Ultrasound, Positron Emission
Tomography, and Single Photon
Emission Tomography
Allen T. Newton, Ph.D.
PAVE 2014
PET in cancer imaging
• Some radioactive isotopes (18F, 15O, etc) emit positrons:
A
Z
X
A
Z 1
Q  e
• Such elements can be incorporated into metabolically relevant compounds
• Emitted positron encounters electron, they annihilate leaving 2 photons traveling
in opposite directions which are measured by ring of detectors
• Images generated using very similar
computations as in CT
• Spatial resolution: humans and
animals ~2 mm
• Most common PET tracer is FDG
(flourodeoxyglucose), a glucose analog
18FDG
18FDG
(blood)
(tissue)
18FDG-6-PO
X
(cells)
4
Positron Emission Tomography
http://www.cerebromente.org.br/n01/pet/pet_hist.htm
J Nucl Med Technol 2002; 30:3949
Types of Coincidence
 True coincidence is the simultaneous detection of the
two emissions resulting from a single decay event.
 Scatter coincidence is when one or both photons
from a single event are scattered and both are
detected.
 Random coincidence is the simultaneous detection of
emission from more than one decay event.
Coincidences: True
Scatter
Random
Positron Emission Tomography
Common Tracers
Positron Emission Tomography
Common Tracers
Half life = 20min
Half life = 110min
PET/CT
CT
PET
General Electric Medical Systems
CT+PET
PET image reconstruction
Projection
r
Radon Transform
P(f , r ) = ò
line (f , r )
f(x,y)
2
1
Object
f ( x, y )dl
PET image reconstruction
Sinogram
Object

Projection
angle
r
Projection bin
PET image reconstruction
Sinogram
Object

r
PET image reconstruction
Sinogram
Object

r
PET image reconstruction
Sinogram
Object

r
PET image reconstruction
Sinogram
Object

r
PET image reconstruction
Sinogram
Object

r
Sinogram
PET: 180º
(2 opposite photons)
SPECT: 360º (1 photon)
•
Other representations can be used instead of the sinogram (linogram, planogram)
2D Reconstruction
PET image reconstruction
• 2D Reconstruction
– Each parallel slice is reconstructed independently
etc
(a 2D sinogram originates a 2D slice)
Slice 5
etc
Slice 4
–PlaneSlices
are
stacked
to
form
a
3D
volume
f(x,y,z)
5
Slice 3
Plane 4
Plane 3
Plane 2
Slice 2
Slice 1
Plane 1
2D reconstruction
2D reconstruction
2D reconstruction
2D reconstruction
2D reconstruction
2D Reconstruction
PET image reconstruction
• Projection
and Backprojection
Projection
Backprojection
PET image reconstruction
4 projections
Backprojection
Filtered
Backprojection
16 projections
128 projections
Noise In PET Images
• Noise in PET images is dominated by the counting statistics of
the coincidence events detected.
• Noise can be reduced at the cost of image resolution by using
an apodizing window on ramp filter in image reconstruction
(FBP algorithm).
105
106
107
counts
Unapodized ramp filter
Hanning window, 4mm
Hanning window, 8mm
PET image reconstruction
• Data corrections are necessary
– the measured projections are not the same as the
projections assumed during image reconstruction
integral of the activity
along the line or tube of
response
Scattered
coincidences
component
assumed
Attenuation
Detector
efficiency
effects
True
coincidences
component
measured
projection
Random
coincidences
component
Object
(uniform
cylinder)
projection
PET Image reconstruction
image space
• Iterative methods
projection
projection space
Estimated
projection
Measured
projection
Current
estimate
Update
Error
image
backprojection
Iteration 1
Error
projection
Compare
(e.g. – or / )
PET Image reconstruction
image space
• Iterative methods
projection
Current
estimate
projection space
Estimated
Estimated
projection
projection
Measured
projection
Update
Error
image
backprojection
Iteration 2
Error
projection
Compare
(e.g. - or / )
PET Image reconstruction
image space
• Iterative methods
projection
Current
estimate
projection space
Estimated
Estimated
Estimated
projection
projection
projection
Measured
projection
Update
Error
image
backprojection
Iteration N
Error
projection
Compare
(e.g. - or / )
Kostakoglu L et al. Radiographics 2003;23:315-340
©2003 by Radiological Society of North America
Figure 2a. Primary carcinoid nodule of the left upper lung.
Kostakoglu L et al. Radiographics 2003;23:315-340
©2003 by Radiological Society of North America
Figure 2b. Primary carcinoid nodule of the left upper lung.
Kostakoglu L et al. Radiographics 2003;23:315-340
©2003 by Radiological Society of North America
Figure 5a. Large cell lung cancer in a 71-year-old woman.
Kostakoglu L et al. Radiographics 2003;23:315-340
©2003 by Radiological Society of North America
Figure 5b. Large cell lung cancer in a 71-year-old woman.
Kostakoglu L et al. Radiographics 2003;23:315-340
©2003 by Radiological Society of North America
Figure 15c. Hodgkin disease involving the mediastinal and right cervical lymph nodes.
Kostakoglu L et al. Radiographics 2003;23:315-340
©2003 by Radiological Society of North America
Figure 15e. Hodgkin disease involving the mediastinal and right cervical lymph nodes.
Kostakoglu L et al. Radiographics 2003;23:315-340
©2003 by Radiological Society of North America
Single Photon Emission Tomography
Single Photon Emission Tomography
Gamma Cameras
Single Photon Emission Tomography
CT scanner
Single Photon Emission Tomography
Single Photon Emission Tomography
http://cdcfd.wordpress.com/
http://quarknet.fnal.gov/
Single Photon Emission Tomography
Each coated with a secondary emissive
material (like a scintilation crystal)
http://cdcfd.wordpress.com/
http://quarknet.fnal.gov/
Single Photon Emission Tomography
Single Photon Emission Tomography
Again, its all about
what molecule you
attach the
radioactive element
to…
Note, these all make use of 99Tc (half life = 6hrs)
Reconstruction of a slice from projections
example = myocardial perfusion, left ventricle, long axis
courtesy of Dr. K. Kouris
Single Photon Emission Tomography
J Nucl Med May 2007 vol. 48 no. 5 696-703
Single Photon Emission Tomography
131I-iodide (half life = 13hrs) scan in a 16 year old patient with thyroid cancer discloses an
iodine-avid focus (arrow). The patient had had three surgical procedures (including total
thyroidectomy) and 37 GBq of 131I, so that this focus indicates the presence of a further
lymph node metastasis. Considering scarring from prior surgeries, exact localization of this
lesion is an essential requisite for its surgical resection
Clinical Applications of SPECT/CT: New Hybrid Nuclear Medicine Imaging System, IAEA-TECDOC-1597
Single Photon Emission Tomography
Uptake of 99mTc-MDP is due to arthrosis of the facet joint.
Single Photon Tomography
“In a recent study comparing the diagnostic accuracy of 99mTc-phosphonate
skeletal scintigraphy to that of [18F]FDG-PET in patients with thyroid carcinoma
[64], sensitivity of the conventional procedure was not significantly different
from that of [18F]FDG-PET. However, its specificity was significantly worse.”
“…there are several highly prevalent benign conditions leading to focally
increased uptake of the radiolabelled phosphonates in the skeleton. Most of
these conditions reflect degenerative processes of the joints increasing in
frequency with age, such as spondylarthrosis or coxarthrosis. Additional benign
causes of enhanced uptake are rheumatic disease or benign bone tumours.
Since most of these benign conditions are readily identifiable on CT, SPECT/CT is
expected to improve specificity of skeletal scintigraphy without reducing its
sensitivity. Besides single case reports illustrating this assumption, several
prospective studies have investigated this issue.”
Ultrasound
System
Facts:
• 1-20MHz
• Tomographic view
• Mechanical vibrations, no ionizing radiation
Transducers
Ultrasound
The Anatomy of a Transducer
Aldrich JE, Basic physics of ultrasound imaging, Crit Care Med 2007 Vol. 35, No. 5 (Suppl.)
Ultrasound
Ultrasound
Aldrich JE, Basic physics of ultrasound imaging, Crit Care Med 2007 Vol. 35, No. 5 (Suppl.)
Ultrasound
http://www.bercli.net/
Aldrich JE, Basic physics of ultrasound imaging, Crit Care Med 2007 Vol. 35, No. 5 (Suppl.)
Ultrasound
Frequency vs Resolution
High frequency
Low frequency
Less penetration
Greater penetration
Greater resolution
Less resolution
Ultrasound
Ultrasound
Ultrasound
Ultrasound
Ultrasound
Ultrasound
Ultrasound
Ultrasound
Ultrasound
Ultrasound
www.4dfirstimpressions.com
www.oakparkultrasound.com
www.firstglimpseultrasound.com