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CSB069 > Functional Imaging > Flashcards

Functional Imaging Flashcards

1
Q

What are the types of functional imaging?

A
  • PET
  • fMRI
  • SPECT
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2
Q

What is the application of functional imaging in RT?

A
  • staging and decision making
  • treatment plan optimisation
  • measuring RT response
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3
Q

What are the problems with CT based anatomical imaging for staging?

A
  • limited spatial resolution and sensitivity

- cant resolve metastatic disease or nodal involvement

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4
Q

What are the problems with CT based anatomical imaging for planning?

A
  • CTV delineation and assumuptions of uniform radiosensitivity (assume each cell will respond the same)
  • OAR contouring (functionality assumed to be uniform)
  • plan optimisation
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5
Q

What are the problems with CT based anatomical imaging for treatment reponse?

A
  • where was the dose actually delivered (hope matches plan but know not 100% accurate)
  • response of disease and normal tissues both during and post treatment
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6
Q

What is functional imaging in context of oncology?

A
  • mapping in 3D the distribution of a tumour, tissue or functional feature and provide information about the clinical repsonse of tumours of healthy tisues to ionising radiation
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7
Q

What MRI is being increasinlgy used for functional imaging?

A
  • dynamic contrast-enhanced MRI and spectroscopy techniques
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8
Q

What are the commonents of SPECT?

A
  • injection of y emitting radiotopes (Tc99m)
  • gamma camera (functional imaging)
  • CT (anatomical imaging)
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9
Q

What is a problem PET/CT?

A
  • when decays emitts positrons compared to gamma emits for SPECT
  • the positron moves mm before it interacks so there is a cloud of uncertainity from where they orginate
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10
Q

What are the two types of MRI imaging?

A
  • T1: gross anatomy

- T2: biological pathology

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11
Q

What are the types of functinoal MRI?

A
  • magnetic resonance spectroscopy imgaing
  • dynamic contrast enhanced MRI
  • diffusion-weighted MRI
  • fast pulse sequence
  • hyperpolarisation
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12
Q

How does nuclear medicine work?

A
  • inject the patent with gamma emitting radiotracer

- detect where the radiotracer goes in the body

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13
Q

What does nuclear medicine measure?

A
  • the distribution of a radionuclide in the body
  • distribution of radionuclide or radiopharmaceutical should correlate with a biological process
  • gamma camera
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14
Q

How does PET work?

A
  • 18F decays emitting positrons
  • positrons annihilate with electrons at the end of their tracks (1-2mm) creating two annihilation photons
  • conservation of energy and momentum (photons energy 511 keV, 180 degrees to each other)
  • detection of two photons in coincidence allows one to reconstuct a tomographic image
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15
Q

What is the coincidence measurement in PET?

A
  • detection of two simultaneous events within a temporal time window (10 nanoseconds)
  • assume annihilation took place along the line connecting the two events
  • as annihilation doesn’t occur in the centre of body, gamma rays will have different time of detection
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16
Q

What is true coincidences in PET?

A
  • coincidences simultaneously detected on both detectors resulting from the same annihilation of a positron and corresponding to the 511 keV energy photons not having undergone any scatter
  • true signcal that one wants to detect
17
Q

What is the scattered radiation coincidence?

A
  • photons from the same annihilation
  • due to scattering the assumption that the annihilation took place on a line joining the two detection points is incorrect
18
Q

What is random coincidences?

A
  • photons emitted by different annihilations but detected in the same time window
  • background noise
  • reduced by lowering coincidence time window
  • axial filters or septa
19
Q

What is the standard uptake value?

A
  • calculate the SUV that are an index of tracer uptake that can be compared between subjects
20
Q

What is the equation for SUV?

A

= TU/Q

  • where TU (MBq/ml) is the tumour uptake from the image
  • Q (MBq/g) is the injected dose per unit mass of the patient
21
Q

What is the application of PET/CT for NSC lung cancer?

A
  • staging changed when used PET/CT fused compared to CT alone
  • shows nodal volumes a lot better
22
Q

What are the lung scan using Krypton 81m gas?

A
  • ventilation

- get pateitn to breath in gas and see how the gas goes into lung

23
Q

What is the application of PET/CT for hypoxia and glucose metabolism?

A
  • hypoxic cells have increased radio and chemo resitance
  • FDG evaluates glucose metabolism
  • FMISO (18F fluoromisonidazole) better for correlation for tumour hypoxia
24
Q

What is dynamic contrast enhanced MRI?

A
  • sequential imaging following the injections of a suitable para-magnetic contrast agent (Gadalidium based)
  • do fast imaging to show the uptake then wash-out the contrast agent
  • fast gradient echo sequences (decreases quality but interested in gunctionality)
25
Q

What are T2 DCE-MRI good for?

A
  • T2 images can be used to measure tissue perfusion and blood volume
26
Q

What are T1 DCE-MRI good for?

A
  • T1 used for extravascular extra-celluar space
27
Q

What is diffusion weighted MRI?

A
  • image contrast that correlates with difference in tissue-water mobility
  • can infer the apparent diffusion coefficient from the measured signal
  • movement of water molecules in tissue is restricted as motion is limited by interactions with cell membranes and macro-molecules
  • tumours with high cellularity the motion of water is more restricted
28
Q

What is DW-MRI good for?

A
  • measure treatment response

- treatment can cause change in Apparent Diffusion Coefficient (ADC) due to swelling, tumour lysis and necrosis

29
Q

What are the commonly used MR nuclei?

A
  • hydrogen
  • phosphorus-31
  • fluorine-19
  • carbon-13
30
Q

How do the MR nuclei work?

A
  • they are present in tissue and concentrations depend on metabolism present in tissue
  • there are pre-defined levels and thus measuring the concentration can see the strength of each element which shows abnormal tissue
31
Q

How does magnetic resonance spectroscopic imaging work?

A
  • the precession frequency for each of the nuclei has a small shift that depends on the local chemical environment
  • MR spectrum contains peaks at different frequencies
  • obtain an MR spectrum for eahc voxel
  • the spectra will depend on the metabolic processes in the tissues
  • changes in metabolism can be messaured (e.g. in tumour)
32
Q

What is hyperpolarisation MRI?

A
  • Nuclei are driven to a very high degree of polarisation increasing the MR
    signal temporarily
  • He-3 and Xe-129 gas are used
  • patient breathes gas then fast imaging to see where gas is going
33
Q

What is the application of functional MRI for brain in RT?

A
  • used to assist in GTV and CTV delineation
  • OAR avoidance
  • measurement of response to therapy through diffusion maps (if diffusion changes fro pre to post, then indicate reponse)
34
Q

What is the application of functional MRI for lung in RT?

A
  • fast image sequence give high spatial and temporal resoluation
  • tumour mobility for dynamic imaging
  • effects of motion on dosimetry using probability density function (dump dose where lung is not functioning)
  • hyperpolarised He-3 determine lung function
  • measurement of response to RT
35
Q

What is the application of functional MRI for prostate in RT?

A
  • MRI superior
  • extent of diease and contouring
  • multiple combinations of MRI sequences, T2, DCE, DW and MRS
  • blood oxygen level dependent sequences for measuring hypoxia
36
Q

What are the PET nuclides?

A
  • 15O, 2 mins HL, cerebral blood flow
  • 11C, 20 mins HL, tumour protein synthesis
  • 13N, 10 mins HL, myocardial blood flow
  • 18F, 110 mins HL, glucose metabolism

CSB069 (7 decks)

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