The wash-in/washout protocol in stable xenon CT cerebral blood flow studies

We conducted a comparative study to optimize the scanning and inhalation protocols for xenon CT cerebral blood flow (CBF) examination (Xe CT), with the aim of improving the practical performance of Xe CT as a routine clinical examination.

Four different inhalation protocols, including 3-min, 6-min, and 8-min wash-in protocols, and a 3-min wash-in/5-min washout protocol, were compared in five healthy volunteers. Each subject underwent two serial Xe CT examinations with an interval of 30 min between the first one (wash-in) and the second one (wash-in/washout). A computer simulation was also performed to support the results of the clinical study. The rate of success was calculated from our experience of 110 clinical cases examined with the wash-in/washout protocol over the last 9 months.

The mean CBF values with 6-min and 8-min wash-in protocols were 59.0 and 59.5 mL/100-g brain per min in the thalamus, and 19.5 and 19.0 mL/100-g brain per min in the frontal white matter, respectively. The mean CBF values with 3-min wash-in/5-min washout protocol were 60.0 mL/100-g brain per min in the thalamus and 18.5 mL/100-g brain per min in the frontal white matter, respectively. Computer simulation showed improved signal-to-noise ratio by employing the 3-min wash-in/5-min washout protocol instead of 8-min wash-in protocol for the same number of data points. The rate of success improved to 99.1% due to the significant decrease in head motion with the shorter period of inhalation.

A wash-in/washout protocol is a useful alternative in Xe CT CBF measurement and more useful than the wash-in method for clinical purposes.