MRI Biomarkers Flashcards
What are MRI biomarkers?
A biomarker used to detect or confirm the presence of a disease or condition of interest or to identify individuals with a subtype of the disease
What range of biological tissue properties can be interrogated with MRI-based imaging biomarkers?
Tissue microstructure
Metabolism
Composition
Function
Morphology
What is quantitative MRI?
Aims to provide quantitative calibrated measures in physical units of specific MRI parameters
It provides specific physical parameters related to the nuclear spin of protons in water, such as relaxation time
What is a disadvantage of quantitative MRI?
You have to do many scans and modulate the imaging parameters each time you repeat a scan
Also need to apply more complicated analysis as there is more data
This means it take much longer
What is a pitfull of quantitative MRI?
The scans take a long time to acquire but need to consider the amount of time the patient is in the scanner
However, if we limit the imaging time then the scan’s accuracy decreases
Need to find a good tradeoff between scanning time and accuracy of the scan
How do we decide the tradeoff between timing and accuracy?
Depends on what you are scanning for
In the early stages of MS, the white matter lesions are very small and therefore, if you are trying to diagnose MS, a very accurate scan will be needed to be able to detect these lesions - longer scan time is crucial
On the other hand, if you are looking for brain metastases in cancer, you don’t need to have high accuracy to be able to locate abnormalities but it is more important to scan the entire brain so you do not miss any abnormalities - less scan time but greater field of view
How can quantification be utilised in MRI biomarkers?
Quantification alone is not enough to be able to identify any abnormalities
If we know how a certain disease effects T1 times of each type of tissue then we can compare these T1 times to our quantified T1 times of the patient
From this, comparisons between the scans will allow you to diagnose abnormalities
How are MRI biomarkers applied in acute stroke?
For treatment selection
Carry out a diffusion weighted scan as well as a perfusion weighted scan
Perfusion shows us the area that is in danger of being damaged from a stroke
Diffusion shows us what area is already damaged from the stroke
Can then compare the two measurements to create a ratio which will inform treatment selection
What else can MRI biomarkers be used to assess?
To assess treatment response e.g., a radiotherapy follow-up to assess if the treatment has reduced tumours
Compare a scan at 3 months to 6 months
What are the characteristics of qualitative MRI?
Different scanners produce different images of the same anatomy
Only image contrast (not intensity) can be
meaningfully interpreted.
The vast majority of all MRI’s taken in clinical
practice
What are the characteristics of quantitative MRI?
Produces the same results on any scanner anywhere in the world
Image intensity is physically meaningful (has
units).
Requires additional scans (scan time!) and more
complex analysis.
Trade-off between scan time and accuracy
What are the characteristics of MRI biomarkers?
Quantitative MRI with a known link to biology
Can be used to study biology & disease
Can be used to inform patient management.
Must be accurate & cost effective.
Why are MRI biomarkers so important?
There is a gap in the diagnostic spectrum
We can test blood or urine which gives us a good idea of infection and disease
We can also test other factors such as blood pressure
We have ultrasounds but they do not give detailed pictures
Consequently, MRI biomarkers are needed to directly assess the structures which have disease
Why are biomarkers better than assessing biofluids?
Biofluids contain markers from all over the body and therefore you need to filter out a lot of information to focus on the specific structure you want to assess
Very diluted
MRI biomarkers are a direct measure of the tissue of interest
MRI not confounded by changes outside of target organ
How can MRI biomarkers be compared to biopsies?
Biopsies come with a high level of risk
You only receive a tiny bit of tissue from a biopsy - if you take the wrong part of tissue, you could be under or over estimating the degree of cancer (sampling error)
You don’t observe the tissue in it’s active state - no blood vessels and then squashed between slides - so not the same as what you would observe in the body
MRI is non invasive and does not disturb the tissue state
