StudentShare solutions
Triangle menu

Echo Planar Imaging, or EPI, Fast Imaging Techniques (MRI) - Essay Example

Nobody downloaded yet

Extract of sample
Echo Planar Imaging, or EPI, Fast Imaging Techniques (MRI)

EPI is fast because it uses single excitation of a slice followed by the continuous readout through the k-space using GRE pulse sequence (Delbeke, Martin, Patton and Sandler, 2002). After the RF excitation MR imaging mostly depends upon the formation of echo at some point. Spin echo (SE) sequences are the most former MR sequences (in fact earlier to imaging) (Westbrook, 2009). EPI is called blip because between echoes phase blip causes change in Ky and a new line is sampled. In EPI each gradient refocused echo contributes one line in k-space. The positive and negative read gradients change the direction in which the line is read. In contemporary MR system that are capable of EPI, the fast varying magnetic field linked with the shifting of the magnetic field gradients is capable to produce currents within tissue, which may exceed the nerve depolarization threshold and cause peripheral nerve stimulation (PNS). However, the chance of cardiac muscle stimulation also exists, as a result presenting an artifact (Delbeke, Martin, Patton and Sandler, 2002). From the research on animals it can be suggested that stimulation of respiratory system takes place at exposure levels of the order of 3 times that necessary for PNS, while cardiac stimulation requires 80 times the PNS threshold. The probability of occurring PNS is mostly in EPI. Particularly one has to be cautious of 2 situations: (a) Whilst sloping slices are utilized and it is probable to have a greater slew rate through adding the contributions from two or three sets of gradient coils. (b) For coronal or segittal EPI where the possible current loops in the torso are greatest when the read gradient is in the head-tool direction. In general, dB/dt is monitored through the scanner and lead to the likelihood of stimulation (Delbeke, Martin, Patton and Sandler, 2002). Spin Echo EPI The most commonly used sequence is known as spin echo. It is characterized by the initial application of a radio-frequency pulse of 90 degrees, followed by one more in front of 180 degrees, then double the time between these two pulses a signal or echo from stimulated tissue is successively applied with several pulse sequences of 90 and 180 degrees, each of which produces an echo which will form the radio wave which provides molecular information. In carefully constructed sequences extra slices are excited while waiting for T1 recovery, so one phase encoding step is acquired for several slices during TR (Weishaupt, Koechli and Marincek, 2008). In a spin echo sequence, the phase encoding changes amplitude every TR. This is to give each echo the correct 'kick' to place it on the right line. You can think of it like a soccer ball tied to a piece of elastic. You need a hefty kick to move it to the outer edges of k-space (large phase encoding gradient), and a little kick for a line closer to the center (small phase encoding gradient). The spins always return to the centre line (i.e. the elastic in our analogy) because you are re-exciting the spins each TR in a spin echo sequence (Bankman, 2008). (Weishaupt, Koechli and Marincek, 2008). Figure shows spin echo pulse diagram, with the sampling of k –space. Reducing the time of the Image For acquiring an image time required is based on the following relation. Tacq = Nacq X Nv X TR Where, Nacq = acquisition number, Ny = Number of steps for phase encoding, and TR= Time period for repetition. Hence in order to reduce time of ...Show more


Echo Planar Imaging, or EPI, Fast Imaging Techniques (MRI) [Writer Name] [Institution Name] Echo Planar Imaging, or EPI, Fast Imaging Techniques (MRI) Answer 1 The concept of EPI was first presented in 1977 by Mansfield. On the other hand, different technical issues related to EPI have been overcome in the last decade…
Author : eleonore46
Echo Planar Imaging, or EPI, Fast Imaging Techniques (MRI) essay example
Read Text Preview
Save Your Time for More Important Things
Let us write or edit the essay on your topic
"Echo Planar Imaging, or EPI, Fast Imaging Techniques (MRI)"
with a personal 20% discount.
Grab the best paper

Check these samples - they also fit your topic

Factors affecting quality of MRI image.Benefits of circular or square spiral EPI methods
Accurate image reconstruction depends on resonance frequency (rf) of a spin, which is achieved by strong homogenous external field and superposition of a spatially linear gradient. If these conditions are not met, then the relative positions of anatomical structures will be misrepresented in the reconstructed MRI image.
10 pages (2500 words) Essay
Any amount of water proton found in the inhomogeneity of the local field will result in off-resonance. The shift in frequency of such spins varies from one region to another, as well as from one patient to another. However, it will still behave like the off-resonance fat.
16 pages (4000 words) Essay
Water proton amounts found in the inhomogeneity of the local field will result in off-resonance. The frequency changes of such spins vary in different regions and in different patients. However, its behavior will still resemble that of off-resonance fat. Several methods have been used in the correction of geometric distortions in MRI diffusion weighted normally resulting from static magnetic field inhomogeneties.
10 pages (2500 words) Essay
Echo Planar Imaging, or EPI, Fast Imaging Techniques (MRI)
Introduction Magnetic susceptibility refers to the process y issue tissue affects magnetic field. The existing boundaries between fat and compact bone are normally affected by the transverse magnetic field de-phasing and signal distortion. The consequent of the above is that frequency positions in the wrong location in the phase direction.
10 pages (2500 words) Essay
BLIP Echo Planar Imaging Method
This method of imaging is used in functional MRI and rapid whole brain imaging. The time required to acquire an image is dependent on Tacq = Nacq x Ny x TR Where Nacq is the no. of acquisitions, Ny is the no. of phase encoding steps and TR is the repetition time.
10 pages (2500 words) Essay
Echo-planar Imaging in Magnetic Resonance Imaging
“EPI is fundamentally just a trick of spatial encoding” (Cohen, 2000, p.3). EPI is a speedy, elastic method of imaging. It has high-quality contrast and resolution capabilities, and also possesses many prospective applications in clinical imaging, including functional MRI and rapid whole brain imaging.
8 pages (2000 words) Essay
Fast Imaging Techniques (MRI)
Receiver bandwidth is generally used to fasten the digitalisation of the MR signals. In this regard, the receiver bandwidth 1 can determine the frequency ranges that will eventually be sampled using the frequency encoding gradient. During the optimization through an increase of receiver bandwidth, the amount of time at the flat top of the gradient is significantly reduced.
6 pages (1500 words) Essay
Perfusion-weighted imaging (PW) MRI (magnetic resonance imaging)
The amalgamation of both practices is tremendously encouraging for the primary recognition and valuation of stroke, for tumour description and for the estimation of neurodegenerative illnesses (Nelson, et al., 1995). Perfusion applications are intended to evaluate the distribution of blood to a vascular bed.
12 pages (3000 words) Essay
These parameters include magnetic susceptibility, k-space line, spin echo sequence, duration of the EPI trajectory, phase direction and gradient (Ye et al, 1996, p.219). Magnetic susceptibility
10 pages (2500 words) Essay
Magnetic Resonance Imaging (MRI)
When in use, the machine takes images of the target organ in various angles which are then processed using a computer to yield a picture of high detail of the area selected for observation. Basically therefore, the technique makes use of a computer, an
6 pages (1500 words) Essay
Hire a pro to write
a paper under your requirements!
Win a special DISCOUNT!
Put in your e-mail and click the button with your lucky finger
Your email
Comments (0)
Click to create a comment
Contact Us