View source for Physics:Positron emission tomography–magnetic resonance imaging

[[File:PET-IRM-cabeza-Keosys.JPG|thumb|Computer screenshot showing a PET image (upper left), MRI image (upper right) and the combined PET-MRI image where PET data is overlaid over the MRI data (lower right)]]
'''Positron emission tomography–magnetic resonance imaging''' ('''PET-MRI''') is a hybrid [[Engineering:Imaging technology|imaging technology]] that incorporates [[Physics:Magnetic resonance imaging|magnetic resonance imaging]] (MRI) [[Physics:Soft tissue|soft tissue]] morphological imaging and [[Physics:Positron emission tomography|positron emission tomography]] (PET) [[Medicine:Functional imaging|functional imaging]].<ref name="AntochBockisch2008">{{cite journal|last1=Antoch|first1=Gerald|last2=Bockisch|first2=Andreas|title=Combined PET/MRI: a new dimension in whole-body oncology imaging?|journal=European Journal of Nuclear Medicine and Molecular Imaging|volume=36|issue=S1|year=2008|pages=113–120|issn=1619-7070|doi=10.1007/s00259-008-0951-6}}</ref>

==Applications==
Presently, the main clinical fields of PET-MRI are [[Medicine:Oncology|oncology]],<ref>{{cite journal |author=Buchbender C |display-authors=4 |author2=Heusner TA |author3=Lauenstein TC|author4=Bockisch A |author5=Antoch G |title=Oncologic PET/MRI, part 1: tumors of the brain, head and neck, chest, abdomen, and pelvis |journal=Journal of Nuclear Medicine |volume=53 |issue=6 |pages=928–38 | date=June  2012 |pmid=22582048 |doi=10.2967/jnumed.112.105338}}</ref><ref>{{cite journal |author=Buchbender C |display-authors=4 |author2=Heusner TA |author3=Lauenstein TC|author4=Bockisch A |author5=Antoch G |title=Oncologic PET/MRI, part 2: bone tumors, soft-tissue tumors, melanoma, and lymphoma |journal=Journal of Nuclear Medicine |volume=53 |issue=8 |pages=1244–52 | date=August  2012 |pmid=22782313 |doi=10.2967/jnumed.112.109306}}</ref><ref>{{cite journal |author=Martinez-Möller A |author2= Eiber M |author3=Nekolla SG |display-authors=0 |title=Workflow and scan protocol considerations for integrated whole-body PET/MRI in oncology |journal=Journal of Nuclear Medicine |volume=53 |issue=9 |pages=1415–26 | date=September  2012 |pmid=22879079 |doi=10.2967/jnumed.112.109348}}</ref> [[Medicine:Cardiology|cardiology]]<ref>{{cite journal |author=Rischpler C |author2=Nekolla SG |author3=Dregely I|author4=Schwaiger M |title=Hybrid PET/MR imaging of the heart: potential, initial experiences, and future prospects |journal=Journal of Nuclear Medicine |volume=54 |issue=3 |pages=402–15 | date=March  2013 |pmid=23404088 |doi=10.2967/jnumed.112.105353}}</ref> and [[Biology:Neurology|neurology]].<ref>http://www.nih.gov/news/health/sep2011/cc-26.htm{{full citation needed|date=January 2015}}</ref><ref>{{cite journal |author=Dimou E |author2= Booij J |author3=Rodrigues M |display-authors=0 |title=Amyloid PET and MRI in Alzheimer's disease and mild cognitive impairment |journal=Current Alzheimer Research |volume=6 |issue=3 |pages=312–9 | date=June  2009 |pmid=19519314 |url=http://www.eurekaselect.com/84516/article |doi=10.2174/156720509788486563}}</ref><ref>{{cite journal |author=Bremner JD |author2=Vythilingam M |author3=Vermetten E |display-authors=0 |title=MRI and PET study of deficits in hippocampal structure and function in women with childhood sexual abuse and posttraumatic stress disorder |journal=The American Journal of Psychiatry |volume=160 |issue=5 |pages=924–32 | date=May  2003 |pmid=12727697 |doi=10.1176/appi.ajp.160.5.924}}</ref> Research studies are actively conducted at the moment to understand benefits of the new PET-MRI diagnostic method. The technology combines the exquisite structural and functional characterization of tissue provided by MRI with the extreme sensitivity of PET imaging of metabolism and tracking of uniquely labeled cell types or cell receptors.
There is discussion and investigation into utilizing PET-MR with Ion Therapy for the purpose of cancer treatment.<ref>{{cite web |url=http://www.dkfz.de/en/medphys/heavy_ion_therapy/index.html |title=Archived copy |accessdate=2014-01-16 |deadurl=yes |archiveurl=https://archive.is/20140116181745/http://www.dkfz.de/en/medphys/heavy_ion_therapy/index.html |archivedate=2014-01-16 |df= }}{{full citation needed|date=January 2015}}</ref> with<ref>http://www.dkfz.de/en/presse/pressemitteilungen/2013/dkfz-pm-13-23-A-Sharper-Image-with-Combined-PET-MR-Technology.php{{full citation needed|date=January 2015}}</ref><ref>{{cite journal |author=Rank CM |display-authors=4 |author2=Tremmel C |author3=Hünemohr N|author4=Nagel AM |author5=Jäkel O|author6=Greilich S |title=MRI-based treatment plan simulation and adaptation for ion radiotherapy using a classification-based approach |journal=Radiation Oncology |volume=8 |issue= |page=51 |date=2013 |pmid=23497586 |pmc=3702461 |doi=10.1186/1748-717X-8-51}}</ref> MRI's ability to accurately depict the proton density of tissue is a good match for the benefits and technical challenges of treatment planning utilizing Ion Therapy systems.

==Manufacturers==
Currently four companies offer combined PET-MR systems: Philips, [[Company:Siemens|Siemens]], [[Company:General Electric|GE]] and MR Solutions. The first two clinical whole body PET-MRI systems were installed by Philips at Mount Sinai Medical Centre in the United States<ref>[http://www.mssm.edu/research/labs/imaging-science-laboratories/facilities Facilities - Icahn School of Medicine at Mount Sinai<!-- Bot generated title -->]</ref> and at Geneva University Hospital in Europe in 2010.<ref>[http://www.hug-ge.ch/hug_cite/inauguration_PET_IRM.html] {{webarchive |url=https://web.archive.org/web/20101225091905/http://www.hug-ge.ch/hug_cite/inauguration_PET_IRM.html |date=December 25, 2010 }}</ref><ref>[http://www.mtbeurope.info/content/ft1005002.htm PET-MRI scanner opens new frontier in medical imaging<!-- Bot generated title -->]</ref> One company, Cubresa, offers an MR-compatible preclinical PET scanner called NuPET™ for use in the bore of an existing MRI, enabling simultaneous PET/MR image acquisition. The first instrument was installed at the Izaak Walton Killam Health Centre in Halifax, Canada in 2016, and more systems have since been installed.<ref>[http://www.prweb.com/releases/cubresa/nupet/prweb13370405.htm Preclinical PET Scanner Released for Simultaneous PET/MRI in Existing MRI Systems]</ref>

===Clinical systems===
Currently Siemens and GE are the only companies to offer a fully integrated whole body and simultaneous acquisition PET-MRI system. The Siemens system (Biograph mMR) received a CE mark<ref>{{cite web
  |url=http://www.siemens.com/press/en/pressrelease/?press=/en/pressrelease/2011/imaging_therapy/him20110630.htm
  |title=Siemens receives CE mark for whole-body molecular MR system 
  |publisher=Healthcare Sector, Siemens AG 
  |date=2011-06-01
  |accessdate=2014-01-05}}
</ref> and FDA approval<ref>{{cite web
  |url=http://www.fda.gov/NewsEvents/Newsroom/PressAnnouncements/ucm258700.htm
  |title=FDA clears new system to perform simultaneous PET, MRI scans 
  |publisher=U.S. Food and Drug Administration 
  |date=2011-06-10
  |accessdate=2014-01-04}}
</ref> for customer purchase in 2011.

The GE system (SIGNA PET/MR) received its 510K & CE mark in 2014.

The first fully RoHS compliant system was delivered in 2014. Over sixty facilities have since installed this technology.

===Preclinical systems===
Currently, the combination of positron emission tomography (PET) and magnetic resonance imaging (MRI) as a hybrid imaging modality is receiving great attention not only in its emerging clinical applications but also in the preclinical field. Several designs based on several different types of PET detector technology have been developed in recent years, some of which have been used for first preclinical studies.<ref>{{cite journal |doi=10.1053/j.semnuclmed.2012.08.004 |title=Applications for Preclinical PET/MRI |date=2013 |last1=Judenhofer |first1=Martin S. |last2=Cherry |first2=Simon R. |journal=Seminars in Nuclear Medicine |volume=43 |pages=19–29 |pmid=23178086 |issue=1}}</ref><ref>{{cite journal |doi=10.1109/NSSMIC.2011.6152496 |title=SiPM based preclinical PET/MR insert for a human 3T MR: first imaging experiments | date=2011 | last1=Schulz |first1=Volkmar | last2=Weissler | first2=Bjoern | last3=Gebhardt | first3=Pierre | last4=Solf | first4=Torsten | last5=Lerche | first5=Christoph | last6=Fischer | first6=Peter | last7=Ritzert | first7=Michael | last8=Piemonte | first8=Claudio | last9=Goldschmidt | first9=Benjamin | last10=Vandenberghe | first10=Stefaan | last11=Salomon | first11= Andre | last12=Schaeffter | first12=Tobias | last13=Marsden | first13 =Paul |journal=Nuclear Science Symposium and Medical Imaging Conference (NSS/MIC), 2011 IEEE |pages=4467–4469}}</ref><ref>{{cite journal |doi=10.1016/j.nima.2013.08.077 |title=PET/MRI insert using digital SiPMs: Investigation of MR-compatibility | date=2013 | last1=Wehner | first1=Jakob | last2=Weissler| first2=Bjoern | last3=Dueppenbecker| first3=Peter | last4=Gebhardt| first4=Pierre | last5=Schug| first5=David | last6=Ruetten| first6=Walter | last7=Kiessling| first7=Fabian | last8=Schulz| first8=Volkmar |journal=Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment|bibcode = 2014NIMPA.734..116W | volume=734 | pages=116–121}}</ref>

A preclinical PET-MRI system with sequential acquisition is commercially available from Mediso Medical Imaging Systems since 2011. The first nanoScan PET-MRI system was installed at Karolinska Experimental Research and Imaging Centre of Karolinska Institutet in March 2011. The compact imaging system utilizes magnetically shielded position sensitive photomultiplier tubes and a compact 1 Tesla permanent magnet MRI platform. The integration has no adverse effects on the PET or on the MRI performance due to increased magnetic shielding of the PET component and low fringe field of the MRI component based on the performance evaluation of the system.<ref>{{cite journal |doi=10.2967/jnumed.112.119065 |title=Performance Evaluation of the Small-Animal nanoScan PET/MRI System |date=2013 |last1=Nagy |first1=Kálmán |last2=Tóth |first2=Miklós |last3=Major |first3=Péter |last4=Patay |first4=Győző |last5=Egri |first5=G. |last6=Häggkvist |first6=Jenny |last7= Varrone|first7=Andrea |last8=Farde |first8=Lars |last9=Halldin |first9=Christer |last10=Gulyás |first10=Balázs |journal=Journal of Nuclear Medicine |volume=54 |pages=1825–1832}}</ref> Bruker Biospin, in collaboration with the University of Tübingen, have produced commercial prototype systems for their preclinical MRI magnets utilizing a Siemens PET platform. The first such system comprising a 7T Clinscan MRI with the PET insert was installed at the CAI in Brisbane Australia in 2012.

[[File:MR Solutions' cryogen-free PET-MRI system.jpg|thumb|MR Solutions' cryogen-free PET-MRI system]]MR Solutions’ high field, cryogen-free MRI system with an in-line PET module was installed at the University of Michigan in January 2016 and at the Georges-François Leclerc center in Dijon, France in February 2016. Data is acquired sequentially and co-registered together automatically.

The aforementioned NuPET™ MR-compatible preclinical scanner from Cubresa is designed to fit into a variety of existing MRI magnets, including those originally used for clinical imaging. Uniquely, this system enables simultaneous PET/MRI acquisition, allowing researchers to generate structural, functional, and molecular data that is both partially and temporally registered and acquired under identical physiological conditions. It can also be used as a compact, standalone PET scanner.

Hybrid PET MRI systems require special devices that balance tradeoffs between PET attenuation and MRI performance.

==PET-MRI versus PET-CT==
Comparisons have been made between PET-MRI and [[Biology:PET-CT|PET-CT]], some sources stating that PET-MRI is simply an X-ray radiation-free version of PET-CT (PET-MRI has as well Radiation from Biomarker). In reality, there are differences beyond X-ray radiation dose.<ref>{{cite book |doi=10.1007/978-3-540-72718-7_6 |chapter=Multimodal Imaging Approaches: PET/CT and PET/MRI |title=Molecular Imaging I |series=Handbook of Experimental Pharmacology |date=2008 |last1=Pichler |first1=Bernd J. |last2=Judenhofer |first2=Martin S. |last3=Pfannenberg |first3=Christina |isbn=978-3-540-72717-0 |volume=185/1 |pages=109–32 |editor1-first=Wolfhard |editor1-last=Semmler |editor2-first=Markus |editor2-last=Schwaiger}}</ref>

This article written at the National Institute of Health in Bethesda, Maryland provides very good information on the technical differences between CT, MRI and PET and their combinations. It also references the advantages of simultaneous or single unit sequential over traditional sequential.<ref>{{cite journal | pmc = 2762705 | pmid=18396179 | doi=10.1053/j.semnuclmed.2008.02.001 | volume=38 | title=Positron emission tomography/magnetic resonance imaging: the next generation of multimodality imaging? | year=2008 | journal=Semin Nucl Med | pages=199–208 |vauthors=Pichler BJ, Wehrl HF, Kolb A, Judenhofer MS |}}</ref>

== PET-MR attenuation correction ==
PET-MRI systems don't offer a direct way to obtain attenuation maps as the old stand-alone PET or PET-CT systems.<ref name=":0">{{Cite journal|last=Keereman|first=Vincent|last2=Mollet|first2=Pieter|last3=Berker|first3=Yannick|last4=Schulz|first4=Volkmar|last5=Vandenberghe|first5=Stefaan|date=2013-02-01|title=Challenges and current methods for attenuation correction in PET/MR|url=https://link.springer.com/article/10.1007/s10334-012-0334-7|journal=Magnetic Resonance Materials in Physics, Biology and Medicine|language=en|volume=26|issue=1|pages=81–98|doi=10.1007/s10334-012-0334-7|issn=0968-5243}}</ref><ref>{{Cite journal|last=van Dalen|first=Jorn A.|last2=Visser|first2=Eric P.|last3=Vogel|first3=Wouter V.|last4=Corstens|first4=Frans H. M.|last5=Oyen|first5=Wim J. G.|date=2007-03-01|title=Impact of Ge-68∕Ga-68-based versus CT-based attenuation correction on PET|url=http://onlinelibrary.wiley.com/doi/10.1118/1.2437283/abstract|journal=Medical Physics|language=en|volume=34|issue=3|pages=889–897|doi=10.1118/1.2437283|issn=2473-4209|bibcode=2007MedPh..34..889V}}</ref>

Stand alone PET systems attenuation corrections (AC) is based on a transmission scan (mμ - map) acquired using a 68Ge (Germanium- 68) rotating rod source, which directly measures photon attenuation at 511keV.<ref name=":0" /><ref name="Wagenknecht 99–113">{{Cite journal|last=Wagenknecht|first=Gudrun|last2=Kaiser|first2=Hans-Jürgen|last3=Mottaghy|first3=Felix M.|last4=Herzog|first4=Hans|date=2013-02-01|title=MRI for attenuation correction in PET: methods and challenges|url=https://link.springer.com/article/10.1007/s10334-012-0353-4|journal=Magnetic Resonance Materials in Physics, Biology and Medicine|language=en|volume=26|issue=1|pages=99–113|doi=10.1007/s10334-012-0353-4|issn=0968-5243}}</ref> PET-CT systems use a low-dose CT scan for AC. Since X-rays have a range of energies lower than 511 keV, AC values need to be approximated from Hounsfield units using validated methods.<ref>{{Cite journal|last=Bai|first=Chuanyong|last2=Shao|first2=Ling|last3=Silva|first3=A. J. Da|last4=Zhao|first4=Zuo|date=October 2003|title=A generalized model for the conversion from CT numbers to linear attenuation coefficients|url=http://ieeexplore.ieee.org/document/1236959/|journal=IEEE Transactions on Nuclear Science|volume=50|issue=5|pages=1510–1515|doi=10.1109/tns.2003.817281|issn=0018-9499|bibcode=2003ITNS...50.1510B}}</ref>

There is no correlation between MR image intensity and electron intensity, therefore conversion of MR images into an attenuation map is difficult.<ref>{{Cite journal|last=Hofmann|first=Matthias|last2=Pichler|first2=Bernd|last3=Schölkopf|first3=Bernhard|last4=Beyer|first4=Thomas|date=2009-03-01|title=Towards quantitative PET/MRI: a review of MR-based attenuation correction techniques|url=https://link.springer.com/article/10.1007/s00259-008-1007-7|journal=European Journal of Nuclear Medicine and Molecular Imaging|language=en|volume=36|issue=1|pages=93–104|doi=10.1007/s00259-008-1007-7|issn=1619-7070}}</ref><ref name=":0"/><ref name="Wagenknecht 99–113"/>

==See also==
* [[Biology:Neuroimaging|Neuroimaging]]
* [[Physics:Avalanche photodiode|Avalanche photodiode]]
* [[Physics:Silicon photomultiplier|Silicon photomultiplier]]

==References==
{{Reflist}}

{{DEFAULTSORT:PET MRI}}
[[Category:Nuclear medicine]]
[[Category:Magnetic resonance imaging]]

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