Effect of Non-Alignment/Alignment of Attenuation Map Without/With Emission Motion Correction in Cardiac SPECT/CT
Effect of Non-Alignment/Alignment of Attenuation Map Without/With Emission Motion Correction in Cardiac SPECT/CT
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DOI：
10.1109/tns.2015.2446895
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发表时间：
2015-08-01
影响因子：
1.8
通讯作者：
King, Michael A.
中科院分区：
文献类型：
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作者：
Dey, Joyoni;Segars, W. Paul;King, Michael A.
目的：我们研究了当用于衰减校正（来自 CT）的衰减图在发射成像期间由于呼吸状态的差异而与患者解剖结构不对准时，在重建发射图像中在没有/有呼吸运动校正的情况下引起的表观显像剂定位的差异。方法：我们研究了使用在 2 cm 幅度呼吸周期的不同状态下获取的衰减图（呼气末、吸气末、中心图、平均传输图和发射成像期间超出呼吸范围的大屏气）来校正 NCAT 体模的几种解剖变体的 MLEM 重建中的衰减，其中包括心脏和膈下区域（例如肝脏、肾脏等）之间有或没有非刚性运动。我们在有或没有发射运动校正和衰减图对齐/不对齐的情况下测试了这些情况。结果：对于 NCAT 默认男性解剖结构，在大多数情况下，通过发射运动校正，由于呼吸导致的错误计数减少在很大程度上被消除。例外情况（对于默认男性）是使用大屏气末吸气图（TI_EXT）、当我们使用呼气末（TE）图以及在较小程度上使用末吸气图（TI）的情况。然而，严格移动衰减图以对齐心脏区域，减少了剩余的计数减少伪影。对于女性患者，由于乳房软组织未对准，使用刚性地图对齐进行运动校正后计数减少仍然存在。定量地讲，在传输（刚性）对准校正之后，对于极端屏气情况，极坐标图 17 段 RMS 误差相对于参考（无运动情况）平均减少了 46.5%。平均而言，呼气末图减少了 40.8%，吸气末图减少了 31.9%，与每个状态使用自己的衰减图进行校正的半理想情况相当。结论：两个主要结论是，即使是严格将心脏区域与衰减图对齐的刚性发射运动校正，在一般情况下也有助于减少计数减少伪影，其次，在研究范围内（例如刚性校正），当肺组织不如心脏时，如本研究中使用的 NCAT 体模，最好避免呼气末图 (TE)，因为它们可能比吸气末 (TI) 图产生更多伪影。
Purpose: We investigate the differences without/with respiratory motion correction in apparent imaging agent localization induced in reconstructed emission images when the attenuation maps used for attenuation correction (from CT) are misaligned with the patient anatomy during emission imaging due to differences in respiratory state. Methods: We investigated use of attenuation maps acquired at different states of a 2 cm amplitude respiratory cycle (at end-expiration, at end-inspiration, the center map, the average transmission map, and a large breath-hold beyond range of respiration during emission imaging) to correct for attenuation in MLEM reconstruction for several anatomical variants of the NCAT phantom which included both with and without non-rigid motion between heart and sub-diaphragmatic regions (such as liver, kidneys etc). We tested these cases with and without emission motion correction and attenuation map alignment/non-alignment. Results: For the NCAT default male anatomy the false count-reduction due to breathing was largely removed upon emission motion correction for the large majority of the cases. Exceptions (for the default male) were for the cases when using the large-breathhold end-inspiration map (TI_EXT), when we used the end-expiration (TE) map, and to a smaller extent, the end-inspiration map (TI). However moving the attenuation maps rigidly to align the heart region, reduced the remaining count-reduction artifacts. For the female patient count-reduction remained post motion correction using rigid map-alignment due to the breast soft-tissue misalignment. Quantitatively, after the transmission (rigid) alignment correction, the polar-map 17-segment RMS error with respect to the reference (motion-less case) reduced by 46.5% on average for the extreme breathhold case. The reductions were 40.8% for end-expiration map and 31.9% for end-inspiration cases on the average, comparable to the semi-ideal case where each state uses its own attenuation map for correction. Conclusions: Two main conclusions are that even rigid emission motion correction to rigidly align the heart region to the attenuation map helps in average cases to reduce the count-reduction artifacts and secondly, within the limits of the study (ex. rigid correction) when there is lung tissue inferior to the heart as with the NCAT phantom employed in this study end-expiration maps (TE) might best be avoided as they may create more artifacts than the end-inspiration (TI) maps.