Xenon-induced flow activation in patients with cerebral insult who undergo xenon-enhanced CT blood flow studies

Abstract

Background and purpose: Stable xenon-enhanced CT ((s)Xe/CT) has gained wide acceptance in the assessment of regional cerebral blood flow (rCBF) in patients with intracranial abnormalities. The aim of this study was to test whether the contrast medium (ie, (s)Xe) itself directly induces relevant changes in rCBF, thereby distorting any valid determination of cerebral perfusion by using (s)Xe/CT.

Methods: To characterize the degree and temporal dynamics of (s)Xe-induced flow activation, a thermal diffusion (TD)-based microprobe was placed subcortically into the frontal lobe on either hemisphere to assess rCBF (TD-rCBF) continuously in 23 patients (mean age, 55 +/- 18 years) with severe intracranial insult who were undergoing (s)Xe/CT.

Results: In 35, the (s)Xe/CT studies TD-rCBF rose from 25 +/- 17 mL/100 g per minute (range, 5-42 mL/100 g per minute) before (s)Xe administration to 28 +/- 21 mL/100 g per minute (range, 6-46 mL/100 g per minute) after arterial (s)Xe saturation was reached. Analysis of the flow activation curve showed a logarithmic shape with an increase in TD-rCBF between 3% and 7% within the first 76 seconds of (s)Xe wash-in (12% after 190 seconds) and showed no further augmentation until the end of the blood flow study.

Conclusion: The observed (s)Xe-induced rCBF activation, which showed significant inter- and intraindividual variability, might lead to overestimation of rCBF in patients with severe intracranial insult. The obtained flow activation curve provides essential information that may allow subsequent refinement of the methodology, aiming to further minimize the influence of (s)Xe-induced rCBF activation on rCBF calculations when using (s)Xe/CT technology.

fig 1.

^sXe-enhanced CT blood flow study in a patient with severe head injury. Left, anatomic reference section (arrow indicates tip of TD-rCBF probe); right, corresponding rCBF (mL/100 g per minute) image shows severe right hemispheric hypoperfusion

fig 2.

Graph shows an original TD-rCBF recording obtained during a 30% ^sXe/CT blood flow study in a patient with head injury. Baseline (BAS): preinhalation TD-rCBF recording (duration, 42 seconds); wash-in (WI): TD-rCBF during ^sXe inhalation (duration, 270 seconds)

fig 3.

Relative changes (in %) in baseline values in TD-rCBF due to ^sXe inhalation as seen in 35 blood flow studies. Solid circles represent individual changes in TD-rCBF at various time periods; open circles depict mean changes in TD-rCBF as compared with baseline. BAS indicates baseline; WI % represents seven periods, each of 38 seconds' duration, of ^sXe inhalation

fig 4.

Time course of arterial ^sXe concentration (open circles) and ^sXe-induced flow activation (solid circles). The x-axis displays relative values of end-tidal ^sXe concentration and TD-rCBF, respectively, with each parameter expressed in percentage of maximum response observed