Radiocontrast agent

Résumé

Radiocontrast agents are substances used to enhance the visibility of internal structures in X-ray-based imaging techniques such as computed tomography (contrast CT), projectional radiography, and fluoroscopy. Radiocontrast agents are typically iodine, or more rarely barium sulfate. The contrast agents absorb external X-rays, resulting in decreased exposure on the X-ray detector. This is different from radiopharmaceuticals used in nuclear medicine which emit radiation. Magnetic resonance imaging (MRI) functions through different principles and thus MRI contrast agents have a different mode of action. These compounds work by altering the magnetic properties of nearby hydrogen nuclei. Radiocontrast agents used in X-ray examinations can be grouped in positive (iodinated agents, barium sulfate), and negative agents (air, carbon dioxide, methylcellulose). Iodinated contrast Iodinated contrast contains iodine. It is the main type of radiocontrast used for intravenous administration. Iodine has a particular advantage as a contrast agent for radiography because its innermost electron ("k-shell") binding energy is 33.2 keV, similar to the average energy of x-rays used in diagnostic radiography. When the incident x-ray energy is closer to the k-edge of the atom it encounters, photoelectric absorption is more likely to occur. Its uses include: Contrast CTs Angiography (arterial investigations) Venography (venous investigations) VCUG (voiding cystourethrography) HSG (hysterosalpingogram) IVU (intravenous urography) Organic iodine molecules used for contrast include iohexol, iodixanol and ioversol. Barium sulfate is mainly used in the imaging of the digestive system. The substance exists as a water-insoluble white powder that is made into a slurry with water and administered directly into the gastrointestinal tract. Upper gastrointestinal series Barium enema (large bowel investigation) and DCBE (double contrast barium enema).

Source officielle

https://en.wikipedia.org/wiki/Radiocontrast_agent

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Performance and reproducibility of C-13 and N-15 hyperpolarization using a cryogen-free DNP polarizer

Hikari Ananda Infinity Yoshihara, Arianna Ferrari

The setup, operational procedures and performance of a cryogen-free device for producing hyperpolarized contrast agents using dissolution dynamic nuclear polarization (dDNP) in a preclinical imaging center is described. The polarization was optimized using the solid-state, DNP-enhanced NMR signal to calibrate the sample position, microwave and NMR frequency and power and flip angle. The polarization of a standard formulation to yield similar to 4 mL, 60 mM 1-C-13-pyruvic acid in an aqueous solution was quantified in five experiments to P(C-13) = (38 +/- 6) % (19 +/- 1) s after dissolution. The mono-exponential time constant of the build-up of the solid-state polarization was quantified to (1032 +/- 22) s. We achieved a duty cycle of 1.5 h that includes sample loading, monitoring the polarization build-up, dissolution and preparation for the next run. After injection of the contrast agent in vivo, pyruvate, pyruvate hydrate, lactate, and alanine were observed, by measuring metabolite maps. Based on this work sequence, hyperpolarized N-15 urea was obtained (P(N-15) = (5.6 +/- 0.8) % (30 +/- 3) s after dissolution).

NATURE PORTFOLIO2022

Glaucoma is one of the leading causes of blindness in the world. It results in an increase of the aqueous humour (AH) outflow pathway which leads to an increase of the intraocular pressure (IOP). Many treatments exists to reduce and stabilize the IOP such as medications, filtering surgery and Glaucoma Drainage Devices. So far computational fluid dynamics (CFD) modeling of the eye drainage system has not yet been well studied. Therefore our goals was to numerically simulate the AH outflow pattern in a model of the eye to further simulate a healthy and glaucomatous eye and various forms of glaucoma surgery. In order to do so, a 3D CDF model of the eye was created based on real geometries. Two methods were tested to this aim. The first one consisted in the injection of a CT contrast agent in an enucleated rabbit eye and visualization by a CT scan. A segmentation process was then achieved on the resulting scans to reconstruct the eye structures. The second one was based on microphotography stacks of histology of human eye whereof digital processing of the eye structure images and 3D reconstruction of a numerical model were performed. Due to resolution limitations several ocular structures could not be extracted from the segmentation process. In the second method, simulations of pressure and flow velocity distribution in healthy eye gave results comparable to physiology. Modeling the glaucomatous eye led to an increase in the IOP around 37 mmHG. We have been able to model the 3D structure of the eye based on real geometry. Flow simulations gave interesting results for the IOP and the flow velocity on a healthy eye. Mimicking glaucoma conditions led to an increase of the IOP from normal range, which went down to lower values after a filtering procedure. Further refinements in the boundary conditions for the filtering procedure shall improve the precision and efficacy of this innovative tool for modeling glaucoma surgery

2010