When a magnetic moment (e.g. hydrogen nuclei) is placed within an external magnetic field (e.g. B0), it begins to oscillate about the direction of the field; this motion is called precession. The frequency of the precession (Larmor frequency) of the nuclide depends on this particular field strength. A higher field strength results in a higher frequency of the precession.

See also Precession.

ProHance® consists of a nonionic gadolinium complex (Gadoteridol) used as a paramagnetic MR contrast agent.
ProHance® provides contrast enhancement of the brain, spine and surrounding tissues resulting in improved visualization (compared with unenhanced MRI) of lesions with abnormal vascularity or those thought to cause a disruption of the normal blood brain barrier. ProHance® can also be used for whole body contrast enhanced MRI including the head, neck, liver, breast, musculoskeletal system and soft tissue pathologies.

WARNING: NEPHROGENIC SYSTEMIC FIBROSIS Gadolinium-based contrast agents increase the risk for nephrogenic systemic fibrosis (NSF) in patients with acute or chronic severe renal insufficiency (glomerular filtration rate less than 30 mL/min/1.73m²), or acute renal insufficiency of any severity due to the hepato-renal syndrome or in the perioperative liver transplantation period.

See Gadoteridol.

The exchange of energy at a particular frequency between two systems; a large amplitude vibration in a mechanical or electrical system caused by a relatively small periodic stimulus with a frequency at or close to a natural frequency of the system.
Resonance is referred to as the property of an atom to absorb energy only at the Larmor frequency. The energy must also be delivered at 90° to the net magnetic vector (NMV) and main magnetic field (B0). Otherwise, no energy will be absorbed, resonance will not have occurred and an image cannot be created. In MRI systems, resonance can refer to the MR itself or to the tuning of the RF circuitry.

A 'Rotating Frame of Reference' is a concept to simplify the complex motions of a magnetization vector. The frame of reference rotates about the axis of the external magnetic field B0 (z-axis) at the Larmor frequency of the applied RF magnetic field B1. In this simplified concept the rotating vector B1 appears stationary.

The T1 relaxation time (also called spin lattice or longitudinal relaxation time), is a biological parameter that is used in MRIs to distinguish between tissue types. This tissue-specific time constant for protons, is a measure of the time taken to realign with the external magnetic field. The T1 constant will indicate how quickly the spinning nuclei will emit their absorbed RF into the surrounding tissue.
As the high-energy nuclei relax and realign, they emit energy which is recorded to provide information about their environment. The realignment with the magnetic field is termed longitudinal relaxation and the time in milliseconds required for a certain percentage of the tissue nuclei to realign is termed 'Time 1' or T1. Starting from zero magnetization in the z direction, the z magnetization will grow after excitation from zero to a value of about 63% of its final value in a time of T1. This is the basic of T1 weighted images.
The T1 time is a contrast determining tissue parameter. Due to the slow molecular motion of fat nuclei, longitudinal relaxation occurs rather rapidly and longitudinal magnetization is regained quickly. The net magnetic vector realigns with B0 leading to a short T1 time for fat.
Water is not as efficient as fat in T1 recovery due to the high mobility of the water molecules. Water nuclei do not give up their energy to the lattice (surrounding tissue) as quickly as fat, and therefore take longer to regain longitudinal magnetization, resulting in a long T1 time.

See also T1 Weighted Image, T1 Relaxation, T2 Weighted Image, and Magnetic Resonance Imaging MRI.