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 t ...

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
/ref> Blood pool agents (also known as intravascular contrast agents) are differentiated from other contrast agents due to their high molecular weight and higher relaxivities.Geraldes CF, Laurent S, Classification and basic properties of contrast agents for magnetic resonance imaging, Contrast Media Mol Imaging, 2009;4:1-23. Their large size prevents diffusion through the

vascular The blood vessels are the components of the circulatory system that transport blood throughout the human body. These vessels transport blood cells, nutrients, and oxygen to the tissues of the body. They also take waste and carbon dioxide away f ...

epithelium Epithelium or epithelial tissue is one of the four basic types of animal tissue, along with connective tissue, muscle tissue and nervous tissue. It is a thin, continuous, protective layer of compactly packed cells with a little intercellul ...

and leakage into the

interstitial space An interstitial space or interstice is a space between structures or objects. In particular, interstitial may refer to: Biology * Interstitial cell tumor * Interstitial cell, any cell that lies between other cells * Interstitial collagenase, ...

, 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 the noise power, often expressed in deci ...

and improved image resolution.

Roles of blood pool agents

Due to their extended time in the

circulatory system The blood circulatory system is a system of organs that includes the heart, blood vessels, and blood which is circulated throughout the entire body of a human or other vertebrate. It includes the cardiovascular system, or vascular system, tha ...

, blood pool agents can be used for delayed steady-state imaging, and additionally these results can be combined with first pass arterial imaging. Their extended circulation time means that they are able to be used for both

arterial An artery (plural arteries) () is a blood vessel in humans and most animals that takes blood away from the heart to one or more parts of the body (tissues, lungs, brain etc.). Most arteries carry oxygenated blood; the two exceptions are the pul ...

and

venous Veins are blood vessels in humans and most other animals that carry blood towards the heart. Most veins carry deoxygenated blood from the tissues back to the heart; exceptions are the pulmonary and umbilical veins, both of which carry oxygenated ...

mapping. Additional uses include: detection of

gastrointestinal bleeding Gastrointestinal bleeding (GI bleed), also called gastrointestinal hemorrhage (GIB), is all forms of bleeding in the gastrointestinal tract, from the mouth to the rectum. When there is significant blood loss over a short time, symptoms may incl ...

; visualization of the vasculature associated with certain tumors; measuring tissue blood volume and perfusion; and detection of endovascular leaks (such as following stent-graft repair of an

aortic aneurysm An aortic aneurysm is an enlargement (dilatation) of the aorta to greater than 1.5 times normal size. They usually cause no symptoms except when ruptured. Occasionally, there may be abdominal, back, or leg pain. The prevalence of abdominal aortic ...

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 (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) 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 Gadobenic acid (INN, brand name Multihance) is a complex of gadolinium with the ligand BOPTA. In the form of the methylglucamine salt meglumine gadobenate ( INNm) or gadobenate dimeglumine (USAN), it is used as a gadolinium-based MRI contrast m ...

(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-17Gadomer-17
(Schering AG, Berlin, Germany) also known as Gd-DTPA-17, SH L 643 A.

References

{{reflist Contrast agents