Stodilka R Z, Kemp B J, Prato F S, Nicholson R L
Department of Nuclear Medicine and Magnetic Resonance, St. Joseph's Health Centre, London, Ontario, Canada.
J Nucl Med. 1998 Jan;39(1):190-7.
The purpose of this study was to determine the effects of nonuniform attenuation on relative quantification in brain SPECT and to compare the ability of the Chang and Sorenson uniform attenuation corrections (UACs) to achieve volumetric relative quantification.
Three head phantoms (dry human skull, Rando and Radiology Support Devices (RSD) phantoms) were compared with a human head using a gamma camera transmission CT (gammaTCT) SPECT system and x-ray CT. Subsequently, the RSD phantom's brain reservoir was filled with a uniform water solution of 99mTc, and SPECT and gammaTCT data were acquired using fanbeam collimation. The attenuating effects of bone, scalp and head-holder in individual projections were determined by an analytical projection technique using the SPECT and gammaTCT reconstructions. The Chang UAC used brain and head contours that were segmented from the gammaTCT reconstruction to demarcate its attenuation map, whereas the Sorenson UAC fit slice-specific ellipses to the SPECT projection data. For each UAC, volumetric relative quantification was measured with varying attenuation coefficients (mus) of the attenuation map.
Gamma camera transmission CT and x-ray CT scans showed that the dry skull and Rando phantoms suffered from a dried trabecular bone compartment. The RSD phantom most closely reproduced the attenuation coefficients of the human gammaTCT and x-ray CT scans. The analytical projections showed that the attenuating effects of bone, scalp and head-holder were nonuniform across the projections and accounted for 18%-37% of the total count loss. Volumetric relative quantification was best achieved with the Chang (zero iterations) attenuation correction using the head contour and mu = 0.075 cm(-1); however, cortical activity was found to be 10% higher than cerebellar activity. For all UACs, the optimal choices of mu were experimentally found to be lower than the recommended 0.12 cm(-1) for brain tissue. This result is theoretically supported here.
The magnitude of errors resulting from uniform attenuation corrections can be greater than the magnitudes of regional cerebral blood flow deficits in patients with dementia, as compared with normal controls. This suggests that nonuniform attenuation correction in brain SPECT imaging must be applied to accurately estimate regional cerebral blood flow.
本研究的目的是确定非均匀衰减对脑SPECT相对定量的影响,并比较张和索伦森均匀衰减校正(UAC)实现体积相对定量的能力。
使用伽马相机透射CT(gammaTCT)SPECT系统和X射线CT,将三个头部模型(干燥的人类头骨、兰多模型和放射学支持设备(RSD)模型)与一个人类头部进行比较。随后,在RSD模型的脑池内注入均匀的99mTc水溶液,使用扇形束准直采集SPECT和gammaTCT数据。通过使用SPECT和gammaTCT重建的分析投影技术,确定各个投影中骨骼、头皮和头托的衰减效应。张UAC使用从gammaTCT重建中分割出的脑和头部轮廓来划定其衰减图,而索伦森UAC则将特定切片的椭圆拟合到SPECT投影数据上。对于每种UAC,在衰减图的衰减系数(μ)变化的情况下测量体积相对定量。
伽马相机透射CT和X射线CT扫描显示,干燥的头骨和兰多模型存在干燥的小梁骨腔。RSD模型最接近地再现了人类gammaTCT和X射线CT扫描的衰减系数。分析投影显示,骨骼、头皮和头托的衰减效应在各个投影中是不均匀的,占总计数损失的18%-37%。使用头部轮廓且μ = 0.075 cm(-1)的张(零迭代)衰减校正能最好地实现体积相对定量;然而,发现皮质活性比小脑活性高10%。对于所有UAC,通过实验发现μ的最佳选择低于脑组织推荐的0.12 cm(-1)。本文从理论上支持了这一结果。
与正常对照相比,均匀衰减校正导致的误差幅度可能大于痴呆患者局部脑血流缺损的幅度。这表明在脑SPECT成像中必须应用非均匀衰减校正来准确估计局部脑血流。