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Result : Searchterm 'Mole' found in 4 terms [] and 79 definitions []
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MRI RisksMRI Resource Directory:
 - Safety -
 
The subacute risks and side effects of magnetic and RF fields (for patients and staff) have been intensively examined for a long time, but there have been no long-term studies following persons who have been exposed to the static magnetic fields used in MRI. However, no permanent hazardous effects of a static magnetic field exposure upon human beings have yet been demonstrated.
Temporary possible side effects of high magnetic and RF fields:
•
Varying magnetic fields can induce so-called magnetic phosphenes that occur when an individual is subject to rapid changes of 2-5 T/s, which can produce a flashing sensation in the eyes. This temporary side effect does not seem to damage the eyes. Static field strengths used for clinical MRI examinations vary between 0.2 and 3.0 tesla;; field changes during the MRI scan vary in the dimension of mT/s. Experimental imaging units can use higher field strengths of up to 14.0 T, which are not approved for human use.
•
The Radio frequency pulses mainly produce heat, which is absorbed by the body tissue. If the power of the RF radiation is very high, the patient may be heated too much. To avoid this heating, the limit of RF exposure in MRI is up to the maximum specific absorption rate (SAR) of 4 W/kg whole body weight (can be different from country to country). For MRI safety reasons, the MRI machine starts no sequence, if the SAR limit is exceeded.
•
Very high static magnetic fields are needed to reduce the conductivity of nerves perceptibly. Augmentation of T waves is observed at fields used in standard imaging but this side effect in MRI is completely reversible upon removal from the magnet. Cardiac arrhythmia threshold is typically set to 7-10 tesla. The magnetohydrodynamic effect, which results from a voltage occurring across a vessel in a magnetic field and percolated by a saline solution such as blood, is irrelevant at the field strengths used.

The results of some animal and cellular studies suggest the possibility that electromagnetic fields may act as co-carcinogens or tumor promoters, but the data are inconclusive. Up to 45 tesla, no important effects on enzyme systems have been observed. Neither changes in enzyme kinetics, nor orientation changes in macromolecules have been conclusively demonstrated.
There are some publications associating an increase in the incidence of leukemia with the location of buildings close to high-current power lines with extremely low-frequency (ELF) electromagnetic radiation of 50-60 Hz, and industrial exposure to electric and magnetic fields but a transposition of such effects to MRI or MRS seems unlikely.
Under consideration of the MRI safety guidelines, real dangers or risks of an exposure with common MRI field strengths up to 3 tesla as well as the RF exposure during the MRI scan, are not to be expected.

For more MRI safety information see also Nerve Conductivity, Contraindications, Pregnancy and Specific Absorption Rate.

See also the related poll result: 'In 2010 your scanner will probably work with a field strength of'
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• For this and other aspects of MRI safety see our InfoSheet about MRI Safety.
• Patient-related information is collected in our MRI Patient Information.

 
• Related Searches:
    • Magnetohydrodynamic Effect
    • Class I, II, III Devices
    • Active Device
    • Cardiac Risks
    • Nerve Conductivity
 
Further Reading:
  Basics:
MRI in Patients with Implanted Devices: Current Controversies
Monday, 1 August 2016   by www.acc.org    
Working with MRI machines may cause vertigo: Study
Wednesday, 25 June 2014   by www.cos-mag.com    
Physics of MRI Safety
   by www.aapm.org    
When Your Kid Needs an MRI: Optimizing the Experience
Tuesday, 29 March 2016   by health.usnews.com    
  News & More:
How safe is 7T MRI for patients with neurosurgical implants?
Thursday, 17 November 2022   by healthimaging.com    
CT contrast reaction raises MRI contrast risk
Tuesday, 22 February 2022   by www.sciencedaily.com    
CSU study explores MRI distress and patient experience
Thursday, 7 May 2020   by www.portnews.com.au    
Noise from Magnetic Resonance Imaging Can Have Short-Term Impact on Hearing
Thursday, 22 February 2018   by www.diagnosticimaging.com    
Women with permanent make-up tattoos suffer horrific facial burns after going in for MRI scans - which create an electric current in the ink
Monday, 4 July 2016   by www.dailymail.co.uk    
FDA Dials in on MRI Safety of Passive Implantable Medical Devices
Wednesday, 24 June 2015   by www.raps.org    
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MagnetForum -
related threads
 
A magnet is by definition an object with magnetic properties (magnetism) that attracts iron and produces a magnetic field. It can be a permanent magnet or an electromagnet.
Permanent magnets do not rely upon outside influences to generate their field. In permanent magnets are the atoms and molecules ordered in long range. The specific electron configuration and the distance of the atoms is what lead to this long range ordering. The electrons exist in a lower energy state if they all have the same orientation. Magnetic domains can be likened to microscopic neighborhoods in which there is a strong reinforcing interaction between particles, resulting in a high degree of order. The greater the degree of ordering within and between domains, the greater the resulting field will be. Long range ordering is one of the hallmarks of a ferromagnetic material.
A current carrying conductor for example a piece of wire, produces a magnetic field that encircles the wire. An electromagnet, in its simplest form, is a wire that has been coiled into one or more loops. This coil is known as a solenoid. The more loops of wire and the greater the current, the stronger the field will be.
Superconducting magnets are a special type of electromagnets, often used in MRI machines with high field strength.
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• View the NEWS results for 'Magnet' (315).Open this link in a new window.
 
Further Reading:
  Basics:
Magnetic Field
   by hyperphysics.phy-astr.gsu.edu    
  News & More:
Philips Signs Research Agreement to Explore New Magnet Technologies
Monday, 5 December 2022   by www.itnonline.com    
Impact of Magnetic Field Inhomogeneity on the Quality of Magnetic Resonance Images and Compensation Techniques: A Review
Saturday, 1 October 2022   by www.dovepress.com    
Magnetic seeds used to heat and kill cancer
Tuesday, 1 February 2022   by www.sciencedaily.com    
Harvard Scientists Create Nanoscale MRI
Monday, 28 April 2014   by www.meddeviceonline.com    
How Academic Research Solved the Puzzle of MRI and CAT Scanning
Monday, 21 April 2014   by www.engineering.com    
MRI Safety Resources 
Claustrophobia - Safety pool - Breast Implant - Cochlear Implant - Shielding
 
Magnetic Resonance SpectroscopyMRI Resource Directory:
 - Spectroscopy pool -
 
(MRS / MRSI - Magnetic Resonance Spectroscopic Imaging) A method using the NMR phenomenon to identify the chemical state of various elements without destroying the sample. MRS therefore provides information about the chemical composition of the tissues and the changes in chemical composition, which may occur with disease processes.
Although MRS is primarily employed as a research tool and has yet to achieve widespread acceptance in routine clinical practice, there is a growing realization that a noninvasive technique, which monitors disease biochemistry can provide important new information for the clinician.
The underlying principle of MRS is that atomic nuclei are surrounded by a cloud of electrons, which very slightly shield the nucleus from any external magnetic field. As the structure of the electron cloud is specific to an individual molecule or compound, then the magnitude of this screening effect is also a characteristic of the chemical environment of individual nuclei.
In view of the fact that the resonant frequency is proportional to the magnetic field that it experiences, it follows that the resonant frequency will be determined not only by the external applied field, but also by the small field shift generated by the electron cloud. This shift in frequency is called the chemical shift (see also Chemical Shift). It should be noted that chemical shift is a very small effect, usually expressed in ppm of the main frequency. In order to resolve the different chemical species, it is therefore necessary to achieve very high levels of homogeneity of the main magnetic field B0. Spectra from humans usually require shimming the magnet to approximately one part in 100. High resolution spectra of liquid samples demand a homogeneity of about one part in 1000.
In addition to the effects of factors such as relaxation times that can affect the NMR signal, as seen in magnetic resonance imaging, effects such as J-modulation or the transfer of magnetization after selective excitation of particular spectral lines can affect the relative strengths of spectral lines.
In the context of human MRS, two nuclei are of particular interest - H-1 and P-31. (PMRS - Proton Magnetic Resonance Spectroscopy) PMRS is mainly employed in studies of the brain where prominent peaks arise from NAA, choline containing compounds, creatine and creatine phosphate, myo-inositol and, if present, lactate; phosphorus 31 MR spectroscopy detects compounds involved in energy metabolism (creatine phosphate, adenosine triphosphate and inorganic phosphate) and certain compounds related to membrane synthesis and degradation. The frequencies of certain lines may also be affected by factors such as the local pH. It is also possible to determine intracellular pH because the inorganic phosphate peak position is pH sensitive.
If the field is uniform over the volume of the sample, "similar" nuclei will contribute a particular frequency component to the detected response signal irrespective of their individual positions in the sample. Since nuclei of different elements resonate at different frequencies, each element in the sample contributes a different frequency component. A chemical analysis can then be conducted by analyzing the MR response signal into its frequency components.

See also Spectroscopy.
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Further Reading:
  News & More:
Accuracy of Proton Magnetic Resonance Spectroscopy in Distinguishing Neoplastic From Non-neoplastic Brain Lesions
Saturday, 2 December 2023   by www.cureus.com    
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Magnetization Transfer Contrast
 
(MTC) This MRI method increases the contrast by removing a portion of the total signal in tissue. An off resonance radio frequency (RF) pulse saturates macromolecular protons to make them invisible (caused by their ultra-short T2* relaxation times). The MRI signal from semi-solid tissue like brain parenchyma is reduced, and the signal from a more fluid component like blood is retained.
E.g., saturation of broad spectral lines may produce decreases in intensity of lines not directly saturated, through exchange of magnetization between the corresponding states; more closely coupled states will show a greater resulting intensity change. Magnetization transfer techniques make demyelinated brain or spine lesions (as seen e.g. in multiple sclerosis) better visible on T2 weighted images as well as on gadolinium contrast enhanced T1 weighted images.
Off resonance makes use of a selection gradient during an off resonance MTC pulse. The gradient has a negative offset frequency on the arterial side of the imaging volume (caudally more off resonant and cranially less off resonant). The net effect of this type of pulse is that the arterial blood outside the imaging volume will retain more of its longitudinal magnetization, with more vascular signal when it enters the imaging volume. Off resonance MTC saturates the venous blood, leaving the arterial blood untouched.
On resonance has no effect on the free water pool but will saturate the bound water pool and is the difference in T2 between the pools. Special binomial pulses are transmitted causing the magnetization of the free protons to remain unchanged. The z-magnetization returns to its original value. The spins of the bound pool with a short T2 experience decay, resulting in a destroyed magnetization after the on resonance pulse.

See also Magnetization Transfer.
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Further Reading:
  News & More:
MRI of the Human Eye Using Magnetization Transfer Contrast Enhancement
   by www.iovs.org    
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Medical Imaging
 
The definition of imaging is the visual representation of an object. Medical imaging began after the discovery of x-rays by Konrad Roentgen 1896. The first fifty years of radiological imaging, pictures have been created by focusing x-rays on the examined body part and direct depiction onto a single piece of film inside a special cassette. The next development involved the use of fluorescent screens and special glasses to see x-ray images in real time.
A major development was the application of contrast agents for a better image contrast and organ visualization. In the 1950s, first nuclear medicine studies showed the up-take of very low-level radioactive chemicals in organs, using special gamma cameras. This medical imaging technology allows information of biologic processes in vivo. Today, PET and SPECT play an important role in both clinical research and diagnosis of biochemical and physiologic processes. In 1955, the first x-ray image intensifier allowed the pick up and display of x-ray movies.
In the 1960s, the principals of sonar were applied to diagnostic imaging. Ultrasonic waves generated by a quartz crystal are reflected at the interfaces between different tissues, received by the ultrasound machine, and turned into pictures with the use of computers and reconstruction software. Ultrasound imaging is an important diagnostic tool, and there are great opportunities for its further development. Looking into the future, the grand challenges include targeted contrast agents, real-time 3D ultrasound imaging, and molecular imaging.
Digital imaging techniques were implemented in the 1970s into conventional fluoroscopic image intensifier and by Godfrey Hounsfield with the first computed tomography. Digital images are electronic snapshots sampled and mapped as a grid of dots or pixels. The introduction of x-ray CT revolutionised medical imaging with cross sectional images of the human body and high contrast between different types of soft tissue. These developments were made possible by analog to digital converters and computers. The multislice spiral CT technology has expands the clinical applications dramatically.
The first MRI devices were tested on clinical patients in 1980. The spread of CT machines is the spur to the rapid development of MRI imaging and the introduction of tomographic imaging techniques into diagnostic nuclear medicine. With technological improvements including higher field strength, more open MRI magnets, faster gradient systems, and novel data-acquisition techniques, MRI is a real-time interactive imaging modality that provides both detailed structural and functional information of the body.
Today, imaging in medicine has advanced to a stage that was inconceivable 100 years ago, with growing medical imaging modalities:
Single photon emission computed tomography (SPECT)
Positron emission tomography (PET)

All this type of scans are an integral part of modern healthcare. Because of the rapid development of digital imaging modalities, the increasing need for an efficient management leads to the widening of radiology information systems (RIS) and archival of images in digital form in picture archiving and communication systems (PACS). In telemedicine, healthcare professionals are linked over a computer network. Using cutting-edge computing and communications technologies, in videoconferences, where audio and visual images are transmitted in real time, medical images of MRI scans, x-ray examinations, CT scans and other pictures are shareable.
See also Hybrid Imaging.

See also the related poll results: 'In 2010 your scanner will probably work with a field strength of', 'MRI will have replaced 50% of x-ray exams by'
Radiology-tip.comradDiagnostic Imaging
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Medical-Ultrasound-Imaging.comMedical Imaging
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• View the NEWS results for 'Medical Imaging' (81).Open this link in a new window.
 
Further Reading:
  Basics:
Image Characteristics and Quality
   by www.sprawls.org    
Multimodal Nanoparticles for Quantitative Imaging(.pdf)
Tuesday, 13 December 2011   by alexandria.tue.nl    
Medical imaging shows cost control problem
Tuesday, 6 November 2012   by www.mysanantonio.com    
  News & More:
iMPI: An Exploration of Post-Launch Advancements
Friday, 29 September 2023   by www.diagnosticimaging.com    
Advances in medical imaging enable visualization of white matter tracts in fetuses
Wednesday, 12 May 2021   by www.eurekalert.or    
Positron Emission Tomographic Imaging in Stroke
Monday, 28 December 2015   by www.ncbi.nlm.nih.gov    
Multiparametric MRI for Detecting Prostate Cancer
Wednesday, 17 December 2014   by www.onclive.com    
Combination of MRI and PET imaging techniques can prevent second breast biopsy
Sunday, 29 June 2014   by www.news-medical.net    
3D-DOCTOR Tutorial
   by www.ablesw.com    
MRI Resources 
Case Studies - Spectroscopy pool - Claustrophobia - MRI Technician and Technologist Schools - Functional MRI - Artifacts
 
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