Clinical applications of magnetic resonance imaging—February 4, 1994

Clinical applications of magnetic resonance imaging—February 4, 1994

Magnetic resonance imaging (MRI) not only displays abnormal signals in solid organs, but also exhibits a special flow void effect. This flow void effect is superior to CT in showing vascular malformations, blood turbulence caused by intracavitary masses, as well as thrombi and calcifications, giving people the feeling of combining angiography and CT scanning into one. ① Flow void effect: The key factor in generating this phenomenon is flow velocity—if the flow is slow, or if protons excited by the magnetic field return along the veins to the signal acquisition area, it can manifest as a strong signal in the vascular structure. ② Changes in hematomas: Over time, hematomas that flow out of blood vessels appear differently in MRI.

a. Within one week (acute): The center of the hematoma appears as a low signal.

b. 1–4 weeks (subacute): The periphery of the hematoma is stronger than the center.

c. After one month (chronic): Low-signal areas appear in the surrounding tissues of the hematoma. In addition, MRI can also display infarcts, calcifications, edema, thrombi, and hemorrhages.