| 1. |
|
|
| 2. |
- Berglund, Johan, et al.
(författare)
-
Motion-insensitive susceptibility weighted imaging.
- 2021
-
Ingår i: Magnetic Resonance in Medicine. - : Wiley. - 0740-3194 .- 1522-2594. ; 86:4, s. 1970-1982
-
Tidskriftsartikel (refereegranskat)abstract
- PURPOSE: To enable SWI that is robust to severe head movement.METHODS: Prospective motion correction using a markerless optical tracker was applied to all pulse sequences. Three-dimensional gradient-echo and 3D EPI were used as reference sequences, but were expected to be sensitive to motion-induced B0 changes, as the long TE required for SWI allows phase discrepancies to accumulate between shots. Therefore, 2D interleaved snapshot EPI was investigated for motion-robust SWI and compared with conventional 2D EPI. Repeated signal averages were retrospectively corrected for motion. The sequences were evaluated at 3 T through controlled motion experiments involving two cooperative volunteers and SWI of a tumor patient.RESULTS: The performed continuous head motion was in the range of 5-8° rotations. The image quality of the 3D sequences and conventional 2D EPI was poor unless the rotational motion axis was parallel to B0 . Interleaved snapshot EPI had minimal intraslice phase discrepancies due to its small temporal footprint. Phase inconsistency between signal averages was well tolerated due to the high-pass filter effect of the SWI processing. Interleaved snapshot EPI with prospective and retrospective motion correction demonstrated similar image quality, regardless of whether motion was present. Lesion depiction was equal to 3D EPI with matching resolution.CONCLUSION: Susceptibility-based imaging can be severely corrupted by head movement despite accurate prospective motion correction. Interleaved snapshot EPI is a superior alternative for patients who are prone to move and offers SWI which is insensitive to motion when combined with prospective and retrospective motion correction.
|
|
| 3. |
- Berglund, Johan, et al.
(författare)
-
Prospective motion correction for diffusion weighted EPI of the brain using an optical markerless tracker.
- 2021
-
Ingår i: Magnetic Resonance in Medicine. - : Wiley. - 0740-3194 .- 1522-2594. ; 85:3, s. 1427-1440
-
Tidskriftsartikel (refereegranskat)abstract
- PURPOSE: To enable motion-robust diffusion weighted imaging of the brain using well-established imaging techniques.METHODS: An optical markerless tracking system was used to estimate and correct for rigid body motion of the head in real time during scanning. The imaging coordinate system was updated before each excitation pulse in a single-shot EPI sequence accelerated by GRAPPA with motion-robust calibration. Full Fourier imaging was used to reduce effects of motion during diffusion encoding. Subjects were imaged while performing prescribed motion patterns, each repeated with prospective motion correction on and off.RESULTS: Prospective motion correction with dynamic ghost correction enabled high quality DWI in the presence of fast and continuous motion within a 10° range. Images acquired without motion were not degraded by the prospective correction. Calculated diffusion tensors tolerated the motion well, but ADC values were slightly increased.CONCLUSIONS: Prospective correction by markerless optical tracking minimizes patient interaction and appears to be well suited for EPI-based DWI of patient groups unable to remain still including those who are not compliant with markers.
|
|
| 4. |
- Norbeck, Ola, et al.
(författare)
-
T1 -FLAIR imaging during continuous head motion : Combining PROPELLER with an intelligent marker.
- 2021
-
Ingår i: Magnetic Resonance in Medicine. - : Wiley. - 0740-3194 .- 1522-2594. ; 85:2, s. 868-882
-
Tidskriftsartikel (refereegranskat)abstract
- PURPOSE: The purpose of this work is to describe a T1 -weighted fluid-attenuated inversion recovery (FLAIR) sequence that is able to produce sharp magnetic resonance images even if the subject is moving their head throughout the acquisition.METHODS: The robustness to motion artifacts and retrospective motion correction capabilities of the PROPELLER (periodically rotated overlapping parallel lines with enhanced reconstruction) trajectory were combined with prospective motion correction. The prospective correction was done using an intelligent marker attached to the subject. This marker wirelessly synchronizes to the pulse sequence to measure the directionality and magnitude of the magnetic fields present in the MRI machine during a short navigator, thus enabling it to determine its position and orientation in the scanner coordinate frame. Three approaches to incorporating the marker-navigator into the PROPELLER sequence were evaluated. The specific absorption rate, and subsequent scan time, of the T1 -weighted FLAIR PROPELLER sequence, was reduced using a variable refocusing flip-angle scheme. Evaluations of motion correction performance were done with 4 volunteers and 3 types of head motion.RESULTS: During minimal out-of-plane movement, retrospective PROPELLER correction performed similarly to the prospective correction. However, the prospective clearly outperformed the retrospective correction when there was out-of-plane motion. Finally, the combination of retrospective and prospective correction produced the sharpest images even during large continuous motion.CONCLUSION: Prospective motion correction of a PROPELLER sequence makes it possible to handle continuous, large, and high-speed head motions with only minor reductions in image quality.
|
|
| 5. |
- Rydén, Henric, et al.
(författare)
-
Chemical shift encoding using asymmetric readout waveforms.
- 2021
-
Ingår i: Magnetic Resonance in Medicine. - : Wiley. - 0740-3194 .- 1522-2594. ; 85:3, s. 1468-1480
-
Tidskriftsartikel (refereegranskat)abstract
- PURPOSE: To describe a new method for encoding chemical shift using asymmetric readout waveforms that enables more SNR-efficient fat/water imaging.METHODS: Chemical shift was encoded using asymmetric readout waveforms, rather than conventional shifted trapezoid readouts. Two asymmetric waveforms are described: a triangle and a spline. The concept was applied to a fat/water separated RARE sequence to increase sampling efficiency. The benefits were investigated through comparisons to shifted trapezoid readouts. Using asymmetric readout waveforms, the scan time was either shortened or maintained to increase SNR. A matched in-phase waveform is also described that aims to improve the SNR transfer function of the fat and water estimates. The sequence was demonstrated for cervical spine, musculoskeletal (MSK), and optic nerve applications at 3T and compared with conventional shifted readouts.RESULTS: blurring. Maintaining the scan times and using asymmetric readout waveforms achieved an SNR improvement in agreement with the prolonged sampling duration.CONCLUSIONS: Asymmetric readout waveforms offer an additional degree of freedom in pulse sequence designs where chemical shift encoding is desired. This can be used to significantly shorten scan times or to increase SNR with maintained scan time.
|
|
| 6. |
- Rydén, Henric, et al.
(författare)
-
RARE two-point Dixon with dual bandwidths.
- 2020
-
Ingår i: Magnetic Resonance in Medicine. - : Wiley. - 0740-3194 .- 1522-2594. ; 84:5, s. 2456-2468
-
Tidskriftsartikel (refereegranskat)abstract
- PURPOSE: To investigate the impact of dual readout bandwidths (dBW) in a dual echo fat/water acquisition and describe a dBW-rapid acquisition relaxation enhanced, or turbo spin echo sequence where the concept is used to improve SNR by removing dead times between refocusing pulses and avoiding redundant Chemical-shift encoded.METHODS: Cramér-Rao bounds and Monte Carlo simulations were used to investigate a two-point fat/water model where the difference in bandwidths is incorporated. In vivo images were acquired at 1.5 and 3 T with the dBW-rapid acquisition relaxation enhanced, or turbo spin echo sequence. Typical bandwidth ratios were 1:2. SNR was compared with a single bandwidth sequence under identical scan parameters at 3T.RESULTS: Monte Carlo simulations and Cramér-Rao analysis demonstrate that number of signal averages can be improved with dual bandwidths compared to conventional single bandwidth acquisitions. The dBW-rapid acquisition relaxation enhanced, or turbo spin echo sequence can acquire images with high readout resolutions with well-conditioned sampling. An SNR improvement of 52% was measured, in line with the theoretical gain of 54%.CONCLUSIONS: The proposed dBW-rapid acquisition relaxation enhanced, or turbo spin echo sequence is a highly SNR-efficient two-point rapid acquisition relaxation enhanced, or turbo spin echo sequence without dead times, and can acquire images at higher resolutions than current vendor-supplied alternatives.
|
|
| 7. |
- Sprenger, Tim, et al.
(författare)
-
NeuroMix-A single-scan brain exam
- 2022
-
Ingår i: Magnetic Resonance in Medicine. - : Wiley-Blackwell. - 0740-3194 .- 1522-2594. ; 87:5, s. 2178-2193
-
Tidskriftsartikel (refereegranskat)abstract
- PURPOSE: Implement a fast, motion-robust pulse sequence that acquires T1 -weighted, T2 -weighted, T2 * -weighted, T2 fluid-attenuated inversion recovery, and DWI data in one run with only one prescription and one prescan.METHODS: A software framework was developed that configures and runs several sequences in one main sequence. Based on that framework, the NeuroMix sequence was implemented, containing motion robust single-shot sequences using EPI and fast spin echo (FSE) readouts (without EPI distortions). Optional multi-shot sequences that provide better contrast, higher resolution, or isotropic resolution could also be run within the NeuroMix sequence. An optimized acquisition order was implemented that minimizes times where no data is acquired.RESULTS: NeuroMix is customizable and takes between 1:20 and 4 min for a full brain scan. A comparison with the predecessor EPIMix revealed significant improvements for T2 -weighted and T2 fluid-attenuated inversion recovery, while taking only 8 s longer for a similar configuration. The optional contrasts were less motion robust but offered a significant increase in quality, detail, and contrast. Initial clinical scans on 1 pediatric and 1 adult patient showed encouraging image quality.CONCLUSION: The single-shot FSE readouts for T2 -weighted and T2 fluid-attenuated inversion recovery and the optional multishot FSE and 3D-EPI contrasts significantly increased diagnostic value compared with EPIMix, allowing NeuroMix to be considered as a standalone brain MRI application.
|
|
| 8. |
- van Niekerk, Adam, et al.
(författare)
-
Control of a wireless sensor using the pulse sequence for prospective motion correction in brain MRI.
- 2022
-
Ingår i: Magnetic Resonance in Medicine. - : Wiley. - 0740-3194 .- 1522-2594. ; 87:2, s. 1046-1061
-
Tidskriftsartikel (refereegranskat)abstract
- PURPOSE: To synchronize and pass information between a wireless motion-tracking device and a pulse sequence and show how this can be used to implement customizable navigator interleaving schemes that are part of the pulse sequence design.METHODS: The device tracks motion by sampling the voltages induced in 3 orthogonal pickup coils by the changing gradient fields. These coils were modified to also detect RF-transmit events using a 3D RF-detection circuit. The device could then detect and decode a set RF signatures while ignoring excitations in the parent pulse sequence. A set of unique RF signatures were then paired with a collection of navigators and used to trigger readouts on the wireless device synchronous to the pulse sequence execution. Navigator interleaving schemes were then demonstrated in 3D RF-spoiled gradient echo, T1 -FLAIR (fluid-attenuated inversion recovery) PROPELLER (periodically rotated overlapping parallel lines with enhanced reconstruction), and T2 -FLAIR PROPELLER pulse sequences.RESULTS: Excitations in the parent pulse sequences were successfully rejected and the RF signatures successfully decoded. For the 3D gradient echo sequence, distortions were removed by interleaving flipped polarity navigators and taking the difference between consecutive readouts. The impact on scan duration was reduced by 54% by breaking up the navigators into smaller parts. Successful motion correction was performed using the PROPELLER pulse sequences in 3 Tesla and 1.5 Tesla MRI scanners without modifications to the device hardware or software.CONCLUSION: The proposed RF signature-based triggering scheme enables complex interactions between the pulse sequence and a wireless device. Thus, enabling prospective motion correction that is repeatable, versatile, and minimally invasive with respect to hardware setup.
|
|
