Yasuhiko Iryo, Presenter: Nothing to Disclose

Toshinori Hirai MD, Abstract Co-Author: Nothing to Disclose

Koya Iwashita, Abstract Co-Author: Nothing to Disclose

Hiroyuki Uetani, Abstract Co-Author: Nothing to Disclose

Mika Kitajima MD, Abstract Co-Author: Nothing to Disclose

Yasuyuki Yamashita MD, Abstract Co-Author: Consultant, DAIICHI SANKYO Group

Yukio Ando MD, Abstract Co-Author: Nothing to Disclose

The purpose of this study was to determine how the gray to white matter contrast in healthy subjects changes on high b-value DWI acquired at 3T and evaluate whether high b-value DWI at 3T is useful for the detection of cortical lesions in inflammatory brain diseases.

Ten healthy volunteers (5 men, 5 women; age range 26 - 83 years; mean 54 years) underwent DWI at b = 1000, 2000, 3000, 4000, and 5000 s/mm2 on a 3T MRI unit. On DW images acquired at the level of the basal ganglia, one radiologist performed region-of-interest measurements of the signal intensity (SI) of 5 gray matter structures. The gray-to-white matter contrast ratio (GWCR) was calculated using the formula GWCR = SIGM/SIWM, where SIGM and SIWM are the SI of the gray matter and frontal white matter, respectively. Ten patients (4 men, 6 women; age range 19 - 82 years; mean 55 years) with inflammatory cortical lesions were also included; 6 presented with infectious encephalitis, 2 with probable sporadic Creutzfeldt-Jakob disease, and one each with suspected autoimmune encephalitis and encephalitis of unknown etiology. All patients underwent conventional MRI and DWI at b = 1000 and 3000 s/mm2. Two neuroradiologists independently interpreted the SI of the cortical lesions on DWI scans using a 4-point grading system. Interobserver agreement was assessed by k statistics.

In the healthy subjects, the b value increased as the GWCR decreased in all evaluated gray matter structures. On DW images acquired at b = 3000 s/mm2, mean GWCR was less than 1.0 in 4 of 5 structures. In evaluating inflammatory cortical lesions, observers 1 and 2 recorded definite visualization (grade 3) for 4 (40%) and 5 (50%) DWI obtained at b=1000 s/mm2 and for 9 (90%) and 10 (100%) DWI acquired at b=3000 s/mm2 studies, respectively. For both observers the mean score was significantly higher for b=3000 s/mm2 than b=1000 s/mm2 (p <0.05). Interobserver agreement for DWI at b=1000 s/mm2 and b=3000 s/mm2 was poor (κ = 0.25) and excellent (κ = 1.0), respectively.

At 3T DWI, the gray-to-white matter contrast in most gray matter structures reverses at b = 3000 s/mm2. In the evaluation of cortical lesions in patients with inflammatory diseases, 3T DWI at b = 3000 s/mm2 was more useful than b = 1000 s/mm2.

We recommend that for evaluating inflammatory cortical lesions on 3T MRI, DWI at b = 3000 s/mm2 be added to the conventional MRI protocol.

Iryo, Y, Hirai, T, Iwashita, K, Uetani, H, Kitajima, M, Yamashita, Y, Ando, Y, Is High-B-Value (B = 3000 s/mm²) Diffusion-weighted Imaging at 3T Useful for Evaluating Cortical Lesions in Inflammatory Diseases?.  Radiological Society of North America 2012 Scientific Assembly and Annual Meeting, November 25 - November 30, 2012 ,Chicago IL. http://archive.rsna.org/2012/12027091.html