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Single Photon Nuclear Medicine for Radiation Oncology
Richard E. Wendt IIIDepartment of Imaging Physics
5-3250, [email protected]
William D. Erwin, M.S., and Rodolfo Nunez, M.D. contributed slides to this presentation.
Radiopharmaceutical Imaging
• Radioactive tracers label physiology and function.
• Detect presence of specific conditions.
• Measure concentration of specific conditions.
• Measure affinity of locations.
01:50 GMT, 13 January 1998http://www.fourmilab.ch/cgi-bin/uncgi/Earth
Radiopharmaceutical Therapy
• Destructive effect targeted to specific “addresses.”
• Occasional delivery errors.
• Occasional incomplete response.
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Exponential Decay• The essence of decay is that the same fraction of
what remains disappears in a given time interval, whereas a linear decrease would remove the same number each time.
Exponential Decay
0
20
40
60
80
100
120
1 9 17 25 33 41 49 57
Tim e
Am
ount
Rem
aini
ng
Remaining Amount
Linear Decay
0
20
40
60
80
100
120
1 9 17 25 33 41 49 57
Tim e
Amou
nt R
emai
ning
Remaining Amount
Nuclear Reactor
http://web.mit.edu/nrl/www/coreview.html
http://web.mit.edu/nrl/www/core.html
Reactor-Produced RadionuclidesRadionuclide Decay
ModeProduction Reaction Natural Abundance of
Target Isotope (%)σc(b)
14C β- 14N(n,p)14C 99.6 1.8124Na (β-,γ) 23Na(n,γ)24Na 100 0.5332P β- 31P(n,γ)32P
32S(n,p)32P10095.0
0.19—
35S β- 35Cl(n,p)35S 75.5 —42K (β-,γ) 41K(n,γ)42K 6.8 1.251Cr (EC,γ) 50Cr(n,γ)51Cr 4.3 1759Fe (β-,γ) 58Fe(n,γ)59Fe 0.3 1.175Se (EC,γ) 74Se(n,γ)75Se 0.9 30125I (EC,γ) 124Xe(n,γ)125Xe→EC 125I 0.1 110131I (β-,γ) 130Te(n,γ)131Te→
β- 131I 34.5 0.24
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Cyclotron
•
•
r r rF qv B= ×r rF qE=
rmvqB
=
fqB
m=
2πE H R Z A( ) . [ ( ( ) ] /MeV T) cm≈ × −4 8 10 3 2
http://lynx.uio.no/cycdescr.html
Cyclotron ProductionProduct Decay Mode Common Production
ReactionNatural Abundance of
Target Isotope (%)13C β
+ 10B(d,n)11C11B(p,n)11C
19.780.3
13N β+ 12C(d,n)13N 98.9
15O β+ 14N(d,n)15O 99.6
18F β+, EC 20Ne(d,α)18F 90.9
22Na β+, EC 23Na(p,2n)22Na 100
43K (β-, γ) 40Ar(α,p)43K 99.667Ga (EC, γ)
68Zn(p,2n)67Ga 18.6111In (EC, γ) 109Ag(α,2n)111In
111Cd(p,n)111In48.712.8
123I (EC, γ)122Te(d,n)123I124Te(p,3n)123I
2.54.6
201Tl (EC, γ)201Hg(d,2n)201Tl 13.2
Working Generator
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γ Camera: Basic Construction
Collimator
Crystal (sealed)
Photomultiplier Tubes (PMTs)
Radioactive Source of γ or X-rays
Light guide (“pipe”)
(Al faceplates)
(glass window)
light seal
All optical interfaces coupled- coupling grease (Lightpipe-to-PMT)- bonding material (other)
Decoding PMT Output (a.k.a. Anger logic)
LE Williams, Nuclear Medicine Physics, Vol. II, Boca Raton: CRC Press, 1987, p. 113.
Note: original Anger design employed capacitors
Adjusting Linearity
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Linearity Correction
RE Henkin, et al., eds., Nuclear Medicine, St. Louis: Mosby, 1996, p. 91, Fig. 7-7
CFOV
UFOV
Quantitative Flood Evaluation
The Central Field of View (CFOV) has half the area, hence 0.75 the extent on each side, of the Useful Field of View (UFOV).
Uniformity Measures• Calculate for the UFOV and for the CFOV
• Evaluate Differential Uniformity over every vertical and horizontal group of 5 pixels within the chosen FOV
%100minmax
minmaxy UniformitIntegral
FOVFOV
FOVFOV ×+
−=
%100minmax
minmaxy UniformitalDifferenti
pixels 5pixels 5
pixels 5pixels 5 ×+
−=
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Uniformity Measures
IU=3% DU=2%
Collimators
LE Williams, Nuclear Medicine Physics, Vol. II, Boca Raton: CRC Press, 1987, Chapter 4.
Collimator Resolution
RE Hendee, et al., eds., Nuclear Medicine, St. Louis: Mosby, 1996, p. 106, Fig. 8-5.
Note the different terminology from figures from other sources.
zTDFBT
TDRg =++= )(
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Intrinsic Resolution• Intrinsic resolution is the
accuracy of localizing events within the crystal.
• Factors are: crystal thickness, light guide design, PMT technology, and number and size of PMTs.
• Measured without a collimator using a slit phantom
RE Henkin, et al., eds., Nuclear Medicine, St. Louis: Mosby, 1996, p. 89, Fig. 7-4
System Resolution
• The collimator’s geometric resolution (Rg) also plays a role.
• The system resolution (Rs) is the root mean square of the intrinsic (Ri) and collimator resolutions (uncertainty error propagation):
222gis RRR +=
Depth-Independent Sensitivity
• The sensitivity of a parallel hole collimator is roughly independent of depth (F in this figure).
• This is true in a limited field of view
RE Hendee, et al., eds., Nuclear Medicine, St. Louis: Mosby, 1996, p. 104, Fig. 8-4.
Note the different terminology from figures from other sources.
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Gamma Energies and Collimators
Energies of Common NM Gamma Emitters
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
0 100 200 300 400 500 600
Energy (keV)
Abu
ndan
ce
Co-57 (271.8d)Ga-67 (3.261d)Tc-99m (6.02h)F-18 (110m)Tl-201 (73.1h)In-111 (2.83d)I-131 (8.04d)
Low Energy
Medium Energy
High Energy
511
Single Photon Emission Computed Tomography
Sorenson & Phelps, Physics in Nuclear Medicine, 2nd Ed., Philadelphia: Saunders, 1987, p. 430.
SPECT Cameras
http://www.digirad.com/cardiology.shtm
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SPECT Camera Gantry
Park Medical Systems Brochure, Nov. 1996 Siemens e.cam at U.T. M. D. Anderson Cancer Center
SPECT/CT Gantries
Projections
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Projections
Projections
The Sinogram
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Unfiltered Backprojection
Animation of Unfiltered Backprojection
Spatial Frequencies
Central Slice TheoremImage Magnitude of the FT
Projection
Central Slice
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Density of Samples in the Spatial Frequency Domain
Filtered Projections
Filtered Backprojection
Animation of Filtered Backprojection
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Filters for Backprojection
Z.-H. Cho, J.P. Jones, and M. Singh, Foundations of Medical Imaging, New York: Wiley, 1993, p. 81
Expectation MaximizationChoose an initial
parameter λ[0]. Set k=0.
E-step: Estimate unobserved data using λ[k]
and the measurements y(d).
M-step: Compute maximum likelihood estimate of parameter
λ[k] using estimated data.
k=k+1. Converged?
Done
Typically use FBPas the initial guess.
Estimate the number of counts in each pixel of the projections that came from each pixel of the image.
∑=+
'
][
][]1[
),'(),()(),(
b
k
kk
dbdbdydbx
λλ
Choose the next estimate of λso that it makes the estimated data above most likely.
∑=
++ =D
d
kk dbpdbxb1
]1[]1[ ),(),()(λ
Why is EM Better than FBP?
• The probability function p(b,d) in
• This captures the probability that a count in a particular pixel of the image slice will wind up in a particular point on the projection, which is affected by collimator blurring, attenuation and scatter.
∑=
++ =D
d
kk dbpdbxb1
]1[]1[ ),(),()(λ
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OSEM Iterative SPECT:OSEM Iterative SPECT:Collimator Resolution ModelingCollimator Resolution Modeling
Standard Filtered
Backprojection
2-D Iterativew/ fan beam
modeling (m=12,n=10)
99mTc Bone Scan (osteosarcoma), Low-Energy High-Resolution Collimator
2-D pre-filter: Butterworth, fc = 0.6 Nyquist, order = 10
3-D Gaussian Post-Filter (7.8 mm FWHM)
3-D Iterativew/ cone beam
modeling (m=25,n=10)
OSEM Iterative SPECT:OSEM Iterative SPECT:Collimator Resolution ModelingCollimator Resolution Modeling
Standard Filtered
Backprojection
67Ga Citrate, Medium-Energy Low-Penetration Collimator
3-D Gaussian Post-Filter (9.6 mm FWHM)
12 iterations, 10 subsets
25 iterations, 10 subsets
2-D pre-filter: Butterworth, fc = 0.65 Nyquist, order = 7
2-D Iterativew/ fan beam
modeling
3-D Iterativew/ cone beam
modeling
Acquisition Orbits
Circular
Elliptical
Body
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How Many Views Are Needed?
• Essentially, the azimuthal spacing between lines of projection should equal the spacing between pixels.
• The center is okay, while the periphery needs more views. projectionin spacing pixeld
FOV ofdiameter D where2
180over Views #
==
=dDπo
θ
D
d
Partial Volume Effect
S.R. Cherry, J.A. Sorenson and M.E. Phelps, Physics in Nuclear Medicine: 3rd Ed., Philadelphia: Saunders, 2003, Fig. 17-16
Recovery Coefficient
• The recovery coefficient is the ratio of the apparent concentration to the true concentration.
• Note that RC can be greater than unity when cold spots are present.
S.R. Cherry, J.A. Sorenson and M.E. Phelps, Physics in Nuclear Medicine: 3rd Ed., Philadelphia: Saunders, 2003, Fig. 17-6
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Anterior
Posterolateral
Primary HyperparathyroidismPrimary Hyperparathyroidism
99m99mTc Sestamibi SPECT imagesTc Sestamibi SPECT images
Primary HyperparathyroidismPrimary Hyperparathyroidism
Primary HyperparathyroidismPrimary Hyperparathyroidism
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Uptake in Lumbar SpineUptake in Lumbar Spine
Uptake in Lumbar SpineUptake in Lumbar Spine
Uptake in Lumbar SpineUptake in Lumbar Spine
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Uptake in Lumbar SpineUptake in Lumbar Spine
111111--In ProstascintIn Prostascint
Negative Negative ProstascintProstascint
Attenuation corrected 111Attenuation corrected 111--In Octreotide SPECTIn Octreotide SPECT
Localize Localize NeuroendocrineNeuroendocrine TumorTumor
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Localize Localize NeuroendocrineNeuroendocrine TumorTumor
CT scan with contrast was equivocal as to pancreas or duodenum.CT scan with contrast was equivocal as to pancreas or duodenum.
Localize Localize NeuroendocrineNeuroendocrine TumorTumor
Localize Localize NeuroendocrineNeuroendocrine TumorTumor
Lesion is in the duodenum, not the pancreas.Lesion is in the duodenum, not the pancreas.
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Clearance
0 hrs 6 hrs 24 hrs 48 hrs 120 hrs 144 hrsLogarithmic images, each scaled separately
Region Time-Activity Curve
Simple MIRD
SourceSourceÃ=A0τ
ÃnE
ÃnEφTargetTarget=ÃnEφ/m=ÃΔΦ=ÃS=A0τS
D
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The MIRD Average Man
The Future of Radiopharmaceutical Therapy
• Voxel-scale dosimetry would allow construction of dose-volume histograms.
• Quantitative SPECT is essential in order to determine time-activity curves and cumulated activity for each voxel.
• Registered CT is highly desirable for determining the attenuation properties to feed into radiation transport calculations.