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