Abstract
Brain vasculature is conventionally represented as straight cylinders when simulating blood oxygenation level dependent (BOLD) contrast effects in functional magnetic resonance imaging (fMRI). In reality, the vasculature is more complicated with branching and coiling especially in tumors. Diffusion and susceptibility changes can also introduce variations in the relaxation mechanisms within tumors. This study introduces a simple cylinder fork model (CFM) and investigates the effects of vessel topology, diffusion, and susceptibility on the transverse relaxation rates R2* and R2. Simulations using Monte Carlo methods were performed to quantify R2* and R2 by manipulating the CFM at different orientations, bifurcation angles, and rotation angles. Other parameters of the CFM were chosen based on physiologically relevant values: vessel diameters (~2‒10 µm), diffusion rates (1 × 10−11‒1 × 10−9 m2/s), and susceptibility values (3 × 10−8–4 × 10−7 cgs units). R2* and R2 measurements showed a significant dependence on the bifurcation and rotation angles in several scenarios using different vessel diameters, orientations, diffusion rates, and susceptibility values. The angular dependence of R2* and R2 using the CFM could potentially be exploited as a tool to differentiate between normal and tumor vessels. The CFM can also serve as the elementary building block to simulate a capillary network reflecting realistic topological features.
Highlights
Ter τD = 0.01 s: this is indicative of the fact that R2 lies within the ELR
Of 1 × 10−9 m2/s was chosen based on the typical value reported for the cerebral cortex[27,28]
The other two lower diffusion rates span the range of expected diffusion rates in tissue[3]
Summary
Ter τD = 0.01 s: this is indicative of the fact that R2 lies within the ELR. These R2* and R2 curves are very similar to Fig. 2 from Boxerman et al.[2] and Fig. 3 from Weisskoff et al.[4] which validates the simulations conducted with the CFM. Thereafter, R2* reaches a plateau while R2 decreases if the echo-time is small compared to τD. This is seen to occur at τD ≈ 10 ms, which agrees with the condition for ELR using our value for τCP = 5
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
