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Dynamic contrast-enhanced MRI in oncology Lecture 12a
Terms in this set (20)
What is oncology?
It is the study of cancer. More formally it is the field of medicine dealing with cancer. It includes study of the origin,development, diagnosis, and treatment of malignant tumours.
What is a tumour?
A tumour is a common term for a neoplasm, which is an abnormal mass of tissue resulting from abnormal growth (proliferation) of cells(called neoplasia)
A tumour can be classified as : (3)
Benign (e.g. fluid-filled cyst);
Pre-malignant (carcinoma in situ); or
(cancer or invasive carcinoma).
what happens after a tumour is found? (3 steps)
0.tissue sample examined under a microscope (to determine cancer)
1.staging; i.e. determining the extent of the disease using CT, MRI and PET
2. removal simple procedure or a serious operation depending on where the tumour is located.
3.Grading systems are used by pathologists to describe how
much the tumour cells differ from normal cells in the
Possible treatments for cancerous tumours?
what are Metastasis?
These secondary tumours are called metastases, it is the process whereby cancer cells leave the original tumour site and spread to other parts of the body through the bloodstream or lymphatic system.
what is angiogenesis?
its the process were a tumour is entirely dependent on its ability to induce the growth of new blood vessels from the existing vasculature.
Describe the contrast-enhanced in Dynamic contrast-enhanced MRI?
Contrast agent is injected through a peripheral vein.
It is typically injected as a bolus injection; i.e. large dose in short time
To ensure consistent injection automatic pressure injectors are typically used.
Chaser injection of normal saline (20-30ml) is given immediately after and at the same rate of injection
How is dynamic MR imaging is usually performed?
After initial anatomical and localisation scans (T1 and T2 weighted images). Then Additional scans may be performed to support subsequent pharmacokinetic analysis of the contrast agent concentration.
(The choice , is entirely dependent on the analysis method to be performed.
what parameters for image acquirement are entirely dependent on the analysis method?
injeandction rate, temporal resolution aso limage acquisition technique
Dynamic MR acquisition techniques
what are the Two generic approaches? and what are they called?
1. Relaxivity-based methods: T1-weighted sequences;
1. Dynamic relaxivity contrast-enhanced MRI (DCE-MRI); and
2. Susceptibility-based methods: T2 or T2*-based sequences.
2. Dynamic susceptibility contrast-enhanced MRI (DSC-MRI).
whats the properties of Gadolinium-containing contrast media? (4)
- Shortens T1, T2 and T2*.
-T1- and T2-shortening are "short-range" phenomena.
-T2*-shortening is a "field effect" extending mm beyond the physical location of the contrast agent.
-Molecules are too large to enter tissue cells but can exit the vasculature into the extravascular extracellular space.
why is DSC-MRI used?
to assess perfusion in the brain (investigation of stroke and brain tumours)
Why is DSC-MRI is more sensitive to small amounts of contrast over a large tissue volume?
it is due to an extended effect of thus affects of water molecules outside the blood vessels for some distance.
what is DCE-MRI used for?
breast cancer, prostate cancer, liver cancer, cerebral tumours.
how does the Relaxivity contrast mechanism work for DCE-MRI
is strongly localised to the contrast molecule itself, its therfor only seen in the immediate vicinity of the agent.
what is the aim of Modelling contrast enhancement?
is to reduce the dimensionality of the voxel time series, to mitigate noise, and possibly to get physiologically meaningful parameters.
what is the Two classes of parametric models?
1. pharmacokinetic (PK)
2. empirical (EP).
PK models seek to measure physiologically meaningful
EP models seek to measure the shape of the enhancement
what are the problems usin PK-modeling? (4)
Need to estimate CA concentation of blood plasma
Must be fitted using non-linear least squares;
Assumed linearity between concentration and observed intensity
Two different models can yield different estimates of same parameter.
what are the problems usin EP-modeling? (4)
No measured parameters or concentration/intensity assumptions.
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