This document discusses the development of PET/MRI technology. It began with small animal imaging in the 1990s to reduce radiation exposure from multiple scans. Clinical PET/MRI development was spurred by the success of PET/CT, which provided better anatomical correlation and attenuation correction. A major challenge was overcoming interference between the MRI magnet and PET photomultiplier tubes. This led to prototypes using attached rooms with patient shuttling, separate gantries, and integrated systems. The first whole-body PET/MRI was Siemens' Biograph mMR in 2010. Potential benefits include superior soft tissue contrast compared to PET/CT, while disadvantages include longer scan times and difficulties with attenuation correction and metal artifacts. Oncolog

1. Nicholas Plaxton, MD, MS
Emory University
October 11, 2013
PET/MRI
BIOMEDICAL ENGINEER’S PERSPECTIVE

2. First PET/MR
 1990’s small-animal imaging
 Multiple scans - decrease radiation exposure
San Raffaele Scientific Institute, Milano, Italy

3. Clinical PET/MR Development
 Success of PET/CT in 2000’s
 Better anatomic correlation
 Improved attenuation correction techniques
 PET/CT limited in soft tissue contrast
 Brain lesions
 Genitourinary cancers
 Breast and colon cancers
 PET/MR could provide superior soft tissue
contrast

4. Major Challenge in PET/MR
 MR high field magnets interfere with PET
photomultiplier tube electrons

5. Types of PET/MR Scanners Developed
 PET/CT and MR in attached rooms with
patient shuttled in between
 PET and MR gantries arranged along axis
with patient handling system between
 Integrated PET and MR

6. PET/CT and MR Suite
 GE prototype 2010 installed in Zurich, Switzerland
 PET/CT with patient shuttled into next room MR
 Utilizes CT for attenuation correction
 Cheaper
 Can upgrade and use components independently

7. Hybrid PET/MR
 Phillips Gemini 2012 coplanar PET TF with
platform rotation into MR
 Minor shielding on PET
 Installed in NYU, NY and Geneva, Switzerland
PET
MRI
MAGMA Nov 21, 2012

8. Integrated PET/MR
 PET and MR imaged simultaneously without
moving patient
 Excellent registration of PET and MR images
 No time required to shuttle patient
 Less physical space needed
 Need to overcome electronic interference

9. Electronic Conflict Solution
 Replace photomultiplier tubes
 avalanche photodiode detectors (APD)
 sold-state semiconductor detectors
 i.e cadmium zinc telluride
DigiRad Corp.

10. Integrated Prototype PET/MR
 Developed by Siemens in 2006
 Utilized standard MR scanner
 PET insert placed in MR bore
 Multiple institution research project
 University of Tubingen, Germany
 Forschungszenrum Julich, Germany
 Massachusetts General Hospital, Boston, MA
 Emory University, Atlanta, GA

11. BrainPET by Siemens
 PET insert ring into MR
 35.5cm diameter ring with 2.5mm LSO crystals
 Coupled with Avalanche Photo Diodes (APD)
MAGMA Nov 21, 2012

12. PET Insert Schematic
MAGMA Nov 21, 2012

13. First PET/MR Image in 2006
 66 y/o female with Siemens BrainPET
J Nucl Med 2012; 53:1916–1925

14. Siemens Biograph mMR
 2010 Siemens developed whole body PET with
3-T MR with a 60 cm gantry (Biograph mMR)
 FDA approved for purchase in 2011
MAGMA Nov 21, 2012

15. Cross section of Biograph mMR
MAGMA Nov 21, 2012

16. Institutions using Biograph mMR
 Mass. General Hospital - Boston, MA
 NIH - Bethesda, MD
 Washington University, St. Louis, MO
 UNC, Chapel Hill, NC
 UPMC, Pittsburgh, PA
 NYU, New York City
 Mt. Sinai Univ, NYC
 Univ Hospital Stonybrook, NYC

17. Benefits of PET/MR
 Soft-tissue characterization
 Lower ionization than PET/CT
 Questionable benefit for oncology patients
 MR breast imaging has high sensitivity but
low specificity, FDG PET has high specificity
but low sensitivity, therefore benefit
combining PET/MR

18. Disadvantages of PET/MR
 Attenuation correction with MR
 Image truncation, RF coils
 Longer acquisition and multiple sequences
 TOF can shorten PET acquisition time
 MR sequences would need to be limited
 2 to 5 sequences per study takes ~ 30 min
 Total time of 1 hour still shorter than separate studies
 Incapable with metal artifacts (pacers or implants)
 Claustrophobia
 CT superior for lung imaging

19. Types of Attenuation Correction
 Template based
 Atlas based
 Direct Segmentation
 Sequence Segmentation

20. Template Attenuation
 Suitable for brain imaging
MAGMA Nov 21, 2012

21. Atlas Attenuation
 Representative CT data set created
 CT data set is deformed to fit patient MR info
 Pseudo CT created for attenuation

22. Direct Segmentation Attenuation
 Standard T1-weighted MR images
 Bone and air have similar intensity on T1
MAGMA Nov 21, 2012

23. Direct Segmentation Attenuation
 Neural network used to distinguish tissues
 Large computation power
MAGMA Nov 21, 2012

24. Sequence Segmentation Attenuation
 Ultrashort echo time
(UTE) sequences
 Developed for very short
spin–spin relaxation times
 Distinguish bone from air
 Seconds to acquire each
bed position
MAGMA Nov 21, 2012

25. Oncologic Applications PET/MR
 Liver and bone metastases
 Brain tumors
 Prostate cancer
 Gynecological cancers
 Breast cancer
 Head and Neck cancers

26. Liver Metastases Rectal NET
Am J Nucl Med Mol Imaging 2012;2(4):458-474

27. Brain Tumors
 Fluorodeoxyglucose (FDG)
metabolism
 Fluoromisonidazole (FMISO)
tissue hypoxia
 Fluorothymidine (FLT)
cellular proliferation
 Fluoroethyltyrosine (FET)
amino acid transport
J Nucl Med 2012; 53:1916–1925

28. Cervical Cancer with Lymph Node
Am J Nucl Med Mol Imaging 2012;2(4):458-474

29. Recurrent Peritoneal Carcinomatosis
Am J Nucl Med Mol Imaging 2012;2(4):458-474

30. Breast Cancer
NYU Lagune

31. Non-Oncologic Applications
 Neurology
 Dementia
 Stroke
 Epilepsy
 Cardiology
 Atherosclerotic inflammation
 64 Cu-DOTA-vascular endothelial growth factor
 Ventricular remodeling

32. Alzheimher’s
J Nucl Med 2012; 53:1916–1925

33. Stroke Penumbra
J Nucl Med 2012; 53:1916–1925

34. Epilepsy
J Nucl Med 2012; 53:1916–1925

35. Take Home Message
 PET/ MR emerging cutting edge technology
 Applications being developed alongside novel
radiotracers
 PET/MR will not replace PET/CT

36. Summer Fun in Atlanta 2013