Clinical MR Imaging and Physics: A Tutorial
Keywords Spin › Electromagnetic radiation › Resonance › Nucleus › Hydrogen › Proton › Certain atomic nuclei possess inherent magnetic Let us summarize the MRI procedure. Te patient properties called spin, and can interact with electro- is placed in a magnetic feld and becomes temporarily 1 magnetic (EM) radiation through a process called magnetized. Resonance is achieved through the - resonance. When such nuclei absorb EM energy they plication of specifc pulses of EM radiation, which is proceed to an excited, unstable confguration. Upon absorbed by the patient. Subsequently, the excess - return to equilibrium, the excess energy is released, ergy is liberated and measured. Te captured signal producing the MR signal. Tese processes are not is processed by a computer and converted to a gray random, but obey predefned rules. scale (MR) image. Te simplest nucleus is that of hydrogen (H), con- Why do we need to place the patient in a m- sisting of only one particle, a proton. Because of its net? Because the earth’s magnetic feld is too weak to abundance in humans and its strong MR signal, H be clinically useful; it varies from 0. 3–0. 7 Gauss (G). is the most useful nucleus for clinical MRI. Tus, foC r urrent clinical MR systems operate at low, mid or our purposes, MRI refers to MRI of hydrogen, and for h igh feld strength ranging from 0. 1 to 3.
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Fast or Turbo Spin Echo Imaging
Selective Fat Suppression
Chemical Shift Imaging
Magnetization Transfer Contrast
Magnetic Substrates of T2 Relaxation
Proton Spin Density Contrast
Free Induction Decay
Integration of T1 T2 and Proton Density Phenomena
Image Formation Fourier Transform Gradients
Gradient Echo Imaging
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abnormality acquisition amplitude artifact Axial a T2w axis black arrows brain carotid chemical shift clinical component contrast administration contrast enhancement coronal cyst dephasing Diagnosis diffusion dipoles echo imaging edema fatty FLAIR flip angle flow fluid Free induction decay gadolinium gradient echo hemorrhage hyperintensity inflow inversion recovery isointense Keywords Larmor equation Larmor frequency lesion lobe longitudinal magnetization Longitudinal relaxation macroscopic magnetic field magnetization vector mass motion MT pulses multiple normal parenchyma patient phase encoding phase shifts pixel post-contrast T1w posterior posterior horn proton density protons pulse sequences relaxation rate RF pulse rotate Sagittal saturation scan Selective fat suppression slice solid spatial resolution spin density spin echo spine STIR T1 curve T1 rates T2 relaxation T2w TSE thickness thin tion tissue contrast TR cycle TR/TE transverse magnetization tumors vascular VENC voxel white arrows white matter xy plane z-axis