MRI settings
Jessie Z -
Hello everyone,
For this blog post, I will be going over the basics of how MRI can help radiologists diagnose numerous conditions. First, it’s important to understand different MRI sequences (also referred to as settings). These settings can affect the type of information obtained, the contrast of tissues, and the overall scan time. Metaphorically speaking, MRI settings function like guitar clips. Different placements of a guitar clip will change the key of the music. Likewise, different timings of radiofrequency pulses will present the tissue in various forms.
The most common MRI sequences are T1-weighted and T2-weighted scans. T1 and T2 weighted MRI images show different tissue characteristics due to variations in how tissues relax in the magnetic field. T1-weighted images are determined by the rate at which excited protons return to their equilibrium state. They are more sensitive to differences in T1 relaxation times, often making fat appear bright (hyperintense) and fluid appear dark (hypointense). Conversely, T2-weighted images are determined by the rate at which excited protons lose phase coherence due to interactions with surroundings. They are more sensitive to T2 relaxation times, often making fluid appear bright and fat appear darker.When describing most MRI sequences, they refer to the shade of grey of tissues or fluid with the word intensity, leading to the following absolute terms:
- high signal intensity = white
- intermediate signal intensity = grey
- low signal intensity = black
Often they refer to the appearance by relative terms:
- hyperintense = brighter than the thing we are comparing it to
- isointense = same brightness as the thing we are comparing it to
- hypointense = darker than the thing we are comparing it to
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