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Conventional and fast spin-echo MR imaging: minimizing echo time
S Vinitski1, D G Mitchell, S G Einstein
1Department of Radiology, Thomas Jefferson University Hospital, Philadelphia, PA.
Abstract:
Magnetic resonance imaging is frequently complicated by the presence of motion and susceptibility gradients. Also, some biologic tissues have short T2s. These problems are particularly troublesome in fast spin-echo (FSE) imaging, in which T2 decay and motion between echoes result in image blurring and ghost artifacts. The authors reduced TE in conventional spin-echo (SE) imaging to 5 msec and echo spacing (E-space) in FSE imaging to 6 msec. All magnetic gradients (except readout) were kept at a maximum, with data sampling as fast as 125 kHz and only ramp waveforms used. Truncated sinc radio-frequency pulses and asymmetric echo sampling were also used in SE imaging. Short TE (5.8 msec) SE images of the upper abdomen were compared with conventional SE images (TE = 11 msec). Also, FSE images with short E-space were compared with conventional FSE images in multiple body sites. Short TE significantly improved the liver-spleen contrast-to-total noise ratio (C/N) (7.9 vs 4.1, n = 9, P < .01) on T1-weighted SE images, reduced the intensity of ghost artifacts (by 34%, P < .02), and increased the number of available imaging planes by 30%. It also improved delineation of cranial nerves and reduced susceptibility artifacts. On short E-space FSE images, spine, lung, upper abdomen, and musculoskeletal tissues appeared crisper and measured spleen-liver C/N increased significantly (6.9 vs 4.0, n = 12, P < .01). The delineation of tissues with short T2 (eg, cartilage) and motion artifact suppression were also improved. Short TE methods can improve image quality in both SE and FSE imaging and merit further clinical evaluation.
Insights
Shortening echo times in magnetic resonance imaging significantly reduces motion and susceptibility artifacts. These optimized techniques enhance image clarity and detail in both conventional spin-echo (SE) and fast spin-echo (FSE) scans.
Area of Science:
- Medical Imaging
- Radiology
- Biophysics
Background:
- Magnetic resonance imaging (MRI) quality is often degraded by motion, susceptibility gradients, and short T2 relaxation times.
- These factors particularly impact fast spin-echo (FSE) imaging, causing blurring and ghost artifacts due to T2 decay and inter-echo motion.
Purpose of the Study:
- To evaluate the effectiveness of reducing echo time (TE) in conventional spin-echo (SE) and echo spacing (E-space) in FSE imaging.
- To assess the impact of these short TE/E-space techniques on image quality, artifact reduction, and diagnostic utility.
Main Methods:
- Conventional SE imaging TE was reduced to 5 msec; FSE imaging E-space was reduced to 6 msec.
- Maximized magnetic gradients (except readout), fast data sampling (125 kHz), ramp waveforms, truncated sinc RF pulses, and asymmetric echo sampling were employed.
- Short TE SE images were compared with conventional SE images (TE=11 msec); short E-space FSE images were compared with conventional FSE images across multiple body sites.
Main Results:
- Short TE significantly improved liver-spleen contrast-to-noise ratio (C/N) in T1-weighted SE images (7.9 vs 4.1, P < .01).
- Ghost artifacts were reduced by 34% (P < .02), and available imaging planes increased by 30% with short TE SE.
- Short E-space FSE improved tissue crispness, increased spleen-liver C/N (6.9 vs 4.0, P < .01), enhanced delineation of short T2 tissues (e.g., cartilage), and suppressed motion artifacts.
Conclusions:
- Short echo time (TE) and echo spacing (E-space) techniques significantly enhance image quality in both SE and FSE magnetic resonance imaging.
- These optimized methods effectively reduce artifacts, improve contrast, and increase diagnostic information.
- Further clinical evaluation of short TE/E-space MRI techniques is warranted.