PET/MRI BIOMEDICAL ENGINEER’S PERSPECTIVE
Nicholas Plaxton, MD, MSEmory UniversityOctober 11, 2013
First PET/MR 1990’s small-animal imaging
Multiple scans - decrease radiation exposure
San Raffaele Scientific Institute, Milano, Italy
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
Major Challenge in PET/MR
MR high field magnets interfere with PET photomultiplier tube electrons
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
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
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
MRI
PET
MAGMA Nov 21, 2012
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
Electronic Conflict Solution Replace photomultiplier tubes
avalanche photodiode detectors (APD) sold-state semiconductor detectors
i.e cadmium zinc telluride
DigiRad Corp.
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
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
PET Insert Schematic
MAGMA Nov 21, 2012
First PET/MR Image in 2006 66 y/o female with Siemens BrainPET
J Nucl Med 2012; 53:1916–1925
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
Cross section of Biograph mMR
MAGMA Nov 21, 2012
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
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
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
Types of Attenuation Correction Template based
Atlas based Direct Segmentation Sequence Segmentation
Template Attenuation Suitable for brain imaging
MAGMA Nov 21, 2012
Atlas Attenuation
Representative CT data set created CT data set is deformed to fit patient
MR info Pseudo CT created for attenuation
Direct Segmentation Attenuation Standard T1-weighted MR images Bone and air have similar intensity
on T1
MAGMA Nov 21, 2012
Direct Segmentation Attenuation Neural network used to distinguish
tissues Large computation power
MAGMA Nov 21, 2012
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
Oncologic Applications PET/MR Liver and bone metastases Brain tumors Prostate cancer Gynecological cancers Breast cancer Head and Neck cancers
Liver Metastases Rectal NET
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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
Cervical Cancer with Lymph Node
Am J Nucl Med Mol Imaging 2012;2(4):458-474
Recurrent Peritoneal Carcinomatosis
Am J Nucl Med Mol Imaging 2012;2(4):458-474
Breast Cancer
NYU Lagune
Non-Oncologic Applications Neurology
Dementia Stroke Epilepsy
Cardiology Atherosclerotic inflammation
64 Cu-DOTA-vascular endothelial growth factor
Ventricular remodeling
Alzheimher’s
J Nucl Med 2012; 53:1916–1925
Stroke Penumbra
J Nucl Med 2012; 53:1916–1925
Epilepsy
J Nucl Med 2012; 53:1916–1925
Take Home Message
PET/ MR emerging cutting edge technology
Applications being developed alongside novel radiotracers
PET/MR will not replace PET/CT
Summer Fun in Atlanta 2013