O. Mawlawi MDACC

PET/CT Technology Updates,Quality Assurance and Applications

OsamaMawlawi, Ph.D.

Department of ImagingPhysicsMD AndersonCancerCenter

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Outline

• Evolution of PET instrumentation• 2D �3D• Dedicated � PET/CT

• Advantages and short comes of PET/CT• Possible solutions to the short comes

• QA for quantitative PET imaging• New features in PET/CT scanners• Future developments in PET/CT imaging

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• Functional imaging modality ascomparedto structural

• Functional imagesshow:• Blood flow• Glucosemetabolism• Receptordensity

WHAT IS PET?

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Pr inciples of PET Imaging• Inj ection of a radioactive tracer to imagechemical/biological

processes.

• Radioactive tracer decaysby Positron Emission.

• When the tracer is intr oduced into the body, its site-specif icuptake can be traced by meansof the labeledatom.

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Positron Decay

p = n + β+ + υ

• A nucleus with too low a neutron-to-protonratio converts a protonto a neutron,emitting a positron(β+) and a neutrino (υ)to carry off theexcessenergy.

β+

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Nucleuspositron

electron

511keVPhoton

Detectorring

511keVPhoton

LOR

Annihilati on

E=mC2

Electron restmass= 9.11x10-31 kgC=3.0x108 m/s

1 joule =1 kg m2/s2

1 e = 1.602x10-19 coulomb1 eV = 1.602x10-19 JThus:E =1.02 MeV

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Axi

al

Modifiedfromhttp://www.crump.ucla.edu/software/lpp/lpphome.html

LOR DataStorage

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Axi

al

Modified from http://www.crump.ucla.edu/software/lpp/lpphome.html

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Sample Sinograms

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Quantification: Power of PET

Ideal measured data

Measured Data

Random subtract

Normalize

Correct Geometry

Calculate/subtract scatter

Correct Attenuation

Dead time

FBP or IR reconstruction

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after theapplicationof severalcorrections

Imagereconstruction

From physicsin NuclearmedicineSorenson andphelps

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LocationEnergyTime

LocationEnergyTime

Location

Timing12 nsec

Energy

x

y

x

y

Overall LOR Determination process

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8*8 Scintillationblock Block / PMT setup

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Physical Properties of PET Scintillators

1.82

No

10

420

40

30000

32

11.4

0.88

66

7.4

LSO

1.85

No

9

440

60

8000

25

14.1

0.70

59

6.7

GSO

1.85

Yes

8

410

230

41000

17

29.1

0.34

51

3.7

NaI(Tl)

-2.15Index of Ref.

NoNoHygroscopic

1512Energy resolution,

%FWHM

-480λ, nm

40300Decay time, ns

315009000Light Output,photons/MeV

3540Photofraction, %

12.510.5Mean free path, mm

0.800.95µ, cm-1 @ 511 keV

-75Atomic number, Z

-7.1Density

LYSO*BGOMaterial

*Properties supplied by GE Healthcare.

Adaptedfrom: Zanzonicoet al. Sem.Nuc. Med.vol 34 No 2 2004

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Total events= Trues + Randoms+ Scatter

Type of recorded events

Scatter Random True

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2D vs 3D PETimaging

From physicsin NuclearmedicineCherry Sorenson andphelps

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In ter-plane Septa

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Line source2D in air Line source2D in water

Line source3D in waterThetheory andpracticeof 3D PET byBendriemandTownsend

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Increasein sensitivity in 3D over 2D* lessinjectedactivity � lesscost* lesspatientexposure* shorterscanningtime

From: Physics in Nuclear Medicine Cherry S et al.From: Physics in Nuclear Medicine Cherry S et al.

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Quantification: Power of PET

Ideal measured data

Measured Data

Random subtract

Normalize

Correct Geometry

Calculate/subtract scatter

Correct Attenuation

Dead time

FBP or IR reconstruction

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Attenuationis dependanton thepathlength and notthedepth of thesourceof activity

Fourways to get anattenuationmap1) Measured(MAC)2) Calculated (CAC)3) Segmented(SAC)4) CT based(CTAC)

11

LP e−= µ 22LP e−= µ

1 2*LP P e−= µ

Nuclear Medicine:Diagnosisand therapy. Harbert J, EckelmanW.,NeumannR.

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Transmissionrod source(68Ge)

Attenuation cor rect ion usingtransmis sion scan

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15.5cm

Tx rod sources

DedicatedPET Imaging

• Emission(2D mode)• Transmission (scansare interleaved)• 5 to 6 bedpositions• 8 min perposition• 5 EM, 3 Tx• Total scan duration 50-60min

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Emission

Transmission

Final

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SUV = (Measuredactivity * Patient weight)/InjecteddoseO. Mawlawi MDACC

• Transmission– Noise due to low gamma ray flux from rod source

– Transmission is contaminated by emission data

• Scan duration– Time consuming (emission & transmission )

– Increased patient movement (image blurring)

• Efficiency– Decreased patient throughput

– Difficulty in correlating images to other diagnosticmodalities accurately

Disadvantages of dedicated PETimaging techniques

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GE Discovery ST

Hybrid Imaging

Siemens/CTI Biograph

Phillips Gemini

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PET/CT: rational e

• Short duration, low noise CT-based attenuation correction

• Improved patient throughput (< 30 min total scan duration)

• Combines functional (PET) and anatomical (CT) imaging

• PET and CT components can be operated independently

• Fully quantitative, whole-body images for SUV calculation

• Improved patient comfort and convenience (single scan)

• Improved imaging accuracy for therapy planning & monitoring

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Short duration, low noise CT-based attenuation correction

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Improved patient throughput

• ReplaceTx scanby CT scan

• 3-5 min Tx scanduration

• 5-7 FOVs� 15-35 min of Tx scanning

• CT scanfor whole bodyis about1min

• About 30 min of timesavingperpatient

• Dedicated PETscan duration of 50 min

• PET/CT scanduration of 20 min

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Combines functionaland

Anatomical data

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CT based attenuation correction

AttenuationCorrection

Inherent Image

Registration

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At tenuation Scal ingwith Energy

• Attenuation Values are

Energy Dependent

• Water (Soft Tissue) and

Bone are Different

• Solution is to Segment

Image into Tissue and

Bone and Scale

Separately

0

0.1

0.2

0.3

0 100 200 300 400 500

Energy (keV)

µ/ρµ/ρµ/ρµ/ρ(cm/g)

Air Muscle Bone

CT PET

Error

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• For CT values< 0 ,materialsareassumedtohaveanenergydependencesimilar to water

• For CT values> 0, materialis assumedto haveanenergydependence similarto a mixtureof bone andwater

• Thegreen line showstheeffect of usingwaterscalingfor all materials

0.000

0.050

0.100

0.150

0.200

-1000 -500 0 500 1000

CT number measur ed at 140kVp

Att

enu

atio

nat

511k

eV

Water/air

Bone/WaterBone/Water

Convertin g CT Numbers toAttenuati on Values

error

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Types of Artifacts

PET/CT imaging artifacts are due to :

• Contrast media• Truncation• Respiratory motion• Metal implants

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Converting CT Numbers toAttenuation Values

• For CT values < 0 ,materials are assumed tohave an energydependence similar towater

• For CT values > 0,material is assumed tohave an energydependence similar to amixture of bone andwater

• The green line shows theeffect of using waterscaling for all materials

0.000

0.050

0.100

0.150

0.200

-1000 -500 0 500 1000

CT number measur ed at 140kVp

Att

enu

atio

nat

511k

eV

Water /air

Bone/WaterBone/Water

error

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Normal CT Contrast enhanced CT

Coronal

Transaxial

contrastbias

Contrast:Optiray320, 100cc,3cc/sec

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CT attenuation map scali ng

0.000

0.020

0.040

0.060

0.080

0.100

0.120

0.140

0.160

0.180

0.200

-1000 -500 0 500 1000 1500

CT Houns field va lu es

Lin

ear

atte

nu

atio

nat

511k

eV1/

cm

140kVp noncontrast120kVp noncontrast100kVp noncontrast140kVp BaSO4

120kVp BaSO4

100kVp BaSO4

140kVp I

120kVp I

100kVp I

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Contrast Ar tifact - IntravenousContrastinjec ted

CT PET CTAC FUSED IMAGE

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With contrast Withoutcontrast

61 yearmalewith historyof esophagealcancer

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SUV change1.23 to 1.9054%inc

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Truncation

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PET Detector

PET 70cmimageFOV

X-ray focalspot

CT Detector

CT 50cmFully sampledFOV

CT and PET Fields of View

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Truncation artifact appears as:

1. Rim of high activity concentration (AC) at the truncationedge in the PET image

2. Area of low activity concentration in the region extendingbeyond the CT FOV on the PET image due to the absenceof attenuation coefficients.

High AC in Rim

Low AC outsi de CTFOV

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Activity concentrationrecoveredto within 5% of original value

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54 yrs. male wi th history of metastati c melanoma ofthe skin. SUV chang ed from 3.25 to 6.05

CT PET FUSED Attenua tio n map

Truncated

Truncate dcorrecte d

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Wide View

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Metal Artifacts

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Metal Ar tifacts

Artifact Artifact

CT PET CTAC FUSEDIMAGE

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Breathing Artifacts

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Breathi ng Art ifact -Curvili near Cold Areas

• CT scans acqui red at fu ll ins piration result in a downward disp lacem entof the diaphragm due to the expansion of the lungs .

•Att enuati on coeffici ents in thi s region will be underestimated since theyrepresent air rather than soft tis sue.

• The attenuation corre cted PET image s will result in a curvili near cold areacor responding to this region .

CT PET FUSEDIMAGE NON AC

Photop enicArtifact

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Breathi ng ArtifactMismatchof lesionlocation betweenhelical CT andPET

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Breathing Ar tifactMismatchof lesionlocation betweenhelicalCT andPET

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Courtesy of J. Brunetti, Holly name

Mismatch between PET and CT – Cardiac Application

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Underestimation of Activity concentration

Blurring due to object motion during data acquisition

Stationary Moving

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Possible solutions

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X-ray onoff

1st table position(0 - 2cm)

2nd table position(2 - 4 cm)

3rd table position(4 - 6 cm)

EE 50% EE 50%

EI 0% EI 0%

0 10 20 30 40 50 60 70 80 90%0 10 20 30 40 50 60 70 80 90%

Image averaging

4DCT averagingHelical CT

Helical CTwithout thorax

Combined helical andrespiration-averaged CT

Respiratory singal

CT images

4D-CT images

Respiration-averaged CT 2

1

Average CT – 4D CT

Courtesy of Tinsu Pan, MDACC

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Clinical Studies

Mismatch 1:

CT diaphragmposition lower

than PET

Mismatch 1:

CT diaphragmposition lower

than PET

Mismatch 2:

CT diaphragmposition higher

than PET

Mismatch 2:

CT diaphragmposition higher

than PET

+57%

Courtesy of Tinsu Pan, MDACC O. Mawlawi MDACC

CT PET Fused RACT PET Fused No AC(A) (B)

(C) (D)

Courtesy of Tinsu Pan, MDACC

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Misregistrationlead to a falsepositiveresponse to chemo.

A truenegative responsewhen misregistration is removedwith ACT

Improve the restaging after chemo

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Impact on treatment planning

PreviousGTV wasoutlined based on CT andclinical PETwithoutmotion correction.New GTV wasredefined based on the correctinformation from PETwith ACT.

Old GTV

New GTV

Courtesy of Tinsu Pan, MDACC

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Gated PET (Used to image repetitively moving objects: cardiac, respiratory)

time

7

3

4 5

6

8

3

45

6

7

Bin 8

82

Trigger1

Bin 1

21

Trigger

• Prospective fixed forward time binning

• Ability to reject cycles (cardiac) that don’t match

• Single 15 cm FOV Gated PET

• User defined number of bins and bin duration

• As number of bins increase, the duration and motion per bin decreases.However images will be noisy unless acquired for longer durations.

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4D-Gated PET

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PhantomStudy

AxialCoronal Sagital Mip

Sphere (volume) Gated Static Error (%)

1 (16.5cc) 31624 33546 -6.1

2 (8.4 cc) 31316 21872 30.2

3 (4 cc) 29919 20607 31.14 (2 cc) 22857 13643 40.35 (1 cc) 19087 8264 56.7

6 (0.5 cc) 11897 5143 56.8

Impact of Whole-body Respiratory Gated PET/CT

• The max SUV of the lesion goes from 2 in the static image to 6 in therespiratory-gated image sequence

Static wholebody Single respiratory phase(1 of 7, so noisier)

1 cc lesion on CT

Courtesy of P Kinahan, UW

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New CT Application… Advantage 4D CT

Respiratory motion def ined retro spective gat ing

X-ray on

First couch position Second couch position Third couch position

“Image acquired”signal to RPMsystem

Respiratory tracking with Varian RPM optical monitor

CT images acquired over complete respiratory cycle

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4D-PET/CT

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4D PET/CT

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Phantom Study

Sphere-to-Background Ratio: 5.18Total Activity: 2.49mCiScan Duration: 3 minNumber of Time Bins: 10

2 cm

18FDG

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0

200

400

600

800

1000

1200

5 10 15 20 25 30 35 40 450

200

400

600

800

1000

1200

5 10 15 20 25 30 35 40 450

200

400

600

800

1000

1200

5 10 15 20 25 30 35 40 450

200

400

600

800

1000

1200

5 10 15 20 25 30 35 40 450

200

400

600

800

1000

1200

5 10 15 20 25 30 35 40 45

Phantom Study Results

Reference gated static MIR(real

motion)

MIR(estimated

motion)

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Quality Assurance in QuantitativePET/CT

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Definitions

• Quality Assurance– “….. systematic monitoring and evaluation of the various

aspects of a project, service, or facility to ensure that standards of quality are being met”

http://www.webster.com/dictionary/quality%20assurance

• Quality Control– “an aggregate of activities (as design analysis and inspection for defects)

designed to ensure adequate quality especially in manufacturedproducts”

http://www.webster.com/dictionary/quality%20control

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Quantitative PET Performance Quantitative PET Performance

3 Factors that may affect SUV measurements• Patient Compliance

– Fasting– Blood Glucose levels

• Scan Conditions– Scan time post injection– Patient anxiety/comfort during uptake (room temperature, etc.)– Patient motion during acquisition– PET/CT artifacts

• Intrinsic System Operating Parameters– Calibration– QA – Maintenance of operating parameters– System performance characterization– Image processing algorithms

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PET Detector Array Format and PET Detector Array Format and DesignDesign

Discovery STe example…• Detector Array consists of 35 modules (0-34)• Each module consists of 8 blocks (0-7)• Each block consists of 8 x 6 BGO crystal array• 1 Timing circuit per crystal pair• 35*8*(8x6)= 13440 total detectors

0 1 2 3 4 ………………………………………………………………………………………………………….

0,1

2,3

4,5

6,7

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PET Detector Calibration OverviewPET Detector Calibration Overview

Set the Baseline

Well Coun terCorrection

(Q)

Update Gains

Update Posi tio nMap

Energy Updat e

CTC

DQA Check

RMS < x

RMS > x

Insta llation/Replacement of

Detecto r block, ci rcuitBoard, etc.

GeometricCalibration

(Q)

12 hour Norm(Q)

CoincidentCalibrations

SinglesCalibrations

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Daily Quality Assurance BaselineDaily Quality Assurance Baseline

• A baseline QA acquisition is taken after Singles and Coincidence calibration are performed following installation of the system

• A baseline QA acquisition is also performed whenever a detector block or circuit board has been replaced

• Used to construct ratio image comparing current DQA results with this baseline acquisition

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PET Daily QA ScanPET Daily QA Scan

– Uses Ge-68 source pin that rotates across face of detector array

– Includes a ~2 min normalization component in which counts from the source flood are acquired

– Also includes a daily CTC after flood acquisition is complete

– Generates a visual map of detector array used to validate detector functionality

– Generates statistics used to indicate scanner performance

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Daily Quality Assurance ScansDaily Quality Assurance Scans

• Purpose– To ensure that optimal clinical images will be obtained

from the scanner on a daily basis

– To quantitatively compare scan results with manufacturer and institutional specifications and standards

– To enforce appropriate device usage by the technologist

– To allow baseline data to be available in order to derive functional trends in image quality

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PET Daily QA ScanPET Daily QA Scan

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PET Daily QA ScanPET Daily QA Scan

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Pre-Normalization Post-Normalization

Normalizationsinogram

Courtesy of magnus Dahlbom

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Coincidence CalibrationsCoincidence Calibrations• Well Counter Correction (WCC)

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Coincidence Calibrations

• Pre-calibrated Phantom

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Coincidence Calibrations

• Pre-calibrated Phantom

– Pros• Eliminates need to prepare a source, fill and calibrate a phantom

– Cons• Based on phantom manufacturer’s dose calibrator readings• Patient studies based on site dose calibrator readings• Therefore, there exists a potential discrepancy between the dose

calibrators used to calibrate the scanner, and the dose calibrators used to assay the doses of patient studies performed on the scanner (un-correlated)

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Normalization effects

Good Norm Bad Norm

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Effect of bad Normalization

Increasedactivity due toerror innormalization

SUVmax=4.5

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Effect of wrong WCC

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Effects of Bad Blocks

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Effects of Bad Blocks

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Effects of Bad Blocks

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Norm alized to Bas elin e for each Sphere

65

70

75

80

85

90

95

100

105

base

line

final

base

line

M5b

lk4

M5b

lk5M

22blk

5

M5b

lk4,5

M5blk

2,3

M5b

lk4,5

M5b

lk4,5

M9blk

4

M5b

lk4,5

M6blk

4

M5b

lk4,5

M22b

lk2,3

M5b

lk4,5

M9blk

4,5

M5b

lk4,5

M22b

lk4,5

M5b

lk4,5

M22b

lk4

M5b

lk4,5

M6blk

4,5

perc

ent

sphere37 mm

sphere28 mm

sphere22 mm

sphere17 mm

sphere13 mm

sphere10 mm

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Quantitative PET Performance Quantitative PET Performance

3 Factors that may affect SUV measurements• Patient Compliance

– Fasting– Blood Glucose levels

• Scan Conditions– Scan time post injection– Patient anxiety/comfort during uptake (room temperature, etc.)– Patient motion during acquisition– PET/CT artifacts

• Intrinsic System Operating Parameters– Calibration– QA – Maintenance of operating parameters– System performance characterization– Image processing algorithms

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a

b d f

c e

(a) 2D-FBP; (b) 2D-OSEM; (c) 3D-RP; (d) 3D-IR; (e) 3D-FORE+FBP; (f) 3D-FORE+OSEM.

Effect of Reconstruction Algorithm

1.091.652.522.712.742.85Al gorithmf

1.101.592.402.642.752.78Al gorithm e

1.332.193.212.982.922.93Al gorithm d

1.071.602.412.622.762.83Al gorithm c

1.742.142.902.823.143.14Al gorithm b

1.121.752.302.522.743.03Al gorithm a

Sphere6Sphere5Sphere 4Sphere3Sphere2Sphere1(x104)

AC max under different reconstruction algorithms (Bq/cc)

O. Mawlawi MDACC4.85.97.79.39.310.4D

4.76.38.39.19.710.3C

2.83.95.56.67.68.6B

3.86.58.99.910.310.8A

654321

A

3D IR2it 20sub

B

3D FORE2it 5sub

C

3D FORE5it 28sub

D

3D FOREFBP

Max SUVbwin differentspheres

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0 20 40 60 80 100 120 140 160 1801

2

3

4

5

6

7

8

9x 10

4

Duration(sec)

Max

d37

scan1scan2scan3scan4

2D 3D

0 20 40 60 80 100 120 140 160 1800

2

4

6

8

10

12

14

16x 10

4

Duration(sec)

Max

d37

scan1scan2scan3scan4

Effect of scan duration and count densityon maximum AC

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Effect of smoothing on measured AC

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Effect of ROI type

Courtesy of Kinahan UW O. Mawlawi MDACC

New PET Scanner Features

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Static3 min

PET data acquisition of different duration per FOV

Static3 min

Static5 min

Static6 min

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LIST Mode

•• Time ticks are fixed at 1msec intervalsTime ticks are fixed at 1msec intervals

•• The number of events between time ticks dependsThe number of events between time ticks depends

on the amount of activity in the field of viewon the amount of activity in the field of view

•• The more activity, the more the events betweenThe more activity, the more the events between

time ticks.time ticks.

•• Very flexible, data can beVery flexible, data can be rebinnedrebinned as static,as static,

dynamic, or gated.dynamic, or gated.

•• Requires large amount of memoryRequires large amount of memory

X1X1 Y1Y1 X2X2 Y2Y2 X3X3 Y3Y3TIMETIME X4X4 Y4Y4 TIMETIME

1msec1msec 1msec1msec

X5X5 Y5Y5 X6X6 Y6Y6

Y8Y8 X9X9 Y9Y9 X10X10 Y10Y10 X11X11 Y11Y11X8X8

X7X7 Y7Y7

X1

Y1X2

Y2X3

Y3

X4

Y4

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Section of a list file (141MB) using a 25MBq (0.7mCi) GeSection of a list file (141MB) using a 25MBq (0.7mCi) Ge--68 rod source acquired for68 rod source acquired fora duration of 15 seconds.a duration of 15 seconds.

LIST data formatLIST data format Tick marksTick marks

1 msec

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Advantagesof List modeacquisition:

• Ability to postprocessthe datausing different prescriptions.

• Modeof acquisitioncanbevaried(static,dynamic,gated….)

• Durationof thescancanbechanged(comparedifferentscandurations)

• Chopoff data segments basedonuserdefinition.

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List mode allows rebinning of acquired data into different durationsO. Mawlawi MDACC

LIST Mode

X1X1 Y1Y1 X2X2 Y2Y2 X3X3 Y3Y3TIMETIME X4X4 Y4Y4 TIMETIME

1msec1msec 1msec1msec

X5X5 Y5Y5 X6X6 Y6Y6

Y8Y8 X9X9 Y9Y9 X10X10 Y10Y10 X11X11 Y11Y11X8X8

X7X7 Y7Y7

TRIGTRIG X12X12 Y12Y12 TIMETIME

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Section of a list file (141MB) using a 25MBq (0.7mCi) GeSection of a list file (141MB) using a 25MBq (0.7mCi) Ge--68 rod source acquired for68 rod source acquired fora duration of 15 seconds.a duration of 15 seconds.

LIST data formatLIST data formatTick markTick mark

Trigger inputTrigger input

Trig gers allows for double gatin gTriggers allows for double gatin g –– respresp and cardiacand cardiac

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New PET Scanner Designs

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Improved sensitivity with TrueV SIEMENS

• thicker LSO crystals

• extended axial FOV

AD

B

Cγγγγ (511 keV)

3D (no septa)

20 mm 30 mm

16.2 cm 21.6 cm

• LSO volume increase: 50%

• sensitivity increase: 77%

• sensitivity increase: 40%

• LSO volume increase: 30%

scintillator

phototubes

planar sensitivity

volume sensitivity

+ 192 PMTs

Courtes y of D Townsend O. Mawlawi MDACC

Advantages of the extended Axial Field-of-View

• increased sensitivity = shorter imaging per bed (or more counts)

• larger axial FOV = fewer bed positions for same axial coverage

• reduction in imaging time (or dose) of ~2 for comparable quality

Sensitivity

FOV

Courtes y of D Townsend

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Biograph TruePoint performance

Noise Equivalent Count Rate

96 kcps @ 34 kBq /ml

161 kcps @ 31 kBq /ml

Activity (kBq/ml)

Biograph TruePoin t

TrueV

Biograph TP

TrueV 34 %

34 %

Scatter (%) (425 keV)Sensit ivity (cps/ kBq )

8.10

4.49Biogr aph TP

TrueV

Spat ial resol uti on (mm)

4.2

4.1

transverse axial

4.7

4.5Biog raph TP

True V

NE

CR

(cp

s)

Patien t NECRs

Courtes y of D Townsend

Staging head and neck cancer

Scan dura tion: 10 min

5/0610.4 mCi , 90 min pi

108 lbs; 2 min /bed, 5 beds4i / 8s; 5f

SUV =18.6

Biogra ph 6 TrueVMolecularImagingProgram

Courtes y of D Townsend

Inn ovation is in our genes.115 Siemens Medical Solutions Molecular Imaging

BrainPET* for MAGNETOM Trio, A Tim System

* Works in Progress. The information about this product is preliminary. The product is under development andis not commercially available in the U.S., and its future availability cannot be ensured.

Inno vation is in our genes.116 Siemens Medical Solutions Molecular Imaging

First ever in-vivo images simultaneously acquired by MR and PET (17.11.06)

BrainPET for MAGNETOM Trio,The first results

PETMR MR-PETCourtesy of Townsend and Nahmias University of Tennessee, USA andSchlemmer, Pichler, Claussen University of Tuebingen, Germany

* Works in Progress. The information about this product is preliminary. The product is under development and is not commerciallyavailable in the U.S., and its future availability cannot be ensured.

PROTOTYPE

Inn ovation is in our genes.117 Siemens Medical Solutions Molecular Imaging

BrainPET for MAGNETOM Trio, A Tim SystemThe first resul ts

Courtesy of University of Tennessee, USA and University of Tuebingen, Germany

Diffusion EPI sequence applied during PET acquisition.

Artifact free imaging even with the most demanding applications

T2 TSE PET MR-PET ADC

GE Healthcare, Molecular Imaging

Page 118

VUE Point – Iterative Reconstruction

Deadtime/Normalization

Correction

RandomsCorrection

RadialRepositioning

QuadrantScatter

Correction

AttenuationCorrection

Iterative Reconstruction

Deadtime/Normalization

Correction

RandomsCorrection

RadialRepositioning

QuadrantScatter

Correction

AttenuationCorrection

Iterative Reconstruction w/ Distance Driven Projectors

Deadtime/Normalization

Correction

RandomsCorrection

Volume ScatterCorrection

AttenuationCorrection

Iterative Reconstruction w/ Distance Driven Projectors

Conventional

VUE Point

VUE Point HD (mid-2007 update)

DetectorGeometryModeling

Volume Scatter Corre ctio nCross block scatter LORMulti-quadrant processingReduced artifact potential

VUE Point - Volume Scatter CorrectionD1

S

D2

LOR

D1

S

D2

LOR

D2

D1

S LOR

D2

D1

S LOR

D2

SLOR

D1

D2

SLOR

D1

Quadran t Scatte r Correction• Direct block scatter LOR• Single-quadrant processing• High activity ratio artifactDiscovery ST

Detector Geometr y Modeling• Allows all corrections to be included

in loop (normalization/deadtime)• Improvement in resolution• Eliminates noise correlation

introduced by radial repositioning• Reduction in spoke artifact

Radial Repositionin g (former)• Data into evenly spaced grid for Fourier

filtering• Crystal position model includes effects of

block gaps and “average” penetration• Output data determined by linear

interpolation between data points

-500 -400 -300 -200 -100 0 100 200 300 400 5001

1.5

2

2.5

3

3.5

Radial Position (mm)

Sin

ogra

mB

inW

idth

(mm

)

Native GeometryRadial Repositoned

VUE Point – Detector Geometry Modeling

GE Healthcare, Molecular Imaging

Page 121

• Targeted Iterative Reconstruction may lead to artifacts andquantitative inaccuracy if the data outside the FOV is not considered

• A full FOV (left) and targeted FOV (center) reconstruction of asimulated phantom (blue circle indicates the bounds of the targetedregion)

• Horizontal profiles through the full FOV (blue) and targeted FOV(black) are shown in the graph on the right.

-200 -150 -100 -50 0 50 100 150 2000

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VUE Point – Targeted Iterative Reconstruction

GE Healthcare, Molecular Imaging

Page 122

A more efficient method to accomplish thetargeted reconstruction can be describedin the following steps:

1.) Reconstruct the full SFOV at a pixelpitch greater than the desired final pixelpitch in the DFOV

2.) Zero out the pixels in this imagecorresponding to the DFOV

3.) Forward-project the resulting image tocreate a sinogram representing theactivity outside the DFOV

4.) Subtract sinogram from the originaldata set, to leave a data set representingonly activity from inside the DFOV

5.) Reconstruct this sinogram at thedesired pixel pitch to create the final,targeted image

1

3

2

4

5

An Improved Solut ion : Keyh ole Reconst ructio n

VUE Point – Targeted Iterative Reconstruction

GE Healthcare, Molecular Imaging

Page 123

Targeted IterativeReconstruction

“Conventional Technique”

Targeted IterativeReconstruction

“Keyhole Technique”

Rb82 Cardiac Exam

VUE Point – Targeted Iterative Reconstruction

GE Healthcare, Molecular Imaging

Page 124

• Detector Geometry Reconstruction enables normalization & deadtime to beincluded in the iterative reconstruction loop

• Normalization & deadtime corrections in the loop increase detector variation stability

• Phantom simulation, 300k counts, 2D image

– edge crystals with 100%, 80%, 60%, 40%, 20% efficiency of the center crystals

Pre-correctionNormalization

“In-the-loop”Normalization

0 20 40 60 80

% degradation in efficiency of edge crystals w.r.t central crystals

VUE Point – Detector Normalization

Motion FreezeImpact of Whole-body Respiratory Gated PET/CT

• The max SUV of the lesion goes from 2 in the static image to 6 in therespiratory-gated image sequence

Static wholebody Single respiratory phase(1 of 7, so noisier)

1 cc lesion on CT

Courtesy of P Kinahan, UWO. Mawlawi MDACC

Time-of-Flight Acquisition:Principles

2

tx c

∆∆ =

C = 3*108 m/s

Backprojectionalong theLOR

O. Mawlawi MDACC

Time of Flight and SNR, examples…

convTOF SNRx

DSNR ⋅

∆≅ctx

2

∆=∆

TimeResolution

(ns)

∆x

(cm)

SNRimprovement(20 cmobject)

SNRimprovement(40 cmobject)

0.1 1.5 3.7 5.2

0.3 4.5 2.1 3.0

0.5 7.5 1.6 2.3

1.2 18.0 1.1 1.5

BestmeasurementonLSO small crystalpair [W. Moses]

Overallpresenttimeresolution on HiRezscanner

30 min scan

MIP

Colon cancer 119 kg (BMI = 46.5)

Improvement in lesion detectability with TOF

non-TOF TOFCT

Average-weight patient study

Tongue CA,lung mets

67 kgBMI = 29.0 20 min scan

CTTOFnon-TOF

Improvement in lesion contrast with TOF

non-TOF TOF

Courtesy of J. karp

non-Hodgkin’s lymphoma 136 kg (45 BMI)

TOF tumor contrast (SUV) higher than non-TOF by 1.5

nonTOF 30 min TOF 30 min TOF 10 min

TOF tumor contrast superior to non-TOF for 10 min as well as 30 min scanCourtesy of J. karp

O. Mawlawi MDACC

FUTURE

O. Mawlawi MDACC

Static

Static

Gated

Mixed acquisition protocol

O. Mawlawi MDACC

10

37 28

22

1713

Standard 8 x 8 detector

HI-REZ 13 x 13 detector

All spheres contain the same activity concentration Profile (10 mm)

Sphere diameter

Rec

over

y(%

)

100

50

0 10

37282217

13

Recovery coefficients

Effect on Partialvoluming

Courtesy of Siemens O. Mawlawi MDACC

Depthof interaction

From physicsin NuclearmedicineCherry, Sorenson andphelps

O. Mawlawi MDACC

Quantitative PET PerformanceQuantitative PET Performance

3 Factors that may affect SUV measurements• Patient Compliance

– Fasting– Blood Glucose levels

• Scan Conditions– Scan time post injection– Patient anxiety/comfort during uptake (room temperature, etc.)– Patient motion during acquisition– PET/CT artifacts

• Intrinsic System Operating Parameters– Calibration– QA – Maintenance of operating parameters– System performance characterization– Image processing algorithms

O. Mawlawi MDACC

Thank You

All of the following are types of events that a

PET scanner detects except :

25%

25%

25%

25%

10

1. True Events2. Scatter Events

3. False Events4. Random Events

Total events= Trues + Randoms + Scatter

Type of recorded events

Scatter Random True

Attenuation in PET imaging isdependent on:

25%

25%

25%

25%

10

1. Annihilation photons path length2. Depth of annihilation event in the

radioactive source3. Amount of radioactivity present in the

source

4. Number of detectors in the scanner

O. Mawlawi MDACC

Attenuation is dependanton thepath length andnotthe depthof the sourceof activity

Four ways to getanattenuation map1) Measured (MAC)2) Calculated (CAC)3) Segmented (SAC)4) CT based(CTAC)

11

LP e−= µ 22LP e−= µ

1 2*LP P e−= µ

NuclearMedicine: Diagnosisand therapy. Harbert J, EckelmanW.,NeumannR.

All of the following are advantages of PET/CT

imaging over dedicated PET imaging except:

25%

25%

25%

25%

10

1. Shorter total scan duration2. Better image resolution

3. Low noise attenuation correction4. Automatic fusion of functional and

anatomical images

O. Mawlawi MDACC

• Transmission– Noise due to low gamma ray flux from rod source

– Transmission is contaminated by emission data

• Scan duration– Time consuming (emission & transmission )

– Increased patient movement (image blurring)

• Efficiency– Decreased patient throughput

– Difficulty in correlating images to other diagnosticmodalities accurately

Disadvantages of dedicated PETimaging techniques

Truncation artifact in PET/CTimaging:

25%

25%

25%

25%

10

1. Reduces activity concentration in the affectedarea

2. Increases the activity concentration in theaffected area

3. Has no effect on activity concentration in thearea of interest

4. Affects mainly small size patients

O. Mawlawi MDACC

Truncation artifact appears as:

1. Rim of high activity concentration (AC) at the truncationedge in the PET image

2. Area of low activity concentration in the region extendingbeyond the CT FOV on the PET image due to the absenceof attenuation coefficients.

High AC in Rim

Low AC outside CTFOV

O. Mawlawi MDACC

Activity concentrationrecoveredto within 5% of original value

All of the following are PET/CT artifacts dueto the use of CT for attenuation correction of

PET data excep t:

25%

25%

25%

25%

10

1. Contrast media artifact2. Tube current artifact3. Metallic artifact4. Breathing motion artifact

O. Mawlawi MDACC

Types of Artifacts

PET/CT imaging artifacts are due to :

• Contrast media• Truncation• Respiratory motion• Metal implants

A well counter calibration in PETimaging is used to:

25%

25%

25%

25%

10

1. Correct for variations in image uniformity

2. Correct for variations in detector gains

3. Correct for differences in detector coincidencetiming

4. Transform detected count rate to activityconcentration

O. Mawlawi MDACC

Coincidence CalibrationsCoincidence Calibrations• Well Counter Correction (WCC)