOI: https://doi.org/10.1007/s11307-008-0157-0

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