El primer paso es sacar las fechas de los DICOM.

Ejemplo con FACEHBI,

[osotolongo@detritus facehbi]$ for x in /nas/corachan/facehbi/*;do n=$(echo ${x} | awk -F"/" {'print $5'}); f=$(find ${x} -type f |grep -v "DTI"| head -1); d=$(dckey -k "AcquisitionDate" ${f} 2>&1); echo ${n},${d}; done > dates_mri.csv
[osotolongo@detritus facehbi]$ sed -i '1iPSubject,Date' dates_mri.csv
[osotolongo@detritus facehbi]$ head dates_mri.csv
PSubject,Date
F001,20141205
F002,20141205
F003,20141211
F004,20141212
F005,20150107
F006,20141223
F007,20141219
F008,20141220
F009,20150110