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1
Q

Anatomical Imaging methods vs Molecular Imaging methods

A

Anatomical Imaging: x ray, CT, MRI

Molecular Imaging: PET, SPECT, functional MRI w/ BOLD

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2
Q

describe the system input and output data in PET imaging

A

input: arterial plasma time activity curve. acquired from arterial blood input function.
output: PET measurement tissue time activity curve. acquired from image reconstruction over time.

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3
Q

what are isotopes

A

Same element, different mass number (different neutrons)

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4
Q

what is the fundamental reason for radioactive decay

A

If a nucleus is proton or neutron deficient, then it undergoes a transformation to a more stable state and releases radioactive decay in the process

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5
Q

how is radioactive decay characterised

A

Half-life of decay

Particle, γ (gamma) and X-ray emissions

N0 = the initial amount of active substance / Exponential decay function

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6
Q

what is the unit of unit of radioactive activity and what is its meaning

A

Becquerel (Bq)

One Bq is defined as one transformation (or decay or disintegration) per second

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7
Q

For a fixed mass of radioactive material, how does the radioactive activity change with time

A

exponential decay function

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8
Q

what is a cyclotron and why is it relevant to medical imaging

A

Cyclotrons accelerate charged particles using a high-frequency, alternating voltage (potential difference)

used to make radioactive tracers for PET

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9
Q

What PET tracers are used for

Glucose metabolism
Bone metabolism
Prostate cancer
Neuroendocrine Tumors
Alzheimer's Disease
Brain epilepsy
Myocardial perfusion
Blood flow/perfusion
Oxygen consumption
A 
18F-FDG
18F-Fluoride
68Ga-PSMA
68Ga-Dotatate
11C-PIB
11C-Flumazenil
13N-Ammonia
15O-Water
15O-O2
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10
Q

how are tracers produced for SPECT

A

Parent tracer decays to daughter tracer using a generator (check table for SPECT tracers)

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11
Q

what is the main imaging device used in nuclear medicine

A

The gamma (Anger) camera

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12
Q

What is a gamma ray

A

A gamma ray is a packet of electromagnetic energy (photon) emitted by the nucleus of some radionuclides following radioactive decay

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13
Q

how are gamma rays converted to electrical pulses

A

photomultiplier tube

used for light detection of very weak signals, is a photoemissive device in which the absorption of a photon results in the emission of an electron

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14
Q

what is Scatter and Collimation in SPECT

A

Scatter: increases the uncertainty of the origin of emitted photons

Collimation: blurs already poorer spatial resolution ??? directs light to a straight line / makes light parallel

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15
Q

What are the specific energy windows to detect the following gamma rays

123 I
201 Tl
99m Tc

A

159 keV

70 keV

140 keV

this means you can simultaneously detect multiple tracers using multiple energy window

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16
Q

what are the different types of Collimator

A

hexagonal holes

square holes

triangular holes

17
Q

What are the advantages and disadvantages of SPECT

A

Low resolution and high noise

Low cost and wide-spread

Simultaneous measurements

A large number of available tracers for diverse purposes

18
Q

describe the process of annihilation in PET

A

PET tracer will emit positrons due to decay in the body

Annihilation is the process that occurs when a subatomic particle collides with its respective antiparticle, in PET: positron+ with electron-

19
Q

what is the energy of a positron / electron

20
Q

what is Coincidence Detection in PET

A

The simultaneous detection of 2 opposite photons within a specified time window is referred to as a coincidence

A line connecting the 2 coincidence detectors is called a Line of Reponses (LOR)

21
Q

what are the two ways of calculating tissue time activity curves (Parameter Estimation)

A

ROI-derived - tissue time activity curve (TTAC) less noisy

Voxel-wise - doesn’t require prior knowledge on how to define ROI

22
Q

what are compartmental models (what is the connection???)

A

describes a system as a series of compartments.

are widely employed to solve a broad spectrum of
physiologic and clinical problems related to the distribution of materials in living systems

23
Q

what are the basic characteristics of compartments

A

Conservation of mass

Finite number of variables can describe the system

mass balance principle

24
Q

what are some variables that can be used to describe compartments

A

compartment mass qi

transfer rate from the jth compartment kji

transfer rate to the jth compartment kij.

Influx rate from outside the system, kio

Excretion rate into outside the system, koi

25
describe properties of transfer rates (kij)
kij is constant, does not depend upon any Qi kij is described by a saturated relationship: Michaelis-Menten equation controlled by the arrival compartment: Langmuir relationship
26
describe the two different types of transfer rates
Nonlinear model: transport rate is nonlinear for most physiological systems e.g. facilitated diffusion and receptor binding systems. Linear model: Advantage: mathematical properties of the linear model. If the dynamic system is in steady state and is time-invariant over the study duration, the administration of a small amount of tracer will not disturb the steady state. Therefore, the linear fractional transfer rate can be assumed.
27
in what situation is it suitable to abstract (combine) compartments
As the transport of FDG across the cell membrane is considered fast compared to the transport across the capillary membrane and the phosphorylation reaction, the interstitial and cellular compartments for FDG can be combined into a single compartment.
28
what are the assumptions for the Kinetic Model of FDG
All the rates are constant (rate constant). The tissue compartment is homogeneous. Arterial plasma concentrations (plasma time-activity curve from blood sampling) are equal to their capillary plasma concentration; FDG and glucose are distributed in a single compartment The tissue extraction fraction is small compared to whole system => linear model.
29
what are the three compartments in the Kinetic Model for FDG
FDG in plasma; FDG in tissue; FDG-6-PO4 in tissue
30
what are the variables in the Kinetic Model for FDG
Cp(t), Ce(t), Cm(t), Ct(t) = Ce(t) + Cm(t) K1 : rate constant of FDG forward transcapillary membrane transport k2 : rate constant of FDG reverse transcapillary membrane transport k3 : rate constant of FDG phosphorylation k4 : rate constant of FDG-6-PO4 dephosphorylation. If rate of constant, K1, is 0.1/min, it means 10% of FDG in plasma is transported into tissue per min
31
what is the functional parameter related to glucose metabolism
CMR Glc: cerebral metabolic rate of glucose consumption (check equations)
32
what is the format of a tissue time activity curve (TTAC)
formatted as list of frames For one frame (tmin, tduration, y) there are three variables: mid-time, sampling duration, and activity mid times and sampling durations make up the sample schedule
33
what is the proccess for simulating a TTAC
Load the plasma time activity curve Specify K1, k2, k3, k4 for white and grey matter Define sample schedule for TTAC Derive Ct(t) respectively for each sample interval using an equation (Check notes)
34
The intrinsic characteristics of functional imaging lead to high level of noise, i.e. low signal to noise ratio (SNR). Computer simulations should take noise into account. what are two methods of estimating the noise distribution
Projection data: Poisson distribution Reconstruction data: Gaussian distribution
35
describe the kinetic model for Glucose Metabolism
Tracer: 18F-FDG Functional parameter is CMR Glc or CMRglu three compartments: FDG in plasma; FDG in tissue; FDG-6-PO4 in tissue k4 is assumed to be ignored i.e. the dephosphorylation rate of FDG-6-PO4 is 0
36
describe the kinetic model for blood flow
Tracer: 15O-H2O Two-compartment and two-parameter model (plasma and tissue) Functional parameter: K1
37
what is a receptor
a protein on the cell membrane (or within the cytoplasm or cell nucleus) that binds to a specific molecule (a ligand), such as a neurotransmitter, hormone, or other substance, and initiates the cellular response to the ligand.
38
describe the compartment model for receptor binding
Cp is the concentration of ligand in plasma. Cf is the free concentration of ligand. Cns is the concentration of nonspecifically bound ligands. Cs is the tissue concentration of specifically bound ligands OR Cf+ns is the concentration of free and non-specifically bound ligand Functional parameter: BP = k3/k4
39
the compartment models for receptor binding can be four or three compartments, why would you use the three compartment model
The three-tissue model is a priori only nonuniquely identifiable i.e. there are multiple solutions for each parameter. To ensure unique identifiability, assume the exchange rates between the free tissue and nonspecific binding pools are sufficiently rapid.

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