PURPOSE

The role of MRI in diagnosis of peripheral neuropathy is depiction of the anatomical detail of peripheral nerves and the pathological changes related to entrapment. As a preliminary, we have developed phase-cycling T1-turbo field-echo (TFE)^1,2 combined with diffusion-sensitized driven equilibrium³ (pc-DSDE) that enables the visualization of peripheral nerves⁴ (Fig. 1). However, pc-DSDE has several limitations, such as low image stability, poor reproducibility, and partially remaining venous signals (Fig. 2). To solve these limitations, we propose a new scheme, called improved diffusion-sensitized driven-equilibrium (iDSDE). The purpose of this study was to evaluate the visualization of peripheral nerves by iDSDE in the extremities such as wrist, elbow, and knee.

METHODS

Theory and pulse sequence: iDSDE includes the two improvement strategies. First, to improve the pulse efficiency in the off-center FOVs, B1-insensitive adiabatic pulses for both excitation/flipback and refocusing are applied. Second, to effectively suppress the veins while preventing signal loss of nerves which are running parallel to veins, orthogonally combined motion- and diffusion-sensitized gradient scheme proposed by Cervantes⁵ is adopted (optimized gradient type)(Fig.3). Expeiments: All subjects were examined using a 1.5 T whole-body clinical system and an eight-channel coil (Ingenia, Philips Healthcare). The study was
approved by the local IRB, and written informed consent was
obtained from all subjects. Five healthy volunteers were included for the examination of peripheral nerves in the extremities. To demonstrate the effect of iDSDE improvement strategies, we compared the two types of RF pulses and three types of motion-sensitized gradient types (unipolar, bipolar and optimized gradient type). We assessed the detectability of peripheral nerves to measure contrast-ratio (CR) among the nerves and background muscle signals, and to examine using subjective visual evaluation method by three trained radiologists. Imaging parameters were; Coronal, voxel
size=1.88×1.88×1.6mm³, b-value=910s/mm², DSDE preparation time=100ms, gradient strength phase/freq/slice=20/5/20mT/m,
shot interval=2800ms, flip angle=8°, turbo factor=60, ProSet 1331,
and total acquisition time=5m09s.

RESULTS AND DISCUSSION

iDSDE clearly depicted the course of peripheral nerves on the MIP images. Image uniformity of iDSDE was improved, because B1-insensitive pulses were applied to improve the RF pulse efficiency in the off-center FOV. Contrast ratio of iDSDE was no different from that of current pc-DSDE. Regional venous signal was effectively suppressed by the use of B1 insensitive pulse on subjective visual evaluation (Fig. 4). Contrast ratio was no significant difference in the MPG gradient types. However, relative ranking score of optimized gradient type on subjective visual evaluation was significantly higher than those of other gradient types (Fig. 5). Because venous signals were well suppressed with optimized gradient type. The unipolar gradient type showed high nerve signals and effective background signal suppression, but venous signal was still remained. The bipolar gradient type indicated effective venous signal suppression, but overall image quality was low compared to others. The optimized gradient type, which applies weak bipolar gradient in the direction parallel to the major nerves (and vessels) and strong unipolar gradients in the direction perpendicular to those objects, showed better visualization without contamination of veins.

CONCLUSION

MR neurography using iDSDE enables improved visualization of peripheral nerves with more insensitive to inhomogeneous and more suppression of venous signal than those of pc-DSDE in the extremities. Further clinical investigation is needed.

Acknowledgements

No acknowledgement found.