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 'Relaxation Rates' 
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Relaxation Rates
 
Reciprocals of the relaxation times, T1 and T2 (R1 = 1/T1 and R2 = 1/T2). There is often a linear relation between the concentration of MR contrast agents and the resulting change in relaxation rate. The rate of relaxation is influenced by molecules with protons that are tumbling. A slower tumble rate will result in faster relaxation rate (shorter relaxation time). Due to the molecular structure of fat with its larger size than water, fat will tumble slower than water molecules. The slower tumble rate of fat enables a faster relaxation rate.
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Further Reading:
  Basics:
Evaluation of Absorbed Dose by MRI Read-Out
Saturday, 18 November 2017   by www.jstage.jst.go.jp    
  News & More:
Multimodal Nanoparticles for Quantitative Imaging(.pdf)
Tuesday, 13 December 2011   by alexandria.tue.nl    
MRI Resources 
Knee MRI - MRI Technician and Technologist Jobs - Quality Advice - Supplies - Implant and Prosthesis pool - Cochlear Implant
 
Dipole Dipole Interaction
 
Interaction between a spin and its neighbors due to their magnetic dipole moments. This is an important mechanism contributing to relaxation rates. In solids and viscous liquids this can result in broadening of the spectral lines.
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Further Reading:
  Basics:
Dipole
   by en.wikipedia.org    
MRI Resources 
MRI Centers - Distributors - Services and Supplies - General - Pregnancy - Pediatric and Fetal MRI
 
Paramagnetic Contrast AgentsInfoSheet: - Contrast Agents - 
Intro, Overview, 
Characteristics, 
Types of, 
etc.MRI Resource Directory:
 - Contrast Agents -
 
Magnetic relaxation in tissues can be enhanced using contrast agents. The most commonly used for MRI are the paramagnetic contrast agents, which have their strongest effect on the T1, by increasing T1 signal intensity in tissues where they have accumulated.
MRI collects signal from the water protons, but the presence of these contrast agents enhances the relaxation of water protons in their vicinity. Paramagnetic contrast agents contain magnetic centers that create magnetic fields approximately one thousand times stronger than those corresponding to water protons. These magnetic centers interact with water protons in exactly the same way as the neighboring protons, but with much stronger magnetic fields, and therefore, have a much greater impact on relaxation rates, particularly on T1. In MRI, contrast agents are routinely injected intravenously to help identify areas of hypervascularity, as in malignant tumors.
See also Contrast Agents, Gadovist®, MultiHance®, Omniscan®, OptiMARK®.

See also the related poll result: 'The development of contrast agents in MRI is'
 
Images, Movies, Sliders:
 MRI Upper Abdomen T1 with Contrast  Open this link in a new window
    
 MRI Orbita T1  Open this link in a new window
 MRI Orbita T1 with Contrast  Open this link in a new window
    
 
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Further Reading:
  Basics:
LEARNING CENTER FOR PARAMAGNETISM
2003   by www.naturesalternatives.com    
Contrast Agents: Safety Profile
   by www.clinical-mri.com    
Contrast Agents in Magnetic Resonance Imaging
1997
  News & More:
Gadolinium-containing contrast agents: removal of Omniscan and iv Magnevist, restrictions to the use of other linear agents
Friday, 5 January 2018   by www.gov.uk    
EMA's final opinion confirms restrictions on use of linear gadolinium agents in body scans
Friday, 21 July 2017   by www.ema.europa.eu    
FDA Drug Safety Communication: FDA warns that gadolinium-based contrast agents (GBCAs) are retained in the body; requires new class warnings
Tuesday, 19 December 2017   by www.fda.gov    
RSNA Statement on Gadolinium-Based MR Contrast Agents
Thursday, 1 February 2018   by www.rsna.org    
Contrast MRIs cause claims, concern, over residual metal in brain
Tuesday, 8 December 2015   by www.afr.com    
MRI Resources 
Homepages - Anatomy - Liver Imaging - Pathology - Cardiovascular Imaging - Jobs pool
 
Paramagnetism
 
Paramagnetic materials attract and repel like normal magnets when subject to a magnetic field. This alignment of the atomic dipoles with the magnetic field tends to strengthen it, and is described by a relative magnetic permeability greater than unity. Paramagnetism requires that the atoms individually have permanent dipole moments even without an applied field, which typically implies a partially filled electron shell. In pure Paramagnetism (without an external magnetic field), these atomic dipoles do not interact with one another and are randomly oriented in the absence of an external field, resulting in zero net moment.
Paramagnetic materials in magnetic fields will act like magnets but when the field is removed, thermal motion will quickly disrupt the magnetic alignment. In general, paramagnetic effects are small (magnetic susceptibility of the order of 10-3 to 10-5).
In MRI, gadolinium (Gd) one of these paramagnetic materials is used as a contrast agent. Through interactions between the electron spins of the paramagnetic gadolinium and the water nuclei nearby, the relaxation rates (T1 and T2) of the water protons are increased (T1 and T2 times are decreased), causing an increase in signal on T1 weighted images.
See also contrast agents, magnetism, ferromagnetism, superparamagnetism, and diamagnetism.
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Further Reading:
  Basics:
Magnet basics
   by my.execpc.com    
Paramagnetism
Wednesday, 23 November 2005   by en.wikipedia.org    
  News & More:
LEARNING CENTER FOR PARAMAGNETISM
2003   by www.naturesalternatives.com    
MRI Resources 
Safety Products - Case Studies - Calculation - Implant and Prosthesis pool - Absorption and Emission - Pregnancy
 
Relaxation Effect
 
The relaxation effect is the transition of an atom or molecule from a higher energy level to a lower one. The return of the excited proton from the high energy to the low energy level is associated with the loss of energy to the surrounding tissue. The T1 and T2 relaxation times define the way that the protons return to their resting levels after the initial radio frequency (RF) pulse. The T1 and T2 relaxation rates have an effect of the signal to noise ratio (SNR) of MR images.
The relaxation process is a result of both T1 and T2, and can be controlled by the dependency of one of the two biological parameters T1 and T2 in the recorded signal. A T1 weighted spin echo sequence is based on a short repetition time (TR) and a change of it will affect the acquisition time and the T1 weighting of the image. Increased TR results in improved SNR caused by longer recovering time for the longitudinal magnetization. Increased TE improves the T2 weighting, combined with a long TR (of several T1 times) to minimize the T1 effect.
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Further Reading:
  News & More:
MRI's inside story
Thursday, 4 December 2003   by www.economist.com    
MRI Resources 
Pacemaker - Abdominal Imaging - Stimulator pool - Liver Imaging - Examinations - Databases
 
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