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Question 1

Anatomical Imaging methods vs Molecular Imaging methods

Answer 1

Anatomical Imaging: x ray, CT, MRI

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

Question 2

describe the system input and output data in PET imaging

Answer 2

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.

Question 3

what are isotopes

Answer 3

Same element, different mass number (different neutrons)

Question 4

what is the fundamental reason for radioactive decay

Answer 4

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

Question 5

how is radioactive decay characterised

Answer 5

Half-life of decay

Particle, γ (gamma) and X-ray emissions

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

Question 6

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

Answer 6

Becquerel (Bq)

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

Question 7

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

Answer 7

exponential decay function

Question 8

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

Answer 8

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

used to make radioactive tracers for PET

Question 9

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

Answer 9

18F-FDG
18F-Fluoride
68Ga-PSMA
68Ga-Dotatate
11C-PIB
11C-Flumazenil
13N-Ammonia
15O-Water
15O-O2

Question 10

how are tracers produced for SPECT

Answer 10

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

Question 11

what is the main imaging device used in nuclear medicine

Answer 11

The gamma (Anger) camera

Question 12

What is a gamma ray

Answer 12

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

Question 13

how are gamma rays converted to electrical pulses

Answer 13

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

Question 14

what is Scatter and Collimation in SPECT

Answer 14

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

Question 15

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

123 I
201 Tl
99m Tc

Answer 15

159 keV

70 keV

140 keV

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

Question 16

what are the different types of Collimator

Answer 16

hexagonal holes

square holes

triangular holes

Question 17

What are the advantages and disadvantages of SPECT

Answer 17

Low resolution and high noise

Low cost and wide-spread

Simultaneous measurements

A large number of available tracers for diverse purposes

Question 18

describe the process of annihilation in PET

Answer 18

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-

Question 19

what is the energy of a positron / electron

Answer 19

511 keV

Question 20

what is Coincidence Detection in PET

Answer 20

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)

Question 21

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

Answer 21

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

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

Question 22

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

Answer 22

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

Question 23

what are the basic characteristics of compartments

Answer 23

Conservation of mass

Finite number of variables can describe the system

mass balance principle

Question 24

what are some variables that can be used to describe compartments

Answer 24

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

Question 25

describe properties of transfer rates (kij)

Answer 25

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

Question 26

describe the two different types of transfer rates

Answer 26

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.

Question 27

in what situation is it suitable to abstract (combine) compartments

Answer 27

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.

Question 28

what are the assumptions for the Kinetic Model of FDG

Answer 28

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.

Question 29

what are the three compartments in the Kinetic Model for FDG

Answer 29

FDG in plasma;
FDG in tissue;
FDG-6-PO4 in tissue

Question 30

what are the variables in the Kinetic Model for FDG

Answer 30

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

Question 31

what is the functional parameter related to glucose metabolism

Answer 31

CMR Glc: cerebral metabolic rate of glucose consumption (check equations)

Question 32

what is the format of a tissue time activity curve (TTAC)

Answer 32

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

Question 33

what is the proccess for simulating a TTAC

Answer 33

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)

Question 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

Answer 34

Projection data: Poisson distribution

Reconstruction data: Gaussian distribution

Question 35

describe the kinetic model for Glucose Metabolism

Answer 35

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

Question 36

describe the kinetic model for blood flow

Answer 36

Tracer: 15O-H2O

Two-compartment and two-parameter model (plasma and tissue)

Functional parameter: K1

Question 37

what is a receptor

Answer 37

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.

Question 38

describe the compartment model for receptor binding

Answer 38

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

Question 39

the compartment models for receptor binding can be four or three compartments, why would you use the three compartment model

Answer 39

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.