59, No. The multiecho spin-echo pulse sequence uses multiple 180° RF pulses to generate multiple echoes (,Fig 22). The gray highlighting shows the differences between this pulse sequence and the basic spin-echo sequence. Looks like you’ve clipped this slide to already. Enter your email address below and we will send you the reset instructions. They are responsible for localizing the “signals” from protons (which are located in the body at different positions) in our images in three dimensions, through the formation of image sections and pixels in those sections. 57, No. If we were to create an image at a time when the transverse magnetization curves were widely separated, then we would have high T2*-weighted contrast between the tissues in our image. The turbo spin-echo pulse sequence can be used to produce T1 and T2 contrast weighting. If the RF pulse rotates the net magnetization into the transverse plane, that is termed a 90° RF pulse. Precession. 17, No. Figure 12. Basics of Magnetic Resonance Imaging John VanMeter, Ph.D. Center for Functional and Molecular Imaging Department of Neurology Georgetown University Medical Center 1. The same thing happens with nuclear precession. After a 90° RF pulse, the longitudinal magnetization is zero. 1863, No. The physics of MRI are complicated and much harder to understand than those underpinning image generation in plain radiography, CT or ultrasound. Now, rather than the spins continuing to dephase, the spins will begin to rephase. 5, Biochimica et Biophysica Acta (BBA) - Molecular Basis of Disease, Vol. Figure 25. 57, No. This type of contrast mechanism is termed T1-weighted contrast. The gyromagnetic ratio is a constant; however, owing to hardware limitations, the main magnetic field is not perfectly homogeneous across the imaging volume. Nuclear magnetic resonance (NMR) continues to be the term of choice in the physical sciences. After a 90° RF pulse, dephasing of the transverse magnetization (T2 decay) occurs while the longitudinal magnetization grows back parallel to the main magnetic field. Kipling’s honest serving men