{ "id": "epjvb89s6g", "slug": "echo-planar-imaging", "title": "Echo-planar imaging", "updated": "2026-10-15", "topic_path": [ { "id": "life", "label": "Life and health", "api_url": "https://www.edgepedia.org/api/v1/topics/life" }, { "id": "life.health", "label": "Human health and medicine", "api_url": "https://www.edgepedia.org/api/v1/topics/life.health" }, { "id": "life.health.clinical", "label": "Clinical assessment and procedures", "api_url": "https://www.edgepedia.org/api/v1/topics/life.health.clinical" }, { "id": "life.health.clinical.clinical-imaging", "label": "Medical imaging and radiography", "api_url": "https://www.edgepedia.org/api/v1/topics/life.health.clinical.clinical-imaging" }, { "id": "life.health.clinical.clinical-imaging.magnetic-resonance-imaging-techniques", "label": "Magnetic resonance imaging techniques", "api_url": "https://www.edgepedia.org/api/v1/topics/life.health.clinical.clinical-imaging.magnetic-resonance-imaging-techniques" } ], "geo": [ { "id": "geo.nongeo.t1946.life.health.clinical.clinical-imaging.magnetic-resonance-imaging-techniques", "label": "Non-geographic · 1946 to 2000: Magnetic resonance imaging techniques", "api_url": "https://www.edgepedia.org/api/v1/geo/geo.nongeo.t1946.life.health.clinical.clinical-imaging.magnetic-resonance-imaging-techniques", "path": [ { "id": "geo.nongeo", "label": "Non-geographic", "api_url": "https://www.edgepedia.org/api/v1/geo/geo.nongeo" }, { "id": "geo.nongeo.t1946", "label": "Non-geographic · 1946 to 2000", "api_url": "https://www.edgepedia.org/api/v1/geo/geo.nongeo.t1946" }, { "id": "geo.nongeo.t1946.life", "label": "Life and health", "api_url": "https://www.edgepedia.org/api/v1/geo/geo.nongeo.t1946.life" }, { "id": "geo.nongeo.t1946.life.health", "label": "Human health and medicine", "api_url": "https://www.edgepedia.org/api/v1/geo/geo.nongeo.t1946.life.health" }, { "id": "geo.nongeo.t1946.life.health.clinical", "label": "Clinical assessment and procedures", "api_url": "https://www.edgepedia.org/api/v1/geo/geo.nongeo.t1946.life.health.clinical" }, { "id": "geo.nongeo.t1946.life.health.clinical.clinical-imaging", "label": "Medical imaging and radiography", "api_url": "https://www.edgepedia.org/api/v1/geo/geo.nongeo.t1946.life.health.clinical.clinical-imaging" }, { "id": "geo.nongeo.t1946.life.health.clinical.clinical-imaging.magnetic-resonance-imaging-techniques", "label": "Magnetic resonance imaging techniques", "api_url": "https://www.edgepedia.org/api/v1/geo/geo.nongeo.t1946.life.health.clinical.clinical-imaging.magnetic-resonance-imaging-techniques" } ] } ], "excerpt": "Echo-planar imaging (EPI) is a fast MRI pulse sequence, proposed by Peter Mansfield in 1977, that acquires images in tens of milliseconds and underlies fMRI and diffusion imaging.", "snippet": "Echo-planar imaging (EPI) is a fast MRI pulse sequence, proposed by Peter Mansfield in 1977, that acquires images in tens of milliseconds and underlies fMRI and diffusion imaging.", "node": "life.health.clinical.clinical-imaging.magnetic-resonance-imaging-techniques", "markdown": "# Echo-planar imaging\n\nEcho-planar imaging (EPI) is a family of magnetic resonance imaging pulse sequences that traverses k-space (raw frequency-data grid from which MRI images are reconstructed) along an echo-planar trajectory by rapidly switching the readout gradient; in single-shot EPI an entire two-dimensional image is acquired after one radiofrequency excitation, while in segmented EPI k-space is divided across multiple excitations. Because conventional sequences collect one or a few k-space lines per excitation, EPI shortens acquisition from minutes to tens of milliseconds, and it is the technique most frequently used for functional MRI (fMRI) and diffusion imaging.[1](https://doi.org/10.1088/0022-3719/10/3/004) • [2](https://www.nobelprize.org/uploads/2018/06/mansfield-lecture.pdf) • [3](https://pubs.rsna.org/doi/10.1148/radiographics.21.3.g01ma23767) • [4](https://link.springer.com/book/10.1007/978-3-642-80443-4)\n\n| Key fact | Value |\n|---|---|\n| Principle | In single-shot EPI, all of k-space is filled after one RF excitation, using an oscillating readout gradient and blipped phase encoding; segmented EPI divides k-space across multiple excitations[3](https://pubs.rsna.org/doi/10.1148/radiographics.21.3.g01ma23767) |\n| Single-shot speed | A whole-brain set of 20 images in 2 s; single images in 20–50 ms[2](https://www.nobelprize.org/uploads/2018/06/mansfield-lecture.pdf) • [3](https://pubs.rsna.org/doi/10.1148/radiographics.21.3.g01ma23767) |\n| Matrix limit (single shot) | Typically no larger than 128×128[3](https://pubs.rsna.org/doi/10.1148/radiographics.21.3.g01ma23767) |\n| Gradient demands | ~20 mT/m amplitude, 0.1 ms rise time, 200 T/m/s slew, 50–60% duty cycle[3](https://pubs.rsna.org/doi/10.1148/radiographics.21.3.g01ma23767) |\n| Typical echo spacing | ~0.4–1 ms (0.58 ms in HCP fMRI; 0.78 ms in HCP diffusion)[5](https://www.humanconnectome.org/hcp-protocols-ya-3t-imaging) • [6](https://labs.dgsom.ucla.edu/file/449825/M229_Lecture7_FastImagingEPI_2023.pdf) |\n| Main applications | BOLD fMRI, diffusion-weighted and tensor imaging, perfusion, cardiac and fetal imaging[7](https://www.science.org/doi/10.1126/science.1925560) |\n| Chief artifacts | Susceptibility geometric distortion, Nyquist (N/2) ghosting, fat shift, T2* blurring[8](https://cds.ismrm.org/protected/23MProceedings/PDFfiles/E8315_M4QM3sSj4.html) |\n\n## How it works\n\nEPI is defined by its k-space trajectory rather than by its radiofrequency excitation. A large oscillating readout gradient traverses \\( k_{x} \\) back and forth, while small \"blip\" gradients of the phase-encoding gradient step the trajectory incrementally along \\( k_{y} \\), producing a single sawtooth (zigzag) path that covers the whole k-space plane.[9](https://cds.ismrm.org/protected/16MProceedings/PDFfiles/7219.html) • [10](https://www.magnetic-resonance.org/ch/08-04.html)\n\nThe signal equation, \\( S(t) \\propto \\int M_{0}(r) e^{ik(t)\\cdot r} e^{-t/T_{2}^{*}(r)} e^{i\\omega(r)t} dr \\), explains EPI's characteristic image quality: \\( T_{2}^{*} \\) decay amplitude-modulates k-space, blurring along the phase-encoding direction, and resonance offsets phase-modulate it, displacing signal in the same direction.[9](https://cds.ismrm.org/protected/16MProceedings/PDFfiles/7219.html)\n\n## How it is done\n\nA practical single-shot EPI sequence runs as follows. An excitation pulse (gradient-echo or spin-echo type) tips the magnetization; prephasing gradients displace the trajectory to the starting corner of k-space, at \\( -k_{x\\mathrm{max}} \\). The echo train then begins: the readout gradient oscillates at full amplitude, and a blip follows each readout to advance one line in \\( k_{y} \\).[2](https://www.nobelprize.org/uploads/2018/06/mansfield-lecture.pdf) • [9](https://cds.ismrm.org/protected/16MProceedings/PDFfiles/7219.html) On modern systems the slew rate, around 200 mT/m/ms, is usually more limiting than gradient amplitude; ramp sampling acquires data during the ramps too, at the cost of resampling to a uniform \\( k_{x} \\) grid and stringent gradient-accuracy requirements.[9](https://cds.ismrm.org/protected/16MProceedings/PDFfiles/7219.html)\n\nDesign choices follow directly from the readout. Echo spacing obeys \\( \\mathrm{ESP} = (T_{s} \\cdot N_{x}) + 2 \\cdot (G_{\\mathrm{read}}/\\mathrm{SR}) \\).[6](https://labs.dgsom.ucla.edu/file/449825/M229_Lecture7_FastImagingEPI_2023.pdf) The echo train length (the \"EPI factor\", 4–64 or more) is limited by \\( T_{2}^{*} \\) decay and off-resonance. For BOLD fMRI the flip angle is matched to the Ernst angle (whole-brain \\( T_{1} \\approx 1500 \\) ms), and phase encoding is placed anterior–posterior because left–right encoding is prone to artifacts near the temporal regions.[11](https://www.dartmouth.edu/dbic/docs/sequences/bold_acquisition.pdf)\n\n## Origin\n\nEcho-planar imaging was proposed by P Mansfield in 1977, in \"Multi-planar image formation using NMR spin echoes\" (Journal of Physics C Solid State Physics), as a two- or three-dimensional imaging method exploiting spin echoes in time-dependent field gradients, capable of producing images faster than previously described planar methods.[1](https://doi.org/10.1088/0022-3719/10/3/004) It built on E. L. Hahn's spin echo ([Physical Review](https://www.edgepedia.org/physical-review), 1950).[12](https://doi.org/10.1103/physrev.80.580) Before EPI, line-scanning took 10–20 minutes for a 64×64 image; EPI promised complete two-dimensional images in 20–50 ms.[2](https://www.nobelprize.org/uploads/2018/06/mansfield-lecture.pdf)\n\nAdoption was slow because the method demands gradient hardware far beyond what was commercially available. Human images, of the thorax of a 3-month-old infant, were obtained in 35 ms at 0.094 T.[3](https://pubs.rsna.org/doi/10.1148/radiographics.21.3.g01ma23767) Until the end of the 1980s few people believed EPI would be clinically useful; by 1990 it acquired complete images in 64–128 ms without movement artifact.[4](https://link.springer.com/book/10.1007/978-3-642-80443-4) • [13](https://royalsocietypublishing.org/doi/10.1098/rsta.1990.0178)\n\n## Variants\n\nEPI is a family of readouts distinguished by magnetization preparation and by how the echo train is segmented.\n\n**Gradient-echo versus spin-echo EPI.** GRE-EPI retains susceptibility (\\( T_{2}^{*} \\)) contrast and suits BOLD fMRI; SE-EPI refocuses static field offsets, minimizing signal loss from B0 inhomogeneity, and is standard for diffusion imaging.[6](https://labs.dgsom.ucla.edu/file/449825/M229_Lecture7_FastImagingEPI_2023.pdf)\n\n**Multishot (segmented) EPI** acquires a portion of k-space per shot, with the number of shots equal to phase-encoding steps divided by the echo train length; it raises resolution and reduces distortion but must manage motion-induced phase inconsistency between shots.[3](https://pubs.rsna.org/doi/10.1148/radiographics.21.3.g01ma23767) • [6](https://labs.dgsom.ucla.edu/file/449825/M229_Lecture7_FastImagingEPI_2023.pdf) Readout-segmented EPI shortens each readout segment, cutting susceptibility and T2* blurring, using a 2D navigator echo for phase correction and real-time reacquisition.[14](https://onlinelibrary.wiley.com/doi/10.1002/mrm.22024)\n\n**Accelerated EPI** relies on parallel imaging and multiband excitation: SENSE (Klaas P. Pruessmann and colleagues, 1999), GRAPPA (Mark A. Griswold and colleagues, 2002), and blipped-CAIPI simultaneous multislice EPI (Kawin Setsompop and colleagues, 2012; published online in 2011).[9](https://cds.ismrm.org/protected/16MProceedings/PDFfiles/7219.html) • [15](https://doi.org/10.1002/%28sici%291522-2594%28199911%2942:5<952::aid-mrm16>3.0.co;2-s) • [16](https://doi.org/10.1002/mrm.10171) • [17](https://doi.org/10.1002/mrm.23097)\n\nEcho-planar time-resolved imaging (EPTI; Fuyixue Wang and colleagues, 2019, with subspace reconstruction added by Zijing Dong and colleagues, 2020) extends EPI into \\( k_{y} \\)–\\( t \\) space to acquire a distortion- and blurring-free multi-echo dataset.[18](https://doi.org/10.1002/mrm.27673) • [19](https://doi.org/10.1002/mrm.28295)\n\n## Applications\n\nEPI's speed lets whole brain volumes be acquired in about 2 s, fast enough to sample the BOLD hemodynamic response and to freeze motion, and its gradient-echo form is intrinsically sensitive to \\( T_{2}^{*} \\), the mechanism underlying BOLD contrast.[3](https://pubs.rsna.org/doi/10.1148/radiographics.21.3.g01ma23767) • [7](https://www.science.org/doi/10.1126/science.1925560) In regions with field inhomogeneity (orbitofrontal cortex, temporal pole, anterior inferior temporal cortex, lateral cerebellum), SE-EPI provides significantly higher BOLD sensitivity than GE-EPI, while GE-EPI is generally more sensitive elsewhere; dual-echo acquisitions combine both.[20](https://www.sciencedirect.com/science/article/abs/pii/S1053811909008726)\n\nDiffusion imaging uses SE-EPI because diffusion weighting requires a long TE, which single-shot acquisition tolerates without motion artifact.[5](https://www.humanconnectome.org/hcp-protocols-ya-3t-imaging)\n\n## Limitations and alternatives\n\n**Susceptibility distortion** is EPI's defining weakness. The phase-encode bandwidth is very low, typically <20 Hz/pixel, so a 100 Hz field offset (typical near the frontal sinuses at 3.0 T) mis-locates signal by 5 pixels; distortion in the phase-encoding direction can reach tens of millimeters in the brainstem, temporal, and frontal regions.[21](https://doi.org/10.1002/%28sici%291097-0193%281999%298:2/3) • [22](https://ris.utwente.nl/ws/files/29507754/1_s2.0_S1053811917303415_main.pdf) Corrections include B0 field maps and reversed phase-encoding acquisitions; reversed phase-encoding correction was formalized as TOPUP (Jesper L.R. Andersson, Stefan Skare, and John Ashburner, 2003).[8](https://cds.ismrm.org/protected/23MProceedings/PDFfiles/E8315_M4QM3sSj4.html) • [23](https://doi.org/10.1016/s1053-8119%2803%2900336-7)\n\n**Nyquist (N/2) ghosting** arises from imperfections in the oscillating readout, eddy currents, and even/odd echo differences, shifting a ghost N/2 pixels in the phase-encode direction; it is corrected with reference scans, navigator echoes, concurrent field monitoring, and dual-polarity GRAPPA (W. Scott Hoge and Jonathan R. Polimeni, 2015).[8](https://cds.ismrm.org/protected/23MProceedings/PDFfiles/E8315_M4QM3sSj4.html) • [24](https://doi.org/10.1002/mrm.25839)\n\n**Chemical shift and blurring.** Fat, resonating about 3.5 ppm below water, can be displaced by centimeters along the phase-encode direction, so fat suppression or water-selective excitation is required. \\( T_{2}^{*}/T_{2} \\) decay during the long readout broadens the point-spread function, causing resolution loss along the phase-encode direction, reducible by shortening the acquisition window with parallel imaging.[9](https://cds.ismrm.org/protected/16MProceedings/PDFfiles/7219.html) • [8](https://cds.ismrm.org/protected/23MProceedings/PDFfiles/E8315_M4QM3sSj4.html) • [6](https://labs.dgsom.ucla.edu/file/449825/M229_Lecture7_FastImagingEPI_2023.pdf)\n\nThe rapidly switched gradients dominate EPI's physiological profile. During early development, teams in the USA and Europe had to change magnets from 2 T to 1 T to avoid physiological effects of fast oscillating field gradients.[10](https://www.magnetic-resonance.org/ch/08-04.html) Published literature has not quantified peripheral nerve stimulation thresholds or SAR limits specific to EPI.\n\n[Fast spin echo](https://www.edgepedia.org/fast-spin-echo) (RARE; J. Hennig, A. Nauerth, and H. Friedburg, 1986)[25](https://doi.org/10.1002/mrm.1910030602) and PROPELLER trade speed for robustness to field inhomogeneity and motion. In pediatric brain DWI at 1.5 T, both readout-segmented EPI (Resolve) and PROPELLER (Blade) showed better image quality than single-shot EPI in distortion, susceptibility-related signal changes, and lesion conspicuity.[26](https://ajronline.org/doi/10.2214/AJR.17.18796) Spiral imaging uses two oscillating gradients and is quite sensitive to static-field inhomogeneities, producing off-resonance blurring rather than pixel relocation.[3](https://pubs.rsna.org/doi/10.1148/radiographics.21.3.g01ma23767) GRASE combines gradient and spin echoes to temper EPI's susceptibility sensitivity.[27](https://doi.org/10.1002/mrm.1910200219) Single-shot EPI remains the choice when motion robustness and speed dominate; multishot and hybrid readouts win when resolution and geometric fidelity matter.[6](https://labs.dgsom.ucla.edu/file/449825/M229_Lecture7_FastImagingEPI_2023.pdf)\n\n## References\n\n1. [P Mansfield (1977). Multi-planar image formation using NMR spin echoes. Journal of Physics C Solid State Physics.](https://doi.org/10.1088/0022-3719/10/3/004)\n2. [Peter Mansfield - Nobel Lecture (2003)](https://www.nobelprize.org/uploads/2018/06/mansfield-lecture.pdf)\n3. [Principles and Applications of Echo-planar Imaging: A Review for the General Radiologist (RadioGraphics, 2001)](https://pubs.rsna.org/doi/10.1148/radiographics.21.3.g01ma23767)\n4. [Echo-Planar Imaging: Theory, Technique and Application (Schmitt, Stehling, Turner, Springer, 1998)](https://link.springer.com/book/10.1007/978-3-642-80443-4)\n5. [HCP 3T Imaging Protocol Overview (Human Connectome Project)](https://www.humanconnectome.org/hcp-protocols-ya-3t-imaging)\n6. [EPI and PROPELLER (Holden Wu, UCLA M229 graduate lecture, 2023)](https://labs.dgsom.ucla.edu/file/449825/M229_Lecture7_FastImagingEPI_2023.pdf)\n7. [Echo-Planar Imaging: Magnetic Resonance Imaging in a Fraction of a Second (Science review)](https://www.science.org/doi/10.1126/science.1925560)\n8. [Echoplanar Imaging: Corrections (ISMRM 2023 educational session)](https://cds.ismrm.org/protected/23MProceedings/PDFfiles/E8315_M4QM3sSj4.html)\n9. [Basics of an EPI Acquisition (Eric C. Wong, ISMRM 2016)](https://cds.ismrm.org/protected/16MProceedings/PDFfiles/7219.html)\n10. [Fast/Rapid Imaging, Echo-Planar Imaging (Rinck, MRI primer)](https://www.magnetic-resonance.org/ch/08-04.html)\n11. [Functional BOLD MRI (fMRI) sequence settings (Dartmouth Brain Imaging Center)](https://www.dartmouth.edu/dbic/docs/sequences/bold_acquisition.pdf)\n12. [E. L. Hahn (1950). Spin Echoes. Physical Review.](https://doi.org/10.1103/physrev.80.580)\n13. [The clinical potential of ultra-high-speed echo-planar imaging (Worthington, Mansfield et al., Phil. Trans. R. Soc. A, 1990)](https://royalsocietypublishing.org/doi/10.1098/rsta.1990.0178)\n14. [High resolution diffusion-weighted imaging using readout-segmented echo-planar imaging, parallel imaging and a two-dimensional navigator-based reacquisition (Magn Reson Med, 2009)](https://onlinelibrary.wiley.com/doi/10.1002/mrm.22024)\n15. [SENSE: Sensitivity encoding for fast MRI (Magnetic Resonance in Medicine, 1999)](https://doi.org/10.1002/%28sici%291522-2594%28199911%2942:5<952::aid-mrm16>3.0.co;2-s)\n16. [Mark A. Griswold and colleagues (2002). Generalized autocalibrating partially parallel acquisitions (GRAPPA). Magnetic Resonance in Medicine.](https://doi.org/10.1002/mrm.10171)\n17. [Kawin Setsompop and colleagues (2011). Blipped‐controlled aliasing in parallel imaging for simultaneous multislice echo planar imaging with reduced g ‐factor penalty. Magnetic Resonance in Medicine.](https://doi.org/10.1002/mrm.23097)\n18. [Fuyixue Wang and colleagues (2019). Echo planar time‐resolved imaging (EPTI). Magnetic Resonance in Medicine.](https://doi.org/10.1002/mrm.27673)\n19. [Zijing Dong and colleagues (2020). Echo planar time‐resolved imaging with subspace reconstruction and optimized spatiotemporal encoding. Magnetic Resonance in Medicine.](https://doi.org/10.1002/mrm.28295)\n20. [Dual echo EPI – The method of choice for fMRI in the presence of magnetic field inhomogeneities? (NeuroImage)](https://www.sciencedirect.com/science/article/abs/pii/S1053811909008726)\n21. [doi.org](https://doi.org/10.1002/%28sici%291097-0193%281999%298:2/3)\n22. [How to choose the right MR sequence for your research question at 7T and above? (NeuroImage, repository copy)](https://ris.utwente.nl/ws/files/29507754/1_s2.0_S1053811917303415_main.pdf)\n23. [How to correct susceptibility distortions in spin-echo echo-planar images: application to diffusion tensor imaging (NeuroImage, 2003)](https://doi.org/10.1016/s1053-8119%2803%2900336-7)\n24. [W. Scott Hoge, Jonathan R. Polimeni (2015). Dual‐polarity GRAPPA for simultaneous reconstruction and ghost correction of echo planar imaging data. Magnetic Resonance in Medicine.](https://doi.org/10.1002/mrm.25839)\n25. [J. Hennig, A. Nauerth, H. Friedburg (1986). RARE imaging: A fast imaging method for clinical MR. Magnetic Resonance in Medicine.](https://doi.org/10.1002/mrm.1910030602)\n26. [Comparison of DWI Methods in the Pediatric Brain: PROPELLER TSE vs Readout-Segmented EPI vs Single-Shot EPI (AJR)](https://ajronline.org/doi/10.2214/AJR.17.18796)\n27. [Koichi Oshio, David A. Feinberg (1991). GRASE (Gradient‐and Spin‐Echo) imaging: A novel fast MRI technique. Magnetic Resonance in Medicine.](https://doi.org/10.1002/mrm.1910200219)\n\n---\n*Topic: Encyclopedia › Life and health › Human health and medicine › Clinical assessment and procedures › Medical imaging and radiography › Magnetic resonance imaging techniques*\n\n*Initially written Sep 29, 2026 · Edited: Oct 15, 2026*\n\n*Copyright 2026 EdgeChat AI, a subsidiary of Biostate AI.*\n\nLicense: Edgepedia Community License 1.0, https://www.edgepedia.org/edgepedia/license\n", "same_as": [], "url": "https://www.edgepedia.org/echo-planar-imaging", "markdown_url": "https://www.edgepedia.org/echo-planar-imaging.md", "license": { "name": "Edgepedia Community License 1.0", "url": "https://www.edgepedia.org/edgepedia/license", "summary": "Free with credit, commercial use included. AI training is open to everyone. For other uses, organizations over USD 100M in revenue or 100M monthly users license separately.", "spdx": "LicenseRef-Edgepedia-Community-1.0" }, "credit": "\"Echo-planar imaging\", Edgepedia (EdgeChat), https://www.edgepedia.org/echo-planar-imaging. Edgepedia Community License 1.0.", "credit_md": "\"[Echo-planar imaging](https://www.edgepedia.org/echo-planar-imaging)\", Edgepedia (EdgeChat), [https://www.edgepedia.org/echo-planar-imaging](https://www.edgepedia.org/echo-planar-imaging). [Edgepedia Community License 1.0](https://www.edgepedia.org/edgepedia/license).", "credit_html": "\"Echo-planar imaging\", Edgepedia (EdgeChat), https://www.edgepedia.org/echo-planar-imaging. Edgepedia Community License 1.0.", "speakable": "Echo-planar imaging is a fast MRI pulse sequence, proposed by Peter Mansfield in 1977, that acquires images in tens of milliseconds and underlies fMRI and diffusion imaging." }