Current and Future Research
Trends in Nuclear Medicine:
NM Instrumentation
Disclosure
Timothy Turkington, Ph.D.
Radiology, Medical Physics,
and Biomedical Engineering
Duke University
Durham, North Carolina, USA
• Research support from GE Healthcare
• Consultant to Data Spectrum Corp.
US Airways Magazine, July 2008
Goals
“Philadelphia has just blossomed in terms of arts and
culture. People love the location between New York
and Boston. And it may very well be the last major
affordable city in the Northeast.”
• Fairness
• Completeness
• Insight
• Wisdom
President of prestigious Philadelphia university
• Accuracy
• Precision
• Interestingness
Page 1
Who needs new technology?
Patient FCH7 - Prostate Image
Androgen-dependent Prostate Carcinoma
CT
FDG-PET
FCH-PET
Tumor SUV = 5.7
Tumor SUV = 2.2
Duke University Medical Center – courtesy of T. R. DeGrado, Ph.D.
Commercially Available PET/CT
General Observations about
PET/CT Instrumentation
• All new PET development is being done on
PET/CT.
Bactrian
• New CT components are available in
PET/CT very quickly after available as
stand-alone CT.
Dromedary
• Each manufacturer offers an
array of combinations of PET
and CT components, but
generally not all possible
combinations.
Dromedary
Dromedary
Page 2
Example Block Detectors
Noise Equivalent Counts
Pprompts = Ttrues + S scatter + Rrandoms
T ′ = P − S ′ − R′
6.4 mm x 6.4 mm
8x8 crystals/block
4.0 mm x 4.0 mm
13x13 crystals/block
6.3 mm x 6.3 mm
6x6 crystals/block
4.7 mm x 6.3 mm
8x6 crystals/block
T ′ = P + S ′ + R′ =
NEC =
P + ?+
0
R
≥ P≥ T
T2
T
=
P (1 + S / T + ( 2 ?)R / T )
More background → more statistical image noise.
Multiple Rings, 2D – 3D
For n detector rings:
Image Noise and Lesion Detection
2D
2D
FBP
direct
slices (n)
cross
slices (n-1)
OS-EM
600s
300s
150s
75s
38s
19s
10s
total slices = 2n-1
Page 3
Higher Sensitivity
(degraded axial resolution)
3D
Typical Gamma Cameras
Iterative Image Reconstruction
• Different (mostly better) noise quality,
compared to FBP
• Capability to correct for physical effects
directly in reconstruction
NaI(Tl) Crystal Thickness – 3/8”, a few thicker
(5/8”, 1”) for higher-energy imaging
FOV ~50cm x ~40cm for general purpose, smaller
for dedicated cardiac
2-headed, variable angle, for general purpose
Fixed 90-degree, 2 head for dedicated cardiac
-
• Capability to reconstruct data not complete
enough for FBP
+
+
Image Reconstruction Methods
Detection Process
FBP
Filtered Back-Projection
ML-EM 10
ML-EM 30
npix
mi = bi +
ML-EM 50
Maximum Likelihood Expectation Maximization
OS-EM 2
OS-EM 3
pij λ j
j = activity at voxel j
mi=measured counts on LOR i
bi = background counts on LOR I
pij = probability of activity in
voxel j leading to a count in LOR i
(28 Subsets)
OS-EM 1
j =1
OS-EM 4
Ordered Subsets Expectation Maximization
What is p-1?
Page 4
jj
ii
Extended Distribution Example
Maximum Likelihood Expectation Maximization (ML-EM)
Shepp LA, Vardi Y., IEEE Trans Med Imag 1:113-121, 1982.
Lange K, Carson R., J Comput Assist Tomo 8:306-316, 1984.
j
j
ii
λ(jn +1) = nbin
1
i =1
npix
mi = bi +
j =1
pij λ j
pij
nbin
i =1
bi +
pij λ(jn )
nvox
k =1
pik λ(kn )
mi
λj(n) is the estimated activity in
voxel j at iteration n.
1
2
3
4
5
10
20
30
40
50
OS-EM 10 subsets
What is p?
npix
mi = bi +
2 ss
ML-EM
4 ss
6 ss
8 ss
1 iter
j =1
pij λ j
2 iter
1
2
3
4
5
10
20
30
40
50
What physics can/does p include?
1) none: 1’s and 0’s - very sparse
2) p is fractional values, depending on how
column intersects with voxel - still pretty
sparse
3) attenuation (lower values) - still pretty
sparse
4) resolution effects (collimator blurring,
depth of interaction, etc) - somewhat
sparse
5) background - not sparse at all
Page 5
jj
ii
PET Attenuation Correction
Incorporating AC Into Reconstruction
AC PET Sino
Raw PET Sino
Single Image
Sinogram of
attenuation
probabilites
Mean Image
OSEM
(precorrected)
AC
OSEM-AC
CT Image
PWLS
Comtat ,et al. IEEE Trans Nucl Sci 45:1083, 1998
Parallel Hole Collimator
Trend
l
d
• Iterative reconstruction algorithms will be
further developed and exploited for noise
properties, physic modeling, and
accommodation of new detector
geometries.
t
R∝
d (D + leff )
leff
R
Sensitivity = K 2
D
Page 6
d2
d2
leff 2 (d + t )2
Extrinsic vs. Intrinsic Resolution
Pinhole collimator - Resolution
(extrinsic resolution)2=(intrinsic resolution)2+(collimator resolution)2
22
18
16
14
Intrinsic Res (mm)
12
3
4
5
6
7
10
8
6
4
Ability to resolve objects depends on:
Distance to hole
Size of hole
Amount of magnification
Intrinsic Camera Resolution*Magnification
2
5
10
15
20
Collimator Blurr (mm)
Pinhole Collimation
Pinhole collimator - Sensitivity
Sensitivity (point source)
Spatial resolution
100
16
~d2/D2
14
ME-PAR
HE-PAR
Pinhole
12
10
80
cps per MBq
0
FWHM (mm)
Extrinsic Resolution (mm)
20
ME-PAR
HE-PAR
Pinhole
60
40
20
8
6
9
12
15
18
distance from collimator (cm)
0
6
9
12
15
18
distance from collimator (cm)
Gilland et al., Trans Nucl Sci, 1996, p. 2230
Courtesy of Ronald Jaszczak, Ph.D.
Page 7
Figure 1
Pinhole collimator with high
resolution detector
2 cm
A
B
C
Courtesy of Bennett Chin, MD
Methods – Resolution Example
Normal Control – Normal Concentric LV Contraction
Micro Hot Spot Phantom
Diameters
0.75, 1.0, 1.35, 1.7, 2.0, and 2.4 mm
Similar parameters as mouse imaging
1.0 mm tungsten pinhole
OSEM (4 subsets, 5th iteration)
Voxel 0.5 x 0.5 x 0.5 mm = 0.125µl
Page 8
Myocardial Infarction - Apical Hypokinesis
D-SPECT™ Cardiac Scanner
Dynamic SPECT
(D-SPECT)
Detector Configuration
Spectrum-Dynamics
Haifa, Israel
Slides Courtesy
Jim Patton, Ph.D.,
Vanderbilt
D-SPECT™ production model
Detector Column Detail
16 elements
~40 mm
Detector
Column
ROI-Centric Scanning
Electrode
Side
View
5 mm
2.46 mm
64 elements
~160 mm
Column Tungsten Collimator
2.46 mm
5 mm thick CZT
Detector Element
1024 elements
per column
Detector Array
Intrinsic Efficiency for 5 mm CZT
at 140 keV = 3/8” NaI(Tl)
Page 9
EKG data acquired simultaneously with image data
IQ
SPECT
CardiArc
cardiarc.com
siemens.com
Gamma Cameras >> PET
but PET/CT > SPECT/CT.
Why?
Trends
• Attenuation Correction
• Animal SPECT will continue to push the
limits of pinhole collimation.
– Considered essential for PET. x-ray provides atten. map faster
than previous methods.
– Considered a luxury for SPECT. Longer scan.
• Solid state detectors will be used where
geometrically beneficial.
• Cost
–
–
–
–
• Dual-nuclide studies may drive additional
applications for solid state.
~10 years ago s.o.a. PET ~ $2M
Now, s.o.a. PET/CT ~$2M
Gamma camera $300k
SPECT/CT $400k and UP
• Clinical Application
– (almost) All patients receiving oncologic PET have CT anyway
– Gamma cameras are used for many diverse applications, some
of which have CT benefit
Page 10
Siemens Symbia
SPECT/CT
CT
SPECT
GE Hawkeye
Slides Courtesy Daniel Gagnon, Ph.D., Philips
BrightView XCT
System Overview
Philips Precedence
•
Volumetric CT components
–
–
–
•
X-Ray Tube &
Collimator
Rotating anode X-ray tube
120 kVp X-ray generator, pulsed or
continuous
4030CB flat panel detector
•
–
–
Low-Profile
Gamma Detector
X-ray collimator and beam shaper
CBCT image reconstruction using GPU
Volumetric CT system goals
–
–
–
–
X-Ray Flat Panel
Detector
10, 30, 60 fps, dynamic gain
SPECT FOV
SPECT
FOV
5454xx 40
cm
40 cm
14 cm
Axial
14 cm axial
Coverage
coverage
X-ray cone-beam overlaps SPECT FOV
o
360 Gantry rotation within a breath-hold
Low-dose CT acquisition parameters
Integrated hybrid software solution
X-Ray Detector
40 x 30 cm
5
Page 11
VUMC
Ventri-VCT
Patient B
Slides Courtesy
Jim Patton, Ph.D.,
Vanderbilt
SPECT/CT Mammotomography
Page 12
Extending the Axial FOV
Trends
2D
3D
• SPECT systems will continue to be
available with a range of CT.
• Applications will direct the tecnology.
Sensitivity ~ axial FOV
Most Efficient Use of Expensive Detector
Sensitivity ~ (axial FOV)2
Improved Spatial Resolution?
Modeling resolution
effects in recon.
vs.
Page 13
Iterative Reconstruction
2
20
5
25
Faster convergence from in-loop
randoms correction
r
ite
15
35
→
30
od
go
10
Gated PET (Used to image repetitively moving objects: cardiac, respiratory)
Trigger
New CT Application… Advantage 4D CT
Respiratory tracking with Varian RPM optical
monitor
Trigger
1
8
2
1
7
3
4
s→
on
a ti
6
CT images acquired over complete respiratory
cycle
8
7
2
3
5
6
4
5
“Image acquired”
signal to RPM
system
time
X-ray on
Bin 1
Bin 8
• 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
First couch position
Second couch position
Third couch position
Slide Courtesy of
Osama Mawlawi, Ph.D.
MDAnderson
• As number of bins increase, the duration and motion per bin decreases.
However images will be noisy unless acquired for longer durations.
Respiratory motion defined retrospective gating
Page 14
Time-of-Flight Image Reconstruction:
Detected Event
Time-of-Flight PET
∆t=(d2-d1)/c=2x/c
x=∆t·c/2
d2
Detector midpoint
x
Annihilation location
d1
Reconstruction: Conventional Ray
Tracing
Reconstruction: pixels actually
giving counts
D = diameter of body
along line of response
D
Page 15
Time Of Flight Results
Time-of-Flight Image Reconstruction:
TOF pixels
1i
6:1 Sphere:Background, 35 cm phantom
10i
2i
5i
20i
5 min nonTOF
5 min TOF
D = diameter of body
along line of response
d
D
d = time-of-flight
resolution
= c(timing resolution)
10i nonTOF
5i TOF
D/d ~ improvement
in image quality
5 min
3
2
1
Karp JS, et al., J Nucl Med 2008; 49:462–470
High Resolution Brain PET
Time Of Flight Results
Non-Hodgkins
Lymphoma
de Jong, et al., Phys. Med. Biol. 52 (2007) 1505–1526
Cho, et al., Int J Imaging Syst
Technol, 17, 252–265 (2007)
Karp JS, et al.,
J Nucl Med 2008;
49:462–470
Page 16
GEMINI TF Big Bore
DSTE Brain
Brilliance Big Bore CT
• 85cm aperture
• 60cm standard FOV
• BB CT features
Dedicated Positron Emission
Mammography (PEM)
PET/MR
• Issues
– Making PET detectors work in magnetic field
– Making PET detectors that don’t perturb the field too
much
– Coming up with enough application to drive the
product
• Use small detectors close to the breast
• Small device, can go in mammography unit.
• Low radiotracer dose requirement
– Easier to image a patient on short notice
– Lower cost for study
• Small Animal – PET insert in magnet
• Human brain –
“
• Human body
Philips – NOT FDG approved
Page 17
Different PEM Geometries
Duke/Jefferson Lab
PEM Collaboration
Jefferson Lab:
Stan Majewski
Drew Weisenberger
Mark Smith
Vladimir Popov
Randy Wojcik
David Abbott
Brian Kross
Doug Kieper
Duke:
Bill Sampson
Thomas Hawk
Robin Davis
Eric Rosen
Ed Coleman
Mary Scott Soo
Jay Baker
Donna Smith
Lesa Kurylo
D.O.E., D.O.D., NIH
Small Sphere Phantom
15 cm x 20 cm PEM
• F-18 in wax (Avoids dead wall issue)
Transaxial
• 8:1 tumor/background
• 6 µCi total in phantom (0.13 µCi/cc in lesions)
• Two planar detectors
• 30 min acq.
• Use paddle of x-ray
system to compress
breast against lower
detector
• Iterative, fully 3D reconstruction
• Perform immediately
after or before x-ray
imaging for correlated
images
8.5 mm
3.0 mm
Page 18
8.0
7.0
6.0
Dia.
3.0
3.5
4.0
4.5
5.0
5.5
6.0
6.5
7.0
7.5
8.0
8.5
Vol.
0.014
0.022
0.033
0.048
0.065
0.087
0.113
0.144
0.180
0.221
0.268
0.321
5.0
4.0
3.0
Coronal
Sagittal
“Attenuation Uniformization”
Patient Study - multiple slices
The Abyss
Comments
• SPECT and PET are based on mature
technologies, but new concepts are being
incorporated
• Iterative image reconstruction is essential
• Quantitation must be a standard
• General purpose systems have been the norm;
specialized devices will proliferate if applications
demand.
• New image-based standards for system
performance will be essential
Page 19