Underdrawings of paintings imaged through infrared photography or IR reflectogra
phy with a vidicon is a tehnique of major importance to numerous art historians.
  Unfortunately for e-mail it's too large of a subject to discuss here, however,
 you might try to contact several individuals who are well know for their use of
 this tool.
 
Prof. Molly Fairies at the Indiana University (812-339-8208; Maryanne Ainsworth
at the Metropolitan Museum of Art; J.R.J. Van Asperen de Boer, Groningen Univers
ity, Netherlands; Rachel Billlinge, The National Gallery of Art, UK.