Yumi Kataoka | PubMed Health

PubMed2004

[Dose estimation with CTDI100, air in computed tomography].

Although the principal dosimetric quantity in computed tomography (CT) can be assessed using a pencil ionization chamber with an active length of 100 mm, standard CT dosimetry phantoms of polymethylmethacrylate (PMMA) , and plates of aluminum, most facilities do not possess the requisites. We present a practical method of estimating CTDI(100, c), CTDI(100, p) and the half-value layer (HVL) from CTDI(100, air), which is measured parallel with the axis of rotation of the scanner to free-in-air. The three data chosen for this method of estimation were as follows: 1) the relation of HVL to CTDI(100, air) per radiographic exposure (mAs); 2) the relation of HVL to CTDI(100, c) per CTDI(100, air); 3) the relation of HVL to CTDI(100, p) per CTDI(100, air). The data were based on the measured values of six CT scanners, so as to avoid dependence on the technical characteristics of a specific manufacturer. The estimated value has a possible maximum uncertainty of 20%, although this method of estimation is practical for dose assessment.

Phantoms, Imaging↗

PubMed2003

[The improvement in the cerebral blood flow analysis software in case of CT-perfusion inspection and the examination of the scan protocol].

In our hospital, CT-perfusion was introduced in April, 2002. It is used to diagnose, to determine what treatment to use and to prognosticate cerebral blood flow after operation in super acute period brain infarct. At the beginning of the introduction, processing time and dosage for partial areas needed improvement. Therefore, we investigated the possibility of shorter processing time and lower dosage of radiation with the help of improvement in the analysis software as well as a different scan method. Two methods of reducing radiation dosage were examined. (1) The speed of X-ray rotation was slowed down; while photon per image was maintained, total mAs was lowered. (2) Continuation scan was replaced by intermission one. Analyzing time with older and newer version of analysis software was compared. The dosage was able to decrease by 25% as a result of the rotation speed slowed down; it became further less by 50% with the intermission scan. Processing such as the vein extraction was automated by using new analysis software and successfully shorten the analysing time without damaging the reliability of analyses. We forecast that more clinical research on further lowering dosage and stabilization of analyzing will enable us to provide better information.

Acute Disease↗