To obtain an anisotropic diffusion phantom with ease, we evaluated the longitudinal stability of commercially available astriction cotton. DTI examinations were performed at 3T using a whole-body scanner with a 20-ch head coil for 131 days intermittently. The DTI analysis was performed and diffusion metricsof the phantom were evaluated by comparing standard deviation over one day to the average change between two consecutive days. The average changes in ADC and FA within the experimental term were 0.03 x 10^-3sec/mm² and 0.002, respectively. The commercially available astriction cotton showed stability of its diffusivity over four months.The recent progress of diffusion tensor imaging (DTI) requires the setting of appropriate acquisition parameters to achieve efficient quality of an image similar to b values for diffusion kurtosis imaging (DKI) and q values for q-space imaging (QSI). In previous ISMRM, several anisotropic DTI phantoms have been proposed [1, 2, 3] for acquisition parameter setting and quality control. However, those phantoms are created with a special apparatus and/or need to be specially ordered from craft specialists and thus are more costly. Therefore, only limited researchers can use these specialized anisotropic DTI phantoms. To overcome this inconvenient situation for the anisotropic DTI research field, we focused on commercially available astriction cotton, which is normally used as a hemostatic material, as an anisotropic DTI phantom. Although the astriction cotton that we employed showed anisotropic water absorption, the stability and diffusional ability had not been previously investigated. In this paper, we evaluated the longitudinal stability of astriction cotton as an anisotropic diffusion phantom.Phantom: The astriction cotton (length = 30 mm, diameter = 20 mm, Hakujuji Co. Ltd., Tokyo, Japan) into acryl tubes (diameter = 25 mm) were arranged in parallel crosses as shown in Figure 1. The phantom size was 12.5 cm wide x 17.0 cm long x 12.0 cm high (polyethylene container). Data acquisition: DTI examinations were performed at 3T using a whole-body scanner (MAGNETOM Skyra 3T, Siemens Healthcare, Erlangen, Germany) using a 20-ch head coil for 131 days intermittently (18 times). For all magnetic resonance images, the field of view was 240 x 240 mm. DTI was acquired using an EPI technique with a matrix of 120 x 108. A b value of 1,000 s/mm2 was used. MPGs were applied in 10 directions. Acquisitions were repeated five times over one day at approximately 22.0°C room temperature. DTI analysis: The DTI analysis was performed with Diffusion Toolkit/TrackVis version 0.5.2.2 [4], and tract-based average diffusion metrics (apparent diffusion coefficient: ADC; fractional anisotropy: FA, FACT algorithms) were calculated with manually placed ROIs on center slices in three orthogonal directions (Figure 2). Evaluation of stability: The stability of diffusion metrics (ADC and FA) of the phantom were evaluated by comparing standard deviation over one day to the average change over two consecutive days.Stability of tractography: Figure 3 shows the number of tracts throughout the scanned day. Although the number of tracts was changed by manual ROI placement, the average change within the experimental term was 3.4%. Stability of ADC: In Figure 4A, the average ADC was 1.70 x 10^-3sec/mm² (SD = 0.293) within the experimental term. The average change within the experimental term was 0.03 x 10^-3sec/mm². The average ratio to the previous time was 1.59% for ADC measurements. The error range over each day of ADC was relatively wider than the average change within the experimental term. This might have been caused by the random sizes of pores in the astriction cotton (average radius = 19.73 ± 25.46 μm). Stability of FA: Figure 5A shows the FA values within the experimental term. The average FA was 0.15 (SD = 0.07) and average change within the experimental term was 0.002. The average ratio to the last time was 1.46% for ADC measurements. The error range for each day of FA was relatively wider than the average change within the experimental term. This might have also been caused by the random sizes of pores in the astriction cotton.Commercially available astriction cotton showed stability of its diffusivity over four months and usability as an anisotropic diffusion phantom.