Keyhole Imaging Combined Phase Contrast MR Angiography Technique

Abstract

Phase Contrast MR Angiography(PC MRA) is excellent MRA technique for measuring the velocity of vessels in the human body. PC MRA need to at least four images for angiogram reconstruction and it caused longer scan time. Therefore, we used keyhole imaging combined PC MRA to reduce the scan time. However, keyhole imaging can lead the erroneous effects as loss of phase information or frequency discontinuous. In this study, we applied the keyhole imaging combined 2D PC MRA for improving the temporal resolution and also measured the velocity to evaluate the accuracy of phase information. We used 0.32T MRI scanner(Magfinder II, Scimedix, Korea). Using the 2D PC MRA pulse sequence, the vascular images for a human brain targeted on the Superior Sagittal Sinus(SSS) were obtained. We applied tukey window function for keyhole images to minimize the ringing artifact and erroneous factors that are induced frequency discontinuous and phase information loss. We also applied zero-padded algorithm to peripheral missing k-space lines to compare keyhole imaging results and the artifact power(AP) value was measured on the complex difference images to validate the image quality. Consider as based on our results, heavy image distortions and artifacts were shown until using at least 50% keyhole factor. Using above the 50% keyhole factors are shown well reconstructed and matched for magnitude images and velocity information measurements. In conclusion, we confirmed the image quality and velocity information of keyhole technique combined 2D PC MRA. Especially, measured velocity information through the keyhole imaging combination was similar to the velocity information of full sampled k-space image despite of frequency discontinuous and phase information loss in the keyhole imaging reconstruction process. Consequently, the keyhole imaging combined 2D PC MRA will give some clinical usefulness and advantages as improving the temporal resolution and measuring the velocity information via selecting the appropriate keyhole factor at low tesla MRI system.

Keyhole‐3D phase contrast magnetic resonance angiography: A time‐resolved reconstruction method

“…The phase encoding lines and phase encoding portion, termed keyhole factors, were varied from 12.5% to 50% of the full k-space. We used a smoothing window function named as Tukey window to minimize the erroneous effects induced by discontinuous frequency distribution when the high-frequency and low-frequency parts were combined (Bernstein et al, 2007;Lee et al, 2012). The frequency discontinuities affected the reconstructed image, which formed a truncation artifact (Bernstein et al, 2007).…”

“…Second, we used quantitative analysis through artifact power (AP) value measurements. The AP was measured as a function of the difference between the original image and the image created as a result of applying keyhole imaging and zero-padding technique (Bankson and Wright, 2002;Ji et al, 2007;Lee et al, 2012). The values were measured in the 3D PC MRA-reconstructed images using the MIP technique at 0 .…”

“…2D PC MRA is mainly used to measure blood flow velocity or image slice localization for determination of the approximate structure of vascular imaging, and the 3D PC MRA is used for visualization of blood vessels in more detail. Previously, Lee et al (2012) reported the keyhole combined 2D PC MRA method. They performed the image reconstruction for 2D in vivo angiography and velocity measurement, and evaluate the applicability of combination method.…”