Conventional MR sequences produce only positive longitudinal magnetization. Conversely, inversion recovery (IR) sequences are displayed after rotating the positive longitudinal magnetization into negative magnetization, so IR sequences can generate more tissue contrast [2]. T1IR is an MRI sequence with 180 radio-frequent pulses with high lesion CNR and GM-WM contrast ratio than T1SE sequence, so it can be used in the evaluation of various neoplastic space-occupying lesions and demyelinating diseases such as multiple sclerosis [1]. In our study, we compared between T1IR and T1SE on 50 patients with different brain diseases aiming to reveal superiority of each sequence in each brain disease. In our study, on non-contrast sequences, T1IR was better than T1SE, giving higher CNR with mean value − 13.04 (1.20) for all types of lesions (multiple sclerosis, intra-axial, and extra-axial space-occupying lesions).
The same of our results were reported by Bing et al. [1] in a study carried on 30 patients with various neurologic diseases, and T1IR was superior to T1SE with improved determination of lesion extent, conspicuity, and lesion delineation; this was because T1SE had the poorest GM-WM contrast and poor lesion-to-background contrast by visual comparison between T1SE and T1IR. As well, Rydberg et al. [11], in a study carried on 15 patients with contrast-enhancing brain space-occupying lesions, showed that T1IR had quantitatively comparable or superior lesion-to-background contrast ratio, GM-WM contrast ratio, and superior CSF-WM contrast ratio; also, it provided qualitatively superior lesion detection compared to T1SE, as well as, superior lesion conspicuity and image contrast. In the same context, Lee et al. [12], in a study carried on 15 patients with 18 lesions, showed that T1IR was superior to T1SE in the determination of lesion extent in 16 lesions and provided higher CNR and GM-WM contrast ratio, but it takes more time than T1SE. However, Qian et al. [3] reported opposite results to our study, as T1SE was sensitive than T1IR in the detection of brain metastasis, but this can be accounted by the difference of nature of the disease, because many of metastatic lesions included in this study were small hemorrhagic lesions that were better detected on T1SE because of its sensitivity to hemorrhagic lesions.
We also reported in our study that after giving intravenous contrast media, T1IR was better than T1SE, giving higher CNR in lesions with low enhancement ratio with mean value 18.91 (2.68) vs 1.05 (0.59). On the other side, T1SE was better than T1SE in lesions with high enhancement ratio with mean value 21.24 (1.92) vs 0.64 (0.37). This goes on with results of Bandai et al. [13], in which T1IR provided higher tumor-to-WM contrast ratio with mean value 38.89 (2.68) in 13 enhanced tumors, and it also revealed 7 non-enhanced and low enhanced tumors that were poorly visualized on T1SE. The same results were reported in other studies [14, 15].
In our study, T1IR aided in the detection of higher number of lesions than T1SE especially in patients with multiple sclerosis with mean value 10.67 (2.26) vs 3.89 (1.05). This seemed consistent with Harel et al. [16], Sethi et al. [17], and Nelson et al [18] who showed that T1IR improved the detection of cortical and juxtacortical lesions in progressive multiple sclerosis with accurate localization of them; this can be due to the higher WM-GM contrast ratio, making it extremely useful in follow-up of these patients.
We encountered some limitations in our study. Firstly, our study included only 50 patients; this number reveals minor differences between T1IR and T1SE especially with different brain lesions. Secondly, most of our MS patients were in inactive state. Therefore, we could not assess their SI on post-contrast lesions. Finally, we did not assess the size of lesions in both sequences. Hence, more studies should be done to reveal the full comparison between both sequences.