3.0 T versus 1.5 T: Coil Design Similarities and Differences
Section snippets
Overview of the role of coils in MR imaging
RF coils have become a vital part of a modern MR imaging system. RF coils are the primary transducers of the magnetic resonance signal, and their geometry and electrical design objectives are primary determiners of obtainable SNR (and hence image resolution). The maximum SNR is set by the coil array and only can decrease through the rest of the receiver system. SNR is the primary parameter in assessing the clarity of a clinical image. Clinical radiology departments need to use clear (high SNR)
Overview of important parameters—signal-to-noise ratio, resolution, time
Understanding the relationship between SNR, resolution, and time is critically important if one is to understand the implications of improved RF coil design. SNR is the raw material from which high-resolution images are formed. From a RF coil designer's perspective, there is only one primary parameter, and that is SNR. The coil designer has no control over the image resolution or the time chosen for a given image acquisition. The MR operator may vary the matrix size and image acquisition time
Overview of coils' importance to signal-to-noise–related parameters
Again, from a RF coil design, perspective SNR is the most important parameter. One, however, also must consider the shape of the region of interest and the degree to which the RF coil provides a homogeneous view of that region. Although there are modern ways of optimizing image uniformity after acquisition, all clinically important parts of an image must have adequate SNR. Therefore, the RF coil must optimize SNR and field shape for each ROI. That is why there are so many different RF coils in
Challenges of coil arrays and preamplifier decoupling, cable currents, and relation to 3.0 T
RF coil arrays have become popular, because they represent the most efficient solution to the problem of maximizing SNR over a large ROI. In essence, a coil array combines the advantages of small, tightly coupled coils, with the ability to cover large ROIs [2]. The SNR of the array then becomes the optimal combination of signal from each coil in the array, and the noise component is minimized through careful decoupling of the coils [2]. The main problem that arises from large coil arrays
Challenges and benefits of parallel imaging and relation to 3.0 T
Spatial encoding of coil elements has been employed recently as part of the spatial sampling procedure and has been used to reduce the amount of phase encoding (and therefore the acquisition time) necessary for a given image resolution [10]. Techniques employing this spatial encoding include Sensitivity Encoding (SENSE), Generalized Autocalibrating Partially Parallel Acquisitions (GRAPPA), modified SENSE (mSENSE), Array Spatial Sensitivity Encoding Technique (ASSET), and SPEEDER. Intuitive
Tissue related changes of field caused by frequency changes—coil behavior that helps overcome this effect
There are two types of interactions that occur between human tissue and the use of high magnetic fields and frequencies. The first and best understood are those interactions caused by the tissue's magnetic susceptibility. Magnetic susceptibility refers to the ability of human tissue to change the density of the static magnetic field [11]. Magnetic susceptibility is seen in regions where there is an abrupt change from tissue to air (as in the brain) at high fields. When the field homogeneity is
Clinical implications of high field coil arrays
From a clinical user's perspective, high-field coil arrays as applied to 3.0 T MR provide a host of advantages and very few disadvantages. Clearly, higher SNR over desired ROI is available, and this can be converted into higher resolution images, higher spectral resolution, or shorter imaging times by the appropriate use of image acquisition parameters (eg, matrix size, Repetition time [TR], and Echo time [TE]). Parallel imaging techniques using large coil arrays provide even more opportunities
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MRI evaluation and safety in the developing brain
2015, Seminars in PerinatologyCitation Excerpt :This has led to the development of lighter saline filled pads.33,34,42,66 Other methods of decreasing radiofrequency inhomogeneity include multichannel transmission body coils and active RF shimming combined with parallel imaging; however, these methods are not always available on commercial MR scanners35,48,52,241,242 and will not be discussed in any further detail in this review. The effects of field inhomogeneity in steady-state free precession (SSFP) sequences result in off-resonance effects that can potentially exacerbate the appearance of banding artifacts, alternating dark and light bands, especially at the edge of the field of view.31,33
MRI Head Coil Malfunction Producing Artifacts Mimicking Malformation of Cortical Development in Pediatric Epilepsy Work-Up
2020, American Journal of Neuroradiology