A variety of diseases or conditions may cause a progressive change in the diameters of tubular structures in the human body, i.e., obstructive jaundice, spinal stenosis syndrome, aneurysm, tracheobronchial diseases, etc. Therefore an accurate measurement of the cross section of these tubular structures may make significant contribution to the diagnosis, planning of treatment and evaluation of prognosis of these diseases.
For a most reliable size determination of tubular structures on a CT, a series of experiments were undertaken to study the factors that may affect the applicability of CT scanning. We performed CT of tubular phantoms consisting of air filled tubes measuring from 1.0/2.Omm to 16.5/20.Omm in inner/outer diameter under varible parameter conditions.
The results show that: 1) Multiple parameters can change the CT dimension of tubular structures; 2) Position control of window center is critical to CT dimension, but window width variation is insensitive to CT dimension; 3) A similar increase in error rate of measurement with decreasing tube size is observed. The range of error is 0.57 to 3.57mm in inner diameter and -1.43 to 2.86mm in outer diameter; 4) Scan time (beam pulse) and object position in scan field are insensitive to CT dimension; 5) Tube angle to scan table shows inverse relationship to error rate of CT dimension in small-sized tube, but similar relationship in large-sized tube; 6) The smaller the scan field by x-ray tube shifting is and higher the KV is, the more reliable the CT dimension is; 7) The optimal window setting for accurate measuring of tube size does not correspond with the setting for producing good looking image.
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