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Advances in and Uses of Contrast Agents for Spectral Photon Counting Computed Tomography
Published in Katsuyuki Taguchi, Ira Blevis, Krzysztof Iniewski, Spectral, Photon Counting Computed Tomography, 2020
Johoon Kim, Pratap C. Naha, Peter B. Noël, David P. Cormode
Small-molecule based iodinated contrast agents are currently the only clinically approved CT contrast agents for intravascular administration. Although there are concerns over renal damage and allergic reactions in subpopulations of patients, the safety of iodinated contrast agents is well-established. In addition, the chemical structures of these iodinated contrast agents can be modified to achieve desired viscosity and osmolarity.49 Despite possible modifications to achieve desired physicochemical properties, the small sizes of these iodinated contrast agents lead to very short circulation times in the blood and rapid extravasation, which in turn leads to a very short time window in which post-injection blood vessel images can be acquired. To resolve this issue, iodine payloads have been formulated into larger dendrimers, emulsions, micelles, and liposomes.50 These nanoparticle-based contrast agents can also be used for targeted molecular CT imaging. Gaikwad et al. recently developed iodinated nanoscale activity-based probes which consist of iodine-loaded spherical nanostructures made of polymeric dendrimers.51 These contrast agents contain short targeting peptides as well as acyloxymethyl ketones to target and covalently bind to cysteine cathepsins that are overexpressed in cancer. These formulations lead to increased tumor accumulation in mice due to active targeting and prolonged blood circulation, allowing signal detection in tumors at a low dose of 20 mg/kg.
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Published in William H. Bush, Karl N. Krecke, Bernard F. King, Michael A. Bettmann, Radiology Life Support (Rad-LS), 2017
Because of very minimal protein binding and their small molecular size, iodinated contrast media are almost totally eliminated by the kidneys via glomerular filtration. In normal individuals, 98 per cent is eliminated by glomerular filtration, and less than 2 per cent is excreted by liver, bowel and salivary glands. The half-life of contrast media before being eliminated into the bladder is approximately 30 min in healthy individuals and 1–2 h in elderly patients. Immediately after injection of intravenous iodinated contrast media, there is equilibration between the interstitial fluid (third space) and the intravascular fluid space. Because of this equilibration, clearance from the body follows an exponential rate. Virtually all of the intravenous iodinated contrast medium should be eliminated by 24 h after the examination. In fact, if a pyelogram is noted on an abdominal CT or on a plain film of the abdomen 24 h after the administration of IV contrast, this is considered abnormal and a sign of impaired clearance, most often due to impaired renal function.
Introduction to medical imaging
Published in David A Lisle, Imaging for Students, 2012
Most patients injected intravenously with iodinated contrast media experience normal transient phenomena, including a mild warm feeling plus an odd taste in the mouth. With modern iodinated contrast media, vomiting at the time of injection is uncommon. More significant adverse reactions to contrast media may be classified as mild, intermediate or severe anaphylactoid reactions: Mild anaphylactoid reactions: mild urticaria and pruritisIntermediate reactions: more severe urticaria, hypotension and mild bronchospasmSevere reactions: more severe bronchospasm, laryngeal oedema, pulmonary oedema, unconsciousness, convulsions, pulmonary collapse and cardiac arrest.
Development and characterization of a synthetic PVC/DEHP myocardial tissue analogue material for CT imaging applications
Published in Journal of Biomaterials Science, Polymer Edition, 2018
Sherif Ramadan, Narinder Paul, Hani E. Naguib
To study the viscoelastic properties of the DEHP-PVC material a TA Instruments DMA Q800 Dynamic Mechanical Analyzer was utilized. To perform the testing ASTM standard D5992 was utilized and consideration was also given to manufacturer specifications and recommendations. A submerged compression clamp was utilized as outlined previously [2,32]. This clamp induces an oscillating strain on a sample at a set frequency and measures the resulting oscillating stress. This allows for a stress-strain frequency dependant curve to be collected. From this data key viscoelastic properties such as the tan delta, storage/loss modulus, and stiffness of the tested sample can be collected. Key settings utilized include a .1 N preload in combination with a 50 μm oscillation depth and a 125% force track. The force track represents a 25% increase of the dynamic force throughout the amplitude. In combination these settings ensure sufficient contact with samples without causing permanent deformation. The frequency range that was utilized varied from 0.5 to 3.5 Hz in 0.25 Hz increments to mimic physiological pumping and heart rates of 30BPM to 210BPM. Additionally, the samples were submerged in a 14:1 mixture of Water: Iodinated contrast agent (Iodixanol, 320 mg/ml, GE Healthcare) to mimic the fluid conditions that the analogue would be exposed to if utilized as an imaging phantom. However, an alternate set of DMA results for samples submerged in water can be found in Appendix 1. All (n = 5) samples for the different DEHP-PVC ratios (n = 3) that were tested were 8 mm by 8 mm by 4 mm (Length × Width × Thickness) square slabs.