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D C Zhu

Publications and source records attributed to D C Zhu.

7 recordsLinked to original sources
PubMed2001

Image-based ghost correction for interleaved EPI.

A new image-based ghost correction technique is described for general interleaved EPI. This technique works reliably with both even- and odd-number interleaved EPI sequences. It estimates the phase distortions causing the ghosts as a general function of (x,y) even in the presence of a significant overlap of parent image and ghosts. If the phase distortion is assumed to be a function of x (frequency-encode direction) only, the new technique is similar to a recently published correction method for general interleaved EPI (Hennel. J Magn Reson 1998;134:206-213). However, that study concluded that the method for general interleaved EPI did not work. It showed that the SNRs of the edge pixels were too low to accurately estimate the phase distortion. The new technique utilizes not one, but many pixels in the image for estimating the phase distortion. The technique requires a user-defined ROI to outline the parent image and identify so-called eligible pixels for estimating the phase distortion. When all eligible pixels are used, the SNR of the phase distortion estimate is comparable to that obtained in single-shot EPI. This study provides the first examples of high-quality, image-based correction of multiple ghosts in general interleaved EPI. Magn Reson Med 45:96-108, 2001.

Artifacts↗
PubMed1999

High spatial resolution EPI using an odd number of interleaves.

Ghost artifacts in echoplanar imaging (EPI) arise from phase errors caused by differences in eddy currents and gradient ramping during left-to-right traversal of kx(forward echo) versus right-to-left traversal of kx (reverse echo). Reference scans do not always reduce the artifact and may make image quality worse. To eliminate the need for reference scans, a ghost artifact reduction technique based on image phase correction was developed, in which phase errors are directly estimated from images reconstructed separately using only the forward or only the reverse echos. In practice, this technique is applicable only to single-shot EPI that produces only one ghost (shifted 1/2 the field of view from the parent image), because the technique requires that the ghosts do not completely overlap the parent image. For higher spatial resolution, typically an even number of separate k-space traversals (interleaves) are combined to produce one large data set. In this paper, we show that data obtained from an even number of interleaves cannot be combined to produce only one ghost, and image phase correction cannot be applied. We then show that data obtained from an odd number of interleaves can be combined to produce only one ghost, and image phase correction can be applied to reduce ghost intensity significantly. This "odd-number interleaf EPI" provides spatial and temporal resolution tradeoffs that are complementary to, or can replace, those of even-number interleaf EPI. Odd-number interleaf EPI may be particularly useful for MR systems in which reference scans have been unreliable.

Artifacts↗
PubMed1992

[Effects erythropoietin on experimental anemia in rats with chronic renal failure].

Erythropoietin (EPO) is a glycoprotein hormone secreted by human kidney cells. Human EPO was induced from human embryo kidney cells, isolated and purified from medium by biochemical method in our laboratory. The hypoproliferative anemia in chronic renal failure (CRF) has been assumed to be the result of decreased EPO production by the damaged kidney and of the shortening of the survival of erythrocytes. In this study, CRF anemia was formed 9 weeks after the removal of five-sixths of the renal mass of rats. These anemic rats were divided into 6 groups: treated with different dosages of EPO or physiological saline. The results indicate that EPO has apparent effects on anemia in rats with CRF. It may stimulate erythropoiesis and improve the anemia state of rats with CRF. Hematological parameters (RBC, Hb, PLT, Ht and Rt) may be reverted to normal levels (P less than 0.001). The level of BUN and Cr were significantly decreased. The optimum dose of EPO was 1000 U/kg. All these results show that injection of EPO has therapeutic effect on anemia in rats with CRF. EPO showed no effect on normal rats.

Anemia↗