A large network of interconnecting blood vessels at the base of the brain that when visualized resembles a circle, the arteries effectively act as anastomoses for each other. This means that if any one of the communicating arteries becomes blocked, blood can flow from another part of the circle to ensure that blood flow is not compromised.
The circle of Willis is formed by both the internal carotid arteries, entering the brain from each side and the basilar artery, entering posteriorly. The connection of the vertebral arteries forms the basilar artery. The basilar artery divides into the right and left posterior cerebral arteries. The internal carotid arteries trifurcate into the anterior cerebral artery, middle cerebral artery, and posterior communicating artery. The two anterior cerebral arteries are joined together anteriorly by the anterior communicating artery. The posterior communicating arteries join the posterior cerebral arteries, completing the circle of Willis.
The time of flight angiography MRI technique allows imaging of the circle of Willis without the need of a contrast medium (best results with high field MRI). A cerebrovasular contrast enhanced magnetic resonance angiography (MRA) depicts the circle of Willis in addition to the vessels of the neck (carotid and vertebral arteries) with one bolus injection of a contrast agent.

For Ultrasound Imaging (USI) see Cerebrovascular Ultrasonography at Medical-Ultrasound-Imaging.com.

Short name: Code 7228, generic name: Ferumoxytol, central moiety: Fe
Code 7228 is the code name for a substance in the development pipeline (AMAG Pharmaceuticals, Inc.) for use as a contrast agent in magnetic resonance angiography (MRA). Ferumoxytol, as a true blood pool agent, resides in the vascular space for an extended period of time and does not leak out into adjacent tissues like currently used gadolinium-based contrast agents. The product is being evaluated in MRA applications for the detection of blood flow in the heart muscle, in exploratory studies for the diagnosis of vulnerable plaque and as a next generation lymph node agent.
Code 7228 is currently in approval phase for use as an iron replacement therapeutic in chronic kidney disease patients receiving erythropoetin.
It is presently contemplated that Ferumoxytol will compete with the contrast agents Vasovist™ from EPIX Pharmaceuticals, Inc. and NC100150 Injection from Nycomed Amersham.

EP-2104R is a molecularly targeted MRI contrast agent for high resolution blood clot imaging within half an hour of injection. This gadolinium based small peptide has high affinity and specificity for human fibrin.
The thrombus agent is a new class of contrast medium for the diagnostic of, e.g. deep venous thrombosis, carotid artery blood clots, coronary artery blood clots and pulmonary embolism. Fibrin is an excellent target for a molecular imaging contrast agent, since it is present in arterial and venous clots at high concentrations (20-100 μM), and is a target for fibrinolytic therapy.
Due to financial problems, the developer EPIX Pharmaceuticals, Inc. had to shut down all operations. As a consequence, the development of EP-2104R is discontinued.

[This entry is marked for removal.]

(July 20, 2009 - EPIX Pharmaceuticals, Inc. announced today that, in light of the company's lack of capital and inability to obtain additional financing or consummate a strategic transaction, it has entered into an Assignment for the Benefit of Creditors, effective immediately, in accordance with Massachusetts law).
EPIX has been a specialty pharmaceutical firm developing targeted contrast agents to improve the capability of MRI as a diagnostic tool for a variety of diseases. Gadofosveset trisodium (formerly MS-325, Vasovistâ„¢, now ABLAVARtâ„¢), is an injectable intravascular contrast agents designed for multiple vascular imaging applications, including peripheral vascular disease and coronary artery disease. EPIX conducted a pivotal Phase III trial for the detection of peripheral vascular disease, as well as a Phase II feasibility trial for coronary artery disease diagnosis.
To ensure rapid development and adoption of gadofosveset trisodium into clinical practice upon regulatory approval, EPIX pursued an aggressive product development plan and commercialization strategy. The Company established an exclusive, worldwide sales and marketing agreement with Bayer Schering Pharma AG. EPIX also established corporate collaborations with GE Healthcare, Philips Medical Systems and Siemens Medical Systems, the three leading MRI manufacturers, which together account for approximately 80 percent of the MRI machines installed worldwide.
EPIX had other MRI contrast agents under development, most significantly a novel prototype blood clot agent (EP-2104R). Potential clinical applications for this type of agent include detection of deep venous thrombosis, pulmonary embolism and blood clots in the coronary and carotid arteries. Currently, there is no high resolution imaging technique to directly visualize blood clots in patients with suspected cardiovascular disease.

A brand name for ferumoxide (same as Feridex®)
Endoremâ„¢ is a black to reddish-brown aqueous colloid of superparamagnetic iron oxide associated with dextran for intravenous administration as a MRI contrast medium for the detection of liver lesions that are associated with an alteration in the RES.
Endoremâ„¢ is taken up by macrophages, found only in healthy liver cells but not in most tumors. Tissues such as metastases, primary liver cancer, cysts and various benign tumors, adenomas and hyperplasia retain their native signal intensity, so the contrast between normal and abnormal tissue is increased.

See also Ferumoxide.