Stephan G. Nekolla and Sibylle Ziegler Hybrid Imaging · 3 x 3 APD matrix (5 x 5 mm2) LSO-APD block detector . Quadrature TRX coil installed inside the PET insert PET scanner parameters

Technische Universität München Nuklearmedizinische Klinik und Poliklinik Klinikum rechts der Isar Technische Universität München Nuklearmedizinische Klinik und Poliklinik Klinikum rechts der Isar Technische Universität München Technische Universität München

Hybrid Imaging Stephan G. Nekolla and Sibylle Ziegler

Technische Universität München Nuklearmedizinische Klinik und Poliklinik Klinikum rechts der Isar Technische Universität München Nuklearmedizinische Klinik und Poliklinik Klinikum rechts der Isar

•  Basic Nuclear Medicine

•  Detectors

•  Gamma Camera, SPECT

•  Positron Emission Tomography

•  Biokinetic Modelling

•  Multimodal Imaging


Unrestricted © 2016 Nuklearmedizinische Klinik der TU München Nekolla + Ziegler

Aims of Nuclear Medicine

•  Diagnostics

Visualisation and quantification of biochemical processes in vivo

•  Therapy:

Treatment of pathologic processes based on selective accumulation in body tissues



Principles of Nuclear Medical Diagnostics

•  Tracer principle Radiopharmaceuticals are distributed, metabolized or excreted in the organism according to their structure

•  Representation of body functions by:

–  Images –  Numerical data –  Graphs



Principles of Nuclear Medical Diagnostics

•  Tracer principle Radiopharmaceuticals are distributed, metabolized or excreted in the organism according to their structure

•  Representation of body functions by:

–  Images –  Numerical data –  Graphs

•  But why hybrid imaging?


Unrestricted © 2016 Nuklearmedizinische Klinik der TU München Nekolla + Ziegler 6

Introduction

•  Micromodal

•  Monomodal

•  Multimodal

1e6 2e6 4e6

1-2e6 1-2e6 5e5


Principles of hybrid devices System design: SPECT/CT vs PET/CT vs PET/MR



CT

PET

Combination PET – CT

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3D reconstruction FORE + OSEM

CT-based attenuation and

scattering corrections

CT acquisition

Fused image

Upper limit

Lower limit

Topogram

PET image

PETCT

PET/CT Standard Protocol

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Change of acquisition durations over time

Year Cardiac PET WB Onco PET Cardiac SPECT Cardiac MRI

1995  60 min 90 min 3h 60 min

2015 60 min 15 min 1h 60 min


Unrestricted © 2016 Nuklearmedizinische Klinik der TU München Nekolla + Ziegler 11

•  Time consuming transmission scan (almost as long as the PET scan) was replaced with very fast CT

•  Axial scan length increased from 10 cm to 25 cm

•  New detector materials are more sensitive

•  Iterative image reconstruction improved image quality –  -> 5 pts -> 25 pts a day

Change of acquisition durations over time



Most basic hybrid imaging: attenuation correction

PET NAC PET AC



A look back: attenuation correction



PET/CT – Melanoma Patient

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Recently featured publications in hybrid nuclear imaging: “The year in cardiology 2015: imaging ” (EHJ 37: 667–675 )

PET-CT in suspected device pocket infection. Example of a positive 18F-FDGPET/CT scan in a patient with pain at the generator pocket site. In: Ahmed FZ, et al. Early diagnosis of cardiac implantable electronic device generator pocket infection using 18F-FDG-PET/CT. Eur Heart J Cardiovasc Imaging 2015;16:521 – 530.



Hybride MR-PET Bildgebung Onkologie •  Indikationen, bei denen MRI und PET synergistisch sind •  Logistische Vorteile (one-stop-shop) •  Mehrwert durch bessere Koregistrierung, PET-Bewegungskorrektur

basierend auf MR-Signal

CUP SCC in cervical lymph node

Contrast enhanced CT MRI T1w + Gd-DTPA MR-PET image fusion

A. Beer 2010



Respiratory gating system:

Image taken from http://www.jcu.edu/biology/RESP4.JPG

Pressure sensor

Patient Belt

Computer

Trigger(s)

End expiration

Gate(s)

End inspiration

List Mode Acquisition

+

Respiratory Movement PET/CT

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System Design – „Tandem“ Design Sequentieller Ganzkörper PET-MR

Achieva 3T MRT und PET Gemini TF (Philips)

+ Existierende Technologie verwendbar + Minimale Interferenz zwischen PET und MR

Installed in Mount Sinai NY , Dec 2009

- Großer Raum - Nicht simultan

Vor- und Nachteile :


MR PET MR/PET



System Design – „Integriertes“ Design Integrierter Ganzkörper PET-MR für simultane Bildgebung

Delso et al., 2009

+ zeitliche Korrelation von PET und MR + multiparametrische Aufnahmen

+ MR-Bewegungskorrektur

- technisch anspruchsvoll - neue Technologie

Pro‘s and Con‘s


aim: simultaneous data acquisition

requirements: No influence of MR on PET

detectors? signal transmission?

No influence of PET on MR magnetic materials? detectors size?

Technology PET/MR

•  Electrical conductivity of semiconductors can be varied by the implantation of impurities (doping)

Avalanche Photodiodes (APDs)

•  Moving charged particles, e.g. electrons, are deflected in magnetic fields by the Lorentz force

! PMTs cannot be used inside an MRI scanner

! Solution: Semiconductor photodetectors

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Nuklearmedizinische Klinik und Poliklinik

B = 0 B ≠ 0 B. Pichler et al.


Y. Shao, S.R. Cherry et al. IEEE TNS 1997 P.K. Marsden et al. Brit. J Radiology 2002

Long light guides and PMTs

Avalanche Photodiodes (APDs)

•  APDs offer an alternative to conventional photo detectors

•  Basically a p-n-junction, a simple device made out of two specifically doped layers

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B = 0 B ≠ 0 B. Pichler et al.


B.J. Pichler et al. J Nucl Med 2006

Experimental PET/MR Systems

10 x 10 LSO crystals (2 x 2 x 12 mm3)

3 x 3 APD matrix (5 x 5 mm2)

LSO-APD block detector

Quadrature TRX coil installed inside the PET insert

PET scanner parameters

Crystal size

1.6 x 1.6 x 4.5 mm³

Crystal material

LSO

Number of detector blocks

10

FOV axial / transaxial

19 mm / 38 mm

Coincidence timing resolution

8 ns

Resolution < 2 mm

PET/MRI Preclinical System

Laboratory for Preclinical Imaging & Imaging TechnologyUniversity of Tübingen, Germany

Pichler et al.



Insert Design •  Siemens BrainPET Prototyp instaled within MAGNETOM Trio

- 23040 LSO Szintillatoren -  1440 APDs

-  axial FOV = 19 cm -  PET Auflösung = 2.5 mm

Catana et al., MGH Boston

MR/PET Designs: Integrated

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Siemens Biograph mMR

Munich MR-PET Consortium

Departments of Nuclear Medicine and Departments of Radiology of

Funded by

Biograph mMR • First fully integrated whole-body MR/PET system • Based on a clinical 3 T MR scanner

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Attenuation Correction in PET

18F-FDG PET not corrected for attenuation

Attenuation Correction

Standalone PET

PET/CT

PET/MR

?

18F-FDG PET corrected for attenuation



Segmentation-based attenuation correction using Dixon imaging

fat image water image

PET NAC PET AC u-map

in phase opposed phase

MR based attenuation correction



Avg ∆SUV lesions: 2.3% Segmented dual-echo Dixon MRI vs. CT

CT-based AC

MRI-based AC

MR MR

Seg CT

Martinez-Möller A, Nekolla SG, et al.; JNM 2009

The method based on segmentation is fast and reliable. Some bias (5-13%) for osseous lesions.

MR-based AC: Dixon imaging for fat/water separation



Potential new artifacts by MR-AC Patient with hip prosthesis on left side; artifacts misinterpreted as air



MR based attenuation correction Atlases and pattern recognition Coregistration to MR atlas

+ bones detected -  errors in coregistration? -  large differences in patients?

Hofmann et al. Eur J Nucl Med 2009 Schreibmann et al. Med Phys 2010



PET/MR Quantification Challenges

Limited MR FOV Attenuation in coils

Correction needed based on PET data

Include coil models in attenuation maps



AC – truncation artefacts

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MR-based field-of-view extension in MR/PET: B(0) homogenization using gradient enhancement (HUGE). Blumhagen JO, Ladebeck R, Fenchel M, Scheffler K. Magn Reson Med. 2012 Nov 30.



Summary Nuclear imaging today offers a wide armamentarium

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SPECT/CT

PET/CT

PET/MRI



Logistical Issues in Hybrid Imaging: •  Human resources

– Cross trained technologists who feel at home in MRI are needed

– Two overlapping shifts with two technologists (0730-1830)

– Tight integration with physicians from radiology department for reading and harmonization of MR imaging protocols

– Standardized protocols – Highly sophisticated hard- and software for

optimal scheduling



Summary However, this is modulated by other factors

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Local , inter- disciplinary expertise

Cost and time effectiveness

Improved understanding of disease

Documents

Stephan G. Nekolla and Sibylle Ziegler Hybrid Imaging · 3 x 3 APD matrix (5 x 5 mm2) LSO-APD block detector . Quadrature TRX coil installed inside the PET insert PET scanner parameters