Capturing Bone Signal in MRI of Pelvis, as a Large FOV Region, Using TWIST Sequence and Generating a 5-Class Attenuation Map for Prostate PET/MRI Imaging.
Capturing Bone Signal in MRI of Pelvis, as a Large FOV Region, Using TWIST Sequence and Generating a 5-Class Attenuation Map for Prostate PET/MRI Imaging.
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DOI：
10.1177/1536012118789314
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发表时间：
2018-01
影响因子：
2.8
通讯作者：
Ay MR
中科院分区：
文献类型：
--
作者：
Shandiz MS;Rad HS;Ghafarian P;Yaghoubi K;Ay MR
前列腺成像在正电子发射断层扫描/磁共振成像（PET/MRI）一体机中有重要应用。目前，全身PET/MRI基于磁共振成像的衰减校正（MRAC）忽略了骨骼结构，这是该混合模式在临床工作流程中成功应用的主要障碍。超短回波时间序列可捕捉骨信号，但需要特定的软硬件，且在大视野（FOV）区域（如骨盆）具有挑战性。本研究的主要目的是：（1）利用基于时间分辨血管造影与交错随机轨迹（TWIST）序列的短回波时间（STE）成像捕捉骨盆部分骨信号；（2）在PET/MRI系统的MRAC中考虑骨盆衰减图（μ -图）中的骨骼。
时间分辨血管造影与交错随机轨迹技术通常用于具有高时空分辨率的磁共振血管造影，本研究将其用于快速/短回波时间磁共振成像。在骨盆区域以0.88毫秒（短回波时间）和4.86毫秒（长回波时间[LTE]）进行数据采集。基于感兴趣区域（ROI）的分析用于比较短回波时间和长回波时间图像中皮质骨的信噪比（SNR）。采用一种混合分割方案，包括图像减法、基于模糊的分割以及专门的形态学操作，用于生成包含皮质骨、含气腔、脂肪、软组织和背景的5类μ -图（μ -图MR - 5c）。还生成了一个基于磁共振成像的4类μ -图（μ -图MR - 4c），该图考虑的是软组织而非骨骼。同样，基于计算机断层扫描（CT）图像生成了双线性（μ -图CT - ref）、5类（μ -图CT - 5c）和4类μ -图（μ -图CT - 4c）。最后，利用μ -图MR - 5c（PET - MRAC5c）、μ -图MR - 4c（PET - MRAC4c）、μ -图CT - 5c（PET - CTAC5c）和μ -图CT - ref（PET - CTAC）对模拟的PET数据进行校正。
长回波时间图像中骨信噪比与含气腔信噪比的比值为0.8，在短回波时间图像中该比值增至4.4。所提出方法对骨分割的骰子相似系数、敏感度和准确度指标分别为72.4%±5.5%、69.6%±7.5%和96.5%±3.5%，其中以分割后的CT作为参考。在模拟的PET图像中，以PET - CTAC作为参考，PET - MRAC5c、PET - MRAC4c和PET - CTAC5c在骨区域的平均相对误差分别为−13.98%±15%、−35.59%±15.41%和1.81%±12.2%。尽管μ -图MR - 4c与μ -图CT - 5c的联合直方图相关性较差（R²>0.78）以及PET - MRAC4c与PET - CTAC5c相关性较差（R² = 0.83），但在μ -图MR - 5c与μ -图CT - 5c（R²>0.94）以及PET - MRAC5c与PET - CTAC5c（R²>0.96）中观察到高度相关性。
根据短回波时间的信噪比，在基于TWIST序列的短回波时间成像中，骨盆骨的皮质骨可与含气腔区分开。所提出的方法生成了包含骨骼和含气腔的基于磁共振成像的μ -图，与MRAC4c相比，其能更准确地估计示踪剂摄取。采用所提出的方法可改善PET/MRI一体机中的摄取估计。
Prostate imaging is a major application of hybrid positron emission tomography/magnetic resonance imaging (PET/MRI). Currently, MRI-based attenuation correction (MRAC) for whole-body PET/MRI in which the bony structures are ignored is the main obstacle to successful implementation of the hybrid modality in the clinical work flow. Ultrashort echo time sequence captures bone signal but needs specific hardware–software and is challenging in large field of view (FOV) regions, such as pelvis. The main aims of the work are (1) to capture a part of the bone signal in pelvis using short echo time (STE) imaging based on time-resolved angiography with interleaved stochastic trajectories (TWIST) sequence and (2) to consider the bone in pelvis attenuation map (µ-map) to MRAC for PET/MRI systems. Time-resolved angiography with interleaved stochastic trajectories, which is routinely used for MR angiography with high temporal and spatial resolution, was employed for fast/STE MR imaging. Data acquisition was performed in a TE of 0.88 milliseconds (STE) and 4.86 milliseconds (long echo time [LTE]) in pelvis region. Region of interest (ROI)-based analysis was used for comparing the signal-to-noise ratio (SNR) of cortical bone in STE and LTE images. A hybrid segmentation protocol, which is comprised of image subtraction, a Fuzzy-based segmentation, and a dedicated morphologic operation, was used for generating a 5-class µ-map consisting of cortical bone, air cavity, fat, soft tissue, and background (µ-mapMR-5c). A MR-based 4-class µ-map (µ-mapMR-4c) that considered soft tissue rather than bone was generated. As such, a bilinear (µ-mapCT-ref), 5 (µ-mapCT-5c), and 4 class µ-map (µ-mapCT-4c) based on computed tomography (CT) images were generated. Finally, simulated PET data were corrected using µ-mapMR-5c (PET-MRAC5c), µ-mapMR-4c (PET-MRAC4c), µ-mapCT-5c (PET-CTAC5c), and µ-mapCT-ref (PET-CTAC). The ratio of SNRbone to SNRair cavity in LTE images was 0.8, this factor was increased to 4.4 in STE images. The Dice, Sensitivity, and Accuracy metrics for bone segmentation in proposed method were 72.4% ± 5.5%, 69.6% ± 7.5%, and 96.5% ± 3.5%, respectively, where the segmented CT served as reference. The mean relative error in bone regions in the simulated PET images were −13.98% ± 15%, −35.59% ± 15.41%, and 1.81% ± 12.2%, respectively, in PET-MRAC5c, PET-MRAC4c, and PET-CTAC5c where PET-CTAC served as the reference. Despite poor correlation in the joint histogram of µ-mapMR-4c versus µ-mapCT-5c (R2 > 0.78) and PET-MRAC4c versus PET-CTAC5c (R2 = 0.83), high correlations were observed in µ-mapMR-5c versus µ-mapCT-5c (R2 > 0.94) and PET-MRAC5c versus PET-CTAC5c (R2 > 0.96). According to the SNRSTE, pelvic bone, the cortical bone can be separate from air cavity in STE imaging based on TWIST sequence. The proposed method generated an MRI-based µ-map containing bone and air cavity that led to more accurate tracer uptake estimation than MRAC4c. Uptake estimation in hybrid PET/MRI can be improved by employing the proposed method.
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DOI：
10.1007/s00259-012-2113-0
发表时间：
2012-07-01
影响因子：
9.1
作者：
Samarin, Andrei;Burger, Cyrill;Kuhn, Felix P.
通讯作者：
Kuhn, Felix P.
影响因子：
9.3
作者：
Leynes, Andrew P.;Yang, Jaewon;Larson, Peder E. Z.
通讯作者：
Larson, Peder E. Z.
影响因子：
9.3
作者：
Hofmann, Matthias;Steinke, Florian;Pichler, Bernd J.
通讯作者：
Pichler, Bernd J.
影响因子：
9.3
作者：
Martinez-Moeller, Axel;Souvatzoglou, Michael;Nekolla, Stephan G.
通讯作者：
Nekolla, Stephan G.
影响因子：
19.7
作者：
Liu, Fang;Jang, Hyungseok;McMillan, Alan B.
通讯作者：
McMillan, Alan B.