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