Format
A list with the following elements: 1) dataMatrix: a 183 samples x 109
variables matrix of numeric type corresponding to the intensity
profiles (values have been log10-transformed); 2) sampleMetadata: a 183 x 3
data frame, with the volunteers' age ('age', numeric), body mass
index ('bmi', numeric), and gender ('gender', factor), and 3) variableMetadata: a 109 x 3 data
frame, with the metabolites' MSI identification level ('msiLevel':
either 1 or 2), HMDB ID when available ('hmdb', character), chemical
class according to the 'super class' taxonomy of HMDB
('chemicalClass', character)