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High Field MRI
 
The principal advantage of MRI at high field is the increase in signal to noise ratio. This can be used to improve anatomic and/or temporal resolution and reduce scan time while preserving image quality. MRI devices for whole body imaging for human use are available up to 3 tesla (3T). Functional MRI (fMRI) and MR spectroscopy (MRS) benefit significantly. In addition, 3T machines have a great utility in applications such as TOF MRA and DTI. Higher field strengths are used for imaging of small parts of the body or scientific animal experiments. Higher contrast may permit reduction of gadolinium doses and, in some cases, earlier detection of disease.
Using high field MRI//MRS, the RF-wavelength and the dimension of the human body complicating the development of MR coils. The absorption of RF power causes heating of the tissue. The energy deposited in the patient's tissues is fourfold higher at 3T than at 1.5T. The specific absorption rate (SAR) induced temperature changes of the human body are the most important safety issue of high field MRI//MRS.
Susceptibility and chemical shift dispersion increase like T1, therefore high field MRI occasionally exhibits imaging artifacts. Most are obvious and easily recognized but some are subtle and mimic diseases. A thorough understanding of these artifacts is important to avoid potential pitfalls. Some imaging techniques or procedures can be utilized to remove or identify artifacts.
See also Diffusion Tensor Imaging.

See also the related poll result: 'In 2010 your scanner will probably work with a field strength of'
Radiology-tip.comMagnetic Resonance Guided Focused Ultrasound,  High Intensity Focused Ultrasound
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    • Superconducting Magnet
    • Low Field MRI
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    • Image Contrast Characteristics
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Further Reading:
  Basics:
CLINICAL WHOLE BODY MRI AT 3.0 T(.pdf)
2001
Dealing with Increased MRI Field Strength
Tuesday, 1 October 2013   by www.evaluationengineering.com    
Musculoskeletal MRI at 3.0 T: Relaxation Times and Image Contrast
Sunday, 1 August 2004   by www.ajronline.org    
  News & More:
Ultra-high-field MRI reveals language centres in the brain in much more detail
Tuesday, 28 October 2014   by medicalxpress.com    
Vascular Filters of Functional MRI: Spatial Localization Using BOLD and CBV Contrast
High-Resolution, Spin-Echo BOLD, and CBF fMRI at 4 and 7 T(.pdf)
October 2002   by otg.downstate.edu    
Turbo-FLASH Based Arterial Spin Labeled Perfusion MRI at 7 T
Thursday, 20 June 2013   by www.plosone.org    
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Brain MRIForum -
related threadsMRI Resource Directory:
 - Brain MRI -
 
Brain imaging, magnetic resonance imaging of the head or skull, cranial magnetic resonance tomography (MRT), neurological MRI - they describe all the same radiological imaging technique for medical diagnostic.
Magnetic resonance imaging of the human brain includes the anatomic description and the detection of lesions. Special techniques like diffusion weighted imaging, functional magnetic resonance imaging (fMRI) and spectroscopy provide also information about the function and chemical metabolites of the brain. MRI provides detailed pictures of brain and nerve tissues in multiple planes without obstruction by overlying bones. Brain MRI is the procedure of choice for most brain disorders. It provides clear images of the brainstem and posterior brain, which are difficult to view on a CT scan. It is also useful for the diagnosis of demyelinating disorders (disorders such as multiple sclerosis (MS) that cause destruction of the myelin sheath of the nerve).
With this noninvasive procedure also the evaluation of blood flow and the flow of cerebrospinal fluid (CSF) is possible. Different MRA methods, also without contrast agents can show a venous or arterial angiogram. MRI can distinguish tumors, inflammatory lesions, and other pathologies from the normal brain anatomy. However, MRI scans are also used instead other methods to avoid the dangers of interventional procedures like angiography (DSA - digital subtraction angiography) as well as of repeated exposure to radiation as required for computed tomography (CT) and other X-ray examinations.
A (birdcage) bird cage coil achieves uniform excitation and reception and is commonly used to study the brain. Usually a brain MRI procedure includes FLAIR, T2 weighted and T1 weighted sequences in two or three planes.
See also Fetal MRI, Fluid Attenuation Inversion Recovery (FLAIR), Perfusion Imaging and High Field MRI.
See also Arterial Spin Labeling.
 
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Further Reading:
  Basics:
New MRI technique offers faster diagnosis of multiple sclerosis
Monday, 1 February 2016   by medicalxpress.com    
Ultra-high-field MRI reveals language centres in the brain in much more detail
Tuesday, 28 October 2014   by medicalxpress.com    
Neuro-Oncology - Diagnosis MRI with Gd-DTPA
A Dutch study has revealed that as many as 13% of healthy adults may have some type of undiagnosed abnormality in the brain.
Sunday, 4 November 2007   by www.news-medical.net:80    
  News & More:
Talking therapy or medication for depression: Brain scan may help suggest better treatment
Monday, 27 March 2017   by www.newsnation.in    
MRI identifies brain abnormalities in chronic fatigue syndrome patients
Wednesday, 29 October 2014   by www.eurekalert.org    
Contrast agent linked with brain abnormalities on MRI
Tuesday, 17 December 2013   by www.sciencecodex.com    
MRIs Useful in Tracking Depression in MS Patients
Tuesday, 1 July 2014   by www.hcplive.com    
MRIs Reveal Signs of Brain Injuries Not Seen in CT Scans
Tuesday, 18 December 2012   by www.sciencedaily.com    
Iron Deposits in the Brain May Be Early Indicator of MS
Wednesday, 13 November 2013   by www.healthline.com    
Migraine Sufferers Have Thicker Brain Cortex
Tuesday, 20 November 2007   by www.medicalnewstoday.com    
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Circle of WillisForum -
related threadsMRI Resource Directory:
 - Anatomy -
 
A large network of interconnecting blood vessels at the base of the brain that when visualized resembles a circle, the arteries effectively act as anastomoses for each other. This means that if any one of the communicating arteries becomes blocked, blood can flow from another part of the circle to ensure that blood flow is not compromised.
The circle of Willis is formed by both the internal carotid arteries, entering the brain from each side and the basilar artery, entering posteriorly. The connection of the vertebral arteries forms the basilar artery. The basilar artery divides into the right and left posterior cerebral arteries. The internal carotid arteries trifurcate into the anterior cerebral artery, middle cerebral artery, and posterior communicating artery. The two anterior cerebral arteries are joined together anteriorly by the anterior communicating artery. The posterior communicating arteries join the posterior cerebral arteries, completing the circle of Willis.
The time of flight angiography MRI technique allows imaging of the circle of Willis without the need of a contrast medium (best results with high field MRI). A cerebrovasular contrast enhanced magnetic resonance angiography (MRA) depicts the circle of Willis in addition to the vessels of the neck (carotid and vertebral arteries) with one bolus injection of a contrast agent.

For Ultrasound Imaging (USI) see Cerebrovascular Ultrasonography at US-TIP.com.

 
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Further Reading:
  News & More:
Magnetic resonance angiography: current status and future directions
Wednesday, 9 March 2011   by www.jcmr-online.com    
Searchterm 'High Field MRI' was also found in the following services: 
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Duty Cycle
 
Duty cycle is the time during which the gradient system can be run at maximum power. The duty cycle is based on the total time and includes the cool down phase. The duty cycle on the RF pulse during MRI is restricted based on the specific absorption rate (SAR) limit.
SAR limits restrict radio frequency heating effects. The specific absorption rate increases with field strength, radio frequency power and duty cycle, type of the transmitter coil and body size. The especially in high and ultrahigh magnetic fields, important SAR issue can be readily addressed by reducing the RF duty cycle due to longer repetition times (TR) and the use of parallel imaging techniques. A TR longer than the minimum needed provides time for the tissue to cool down, but for the cost of a longer scan time. A parallel imaging technique reduces the RF exposure and the scan time.
See also High Field MRI (3 tesla 3T).
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Electromagnet
 
A type of magnet that utilizes coils of wire, typically wound on an iron core, so that as current flows through the coil it becomes magnetized. The direction of the magnetic field is parallel to the long axis of the coil. Whole body electromagnets, used in medical imaging (also called resistive) are limited to their field strength, because the weight becomes prohibitively large at high field MRI. The magnetic field shuts down, if the current is switched of. Because this type of magnet generates heat, a good cooling system is essential.
For a stronger magnetic field, the wires must be manufactured of superconducting materials to reduce the power needed to produce the field.
See also Resistive Magnet, Superconducting Magnet and Upright™ MRI

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Further Reading:
  Basics:
What types of magnets are there?
   by my.execpc.com    
  News & More:
Continued access to MRI for patients in Europe
Wednesday, 12 June 2013   by www.european-hospital.com    
Concentration And Visuospatial Awareness Affected By MRI Scanners
Thursday, 30 August 2012   by www.redorbit.com    
'Electromagnetic Wormhole' Possible with Invisibility Technology
Monday, 15 October 2007   by www.brightsurf.com    
Superconductors Face the Future
Wednesday, 15 September 2010   by www.nanotech-now.com    
MRI Resources 
Implant and Prosthesis - Safety pool - RIS - Service and Support - Libraries - Non-English
 
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