抄録
MRI angiography is useful for the diagnosis of blood vessels and blood fiow. The phase contrast method is suitable for quantitatively evaluating blood flow velocity because it is reflected in the phase. However, the velocity is low near the vessel wall, and the effect of the dephasing cannot be ignored in this region. On the other hand, the vessel wall is static and the effect of dephasing could be weak. The maximum velocity in the blood vessel also seems to be an accurate parameter because of the weak effect of dephasing. The static and maximum velocity regions therefore seem helpful for extraction of the vessel region, although the influence of the relaxation times and sequence parameters on dephasing have not yet been clarified. In this study we investigate the effects of these parameters on the measurement accuracy of the velocity and design a simple method for the regional extraction of blood vessels. The relaxation times, TR, TE and VENC, influenced the accuracy of velocity measurement. Although no dominant parameter was found among them, several combinations of parameters resulted in a significant difference in accuracy. The standard deviation of the phase in the static region increased with increasing relaxation time. We also extracted the popliteal artery region by growing the region until the phase reached a threshold value. This threshold value was set based on the standard deviation of the area in a static region. This method was found to be suitable for extracting the blood vessels from MR images obtained when using the phase contrast method.
