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Magnetic Source ImagingInfoSheet: - Sequences - 
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 - Functional MRI -
(MSI) The combination of biomagnetic field detection and MR imaging into a merged data set. Most applications of MSI involve the combined use of MRI and measurement of magnetic fields created by electric currents in the brain, so-called magnetoencephalography MEG.
MEG allows calculation of the source of the measured biomagnetic fields, and thereby localization of many regional brain functions, such as mapping of the sensorimotor, auditory and visual cortex and also localization of epileptogenic foci. The MEG coordinate system is defined by anatomical landmarks, which are easily identified also with MRI, making it possible to align the 3D MEG data with the 3D MR image data. The resulting magnetic source images show the spatial relationships between the functional area provided by MEG and the neighboring anatomy and pathology, both provided by MRI.
Cardiac applications of MSI are also being explored. The electric currents in the myocardium create extrathoracic magnetic fields and the source of these fields may be calculated by the same principles as those used in MEG. Possible cardiac applications include mapping of arrhythmogenic sites prior to ablation therapy.
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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:
X-ray projection imaging
Computed tomography (CT / CAT)
Ultrasound imaging (US)
Magnetic resonance imaging (MRI)
Magnetic resonance spectroscopy (MRS)
Single photon emission computed tomography (SPECT)
Positron emission tomography (PET)
Magnetic source imaging (MSI)
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 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.comDiagnostic Imaging
Radiology-tip.comMedical Imaging

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Image Characteristics and Quality
Multimodal Nanoparticles for Quantitative Imaging(.pdf)
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Time of Flight AngiographyInfoSheet: - Sequences - 
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 - MRA -
(TOF) The time of flight angiography is used for the imaging of vessels. Usually the sequence type is a gradient echo sequences with short TR, acquired with slices perpendicular to the direction of blood flow.
The source of diverse flow effects is the difference between the unsaturated and presaturated spins and creates a bright vascular image without the invasive use of contrast media. Flowing blood moves unsaturated spins from outside the slice into the imaging plane. These completely relaxed spins have full equilibrium magnetization and produce (when entering the imaging plane) a much higher signal than stationary spins if a gradient echo sequence is generated. This flow related enhancement is also referred to as entry slice phenomenon, or inflow enhancement.
Performing a presaturation slab on one side parallel to the slice can selectively destroy the MR signal from the in-flowing blood from this side of the slice. This allows the technique to be flow direction sensitive and to separate arteriograms or venograms. When the local magnetization of moving blood is selectively altered in a region, e.g. by selective excitation, it carries the altered magnetization with it when it moves, thus tagging the selected region for times on the order of the relaxation times.
For maximum flow signal, a complete new part of blood has to enter the slice every repetition (TR) period, which makes time of flight angiography sensitive to flow-velocity. The choice of TR and slice thickness should be appropriate to the expected flow-velocities because even small changes in slice thickness influences the performance of the TOF sequence. The use of sequential 2 dimensional Fourier transformation (2DFT) slices, 3DFT slabs, or multiple 3D slabs (chunks) are depending on the coverage required and the range of flow-velocities.
3D TOF MRA is routinely used for evaluating the Circle of Willis.
See also Magnetic Resonance Angiography and Contrast Enhanced Magnetic Resonance Angiography.
Images, Movies, Sliders:
 TOF-MRA Circle of Willis Inverted MIP  Open this link in a new window

 Circle of Willis, Time of Flight, MIP  Open this link in a new window
SlidersSliders Overview

Radiology-tip.comCT Angiography,  Coronary Angiogram
Radiology-tip.comColor Power Angio,  Doppler Ultrasound

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Further Reading:
  News & More:
Magnetic resonance angiography: current status and future directions
Wednesday, 9 March 2011   by    
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MRIForum -
related threads
Magnetic resonance imaging is a radiological diagnostic procedure without X-rays.

Magnetic resonance imaging, see also: MRI history, medical imaging, nuclear magnetic resonance, spin, precession, T1 time, T2 time, MRI equipment, MRI devices, MRI coils, MRI sequences, MRI contrast agents.

MRI resources, MRI congresses, and MRI news.

Images, Movies, Sliders:
 Sagittal Knee MRI Images STIR  Open this link in a new window

 Cardiac Infarct Short Axis Cine Overview  Open this link in a new window
 Breast MRI Images T2 And T1  Open this link in a new window
 TOF-MRA Circle of Willis Inverted MIP  Open this link in a new window


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Further Reading:
A Short History of the Magnetic Resonance Imaging (MRI)
Magnetic Resonance Imaging, History & Introduction
2000   by    
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The 2003 Nobel Prize in Physiology or Medicine
2003   by    
Bringing innovative technologies together
Monday, 18 November 2013   by    
Advancing MRI scans for foetal development
Wednesday, 27 November 2013   by    
MRI Use Common, But Not Always Evidence-Based
Sunday, 15 December 2013   by    
Searchterm 'Magnetic Source Imaging' was also found in the following services: 
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Machine Imperfection ArtifactInfoSheet: - Artifacts - 
Case Studies, 
Reduction Index, 
etc.MRI Resource Directory:
 - Artifacts -
Quick Overview
Please note that there are different common names for this artifact.

Artifact Information
NAME Machine imperfection, data error
DESCRIPTION Striped ghosts with a shift of half the field of view
REASON Non-uniform sampling, phase differences
HELP Data correction

Machine imperfection-based artifacts manifest themselves due to the fact that the odd k-space lines are acquired in a different direction than the even k-space lines. Slight differences in timing result in shifts of the echo in the acquisition window. By the shift theorem, such shifts in the time domain data then produce linear phase differences in the frequency domain data.
Without correction, such phase differences in every second line produce striped ghosts with a shift of half the field of view, so-called Nyquist ghosts. Shifts in the applied magnetic field can also produce similar (but constant in amplitude) ghosts.
This artifact is commonly seen in an EPI image and can arise from both, hardware and sample imperfections.
A further source of machine-based artifact arises from the need to acquire the signal as quickly as possible. For this reason the EPI signal is often acquired during times when the gradients are being switched. Such sampling effectively means that the k-space sampling is not uniform, resulting in ringing artifacts in the image.

Image Guidance
Such artifacts can be minimized by careful setup of the spectrometer and/or correction of the data. For this reasons reference data are often collected, either as a separate scan or embedded in the imaging data. The non-uniform sampling can be removed by knowing the form of the gradient switching. It is possible to regrid the data onto a uniform k-space grid.

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Further Reading:
MRI Artifact Gallery
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