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Background: Pericoronary adipose tissue (PCAT) attenuation has been identified as a marker for cardiovascular risk. The effect of contrast enhancement on fat attenuation is unknown. We aim to compare precontrast coronary scans to postcontrast CCTA for quantification of pericoronary fat volume and attenuation., Methods: Thin slice pre- and post-contrast studies obtained at 120 kVp, heart rate <60, with no plaque or artifact in the right coronary artery (RCA) were selected. Analysis was limited to pixels -30 Hounsfield units (HU) to -190 HU and from 10 mm to 50 mm distal to the RCA origin at a radial distance equal to the vessel diameter. A subgroup with no plaque across all coronaries was also analyzed., Results: Of 119 study pairs, the average RCA diameter was highly correlated at 3.85 mm (postcontrast) and 3.84 mm (precontrast), r = 0.97, p < 0.0001. The mean attenuation of pre- and postcontrast images was also highly correlated at -87.02 ± 7.15 HU and -82.74 ± 6.54 HU, respectively (r = 0.65, p < 0.0001). Pericoronary fat volume in the -190 to -30 HU range was 396 mm³ lower in the post contrast versus pre-contrast, consistent with higher attenuation (less negative) voxels postcontrast (p < 0.0001). Inter- and intra-reader agreement ranged 95-100% and 90% for precontrast and 85-90% for postcontrast studies, respectively. Subgroup analysis revealed precontrast attenuation -85.59 ± 7.53 HU and postcontrast -82.21 ± 7.15 HU were highly correlated r = 0.67, p < 0.0001., Conclusion: Pericoronary fat enhances with iodinated contrast, potentially explaining some of its risk-predictive capabilities. Fat attenuation and volume can be reliably measured from precontrast calcium scans, with volume quantification showing particularly strong correlation. Excellent inter- and intra-reader agreement is also demonstrated., Competing Interests: Declaration of competing interest The authors have no conflicts of interest to report., (Copyright © 2020 Society of Cardiovascular Computed Tomography. Published by Elsevier Inc. All rights reserved.)

Because simultaneous noninvasive noncontrast imaging of cervical and cerebral vasculature and brain is possible with magnetic resonance angiography (MRA) and imaging (MRI), the following study was undertaken from July 1990 to January 1992. One hundred twenty-eight patients were examined with General Electric 1.5 Tesla MRI systems. Axially acquired volumetric three-dimensional time-of-flight MRA with 0.7 mm3 voxel size with regional maximum intensity projection after processing followed a two-dimensional time-of-flight localizing sequence. These two MRA sequences combined with spin-echo parenchymal brain MRI were compared with duplex scans, contrast angiograms, and surgical findings. Blinded readings by a radiologist and vascular surgeon allowed comparison of grades of luminal diameter narrowing (normal, mild, moderate, severe, and occluded) seen on MRA to be compared with those of Doppler and contrast angiography. Excluding 12 nondiagnostically imaged internal carotid arteries (10 MRA) and limiting duplex correlation to within 5 days of the MRA examination allowed critical appraisal of 182 internal carotid arteries. Exact correlation of grade of stenosis was obtained by the radiologist in 136 (74.7%) of 182 arteries and the surgeon in 138 (75.8%) of 182 arteries. Spearman rank correlation analysis found rank correlation coefficients of 0.88 (p < 0.001) and 0.83 (p < 0.001), respectively, for the radiologist and vascular surgeon. Disagreement one category apart was found by the radiologist in 35 studies (19.3%) and the surgeon in 28 studies (15.4%). Two or more grades of disagreement were found by the radiologist in 11 studies (6%) and the surgeon in 16 studies (8.8%). Contrast angiogram-MRA agreement was found in 86% of 36 internal carotid arteries. The degree of stenosis detected by MRA was concordant with surgical findings in 39 of 40 patients. Thus MRA emerges as a useful and accurate method of obtaining cerebrovascular evaluation in clinical practice.

We examined the magnetic resonance properties of 12 paramagnetic piperidinyl nitroxyls in water and plasma solutions. Paramagnetic contributions to proton relaxation times were measured using 10.7 and 100 MHz spectrometers. Proton relaxation enhancement from nitroxyls increased with ascending molecular weight, in plasma solutions versus equimolar aqueous solutions, and with measurements at 10.7 MHz compared to 100 MHz. Relaxation rates were observed to approximately double at 10.7 MHz compared to 100 MHz and from water to plasma solutions. The data indicate that proton spin-lattice relaxation enhancement is magnetic field-dependent, and increases using nitroxyls of large molecular weight and with chemical substitutents that increase the microviscosity of solvent water molecules. The development of nitroxyls for diagnostic MRI will be aided by understanding these in vitro physical characteristics and trends.

Nitroxyl spin labels have been shown to be effective in vivo contrast agents for magnetic resonance imaging (MRI) of the central nervous system, myocardium, and urinary tract. A new pyrrolidine nitroxyl contrast agent (PCA) with better resistance to in vivo metabolic inactivation than previously tested agents was studied for its potential to enhance subcutaneous neoplasms in an animal model. Twenty-two contrast enhancement trials were performed on a total of 15 animals 4-6 weeks after implantation with human renal adenocarcinoma. Spin echo imaging was performed using a .35 T animal imager before and after intravenous administration of PCA in doses ranging from 0.5 to 3mM/kg. The intensity of tumor tissue in the images increased an average of 35% in animals receiving a dose of 3 mM/kg. The average enhancement with smaller doses was proportionately less. Tumor intensity reached a maximum within 15 min of injection. The average intensity difference between tumor and adjacent skeletal muscle more than doubled following administration of 3 mM/kg of PCA. Well-perfused tumor tissue was more intensely enhanced than adjacent poorly perfused and necrotic tissue.

Delineation of the gastrointestinal tract in magnetic resonance imaging (MRI) remains a problem. Ferric ammonium citrate is paramagnetic, producing a high MRI signal intensity by virtue of its spin-lattice (T1) relaxation rate enhancement properties. Water is diamagnetic, producing a low MRI signal intensity, especially with short TR and TE times. To compare efficacy for gastrointestinal contrast alteration, ferric ammonium citrate was administered to 18 patients and water was given to 10 patients. Spin-echo imaging at 0.35T was performed after administration of these agents. Ferric ammonium citrate produced high signal intensity within the esophagus, stomach, duodenum, and small intestine that aided in the differentiation of the gastrointestinal tract from adjacent tumors, vessels, and viscera. Delineation of the gut wall was superior using ferric ammonium citrate compared to that produced by water. Delineation of the margins of the pancreas, liver, and kidney from adjacent gastrointestinal tract was also better with ferric ammonium citrate. Optimal distinction between bowel and fat was better with water. Longer TE times (75 to 200 ms) may allow improved contrast between gut and intrabdominal fat using ferric ammonium citrate.