Dey Joyoni, Segars W Paul, Pretorius P Hendrik, King Michael A
IEEE Trans Nucl Sci. 2015 Aug;62(4):1813-1824. doi: 10.1109/TNS.2015.2446895. Epub 2015 Jul 23.
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.
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.
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.
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 endexpiration maps (TE) might best be avoided as they may create more artifacts than the end-inspiration (TI) maps.
我们研究在发射成像过程中，由于呼吸状态不同，用于衰减校正（来自CT）的衰减图与患者解剖结构未对齐时，重建发射图像中表观成像剂定位在有无呼吸运动校正情况下的差异。
我们研究了在2厘米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、平均透射图以及发射成像期间超出呼吸范围的一次大屏气），用于校正NCAT体模几种解剖变体的MLEM重建中的衰减，这些变体包括心脏和膈下区域（如肝脏、肾脏等）之间有无非刚性运动的情况。我们对这些情况进行了有无发射运动校正以及衰减图对齐/未对齐的测试。
对于NCAT默认男性解剖结构，在大多数情况下，发射运动校正后，由于呼吸导致的假计数减少在很大程度上被消除。例外情况（对于默认男性）是使用大屏气吸气末图（TI_EXT）、呼气末图（TE）以及在较小程度上使用吸气末图（TI）的情况。然而，将衰减图刚性移动以对齐心脏区域，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齐，使用刚性图对齐进行运动校正后仍存在计数减少。定量地说，在透射（刚性）对齐校正后，对于极端屏气情况，相对于参考（无运动情况）的极坐标图17段均方根误差平均降低了46.5%。呼气末图平均降低40.8%，吸气末情况平均降低31.9%，与每个状态使用其自己的衰减图进行校正的半理想情况相当。
两个主要结论是，即使是将心脏区域与衰减图进行刚性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，在本研究的范围内（例如刚性校正），当心脏下方存在肺组织时，如本研究中使用的NCAT体模，呼气末图（TE）可能最好避免使用，因为它们可能比吸气末图（TI）产生更多伪影。
