JHA410H1 Lecture Notes - Lecture 2: Gadolinium, Frontal Lobe, Aging Brain
Document Summary
An rf pulse is emitted by an rf coil which temporarily disrupts the alignment of the hydrogen atoms - typically at. 90 degrees or 180 relatives to the constant. The rf coil also receives the radiowaves emitted by the atoms while returning to realignment with the constant field. The contrast on the mr image can be manipulated by changing the pulse sequence parameters. A pulse sequence sets the: number, strength, and timing of rf pulse. There are 3 key parameters: time to relaxation (tr): time between to pulses, time of echo (te): time between the initial pulse and its echo. The recipe of tr, te, and flip angle lead to the type of image you ultimately view. Detectors in the rf coil recorded the energy emitted by protons responding to the pulse sequence as they begin to return to their original (resting) state (i. e. relaxation time)
