Prog Med Phys.  2022 Dec;33(4):88-100. 10.14316/pmp.2022.33.4.88.

Contribution of Microbleeds on Microvascular Magnetic Resonance Imaging Signal

• Yoo CH
• Goh J
• Jahng GH

• KMID: 2537876
• DOI: http://doi.org/10.14316/pmp.2022.33.4.88

Abstract

Purpose
Cerebral microbleeds are more susceptible than surrounding tissues and have been associated with a variety of neurological and neurodegenerative disorders that are indicative of an underlying vascular pathology. We investigated relaxivity changes and microvascular indices in the presence of microbleeds in an imaging voxel by evaluating those before and after contrast agent injection.
Methods
Monte Carlo simulations were run with a variety of conditions, including different magnetic field strengths (B ₀ ), different echo times, and different contrast agents. ΔR2^* and ΔR2 and microvascular indices were calculated with varying microvascular vessel sizes and microbleed loads.
Results
As B ₀ and the concentration of microbleeds increased, ΔR2^* and ΔR2 increased. ΔR2^* increased, but ΔR2 decreased slightly as the vessel radius increased. When the vessel radius was increased, the vessel size index (VSI) and mean vessel diameter (mVD) increased, and all other microvascular indices except mean vessel density (Q) increased when the concentration of microbleeds was increased.
Conclusions
Because patients with neurodegenerative diseases often have microbleeds in their brains and VSI and mVD increase with increasing microbleeds, microbleeds can be altered microvascular signals in a voxel in the brain of a neurodegenerative disease at 3T magnetic resonance imaging.

Keyword

Brain; Gadolinium-chelated; Microbleed; Microvascular; Magnetic resonance imaging

Figure

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  Fig. 1 Variations of ΔR2* at the echo time of 40 ms (blue line) and ΔR2 at the echo time of 80 ms (red line) with increasing vessel radius. Microbleed concentrations were assumed to be 1.83% (straight line with ○) and 3.81% (dot line with ◁). We also simulated with gadolinium (Gd) and superparamagnetic iron oxide nanoparticle (SPION) contrast agents with the 1.5T, 3.0T, and 7.0T magnetic field strengths. GE, gradient-echo.

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  Fig. 2 Variations of ΔR2* at the echo time of 15 ms (blue line) and ΔR2 at the echo time of 20 ms (red line) with increasing vessel radius. Microbleed concentrations were assumed to be 1.83% (straight line with ○) and 3.81% (dot line with ◁). We also simulated with gadolinium (Gd) and superparamagnetic iron oxide nanoparticle (SPION) contrast agents with the 1.5T, 3.0T, and 7.0T magnetic field strengths. GE, gradient-echo.

• 

  Fig. 3 Variations of ΔR2* at the echo time of 60 ms (blue line) and ΔR2 at the echo time of 100 ms (red line) with increasing vessel radius. Microbleed concentrations were assumed to be 1.83% (straight line with ○) and 3.81% (dot line with ◁). We also simulated with gadolinium (Gd) and superparamagnetic iron oxide nanoparticle (SPION) contrast agents with the 1.5T, 3.0T, and 7.0T magnetic field strengths. GE, gradient-echo.

• 

  Fig. 4 Variations of microvascular indices with increasing vessel radius. These simulations were performed with the echo times of 15 and 20 ms for gradient-echo (GE) and spin-echo (SE), respectively (black line), and 60 and 100 ms for GE and SE, respectively (red line). Microbleed concentrations were assumed to be 1.83% (straight line with ○) and 3.81% (dot line with ◁). mVD, mean vessel diameter; BVF, blood volume fraction; VSI, vessel size index; Q, mean vessel density; MvWI, microvessel-weighted imaging.

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  Fig. 5 Variations of ΔR2* and ΔR2 with increasing microbleed loads for 5-, 15-, and 25-μm microvessel sizes with the echo times of 40 ms for gradient-echo (GE, blue line) and 80 ms for spin-echo (SE, red line). We also simulated with gadolinium (Gd) and superparamagnetic iron oxide nanoparticle (SPION) contrast agents with 3.0T and 7.0T magnetic field strengths.

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  Fig. 6 Variations of ΔR2* and ΔR2 with increasing microbleed loads for 5-, 15-, and 25-μm microvessel sizes with the echo times of 15 and 60 ms for gradient-echo (GE, blue line) and 20 and 100 ms for spin-echo (SE, red line). We also simulated with gadolinium (Gd) and superparamagnetic iron oxide nanoparticle (SPION) contrast agents with 3.0T and 7.0T magnetic field strengths.

• 

  Fig. 7 Variations of microvascular indices with increasing microbleed loads. These simulations were performed with a microvessel size of 5 μm and echo times of 40 and 80 ms for gradient-echo (GE) and spin-echo (SE), respectively. We also simulated with gadolinium (Gd) and superparamagnetic iron oxide nanoparticle (SPION) contrast agents with 3.0T and 7.0T magnetic field strengths. mVD, mean vessel diameter; BVF, blood volume fraction; VSI, vessel size index; Q, mean vessel density; MvWI, microvessel-weighted imaging.

Reference

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