1. 2017 Fully Three-Dimensional Image Reconstruction in Radiology and Nuclear Medicine
Theoretical Study of Benefit of Long Axial Field-of-View PET: Impact on Quantification Performance
Xuezhu Zhang, Ramsey Badawi, Simon Cherry and Jinyi Qi
University of California, Davis

2. EXPLORER: EXtreme-Performance LOng REsearch scanneR
Impact: massively increased sensitivity can expand PET applications to pediatric and adolescent populations, studying and monitoring chronic disease
15 – 30 cm axial FOV
200 cm axial FOV
Image all organs simultaneously
~40-fold increased sensitivity for total-body imaging

3. Objective
Quantify the benefits of long axial FOV PET for region of interest (ROI) quantification
Base on theoretical prediction of contrast vs. noise tradeoff for penalized likelihood image reconstruction
Compare scanners with axial FOV ranging from 22 cm (existing scanner) to 220 cm.
Preliminary animal studies prior to mini-EXPLORER deployment to California National Primate Research Center

4. Scanner configurations
4R - 22 cm AFOV
Siemens mCT PET
8R – 44 cm AFOV
20R cm AFOV
40R cm AFOV 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40
Single-bed scan
Multi-bed scan (110 cm AFOV)

5. Use SimSET simulation to measure the sensitivity of a point source at variable locations inside a XCAT phantom
Compute sensitivity ratio of scanners with different AFOV over the 22-cm scanner.
Compare with results of point source inside a uniform cylinder

6. A 20-cm cylinder provides a good approximation of the XCAT average in terms of sensitivity gain as a function of axial FOV

7. Single Bed Imaging A 2-mm or 10-mm ROI inside a uniform cylinder 1 2 34 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40
A 2-mm or 10-mm ROI inside a uniform cylinder

8. Single Bed Imaging: Axial Sensitivity Profiles
No attenuation
w/ water cylinder attenuation

9. Single Bed Imaging: CRC & Variance Reduction
ROI 2 mm
Variance reduction
CRC
Variance
CRC
ROI 10 mm
TOF 500 ps w/o DOI
CRC
Variance
CRC

10. Multi-Bed Imaging: Extended 110 cm AFOV
22cm - 11 Beds
44cm - 6 Beds
110cm - 3 Beds
220cm - 1 Bed 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40
110 cm Axial FVO
50% overlap between adjacent beds
Same total scan time

11. Multi-Bed Imaging: Axial Sensitivity Profile
center (no attenuation)
center in water cylinder
AFOV 110 cm

12. Multi-bed Imaging: Variance Reduction
ROI 2 mm
Variance reduction
CRC
Variance
CRC
ROI 10 mm
TOF 500 ps w/o DOI
CRC
Variance
CRC

13. Effects of DOI and TOF
NO DOI-TOF
DOI
DOI+TOF

14. Variance Reduction – DOI & TOF
ROI 2 mm
ROI 10 mm
4R 500ps: 1.8x
DOI has larger impact on longer scanner and smaller ROI
TOF has similar impact on 2-mm ROI and 10-mm ROI (both are smaller than TOF resolution).

15. Conclusions
The evaluation study showed that a 2.2-meter long scanner offers
1.4~2.8-fold variance reduction for single-bed imaging of a 2∼10-mm ROI at the FOV center compared with a 22-cm AFOV scanner
25~30-fold variance reduction for imaging 2∼10-mm ROI in an extended 110-cm axial FOV over a 22-cm long scanner, and 2∼3.5-fold variance reduction over a 1-meter long scanner
70∼90-fold variance reduction w/ 320-ps TOF and 4-mm DOI over a 22-cm AFOV scanner without TOF and DOI

16. Acknowledgements NIH Transformative Research Award R01 CA206187
NIH / NCI Grant (R01 CA170874)
UC Davis RISE Award
Members of Cherry-Qi-Badawi Lab at UC Davis
Thank you very much for you attention (gentlemen) !

18. Theoretical ROI Quantification
Qi and Leahy 1999; Qi and Leahy 2000; Qi and Huesman 2006
Add PML formula
Derived for penalized likelihood image reconstruction to compute contrast recovery coefficient (CRC) and variance of ROI quantification
Fisher information matrix
Forward projection (PET imaging)
ROI approximation

19. Sensitivity at Different Axial Location of XCAT2.0
center:
Bladder (water)
Intestine (water)
Bone
Torso/Bone
Heart
Trachea (Air)
Bone/neck
Brain
Top head (Skull)
Design 22 – 220 cm
Lowest sensitivity ratio (close to bone)
Medium sensitivity ratio (close to water)
Highest sensitivity ratio (close to air)

20. DOI vs non-DOI: Variance Reduction Gain
ROI 2 mm3
noDOI
DOI-10mm
DOI-4mm
ROI 10 mm3
noDOI
DOI-10mm
DOI-4mm
Procedure
Image quality

21. DOI vs non-DOI: Variance Reduction Gain
DOI-10mm over noDOI (ROI 2 mm3)
DOI-4mm over noDOI (ROI 2 mm3)
DOI-10mm over noDOI (ROI 10 mm3)
DOI-4mm over noDOI (ROI 10 mm3)