sibylle i. ziegler nuclear medical instrumentation

Technische Universität München

Nuklearmedizinische Klinik und Poliklinik

Klinikum rechts der Isar Technische Universität München


Klinikum rechts der Isar Technische Universität München Technische Universität München

Nuclear Medical Instrumentation

Sibylle I. Ziegler





Klinikum rechts der Isar

• Basic Nuclear Medicine

• Detectors

• Gamma Camera, SPECT

• Positron Emission Tomography

• Multimodal Imaging

• Biokinetic Modelling






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

Radiation

Source

Radiology vs. Diagnostic Nuclear Medicine

Radiology

Contrast between tissues with

different densities for x-rays,

e.g. lung vs. bone.

Detector


Nuclear Medicine

Detector


Nuclear Medicine

Detector

Activity distribution equivalent

to distribution of the injected

substance.

Radiation

Source


Radiology Nuclear Medicine

Detector






Radiopharmaceuticals

• Selection of the pharmaceutical according to the organ-

specific question

• Labelling of pharmaceuticals with radioactive isotopes

External detection possible

• Radiopharmaceuticals must not affect the metabolism

01.06.2015 9






Types of Radiation – Range in Tissue

Energy Range

α some MeV < 1mm

β 100 keV – 1MeV ~ some mm

γ 100 keV – 500 keV < some cm

10 01.06.2015






Isotopes for Nuclear Medical Imaging

Nuclide Half Life Type Energy [keV]

99mTc 6 h γ 140

201Tl 73 h γ 70

123I 13 h γ 159

131I 8 d γ 364

18F 110 min e+, γγ 511

01.06.2015 11






Blockierter Metabolismus

[18F]FDG

AST PS

MAb, Fragmente

Hormone

Drugs

Peptide

Internalisation

AS Transport

Protein Synthese

Target Structure

Immunreaktion

Anti-Gen Strategie,

DNA - Synthese

Katecholamin-

Transport

Rezeptor-Darstellung

Red. DNA-S

HED

Extrazelluläre

Strukturen

Transport






Interaction of Gamma Quanta with Matter

Gamma energy in nuclear medicine:

Compton scattering and photoelectric effect

Interaction depends on:

• Energy Ehν of gamma quantum

• Density ρ of material

• Atomic number Z of material

• Thickness D of material

01.06.2015 13






e e e

e e

e e e

e e

Energy of gamma quantum gets absorbed

Gamma Radiation – Photoelectric Effect

01.06.2015 14






34

hE

A

Z

Photoelectric Effect

01.06.2015 15






Parts of -energy are transferred to the electron

-quantum changes energy and direction

e

e

e

Gamma Radiation – Compton Scattering

01.06.2015 16






hEf

A

Z

Compton Scattering

01.06.2015 17






Compton Scattering - Angular Distribution

01.06.2015 18






Probability of γ Interaction with Matter

01.06.2015 19

Diagnostic

Lead

NaI

Tissue

Photo effect

Compton effect

Gamma Energy [keV]

Ato

mic

Nu

mb

er

Z






µm = + Attenuation coefficient photo effect:

Attenuation coefficient Compton effect:

out of Sorenson, Phelps: Physics in Nuclear Medicine 1980

Attenuation Coefficient

01.06.2015 20






conduction band

activator level (doping)

valence band

activator ground level

gap

Scintillation Crystals – Inorganic Crystals

Electron ionizes electron hole pare hole ionizes

activator, electron “drops“ into activator activator

deactivates by emission of a photon (10-7 sec)

01.06.2015 21






Scintillation Crystals

Property NaI BGO LSO GSO

NaI:Tl Bi4Ge3O12 Lu2SiO5:Ce Gd2SiO5:Ce

Density (g/cm3) 3,67 7,1 7,4 6,7

Effective Z 51 73 65 59

Attenuation length at 511keV (mm) 29,1 10,4 11,4 14,1

Light yield (photons/MeV) 41 000 9 000 26 000 8 000

Decay time (ns) 230 300 40 60

Emission (nm) 410 480 420 440

01.06.2015 22

Lu-176 (2,6%): + >350 keV: ~100/sec per cm3






1 cm

light sensitive

cathode

anode HV

Photomultiplier

01.06.2015 23






LSO BGO

Hamamatsu Photonics

Quantum Efficiency Photomultiplier

quantalight#

electronsphoto#QE

01.06.2015 24






Kristall

photomultiplier

electrons light

γ

electrical signal

crystal Tl doped

sodium iodide (NaI)

Scintillation Detector

energy ~ light quantity ~ signal height

01.06.2015 25






γ

Scintillation light

NaI-Crystal (40 cm x 40 cm)

Light guide

Photomultiplier

Position,

Energy

Gamma Camera – Anger Principle

01.06.2015 26






• High efficiency (>85%)

• Good energy resol. (<15 keV fwhm)

• High spatial resol.

• (<4 mm)

• Small costs (<€15/cm2)

• “Short” deadtime (<2000 s cm2)

*Image courtesy of L. Shao, Philips Medical Systems

Scintillation Crystals (NaI:Tl)

Photomultiplier

At 140keV:

SPECT Detector Requirements

01.06.2015 27






ideal

intrinsic

crystal light guide

photomultiplier

Source position

PM

T S

ign

al *

Gamma Camera – Linearity

01.06.2015 28






(about 30 000 pulses per second)

Without homogeneity

correction matrix

UFOV Integral 6,17%

CFOV Integral 5,25%

UFOV Differential 4,46%

CFOV Differential 4,46%

01.06.2015 29

99mTc Point Source






(about 30 000 pulses per second)

With homogeneity correction

matrix

UFOV Integral 2,49%

CFOV Integral 2,44%

UFOV Differential 1,99%

CFOV Differential 1,99%

99mTc Point Source

01.06.2015 30






ADC

ADC

ADC

ADC

ADC

ADC

ADC

ADC

integration time,

X-Y,

linearity correction,

energy discrimination

X Y

collimator

NaI crystal

light guide

photomultiplier

with preamplifier

digital

pulse processing

01.06.2015 31






γ γ

γ

Crystal

γ

Light quantity

γ

Scintillation Detector – Deposited Energy

01.06.2015 32






Out of Sorenson, Phelps: Physics in Nuclear Medicine 1980

Scintillation Detector – Ideal Spectrum

01.06.2015 33






primary

scattered

all

Ab

undance

Gamma Camera – Energy Spectrum

01.06.2015 34






Energy Window – 99mTc Sphere Phantom

01.06.2015 35

140 keV (15%)

Events: 100%

104 keV (20%)

Events: 35%

Matrix: 128x128

Pixel size: 3,8mm






Gamma Camera – H. Anger 1964

01.06.2015 36

Crystal

Collimator Photomultiplier

Position

Energy






Collimator – Limiting Component Septum thickness depends on energy and attenuation coefficient

01.06.2015 37

Principle

Septa Crystal

γ

γ

Lead collimator, several

hundreds holes






Collimator – Resolution Sensitivity

01.06.2015 38

crystal crystal crystal

e.g.: length 35 mm, distance 1.5 mm, thickness 0.2 mm

more events

or

higher resolution

signal to noise

Planar Scintigraphy

Detector size ca. 50 cm x 60 cm

ca. 60 photomultiplier tubes per

detector

Energy resolution:

< 10% @140 keV

Intrinsic spatial resolution:

3.5 - 4 mm

Extrinsic spatial resolution

(Collimator): 8 - 20 mm

Planar Scintigraphy

bone scintigraphy shows

increased metabolism in bone,

e.g. due to

- bone fractures

- inflammatory processes

- degenerative processes

- bone metastasis

99mTc-Bisphosphonat ventral dorsal

Planar Scintigraphy

rib

fracture

knee

arthrosis

bone

metastasis






Planar Scintigraphy Cameras for special use, e.g. thyroidal gland

Planar Scintigraphy

thyroidal scintigraphy

normal finding unifocal autonomy

Planar Scintigraphy

99mTc-MAG3 (Mercaptoacetyltriglzcin)

Acquisition over time, e.g. renal scintigraphy

Planar Scintigraphy

Visual and quantitative analysis

99mTc-MAG3 (Mercaptoacetyltriglzcin)






Tomography

SPECT Recording

Gamma Camera

Gamma Camera

measures

projections of

activity distribution Spatial Resolution

clinical: ~8 – 20 mm

01.06.2015 46






Images of Different Directions






Single Photon Emission CT SPECT






Emission Tomography

• Measurement of many projections, many angles

• Mathematical reconstruction

• Tomographic images / slices through body






Projection, Discrete Sampling






SPECT Imaging – Projection

01.06.2015 51






Reconstruction – Back Projection

Back projection

of two projections Back projection

of three projections






Filtration of Line Profile

01.06.2015 53

Unfiltered without

noise

with

noise

Filter

hamming

cutoff = 0.2

Filtered






Filtered Back Projection

01.06.2015 54

Without

Filter






Projection

Acceleration: OSEM, Cluster

Estimate

Back-projection

Comparison

Object Space Projection Space

Correction

Error- Estimate

Error- Estimate

Estimated Projection

Measured Projection

Error - Projection

Statistical Iterative Reconstruction

01.06.2015 55






Quality Control

• Daily Background

Energy window

Tilt angle

• Weekly Efficiency

Inhomogeneity

Flood correction

Rotation Centre

• Half-yearly Geometric scale

Linearity

Spatial resolution

Tomographic inhomogeneity

01.06.2015 56





Klinikum rechts der Isar Technische Universität München Technische Universität München

New Developments

Single Photon Detection






Consequence: higher percentage of inactive area

worse spatial and energy resolution

Gamma Camera – Anger Principle

• Collimator system resolution

• Intrinsic resolution ~ 4 mm

dependent on energy, crystal thickness

Reduction by:

narrower distribution of light

smaller photomultipliers

more photomultipliers

01.06.2015 58






Requirements:

• Compact

• High intrinsic resolution

• Good energy resolution

High Resolution Gamma Camera

Imaging close to the object: thyroid

mammography

small animals

01.06.2015 59






Crystal

Photomultiplier

Photodiodes

Semiconductor

detector

Detectors

01.06.2015 60






signal

distribution

anode wires (X-Y)

scintillation light

X

light sensitive

cathode

Position Sensitive Photomultiplier PSPMT

01.06.2015 61






FZ Jülich

28 X and 28 Y Anode wires

+ center of mass determination

NaI(Tl) slice

( 13 cm, thickness 3 mm)

collimator

PSPMT Hamamatsu

250m

m

164mm

Intrinsic: < 2 mm

E/E(140 keV): 9,6%

High Resolution Gamma Camera PSPMT

01.06.2015 62






Patt et al., Majewski et al., LumaGEM, Dilon

NaI(Tl) pixel: 2 x 2 x 6 mm

2,8 x 2,8 cm2 x 2,7 cm

4 X and 4 Y wires

(Hamamatsu)

Intrinsic: < 2 mm; E/E(140 keV): 18%

Matrix of Compact PSPMT

01.06.2015 63






Dilon

Matrix of PSPMT and NaI pixel

compact detector head

01.06.2015 64






• One-to-one coupling crystal – sensor

pixel size intrinsic resolution

• Silicon photo diodes (PD) versus PMT:

− high quantum efficiency − very compact − no amplification − noise, electronic necessary

Scintillation Read-Out with Semiconductor

Detectors

01.06.2015 65






Luminous Scintillators

Properties NaI(Tl) CsI(Tl)

Density 2.3 4.5

Effective Z 32 54

Attenuation length at

140 keV (mm) 3.4 2.2

Light yield (%) 100 165

Wavelength (nm) 410 550

Decay time (ns) 230 1000

Hygroscopic ++ (+)

01.06.2015 66

Yield PMT / yield PD (at 550nm) = 1 : 3






UCLA, LBL, Digirad

Digirad

4096 CsI(Tl) Crystals

5 cm

Collimator

Electronics

Crystal pixel size: 1.5 mm to 3 mm

Individual Read-Out with PD-Matrix

01.06.2015 67






Detector Head

(21 cm x 21 cm)

Digirad

Gamma Camera with CsI-PD Detector

01.06.2015 68






Semiconductor Detector

• Direct detection of gamma quanta

• Low noise

• Excellent energy resolution

Cadmium-Zinc-Telluride CZT:

• High atomic number

7 mm CZT = 1 cm NaI (at 140keV)

• Room temperature

• Energy resolution 6%

Individual pixels, size: 330µm ... 5mm

01.06.2015 69






Siemens, Hoffman Estates 1999

top view

bottom view

Cadmium Zinc Telluride Camera

Detector Element

01.06.2015 70






Cardiac Imaging

Semiconductor Detector

pinhole collimators

focus on heart

Spectrum Dynamics D-SPECT Camera






Positron Emission Tomography (PET)

Most sensitive method for

quantitative measurement of

physiologic processes

in vivo

01.06.2015 72






Coincidence circuit

PET Measuring Principle

Electronic Collimation

(511 keV)

(511 keV)

Nucleus

e+

e-

180±0.25°

01.06.2015 73






PET Nuclides

Nuclide Half life

(min)

EMax

(MeV)

Rmax

(mmH2O)

Ravg

(mm H2O)

11C 20.40 0.97 5.0 0.3

13N 9.90 1.19 5.4 1.4

15O 2.05 1.72 8.2 1.5

18F 109.70 0.64 2.4 0.2

01.06.2015 74

E: Energy, R: Range






Detector

Element

PET

Coincidence

lines

Field

of view

01.06.2015 75






Positron Emission Tomography – 3D

Scattered within FOV

Random Coincidences

True Coincidences

Scattered outside FOV

Crystal Shielding

Short Coincidence Window

Good Energy Resolution

High Crystal Efficiency

Crystal

01.06.2015 76






PET Block Detector

01.06.2015 77






PET Block Detector

X

y

A

C D

B X =

y =

(B+D) - (A+C)

(A+B+C+D)

(A+B) - (C+D)

(A+B+C+D)

Crystal Identification

01.06.2015 78






PET Block Detector BGO Crystals, 20 or 30 mm long

01.06.2015 79






80

crystals

(4 mm x 6 mm x 20 mm)

continuous

light guide

PMTs

Karp et al. 2000

GSO Pixel-Detector

• Anger principle

• Light spread defined by light guide

• Coincidence window: 8 ns

• Energy resolution (511 keV): 15%

01.06.2015






0.0 5 10 15

1.0

0.5

0.0

Resolution

10 mm

4 mm

Object Size (mm)

Re

co

ve

ry C

oe

ffic

ien

t

~0.8

~0.4

Effect of Spatial Resolution

01.06.2015 81






Characteristics PET – Determining Factors

• Detector material

decay time time resolution coincidence window

light yield energy resolution scattering fraction

atomic number attenuation length sensitivity

• Tomograph

detector concept spatial resolution

diameter sensitivity

scattering fraction

shielding randoms

01.06.2015 82






Scintillation Crystals

Property NaI BGO LSO GSO

NaI:Tl Bi4Ge3O12 Lu2SiO5:Ce Gd2SiO5:Ce

Density (g/cm3) 3,67 7,1 7,4 6,7

Effective Z 51 73 65 59

Attenuation length at

511keV (mm)

29,1 10,4 11,4 14,1

Light yield (photons/MeV) 41 000 9 000 26 000 8 000

Decay time (ns) 230 300 40 60

Emission (nm) 410 480 420 440

01.06.2015 83

Lu-176 (2,6%): + >350 keV: ~100/sec per cm3






PET Systems: Characteristics, Limitations

• Spatial resolution

• Sensitivity

• Scattering

• Random coincidences

• Dead time of system

Measurement in realistic situation

Values can differ depending on the object

01.06.2015 84






Clinical PET

Crystals BGO, LSO,LYSO, GSO

Spatial resolution (mm) 4.5 - 5.0

Energy resolution (%) 12 - 23

Scatter fraction 2D (%) 10 - 15

Scatter fraction 3D (%) 35 - 42

Sensitivity 2D (cps/Bq/ml) 6 - 9

Sensitivity 3D (cps/Bq/ml) 35 - 55

max. NEC 2D 50 - 100

max. NEC 3D 70 - 180

01.06.2015 85






New Cer-doped Scintillators

Property RbGd2

Br7 LaCl3 LaBr3

Light yield

(photons/MeV)

56 000 50 000

56 000

Energy resolution

(662 keV)

4.5% 3.2% 2.9%

Decay time (ns) 45 20 25

Density (g/cm3) 4.7 3.9 5.3

01.06.2015 86

*Image courtesy of M. Balcerzyk, Soltan Institute

1˝ LaCl3:Ce






500 ps timing resolution 7.5 cm localization

D

Mid 1980s: BaF2

Now: LaBr3, LSO

Time-of-Flight PET

TOF

01.06.2015 87






System time resolution: 460 ps System energy resolution: 7.5%

LaBr3 (5% Ce) 4 x 4 x 30 mm3

LaBr TOF PET Scanner

Joel Karp et al. MIC 2005

01.06.2015 88






PET - Quantification

Goal: Physiologic parameter

Standardized uptake values (SUV)

Requirement: Absolute activity concentration

Necessary: Corrections for

• detector differences (sensitivity)

randoms

scatter

attenuation

dead time

01.06.2015 89






Attenuation Losses due to Compton and photo effect

01.06.2015 90






Coincidence method

Ge-68 rod source

Single photon method

Cs-137 point source shielded

(662 keV) high rate

PET – Transmission Measurement

01.06.2015 91






Standardized Uptake Value (SUV)

at a specific time point

SUV = Activity concentration in image (kBq/ml)

Injected activity (kBq) / body weight (kg)






~90% of all laboratory animals are mice

worldwide > 25 Mio. (Science 04/2000)

Animal Models

• Brain sciences: rat

• Oncology: rat, mouse

• Genetic research: mouse (“knock-out”)

01.06.2015 93






• C-11, F-18 tracers

• Measurement of time course

in one animal

• Repeat measurements

in the same animal

Size spatial resolution: 1-2 mm

Specific activity sensitivity: high (>2%)

Small Animal PET

in vivo autoradiography

01.06.2015 94






8 x 8 array of

LSO crystals (2 x 2 x 10 mm)

Optical fibers Position sensitive PMT

Densely packed crystals

Cherry, 1997

UCLA microPET

01.06.2015 95






18F-FDG Rat Heart

01.06.2015 96

microPET

Crump Institute for Molecular Imaging

74 MBq, 45 min acquisition time






Crump Institute for Molecular Imaging

MicroPET P4

• 26 cm ring diameter

• 20 cm transverse FOV

• 7.8 cm axial FOV

• 168 detector modules (8x8)

• 4 rings of 42 detectors

• 10,752 individual detectors

• Transmission source

• Resolution 2.2 mm (10 ml)

• Sensitivity ~ 2%

01.06.2015 97






18F- FDG

Whole-Body

Biodistribution

in the Mouse

0

5

10

15

20

25

30

0 10 20 30 40 50 60

liverkidney

bladdertumor

Time (min.)

Crump Institute for

Molecular Imaging

01.06.2015






microPET II 17,640 LSO elements (0.95x0.95x12.5 mm)

8 cm transaxial field of view

4.8 cm axial field of view

Reconstructed resolution ~ 1.2 mm

(filtered backprojection)

Sensitivity: ~2.3% at center of FOV

(250-750 keV)

01.06.2015 99

DEPARTMENT OF BIOMEDICAL ENGINEERING






Avalanche Photodiodes versus PMTs

• PRO:

– very compact (one-to-one coupling)

– high quantum efficiency

– low bias voltage

– work in magnetic fields

• CON:

– noise

– lower gain

– costs (is changing)

01.06.2015 100






Resolution 1.75 mm (intrinsic) 2.1 2.1 3.1 mm3 or 14 µl

Efficiency 200 cps/µCi ( 0.51% )

Sensitivity 2 kcps/µCi/ml/cm

Peak NEC 61 kcps (11 cm)

Lecomte et al, IEEE TNS 43 (1996) 1952-7

APD Detector Module

BGO

Scintillator

Avalanche

Photodiode

Sherbrooke Animal PET Scanner

01.06.2015 101






0

20

40

60

80

100

120

140

160

180

0 4 8 12 16 20 24 28 32

LV V

olu

me

(µl)

Gate Number

Normal Rat, 250 g

ECG-Gating

1 cm

FDG-PET Study of Cardiac Function in Rat

01.06.2015 102






Hamamatsu

Photonics 1 cm

Photomultiplier

Avalanche photodiodes

APD Matrices

01.06.2015 103






APD matrix

LSO crystals (3.7 x 3.7 x 12 mm3)

- Energy resolution: 15%

- Spatial resolution: 2.3 mm

- Sensitivity: 0.04 %

4 mm

Munich Avalanche Diode PET Prototype

01.06.2015 104

MPI






0 100%

MADPET – In Vivo Study

FDG in the myocardium of a rat

1 mCi, 45 min p.i.,

18 min acquisition time

Realigned images

MPI

01.06.2015 105






Depth-of-Interaction

(DOI)

Coincidence Response Function Depends on ring diameter, crystal length

01.06.2015 106






crystal

light sensor

light sensor

ratio of signals

DOI

LSO

GSO crystal

light sensor

light sensor

crystal

signal shape

DOI

individual layers

DOI

Depth Of Interaction (DOI) Measurement

01.06.2015 107






• Custom 64 element PD array identifies hit crystal

• PD/(PD+PMT) determines depth of interaction

• Photomultiplier tube provides timing pulse

LSO Array

64

Element

PD Array

1” Square PMT 1" Square Photomultiplier Tube

20mm

Array of 64 Photodiodes

64 LSO Crystals 3 mm square

1"

1"

B. Moses, Lawrence Berkeley Laboratory

LBL PET Detector Concept

01.06.2015 108






LGSO/LYSO

GSO

Phoswich Detector – DOI

01.06.2015 109

Block detector

with pulse shape

discriminator

PMT PMT

HRRT: MPI Köln, CTI 1998

ATLAS: NIH, 2001

Light guide






Individual read-out of

2 radial crystal layers

1.6 mm x 1.6 mm

70 mm diameter

monolithic APD Matrix

MADPET II Dual Layer Tomograph

MPI

01.06.2015 110






• Energy resolution:

~ 15% @ 511 keV

• Time resolution: 2,5 ns

APD-Matrix

LSO Crystals (2x2x8 mm3)

APD-Matrix LSO Crystals (2x2x6 mm3)

LSO-APD-Detector Module for 2 Radial Layers

01.06.2015 111






Small Animal PET – Systems System Res.(mm) Sens. D(mm) LZ(mm) Detector Type

RAT –PET 2.4 4.3% 115 50 BGO PMT

Sherbrooke 2.1 0.51% 310 10.5 BGO APD

TierPET 2.1 0.32% 160 – 500 40 YAP PSPMT

MicroPET P4# 2.0 1.35% 260 80 LSO PSPMT

Brussels 3.0 3.5% 200 52 BaF2 Drift Ch.

YAP-PET 2.0 1.7% 100 – 250 40 YAP PSPMT

HIDAC# 1 0.9% 100 – 200 210 MWPC

ATLAS 1.9 1.8% 118 20 phoswich§ PSPMT

Massachusetts 1.3 0.08% 120 4.5 LSO PMT

MADPET 2.30 0.035% 86 3.6 LSO APD

MADPET II 1.0 2% 71 18.1 LSO APD m.

01.06.2015 112

Sensitivity at different energy thresholds #commercial; §GSO + LGSO






• Anesthesia

• Preparation of animals

• Fixation of animal

• Triggering (respiration, ECG)

• Morphologic Imaging

Animal PET – Other Issues

01.06.2015 113






Combination PET–CT

• Functional (PET) and anatomic

(CT) information

• High accuracy of coregistration

• CT- based attenuation correction

– scale HU to (511keV)

• Quantitative data

114






PET CT


115






PET CT


116






PET CT


117






X-ray tube

detectores

absorber

Measured attenuation coefficients are converted to

Hounsfield-units

X-Ray CT: What is measured?

118






water

air

pancreas

fat

lung

liver blood

heart

bones

mamma

kidney spleen

glands

3000

60

40

0

-100

-200 -900

-1000

HU

spatial resolution

clinical: < 1mm

preclinical: ~50m

What is represented in a CT-Image

01.06.2015 119






0

0.1

0.2

0.3

0 100 200 300 400 500

Energie (keV)

/ (cm/g)

PET 511 keV CT ~70 keV

bones

tissue

tissue bones

511 keV

PET Attenuation Correction with CT-Data Kinahan 1998

01.06.2015 120






Scale CT Image Smooth to

match PET Res. Forward project

for ACFs

CT–based attenuation coefficients

0.20

0.15

0.10

0.05

0.00

-1000 -500 1000 1500 500 0

scale factor = 0.495

scale factor = 0.406

non-bone tissue bone-like tissue H.U.

5

11 (

cm

-1)

300 H.U. air water cortical bone

01.06.2015 121






PET/CT

• Measurement duration CT << Measurement duration PET

• Movement?

• Respiration?

respiration protocol

triggering, gating

01.06.2015 122






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

01.06.2015 123






3D reconstruction

FORE + OSEM

CT-based

attenuation and

scattering corrections

CT

acquisition

Fused image

Upper limit

Lower limit

Topogram

PET image

PET CT

PET/CT Standard Protocol

01.06.2015 124






CT

PET

Combination PET – CT

01.06.2015 125






PET/CT – Melanoma Patient

01.06.2015 126






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






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

Vor- und Nachteile :






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






Y. Shao, S.R. Cherry et al. IEEE TNS 1997

P.K. Marsden et al. Brit. J Radiology 2002

Long light guides and PMTs






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 Technology

University of Tübingen, Germany

Pichler et al.






Insert Design • Siemens BrainPET Prototyp innerhalb MAGNETOM TIM installiert

- 23040 LSO Szintillatoren

- 1440 APDs

- axial FOV = 19 cm

- PET Auflösung = 2.5 mm

Catana et al., MGH Boston






System Design – Integrierte Ansätze Siemens:

PET Detektorring zwischen HF- und Gradienten-Spulen

Philips:

„Gesplitteter“ Gradient , dazwischen PET Ring

HYPERImage

MR/PET Designs: Integrated

137


Siemens Biograph mMR

Munich MR-PET Consortium

Departments of Nuclear Medicine and

Departments of Radiology of

Funded by

• 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

138


B = 0 B ≠ 0

B. Pichler et al.

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

139


B = 0 B ≠ 0

B. Pichler et al.

Biograph mMR

• First fully integrated whole-body MR/PET system

• Based on a clinical 3 T MR scanner

140


PET Detector Blocks

141


• 8 rings with 56 detector blocks each (ø 65.6 cm,

transaxial FOV: 59.4 cm, axial FOV: 25.8 cm)

• Each detector block contains:

• 8 x 8 LSO crystals (4 x 4 x 20 mm3)

• Crystal read-out by 3 x 3 APDs

• Cooling channels

• Pre-amplifiers, etc.

• Total number of

• detector blocks: 448

• crystals: 28,672

• APDs: 4,032

Courtesy of Siemens






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






• Nuclide: -emitter

• Scintillation detector: -energy pulse height

• Gamma camera: 2D distribution, projection

• Tomography: slices without overlap

• PET: coincidence electronic collimation

Nuclear Medical Imaging

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sibylle i. ziegler nuclear medical instrumentation

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