with ImageJ or Dicom viewer such as dicomworks , Amide, radiant etc

The most conventional measure is probably the contrast-to-noise ratio (CNR), which is frequently used for CT image data (see attached link). A simple related approach to evaluate the detectability of a structure is the Rose criterion, which is based on the effective CNR,  i.e. on CNR × sqrt(pixel number); according to the Rose criterion, the effective CNR should be greater than about 5 (see attached publications).

http://www.ncbi.nlm.nih.gov/pubmed/?term=%22contrast-to-noise+ratio%22+%22computed+tomography%22

Article The Rose model, revisited

Article Handbook of Medical Imaging. Volumes 1 3

Article Vision : human and electronic / Albert Rose

Você quis dizer: Estimado Colega. Espero ter compreendido sua questão. Assim, estas duas referencias acredito serem uteis. (1) Dose and image quality evaluation of a dedicated cone-beam CT system for high-contrast neurologic applications. Yu L1, Vrieze TJ, Bruesewitz MR, Kofler JM, DeLone DR, Pallanch JF, Lindell EP, McCollough CH. (2) How to measure CT image quality: Variations in CT-numbers, uniformity and low contrast resolution for a CT quality assurance phantom Kristine Gulliksrud, , Caroline Stokke, b, Anne Catrine Trægde Martinsen, Coloco-me a disposição.

Dear Colleague.

I hope I understood your question.

So these two references believe are useful.

(1) Dose and image quality evaluation of a dedicated cone-beam CT system for high-contrast neurologic applications.

Yu L1, Vrieze TJ, Bruesewitz MR, Kofler JM, DeLone DR, Pallanch JF, Lindell EP, McCollough CH.

(2) How to measure CT image quality: Variations in CT-numbers, uniformity and low contrast resolution for a CT quality assurance phantom

Kristine Gulliksruda, Caroline Stokkea, b, Anne Catrine Trægde Martinsena,

I put myself at the disposal.

you can use mimics software.

I think imagej would do what you want

 I use ImageJ to evaluate physical parameters like contrast and so on for my phantoms.