Week 12 - Functioning and Molecular Imaging Flashcards
application for radiotherapy
- staging and decision making
- treatment plan optimisation
- measuring radiotherapy response
problems with CT based anatomical imaging (staging)
- CT has limited spatial resolution and sensitivity
- often can’t resolve metastatic disease or nodal involvement
problems with CT based anatomical imaging (treatment planning)
- CTV delineation and assumption of uniform radiosensitivity
- organ at risk contouring. Function usually not considered and assumed to be uniform
problems with CT based anatomical imaging (treatment response)
- where was the dose actually delivered
- response of disease and normal tissues both during and post-treatment
what is FI in RO
mapping in three dimensions the distribution of a tumour, tissue or functional feature and to provide information about the clinical response of tumours or healthy tissues to ionising radiation
provide information about the functional and metabolic characteristics of tissues and tumors in a patient’s body. provides insights into how tissues are functioning, metabolizing, and responding to various processes, such as disease or treatment
MRI T1 images for
gross anatomy
MRI T2 images for
biological pathology
nuclear medicine
measure the distribution of a radionuclide in the body
- inject the patient with the gamma emitting radiotracer
- detect where the radiotracer goes in the body
SPECT
allows a 3D distribution of radionuclide to be reconstructed from multiple 2D projections
Explain how PET/CT works
Positron emitting radionuclide injected into patient, positrons annihilate with electrons creating 2 photons which are detected via coincidence detection allowing a tomographic image to be created
Discuss the rationale behind PET/CT
PET & CT occurs on the same day, in the same position, CT provides more anatomical definition allowing for a more accurate location of PET uptake to be determined.
Discuss how MRI imaging/ functional imaging is used in lung
Fast MRI imaging sequences (high spatial and temporal resolution) & hyperpolarised He-3 to determine lung function.
Perfusion - absorption of gas into the blood (Krypton-81m gas)
Ventilation - measures gas intake into the lungs
Define true coincidence
- 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
- the true signal that one wants to detect
Define random coincidence
- Photons emitted by different annihilations but detected in the same window
- background noise
- reduced by lowering coincidence time window
- alpha filters or septa
What is the 1/2 life of 18F?
110 minutes
What is the 1/2 life of 11C?
20 minutes
What is the application for 18F?
glucose metabolism
What is the application for 11C?
tumour protein synthesis
Why should PET/CT be used in lung cancer?
PET can increase accuracy of tumour delineation and detect unsuspected nodal and metastatic disease
How does diffusion weighted MRI help in functional imaging?
Provides contrast which correlates with differences in water-tissue mobility which can be restricted in tumours with high cellularity - treatment can cause a change in this
provides information about the movement of water molecules within tissues. Malignant tumors often have higher cell density (high cellularity) and restricted water diffusion.
List 5 applications of functional MRI in lung RT
- Fast imaging sequences (high spatial and temporal resolution)
- Tumour mobility (dynamic imaging)
- Effect of motion on dosimetry using probability density function
- Hyperpolarised He-3 to determine lung function
- Measure response to radiation
List 2 applications of functional MRI in prostate RT
- Superior imaging modality to determine disease extent and contouring
- Blood oxygen level dependant sequences for measuring hypoxia
List 5 functional magnetic resonance imaging
- Spectroscopy
- Dynamic contrast enhanced
- Diffusion weighted imaging
- Fast pulse sequences
- Hyperpolarising
define functional imaging
Functional imaging refers to mapping in three dimensions the distribution of a tumour, tissue or functional feature, and to provide information about the clinical responses of tumours or normal tissues to ionising radiation.
Define SUV
- standard uptake value
- assesses the level of radioactivity within a region of interest in the body
What is the role of dynamic contrast enhanced MRI (DCE-MRI) in fMRI?
- performed following the injection of a contrast such as Gadolinium
- image sequence used to assess uptake of contrast (higher uptake of contrast in tumours due to leaky blood vessels)
- used to measure extravascular extra-cellular space (T1) or tissue perfusion and blood volume (T2*)
What is the role of magnetic resonance spectroscopic imaging (MRSI) in fMRI?
- image sequence used to assess the concentration of isotopes in tissue (changes in concentration in tumour due to changes in metabolism)
- used to detect tumours
What is the role of diffusion weighted MRI (DW-MRI) in fMRI?
- image contrast that correlates with differences in tissue-water mobility
- image sequence used to assess the ease with which water molecules move in tissue (reduced motion of water molecules in tumours due to higher cellularity)
- used to measure tumour response (i.e., swelling, lysis, and/or necrosis) using apparent diffusion coefficient (ADC) maps
List 5 applications of functional MRI in lung RT
- Fast imaging sequences (high spatial and temporal resolution)
- Tumour mobility (dynamic imaging)
- Effect of motion on dosimetry using probability density function
- Hyperpolarised He-3 to determine lung function
- Measure response to radiation
List 2 applications of functional MRI in prostate RT
- Superior imaging modality to determine disease extent and contouring
- Blood oxygen level dependant sequences for measuring hypoxia
List 5 functional magnetic resonance imaging
- Spectroscopy
- Dynamic contrast enhanced
- Diffusion weighted imaging
- Fast pulse sequences
- Hyperpolarising
PET
- 18F decays by emitting positrons
- positron annihilate with electrons at the end of their tracks (1-2mm) creating two annihilation photons
- conservation of energy and momentum
- photon energy equals 511keV
- 180 degrees to each other
advantages of PET over normal nuclear medicine techniques
- spatial resolution
- quantification
What is the 1/2 life of 15O
2 minutes
application of 15O
cerebral blood flow
What is the 1/2 life of 13N
10 minutes
application of 13N
myocardial flood flow
hyperpolarisation
- nuclei are driven to a very high degree of polarisation increasing the MR signal temporarily
application of fMRI in RT - brain
- used frequently to assist in GTV and CTV delineation in planning
- fOAR for conformal avoidance
- measurement of response to therapy
- diffusion maps
application of fMRI in RT - lung
- fast image sequences can give high spatial and temporal resolution. up to 10 images per second
- tumour mobility from dynamic imaging
- effects of motion on dosimetry using probability density function
- hyperpolarised He-3 to determine lung function
- avoidance of functioning lung during planning
application of fMRI in RT - prostate
- MRI is superior imaging modality for the prostate
- extent of disease and contouring
- multiple combinations of MRI sequences
- T2, DCE, DW and MRS all have a role in improving cancer detection and mapping
- blood oxygen level dependent (BOLD) sequences for measuring hypoxia
fMRI in brain
- used frequently to assist in GTV and CTV delineation in planning
- Measurement of response to therapy - diffusion maps
- Can do correlation between diffusion coefficient pre-post treatment
application of PET in NSCLC
- Unsuspected nodal disease can be detected
- Two types of imaging: ventilation and perfusion using Krypton gas
- Can highlight blood flow
application of PET in hypoxia and glucose metabolism
- hypoxia cells in tumours have an increased radio resistance
- F18 and FMISO can evaluate glucose metabolism and correlation for tumour hypoxia
- However, hypoxia is not the sole cause of increase in glucose metabolism observed in cancer cells *specific to tumour type
application of PET in breast cancer
- Patient treated for breast cancer with bone and supraclavicular lymph node metastases detected by PET/CT
