Nuclear Medicine
SPECT & PET
Physics and instrumentation
Brain functional imaging
Nuclear Medicine
Ø Nuclear medicine is a branch of medical
imaging that uses radionuclides for diagnosis
and treatment of disease
Ø Radionuclides are combined with other
chemical compounds to form
radiopharmaceuticals
Beta Amyloid Imaging
Nuclear Medicine
The radiopharmaceuticals
Ø localize to specific organs or cellular receptors
Ø allow to diagnose or treat a disease based on the
cellular function and physiology
Ø rather than relying on the anatomy
Beta Amyloid Imaging
Radioactive nuclei
Ø The nucleus is consisting of b
Parent
ν nucleus
(A,Z)
a
protons (Z) and neutrons a
l A=protons (Z) + neutrons b-
electron He nucleus
Ø Radioactive isotopes have €
(A,Z+1)
instable nuclei
l If Z>83 the nucleus is (A-4,Z-2)
radioactive
g
Ø In radioactive decays a or b
rays are emitted g
Ø In both cases a g ray is daughter daughter
emitted nucleus nucleus
Alpha decay
Beta-minus decay
Beta-plus decay
Radioactive decay
Ø N0 initial number
of radioactive
atoms
Ø Nt number of
radioactive atoms
at time t
Ø A0 initial activity
Ø l decay constant
Ø Half-live: time
required for the
number of
radioactive atoms
in a sample to
decrease by one-
half
DPS: decays per second
DPM decays per minute
Curie: traditional units
Nuclear Medicine
The radiopharmaceuticals can localize
to specific organs or cellular receptors
Thyroid scintigraphy
bone scintigraphy
Radionuclides for
nuclear medicine
Ø Nuclear medicine images are obtained with g
emission (photons) only
Ø Half-time: time required for the number of radioactive
atoms in a sample to decrease by one-half
Scintigraphy
Gamma camera
patient
Ø Diagram of photon interactions inside a patient and collimation of the
exiting photons before detection
l a indicates interaction in which the photon is totally absorbed by an atom
l b and b’ indicate a scatter interaction in which the photon changes its
direction of travel
l B and c pass through holes of the collimator and are detected by the
detector
l b’ and d are photons that are blocked by the collimator hole septa and are
not detected by the detector
Image acquisition
Difference between radiology (transmission)
and nuclear medicine (emission)
X-ray
transmission tube
emission
detector
Image signal No collimator
No imaging
Image acquisition
Scintigraphy
emission
With collimator
From planar imaging
to tomography (SPECT)
Ø SPECT
Single Photon Emission
Computed Tomography
SPECT set-up
CT scanner
SPECT image acquisition
To allow
tomographic
reconstruction
multiple images
are necessary
in different
detector
position around
the patient
SPECT imaging in
cerebrovascular disease
Ø Measurement of regional cerebral
blood flow (rCBF)
Ø Sensitive indicator of perfusion
Ø Diagnosis and prognosis of
cerebro-vascular disease
SPECT perfusion image
Ø Acute brain ischemia
Ø Perfusion defects after resolution of TIA
Ø Cerebral infarction
Ø Delayed ischemic deficits after SAH
Ø Determine pathophysiological
mechanisms of stroke
Ø Monitor medical and surgical therapies
CT and 99mTc SPECT images
from 16-y-old patient with Perfusion
traumatic brain injury
(A) at time of admission shows study
subarachnoid hemorrhage with
small contusional hemorrhagic foci
in both frontal lobes (orange arrow)
(B) images obtained 1 mo later at
time of discharge after clinical
recovery
Ø Hypodense images in both frontal
lobes can be seen on CT as
consequence of hematoma’s
resolution
Ø Corresponding cold areas persist
on SPECT image (orange arrow)
but show improvement in global
cerebral perfusion, particularly in
both frontal lobes (white arrows)
SPECT/CT
scanner
SPECT/CT Image fusion
PET images
Ø Blood flow studies
l H215O
Ø Metabolic activity
l FDG
D. Le Bihan Phys. Med. Biol. 52 (2007) R57–R90
PET brain mapping
The first PET studies involving activation
brain imaging emerged in the 1980s
Ø intravenously administered 15O-water for
measurement of regional cerebral blood
flow
l rCBF
Øa sensitive method for quantifying regional
brain activation during specific tasks
PET brain mapping
Positron is
antimatter
Beta-plus decay
Annihilation
reaction
ü Positrons ( b+ ) released
from the nucleus
annihilate with electrons
(b-), releasing 2
coincidence 511 keV
photons (g )
• which are detected by 2
detectors
• blue rectangles
N neutron
P proton
Kapoor et al
RadioGraphics 2004; 24:523
Annihilation coincidence detection
Coincidence detection allows
propagation direction detection
Positron Emission Tomography
PET
Ø Process:
l Injection of nuclides that
emit positron
l Positron annihilates on
electrons
l 2 photons produced in
exactly opposite directions
l Detector that receives both
photons determines
position of original
nuclides
Ø 1-2 mm spatial resolution
scanner
PET
ü No collimator
ü The coincidence processing
unit works for signal
localization
SPECT vs PET
ü Coincidence detection allows propagation
direction detection
ü In PET no collimation is required:
Better spatial resolution and lower doses
1952: first PET acquisition
https://www.youtube.com/watch?v=qCT3KQitrCQ
Image fusion: PET & CT
An introduction to PET-CT Imaging”,V. Kapoor et al,
RadioGraphics 2004; 24:523–543
PET-CT systems
Ø the PET (P) and CT (C)
components
Ø The PET and CT
scanners are
mechanically
independent and can
be used in isolation for
PET or CT only
https://www.youtube.com/watch?v=qCT3KQitrCQ
The cyclotron
Ø b+ isotopes are not available in nature
l
11C, 13N, 15O,18F
Ø They are produced on-site using a cyclotron
Ø 18F- is produced in a cyclotron by
bombarding 18O-enriched water with high-
energy protons
Synthesis of FDG
Ø Bombarding 18O-enriched water with protons
in the cyclotron results in a mixture of H2(18F)
and 18O-enriched water
Ø Synthesis of FDG from this mixture is an
automated computer-controlled
radiochemical process
l takes approximately 50 minutes to complete
Ø The FDG thus produced is a sterile,
nonpyrogenic, colorless, and clear liquid
l residual solvent of less than 0.04%
Uptake of FDG
ü FDG is a glucose
analog that is taken up
by metabolically active
cells via glucose
transporters (Glut)
ü In the cell cytoplasm,
FDG undergoes
phosphorylation to
form FDG-6-phosphate
• which cannot
undergo further
metabolism and
becomes trapped
within the cell
FDG brain imaging
Ø 18F-FDG is the most accurate in vivo method
for investigating regional human brain
metabolism
Ø its clinical use is established for a number of
diagnostic questions in neurology and
psychiatry
l dementia disorders, movements disorders
Ø 18F-FDG PET imaging keeps an important
clinical interest in epilepsy
l particularly at inter-ictal state
Functional PET
Original methodologic approaches
Ø an analysis pipeline similar to that of
fMRI
Ø a constant infusion of 18F-FDG defining
within-session differential metabolic
responses
l slowly infusing 18F-FDG over the course of
the scan enables dynamic tracking of 18F-
FDG uptake
A Verger, E Guedj European Journal of Nuclear Medicine
and Molecular Imaging (2018) 45:2338–2341
Image fusion PET MRI
Image fusion: PET MRI
PET results
PET results
fPET
Control subjects Patients without ICDs Patients with ICDs
PET/MR systems
the multimodality approach integrates functional
connectivity obtained with fMRI with the PET
data
Ø potential complementarity offered by both modalities
Chen et al. Hum Brain Mapp. 2018;39:5126–5144
The results are comparable, but with more focused activity
in the FDG-fPET than BOLD-fMRI data
Amyloid PET Scan for
Alzheimer's Disease Assessment
New tracers for
dementia
studies
Nordberg, A. et al. (2010)
Nat. Rev. Neurol. 6, 78–87
