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2 Dimensional Acquisition
 
Data acquisition of single slices.
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MRI History
 
Sir Joseph Larmor (1857-1942) developed the equation that the angular frequency of precession of the nuclear spins being proportional to the strength of the magnetic field. [Larmor relationship]
In the 1930's, Isidor Isaac Rabi (Columbia University) succeeded in detecting and measuring single states of rotation of atoms and molecules, and in determining the mechanical and magnetic moments of the nuclei.
Felix Bloch (Stanford University) and Edward Purcell (Harvard University) developed instruments, which could measure the magnetic resonance in bulk material such as liquids and solids. (Both honored with the Nobel Prize for Physics in 1952.) [The birth of the NMR spectroscopy]
In the early 70's, Raymond Damadian (State University of New York) demonstrated with his NMR device, that there are different T1 relaxation times between normal and abnormal tissues of the same type, as well as between different types of normal tissues.
In 1973, Paul Lauterbur (State University of New York) described a new imaging technique that he termed Zeugmatography. By utilizing gradients in the magnetic field, this technique was able to produce a two-dimensional image (back-projection). (Through analysis of the characteristics of the emitted radio waves, their origin could be determined.) Peter Mansfield further developed the utilization of gradients in the magnetic field and the mathematically analysis of these signals for a more useful imaging technique. (Paul C Lauterbur and Peter Mansfield were awarded with the 2003 Nobel Prize in Medicine.)
In 1975, Richard Ernst introduced 2D NMR using phase and frequency encoding, and the Fourier Transform. Instead of Paul Lauterbur's back-projection, he timely switched magnetic field gradients ('NMR Fourier Zeugmatography'). [This basic reconstruction method is the basis of current MRI techniques.]
1977/78: First images could be presented. A cross section through a finger by Peter Mansfield and Andrew A. Maudsley. Peter Mansfield also could present the first image through the abdomen.
In 1977, Raymond Damadian completed (after 7 years) the first MR scanner (Indomitable). In 1978, he founded the FONAR Corporation, which manufactured the first commercial MRI scanner in 1980. Fonar went public in 1981.
1981: Schering submitted a patent application for Gd-DTPA dimeglumine.
1982: The first 'magnetization-transfer' imaging by Robert N. Muller.
In 1983, Toshiba obtained approval from the Ministry of Health and Welfare in Japan for the first commercial MRI system.
In 1984, FONAR Corporation receives FDA approval for its first MRI scanner.
1986: Jürgen Hennig, A. Nauerth, and Hartmut Friedburg (University of Freiburg) introduced RARE (rapid acquisition with relaxation enhancement) imaging. Axel Haase, Jens Frahm, Dieter Matthaei, Wolfgang Haenicke, and Dietmar K. Merboldt (Max-Planck-Institute, Göttingen) developed the FLASH (fast low angle shot) sequence.
1988: Schering's MAGNEVIST gets its first approval by the FDA.
In 1991, fMRI was developed independently by the University of Minnesota's Center for Magnetic Resonance Research (CMRR) and Massachusetts General Hospital's (MGH) MR Center.
From 1992 to 1997 Fonar was paid for the infringement of it's patents from 'nearly every one of its competitors in the MRI industry including giant multi-nationals as Toshiba, Siemens, Shimadzu, Philips and GE'.
 
Images, Movies, Sliders:
 Cardiac Infarct Short Axis Cine Overview  Open this link in a new window
    

Courtesy of  Robert R. Edelman
 
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Further Reading:
  Basics:
Magnetic Resonance Imaging, History & Introduction
2000   by www.cis.rit.edu    
A Short History of the Magnetic Resonance Imaging (MRI)
   by www.teslasociety.com    
Fonar Our History
   by www.fonar.com    
  News & More:
Scientists win Nobels for work on MRI
Tuesday, 10 June 2003   by usatoday30.usatoday.com    
2001 Lemelson-MIT Lifetime Achievement Award Winner
   by web.mit.edu    
MRI's inside story
Thursday, 4 December 2003   by www.economist.com    
MRI Resources 
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MagneVu 1000InfoSheet: - Devices -
Intro, 
Types of Magnets, 
Overview, 
etc.MRI Resource Directory:
 - Devices -
 
www.mri4ra.com/isis.html From MagneVu;
The MagneVu 1000 is a compact, robust, and portable, permanent magnet MRI system and operates without special shielding or costly site preparation.
This MRI device utilizes a patented non-homogeneous magnetic field image acquisition method to achieve high performance imaging. The MagneVu 1000 MRI scanner is designed for MRI of the extremities with the current specialty areas in diabetes and rheumatoid arthritis. Easy access is afforded for claustrophobic, pediatric, or limited mobility patients.
In August 1998 FDA marketing clearance and other regulatory approvals have been received.
Until 2008, over 130 devices in the US are in use. Some further developments of MagneVu's extremity scanner are: 'truly Plug n' Play MRI™' and iSiS ( which adds wireless capability to the second generation MV1000-XL).
Device Information and Specification
CLINICAL APPLICATION
Dedicated extremity
CONFIGURATION
Portable open MRI
IMAGING MODES
3-dimensional multi-echo data acquisition
3D: 0.6-1 mm
MAGNET TYPE
Permanent
MAGNET WEIGHT
about 50 kg
POWER REQUIREMENTS
110 V
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Further Reading:
  News & More:
VALUE OF 3D T1W & STIR MRI SEQUENCES IN DIAGNOSING EROSIONS IN RHEUMATOID ARTHRITIS
   by www.bocaradiology.com    
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Image Selected In Vivo Spectroscopy
 
(ISIS) Image selected in vivo spectroscopy is used as a localization sequence to provide complete gradient controlled three-dimensional localization with a reduced number of sequence cycles, e.g. for in vivo 31P spectroscopy. The ISIS method generates three 180° pulses prior to a 90° pulse, after which the free induction decay is recorded. Specific 180° pulses (slice-selective) are combined and the FID's added or subtracted to generate a spectrum.
An advantage of the ISIS method is that the magnetization (before the final 90° pulse) is predominantly along the z-axis and so T2 effects are relatively small. This explains the value of this technique for 31P data acquisition, because some phosphorus metabolites (e.g. ATP) have short T2 values.
A disadvantage is that eight acquisitions are required to accomplish the spatial localization, therefore the sequence cannot be used for localized shimming. Another problem, because any variation between these data collections (for example, due to movement) will degrade these applications, can be solved by incorporating outer volume suppression techniques such as OSIRIS (modified ISIS).
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MRI Resources 
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Sensitivity EncodingInfoSheet: - Sequences - 
Intro, 
Overview, 
Types of, 
etc.
 
(SENSE) A MRI technique for relevant scan time reduction. The spatial information related to the coils of a receiver array are utilized for reducing conventional Fourier encoding. In principle, SENSE can be applied to any imaging sequence and k-space trajectories. However, it is particularly feasible for Cartesian sampling schemes. In 2D Fourier imaging with common Cartesian sampling of k-space sensitivity encoding by means of a receiver array enables to reduce the number of Fourier encoding steps.
SENSE reconstruction without artifacts relies on accurate knowledge of the individual coil sensitivities. For sensitivity assessment, low-resolution, fully Fourier-encoded reference images are required, obtained with each array element and with a body coil.
The major negative point of parallel imaging techniques is that they diminish SNR in proportion to the numbers of reduction factors. R is the factor by which the number of k-space samples is reduced. In standard Fourier imaging reducing the sampling density results in the reduction of the FOV, causing aliasing. In fact, SENSE reconstruction in the Cartesian case is efficiently performed by first creating one such aliased image for each array element using discrete Fourier transformation (DFT).
The next step then is to create a full-FOV image from the set of intermediate images. To achieve this one must undo the signal superposition underlying the fold-over effect. That is, for each pixel in the reduced FOV the signal contributions from a number of positions in the full FOV need to be separated. These positions form a Cartesian grid corresponding to the size of the reduced FOV.
The advantages are especially true for contrast-enhanced MR imaging such as dynamic liver MRI (liver imaging) , 3 dimensional magnetic resonance angiography (3D MRA), and magnetic resonance cholangiopancreaticography (MRCP).
The excellent scan speed of SENSE allows for acquisition of two separate sets of hepatic MR images within the time regarded as the hepatic arterial-phase (double arterial-phase technique) as well as that of multidetector CT.
SENSE can also increase the time efficiency of spatial signal encoding in 3D MRA. With SENSE, even ultrafast (sub second) 4D MRA can be realized.
For MRCP acquisition, high-resolution 3D MRCP images can be constantly provided by SENSE. This is because SENSE resolves the presence of the severe motion artifacts due to longer acquisition time. Longer acquisition time, which results in diminishing image quality, is the greatest problem for 3D MRCP imaging.
In addition, SENSE reduces the train of gradient echoes in combination with a faster k-space traversal per unit time, thereby dramatically improving the image quality of single shot echo planar imaging (i.e. T2 weighted, diffusion weighted imaging).
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Further Reading:
  News & More:
Image Characteristics and Quality
   by www.sprawls.org    
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Claustrophobia - Online Books - Health - Safety Training - Mobile MRI - PACS
 
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