Blood pool agents (BPAs) are a class of

magnetic resonance angiography Magnetic resonance angiography (MRA) is a group of techniques based on magnetic resonance imaging (MRI) to image blood vessels. Magnetic resonance angiography is used to generate images of arteries (and less commonly veins) in order to evaluate ...

contrast agents A contrast agent (or contrast medium) is a substance used to increase the contrast of structures or fluids within the body in medical imaging. Contrast agents absorb or alter external electromagnetism or ultrasound, which is different from radiop ...

. Blood pool agents (also known as intravascular contrast agents) are differentiated from other contrast agents due to their high molecular weight and higher relaxivities. Their large size prevents diffusion through the

vascular Vascular can refer to: * blood vessels, the vascular system in animals * vascular tissue Vascular tissue is a complex transporting tissue, formed of more than one cell type, found in vascular plants. The primary components of vascular tissue ...

epithelium Epithelium or epithelial tissue is a thin, continuous, protective layer of cells with little extracellular matrix. An example is the epidermis, the outermost layer of the skin. Epithelial ( mesothelial) tissues line the outer surfaces of man ...

and leakage into the

interstitial space An interstitial space is an intermediate space located between regular-use floors, commonly located in Hospital, hospitals and laboratory-type buildings to allow space for the mechanical systems of the building. By providing this space, laborator ...

, and because of this they stay in the vascular system for a longer time period. Most contrast agents, leave the vascular system within a few minutes, however blood pool agents remain in the circulation for up to an hour, extending the window available for imaging. Longer image acquisition times allow better

signal-to-noise ratio Signal-to-noise ratio (SNR or S/N) is a measure used in science and engineering that compares the level of a desired signal to the level of background noise. SNR is defined as the ratio of signal power to noise power, often expressed in deci ...

and improved image resolution.

Roles of blood pool agents

Due to their extended time in the

circulatory system In vertebrates, the circulatory system is a system of organs that includes the heart, blood vessels, and blood which is circulated throughout the body. It includes the cardiovascular system, or vascular system, that consists of the heart ...

, blood pool agents can be used for delayed steady-state imaging, and additionally these results can be combined with first pass arterial imaging.

Classes of blood pool agents

Albumin-binding gadolinium complexes

This class of BPAs is based on the noncovalent binding of low molecular weight Gd³⁺-based complexes to

human serum albumin Human serum albumin is the serum albumin found in human blood. It is the most abundant protein in human blood plasma; it constitutes about half of serum protein. It is produced in the liver. It is soluble in water, and it is monomeric. Albumin ...

. The first commercial agent to be approved in this class is

gadofosveset trisodium Gadofosveset (trade names Vasovist, Ablavar) is a gadolinium-based MRI contrast agent. It was used as the trisodium salt monohydrate form. It acts as a blood pool agent by binding to human serum albumin. The manufacturer ( Lantheus Medical) disc ...

(also known as Vasovist or Ablavar, and previously known as MS-325). Many clinical and case studies documenting the use of this BPA have been published, and its efficacy in enhancing blood vessels visibility has been demonstrated. The manufacturer (

Lantheus Medical Lantheus, headquartered in Billerica, Massachusetts, is a company in the radiopharmaceuticals business. It has strategic partnerships with Bayer, Novartis, Regeneron as well as GE Healthcare and Siemens Healthineers Siemens Healthineers is a ...

) discontinued production in 2017 though, due to poor sales. Gadocoletic acid (Bracco SpA), also known as B-22956 and B22956/1, is a Gd-DTPA derivative that is currently in development, but has not yet been approved for clinical use. Gadobenic acid (MultiHance) is sometimes categorized as a BPA; however, as it only binds weakly to albumin and because hepatobiliary uptake of this compound occurs, this contrast agent should not be classified as a BPA.

Polymeric gadolinium complexes

Polymeric Gd³⁺ chelates are large in size, which prevents leakage into the interstitial space, and provides long imaging windows. Several polymeric gadolinium-based BPAs are currently in development but have not yet been approved for clinical use: Gadomelitol (Guerbet, France), also known as Vistarem and P792 Gadomer-17 (Schering AG, Berlin, Germany) also known as Gd-DTPA-17, SH L 643 A.

References

{{reflist Contrast agents