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Experience of NMR Exposure Conditions
Published in Bertil R. R. Persson, Freddy Ståhlberg, Health and Safety of Clinical NMR Examinations, 2019
Bertil R. R. Persson, Freddy Ståhlberg
Nuclear magnetic resonance imaging (MRI) and spectroscopy (MRS) are powerful noninvasive medical examination procedures that are gaining rapid clinical acceptance. The imaging procedure entails the concurrent exposure of subjects to a high static magnetic field, an Rf electromagnetic field and time-varying pulsed magnetic gradient fields. Biological effects of NMR exposure conditions (i.e., the combination of static magnetic fields, extremely low frequency (ELF) gradient magnetic fields and Rf radiation have been investigated by several authors in order to prove that no unacceptable hazardous effects are associated with medical applications of NMR in vivo spectroscopy (MRS) and NMR imagine (MRI). There is, however, not yet any special study of the effect of gradient switching, although the exposure to the short pulse lengths used in clinical NMR imaging (i.e., less than 2 T/ sec) is close to the threshold of 3 T/sec producing retinal stimulation. The biological effects of all combined fields used in NMR imaging have been studied by several investigators.5,32,35,39
Fundamentals Of Nmr Imaging
Published in A. Robb Ph.D. Richard, Three-Dimensional Biomedical Imaging, 2017
C. Hill Barbara, Waldo S. Hinshaw
Magnetic fields are inherently three-dimensional, and therefore nuclear magnetic resonance imaging can truly be said to be an inherently three-dimensional imaging technique. In the absence of active measures to restrict resonance to a specific plane, line, or point, the received NMR signal will arise from the entire volume within the bore of the magnet to which the rf receiver coil is sensitive. It is often desirable to obtain an NMR image of a single plane in the patient’s body instead of collecting data from the whole volume, because planar techniques require fewer iterations of the pulse sequence to obtain the same spatial resolution.
Introductory Remarks
Published in Dongyou Liu, Tumors and Cancers, 2017
MRI (magnetic resonance imaging, also called nuclear magnetic resonance imaging or NMRI) utilizes a magnet, radio waves, and a computer to take detailed pictures of affected areas inside the body that help pinpoint the location and dimension of the tumor mass.
Factors affecting the dynamics and heterogeneity of the EPR effect: pathophysiological and pathoanatomic features, drug formulations and physicochemical factors
Published in Expert Opinion on Drug Delivery, 2022
Rayhanul Islam, Hiroshi Maeda, Jun Fang
As described above, poor tumor blood flow and vascular occlusion are the major causes of EPR effect heterogeneity. Thus, restoring tumor blood flow is important to optimize therapeutic protocols. Such vascular flow can be visualized by arterial angiography with a contrast agent. Maeda’s group is the pioneer in using the lipid contrast agent Lipiodol®, specifically SMANCS/Lipiodol®, and computed tomographic scanning for quantification, visualization, and monitoring of SMANCS accumulated in tumor. This technology made it possible to visualize and monitor tumor location, tumor size, extent of drug retention, and heterogeneity of drug (SMANCS) deposition [22,45,72,73]. Later, Maeda’s group discovered that the dose of SMANCS given by infusion should parallel tumor size (i.e. the larger the tumor, the higher the dose of drug) [11]. Angiography demonstrated significantly improved tumor blood flow during angiotensin-induced hypertension in poorly vascularized tumors including pancreatic, metastatic liver, and gallbladder cancers [45]. Also, one study reported a positive correlation between the FDA-approved carboxymethyl dextran-coated magnetic nanoparticle ferumoxytol and accumulation of nanoparticles in the TME, although the clinical benefit remained to be verified [74]. Certain groups have utilized nuclear magnetic resonance imaging to visualize tumor vasculature [75]. These imaging techniques for solid tumor vasculature can be useful to characterize the EPR effect in cancer patients and to achieve optimal anticancer drug (nanomedicine) administration.
NeuroEthics and the BRAIN Initiative: Where Are We? Where Are We Going?
Published in AJOB Neuroscience, 2020
Walter J. Koroshetz, Jackie Ward, Christine Grady
In contrast to EEG and MEG, nuclear magnetic resonance imaging (MRI) signals related to changes in blood flow that increase with brain activity enable scientists to use MRI scanners to identify regions of the human brain that become active during a behavior or when stimulated. For example, because visual images map to precise regions in the brain, the functional MRI (fMRI) read-out can be used to play back a fuzzy version of the movie that a person is watching (Huth et al. 2016). BRAIN Initiative investigators are improving the spatial resolution of this technique but it has inherently poor temporal resolution because after a brain region is activated, the changes in blood flow occur with a delay. Though there are precedents for its introduction in court proceedings (Farahany 2016), fMRI data is not considered to have the required level of validity. The convergence of knowledge from studies of monitoring brain activity in very precise animal studies will surely inform the interpretation of the less comprehensive and less precise human recordings and advance the understanding of human disorders of neural circuits.
Stimuli-responsive nanoscale drug delivery systems for cancer therapy
Published in Journal of Drug Targeting, 2019
Li Li, Wu-Wei Yang, Dong-Gang Xu
Lee et al. engineered a supramolecular nanoparticle which contained beta-cyclodextrin grafted with polyethylenimine (CD-PEI), adamantine-modified PEG (Ad-PEG) and adamantane modified polyamines amine dendrimer (Ad-PAMAM). Then adamantane grafted Zn0.4Fe2.6O4 magnetic nanoparticle (Ad-MNP) was embedded in it to form a block polymer. It was approved that the polymer described above could be used to encapsulate DOX [102]. Guisasola et al. [103] prepared an iron oxide MNP embedded in a mesoporous silica matrix, which can provoke the release of anti-tumour drug DOX trapped inside the silica pores. In vivo and in vitro experiments showed that significant tumour growth inhibition was achieved in 48 h after treatment [103]. Moreover, magnetic materials could also be applied into nuclear magnetic resonance imaging to realise the integrated diagnosis and treatment of diseases [104–109].