Contrast enhancement agents and radiopharmaceuticals
A Stewart Whitley, Jan Dodgeon, Angela Meadows, Jane Cullingworth, Ken Holmes, Marcus Jackson, Graham Hoadley, Randeep Kumar Kulshrestha in Clark’s Procedures in Diagnostic Imaging: A System-Based Approach, 2020
Paramagnetic contrast agents contain magnetic centres that create magnetic fields that are approximately 1,000 times stronger than those corresponding to water protons. They interact with the water protons in exactly the same way as they do the neighbouring protons but with stronger magnetic fields and have a greater impact on relaxation rates. Gadolinium is a chemical element that is silvery-white, malleable and a rare-earth metal. In the periodic table it is labelled as symbol Gd with an atomic number of 64. It is a mined material and only found in its combined salt form. The gadolinium ion occurring in water-soluble salts can be relatively toxic to humans in an unchelated form; however, chelated gadolinium compounds are far less toxic because they are excreted from the body via the kidneys before the free ion can be released into tissue. When considering the binding of gadolinium to the chelates, reference should always be made to the thermodynamic stability of the compound. The lower the stability factor the weaker the bonds of the chelate are, and thus a higher risk of possible free gadolinium.
Optical Nanoprobes for Diagnosis
D. Sakthi Kumar, Aswathy Ravindran Girija in Bionanotechnology in Cancer, 2023
Paramagnetic gadolinium complexes are often used as clinical contrast agents. Gadolinium (Gd) is a metal with large magnetic moment due to seven unpaired electrons in its 4f orbital. The magnetic dipoles of these electrons interact with neighboring nuclear dipoles. The interaction instigates the nuclear dipoles to align more quickly in the presence of an external magnetic field. The proton relaxation enhancement, in addition to the slow electron relaxation time, marks Gd as a promising agent for MR enhancement. Gd has the largest T1-relxation enhancement effect of all the known elements [277]. Gd chelates have played a significant role in MR imaging in the past two decades. However, the efficiency of Gd chelates is low in terms of the detection of molecular events. Therefore, new MR contrast agents with Gd and LDH are being developed for molecular imaging purposes.
Diagnostic imaging
Professor Sir Norman Williams, Professor P. Ronan O’Connell, Professor Andrew W. McCaskie in Bailey & Love's Short Practice of Surgery, 2018
Concerns about lactic acidosis in patients on metformin receiving contrast led to various recommendations for stopping the metformin. The latest RCR recommendations are that it can be continued in patients with normal renal function. If there is a raised creatinine or reduced estimated glomerular filtration rate (eGFR) below 60 then any decision to stop metformin should be made with the radiologist and the physician managing the patient’s diabetes. Gadolinium- containing contrast agents are used in MRI examinations. Allergic reactions to these agents are very rare. However, they can be nephrotoxic in patients with renal failure. In addition, they are associated with a risk of nephrogenic systemic fibrosis (NSF), an extremely rare but serious life-threatening condition whereby connective tissue forms in the skin causing it to become coarse and hard. NSF may also affect other organs, including joints, muscle, liver and heart. High-risk gadolinium-containing contrast agents are contraindicated in severe renal failure, in neonates and in the perioperative period of liver transplantation, and are not recommended in pregnancy. However, lower-risk gadolinium preparations are available that may be used with caution.
Gadolinium-based contrast agents – what is the evidence for ‘gadolinium deposition disease’ and the use of chelation therapy?
Published in Clinical Toxicology, 2020
Kerry A. Layne, David M. Wood, Paul I. Dargan
Gadolinium is a rare-earth metal that has been used as a contrast agent for magnetic resonance imaging (MRI) scans since the late 1980s. It is bonded with either linear or macrocyclic ligands to form gadolinium chelates that are used as gadolinium-based contrast agents during MRI [1]. Macrocyclic chelates form stronger bonds with gadolinium ions, and therefore the gadolinium is less likely to dissociate from the gadolinium-based contrast agent complex compared with linear chelates [1–3]. Gadolinium-based contrast agents are an essential tool in MRI diagnostics and, until recently, had been generally considered to have an excellent safety profile, aside from the risk of nephrogenic systemic fibrosis in those patients with end-stage renal failure and very infrequent cases of acute neurotoxicity [4–6].
Acute Necrotizing Encephalopathy Associated with Influenza A
Published in The Neurodiagnostic Journal, 2020
Neuroimaging features of ANE are characterized by bilateral symmetrical lesions of high intensity on both TI and T2 weighted images in the areas of the thalami, frequently with accompanying lesions in the brain stem tegmentum, periventricular white matter, putamina, and cerebellum (Mizuguchi et al. 1995; Wong et al. 2006). An MRI was performed with and without contrast administration using 1 mL of gadolinium. Imaging found nearly confluent T2 hyperintense signal and restricted diffusion within bilateral centrum semiovale, bilateral thalami, the pontine tegmentum, cerebellar vermis and the deep cerebellar hemispheres bilaterally with also susceptibility artifact within bilateral thalami and the pontine tegmen. These results were consistent with either the sequela of acute hemorrhagic or encephalitis or severe anoxic injury.
Post-traumatic glomus tumor of the left anterior supraclavicular nerve: a case report
Published in Neurological Research, 2023
Alessandra Turrini, Guido Staffa, Giulio Rossi, Crescenzo Capone
Among the various diagnostic investigations, MRI with intravenous Gadolinium is the one that provides the most information and is useful for preoperative planning, especially of deep tumors. Performed on more than half of patients with peripheral nerve GTs, MRI usually showed an enlarged nerve with focal or fusiform contrast enhancement and may detect masses smaller than 2 mm [4,7]. Because of the typical fusiform shape on MRI, we hypothesized that the lesion of our patient was most likely a neuroma, as the consequence of injury caused to the cervical plexus nerves following the trauma. Peripheral nerve GTs should therefore be included in differential diagnosis not only with other peripheral nerve tumors but also with non-cancerous growths of nerve tissue such as neuroma [4,16,26]. Although clinical history and imaging may address one diagnostic suspicion rather than another, only histological examination provides a definitive diagnosis. Hence, surgical management remains the best option. At surgery, peripheral nerve GTs may present as intraneural well-circumscribed lesions [1,18], or diffuse intraneural tumors, requiring the resection of the concerned fascicles or even of the whole nerve [3,4,7,12,22,24]. Complete resection leads to the total resolution of painful symptoms and confirms that surgery is the treatment of choice [10].
Related Knowledge Centers
- Chelation
- Chromium
- Organic Chemistry
- Oxygen
- Kidney
- Nickel
- Redox
- Neutron Imaging
- Coordination Complex
- Intravenous Therapy