Ultrasound, Positron Emission Tomography, and Single Photon Emission Tomography Allen T. Newton, Ph.D. PAVE 2014

Ultrasound, Positron Emission Tomography, and Single Photon Emission Tomography

Allen T. Newton, Ph.D.PAVE 2014

PET in cancer imaging

• Images generated using very similar computations as in CT

• Spatial resolution: humans and animals ~2 mm

• Some radioactive isotopes (18F, 15O, etc) emit positrons:

• 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

1

A AX Q e

Z Z

• Most common PET tracer is FDG (flourodeoxyglucose), a glucose analog

18FDG

(blood)

18FDG

(tissue)

18FDG-6-PO4

(cells)X

Positron Emission Tomography

J Nucl Med Technol 2002; 30:3949

http://www.cerebromente.org.br/n01/pet/pet_hist.htm

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 TomographyCommon Tracers

Positron Emission TomographyCommon Tracers

Half life = 110minHalf life = 20min

PET/CT

CT PET CT+PET

General Electric Medical Systems

PET image reconstructionProjection

Object

P( 2 ,r) Radon Transform

1

2

P(1 ,r)

f(x,y)

r

r

PET image reconstructionSinogram

r

Projectionangle

Projection bin

Object

PET image reconstructionSinogramObject

r


r


r


r

PET image reconstruction

r

SinogramObject

Sinogram

• Other representations can be used instead of the sinogram (linogram, planogram)

SPECT: 360º (1 photon)

PET: 180º (2 opposite photons)


• 2D Reconstruction– Each parallel slice is reconstructed independently

(a 2D sinogram originates a 2D slice)– Slices are stacked to form a 3D volume f(x,y,z)

2D reconstruction

Plane 5

Slice 5etc

etc

2D reconstruction

Plane 4

Slice 4

2D reconstruction

Plane 3

Slice 3

2D reconstruction

Plane 2

Slice 2

2D reconstruction

Plane 1

Slice 1

2D Reconstruction


• Projection and BackprojectionProjection Backprojection

2D Reconstruction

4 projections 16 projections 128 projections

Backprojection

FilteredBackprojection


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

Scatteredcoincidences component

Attenuation

Random coincidencescomponent

Detector efficiencyeffects True

coincidencescomponent

PET image reconstruction• Data corrections are necessary

– the measured projections are not the same as the projections assumed during image reconstruction

Object(uniformcylinder)

projectionmeasured

projectionassumed

integral of the activity along the line or tube of response

PET Image reconstruction

• Iterative methods

Current estimate

Measured projection

Compare

(e.g. – or / )

Error projection

projectionEstimated projection

image space projection space

backprojectionErrorimage

Update

Iteration 1



Current estimate

Measured projection

Compare

(e.g. - or / )

Error projection

projectionEstimated projection



Update

Estimated projection


Iteration 2



Current estimate

Measured projection

Compare

(e.g. - or / )

Error projection

projection



Update





Iteration N

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.



Figure 2b. Primary carcinoid nodule of the left upper lung.



Figure 5a. Large cell lung cancer in a 71-year-old woman.



Figure 5b. Large cell lung cancer in a 71-year-old woman.



Figure 15c. Hodgkin disease involving the mediastinal and right cervical lymph nodes.



Figure 15e. Hodgkin disease involving the mediastinal and right cervical lymph nodes.



Single Photon Emission Tomography


Gamma Cameras


CT scanner



http://cdcfd.wordpress.com/

http://quarknet.fnal.gov/


http://cdcfd.wordpress.com/

http://quarknet.fnal.gov/

Each coated with a secondary emissive material (like a scintilation crystal)



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 projectionsexample = myocardial perfusion, left ventricle, long axis

courtesy of Dr. K. Kouris


J Nucl Med May 2007 vol. 48 no. 5 696-703


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


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.”

UltrasoundSystem Transducers

Facts:• 1-20MHz• Tomographic view• Mechanical vibrations, no ionizing radiation

Ultrasound

Aldrich JE, Basic physics of ultrasound imaging, Crit Care Med 2007 Vol. 35, No. 5 (Suppl.)

The Anatomy of a Transducer

Ultrasound

Ultrasound


Ultrasound


http://www.bercli.net/

Ultrasound

High frequency

Less penetration

Greater resolution

Frequency vs Resolution

Low frequency

Greater penetration

Less resolution

Ultrasound

Ultrasound

Ultrasound

Ultrasound

Ultrasound

Ultrasound

Ultrasound

Ultrasound

Ultrasound

Ultrasound

www.4dfirstimpressions.com

www.oakparkultrasound.com

www.firstglimpseultrasound.com

Documents

Ultrasound, Positron Emission Tomography, and Single Photon Emission Tomography Allen T. Newton, Ph.D. PAVE 2014