Liu Wenyang, Sung Kyunghyun, Ruan Dan
Department of Bioengineering, University of California, Los Angeles 90095.
Department of Bioengineering, University of California, Los Angeles 90095 and Department of Radiological Sciences, University of California, Los Angeles 90095.
Med Phys. 2014 Dec;41(12):122302. doi: 10.1118/1.4900600.
To incorporate a newly developed shape-based motion estimation scheme into magnetic resonance urography (MRU) and verify its efficacy in facilitating quantitative functional analysis.
The authors propose a motion compensation scheme in MRU that consists of three sequential modules: MRU image acquisition, motion compensation, and quantitative functional analysis. They designed two sets of complementary experiments to evaluate the performance of the proposed method. In the first experiment, dynamic contrast enhanced (DCE) MR images were acquired from three sedated subjects, from which clinically valid estimates were derived and served as the "ground truth." Physiologically sound motion was then simulated to synthesize image sequences influenced by respiratory motion. Quantitative assessment and comparison were performed on functional estimates of Patlak number, glomerular filtration rate, and Patlak differential renal function without and with motion compensation against the ground truth. In the second experiment, the authors acquired a temporal series of noncontrast MR images under free breathing from a healthy adult subject. The performance of the proposed method on compensating real motion was evaluated by comparing the standard deviation of the obtained temporal intensity curves before and after motion compensation.
On DCE-MR images with simulated motion, the generated relative enhancement curves exhibited large perturbations and the Patlak numbers of the left and right kidney were significantly underestimated up to 35% and 34%, respectively, compared with the ground truth. After motion compensation, the relative enhancement curves exhibited much less perturbations and Patlak estimation errors reduced within 3% and 4% for the left and right kidneys, respectively. On clinical free-breathing MR images, the temporal intensity curves exhibited significantly reduced variations after motion compensation, with standard deviation decreased from 30.3 and 38.2 to 8.3 and 11.7 within two manually selected regions of interest, respectively.
The developed motion compensation method has demonstrated its ability to facilitate quantitative MRU functional analysis, with improved accuracy of pharmacokinetic modeling and quantitative parameter estimations. Future work will consider performing more intensive clinical verifications with sophisticated pharmacokinetic models and generalizing the proposed method to other quantitative DCE analysis, such as on liver or prostate function.
将新开发的基于形状的运动估计方案纳入磁共振尿路造影（MRU），并验证其在促进定量功能分析方面的功效。
作者提出了一种MRU中的运动补偿方案，该方案由三个连续模块组成：MRU图像采集、运动补偿和定量功能分析。他们设计了两组互补实验来评估所提出方法的性能。在第一个实验中，从三名镇静受试者获取动态对比增强（DCE）MR图像，从中得出临床有效的估计值并作为“真实情况”。然后模拟生理上合理的运动以合成受呼吸运动影响的图像序列。对有无运动补偿情况下的Patlak数、肾小球滤过率和Patlak肾微分功能的功能估计值与真实情况进行定量评估和比较。在第二个实验中，作者从一名健康成年受试者在自由呼吸状态下获取了一系列非对比MR图像。通过比较运动补偿前后获得的时间强度曲线的标准差，评估所提出方法在补偿真实运动方面的性能。
在具有模拟运动的DCE-MR图像上，生成的相对增强曲线表现出较大的扰动，与真实情况相比，左肾和右肾的Patlak数分别被显著低估高达35%和34%。运动补偿后，相对增强曲线的扰动明显减少，左肾和右肾的Patlak估计误差分别降至3%和4%以内。在临床自由呼吸MR图像上，运动补偿后时间强度曲线的变化显著减少，在两个手动选择的感兴趣区域内，标准差分别从30.3和38.2降至8.3和11.7。
所开发的运动补偿方法已证明其能够促进定量MRU功能分析，提高药代动力学建模和定量参数估计的准确性。未来的工作将考虑使用复杂的药代动力学模型进行更深入的临床验证，并将所提出的方法推广到其他定量DCE分析，如肝脏或前列腺功能分析。
