Josh-D. S. Davis

Xaminmo / Omnimax / Max Omni / Mad Scientist / Midnight Shadow / Radiation Master

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Things I rediscovered that are interesting
Josh 2004 Happy
Things I rediscovered that are interesting:
1) When you burn a gram of glycogen from your muscles, you also lose 2-4 grams of water that was part of the glycogen matrix. Also, Glycogen is almost exactly the same as starch in plants. Pectin and amylopectin - trees of glucose molecules, bound together.

2) While a gram of fat contains 9 kcalories, it's a gram of pure fat. Animal fat is about 13-15% water (including humans). So that's why the math of 3500 kcalories in a pound of body fat comes out to 7.7 kcal per gram.

3) STIR MRI sequences are really interesting. They use an inverse field for the 180 degree plane, leading to nice, high contrast images (T1 and T2 echo contrasts are additive). Since the signal passes through null before swinging positive, they can add a delay corresponding to the type of tissue they want to be invisible (aka 160-180ms to make fat invisible). This helps the clarity. On the flip side, there is a little more noise, and some of the T2 weighted details get clobbered (ie, disc jelly, and other watery things). Also, the higher energy in the 180 pulse causes increased tissue heating. (I felt this during my STIR sequence as 10-15 degrees of warming on my forearms.)

4) It seems that the most detail on a spinal MRI is found in the T2 weighted images. This means a longer delay for picking up the echoes. This means some of the brighter echoes have already passed, allowing the visualization of lower-signal tissues. The drawback is lower contrast, since some of the faster echo signals have decayed substantially. This is the only image type that shows the disc jelly that has extruded past the bulged disc edge. The jelly shows as very dark, almost black, because it has very high water content.


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