Nambu PVA gel which is produced by repeated freezing and thawing of PVA solution has overcome almost all of the problems which present substances have: It is close to human soft tissue in MRI parameters. MRI parameters (1H density, T1, T2) are adjustable to some extent. It has appropriate physical characteristics. The important problem with PVA gel is long-term stability. It is assumed that this problem can be solved by its periodic calibration and replacement.