Xrayfund
7/15/99
- larmor equation
- ¦
= larmor frequency
- g
/2p
= gyromagnetic ratio—known for every polar proton
- B°
= magnetic field in Tesla
- Hydrogen spins about 1million times per se w/1Tesla magnet
- H is the most abundant polar proton in our bodies
- Easiest to make pictures out of
- Could use others but would take stronger magnets
- Government allows for 1Tesla magnetics easily, stronger ones heat up tissues and not sure of long range affects
- When the radiowave is turned off the excess energy stored in the protons is given back in the form of another radiowave
- This results in a free induction decay (FID)
- Tranverse decreases over time
- Longitudinal increases over time
- Be able to know if T1 or T2 image—rate of relaxation of H protons
- Compact (cortical) bone generates low signal on all pulse sequences (not much H, looks black b/c no signal emitted)
- Free water is dark on T1 and bright on T2 (in bladder, nucleus pulposus of disc and CSF)
- Fat is bright on T1 and T2 (subcutaneous)
- Should do both T1 and T2 scan
- Imaging parameters noted on film
- TR—time to repetition
- TE—time to echo—how long to expose
- NEX—number of excitations—double time every time increase NEX by 1
- FOV—field of view—how much anatomy are we going to display
- Slice thickness
- T1 displays anatomy well
- T2 displays volumes of water (nucleus polposis, CSF)
- An image that is not T1 or T2 weighted is a spin density image
- Contradindications
- Cochlear implants
- Pacemakers
- Shrapnel
- Some sheet metal workers
- Some vascular clips
- Tatooed eyeliner
- Pregnancy
- IVC umbrella filter, Gianturco coil (embolus coil)
- Artificial heart valves
- Hearing aid