DIMINISHING VARIANCE ALGORITHM RESPIRATORY COMPENSATION FOR FAST SPIN ECHO

简介：快速自旋回波（FSE）与有序 相位编码呼吸补偿。 对于无法 屏气或当需要额外的SNR或分辨率时，信号 平均、呼吸触发和多次屏气技术 都是可用的。 我们提出了一种易于实现的方法， 没有病人合作。 我们修改了方差递减 算法（DVA）工作在长TR，多个切片序列，没有 领航员回声。 方法：采用气动波纹管， 呼吸位置信息而不是导航器回波。 虽然 导航仪更精确，导航仪留下信号损失带 并需要额外的处理时间。 波纹管 信息很容易获得，并且采样率较高。 期间 第一次通过序列，呼吸位置及其 对应的激励被存储在单独的直方图中 切片 在完成第一遍之后，来自所有 直方图用于确定受试者最常见的呼吸 位置（模式）。 此后，每个单独切片的直方图 在重新捕获期间关于模式变窄。 之前 每次重新获得激励，波纹管提供呼吸 位置 如果此位置将缩小切片的直方图，则 重新获得切片的最差激励。 重新捕获时段 继续，直到所有直方图都足够窄，或者扫描 达到预定义的时间限制。 结果：虽然DVA和 呼吸触发具有类似的目标，DVA保证 固定扫描时间内呼吸位置的最小方差。 DVA 还允许独立于呼吸速率的一致TR。 结论：FSE的DVA补偿减少了运动伪影， 有效利用扫描时间。 它易于实现， 不合作的受试者，并且不限制其他门控或对比度 参数

Introduction: Fast Spin Echo (FSE) is incompatible with ordered phase encoded respiratory compensation. For patients incapable of breath-holds or when additional SNR or resolution is desired, signal averaging, respiratory triggering and multiple breath-holds techniques are available. We propose an easily implemented method that requires no patient cooperation. We have modified the diminishing variance algorithm (DVA) to work on long TR, multiple slice sequences without a navigator echo. Methods: We use pneumatic bellows to provide respiratory position information instead of navigator echos. Though navigators are more accurate, navigators leave a signal loss band across the abdomen and require additional processing time. Bellows information is available easily and at a higher sampling rate. During the first pass through the sequence, the respiratory position and its corresponding excitation are stored in a separate histogram for each slice. After completing the first pass, information from all the histograms is used to determine the subject's most common respiratory position (mode). Thereafter, the histogram of each individual slice is narrowed about the mode during a reacquisition period. Prior to each reacquisition excitation, the bellows provide a respiratory position. If this position will narrow the slice's histogram, then the slice's worst excitation is reacquired. The reacquisition period continues until all histograms are sufficiently narrow or the scan reaches a pre-defined time limit. Results: Though DVA and respiratory triggering have similar objectives, DVA guarantees the smallest variance of respiratory positions for a fixed scan time. DVA also allows a consistent TR independent of respiration rate. Conclusions: DVA compensation for FSE reduces motion artifacts while efficiently using scan time. It is easy to implement, works with uncooperative subjects, and does not limit other gating or contrast parameters.