MRI-PET; A new approach for multi modality imaging system

MRI-PET; A new approach for multi modality imaging systemKarl Ziemons Member of Crystal Clear CollaborationDr. Karl ZiemonsForschungszentrum Jlich GmbHCentral Institute of Electronics

Tel.: +49-2461-615685Fax: +49-2461-613990E-Mail: [email protected]

Frontiers in Imaging Science - Rome 2006

Forschungszentrum JlichCentral Institute of Electronics

MotivationsPET & MRI are medical imaging techniques that in widespread use both for patient diagnosis and management, and in clinical research

playing a key role in a wide range of fields from mapping of the human brain to the development of new treatments for cancer



MotivationsPET in-vivo information about metabolism and functionality

(f)MRI Anatomical information with a better soft tissue contrast as CT and does not apply additional radiation dose in-vivo information about neuronal activities; the so-called blood oxygenation level dependent (BOLD) contrast has proved to be a very sensitive MRI marker



Complementary nature of MRI & PETHence: The Sum of PET and MRI should be excellent and even better MRI + PET minimal scatterGradients need more currentStronger coupling of RF coil

M.Schwaiger, S.Ziegler, et al., 2005



PET/MR Design ChallengesLimited space for the PET detectorNeed minimum space for patientPET detector must not use magnetic materialsCould distort MR imagePET detector must not emit in MR frequencyCould produce MR image artifacts MR-compatible PET shielding materialsCould distort MR image



PET/MR Design ChallengesPET detector must not use magnetic materialsDistortions and interference lines are produced in a uniform phantom imageCourtesy by R.Grazioso, Siemens



PET/MR Design ChallengesPET detector must not emit in MR frequencyRF artifacts can be seen in the RF noise measurement due to improper shielding of the PET electronics.Courtesy by R.Grazioso, Siemens



PET/MR Design ChallengesMR-compatible PET shielding materialsBulk leadHot-pressed lead monoxideBGOPure lead powderRed lead oxide powder(Courtesy of D. Struhl, et al., TNS 2003)Spin-echoGradient-echoVarious materials can produce an MR signature even if it is not conductive or magnetic.



PET/MR Design Challenges

MR gradient field-eddy currentsCould produce noise in detectorCould heat detectorMR RF transmitCould produce false PET eventsMR materialsWill produce more gamma attenuation



PET/MR Design ChallengesMR Radio frequency

degrading the energy and timing resolution of the PET system.

Courtesy by R.Grazioso, Siemens



PET Insert for a Clinical MRI ScannerSimultaneous Measurement in 1.5 T

APD based detectorMulti-slice PET images High quality MR images

Courtesy by R.Grazioso a. M.Schmand, Siemens



BrainPET Project(G)-APD PET insert:trapezoid monolithic block design: LSO block with two (G)-APD in double readout technology and MR compatibleSystem peak sensitivity: > 15%Spatial resolution: < 1.3mm over the whole FOVCurrent CCC projectGoal:



MRTPETSimultaneous Imaging of a [F-18]-FDG Mouse HeadStep and shoot PET acquisition (12 angles, each 6 min) while MRT images were taken.Filtered Back Projection (2.5 mm Gaussian image filtering post reconstruction)70/30 Bruker Biospec system. B-GA20 gradient set. Micro Imaging Coil. FLASH MRT sequence. 1mm slice thickness. with Two Coincident APD Based LSO Block-Detectors and a 7Tesla Small Animal MRT SystemCourtesy by B.Pichler, Tbingen



New MR-compatible solid-state PET detectorsMagnetically insensitive detectors for MR/PETSilicon photomultipliers (SiPM)an array of geiger-mode APDs showing good timing and energy resolution but not fully developed yet (Eres:12.5%, Tres: 560 psec). (Lorenz et al., Some studies for a development of a small animal PET based on LYSO crystals and geigermode-APDs)Cadmium Zinc Telluride (CZT)has been investigated for a long time but new for PET. Some recent results show good timing (2.6ns vs BaF2). (Verger at al., New trends in gamma-ray imaging with CdZnTe/CdTe at CEA-LETI)Hybrid Photodiode (HPD)sensitive to magnetic fields but can operate normally if positioned parallel to the magnetic field. (Igor Rubashov, Apparatus for combined nuclear imaging and magnetic resonance imaging, and method thereof,)



MRI-PET: Which Problems to solve?to measure or calculate attenuation maps for quantitative PET image reconstructionNeed such a solution for Brain and WholeBody Imaging!!to assess motion in the FOVMotion can deteriorate MR and PET images and may cause serious artefacts! This is especially true for images derived from multiple acquisitions!MRI



MRI based AC: BrainPET-based Attenuation CorrectionCorresponding MR imagesMRI-based segmentation (whole brain, bone, soft-tissue, sinus arca)

(IEEE, 2006: E. Rota Kops, et al.)CTMRIDifferentBone signal



Problem of Patient Motion (18F-Altanserin)[Herzog et al., JNM, 2005]Motion affectedMotion correctedShould be derived from MRI?!



Why MRI-PET Hybrid Imaging?Want true simultaneous data acquisition in a single device Want combined functional and morphological data acquisition at the same timeWant multi modal functional acquisitions at the same time (fMRI / MRS - PET)Want to cross-validate activations measured with PET and fMRI under the same conditions, at the same time, in the same status

but still want quantitative PET imageMRI



ConclusionPET/CT was a medical revolution and a technical evolution

MR/PET seems to be a technical revolution and a medical evolution



AcknowledgmentsThanks to Ralph Ladebeck and Ron Grazioso (Siemens) for MR specifications and material

N.J.Shah and U.Pietrzyk (IME) ,T. Beyer (Essen) And all the others for images and material


The MR will emit RF at a specified frequency (42.58 MHz/T for hydrogen). The RF can interfere with the detector electronics.

MRI-PET; A new approach for multi modality imaging system

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