Aims of the Project:
To optimise functional MRI at low field based on T1 contrast which will involve:
- Modelling signal changes during brain activity based on blood and tissue T1s verses field strength to determine optimal imaging pulse sequence approaches
- Improve sequence efficiency using Magnetisation Transfer (MT) preparation
- Experimentally validate expected low-field (0.55T) performance
Functional MRI is an important method to understand brain function and development. For example, it can be used to measure how the brain is functionally connected. Because MRI is non-invasive it can be used to study children and adults, and repeatedly scan, allowing for measurement of developmental changes and disease monitoring. For example, maternal nutrition can affect brain development, and this can be measured with fMRI. However, MRI scanners are expensive and hard to maintain, particularly in the low- and middle-income countries (LMICs) where these types of studies are most needed.
To overcome these barriers to access there has been renewed focus on low-cost and lower-field scanners, including in our school, which now has 0.55T and 0.064T scanners alongside high field (3T) and ultra-high field (7T) systems. At these lower field strengths, the normal approach used for measuring brain activity does not work effectively. Traditional fMRI at 1.5T-7T relies on T2* contrast, but this contrast is reduced at 0.55T (and 0.064T). The slower signal decay (longer T2*) found at lower field strengths also means that scanning becomes slower.
However, T1 contrast can also be used to measure brain activity using the differences in blood and tissue T1 to generate contrast based on blood volume changes. Interestingly, the difference in T1 between blood and tissue may increase at lower field strengths, while both T1s get shorter. This means that at lower field strength the contrast should be increased, while imaging can be made faster. We therefore think that T1-based fMRI might enable fMRI at lower-field; this project aims to test this hypothesis.
In this project we will characterise the potential of T1-based functional MRI using simulations and experimental validation at high and low field strengths, benefiting from the access to the wide range of different scanners available. Having characterised the potential contrast available, we will optimise the image acquisition approach at low field, considering the hardware limitations of low-cost systems. We will also take advantage of the reduced Radio Frequency (RF) power constraints at low field where T1-based contrast can have its efficiency significantly enhanced by the addition of Magnetisation Transfer preparation.