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مشاركةبواسطة دكتور كمال سيد » الثلاثاء مايو 21, 2013 5:55 pm

Magnetic resonance imaging

Magnetic resonance imaging (MRI), nuclear magnetic resonance imaging (NMRI), or magnetic resonance tomography (MRT) is a medical imaging technique used in radiology to visualize internal structures of the body in detail. MRI makes use of the property of nuclear magnetic resonance (NMR) to image nuclei of atoms inside the body.
MRI can create more detailed images of the human body than possible with X-rays.

An MRI scanner is a device in which the patient lies within a large, powerful magnet where the magnetic field is used to align the magnetization of some atomic nuclei in the body, and radio frequency magnetic fields are applied to systematically alter the alignment of this magnetization.
This causes the nuclei to produce a rotating magnetic field detectable by the scanner—and this information is recorded to construct an image of the scanned area of the body.
Magnetic field gradients cause nuclei at different locations to precess at different speeds, which allows spatial information to be recovered using Fourier analysis of the measured signal. By using gradients in different directions, 2D images or 3D volumes can be obtained in any arbitrary orientation.
MRI provides good contrast between the different soft tissues of the body, which makes it especially useful in imaging the brain, muscles, the heart, and cancers compared with other medical imaging techniques such as computed tomography (CT) or X-rays. Unlike CT scans or traditional X-rays, MRI does not use ionizing radiation.

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Re: introduction

مشاركةبواسطة دكتور كمال سيد » الجمعة أكتوبر 31, 2014 9:36 pm


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Re: introduction

مشاركةبواسطة دكتور كمال سيد » السبت نوفمبر 01, 2014 10:02 am


Magnetic resonance imaging (MRI) is an imaging technique used primarily in medical settings to produce high quality images of the inside of the human ****. MRI is ****d on the principles of nuclear magnetic resonance (NMR), a spectroscopic technique used by scientists to obtain microscopic chemical and physical information about molecules. The technique was called magnetic resonance imaging rather than nuclear magnetic resonance imaging (NMRI) because of the negative connotations associated with the word nuclear in the late 1970's.

MRI started out as a tomographic imaging technique, that is it produced an image of the NMR signal in a thin slice through the human ****. MRI has advanced beyond a tomographic imaging technique to a volume imaging technique. This package presents a comprehensive picture of the basic principles of MRI.

Before beginning a study of the science of MRI, it will be helpful to reflect on the brief history of MRI. Felix Bloch and Edward Purcell, both of whom were awarded the Nobel Prize in 1952, discovered the magnetic resonance phenomenon independently in 1946. In the period between 1950 and 1970, NMR was developed and used for chemical and physical molecular analysis.

In 1971 Raymond Damadian showed that the nuclear magnetic relaxation times of tissues and tumors differed, thus motivating scientists to consider magnetic resonance for the detection of disease. In 1973 the x-ray-****d computerized tomography (CT) was introduced by Hounsfield.

This date is important to the MRI timeline because it showed hospitals were willing to spend large amounts of money for medical imaging hardware. Magnetic resonance imaging was first demonstrated on small test tube samples that same year by Paul Lauterbur. He used a back projection technique similar to that used in CT.

In 1975 Richard Ernst proposed magnetic resonance imaging using phase and frequency encoding, and the Fourier Transform. This technique is the basis of current MRI techniques. A few years later, in 1977, Raymond Damadian demonstrated MRI called field-focusing nuclear magnetic resonance. In this same year, Peter Mansfield developed the echo-planar imaging (EPI) technique. This technique will be developed in later years to produce images at video rates (30 ms / image).

Edelstein and coworkers demonstrated imaging of the **** using Ernst's technique in 1980. A single image could be acquired in approximately five minutes by this technique. By 1986, the imaging time was reduced to about five seconds, without sacrificing too much image quality.

The same year people were developing the NMR microscope, which allowed approximately 10 µm resolution on approximately one cm samples. In 1987 echo-planar imaging was used to perform real-time movie imaging of a single cardiac cycle. In this same year Charles Dumoulin was perfecting magnetic resonance angiography (MRA), which allowed imaging of flowing blood without the use of contrast agents.

In 1991, Richard Ernst was rewarded for his achievements in pulsed Fourier Transform NMR and MRI with the Nobel Prize in Chemistry. In 1992 functional MRI (fMRI) was developed. This technique allows the mapping of the function of the various regions of the human brain. Five years earlier many clinicians thought echo-planar imaging's primary applications was to be in real-time cardiac imaging.

The development of fMRI opened up a new application for EPI in mapping the regions of the brain responsible for thought and motor control. In 1994, researchers at the State University of New York at Stony Brook and Princeton University demonstrated the imaging of hyperpolarized 129Xe gas for respiration studies

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Re: introduction

مشاركةبواسطة دكتور كمال سيد » السبت نوفمبر 01, 2014 10:16 am

Opportunities in MRI

In 2003, there were approximately 10,000 MRI units worldwide, and approximately 75 million MRI scans per year performed. As the field of MRI continues to grow, so do the opportunities in MRI.
There will always be a need for radiologists trained in MRI to read the magnetic resonance images. A radiologist is a medical doctor that has specialized in the field of radiology. The need is expected to grow so much that there will be and increased use of Radiology Practitioner Assistants and Radiology Physician Assistants.

An MRI technologist is an individual that operates the MRI scanner to obtain the images that a radiologist prescribes. ****d on the number of current MRI systems, it is estimated that there will be a constant need for over 1000 MRI technologists per year. A good resource for MRI technologists is the Society for Magnetic Resonance Technologists (SMRT).

Two new specialist positions have recently evolved in MRI: the post processing technologist and the health safety specialist. The MRI post processing technologist applies various post processing algorithms to magnetic resonance images to either extract more information from or enable better visualization of information in magnetic resonance images. An MRI health safety specialist assists hospitals and clinics in setting up and maintaining a safe MRI system.

Because of the complexity of the MRI system, there will always be a need for MRI service technicians. Service technicians are hired by both the MRI manufacturers and some larger sites to keep the MRI system operating properly. MRI service technicians usually have a BS or associates degree in electrical technology and a good knowledge of MRI.

In any field, there will be a need for scientists trained in the basic sciences of chemistry, biology, and physics to perform basic research and push back the frontiers of the science. Some specific needs for these scientists include contrast agent and molecular imaging development, and advanced imaging pulse sequence design.
These individuals typically have an advanced degree in their respective field and have had significant training in MRI. A good resource for scientists is the International Society for Magnetic Resonance in Medicine (ISMRM).

Biomedical engineers and material scientists are needed for MRI subsystem development. One of these subsystems where continued demand is seen is imaging coil development. An emerging area requiring many skilled individuals is the development of MRI compatible devices.

These devices include pacemakers, defibrillators, surgical clips and pins, and catheters. Many of these devices will require discoveries at the molecular level, such as biocompatible antireflective coatings for pacemaker wires and strong non ****llic synthetic joints and pins.

Imaging scientists are needed for algorithm development for post processing of magnetic resonance images, and intelligent code for identifying and diagnosing pathology. Computer scientists are still needed to design user friendly efficient graphical user interfaces (GUI) for newly developed software.
Lastly, there is a need for architects to design safe and efficient MRI centers and clinics.

The Basics of MRI is a good starting place for all the above individuals interested in starting their training in pursuit of a career in MRI or a related field.
If you are interested in one of these professions, familiarize yourself with the profession and MRI. Explore various options for obtaining the education needed for the profession.

Currently, there are approximately six major clinical MRI original equipment manufacturers (OEMs). In addition to these clinical OEMs, there are two major experimental MRI OEMs. Other MRI related subsystem manufacturers include RF coil, contrast agents, compatible devices, RF amps, and magnets.

The following tables contain the ****s of some of the major manufacturers of these devices. Click on the **** for an external link to the company. Because they are links external to The Basics of MRI, they are subject to change.

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