Principles and Applications of Echo-planar Imaging: A Review for the General Radiologist

Abstract

Echo-planar imaging is a very fast magnetic resonance (MR) imaging technique capable of acquiring an entire MR image in only a fraction of a second. In single-shot echo-planar imaging, all the spatial-encoding data of an image can be obtained after a single radio-frequency excitation. Multishot echo-planar imaging results in high-quality images comparable to conventional MR images. However, echo-planar imaging offers major advantages over conventional MR imaging, including reduced imaging time, decreased motion artifact, and the ability to image rapid physiologic processes of the human body. The use of echo-planar imaging has already resulted in significant advances in clinical diagnosis and scientific investigation, such as in evaluation of stroke and functional imaging of the human brain, respectively. The clinical indications for echo-planar imaging are expanding rapidly, and it can now be applied to many parts of the body, including the brain, abdomen, and heart. Today, with the availability of echo-planar imaging-capable MR imagers at many sites, the general radiologist can benefit from echo-planar imaging and its clinical applications.

Optimization and Clinical Feasibility of Free-breathing Diffusion-weighted Imaging of the Liver: Comparison with Respiratory-Triggered Diffusion-weighted Imaging

“…In addition to use of a large bandwidth, advances in MR systems may minimize the susceptibility and chemical shift artifacts of the EPI technique and blurring from T 2 * signal intensity decay during the gradientecho train to improve the quality of images acquired with FB-DWI regardless of the many EPI factors. 21,22 Although enlarging the bandwidth decreases the SNR, a combination of high magnetic fields of the MR system, a 32-channel receiver coil, and the free-breathing technique can compensate for this shortcoming because these devices and technique can increase the SNR. Therefore, FB-DWI can produce good SNRs and CNRs, which is consistent with the previous result.…”

MRI-based communication for untethered intelligent medical microrobots

“…Each line is phase-encoded separately by phase-encoding blips on the phase-encoding axis [94] (Figure 4-15). Reduction of the acquisition time in EPI sequences has been carried out by decreasing the echo train time by applying fast gradient.…”

“…Reduction of the acquisition time in EPI sequences has been carried out by decreasing the echo train time by applying fast gradient. Echo-planar imaging employs gradient coils capable of a maximum amplitude of 20mT/m, a minimum rise time of 0.1ms, a slew rate of 200T/m per second, and a duty cycle of 50%-60% [94]. However, the switching rate is limited for safety consideration because fastswitching gradients induce a time-varying electric field that may cause peripheral nerve stimulation (PNS) at sufficiently high amplitudes [103][104][105].…”

“…(4-3), an alternative magnetic field generated by a transmitting coil (ΔBm) leads to an alternative MR signal variation over time, the frequency of which can be detected by applying a Fourier transform after sampling the signal over time. Single-shot Echo-Planar Imaging (EPI) [93] is a very fast imaging method that can acquire a complete image in a fraction of a second [94]. As a result, the alternative signal can be sampled using real-time EPI images.…”

Radiofrequency artefacts in echoplanar imaging induced by two 1.5 T MR scanners in close proximity

“…It has been reported that applying the wider BW in EPI DWI, which is a fast acquisition sequence and is resistant to moving artefacts, [1][2][3][4][5] can result in RF interference by the environment, leading to artefacts being produced. 6 When an EPI DWI is selected on Magnetom® Avanto (Siemens Medical Solutions, Erlangen, Germany), the RF of Magnetom Symphony (Siemens Medical Solutions) will be picked up by the receiver coil of Avanto, resulting in RF artefacts on the images.…”