Synopsis
MR neurography achieves selective depiction of peripheral nerves and detects pathological changes related to neuropathies as a signal abnormality. Recently, we proposed a novel MR neurography sequence (SHINKEI) that provides high-quality MR neurography in the brachial plexus and the lumbosacral plexus. However, SHINKEI could not quantitatively assess the nerve pathology. In this study, we developed a new sequence (SHINKEI-Quant) to simultaneously acquire MR neurography and T2 mapping by further optimizing the iMSDE preparation. SHINKEI-Quant could simultaneously provide both MR neurography and T2 maps without prolongation of acquisition time compared with the conventional SHINKEI sequence. This quantitative sequence may be helpful to quantitatively assess the nerve pathology such as chronic inflammatory demyelinating polyneuropathy.Purpose
MR neurography achieves selective depiction of peripheral nerves
and provides useful information for diagnosing peripheral neuropathies. MR
neurography can depict the nerve anatomy in detail and also detect pathological
changes related to neuropathies as a signal abnormality1-4.
Chronic Inflammatory Demyelinating Polyneuropathy (CIDP) is an
acquired immune-mediated peripheral neuropathy that presents as either a
chronic progressive or a relapsing-remitting disorder5. CIDP produces increased T2
signal intensity (prolongation of the T2 value) in the nerve
involving fascicular enlargement6.
T2 values are dependent on the locations along the
same injured nerve. T2 values correlated with nerve injury and its
functional recovery7. Hitherto, several studies have reported that
the T2 assessment may offer functional information about the nerve
injuries7-9. Thus, quantitative evaluation by using T2
value might be clinically useful to estimate the effect of treatment and/or to
determine the prognosis.
Recently, we proposed a novel MR neurography sequence
(nerve-SHeath signal increased with INKed rest-tissue RARE Imaging: SHINKEI)
based on improved motion-sensitized driven-equilibrium (iMSDE) prepared 3D T2-weighted
turbo spin-echo (TSE)10. By using this sequence,
high-quality MR neurography has been obtained in the brachial plexus and the
lumbosacral plexus10-12. However, SHINKEI could
not quantitatively assess the nerve pathology.
In this study, we developed a new sequence (SHINKEI-Quant) to
simultaneously acquire MR neurography and T2 mapping by further
optimizing the iMSDE preparation.
Methods
Theory and pulse sequence:
Conventional SHINKEI consists of iMSDE, fat suppression
pre-pulse and 3D T2-weighted TSE sequence. iMSDE with long preparation duration
(prep-time, typically 50ms) is applied for suppressing flow and muscle signal
simultaneously10 [Fig.1].
SHINKEI-Quant applies two different prep-times in the first half
and the latter half of the acquisition. To stabilize the signal behavior
between both iMSDE prep-times, we applied identical RF pulse interval for both
prep-times and changed only the number of RF pulses [Fig.2].
MR neurography is obtained by simple image addition. A T2
map is calculated by pixel-by-pixel fitting of the magnitude image intensities from
both prep-times to a mono-exponential relaxation model13. Accordingly, this
sequence can provide both neurography images and T2 maps without
prolongation of acquisition time [Fig.1].
Experiments:
A total of seven volunteers and one patient were examined on
3.0T systems (Achieva TX/Ingenia, Philips Healthcare). The study was approved
by the local IRB, and written informed consent was obtained from all
subjects.
(1) Direct comparison of SHINKEI-Quant with conventional
methods
To validate both the neurography images and the T2
maps obtained by SHINKEI-Quant, coronal brachial plexus images were acquired in
seven volunteers and were quantitatively compared with conventional methods.
Neurography images were compared with conventional SHINKEI for
image quality. We measured/calculated the SNR of the nerve and the
contrast-ratio (CR) between the nerve and the muscle.
Subsequently, the T2 maps were assessed for accuracy
by comparing with a conventional 2D multi-echo spin-echo T2 mapping
sequence. We measured the T2 value of the nerve (average value of
both the left and right DRGs from C6 to C8), spinal cord and
sternocleidomastoid muscle respectively. Spearman’s correlation coefficient in
T2 value was calculated. The SNR, CR and respective T2
values were assessed by using paired t-test. Imaging parameters are shown in Table
1.
(2) Initial evaluation of the clinical feasibility of
SHINKEI-Quant
We performed an initial evaluation of the SHINKEI-Quant sequence
in a patient with CIDP. We measured the T2 value of the nerve (average
value of both the left and right entire nerves from C6 to C8) and
sternocleidomastoid muscle respectively.
Results and Discussion
Table 2(a) shows the comparison of image quality between
conventional SHINKEI and SHINKEI-Quant. Both the SNR and CR of SHINKEI-Quant
showed similar values compared to those of conventional SHINKEI. There were no
significant differences. Table 2(b) shows the comparison of T
2 values
between conventional multi-echo SE T
2 mapping and SHINKEI-Quant. The
T
2 values obtained with SHINKEI-Quant in each tissue indicated
slightly longer value compared to those from conventional T
2
mapping. Nevertheless, the T
2 value of nerves measured in
SHINKEI-Quant correlated with the one measured in conventional T
2 mapping
(R=0.81, P<0.01). Thus, the T
2 values measured in SHINKEI-Quant
may have same trends with one measured in conventional T
2 mapping.
Figure 3 shows the results of initial clinical evaluation. In a patient with
CIDP, T
2 value of nerves indicated longer value compared with that
of two healthy volunteers. Although further clinical evaluation is needed, this
may be helpful for quantitative assessment of CIDP.
Conclusion
SHINKEI-Quant could simultaneously provide both MR neurography
and T
2 maps without prolongation of acquisition time compared with the
conventional SHINKEI sequence. This quantitative sequence may be helpful to
quantitatively assess the nerve pathology.
Acknowledgements
No acknowledgement found.References
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