J Korean Radiol Soc.  1987 Aug;23(4):513-523. 10.3348/jkrs.1987.23.4.513.

An experimental study on the variability of the CT number using phantom models

• Kim IO
• Chang KH
• Han MC
• Kim CW

• KMID: 2359416
• DOI: http://doi.org/10.3348/jkrs.1987.23.4.513

Abstract

The study was undertaken to evaluate the reliability and limitation of the CT number through determining the range of variation of CT number under a variety of different conditions using experimental models. Three cylindrical phantom models containing lesion-simulating-rods were used. After filling the different-density-solutions within the phantoms, the CT was performed under a variety of different conditions inorder to demonstrate the variability of CT number of the same lesion. The CT number of the rods within the phantom models was measured and analyzed. The results were as follows; 1. The CT number of the lesion proportionately increased as the CT number of surround increased, and the increase of the CT number of the lesion showed linear response to the increase of the CT number of surrounds. The CT number of lesion was standardized to get constant CT number for the same lesion regardless of the change of surround, the standardized CT number was expressed as: Standardized CT No. of lesion = CT No. of lesion -b x CT No. of surround b-0.19 ; polystyrene, Polyethylene b x0.16 ; Nylon, Lexan, Plexiglass 2. Time interval, change of mAs, or slice thickness had no effect on the CT numberof the lesions. 3. The CT number of the lesions tended to vary wider in the body model than the head model. 4. The range of the CT number variation increased as the lesion decreased in size, and it was more pronounced as the difference between the CT number of the lesion and surround increased. The above results suggest that CT number should be carefully used for diagnosis with consideration of its variability under a variety of different conditions.

MeSH Terms

Diagnosis
Head
Models, Theoretical
Nylons
Polyethylene
Polymethyl Methacrylate
Polystyrenes
Nylons
Polyethylene
Polymethyl Methacrylate
Polystyrenes