Multiple sclerosis is a chronic inflammatory, degenerative, demyelinating disorder of the CNS that is most prevalent in young adults. This disease is characterized by relapses of attacks affecting different areas of the brain, optic nerves, and spinal cord over time. It is the most common cause of disability in young adults after trauma .
In our present study, 3D Cube FLAIR sequence at 1.5 T was used alongside the conventional MRI sequences in the assessment of patients with MS to measure its value in the detection of supra-tentorial and infra-tentorial lesions and comparing the results of the 3D sequence and its axial MIP reconstruction with those of 2D FLAIR that is routinely used.
3D sequences have numerous advantages over 2D sequences. Images obtained by 3D sequences have isotropic voxel dimensions without inter-slice gap so it can be easily reformatted without affecting the image quality. In 3D images, the thinner slice thickness leads to an increased number of detected lesions. Furthermore, Cube FLAIR was shown to produce almost no CSF flow artifacts when applied in brain imaging which improves visualization of lesions in the infra-tentorial region. Detecting these lesions is very vital because they have major impact on clinical disability of MS patients .
Earlier, 3D sequences took long acquisition time as they were multi-slab mode, but that drawback was attuned by using single-slab mode . In our study, although 3D-FLAIR sequence has a longer time (5:21 min) compared to (2:10 min) in 2D FLAIR sequence, it is not considered a disadvantage as the 3D sequence also allows axial, coronal, and sagittal reformatting.
2D and 3D FLAIR scans were compared, and lesions on each sequence were counted. Only hyper intense areas larger than 2 mm were calculated.
In current study, the detected lesions were mostly in the supra-tentorial regions (juxta-cortical, periventricular and DWM). 3D FLAIR sequence showed significantly more lesions than 2D FLAIR, that in keeping with Gramsch et al.,  that state that adding 3D FLAIR sequence in standard MS protocols can considerably increase MS lesion detection and provide the possibility of an adequate replacement of both axial 2D FLAIR and mid-sagittal T2W sequences. This results also matched with Tawfik et al.,  and Patzig et al.,  who used 3 Tesla MRI machine.
Among the 160 patients, infra-tentorial lesions were detected in 48 patients in the 2D sequence and 104 patients in the 3D sequence. The 3D FLAIR showed higher detection rate of lesions with a percentage increase of 190% as the 2D-FLAIR was generally reported as less sensitive mostly due to CSF and blood inflow artifacts. The use of 3D FLAIR overcomes these issues because it can achieve homogeneous CSF suppression. Tawfik et al.,  and Patzig et al.,  also noted a 3D detection percentage increase of 80% and 140% respectively. A significant positive association between infratentorial lesions and higher EDSS score or clinical disability was noted as Almutairi et al., also observed .
The overall results in this study were compatible with the results reported by the other studies regarding the comparison between 2D FLAIR and 3D FLAIR sequences in the detection of MS lesions. However, there were some differences between the present study and other ones, including:
At 2 mm reformatting, there is no difference in the detection of MS lesion between sagittal 3D FLAIR and axial MIP reconstruction, so MIP algorithm can be used to simplify lesion detection by reducing the number of images with the same degree of reliability which is in agreement with what Bravo et al.,  observed.
MIP 3D FLAIR sequence overcame the problem of small size cortical lesions and the partial volume effects with cerebrospinal fluid in the sulci. The significant higher numbers of detectable lesions in regions classified as juxtacortical using 3D FLAIR sequences compared to 2D sequences also argued for an integration of 3D FLAIR sequences into standard MRI protocols. The higher detection rate of hemispheric and infratentorial lesions and similar detection rate in the corpus callosum suggested that 3D FLAIR sequences could substitute both dual-echo sequences and sagittal T2W sequences. However, a replacement of the conventional MRI sequences by the newer one will certainly require critical reconsidering of MS diagnostics. 3D FLAIR sequence can detect smaller MS lesions started at sizes of one mm; this could have a non-negligible impact on the evaluation of a patient’s examination in terms of the revised McDonald criteria. The more sensitive MR sequences used, the earlier these criteria were met and the more significantly diagnosis differs between imaging centers because many sites use only conventional sequences.
Our study has some limitations: First, the results of the study are somewhat limited by the relatively small number of patients. Also, the results may be exclusive to the scanner and coil hardware used as no other systems were used or tested. Second, a low 1.5 Tesla field strength MRI machine was used. A 3 T or higher MRI would have enabled the detection of more lesions. Finally, because we did not correlate results to pathology specimens, we cannot be certain that all lesions detected were MS lesions. This would have implied post-mortem exams, which were not obtainable.
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