# Evaluating flow modulating treatment response in intracranial aneurysms using black-blood MRI in vitro

## TL;DR

Black-blood MRI may help assess treatment success in brain aneurysms by detecting reduced blood flow, even when metal implants cause imaging issues.

## Contribution

The study demonstrates that black-blood MRI can detect flow reductions in aneurysms caused by implanted devices, offering a potential alternative to 4D flow MRI in the presence of metal artifacts.

## Key findings

- Black-blood signal increases in treated aneurysms correlate inversely with reduced blood flow velocity.
- Metal artifacts are less pronounced in black-blood MRI compared to 4D flow MRI.
- Flow reductions observed experimentally match numerical simulations.

## Abstract

Changes in blood flow after brain aneurysm treatment are linked to treatment success. While 4D flow magnetic resonance imaging (MRI) can measure these changes, it is sensitive to metal artifacts from implants. Black-blood MRI, less affected by artifacts, may complement 4D flow MRI. We investigated whether changes in black-blood signal reflect reductions in blood flow and could indicate the success of aneurysm treatment.

We performed 22 flow experiments using 3D printed models of two patient-derived brain aneurysms and two straight vessels. Flow-modulating devices, including flow-diverter stents and intrasaccular devices, were inserted into 15 aneurysm models, while untreated models served as controls. All models were imaged with 4D flow and black-blood MRI on a 3 T clinical system. Numerical flow simulations were also performed. Blood flow velocity and black-blood signal were compared between treated and untreated models using non-parametric statistical tests, and their relationship was evaluated with correlation analysis.

Here we show that the black-blood signal in straight vessels decreases with increasing velocity (rho = −0.92, p-value = 3.29E-04). Implanted devices reduce blood flow within aneurysms while leaving flow in the parent vessels essentially unchanged. Treated aneurysms exhibit a significant increase in black-blood signal, which correlates inversely with measured velocity (rho = −0.82, p-value = 6.24E-04). The experimentally observed flow reductions match the numerical simulations. Metal artifacts are more pronounced on 4D flow compared to black-blood MRI.

Black-blood MRI may serve as a surrogate marker of blood flow reduction after aneurysm treatment, particularly in cases where metal artifacts limit conventional imaging.

Brain aneurysms are bulges in blood vessels that can cause life-threatening bleeding if they rupture. Implanted devices such as stents or coils can be used as treatment to reduce blood flow inside the aneurysm and promote healing, but they can also fail to work. Therefore, it is important to monitor flow changes after treatment. We tested an imaging technique called black-blood MRI, using 3D printed aneurysm models with and without implanted devices. The used method showed that areas with reduced blood flow after treatment exhibited a stronger MRI signal, whereas normal vessels remained unaffected. This suggests that black-blood MRI could provide a way to assess treatment success and complement other methods. However, future studies in patients are needed to confirm its usefulness.

Pravdivtseva et al. use 3D-printed models of brain aneurysms to test whether black-blood MRI can show the effects of flow-modulation devices. The black-blood signal increases where blood flow is reduced after device placement, suggesting it could indicate treatment success, even with metal implants.