Vall Hebron University Hospital
Neuroradiology

Author Of 2 Presentations

Imaging Poster Presentation

P0540 - Assessing the relationship between the ratio of T1- T2-weighted images and MRI sequences by using the structural similarity index (ID 1260)

Speakers
Presentation Number
P0540
Presentation Topic
Imaging

Abstract

Background

Background: The ratio of T1- T2-weighted images (T1/T2) has been proposed as a biomarker of tissue integrity, although comparison with MRI-derived tissue metrics has not been perfomed.

Objectives

Objectives: In this study, T1/T2 has been compared to the T1/FLAIR, Phase-sensitive inversion recovery (PSIR), the fractional anisotropy (FA) and the orientation dispersion (ODI) in normal appearing grey, white matter and lesion mask, by using the structural similarity (SSIM) index. The SSIM is the product of 3 terms that take into account the luminance, the contrast and the structural information of the images compared. It ranges between [-1,1], with 1 indicating that the two images compared are identical.

Methods

Material and methods: MRIs of patients with a clinically isolated syndrome were included in this study. Images were acquired in a 3.0 T sytem (Trio, Siemens) using established acquisition protocols. The FA and ODI images were generated with the TBSS/FSL and NODDI/SPM toolboxes, respectively. The SSIM maps were calculated with the function implemented in Matlab. T1-weighted images were segmented with SPM12 and the lesion masks were generated from the FLAIR with the LST tool. Mean SSIM values were calculated over the normal-appearing grey (NAGM) and white (NAWM) matter, as well as in the lesion masks. The contribution of each term and the total SSIM were computed separately.

Results

Results: When T1/T2 images were compared to T1/FLAIR, in NAGM and NAWM the luminance, contrast and structural terms ranged between [0.81-0.99]; for the lesion mask, between [0.61, 0.92]. When T1/T2 was compared to FA, both the luminance and contrast terms ranged between [0.72, 0.92] in the three compartments; while the structural term ranged between [0.49, 0.61]. When T1/T2 was compared to ODI, the luminance term was quite high for the 3 masks [0.72, 0.93], intermediate for the contrast term [0.58, 0.67] and very low and negative [-0.19, -0.11] for the structural term. Finally, regarding the PSIR comparison, the structural term showed a high correspondence in the 3 compartments [0.72, 0.79], while the luminance and contrast terms were below 0.01 for the 3 compartments.

Conclusions

Conclusions: As expected, T1/T2 and T1/FLAIR are highly equivalent, in all aspects. When T1/T2 was compared to FA and ODI, a poor structural correspondence was found, whereas when T1/T2 was compared to PSIR, the structural correspondence was very high, suggesting that the anatomical features are reproduced in a similar way in both sequences. The SSIM index could be used as a measure to assess the equivalency between MRI sequences in a more thorough way.

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Imaging Poster Presentation

P0567 - Diffusion-based Structural connectivity abnormalities in MS phenotypes. (ID 1271)

Abstract

Background

People with MS present disruption of structural brain networks, but the differential characteristics of such changes among MS phenotypes and their clinical impact are not well elucidated.

Objectives

To characterize diffusion-based brain connectivity abnormalities in different MS phenotypes and their relation with disability in a large cohort of patients.

Methods

In this multicenter, retrospective, cross-sectional study, we collected clinical and brain MRI data from 344 patients with MS [median Expanded Disability Status Scale, EDSS 2.0 (range 0-7.0)] and 91 healthy volunteers (HV) from four MAGNIMS centers. Cognition was assessed with the Paced Auditory Serial Addition Test (PASAT) and Symbol Digits Modalities Test (SDMT) in 298 patients. We collected 3D-T1, FLAIR, diffusion-weighted images (DWI) and T2 or field maps acquisitions. FSL and ANTs packages were used to carry out DWI preprocessing and MRtrix software to generate connectivity matrices based on fractional anisotropy values. We computed six network measures (strength, global and local efficiency, clustering coefficient, assortativity and transitivity), and applied the ComBat tool to reduce inter-site variability. We calculated age-adjusted differences in graphs between groups using Mann-Whitney with FDR correction or Kruskal-Wallis with Dunn’s Test when necessary. Associations with clinical features were explored with Spearman’s rank correlation.

Results

Thirty-eight (11%) patients presented a clinically isolated syndrome (CIS), 262 (76%) had relapsing-remitting (RR) and 44 (13%) secondary progressive (SP) MS. CIS patients showed reduced global and local efficiency, clustering coefficient and transitivity compared to HV (corrected p<0.001), whilst RRMS did not differ from CIS patients. Compared with CIS and RRMS, patients with SPMS showed larger changes for the same previous graphs measures (corrected p<0.05), and lower strength than RRMS (corrected p=0.019).

In patients, reduced measures of strength, global and local efficiency, clustering and transitivity correlated with higher EDSS (rho:-0.12–-0.16, corrected p<0.034), lower PASAT (rho:0.26–0.30, corrected p<0.001) and worse SDMT scores (rho:0.28–0.32, corrected p<0.001).

Conclusions

Structural network integrity at the whole brain level is already widely reduced in people with MS from the earliest phases of the disease and becomes more abnormal in SPMS. Network modifications may contribute to the clinical manifestations of the disease.

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Presenter Of 1 Presentation

Imaging Poster Presentation

P0540 - Assessing the relationship between the ratio of T1- T2-weighted images and MRI sequences by using the structural similarity index (ID 1260)

Speakers
Presentation Number
P0540
Presentation Topic
Imaging

Abstract

Background

Background: The ratio of T1- T2-weighted images (T1/T2) has been proposed as a biomarker of tissue integrity, although comparison with MRI-derived tissue metrics has not been perfomed.

Objectives

Objectives: In this study, T1/T2 has been compared to the T1/FLAIR, Phase-sensitive inversion recovery (PSIR), the fractional anisotropy (FA) and the orientation dispersion (ODI) in normal appearing grey, white matter and lesion mask, by using the structural similarity (SSIM) index. The SSIM is the product of 3 terms that take into account the luminance, the contrast and the structural information of the images compared. It ranges between [-1,1], with 1 indicating that the two images compared are identical.

Methods

Material and methods: MRIs of patients with a clinically isolated syndrome were included in this study. Images were acquired in a 3.0 T sytem (Trio, Siemens) using established acquisition protocols. The FA and ODI images were generated with the TBSS/FSL and NODDI/SPM toolboxes, respectively. The SSIM maps were calculated with the function implemented in Matlab. T1-weighted images were segmented with SPM12 and the lesion masks were generated from the FLAIR with the LST tool. Mean SSIM values were calculated over the normal-appearing grey (NAGM) and white (NAWM) matter, as well as in the lesion masks. The contribution of each term and the total SSIM were computed separately.

Results

Results: When T1/T2 images were compared to T1/FLAIR, in NAGM and NAWM the luminance, contrast and structural terms ranged between [0.81-0.99]; for the lesion mask, between [0.61, 0.92]. When T1/T2 was compared to FA, both the luminance and contrast terms ranged between [0.72, 0.92] in the three compartments; while the structural term ranged between [0.49, 0.61]. When T1/T2 was compared to ODI, the luminance term was quite high for the 3 masks [0.72, 0.93], intermediate for the contrast term [0.58, 0.67] and very low and negative [-0.19, -0.11] for the structural term. Finally, regarding the PSIR comparison, the structural term showed a high correspondence in the 3 compartments [0.72, 0.79], while the luminance and contrast terms were below 0.01 for the 3 compartments.

Conclusions

Conclusions: As expected, T1/T2 and T1/FLAIR are highly equivalent, in all aspects. When T1/T2 was compared to FA and ODI, a poor structural correspondence was found, whereas when T1/T2 was compared to PSIR, the structural correspondence was very high, suggesting that the anatomical features are reproduced in a similar way in both sequences. The SSIM index could be used as a measure to assess the equivalency between MRI sequences in a more thorough way.

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