Introducing MRI: Chemical Shift (28 of 56)

www.einstein.yu... - The twenty-eighth chapter of Dr. Michael Lipton's MRI course covers Chemical Shift. Dr. Lipton is associate professor radiology at Albert Einstein College of Medicine and associate director of its Gruss Magnetic Resonance Research Center.

[@MonaLisa-sv7cm]

Thank you Dr. Lipton. Hello from Nepal

[@saeedak2669]

why did the pancreas and the blood in aorta and IVC had increased signal in outphased image comparing to inphased one?

[@alehsudakou1277]

Best explanation! very clear!

[@ksawery6568]

Great lectures, thank you!

[@carcaperu4041]

12:00 Shouldn't it be shifted by two positions (224/100)?

[@Thaifunn1]

yes

[@elmitte]

Shouldn't the frequency encoding direction be opposite of what is depicted during 9'-17'' ? [given fat spinning slower than water, it will be misregistered in lower frequency (shifted the opposite direction to the frequency encoding). In a left to right frequency encoding we will have higher gradient (and hence higher frequencies) on the right side]

[@connorgemmell5789]

Yes, in his diagram of the water/olive oil example he misdrew the chem shift in the opposite direction. Fat signal should be shifted against the frequency encoding direction, so really what should happen in that diagram is a bright stripe on the rightward border of the water, and a dark stripe on the rightward border of the oil. Similarly, in his example image of the psoas muscles, the frequency encoding direction is in the opposite direction of how he labelled the images. We see fat signal is shifted to the right on the image (patient's left), which means the frequency encoding gradient is from right-to-left on the image (or, left-to-right for the patient).

[@Narender0singh]

thanks man, i wasted 15 minutes because of that

[@lester_ernesto]

Great explanation !! BTW, does anyone knows what the actual Bandwidths are in the example prof. Lipton presents in minute 24:00? (H.D shoulder comparison imaging) The slide was cut short in the lower part. Thanks

[@spdn]

no idea. I thought it is labeled wrong, the left should be "WFS = 3 pixels = 1.5mm" instead. also the conclusion at 24:20 should be "higher bandwith is both giving us a decrease in signal-to-noise as well as decreasing the amount of chemical shift effects"

[@connorgemmell5789]

The numbers appear to be BW of 57 kHz in the right image, and about 19 kHz (19.3 I believe) in the left image. If we divide 57 kHz into a 256-pixel width in the frequency-encoding direction, that means each pixel is 57 kHz / 256 = 222 Hz wide. Given a chem shift of 224 Hz at 1.5T, that results in a chem shift spatially of almost exactly one pixel, just as is reported. Conversely, with a 19 kHz bandwidth, each pixel is 19 kHZ / 256 = 74 Hz wide, so a 224 Hz shift translates to 3 pixels spatially. Also, I agree with spdn. The left image should be labelled WFS of 3 pixels, 1.5mm. And he misspoke at 24:20, the higher bandwidth in the right image results in a tradeoff, decreased chem shift effect but reduced SNR.

[@shekharkalia5856]

AMAZING!

[@juancalle9213]

Great!!

[@amitkumaryadav9228]

i was searching so hard for someone to explain chemical shift and india ink artefacts. this lecture made it sound so easy. cleared all my doubts. Thank you so much...

[@praveenr5403]

thanks for the wonderful explanations