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Inductance
 
Measure of the magnetic coupling between two current carrying loops (mutual) reflecting their spatial relationship or of a loop(such as a coil) with itself (self). One of the principal determinants of the resonance frequency of a RF circuit.
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Array CoilInfoSheet: - Coils - 
Intro, 
Overview, 
etc.MRI Resource Directory:
 - Coils -
 
An array coil combines the advantages of smaller coils (high SNR) with those of larger coils (large measurement field). This type of RF coil is composed of separate multiple smaller coils, which can be used individually (switchable coil) or combined.
When used simultaneously, the elements can either be:
coupled array coils - electrically coupled to each other through common transmission lines or mutual inductance
isolated array coils - electrically isolated from each other with separate transmission lines and receivers and minimum effective mutual inductance, and with the signals from each transmission line processed independently or at different frequencies
phased array coils - multiple small coils arranged to efficiently cover a specific anatomic region and obtain high-resolution, high-SNR images of a larger volume. The data from the individual coils is integrated by special software to produce the high-resolution images.

See also the related poll result: '3rd party coils are better than the original manufacturer coils'
 
Images, Movies, Sliders:
 Anatomic Imaging of the Lumbar Spine  Open this link in a new window
      

Courtesy of  Robert R. Edelman

 
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Further Reading:
  News & More:
3T MRI-Compatible Small Body Array Gets FDA Nod
Monday, 15 January 2024   by www.diagnosticimaging.com    
Endorectal Coil Improves Prostate Cancer Detection
Friday, 25 November 2005   by www.sciencedaily.com    
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DeviceForum -
related threadsInfoSheet: - Devices -
Intro, 
Types of Magnets, 
Overview, 
etc.
 
Magnetic resonance imaging (MRI) is based on the magnetic resonance phenomenon, and is used for medical diagnostic imaging since ca. 1977 (see also MRI History).
The first developed MRI devices were constructed as long narrow tunnels. In the meantime the magnets became shorter and wider. In addition to this short bore magnet design, open MRI machines were created. MRI machines with open design have commonly either horizontal or vertical opposite installed magnets and obtain more space and air around the patient during the MRI test.
The basic hardware components of all MRI systems are the magnet, producing a stable and very intense magnetic field, the gradient coils, creating a variable field and radio frequency (RF) coils which are used to transmit energy and to encode spatial positioning. A computer controls the MRI scanning operation and processes the information.
The range of used field strengths for medical imaging is from 0.15 to 3 T. The open MRI magnets have usually field strength in the range 0.2 Tesla to 0.35 Tesla. The higher field MRI devices are commonly solenoid with short bore superconducting magnets, which provide homogeneous fields of high stability.
There are this different types of magnets:
The majority of superconductive magnets are based on niobium-titanium (NbTi) alloys, which are very reliable and require extremely uniform fields and extreme stability over time, but require a liquid helium cryogenic system to keep the conductors at approximately 4.2 Kelvin (-268.8° Celsius). To maintain this temperature the magnet is enclosed and cooled by a cryogen containing liquid helium (sometimes also nitrogen).
The gradient coils are required to produce a linear variation in field along one direction, and to have high efficiency, low inductance and low resistance, in order to minimize the current requirements and heat deposition. A Maxwell coil usually produces linear variation in field along the z-axis; in the other two axes it is best done using a saddle coil, such as the Golay coil.
The radio frequency coils used to excite the nuclei fall into two main categories; surface coils and volume coils. The essential element for spatial encoding, the gradient coil sub-system of the MRI scanner is responsible for the encoding of specialized contrast such as flow information, diffusion information, and modulation of magnetization for spatial tagging.
An analog to digital converter turns the nuclear magnetic resonance signal to a digital signal. The digital signal is then sent to an image processor for Fourier transformation and the image of the MRI scan is displayed on a monitor.

For Ultrasound Imaging (USI) see Ultrasound Machine at Medical-Ultrasound-Imaging.com.

See also the related poll results: 'In 2010 your scanner will probably work with a field strength of' and 'Most outages of your scanning system are caused by failure of'
Radiology-tip.comradGamma Camera,  Linear Accelerator
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Medical-Ultrasound-Imaging.comUltrasound Machine,  Real-Time Scanner
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• View the DATABASE results for 'Device' (141).Open this link in a new window


• View the NEWS results for 'Device' (29).Open this link in a new window.
 
Further Reading:
  News & More:
small-steps-can-yield-big-energy-savings-and-cut-emissions-mris
Thursday, 27 April 2023   by www.itnonline.com    
Portable MRI can detect brain abnormalities at bedside
Tuesday, 8 September 2020   by news.yale.edu    
Point-of-Care MRI Secures FDA 510(k) Clearance
Thursday, 30 April 2020   by www.diagnosticimaging.com    
World's First Portable MRI Cleared by FDA
Monday, 17 February 2020   by www.medgadget.com    
Low Power MRI Helps Image Lungs, Brings Costs Down
Thursday, 10 October 2019   by www.medgadget.com    
Cheap, portable scanners could transform brain imaging. But how will scientists deliver the data?
Tuesday, 16 April 2019   by www.sciencemag.org    
The world's strongest MRI machines are pushing human imaging to new limits
Wednesday, 31 October 2018   by www.nature.com    
Kyoto University and Canon reduce cost of MRI scanner to one tenth
Monday, 11 January 2016   by www.electronicsweekly.com    
A transportable MRI machine to speed up the diagnosis and treatment of stroke patients
Wednesday, 22 April 2015   by medicalxpress.com    
Portable 'battlefield MRI' comes out of the lab
Thursday, 30 April 2015   by physicsworld.com    
Chemists develop MRI technique for peeking inside battery-like devices
Friday, 1 August 2014   by www.eurekalert.org    
New devices doubles down to detect and map brain signals
Monday, 23 July 2012   by scienceblog.com    
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Oscillating Gradient System
 
A gradient system, which changes the readout gradient sinusoidally by connecting a capacitor to the self inductance generated by the gradient coil. Oscillating gradient systems were initially used in the development of EPI.
This electrical oscillating circuit can be driven with minimal power to generate the gradient amplitudes and switching frequencies required for echo planar imaging (EPI).
Disadvantages are that it is not possible to use any arbitrary trapezoidal gradient wave form as can be used in standard MRI. Also, the gradients are inflexible and cannot be used to create other ultrafast sequences and beside, nonlinear sampling of the MR signal is required.
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Quality Factor
 
The quality factor (Q) applies to any resonant circuit component; most often the quality factor of the coil determines the overall Q of the circuit.
Inversely related to the fraction of the energy in an oscillating system lost in one oscillation cycle. Q is inversely related to the range of frequency over which the system will exhibit resonance.
In a parallel tuned circuit (such as used in a MR coil), the quality factor is defined as:
Q = vL/R
where L is the coil inductance, R is the circuit resistance, and v is the angular frequency. Increasing quality factor results in improving the signal to noise ratio SNR by a factor √Q and also produces a sharper frequency response (decreased band width). The Q of a coil will depend on the circumstances under which it is measured, e.g. whether it is 'unloaded' (no patient) or 'loaded' (patient).
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