Comparison of wideband steady-state free precession and T₂-weighted fast spin echo in spine disorder assessment at 1.5 and 3 T

Motion resilience of the balanced steady-state free precession geometric solution

PURPOSE

Many MRI sequences are sensitive to motion and its associated artifacts. The linearized geometric solution (LGS), a balanced steady-state free precession (bSSFP) off-resonance signal demodulation technique, is evaluated with respect to motion artifact resilience.

THEORY AND METHODS

The mechanism and extent of LGS motion artifact resilience is examined in simulated, flow phantom, and in vivo clinical imaging. Motion artifact correction capabilities are decoupled from susceptibility artifact correction when feasible to permit controlled analysis of motion artifact correction when comparing the LGS with standard and phase-cycle-averaged (complex sum) bSSFP imaging.

RESULTS

Simulations reveal that the LGS demonstrates motion artifact reduction capabilities similar to standard clinical bSSFP imaging techniques, with slightly greater resilience in high SNR regions and for shorter-duration motion. Flow phantom experiments assert that the LGS reduces shorter-duration motion artifact error by ∼24%-65% relative to the complex sum, whereas reconstructions exhibit similar error reduction for constant motion. In vivo analysis demonstrates that in the internal auditory canal/orbits, the LGS was deemed to have less artifact in 24%/49% and similar artifact in 76%/51% of radiological assessments relative to the complex sum, and the LGS had less artifact in 97%/81% and similar artifact in 3%/16% of assessments relative to standard bSSFP. Only 2 of 63 assessments deemed the LGS inferior to either complex sum or standard bSSFP in terms of artifact reduction.

CONCLUSION

The LGS provides sufficient bSSFP motion artifact resilience to permit robust elimination of susceptibility artifacts, inspiring its use in a wide variety of applications.

The value of contrast-enhanced three-dimensional isotropic T2-weighted turbo spin-echo SPACE sequence in the diagnosis of patients with lumbosacral nerve root compression

PURPOSE

To investigate the diagnostic value of contrast-enhanced three-dimensional (3D) T2-weighted turbo spin-echo SPACE (T2-SPACE) sequence in LNRC.

METHODS

A total of 90 surgically confirmed LNRC patients with 165 explored nerve roots were enrolled in this study. Diagnostic values were quantified using sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and accuracy. The consistency between 2D MRI and 3D T2-SPACE MRI was quantified using kappa test. The compression of specific branch in nerve root was evaluated on 2D MRI, 3D T2-SPACE MRI, and surgical findings. The pedicle height, vertebral body height (VH), proximal tilting angle of nerve root (PTA) were measured on MR images.

RESULTS

The sensitivity, specificity, PPV, NPV, and accuracy by 2D MRI were 78.3%, 72.7%, 94.9%, 34.0%, and 77.6%, respectively. For 3D T2-SPACE MRI imaging, the sensitivity, specificity, PPV, NPV, and accuracy were 91.6%, 86.4%, 97.8%, 61.3%, and 90.9%, respectively. 2D MRI and 3D T2-SPACE MRI for detection of intra-foramen and extra-foramen nerve compression showed poor homogeneity (Kappa = 0.333, Kappa = 0.276, respectively). Smaller VHs and larger PTAs could be indicators for the diagnosis of foraminal nerve root compression.

CONCLUSIONS

3D T2-SPACE MRI had a higher sensitivity, specificity, PPV, NPV, and accuracy than 2D MRI for detecting LNRC. The 3D T2-SPACE scan could be a good substitute to routine 2D MRI in LNRC diagnosis, especially for foraminal nerve root compression patients.

LEVEL OF EVIDENCE

III.

Comparison with Magnetic Resonance Three-Dimensional Sequence for Lumbar Nerve Root with Intervertebral Foramen

Study Design

Prospective study based on magnetic resonance (MR) imaging of the lumbar spinal root of the intervertebral foramen.

Purpose

This study was to compare MR three-dimensional (3D) sequences for the evaluation of the lumbar spinal root of the intervertebral foramen.

Overview of Literature

The diagnosis of spinal disorders by MR imaging is commonly performed using two-dimensional T1- and T2-weighted images, whereas 3D MR images can be used for acquiring further detailed data using thin slices with multi-planar reconstruction.

Methods

On twenty healthy volunteers, we investigated the contrast-to-noise ratio (CNR) of the lumbar spinal root of the intervertebral foramen with a 3D balanced sequence. The sequences used were the fast imaging employing steady state acquisition and the coherent oscillatory state acquisition for the manipulation of image contrast (COSMIC). COSMIC can be used with or without fat suppression (FS). We compared these sequence to determine the optimized visualization sequence for the lumbar spinal root of the intervertebral foramen.

Results

For the CNR between the nerve root and the peripheral tissue, these were no significant differences between the sequences at the entry of foramen. There was a significant difference and the highest CNR was seen with COSMIC-FS for the intra- and extra-foramen.

Conclusions

In this study, the findings suggest that the COSMIC-FS sequences should be used for the internal or external foramen for spinal root disorders.

Evaluation of the dependence of CEST-EPI measurement on repetition time, RF irradiation duty cycle and imaging flip angle for enhanced pH sensitivity

Chemical exchange saturation transfer (CEST) is a magnetic resonance imaging (MRI) contrast mechanism that can detect dilute CEST agents and microenvironmental properties, with a host of promising applications. Experimental measurement of the CEST effect is complex, and depends on not only CEST agent concentration and exchange rate, but also experimental parameters such as RF irradiation amplitude and scheme. Although echo planar imaging (EPI) has been increasingly used for CEST MRI, the relationship between CEST effect and repetition time (TR), RF irradiation duty cycle (DC) and EPI flip angle (α) has not been fully evaluated and optimized to enhance CEST MRI sensitivity. In addition, our study evaluated gradient echo CEST-EPI by quantifying the CEST effect and its signal-to-noise ratio per unit time (SNRput) as functions of TR, DC and α. We found that CEST effect increased with TR and DC but decreased with α. Importantly, we found that SNRput peaked at intermediate TRs of about twice the T1 and α, at approximately 75°, and increased with RF DC. The simulation results were validated using a dual-pH creatine-gel CEST phantom. In summary, our study provides a useful framework for optimizing CEST MRI experiments.