Lesion detectability on diffusion-weighted imaging in transient global amnesia: the influence of imaging timing and magnetic field strength.

Introduction: Transient global amnesia (TGA) is a benign disease with a sudden-onset, transient memory disturbance. Characteristic punctate high-signal intensity lesions in the hippocampus on diffusion-weighted imaging (DWI) have been reported in variable frequencies. We investigated the influence of the timing of DWI and the magnetic field strength on the lesion detectability in TGA.
Methods: Seventy-three patients diagnosed with TGA underwent DWI within 24 h after the symptom onset and again on day 3 at either 1.5 (n = 31) or 3 T (n = 42). The patients were divided into three subgroups according to the time lapse after the symptom onset to the first DWI (0-6 h, 6-12 h, and 12-24 h).
Results: The detection rate of the lesions during the first 24 h rose statistically significantly with increased time lapse after the symptom onset (34% in 0-6 h, 62% in 6-12 h, and 67% in 12-24 h). It increased up to 75% on day 3. The detection rate was higher at 3 T than at 1.5 T in all time points (41% vs. 27% in 0-6 h, 70% vs. 44% in 6-12 h, 80% vs. 57% in 12-24 h, and 86% vs. 61% on day 3), but the statistical significance was achieved only on day 3.
Conclusion: Awareness of the different lesion detectability on DWI according to the time lapse after the symptom onset can help in diagnosing the patients with suspected TGA. High field strength is another important factor to increase the lesion detectability on DWI.