# Evaluating the Effect of Intensity Standardisation
## 2 Materials and Methods  
### Datasets  
We considered two publicly available longitudinal MRI repositories: Open Access Series of Imaging Studies (OASIS) [19] and Alzheimer's Disease Neuroimaging Initiative (ADNI) [20]. For the sake of reproducibility, we attach the list of selected cases from ADNI and OASIS as Supplementary Materials.  
OASIS. We used a subset of the OASIS2 longitudinal dataset comprising scans from 122 different subjects. In each imaging session, each subject was scanned three to four times using an MP-RAGE sequence and a 1.5T Vision scanner (Siemens, Erlangen, Germany). Imaging acquisition details can be found in Table 1. All subjects in the study were evaluated using the clinical dementia rating to determine their dementia status and classified into non-demented or very mild to mild Alzheimer's disease. We downloaded the complete OASIS2 longitudinal dataset and selected patients who remained in either category throughout the entire study and had their follow-up scan approximately between six months and three years of their baseline visit, as depicted in Figure 1. The resulting sample consisted of 60 Alzheimer's disease patients (mean age (SD) = 75.05 (6.89); female proportion = 47%) and 62 control subjects (mean age (SD) = 75.40 (8.70); female proportion = 74%).  
ADNI. We used a subset of the ADNI longitudinal dataset comprising scans from 147 different subjects. Each subject was scanned using an MP-RAGE sequence and multiple scanners (General Electric (GE) Healthcare; Philips Medical Systems; and Siemens Medical Solutions). Imaging acquisition details can be found in Table 1. All subjects in the study were evaluated via global, functional and behavioural assessments, including the clinical dementia rating, to determine their dementia status. We used the advanced search tool in the ida.loni.usc.edu platform to extract our subsample. The inclusion criteria were image type = original (raw); field strength = 1.5T; slice thickness = 0.5-1.9 mm, weighting = T1, image description = MP-RAGE, subject group = AD or NC; visits = ADNI screening and ADNI1/GO Month 12. The resulting sample consisted of 64 Alzheimer's patients (mean age (SD) = 75.58 (8.16); female proportion = 45%) and 83 control subjects (mean age (SD) = 77.59 (4.56); female proportion = 53%). Subjects had their follow-up scan approximately one year after their baseline visit, as illustrated in Figure 1.  
The ADNI was launched in 2003 as a public-private partnership, led by Principal Investigator [PERSON], MD. The primary goal of ADNI has been to test whether serial magnetic resonance imaging (MRI), positron emission tomography (PET), other biological markers, and clinical and neuropsychological assessment can be combined to measure the progression of mild cognitive impairment (MCI) and early Alzheimer's disease (AD). For up-to-date information, see www.adni-info.org [accessed on 10 February 2021]).  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Parameter** & **OASIS** & **ADNI** \\ \hline Sequence & MP-RAGE & MP-RAGE \\ Repetition time (ms) & 9.7 & 3000 \\ Echo time (ms) & 4.0 & \(-\) \\ Flip angle & \(10^{\circ}\) & \(8^{\circ}\) \\ Inversion time (ms) & 20 & 1000 \\ Orientation & Sagittal & Sagittal \\ Thickness (mm) & 1.25 & 1.20 \\ Slice number & 128 & 184–208 \\ Resolution & \(256\times 256\) & \(192\times 192\) \\  & 1\(\times\)1 mm & \(1.25\times 1.25\) mm \\ \hline \hline \end{tabular}
\end{table}
Table 1: Image acquisition details of considered OASIS and ADNI scans. We extracted the information in this table from the publications in [19; 20].  
Figure 1: Distribution of time between visits in the considered ADNI and OASIS datasets.