J Korean Radiol Soc.  1985 Jun;21(3):368-374. 10.3348/jkrs.1985.21.3.368.

An experimental study on accuracy and error range of CT measurement

• Han JK
• Chang KH
• Han MC
• Kim CW

• KMID: 2462449
• DOI: http://doi.org/10.3348/jkrs.1985.21.3.368

Abstract

The measurement of the relative X-ray abssorption coefficient (CT No.) and the size of the lesion on CT ishighly valuable in the diagnosis of the certain disease, guide to treatment planning, and follow-up of patientunder treatment. But as the CT is a synthetic image, CT No. and size displayed in CT are greatly influenced byvarious factors such as KVp, slice thickness, scan time, CT No. of the surrounding, geometry of lesion in gantry,window width(W.W) and window level(W.L) etc. The study was performed ot evaluate the accuracy and error range ofthe CT measurement, including CT No. and size affected by various conditons using phantom model designed byauthor., Author also propose the optimum window width and window level for measurement of real size on CT. Theresulsts are as follows; 1. The CT No. of the lesion increases as the CT N. of surround increase if the CT No. ofthe lesion is below-100 H.U., while the CT No. of the lesion decreases as the CT No. of surround increases if theCT No. of the lesion is above 900 H.U. 2. The CT No. increases as photon influx (mAs) during scan increases. The higher the CT No. of the lesion, the greater the degree of increases are. 3. If the CT No. of the lesion is greater than that of surround, the size of the lesion increases as window level decreases. The narrower the windowwidth, the larger the difference between the maximum and minimum value of measurement and the steeper the slope ofchange is. 4. The window width affects the size if the measured size is sufficiently different from the true size.5. The greater the difference between the CT No. of the lesion and that of surround, the greater the differencebetweeen the maximum and minimum value of measurement. and as the CT No. of surround increases, the differencebetween the minimum and maximum value also increases. 6. The optimal window width and level for size measurementareas follows; Soft tissue - soft tissue; W.W 250, W.L 40-60 Soft tissue -fat ; W.W 500, W.L - 100-60 Soft tissue-bone ; W.W 500, W.L - 100-300 Soft tissue -air ; W.W 500, W.L - 700-600

MeSH Terms

Diagnosis
Follow-Up Studies