o. mawlawi mdacc · from physics in nuclear medicine cherry sorenson and phelps o. mawlawi mdacc...
TRANSCRIPT
-
O. Mawlawi MDACC
PET/CT Technology Updates,Quality Assurance and Applications
OsamaMawlawi, Ph.D.
Department of ImagingPhysicsMD AndersonCancerCenter
O. Mawlawi MDACC
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
O. Mawlawi MDACC
• Functional imaging modality ascomparedto structural
• Functional imagesshow:• Blood flow• Glucosemetabolism• Receptordensity
WHAT IS PET?
O. Mawlawi MDACC
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.
-
O. Mawlawi MDACC
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+
O. Mawlawi MDACC
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
O. Mawlawi MDACC O. Mawlawi MDACC
Axi
al
Modifiedfromhttp://www.crump.ucla.edu/software/lpp/lpphome.html
LOR DataStorage
-
O. Mawlawi MDACC
Axi
al
Modified from http://www.crump.ucla.edu/software/lpp/lpphome.html
O. Mawlawi MDACC
Sample Sinograms
O. Mawlawi MDACC
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
O. Mawlawi MDACC
after theapplicationof severalcorrections
Imagereconstruction
From physicsin NuclearmedicineSorenson andphelps
-
O. Mawlawi MDACC O. Mawlawi MDACC
LocationEnergyTime
LocationEnergyTime
Location
Timing12 nsec
Energy
x
y
x
y
Overall LOR Determination process
O. Mawlawi MDACC
8*8 Scintillationblock Block / PMT setup
O. Mawlawi MDACC
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
-
O. Mawlawi MDACC
Total events= Trues + Randoms+ Scatter
Type of recorded events
Scatter Random True
O. Mawlawi MDACC
2D vs 3D PETimaging
From physicsin NuclearmedicineCherry Sorenson andphelps
O. Mawlawi MDACC
In ter-plane Septa
O. Mawlawi MDACC
Line source2D in air Line source2D in water
Line source3D in waterThetheory andpracticeof 3D PET byBendriemandTownsend
-
O. Mawlawi MDACC
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.
O. Mawlawi MDACC
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
O. Mawlawi MDACC
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.
O. Mawlawi MDACC
Transmissionrod source(68Ge)
Attenuation cor rect ion usingtransmis sion scan
-
O. Mawlawi MDACC
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
O. Mawlawi MDACC
Emission
Transmission
Final
O. Mawlawi MDACC
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
-
O. Mawlawi MDACC
GE Discovery ST
Hybrid Imaging
Siemens/CTI Biograph
Phillips Gemini
O. Mawlawi MDACC
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
O. Mawlawi MDACC
Short duration, low noise CT-based attenuation correction
O. Mawlawi MDACC
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
-
O. Mawlawi MDACC
Combines functionaland
Anatomical data
O. Mawlawi MDACC
CT based attenuation correction
AttenuationCorrection
Inherent Image
Registration
O. Mawlawi MDACC
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
O. Mawlawi MDACC
• 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
-
O. Mawlawi MDACC
Types of Artifacts
PET/CT imaging artifacts are due to :
• Contrast media• Truncation• Respiratory motion• Metal implants
O. Mawlawi MDACC
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
O. Mawlawi MDACC
Normal CT Contrast enhanced CT
Coronal
Transaxial
contrastbias
Contrast:Optiray320, 100cc,3cc/sec
O. Mawlawi MDACC
-
O. Mawlawi MDACC
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
O. Mawlawi MDACC
Contrast Ar tifact - IntravenousContrastinjec ted
CT PET CTAC FUSED IMAGE
O. Mawlawi MDACC
With contrast Withoutcontrast
61 yearmalewith historyof esophagealcancer
O. Mawlawi MDACC
SUV change1.23 to 1.9054%inc
-
O. Mawlawi MDACC
Truncation
O. Mawlawi MDACC
PET Detector
PET 70cmimageFOV
X-ray focalspot
CT Detector
CT 50cmFully sampledFOV
CT and PET Fields of View
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 outsi de CTFOV
O. Mawlawi MDACC
Activity concentrationrecoveredto within 5% of original value
-
O. Mawlawi MDACC
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
O. Mawlawi MDACC
Wide View
O. Mawlawi MDACC
Metal Artifacts
O. Mawlawi MDACC
Metal Ar tifacts
Artifact Artifact
CT PET CTAC FUSEDIMAGE
-
O. Mawlawi MDACC
Breathing Artifacts
O. Mawlawi MDACC
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
O. Mawlawi MDACC
Breathi ng ArtifactMismatchof lesionlocation betweenhelical CT andPET
O. Mawlawi MDACC
Breathing Ar tifactMismatchof lesionlocation betweenhelicalCT andPET
-
O. Mawlawi MDACC
Courtesy of J. Brunetti, Holly name
Mismatch between PET and CT – Cardiac Application
O. Mawlawi MDACC
Underestimation of Activity concentration
Blurring due to object motion during data acquisition
Stationary Moving
O. Mawlawi MDACC
Possible solutions
O. Mawlawi MDACC
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
-
O. Mawlawi MDACC
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
O. Mawlawi MDACC
Misregistrationlead to a falsepositiveresponse to chemo.
A truenegative responsewhen misregistration is removedwith ACT
Improve the restaging after chemo
Courtesy of Tinsu Pan, MDACC O. Mawlawi MDACC
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
-
O. Mawlawi MDACC
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.
O. Mawlawi MDACC
4D-Gated PET
O. Mawlawi MDACC
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
-
O. Mawlawi MDACC
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
O. Mawlawi MDACC
4D-PET/CT
O. Mawlawi MDACC
4D PET/CT
O. Mawlawi MDACC
Phantom Study
Sphere-to-Background Ratio: 5.18Total Activity: 2.49mCiScan Duration: 3 minNumber of Time Bins: 10
2 cm
18FDG
-
O. Mawlawi MDACC
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)
O. Mawlawi MDACC
Quality Assurance in QuantitativePET/CT
O. Mawlawi MDACC
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
O. Mawlawi MDACC
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
-
O. Mawlawi MDACC
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
O. Mawlawi MDACC
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
O. Mawlawi MDACC
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
O. Mawlawi MDACC
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
-
O. Mawlawi MDACC
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
O. Mawlawi MDACC
PET Daily QA ScanPET Daily QA Scan
O. Mawlawi MDACC
PET Daily QA ScanPET Daily QA Scan
O. Mawlawi MDACC
Pre-Normalization Post-Normalization
Normalizationsinogram
Courtesy of magnus Dahlbom
-
O. Mawlawi MDACC
Coincidence CalibrationsCoincidence Calibrations• Well Counter Correction (WCC)
O. Mawlawi MDACC
Coincidence Calibrations
• Pre-calibrated Phantom
O. Mawlawi MDACC
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)
O. Mawlawi MDACC
Normalization effects
Good Norm Bad Norm
-
O. Mawlawi MDACC
Effect of bad Normalization
Increasedactivity due toerror innormalization
SUVmax=4.5
O. Mawlawi MDACC
Effect of wrong WCC
O. Mawlawi MDACC
Effects of Bad Blocks
O. Mawlawi MDACC
Effects of Bad Blocks
-
O. Mawlawi MDACC
Effects of Bad Blocks
O. Mawlawi MDACC
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
O. Mawlawi MDACC
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
O. Mawlawi MDACC
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
O. Mawlawi MDACC
O. Mawlawi MDACC
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
O. Mawlawi MDACC
Effect of smoothing on measured AC
-
O. Mawlawi MDACC
Effect of ROI type
Courtesy of Kinahan UW O. Mawlawi MDACC
New PET Scanner Features
O. Mawlawi MDACC
Static3 min
PET data acquisition of different duration per FOV
Static3 min
Static5 min
Static6 min
O. Mawlawi MDACC
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
-
O. Mawlawi MDACC
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
O. Mawlawi MDACC
Advantagesof List modeacquisition:
• Ability to postprocessthe datausing different prescriptions.
• Modeof acquisitioncanbevaried(static,dynamic,gated….)
• Durationof thescancanbechanged(comparedifferentscandurations)
• Chopoff data segments basedonuserdefinition.
O. Mawlawi MDACC
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
-
O. Mawlawi MDACC
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
O. Mawlawi MDACC
New PET Scanner Designs
O. Mawlawi MDACC
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
-
O. Mawlawi MDACC
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
20
40
60
80
100
120
140
160
180
200
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)