Functional Imaging

Question 1

What are the types of functional imaging?

Answer 1

• PET
• fMRI
• SPECT

Question 2

What is the application of functional imaging in RT?

Answer 2

• staging and decision making
• treatment plan optimisation
• measuring RT response

Question 3

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

Answer 3

• limited spatial resolution and sensitivity

- cant resolve metastatic disease or nodal involvement

Question 4

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

Answer 4

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

Question 5

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

Answer 5

• 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

Question 6

What is functional imaging in context of oncology?

Answer 6

• 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

Question 7

What MRI is being increasinlgy used for functional imaging?

Answer 7

• dynamic contrast-enhanced MRI and spectroscopy techniques

Question 8

What are the commonents of SPECT?

Answer 8

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

Question 9

What is a problem PET/CT?

Answer 9

• 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

Question 10

What are the two types of MRI imaging?

Answer 10

• T1: gross anatomy

- T2: biological pathology

Question 11

What are the types of functinoal MRI?

Answer 11

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

Question 12

How does nuclear medicine work?

Answer 12

• inject the patent with gamma emitting radiotracer

- detect where the radiotracer goes in the body

Question 13

What does nuclear medicine measure?

Answer 13

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

Question 14

How does PET work?

Answer 14

• 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

Question 15

What is the coincidence measurement in PET?

Answer 15

• 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

Question 16

What is true coincidences in PET?

Answer 16

• 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

Question 17

What is the scattered radiation coincidence?

Answer 17

• 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

Question 18

What is random coincidences?

Answer 18

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

Question 19

What is the standard uptake value?

Answer 19

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

Question 20

What is the equation for SUV?

Answer 20

= 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

Question 21

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

Answer 21

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

Question 22

What are the lung scan using Krypton 81m gas?

Answer 22

• ventilation

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

Question 23

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

Answer 23

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

Question 24

What is dynamic contrast enhanced MRI?

Answer 24

• 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)

Question 25

What are T2 DCE-MRI good for?

Answer 25

- T2 images can be used to measure tissue perfusion and blood volume

Question 26

What are T1 DCE-MRI good for?

Answer 26

- T1 used for extravascular extra-celluar space

Question 27

What is diffusion weighted MRI?

Answer 27

- 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

Question 28

What is DW-MRI good for?

Answer 28

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

Question 29

What are the commonly used MR nuclei?

Answer 29

- hydrogen - phosphorus-31 - fluorine-19 - carbon-13

Question 30

How do the MR nuclei work?

Answer 30

- 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

Question 31

How does magnetic resonance spectroscopic imaging work?

Answer 31

- 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)

Question 32

What is hyperpolarisation MRI?

Answer 32

- 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

Question 33

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

Answer 33

- 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)

Question 34

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

Answer 34

- 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

Question 35

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

Answer 35

- 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

Question 36

What are the PET nuclides?

Answer 36

- 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