FIG 2. Bar graph shows the preventive effect of UV on the development of vasospasm for different irradiation time periods. Four groups are shown, for which the irradiation time was 0, 5, 10, or 20 seconds. UV irradiation with durations of 10 and 20 seconds significantly prevented the development of vasospasm (P < .001). Values represent the ratio of the relative diameter in each group on day 2 to that on day 0. The preventive effect seems to be close to maximum at an irradiation period of 10 seconds. Bars represent mean ± SD. *, P < .05 compared with no irradiation.