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