# Ch 1

 What is a mass number? Total number of nucleons in a nucleus Why is mass number important to MRI? Determines weather a nucleus has a net magnetic moment or not. What conditions are necessary for resonance? Energy must be applied at the precessional frequency of the nucleus And at right angles to the main field. What is phase? Position of the magnetic moment at any point in time What is frequency? Number of revolutions per secondOrThe speed of the precession What is the most common atom in the body? Hydrogen Isotopes Atoms of elements with the same number of protons but different number of neutrons Ionization The process of knocking out electrons Angular moment Net spin of a nucleus because of an odd number of protons and neutrons MR Active Nuclei Nuclei with an odd mass number or atomic weight Law of electromagnetic induction (Faraday 1833) Connection between electric and magnetic fields and motion.A moving electric field produces a magnetic field and vise versa Magnetic Moment Each nucleus in a magnetic field has vector properties(Size and direction) MR active Nuclei (list) HydrogenCarbonNitrogenOxygenFluorineSodium Mass number of hydrogen 1 H Mass number of carbon 13 C Mass number of nitrogen 15 N Mass number of oxygen 17 O Mass number of fluorine 19 F Mass number of sodium 23 NA Name the isotope of hydrogen Protium What is the most common MR active nucleus Protium (the isotope of hydrogen) Alignment When placed in a strong static external magnetic field, the magnetic moments of H1 Nuclei orientate with the magnetic field. Parallel Alignment Magnetic moments in the same direction as the main B0 field Spin up is also known as: Parallel Alignment Antiparallel Alignment Magnetic moments in the opposite direction to the main B0 field. Spin-down is also known as: Antiparallel Alignment Net magnetic vector After alignment there are alway more spin-ups than spin-down. Zeeman Interaction Protons of H1 couple with the external magnetic field B0 and cause a discreet number of energy states Low-energy Nuclei Not enough energy to oppose B0 High-energy nuclei Enough energy to oppose B0 What is B0 The large magnetic field of an MRI scanner. How is B0 measured? Tesla (T) Avogadro's Law 6 x 10 (to the 23rd power) molecules per gram of tissue, and the number of excess spins is in the order of 6 x 10(to the 17th power) per gram of tissue. Precession Secondary spin, causes magnetic moments to circle around B0 Precessional Path Course magnetic moments take around B0 Precessional Frequency The speed magnetic moments precess around B0 Larmor Frequency Precessional Frequency. Is determined by the Larmor Equation Unit that precessional Frequency is measured Hertz (Hz) Gyromagnetic ratio Expresses the relationship between angular momentum and the magnetic moments of each MR active nucleus How is gyromagnetic ratio expressed MHz/T What is the gyromagnetic ratio for hydrogen 42.58 MHz/T What is the Larmor Frequency of Hydrogen at 1.5T 63.8646 MH/T Precessional Phase Position of magnetic moments on their precessional Path What is the unit of Phase? Radian Incoherent Out of phase Coherent In phase Resonance Occurs when an object is exposed to an oscillating perturbation that has a frequency close to its own. RF excitation pulse Produced by a transmit coil. How resonance is achieved. How is the RF excitation pulse different from B0 B1 (RF excitation) produces an oscillating magnetic field 90 degrees to B0.Very weak. What axis is the transverse plane on? X - y axis Which axis is the longitudinal plane Z-axis Nutation The spiral motion cause by 2 precessional motions that happened simultaneously. Saturation When spins are unable to absorb more energy or to be stimulated and release more energy Electromotive force (emf) Energy available from a unit of charge traveling once around a loop Authoradavis ID350868 Card SetCh 1 DescriptionMRI in practice ch 1 Updated2020-11-03T23:08:03Z Show Answers