presentation ictr-phe 2012 ratib.pdf

Hybrid systems in Medical Imaging

Osman Ratib, MD, PhD, FAHAProfessor and chairDepartment of Medical Imaging and Information SciencesHead of division of Nuclear MedicineUniversity Hospital of Geneva

from PET/CT to PET/MR

©2010 Hôpitaux Universitaires de Genève

History of hybrid imagingOrigin of PET / CT

19941998

University of PittsburghMedical Center


History of hybrid imagingSequential PET-CT


5

10

15

SUV

Hot Medium Hot Not So Hot

Lobular CAMucinous CAProstate CAPrimary ovarian CAWell diff - thyroid

MelanomaHG NHLHDColorectal CANSCLCEsophageal CAHead/NeckHG sarcoma

Infiltrating ductal CAPoorly diff - thyroidTesticular CAPancreasRecurrent ovarian CALG NHLBronchoalveolar CACervical CARenal cell CA

Universal tracer?FDG uptake in Tumors


New tracers in PET imaging

- Hepatocellular cancers- Renal cancers- Prostate cancers

Applications:

C11 - ACETATE


- Glyomas and brain cancersApplications:

New tracers in PET imagingF18 - Tyrosine (FET)

PET-CTMRI


- Prostate cancers (recurrence)Applications:

New tracers in PET imaging18F - Choline


New tracers in PET imaging

- Endocrine tumors- Carcinoïd tumors

Applications:

18F - Dopamine

18F-DOPA18F-FDG


New tracers in PET imaging18F PET


New tracers in PET imaging18F - NaF PET

Planar SPECT 18F NaF - PET

©2011 Hôpitaux Universitaires de Genève 11

FDG PET impact on patient management

©2011 Hôpitaux Universitaires de Genève 12

Reference No.pts Change in mgmt Delbeke et al, J Nucl Med 2000; 41: 275P 27 31% Yap et al, J Nucl Med 2000; 41: 109 58 50% Dittman et al, J Nucl Med 2000; 41: 71P 24 8% Seltzer et al, J Nucl Med 2000; 41: 108P 536 50% Kostakoglu et al, J Nucl Med 2000; 41: 118P 62 5% Shah et al, Br J Radiology 2000; 73: 482 29 34% Jerusalem et al, NM Commun 1999; 20: 13 60 3% Moog et al, Radiology 1998; 206: 475 81 16% Bangerter et al, Ann Oncol 1998; 9: 1117 44 14% Hoh et al, J Nucl Med 1997; 38: 343 18 22% Moog et al, Radiology 1997; 203: 795 60 7%

Staging

RecurrenceSpaepen et al, J Nucl Med 2000; 41:70 96 14%Kostakoglu et al, J Nucl Med 2000; 41: 118P 62 5%

Total: 999 21%

Total: 158 10%

FDG PET: Impact on patient management


0

10

20

30

40

50

60

Up Down No Change No Answer

5

56

14

25

5

49

15

31

Lung Cancer (n = 285)Non-Lung (n = 298)

Seltzer et al, UCLA School of Medicine

Changes in clinical staging(n = 583)

PET in oncologyImpact of PET imaging on clinical management


Changes in treatment(n = 583)

43

15

36

6

42

18

34

6

0

10

20

30

40

50

Major Minor No Change No Answer

%

Lung Cancer (n = 285)Non-Lung (n = 298)

PET in oncology

Seltzer et al, UCLA School of Medicine

Impact of PET imaging on clinical management


FDG PET vs PET-CT in Oncology


PET/CT in oncologyAdvent of hybrid imaging

Currently available data indicate that PET/CT is more sensitive and specific than either of its constituent imaging methods alone and probably more so than images obtained separately from PET and CT and viewed side by side.

Published results on the use of PET/CT in oncology are still limited, but several well-designed studies have demonstrated the benefits of PET/CT, especially in staging of non–small cell lung cancer, recurrent colorectal cancer, and malignant lymphoma


PET/CT in oncologyAdvent of hybrid imaging


PET/CT in oncology


Hybrid imagingFrom PET-CT to PET-MR

CT PET

CT

PET-CT PET-MRI

PET-CT

PET

MRI

MRI

PET-MRI


PET-MRI developementsPioneer work by S. Cherry 1994-1996


PET-MRI developmentsFirst animal prototype S. Cherry 2004-2006


Hybrid imagingWhole body PET-MR

PET MRIPET-MRI


PET-MRI developments

PET/MRI system design

Gaspar Delso & Sibylle Ziegler

Published online: 23 December 2008# Springer-Verlag 2008

AbstractIntroduction The combination of clinical MRI and PETsystems has received increased attention in recent years. Incontrast to currently used PET/CT systems, PET/MRI offersnot only improved soft-tissue contrast and reduced levels ofionizing radiation, but also a wealth of MRI-specificinformation such as functional, spectroscopic and diffusiontensor imaging. Combining PET and MRI, however, hasproven to be very challenging, due to the detrimental cross-talk effects between the two systems.Objective Significant progress has been made in the recentyears to overcome these difficulties, with several groupsreporting PET/MRI prototypes for animal imaging and aclinical insert for neurological applications being demon-strated at the 2007 Annual Meeting of the Society ofNuclear Medicine.Discussion In this paper we review different architecturesfor clinical PET/MRI systems, and their possibilities,limitations and technological obstacles.

Keywords Positron emission tomography .Magneticresonance imaging . Instrumentation . Equipment design

Introduction

Following the extensive research effort dedicated tosoftware coregistration in the 1990’s, the introduction ofcombined positron emission tomography (PET) and com-

puted tomography (CT) systems [1] was met with enthu-siasm by the medical community. Nine out of ten PETscanners purchased today are combined PET/CT systems.The key to this success was not just the straightforwardsolution to the coregistration problem in most applications,but also the significant improvement in workflow fromscanning the patient quasi-simultaneously and from avoid-ing a standard PET transmission scan. PET/CT is currentlyfully integrated into clinical routine, but although itsadvantages are many, CT still provides limited soft-tissuecontrast and, when used for whole-body diagnosis, mayexpose the patient to high radiation doses (over 10 mSv)[2]. An alternative source of anatomical information wouldbe magnetic resonance imaging (MRI) [3].

Combining MRI and PET, however, has proven to bevery challenging, due to known and potential crosstalkeffects. Indeed, the static magnetic field, rapidly changinggradient fields and radiofrequency (RF) signals from theMR affect the light yield of scintillator materials [5],prevent the normal operation of photomultiplier tubes(PMT) and induce interference in the front-end electronicsof PET detectors. Conversely, the mere presence of the PETdetector causes inhomogeneities in the magnetic field,which can lead to artefacts in the MR images. Furthermore,it can emit signals interfering with the RF and gradientcoils, both due to its normal operation and to Eddy currentsinduced by the changing magnetic field.

However, in recent years, progress has been made inidentifying scintillators with adequate magnetic properties[6], in developing suitable PET detectors which use opticalfibres to guide the scintillation light away from the MRmagnetic fields [4, 7–10] or that replace the PMTs bymagnetic field-insensitive avalanche photodiodes (APD)[11, 12, 14–16], or design shielded PET electronics to avoidelectromagnetic interference [17].

Eur J Nucl Med Mol Imaging (2009) 36 (Suppl 1):S86–S92DOI 10.1007/s00259-008-1008-6

G. Delso (*) : S. ZieglerNuklearmedizinische Klinik und Poliklinik,Klinikum rechts der Isar, Technische Universität München,Ismaniger Str. 22,81675 Munich, Germanye-mail: [email protected]

Head Insert

Whole body sequential

Whole body simultaneous

Sequential vs simultaneous acquisition


PET-MRI hybrid imagingWhole-body PET-MRI

MRI PET

3m


First whole-Body PET-MRI prototypeTwo first luminary sites

Mount Sinai Medical Center (New York)

Geneva University Hospital (Geneva)

Pr. Z.Fayad Pr. O.Ratib

February 2010


Whole-body PET-MRIMR-based attenuation correction

+

Spine 15ch Cardiac 32ch posterior Breast 7ch Head 8ch NV 16ch

Uncorrected DIXONin phase

DIXONfat

DIXONwater

Attenuationmap Corrected

Bed and surface coils attenuation maps


Whole-body PET-MRIClinical workflow

1 2

31. Whole body MRI (AC and localization)2. Whole body PET3. Additional diagnostic MR images


PET-MRI in GenevaAlpha & beta phase

• 62 patients had a PET-CT followed by a PET-MR

• Average time between studies was 85 ± 22 minutes ranging from 49 minutes to 120 minutes

• Most patients had a complementary diagnostic MRI

• Images were interpreted by a team of radiologists and nuclear medicine physicians

• PET Image quality was graded and compared between PET-CT and PET-MR

• SUV were measured and compared on both PET studies


PET-MRI in GenevaAlpha & beta phase

CTPET 1CTIodineFDG

0 15’ 30’ 45’ 60’ 75’ 90’ 105’ 120’

PET-CT

MRPET 2MRGadolinium

PET-MR

PET-CT & PET-MRworkflow


PET-MRI in GenevaResullts

• No significant difference in image quality and identification of abnormal lesions were found between the two PET scans of each case

• Images performed on the PET-MR were comparable to those acquired on the PET-CT scanner and often showed higher contrast with less background noise due to a well known FDG redistribution

• No significant artifacts from attenuation correction or from interference between the two scanners were observed

• Whole-body MRI sequence were often suboptimal for accurate anatomical localization and additional high resolution images of selected anatomical regions were used



• SUV measurements performed on two sequential PET studies (separated by 85 ± 22 minutes) showed a significant variation in biodistribution in different organs, but showed comparable results in tumor lesions

PET-CT PET-MR



• SUV measurements performed on two sequential PET studies (separated by 85 ± 22 minutes) showed a significant variation in biodistribution in different organs, but showed comparable results in tumor lesions

Clinical Studies


PET-MRI in clinical routine

I. INTRODUCTION PET/MR has started gaining more interest recently because of

its obvious advantages over PET/CT: firstly MRI offers much better soft-tissue contrast; secondly it does not cause patientsF exposure to extra radiation dose. However, it is technically very challenging to bring an MRI system together with a PET system. Interference between the two systems has to be removed. Additionally, MR image intensity is a function of proton density and other MR tissue properties, including T1 and T2 relaxation rates, which is not directly related to the attenuation of the photons generated in PET. Thus, deriving the photon attenuation map using MRI is not as straight-forward as the CT-based attenuation correction (CT-AC) which directly measures the attenuation property of the object.

To facilitate the investigation of PET/MR clinical value, Philips is developing a commercial whole-body PET/MR system. However, this study focuses on MR-based attenuation correction (MR-AC) accuracy in different clinical scenarios using PET/CT and MRI data acquired separately. There have been several investigations on MR-AC, but the emphasis has been mainly on MR image segmentation for derivation of an attenuation map [1,2]. Besides image segmentation, this study also addresses other technical challenges for effective attenuation correction in a commercial whole-body PET-MR, including compensation for MR image truncation and correction for RF coils and accessories. The initial evaluation of the MR-AC technique on patient data collected on separate PET/CT and MR systems is presented.

Figure 1: Philips PET-MR system design as viewed from behind the PET system

II. MATERIALS AND METHODS

A. PET-MRI system design and general workflow The Philips PET-MRI system consists of a GEMINI TF PET

system and an Achieva 3T X-series MRI system (Fig. 1). The two scanners were placed in the same room, with a patient table between the two, forming a sequential system. The PET was redesigned to operate in the presence of an MRI. The gantry was re-crafted to provide magnetic shielding for PMTs so that they operate in nominal magnetic flux levels. Additional modifications were done to move all electronics from the PET gantry to the equipment room so as to satisfy the strict noise requirements of the MRI. PET modifications were realized to ensure no compromise in system performance in either PET or MRI.

In a typical clinical environment, an MR image is first acquired for PET attenuation correction (termed atMR, Fig. 2 left), then the patient is moved to the PET scanner for scanning. The patient will then be moved back to the MR scanner for diagnostic MR imaging/spectroscopy, as requested by the clinical indication. For reading the PET images, the atMR image can also be used for localizing patient anatomic structures similar to the practice of using low-dose CT image in current PET/CT systems.

B. MR image acquisition A multi-station whole-body protocol was developed, suitable

for deriving a PET attenuation map. The quadrature body coil (QBC) was used for signal reception. A 3D multi-station spoiled gradient echo sequence was used with flip angle 10 degree, TE 2.3 ms, TR 4 ms, smallest water-fat shift, 530 mm transverse FOV with a 3D slab thickness of 60 mm, voxel size 3x3x6 mm3, and 6 mm overlap between adjacent stations. The homogeneity of the main magnetic field B0 limits the maximum useable transverse FOV. The 60 mm 3D slab thickness was used to reduce the truncation artifact observed on whole-body MR images.

Figure 2: The atMR image (left), suitable for localization and the attenuation correction (AC) map (middle) derived from the atMR image using a 3-segment approach. AC map of a different patient scanned on a Philips Allegro system with stand-alone transmission source is shown on the right.

C. MR image segmentation Different physical mechanisms are involved in MRI image

formation and PET attenuation. MRI intensity is generally related to proton density which has no direct relation with photon attenuation in PET. Thus, the simple approach of PET/CT to scale the CT values to a different energy range in order to construct the attenuation map is not feasible for PET/MR. Hence our approach employs a segmentation of the image with subsequent assignment of attenuation coefficients to individual segments.

The segmentation algorithm attempts to distinguish 4 biological classes: air, lungs, soft tissue, and bone. While soft tissue can be relatively easily distinguished based on intensity, for the remaining tissue classes a priori knowledge of the individual structures (e.g. typical positions and sizes of lung and femur bone relative to the overall body, as well as typical morphological features like compactness) was incorporated into the algorithm.

In the first stage, the MR image was analyzed in terms of gray values (histogram analysis) for initial estimation of patient size and orientation. In the second stage, a combined voxel-analysis (region-growing) / model-adaptation scheme was used, where the model-based part was used to control the voxel-based analysis (e.g. to prevent leakage and other gross errors). In a baseline implementation, body outline and the lungs were segmented. Detection and segmentation of other structures (e.g. femur bones, arm bones, pelvis) are available in an experimental stage; the tradeoffs of including those structures in terms of robustness, accuracy and runtime are currently being assessed, but not presented here.

Z. Hu, N. Ojha, S. Renisch, V. Schulz, I. Torres, A. Buhl, D. Pal, G. Muswick, J. Penatzer, T. Guo, P. Bönert, C. Tung, J. Kaste, M. Morich, T. Havens, P. Maniawski, W. Schäfer, R.W. Günther, G.A. Krombach, and L. Shao

MR-based Attenuation Correction for a Whole-body Sequential PET/MR System

• Pediatric oncology and epilepsy workup

• Oncology investigation that require already a diagnostic MRI in addition to PET-CT:

• Head & Neck cancer (pre and post-op) • Prostate cancers • Breast imaging

• New emerging clinical applications:• Cardiac imaging (viability, ischemia?)• Gynecological cancers• Bone metastases (F18-NaF)

Potential clinical applications


PET-MR in Geneva

Steering committee

• Osman Ratib• Christophe Becker• Magalie Vialon• Habib Zaidi• Jean-Paul Vallée• Maria Isabel Vargas• Michael Wissmeyer• François Riondel• Béatrice Paridant• Michel Velazquez• Jean-Noel Hyacinthe

Research team

Team (1) – Oncology H&N:• Minerva Becker • Michael Wissmeyer + Olivier Rager• Magalie Vialon

Team (2) – Oncology prostate:• Jean Paul Vallée • Charles Steiner + Valentina Garibotto• Jean-Noel Hyacinthe

Team (3) – Oncology breast:• Pierre Loubeyre • Olivier Rager + Jean-Pierre Willi • Jean-Noel Hyacinthe

!Philips support and R&D team

• Jeffrey Kaste• Troy Havens• Piotr Maniawski• Susanne Heinzer• Antonis Kalemis• Navdeep Ojha• Zhiqiang Hu• Kevin Kilroy• Michelle Granny• Dominique Joliat


PET-MR in Geneva

Steering committee

• Osman Ratib• Christophe Becker• Magalie Vialon• Habib Zaidi• Jean-Paul Vallée• Maria Isabel Vargas• Michael Wissmeyer• François Riondel• Béatrice Paridant• Michel Velazquez• Jean-Noel Hyacinthe

Research team

Team (1) – Oncology H&N:• Minerva Becker • Michael Wissmeyer + Olivier Rager• Magalie Vialon

Team (2) – Oncology prostate:• Jean Paul Vallée • Charles Steiner + Valentina Garibotto• Jean-Noel Hyacinthe

Team (3) – Oncology breast:• Pierre Loubeyre • Olivier Rager + Jean-Pierre Willi • Jean-Noel Hyacinthe

!Philips support and R&D team

• Jeffrey Kaste• Troy Havens• Piotr Maniawski• Navdeep Ojha• Zhiqiang Hu• Kevin Kilroy• Michelle Granny• Laurent Renevey• Sylvain Sans• Dominique Joliat

presentation ictr-phe 2012 ratib.pdf

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