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

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

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

Scanner configurations 4R - 22 cm AFOV Siemens mCT PET 8R – 44 cm AFOV 20R - 110 cm AFOV 40R - 220 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)

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

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

Single Bed Imaging A 2-mm or 10-mm ROI inside a uniform cylinder 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 A 2-mm or 10-mm ROI inside a uniform cylinder

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

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

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

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

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

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

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).

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

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 http://explorer.ucdavis.edu/ Thank you very much for you attention (gentlemen) !

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

Sensitivity at Different Axial Location of XCAT2.0 Tissue @ 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)

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

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)