Including a standard curve of your miRNA of interest--different concentrations of a synthetic oligo--allows accurate copy number estimation.

did you mean the absolute quantification??

If you have time please check the paper

http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0084686

where in Figure 4A they used ct and miRNA concentration.

@ Kenneth

In this paper, the "miRNA concentration" is provided as "arbitrary units." Although the materials and methods section is not extensive, this calculation is relative and is presumably based on an ideal (100% efficient) reaction and dCt values. A rough estimate, then; conclusions about the actual concentration would require a standard curve and/or, potentially, a digital approach.