Ischemic stroke: MRI, the "superhero" that reveals the secrets of the brain

Author: Jia Wenxin Pingliang Second People's Hospital

Reviewer: Li Zuojin, deputy chief physician of Pingliang Second People's Hospital

Wu Xiaolian, Chief Physician, Pingliang Second People's Hospital

Imagine that the brain is like a busy city, relying on countless densely interwoven "road networks" to maintain operation. When a "road" is suddenly blocked somewhere, it is like a traffic jam. This is what we often call ischemic stroke, or cerebral infarction. At this time, a technology called magnetic resonance imaging (MRI) comes on the scene. It can reveal the location of the lesion in a timely manner like a superhero, and even help doctors make the best treatment strategy.

1. Diffusion Weighted Imaging: Catching Invisible Enemies

Diffusion-weighted imaging (DWI) is a special technique of MRI that mainly relies on the movement of water molecules for imaging. DWI can be called the eagle eye of modern medical technology. It can detect the diffusion disorder of water molecules caused by cytotoxic edema within minutes or even hours after the onset of ischemic stroke. The high sensitivity of this technology makes it a frontier sentinel for identifying hyperacute cerebral infarction, and it can provide insight into the threat to brain tissue even in the hidden stage before symptoms appear. On the DWI image, the core of the infarction appears as a bright signal area, like a beacon illuminating the night, pointing to the urgent direction of treatment. At the same time, the application of the ADC ratio provides a deeper analysis for determining the boundaries and characteristics of the infarct area by accurately measuring the degree of restricted diffusion of water molecules. This technology is particularly good at capturing the moment when cerebral infarction just sprouts, winning golden time for rescue.

Figure 1 Water molecule diffusion (copyright image, no permission to reprint)

2. Brain perfusion imaging: detecting signs of life

Perfusion imaging (PWI) is the detective in the MRI family. This warrior focuses on the blood microcirculation in the brain and determines the state of the ischemic penumbra by revealing the blood flow velocity and quantitative changes. PWI measures the margin of life like a precise ruler by presenting a series of parameters such as cerebral blood flow (CBF), cerebral blood volume (CBV), mean transit time (MTT) and time to peak (TTP). This technology can not only help identify brain tissues with a higher probability of survival, but also provide precise targeting coordinates for thrombolytic therapy, so that each intervention can achieve the maximum effect.

PWI focuses on blood circulation status and is particularly suitable for evaluating blood flow in ischemic areas. It is a good helper in formulating thrombolytic strategies.

Figure 2 PWI image (copyright image is not authorized for reproduction)

3. Magnetic Susceptibility Weighted Imaging: Uncovering Potential Hidden Dangers

Susceptibility-weighted imaging (SWI) is also a special technique of MRI that uses the differences in magnetic sensitivity between different tissues to form unique contrast-enhanced images. SWI is like having a super-strong sensor. With its extraordinary sensitivity, it can detect even tiny hemorrhages and iron deposits, as well as subtle changes in blood vessels. In the context of ischemic stroke, SWI shows a unique field of view that can provide insight into the presence of microbleeds. By enhancing the appearance of venous shadows (VE) and prominent vascular signs (PVS), and monitoring the widened borders of the vascular paramagnetic effect, it reveals the pathological details hidden deep inside, which is particularly critical for assessing the severity of the disease and predicting prognosis.

SWI is sensitive to microbleeds and can clearly show vascular abnormalities, which is crucial for prognosis and finding the cause.

Figure 3 SWI image (copyright image is not authorized for reproduction)

4. Comprehensive application and decision-making

Combining technologies such as DWI, PWI and SWI is like forming a super team. They perform their respective duties and work together to not only quickly locate the lesion, but also assess the extent of damage and guide the best window for thrombolytic therapy. For example, if the areas shown by DWI and PWI images do not match, it means there is still a chance to save some dying brain tissue, and thrombolysis may work a miracle.

In summary, MRI has become a powerful weapon in the fight against ischemic stroke through its diverse and powerful examination methods. It can not only detect danger at the first time, but also assess the degree of damage and guide personalized treatment. The ultimate goal is to save life and function to the greatest extent. In the face of such emergencies, we are no longer at a loss because we have the protection of these "superheroes".

References

【1】Zhu Chen, Deng Caihong, Zhao Hongjian, et al. Study on the clinical significance of susceptibility-weighted imaging and diffusion-weighted imaging in defining the ischemic penumbra in the acute phase of stroke and its comparison with perfusion-weighted imaging[J]. Chinese Journal of Medical Equipment, 2020, 17(09): 64-68.

【2】Sun Qiang, Xu Ying, Wu Di, et al. Predictive value of susceptibility-weighted imaging for early treatment effect in patients with acute ischemic stroke[J]. Journal of Clinical Military Medicine, 2024, 52(03): 318-320.