Magnitude, real and phase images

Not all clinical MR images are created equal.*

After the using the Fourier transform to transform our measured k-space data into image space, the image data is of complex type. This image data is then manipulated for different clinical utility. For example, a magnitude image is used to maximise the signal-to-noise ratio (SNR). Phase images are used to measure flow. Let’s look at how our MR signal is recorded and how these image types are calculated.

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Spatial and precessional frequencies

Here’s a top tip for any student of MRI physics: never say a sentence about “frequencies” without specifying what type of frequencies you mean. So “frequency relates to position” is not allowed.

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Off-resonance effects

Whilst learning MRI theory I occasionally came across statements which, whilst describing sources of error in MRI images, ended with

“…and other off-resonance effects.”

It turns out, off-resonance effects are not a black art or higher plane of MR knowledge after all. Here’s a quick recap. What are off-resonance effects? Continue Reading »

Teaching MRI: Spin echo first?

Most students find that learning the basic physics of MRI is challenging. Even now I notice certain aspects of MRI theory which I thought I understood, but then I find out that my understanding is inadequate. (The latest of which can be read elsewhere on ReviseMRI.com.) A confusion which occurred in my mind when I first learned basic MRI physics was misunderstanding of the spin echo pulse sequence vs. the gradient echo pulse sequence.

Perhaps one way we can help students to understand MRI pulse sequences is to teach gradient echo before we introduce spin echo. Continue Reading »

Post-it notes in formative assessment

At a workshop on teaching and learning in large groups, guru Phil Race suggested (and used) Post It™ note pads as a way to encourage formative assessment when teaching in large groups. In my initial experience, it can work well. Continue Reading »