Injectable contrast agents

Endoscopic retrograde cholangiopancreatography (FRCP) is an important procedure that is used to evaluate and treat diseases of the biliary tree and pancreas. By injecting contrast agents throngh a catheter... 

Radiographers who inject contrast agents must be trained in emergency treatment of severe adverse reactions and basic life support. The most severe adverse reaction is anaphylactic shock. This is treated as an emergency with adrenaline, atropine and oxygen. Antihistamines, aminophylline, salbutamol and corticosteroids may also be necessary. 

Several injectable prolonged release biodegradable microspheres are available as licensed products, e.g. Lupron Depot and Risperdal Consta [18, 19]. The injectable ultrasound contrast agent (Optison ) consists of heat-denaturated albumin microspheres filled with the gas octafluoropropane. In a similar manner sulphur hexafluoride containing microspheres (SonoVue ) are used as injectable contrast agent in echocardiography. 

Biomedical and Biotechnology. The use of mictocapsules for a variety of biomedical and biological appHcations has been promoted for many years (50,51). Several biomedical mictocapsule appHcations ate in clinical use or have approached clinical use. One appHcation is the use of air-fiUed human albumin mictocapsules as ultrasound contrast agents. Such mictocapsules, caUed mictobubbles, ate formed by ultrasonicating 5% albumin solutions to produce 4—10-)J.m diameter air-fiUed capsules (52). When injected the capsules act as a useful transpulmonary echo contrast agent (53) that has been approved for use in humans by the U.S. FDA. 

Limitations are obvious if the diseased tissue does not differ from normal tissue or successfully treated tissue in respect of the above-mentioned criteria. Under these conditions, even a contrast agent with high absorption of X-rays is of no help. Another drawback is the short-lasting contrast which requires repeated injections if the diagnosis is missed during the first scan or if persistent visualization of a lesion is required during an interventional procedure. 

CTP is a relatively recent development in acute stroke imaging that is already in routine clinical use in many centers. CTP and MRP are similar in that both techniques are based on rapid serial image acquisition during intravenous injection of a bolus of contrast material. In both techniques, measurements of density over time (for CTP) or signal intensity over time (for MRP) are converted to contrast agent-versus-time curves, and these are processed in similar ways to yield the same perfusion measurements (most often CBV, CBF, and MTT). Example CTP images are shown in Figure 2.12. 

A possible way to improve differentiation between normal and diseased tissues is the use of non-specific contrast agents which achieve contrast enhancement based on morphological and physiological properties of tumour tissue. Contrast agents for X-ray, CT and MRI are preferentially taken up by tumour tissue shortly after intravenous injection due to increased tumour vasculature, leaky endothelial structures and enlarged extracellular volumes [34], a phenomenon that is in principle exploitable for optical contrast agents. 

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