Spatiotemporal filtering of MR-temperature artifacts arising from bowel motion during transurethral MR-HIFU.
Spatiotemporal filtering of MR-temperature artifacts arising from bowel motion during transurethral MR-HIFU.
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DOI：
10.1118/1.4897382
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发表时间：
2014-10
期刊：
影响因子：
3.8
通讯作者：
A. Schmitt;C. Mougenot;Rajiv Chopra
中科院分区：
文献类型：
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作者：
A. Schmitt;C. Mougenot;Rajiv Chopra
目的经尿道磁共振高强度聚焦超声（MR-HIFU）是一种微创的图像引导治疗前列腺癌的方法，能够精确靶向腺体内的组织。治疗在临床MRI中进行，以获得实时MR测温，用作主动反馈，以控制前列腺中的空间加热模式并监测对周围组织的潜在损伤。这要求MR测温测量准确表示真实组织温度。所使用的质子共振频移测温法对组织运动和局部磁化率的变化敏感，局部磁化率的变化可能由直肠中气泡的运动引起，这可能影响经尿道MR-HIFU在腺体的这些区域中的性能。方法提出了一种基于温度的时间方差，使用超声加热束的经验和动态位置知识以及测量噪声的估计来过滤温度伪影的方法。引入了两步校正策略，该策略消除了伪影检测到的温度变化，同时通过空间平均保持低噪声水平。结果滤波器已通过对五次经尿道超声治疗的数据进行后处理进行了评估。两步校正过程导致伪影所在的前列腺和直肠区域的最终温度标准差降低，而不会对伪影远端区域产生负面影响。还发现过滤器的性能在评价的所有6个数据集中一致。检测标准参数M的评估确定了M = 3的值实现了在该过程期间具有最小空间分辨率损失的保守滤波器。结论：在经尿道MR-HIFU治疗过程中，由于直肠内存在移动气泡，该滤波器能够去除大多数伪影。滤波器能力的定量估计显示直肠区以及整个采集切片中的校正温度图的标准偏差的系统性改善。
PURPOSE Transurethral MR-HIFU is a minimally invasive image-guided treatment for localized prostate cancer that enables precise targeting of tissue within the gland. The treatment is performed within a clinical MRI to obtain real-time MR thermometry used as an active feedback to control the spatial heating pattern in the prostate and to monitor for potential damage to surrounding tissues. This requires that the MR thermometry measurements are an accurate representation of the true tissue temperature. The proton resonance frequency shift thermometry method used is sensitive to tissue motion and changes in the local magnetic susceptibility that can be caused by the motion of air bubbles in the rectum, which can impact the performance of transurethral MR-HIFU in these regions of the gland. METHODS A method is proposed for filtering of temperature artifacts based on the temporal variance of the temperature, using empirical and dynamic positional knowledge of the ultrasonic heating beam, and an estimation of the measurement noise. A two-step correction strategy is introduced which eliminates artifact-detected temperature variations while keeping the noise level low through spatial averaging. RESULTS The filter has been evaluated by postprocessing data from five human transurethral ultrasound treatments. The two-step correction process led to reduced final temperature standard deviation in the prostate and rectum areas where the artifact was located, without negatively affecting areas distal to the artifact. The performance of the filter was also found to be consistent across all six of the data sets evaluated. The evaluation of the detection criterion parameter M determined that a value of M = 3 achieves a conservative filter with minimal loss of spatial resolution during the process. CONCLUSIONS The filter was able to remove most artifacts due to the presence of moving air bubbles in the rectum during transurethral MR-HIFU. A quantitative estimation of the filter capabilities shows a systematic improvement in the standard deviation of the corrected temperature maps in the rectum zone as well as in the entire acquired slice.