Molecular Imaging Instrumentation Laboratory  

Integration of PET with Magnetic Resonance Imaging (MRI) without Mutual Interference

PET is very sensitive at detecting and quantifying a low abundance molecular target on or within diseased cells. MRI is capable of providing exquisite anatomy as well as physiological measurements of disease states. Thus, the two modalities provide complimentary information, and as a result, recently there have been efforts to combine the two modalities by inserting a PET system into an MRI system and operating them simultaneously for highly accurate spatial and temporal registration. If successful, the result would be a powerful tool to characterize disease in living subjects. However, this is a very difficult instrumentation problem since with existing PET and MR technologies, there would be substantial mutual interference between the two modalities: The standard PET system design would have a significant electrical footprint, which would interfere with the MRI system’s performance, and the latter creates an extremely noisy environment for the former to operate. Siemens has built a prototype brain-only PET insert for their MR system, by adding conductive shielding around the PET components; but scaling that design up to a whole-body version, which is currently the clinical “standard-of-care”, would mean a log-order increase in the electrical footprint (e.g. the volume of conductors and coaxial shielded cables used for signal transmission out of the MRI system would greatly increase).

PET/MR PET/MR
PET/MR PET/MR

We are addressing this considerable engineering problem by drawing from the field of optical communications. It turns out that the analog PET scintillation detector signals can directly couple to and be used to drive a telecommunications-grade vertical cavity surface emitting laser (VCSEL), and all the required information may be carried out as light pulses using multi-mode fiber optics, rather than as electrical signals down shielded coaxial cables. As long as the front-end scintillation detector components (scintillation crystals and photodetectors) as well as the VSCEL can be made non-magnetic (which we have shown), and introducing this electro-optical coupling step does not introduce temporal or amplitude dispersion (which we have shown), the result would be a system with very low electrical footprint (no signal cables or shielding required), scalable to a whole body PET geometry.

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    Author Title Year Jour./Proc./Book
    Levin, C.S. & Zaidi, H. Current Trends in Pre-Clinical Positron Emission Tomography System Design 2007 PET Clinics
    Vol. 2, pp. 125-160  
    BibTeX:
    @article{Levin2007,
      author = {C. S. Levin and H. Zaidi},
      title = {Current Trends in Pre-Clinical Positron Emission Tomography System Design},
      journal = {PET Clinics},
      year = {2007},
      volume = {2},
      number = {2},
      pages = {125-160}
    }
    					
    Olcott, P.D. & Levin, C.S. Pulse Width Modulation: A Novel Readout Scheme For High Energy Photon Detection 2008 Conference Record of the 2008 IEEE Nuclear Science Symposium and Medical Imaging Conference, pp. 4530-4535  
    BibTeX:
    @conference{Olcott2008,
      author = {P. D. Olcott and C. S. Levin},
      title = {Pulse Width Modulation: A Novel Readout Scheme For High Energy Photon Detection},
      booktitle = {Conference Record of the 2008 IEEE Nuclear Science Symposium and Medical Imaging Conference},
      year = {2008},
      pages = {4530-4535}
    }
    					
    Olcott, P.D.; Peng, H. & Levin, C.S. Novel Electro-Optical Coupling Technique for Magnetic Resonance-Compatible Positron Emission Tomography Detectors 2009 MOLECULAR IMAGING
    Vol. 8, pp. 74-86  
    Abstract: A new magnetic resonance imaging (MRI)-compatible positron emission tomography (PET) detector design is being developed that uses electro-optical coupling to bring the amplitude and arrival time information of high-speed PET detector scintillation pulses out of an MRI system. The electro-optical coupling technology consists of a magnetically insensitive photodetector output signal connected to a nonmagnetic vertical cavity surface emitting laser (VCSEL) diode that is coupled to a multimode optical fiber. This scheme essentially acts as an optical wire with no influence on the MRI system. To test the feasibility of this approach, a lutetium-yttrium oxyorthosilicate crystal coupled to a single pixel of a solid-state photomultiplier array was placed in coincidence with a lutetium oxyorthosilicate crystal coupled to a fast photomultiplier tube with both the new nonmagnetic VCSEL coupling and the standard coaxial cable signal transmission scheme. No significant change was observed in 511 keV photopeak energy resolution and coincidence time resolution. This electro-optical coupling technology enables an MRI-compatible PET block detector to have a reduced electromagnetic footprint compared with the signal transmission schemes deployed in the current MRI/PET designs.
    BibTeX:
    @article{Olcott2009,
      author = {P. D. Olcott and H. Peng and C. S. Levin},
      title = {Novel Electro-Optical Coupling Technique for Magnetic Resonance-Compatible Positron Emission Tomography Detectors},
      journal = {MOLECULAR IMAGING},
      year = {2009},
      volume = {8},
      number = {2},
      pages = {74-86},
      doi = {http://dx.doi.org/10.2310/7290.2009.00012}
    }
    					
    Olcott, P.D.; Peng, H. & Levin, C.S. Novel Electro-Optically Coupled MR Compatible PET Detectors 2008 Conference Record of the 2008 IEEE Nuclear Science Symposium and Medical Imaging Conference, pp. 4640-4645  
    BibTeX:
    @conference{Olcott2008a,
      author = {P. D. Olcott and H. Peng and C. S. Levin},
      title = {Novel Electro-Optically Coupled MR Compatible PET Detectors},
      booktitle = {Conference Record of the 2008 IEEE Nuclear Science Symposium and Medical Imaging Conference},
      year = {2008},
      pages = {4640-4645}
    }
    					
    Peng, H.; Levin, C.S. & Chronik, B.A. Simulation study of PET spatial resolution and contrast recovery improvement for PET/MRI dual modality systems 2009 Medical Physics  
    BibTeX:
    @article{Peng2009a,
      author = {H. Peng and C. S. Levin and B. A. Chronik},
      title = {Simulation study of PET spatial resolution and contrast recovery improvement for PET/MRI dual modality systems},
      journal = {Medical Physics},
      year = {2009},
      note = {Submitted}
    }
    					
    Peng, H.; Olcott, P.D. & Levin, C.S. Can large-area avalanche photodiodes be used for a clinical PET/MRI block detector? 2008 Conference Record of the 2008 IEEE Nuclear Science Symposium and Medical Imaging Conference, pp. 4675-4680  
    BibTeX:
    @conference{Peng2008,
      author = {H. Peng and P. D. Olcott and C. S. Levin},
      title = {Can large-area avalanche photodiodes be used for a clinical PET/MRI block detector?},
      booktitle = {Conference Record of the 2008 IEEE Nuclear Science Symposium and Medical Imaging Conference},
      year = {2008},
      pages = {4675-4680}
    }
    					
    Peng, H.; Olcott, P.D.; Spanoudaki, V.C. & Levin, C.S. Can large-area avalanche photodiodes be used for a PET detector insert for an MRI system? 2009 Medical Physics  
    BibTeX:
    @article{Peng2009b,
      author = {H. Peng and P. D. Olcott and V. C. Spanoudaki and C. S. Levin},
      title = {Can large-area avalanche photodiodes be used for a PET detector insert for an MRI system?},
      journal = {Medical Physics},
      year = {2009},
      note = {Submitted}
    }
    					

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