The acronyms of MR

Communicating to Patients Article 4 Minute Read GE Healthcare Global

“Text speak” may have invaded our everyday lives. Conversations may include abbreviations and acronyms such as LOL or TTYL. However, the average citizen may believe that scientists love their acronyms more than most. This may cause scientific posts and journals to seem as though they are written in a different language. However, understanding scientific articles is fairly reliant upon knowing what the acronym stands for, as well as understanding the scientific principles. The acronyms below are some of the most commonly used in magnetic resonance imaging (MRI), after MR or MRI of course.

An overview of acronyms and their meanings

  • ADC: The apparent diffusion coefficient (ADC) is the quantification of the diffusion within tissue and is measured in units of mm2/s.1 This number is calculated during diffusion weighted imaging. It may provide many types of information for radiologists, including information to help determine whether a tumor is benign or malignant.2 One study found that the ADC was significantly lower in malignant lesions than in benign ones.
  • DTI: Diffusion tensor imaging (DTI) is a form of diffusion imaging which takes advantage of the random motion of water molecules (Brownian motion).3,4 When a strong magnetic field is applied, the water molecules react before relaxing again once the field relaxes. Diffusion techniques allow radiologists to clearly see the tissue structures of the body. DTI utilizes information obtained from diffusion weighted imaging which can be translated into tensor estimations, average diffusion or the anisotropy per voxel among other measurements. DTI can be used help physicians to determine brain abnormalities, connectivity and ischemia (reduced blood flow).4
  • DWI: Diffusion weighted-imaging (DWI) uses the diffusion of molecules in the body to generate images of tissue structures.5,6 It also provides the necessary data to calculate the apparent diffusion coefficient and to produce diffusion tensor images. Like diffusion tensor imaging, it can be used to help determine brain abnormalities and ischemia. However, it can also be used to assist detection of brain development and degradation, head, neck and thoracic malignancies and tumors.
  • EPI: A single MR image can be obtained in as little as 20 msec using the echo planar imaging (EPI)  technique.7 EPI obtains all spatial-encoding information after a single radio-frequency excitation, shortening the acquisition. The typical imaging study requires multiple excitations separated by a repetition time. EPI is less sensitive to motion than standard MR imaging, allowing for imaging of changing physiologic processes. It can be used for perfusion or diffusion imaging of the brain, as well as functional MRI.

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  • FSE: One way to abbreviate scanning time is through the use of the fast spin echo (FSE) sequence.8 The fast spin echo’s reduction of scanning time is proportional to the number of echoes produced in each cycle. This frequently works well with a rectangular field of view, as in spinal imaging. FSE uses 180-degree inversion pulses, enabling the sequence to correct for external magnetic field inhomogeneity (uniformity). This sequence results in a reduce signal to noise ratio compared to the conventional spin echo sequence.
  • GRE: The gradient echo (GRE) sequence is one of the basic sequences in MR, alongside the spin echo.9,10 The GRE sequence uses gradient fields to generate transverse magnetisation and flip angles of less than 90-degrees. GRE sequences are more versatile than spin echo and is used in a number of different techniques. This sequence is made up of repetition time and echo time but is also influenced by the flip angle of the spins. GRE sequences may be used in cardiac MR and contrast-enhanced angiography.
  • SE: Early on in the history of MRI, spin echo (SE) pulse sequences were developed and used frequently.11 Like gradient echo sequences, the spin echo sequence is one of the basic sequences. They are made up of two variables: repetition time and echo time. One echo is measured during each repetition time. They also have a slice selective 90-degree pulse followed by one or more 180-degree refocusing pulses. SE has a higher signal to noise ratio than the fast spin echo. Currently, the SE is used in its quicker form, the fast spin echo.

These acronyms may help people to understand what is being said about the sequences and techniques used by radiologists on a daily basis. The sequences listed above, FSE, GRE and SE, are some of the basic sequences for understanding magnetic resonance. The techniques, DTI, DWI and EPI, may be among the most commonly used imaging techniques and the ADC measurement works with the diffusion imaging techniques to provide valuable, additional information. Although there may be an abundance of magnetic resonance acronyms, patients and clinicians alike should be able to understand the scientific writings that they see. After all, it isn’t so different from the text speak that has invaded their everyday lives, such as LOL.

References

1. Henry Knipe, et al. “Apparent diffusion coefficient.” Radiopaedia. Web. 16 January 2019. <https://radiopaedia.org/articles/apparent-diffusion-coefficient-1?lang=us>.

2. Khaled Hussein, et al. “Role of MRI Apparent Diffusion Coefficient (ADC) Quantification in the differentiation between benign and malignant pulmonary lesions.” European Respiratory Society. 6 December 2017. Web. 16 January 2019. <https://erj.ersjournals.com/content/50/suppl_61/PA3741.article-info>.

3. José M. Soares, et al. “A hitchhiker’s guide to diffusion tensor imaging.” Front Neurosci. 12 March 2013; 7:31. Web. 28 January 2019. doi: 10.3389/fnins.2013.00031.

4. Denis Le Bihan, et al. “Diffusion Tensor Imaging: Concepts and Applications.” Journal of Magnetic Resonance Imaging. 2001; 13:534-546. Web. 28 January 2019. <http://vis.cs.brown.edu/docs/pdf/Bihan-2001-DTI.pdf>.

5. Vinit Baliyan, et al. “Diffusion weighted imaging: Technique and applications.” World J Radiol. 28 September 2016; 8(9): 785-798. Web. 29 January 2019. <https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5039674/>.

6. Dow-Mu Koh and David J. Collins. “Diffusion-Weighted MRI in the Body: Applications and Challenges in Oncology.” American Journal of Roentgenology. June 2007; 188(6): 1622-1635. Web. doi: 10.2214/AJR.06.1403.

7. Robert L. DeLaPaz. “Echo-planar Imaging.” RadioGraphics. September 1994. Web. 28 January 2019. <https://pubs.rsna.org/doi/pdf/10.1148/radiographics.14.5.7991813>.

8. Andrew Murphy, et al. “Fast spin echo.” Radiopaedia.org. 2018. Web. 29 January 2019. <https://radiopaedia.org/articles/fast-spin-echo?lang=us>.

9. Yuranga Weerakkody, et al. “Gradient echo sequences. Radiopaedia.org. 2018. Web. 29 January 2019. <https://radiopaedia.org/articles/gradient-echo-sequences-1?lang=us>.

10. Michael Markl. “Gradient echo imaging.” JMRI. 15 May 2012. Web. 29 January 2019. doi: https://doi.org/10.1002/jmri.23638.

11. J. Ray Ballinger, et al. “Spin echo sequences.” Radiopaedia.org. 2017. Web. 29 January 2019. <https://radiopaedia.org/articles/spin-echo-sequences/revisions?lang=us>.