Abstract metadata for multidimensional image data considered as functions B Gibaud 25/10/2007

Goals Provide documentation of the bulk data Concerning – logical organization Range of the function : scalar or not, data type used (uchar, char, int, float, double, etc) Domain of the function : Number of variables, order of variables, number of samples along each dimension, regular sampling or not –Semantics Of components Of variables

Spec of domain and range Range (components) –Scalar Data-type, e.g. int32 Semantics, e.g. T1weightedMRIsignalintensity –Vector Nb-components ; table of (Data-type, Semantics) Domain (variables) –Nature of interval Regular-interval –Nb-samples ; inter-sample-distance ; sample-width Non regular interval –Nb-samples ; origin ; table of (dist-to-origin, sample-width ) –Semantics : e.g. space, time, energy

Example 1 T1weighted MR dataset –Scalar Range Data-type=int32 Semantics = ‘T1weightedMRsignalintensity’ –3 variables Regular interval –Nb-samples=256, inter_sample-dist=1mm, sample-width=1mm – semantics = ‘space along X’ Regular interval –Nb-samples=256, inter_sample-dist=1mm, sample-width=1mm – semantics = ‘space along Y’ Regular interval –Nb-samples=120, inter_sample-dist= 4mm, sample-width=4mm – semantics = ‘space along Z’

Example 2 fMRI dataset –Scalar Range Data-type=int16 Semantics = ‘T2STARMRsignalintensity’ –4 variables Regular interval –Nb-samples=128, inter_sample-dist=4mm, sample-width=4mm – semantics = ‘space along X’ Regular interval –Nb-samples=128, inter_sample-dist=4mm, sample-width=4mm – semantics = ‘space along Y’ Regular interval –Nb-samples=12, inter_sample-dist= 9mm, sample-width=9mm – semantics = ‘space along Z’ Regular interval –Nb-samples=200, inter_sample-dist= 1s, sample-width=0.5s – semantics = ‘time’

Example 3 SPECT acquisition dataset (TOMO) –Scalar Range Data-type=int16 Semantics = ‘Number of counts’ –3 variables Regular interval –Nb-samples=128, inter_sample-dist=4mm, sample-width=4mm – semantics = ‘space along X’ Regular interval –Nb-samples=128, inter_sample-dist=4mm, sample-width=4mm – semantics = ‘space along Y’ Regular interval –Nb-samples=128, inter_sample-dist= 2.81°, sample-width=2.81° – semantics = ‘space along theta (projection angle)’

Example 4 3D displacement field (non linear registration) –Vector Range 3 components –(Data-type=float ; Semantics = ‘space displacement along X’) –(Data-type=float ; Semantics = ‘space displacement along Y’) –(Data-type=float ; Semantics = ‘space displacement along Z’) –3 variables Regular interval –Nb-samples=256, inter_sample-dist=1mm, sample-width=1mm – semantics = ‘space along X’ Regular interval –Nb-samples=256, inter_sample-dist=1mm, sample-width=1mm – semantics = ‘space along Y’ Regular interval –Nb-samples=120, inter_sample-dist= 4mm, sample-width=4mm – semantics = ‘space along Z’

Example 5-1 RGB 2D image –Vector Range 3 components –(Data-type=int16 ; Semantics = ‘Luminance in Red’) –(Data-type=int16 ; Semantics = ‘Luminance in Green’) –(Data-type=int16 ; Semantics = ‘Luminance in Blue’) –2 variables Regular interval –Nb-samples=1024, inter_sample-dist=0.5mm, sample- width=0.5mm – semantics = ‘space along X’ Regular interval –Nb-samples=1024, inter_sample-dist=0.5mm, sample- width=0.5mm – semantics = ‘space along Y’

Open issues 1 Need to have a sort of ‘qualitative variable’ to manage e.g. RGB images in 3 separate planes, indexed by this variable ? – semantics of the corresponding variable would be : ‘Red’, ‘Green’, ‘Blue’ ? –semantics of the corresponding (scalar) range would be ‘luminance’ ? Probably needed It would become somewhat arbitrary to choose between a « vector range » versus a colour qualitative variable

Example 5-2 RGB 2D image (as 3 separate planes) –Scalar Range (Data-type=int16 ; Semantics = ‘Luminance’) –3 variables Regular interval –Nb-samples=1024, inter_sample-dist=0.5mm, sample-width=0.5mm – semantics = ‘space along X’ Regular interval –Nb-samples=1024, inter_sample-dist=0.5mm, sample-width=0.5mm – semantics = ‘space along Y’ Qualitative variable –Nb-samples=3 –(Semantics = ‘Luminance in Red’) –(Semantics = ‘Luminance in Green’) –(Semantics = ‘Luminance in Blue’)

Open issues 2 Need to manage ‘related variables’ ? for instance in the SPECT example (TOMO), the indexing could be done both on the ‘projection angle’ and on ‘time’ –Useful ? –Is sampling necessarily regular with both variables (linear relationship between the two) ?

Open issues 3 Need to manage units in which scalar components are represented (Hounsfield, NM units, etc.) ? –Useful ?

Example 6 MR Spectro –TBD