Introduction to NMR Imaging Techniques

A technique that uses magnetic fields to image the body without ionizing radiation, primarily focusing on the hydrogen atoms and their interactions with the field.

The region around a magnet or a current-carrying wire where magnetic forces can be observed.

Units of magnetic field strength, where 1 Tesla (T) is equivalent to 10,000 Gauss (G).

The property of atomic nuclei with an odd number of protons or neutrons, causing them to spin and generate a magnetic moment.

The intrinsic magnetic dipole moment of a particle, generated by its nuclear spin and related to the gyromagnetic constant. The greater the spin, the stronger the magnetic moment.

The property of atomic nuclei to align themselves in a specific direction when exposed to a magnetic field, creating a measurable signal that MRI utilizes.

A medical imaging technique that utilizes NMR principles to produce detailed images of soft tissues and internal organs, revealing structural and chemical information.

MRI offers clear images of soft tissues by using the principles of NMR, providing insights into body structures unavailable in other techniques like CT or ultrasound.

The alignment of protons in a magnetic field, where most protons align with the field (Mz) and a few are perpendicular to it (Mxy).

A radiofrequency electromagnetic pulse applied perpendicular to the main magnetic field (B0) causing protons to spin in a new direction.

The angle at which the RF pulse tips the magnetization away from the z-axis.

The movement of protons around the magnetic field after being tipped by the RF pulse, generating a signal.

The process where the magnetization returns to its original state (equilibrium) after the RF pulse is removed.

The signal detected from the precessing magnetization, caused by fluctuating magnetic flux.

The signal detected in the time domain as an oscillating, decaying signal from the precessing magnetization.

The magnetic dipole moment of a proton due to its spin within the nucleus. It's directly related to the nuclear spin vector by the gyromagnetic ratio.

The total vector sum of magnetic moments of all nuclei in a sample. In a magnetic field, nuclei align slightly, leading to a net magnetization.

A coil placed around the sample to emit and receive the RF pulse, generating and detecting the NMR signal.

The rotation of a nucleus' magnetic moment around the magnetic field when it's not aligned with the field.

A state where a system oscillates at its natural frequency. This requires energy input at precisely the right frequency, leading to increased amplitude.

The frequency at which a nucleus precesses in a magnetic field. It's directly proportional to the magnetic field strength and the gyromagnetic ratio.

The alignment of the protons in a magnetic field so that their magnetic moments are mostly parallel or anti-parallel to the field.

The frequency at which a nucleus absorbs energy from an electromagnetic field in an NMR setting. It is influenced by the surrounding magnetic environment of the nucleus.

The precise Larmor frequency of a specific proton is determined by its local magnetic field. This effect is influenced by the surrounding electron orbitals, which either shield or deshield the proton.

The effect where electrons around a proton alter the local magnetic field, influencing the proton's resonance frequency. Shielding reduces the resonance frequency, while deshielding increases it.

The time it takes for the longitudinal magnetization (Mz) to recover to 63% of its equilibrium value after a radiofrequency pulse. It is influenced by the surrounding environment of the nucleus.

The time it takes for the transverse magnetization (Mxy) to decay to 37% of its initial value after a radiofrequency pulse. It is also influenced by the surrounding environment of the nucleus.

The rate at which the transverse magnetization (Mxy) decays in a magnetic field, influenced by factors like magnetic field inhomogeneities and magnetic susceptibility effects. Often shorter than T2.

The angle to which the magnetization vector is rotated by the RF pulse, affecting signal intensity by deciding how strongly the RF pulse 'knocks over' the magnetization

The energy required to flip the magnetization vector, influencing signal intensity. Higher frequency requires more energy

Transverse relaxation time (T2) is affected by magnetic field inhomogeneities, leading to a faster decay than expected. T2* accounts for these inhomogeneities, resulting in a shorter relaxation time.

T1, T2, and T2* relaxation times vary depending on the tissue type and magnetic field strength. These variations allow us to differentiate between healthy and diseased tissues.

The flip angle (α) determines the amount of magnetization that is flipped away from the main magnetic field. It's controlled by the pulse duration and strength.

MRI utilizes a sequence of RF pulses and gradient pulses to generate images. This sequence can be customized to highlight different tissue characteristics, such as T1, T2, or T2*.

The Saturation Recovery Sequence is used to measure T1 relaxation time by saturating the magnetization before allowing it regain its alignment.

The Spin-Echo Sequence is used to measure T2 relaxation time by using a 180 degree pulse to refocus the spins. This corrects for magnetic field inhomogeneities.

The Gradient Echo Sequence is used to measure T2* relaxation by using gradient pulses instead of 180 degree pulses. It's sensitive to magnetic field inhomogeneities.

The Inversion Recovery Sequence enhances contrast based on T1 relaxation. It utilizes a 180 degree pulse to invert the magnetization before measuring the recovery time.