Susceptibility map-weighted imaging (SMWI) is a recently proposed magnetic susceptibility imaging method that utilizes a quantitative susceptibility map (instead of a phase image) as the mask for susceptibility weighting. This new approach improves both CNR and SNR in comparison with conventional SWI.¹ We hypothesized that nigrosome imaging using SMWI has higher interobserver agreement as well as higher diagnostic performance than that of MEDIC. The aim of this study was to compare SMWI and MEDIC for nigrosome 1 imaging. A total 74 subjects (median age, 71 [IQR, 65-75]; 30 males; PD [n=44], DIP [n=13], healthy subjects [n=10], NPH [n=2], essential tremor [n=1], MSA-C [n=1], MSA-P [n=1], PSP [n=1], and vascular parkinsonism [n=1]) underwent 3T MRI using a 32-channel head coil. Oblique axial 3D MEDIC imaging was obtained vertical to the longitudinal axis of the midbrain. The scan parameters for MEDIC were as follows: TR, 88 ms; minimum TE, 11.1 ms; maximum TE, 66.9 ms (the number of echoes, 6; echo spacing, 11.1 ms); FA, 10°; ETL, 6; thickness, 1 mm; number of slices, 28; matrix, 384×384; FOV, 192×192; reduction factor of parallel imaging, 2. From the multi-echo k-space data of MEDIC, QSM was caculated using iLSQR,² and then SMWI was generated by using the QSM images as a weighting mask (threshold value, 1 ppm; number of multiplications, 4).¹ Details of the SMWI processing for the nigrosome 1 imaging are described in a separate abstract. Four independent raters (two experienced [a neuroradiologist and a neurologist; R1 and R2] and two less experienced [third- and fourth year radiology residents] reviewers; R3 and R4) classified the bilateral nigrosome 1 as ‘normal’ (iso- or hyperintensity in the central portion of the presumed nigrosome 1 area), ‘possibly abnormal’ (hypointensity in less than 50% of the presumed nigrosome 1 area and ‘definitely abnormal’ (hypointensity in equal to or more than 50% of the presumed nigrosome 1.^5,6 Each side was rated separately separately on both MEDIC and SMWI. For a simplified statistical analysis, the subjects were re-classified as abnormal if any abnormality was determined on either side of the nigrosome 1 area; a subject was classified as normal when both nigrosome 1 regions were determined as normal. As both PD and MSA-P showed abnormality in nigrosome 1, they were considered as an abnormal group. The other subjects were categorized as a normal group. The generalized kappa test was used to test if there is any improvement of interobserver agreement between MEDIC and SMWI. ROC curve analyses were conducted to test if there is any significant difference between the reviewers.Compared to MEDIC, SMWI showed more conspicuous borders of the substantia nigra and nigrosome 1 regions (Fig. 1), and helped to determine if there was abnormality in the presumed nigrosome 1 regions (Fig. 2, 3). The MEDIC imaging had the generalized kappa of 0.989 (CI, 0.896-1.082), whereas SMWI showed a higher kappa value of 1.339 (CI, 1.232-1.446) without an overlap of CIs, suggesting significant improvement of interobserver agreement. In the MEDIC imaging, the AUCs of R3 and R4 were 0.741 and 0.692, respectively, whereas those of R1 and R2 were 0.870 and 0.826, respectively. The ROC curve analyses showed significant difference between the experienced and less experienced reviewers (P = 0.0138 between R1 and R3, P = 0.0031 between R1 and R4, P = 0.0211 between R2 and R4). In SMWI, the AUCs of R3 and R4 increased to 0.894 and 0.894, respectively. Both R1 and R2 also showed higher AUCs (0.933 and 0.933, respectively). There was no significant difference among the all reviewers in SMWI (P > 0.05).Here we demonstrated that the SMWI improved the diagnostic utility of the nigrosome 1 imaging at 3T by increasing interobserver agreement between the experienced and less-experienced reviewers and by enhancing diagnostic performance. In previous nigrosome 1 imaging studies at 3T, various imaging techniques, including PRESTO,³ SWAN,⁴ and MEDIC^5,6 have been applied. All these methods are proprietary and had relatively limited SNR and CNR. Thus, it is desirable to standardize an imaging technique for visualization of nigrosome 1. Although MEDIC had higher SNR, it exhibited relatively low susceptibility weighting, limiting its diagnostic sensitivity for the nigrosome 1 imaging. On the other hand, SMWI provided high quality images with good contrast and SNR. SMWI could also enable us to measure susceptibility values in the substantia nigra by using the QSM map, thereby quantifying the level of degeneration.