Short name: Fe O-BPA, central moiety: Fe3+/Fe2+
An ultrasmall superparamagnetic iron oxide under development (preclin.) as a vascular contrast agent for MR angiography.

See also USPIO.

Flow phenomena are intrinsic processes in the human body. Organs like the heart, the brain or the kidneys need large amounts of blood and the blood flow varies depending on their degree of activity. Magnetic resonance imaging has a high sensitivity to flow and offers accurate, reproducible, and noninvasive methods for the quantification of flow. MRI flow measurements yield information of blood supply of of various vessels and tissues as well as cerebro spinal fluid movement.
Flow can be measured and visualized with different pulse sequences (e.g. phase contrast sequence, cine sequence, time of flight angiography) or contrast enhanced MRI methods (e.g. perfusion imaging, arterial spin labeling).
The blood volume per time (flow) is measured in: cm3/s or ml/min. The blood flow-velocity decreases gradually dependent on the vessel diameter, from approximately 50 cm per second in arteries with a diameter of around 6 mm like the carotids, to 0.3 cm per second in the small arterioles.

Different flow types in human body:
See also Flow Effects, Flow Artifact, Flow Quantification, Flow Related Enhancement, Flow Encoding, Flow Void, Cerebro Spinal Fluid Pulsation Artifact, Cardiovascular Imaging and Cardiac MRI.

Motion of material being imaged, particularly flowing blood, can result in many possible effects in the images.
Fast moving blood produces flow voids, blood flowing in to the outer slices of an imaging volume produces high signals (flow related enhancement, entry slice phenomenon), pulsatile flow creates ghost images of the vessel extending across the image in the phase encoding direction (image misregistration).
Flow-related dephasing occurring when spin isochromats are moving with different velocities in an external gradient field G so that they acquire different phases. When these phases vary by more then 180° within a voxel, substantial spin dephasing results leading to considerable intravascular signal loss.
These effects can be understood as caused by time of flight effects (washout or washin due to motion of nuclei between two consecutive spatially selective RF excitations, repeated in times on the order of, or shorter than the relaxation times of blood) or phase shifts (delay between phase encoding and frequency encoding) that can be acquired by excited spins moving along magnetic field gradients.
The inconsistency of the signal resulting from pulsatile flow can lead to artifacts in the image. The flow effects can also be exploited for MR angiography or flow measurements.

See also Flow Artifact.

Short name: (Gd-DTPA)-17, 24 cascade polymer, generic name: Gadomer-17, 24, central moiety: Gd2+, relaxivity: r1=11.9, B0=1.0 T, r2=16.5, Dose: 0.05 mmol/kg
An intravascular macromolecular MRI contrast agent with positive enhancement under development (Bayer Schering Pharma AG) for MR angiography and tumor differentiation. The synthetic dendrimer with large molecular weight (17kD - limits agent to vascular space) is linked to Gadolinium. The renal excretion is slowed to intermediate molecular size. In MRA a longer lasting venous and arterial enhancement was seen with Gadomer-17 due to the particular pharmacokinetics of this agent.

See also Tumor Specific Agents, and Intravascular Contrast Agents.

Gadovist® is an extracellular, neutral macrocyclic (gadolinium (Gd) complex) MRI contrast agents for central nervous system indications, particularly suited for studies in which high doses are required or advantageous. Gadovist® (also Gadograf) was available in two concentrations, currently only Gadovist® 1.0 is marketed.
The product was approved in Switzerland in 1999 and in Germany in 2000. Gadovist® 1.0 is in USA currently in the drug development and approval process, particularly for magnetic resonance angiography.

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 also Paramagnetic Contrast Agents and Gadobutrol.