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6/30/2008
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Factors Affecting Accurate Quantification In PET/CT
Osama Mawlawi, Ph.D.
O. Mawlawi MDACC
Department of Imaging PhysicsMD Anderson Cancer Center
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53 year old man with lymphoma with increased FDG uptake in the spleen and multiple intra and extra-thoracic nodes consistent withMulti-focal malignancy.
Power of PET : Quantification
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Quantification: Power of PET
Measured Data
Random subtract
Normalize
Dead time
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Ideal measured data
Correct Geometry
Calculate/subtract scatter
Correct Attenuation
Dead time
FBP or IR reconstructioncalibration
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decay-corrected dose/ml of tumorSUVinjected dose/patient weight in grams
=
SUV
• The standardized uptake value (SUV) is
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p ( )one means of making PET results more quantitative.
• Tracer kinetic modeling is used extensively in quantitative PET (may include blood samples and dynamic imaging).
SUV Modifiers
• SUVbw (gm/ml)
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• SUVBSA (m2/ml)
• SUVLBM (gm/ml)
SUV Modifiers
• SUVig (gm/ml)
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Quantitative PET Performance Quantitative PET Performance
3 categories that “might” affect SUV measurements• Patient Compliance
– Fasting– Blood Glucose levels
• Scan Conditions
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– Scan time post injection– Patient anxiety/comfort during uptake (room temperature, etc.)– Patient motion during acquisition– PET/CT vs dedicated PET
• Intrinsic System Parameters and Capability– Calibration– QA – Maintenance of operating parameters– Performance characteristics of scanners – Partial Volume
effects– Image processing algorithms
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Improper Prep. Non fasting
• High protein/low carbs.• 6-8 glasses of water• 6 hrs fasting• Avoid strenuous exercise
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Fast Track Insulin Scan
• 70 ––150 mg/dL – Ideal• 150 ––200 mg/dL - clinical decision• > 200 mg/dL - cancel
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Muscle Uptake
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Crutch Utilized Left Side
Quantitative PET Performance Quantitative PET Performance
3 Categories that “might” affect SUV measurements• Patient Compliance
– Fasting– Blood Glucose levels
• Scan Conditions
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– Scan time post injection– Patient anxiety/comfort during uptake (room temperature, etc.)– Patient motion during acquisition– PET/CT vs Dedicated PET
• Intrinsic System Parameters and Capability– Calibration– QA – Maintenance of operating parameters– Performance characteristics of scanners – Partial Volume
Effects– Image processing algorithms
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N=20
Effect of Scan time post injection: Beast Cancer
O. Mawlawi MDACCBeaulieu S et al JNM 2003
PET-CT Normal “Brown” Fat
Max SUV 15.7
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Cor MIP Fused
Ax PETAx CT
Phantom Study
AxialCoronal Sagital Mip
Motion Effects
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Sphere (volume) Gated Static Error (%)1 (16.5 cc) 31624 33546 -6.1
2 (8.4 cc) 31316 21872 30.23 (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
Patient Movement
Patient movement occurred
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occurred after the CT image was acquired.
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Impact of Whole-body Respiratory Gated PET/CT
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The max SUV of the lesion goes from 2 in the static image to 6 in the respiratory-gated image sequence
Static wholebody Single respiratory phase(1 of 7, so noisier)
1 cc lesion on CT
Courtesy of P Kinahan, UW
• Transmission – Noise due to low gamma ray flux from rod source
Disadvantages of dedicated PET imaging techniques
PET/CT vs Dedicated PET
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g y– Transmission is contaminated by emission data
• Scan duration– Time consuming (emission & transmission )– Increased patient movement (image blurring)
• Efficiency– Decreased patient throughput– Difficulty in accurately correlating images to other
diagnostic modalities
Short duration, low noise CT-based attenuation correction
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Attenuation MeasurementRod or Pin Source (Ge-68, T½= 271 days)
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Patient Transmission Scan
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PET-CT
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AttenuationCorrection
Inherent Image
Registration
• For CT values < 0 , materials are assumed to have an energy dependence similar to water
• For CT values > 0, material is assumed to have an 0.100
0.150
0.200
atio
n at
511
keV
Bone/WaterBone/Water
Converting CT Numbers to Converting CT Numbers to Attenuation ValuesAttenuation Values
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energy dependence similar to a mixture of bone and water
• The green line shows the effect of using water scaling for all materials
0.000
0.050
-1000 -500 0 500 1000CT number measured at 140kVp
Atte
nua
Water/air
PET/CT imaging artifacts are due to :PET/CT imaging artifacts are due to :
Respiratory motionRespiratory motionMetal implantsMetal implants
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ppTruncationTruncationContrast mediaContrast media
Breathing Artifact-Curvilinear Cold Areas
Photopenic Artifact
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CT PET FUSEDIMAGE NON AC
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Breathing ArtifactMismatch of lesion location between helical CT and PET
O. Mawlawi MDACCInaccurate attenuation correction inaccurate quantification
Mismatch between PET and CT – Cardiac Application
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Courtesy of J. Brunetti, Holly name
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%
Respiratory singal
CT i
Average CT – 4D CT
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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
CT images
4D-CT images
Respiration-averaged CT 2
1
Courtesy of Tinsu Pan, MDACC
Clinical Studies
Mismatch 1:
CT diaphragm position lower
than PET
Mismatch 1:
CT diaphragm position lower
than PET
+57%
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Mismatch 2:
CT diaphragm position higher
than PET
Mismatch 2:
CT diaphragm position higher
than PET
Courtesy of Tinsu Pan, MDACC
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4D-PET/CT
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4D PET/CT
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Phantom Study
AxialCoronal Sagital Mip
Motion Effects
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Sphere (volume) Gated Static Error (%)1 (16.5 cc) 31624 33546 -6.1
2 (8.4 cc) 31316 21872 30.23 (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
METAL & CONTRAST artifactsMETAL & CONTRAST artifacts
For CT values < 0 , materials For CT values < 0 , materials are assumed to have an are assumed to have an energy dependence similar to energy dependence similar to water water For CT values > 0, material For CT values > 0, material is assumed to have an is assumed to have an 0.100
0.150
0.200
tion
at 5
11ke
V
Bone/WaterBone/Water
error
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energy dependence similar to energy dependence similar to a mixture of bone and watera mixture of bone and water
The green line shows the The green line shows the effect of using water scaling effect of using water scaling for all materialsfor all materials 0.000
0.050
-1000 -500 0 500 1000CT number measured at 140kVp
Atte
nuat
Water/air
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Metal ArtifactsMetal Artifacts
ArtifactArtifact
O. Mawlawi MDACCCT PET CTAC FUSED IMAGE
Metal ArtifactsMetal Artifacts
Cold spot
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CT SCAN PET AC NO AC
Transaxial
contrast bias
Contrast Effects
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Normal CT Contrast enhanced CT
Coronal
Contrast: Optiray 320, 100cc, 3cc/sec
Contrast ArtifactContrast Artifact-- Intravenous Intravenous Contrast injected
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With contrast Without contrast
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61 year male with history of esophageal cancer
SUV change
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1.23 to 1.9054% inc
PET Detector
PET 70cm image FOV
X-ray focal spot
CT and PET Fields of ViewCT and PET Fields of View
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CT Detector
CT 50cm Fully sampled FOV
Truncation ArtifactsTruncation ArtifactsOccur when objects extend outside the CT field Occur when objects extend outside the CT field of view (50cm), but are in the PET field of view of view (50cm), but are in the PET field of view (70cm). (70cm).
CT FOV
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Truncation artifacts are observed in very large patients or patients scanned with arms down.
PET FOV
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SUVmax changed from 3.25 to 6.05
CT PET FUSED Attenuation map
Truncated
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54 yrs. male with history of metastatic melanoma of the skin. SUV changed from 3.25 to 6.05
Truncated corrected
Quantitative PET Performance Quantitative PET Performance
3 Factors that may affect SUV measurements• Patient Compliance
– Fasting– Blood Glucose levels
• Scan Conditions
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– Scan time post injection– Patient anxiety/comfort during uptake (room temperature, etc.)– Patient motion during acquisition– PET/CT vs dedicated PET
• Intrinsic System Operating Parameters– Calibration– QA – Maintenance of operating parameters– System performance characterization – Partial Volume – Image processing algorithms
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Coincidence CalibrationsCoincidence Calibrations• Well Counter Correction (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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Normalized to Baseline for each Sphere
85
90
95
100
105
erce
nt
sphere37 mm
sphere28 mm
sphere22 mm
h
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65
70
75
80
base
line
final
base
line
M5blk4
M5blk5
M22
blk5
M5blk4
,5 M5blk
2,3
M5blk4
,5
M5blk4
,5 M9blk
4
M5blk4
,5 M6blk
4
M5blk4
,5 M22b
lk2,3
M5blk4
,5 M9blk
4,5
M5blk4
,5 M22b
lk4,5
M5blk4
,5 M22b
lk4
M5blk4
,5 M6blk
4,5
pe sphere17 mm
sphere13 mm
sphere10 mm
Normalization effects
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Good Norm Bad Norm
Effect of bad Normalization
SUVmax=4.5
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Increased activity due to error in normalization
Effect of wrong WCC
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10
37 28
22
1713All spheres contain the same activity concentration Profile (10 mm)
%)
Effect on Partial voluming
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Standard 8 x 8 detector
HI-REZ 13 x 13 detectorSphere diameter
Rec
over
y (
100
50
0 10
37282217
13
Recovery coefficientsCourtesy of Siemens
a
b d f
c e
Effect of Reconstruction Algorithm
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(a) 2D-FBP; (b) 2D-OSEM; (c) 3D-RP; (d) 3D-IR; (e) 3D-FORE+FBP; (f) 3D-FORE+OSEM.
(x104) Sphere 1 Sphere 2 Sphere 3 Sphere 4 Sphere 5 Sphere 6
Algorithm a 3.03 2.74 2.52 2.30 1.75 1.12
Algorithm b 3.14 3.14 2.82 2.90 2.14 1.74
Algorithm c 2.83 2.76 2.62 2.41 1.60 1.07
Algorithm d 2.93 2.92 2.98 3.21 2.19 1.33
Algorithm e 2.78 2.75 2.64 2.40 1.59 1.10
Algorithm f 2.85 2.74 2.71 2.52 1.65 1.09
AC max under different reconstruction algorithms (Bq/cc)
A
3D IR 2it 20sub
B
3D FORE 2it 5sub
C D
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1 2 3 4 5 6
A 10.8 10.3 9.9 8.9 6.5 3.8
B 8.6 7.6 6.6 5.5 3.9 2.8
C 10.3 9.7 9.1 8.3 6.3 4.7
D 10.4 9.3 9.3 7.7 5.9 4.8
3D FORE 5it 28sub
3D FORE FBP
Max SUVbw in different spheres
A
2D OSEM
2it 20sub
B
2D OSEM
2it 28sub
C
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2D OSEM
4it 28sub
1 2 3 4 5 6
A 12.7 11.9 11.7 12.7 7.4 4.1
B 15.0 12.3 11.7 13.4 9.6 5.4
C 16.0 13.6 11.9 14.7 10.3 6.3
Max SUVbw in different spheres
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Effect of acquisition time on convergence of reconstruction algorithm (2it 21ss)
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6
7
8
9 x 104
7
scan1scan2scan3scan4
2D 3D
10
12
14
16 x 104
7
scan1scan2scan3scan4
Effect of scan duration and count density on maximum AC
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0 20 40 60 80 100 120 140 160 1801
2
3
4
5
Duration(sec)
Max
d3
scan4
0 20 40 60 80 100 120 140 160 1800
2
4
6
8
Duration(sec)
Max
d3 scan4
Effect of smoothing on measured AC
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Effect of ROI type
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Conclusion
• SUV is reproducible
• SUV is reliable as long as mediating factors
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SUV is reliable as long as mediating factors are accounted for
• Standardization across institutions might be a more difficult task