DIAGNOSTIC NEURORADIOLOGY Lesion detectability on diffusion-weighted imaging in transient global amnesia: the influence of imaging timing and magnetic field strength Inseon Ryoo & Jae Hyoung Kim & SangYun Kim & Byung Se Choi & Cheolkyu Jung & Sung Il Hwang Received: 24 February 2011 /Accepted: 9 May 2011 /Published online: 21 May 2011 # Springer-Verlag 2011 Abstract 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 un- derwent 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. Keywords Transient global amnesia . Diffusion-weighted imaging . Lesion detectability . Hippocampus Introduction Transient global amnesia (TGA) is defined by a sudden onset of an anterograde and retrograde amnesia, yet with preserved consciousness and self-awareness [1]. Patients recover from this cognitive disturbance within several hours without any long-term sequelae. The incidence of TGA has been reported to be 3–8 cases per 100,000 people per year [2–5]. Recently, many studies have consistently reported that 1- to 5-mm-sized punctate high-signal intensity lesions were frequently found in the lateral portion of the hippocampus (i.e., CA1 region) on diffusion-weighted imaging (DWI) in TGA [ 6–10]. DWI can help in diagnosing TGA within several hours after the onset of symptoms in the emergency department by excluding other possible differential diagnoses such as transient ischemic attack, epilepsy, and psychiatric disorders [11–14]. Detec- tion of typical TGA lesions on DWI can also support a confirmative diagnosis, particularly in patients with atypical clinical findings. The detection rate of these TGA lesions on DWI has varied in a range between 0% and 84% [9, 10, 15–18] since Strupp et al. [16] first reported. Variable detection rates of TGA lesions are attributable to different DWI parameters such as b value, section thickness, and the timing of imaging from the onset of symptoms. A high b value (i.e., b =2,000–3,000 s/mm 2 ) and thin section I. Ryoo : J. H. Kim (*) : B. S. Choi : C. Jung : S. I. Hwang Department of Radiology, Seoul National University College of Medicine, Seoul National University Bundang Hospital, 166 Gumiro, Bundang-gu, Seongnam-si 463-707, South Korea e-mail: jaehkim@snu.ac.kr S. Kim Department of Neurology, Seoul National University College of Medicine, Seoul National University Bundang Hospital, 166 Gumiro, Bundang-gu, Seongnam-si 463-707, South Korea Neuroradiology (2012) 54:329–334 DOI 10.1007/s00234-011-0889-4