摘 要:传统单光子发射计算机断层成像(SPECT)与计算机断层扫描(CT)结合使用可显示病灶形态学改变及显像剂分布状态,可提高肿瘤和非肿瘤疾病成像敏感性和特异性。SPECT/CT通过一次成像观察多部位病灶,可用于分析解剖结构及代谢状态,从而提高了疾病鉴别与诊断准确性。新型混合SPECT/CT设备缩短了图像采集时间并提供精准衰减校正和融合成像,为临床合理选择治疗方案提供了科学基础。本文综述了SPECT/CT技术临床应用进展。
关键词:单光子发射计算机断层成像;计算机断层扫描;标准摄取值;核医学;临床应用;
Progress in application of single-photon emission computed tomography/computed tomography(SPECT/CT) imaging in clinical practice
LU Xiao-qian ZONG Ling-yan SHEN Qi
Department of Medical Devices, Changzhou Second People's Hospital Affiated to Nanjing Medical University Departmer
t of Equipment and Material
Purchase and Supervision, Changzhou Municipal First People's Hospital
Abstract:The combination of conventional single-photon emission computed tomography (SPECT) and computed tomography (CT) may display the morphological changes of lesions and distribution of imaging agents, which is effective to improve the imaging sensitivity and specificity of tumors and non-tumor diseases. SPECT/CT is feasible to analyze the anatomical structure and metabolic status through displaying multi-site lesions with single imaging, thereby improving differential diagnosis and diagnostic accuracy of diseases. In addition, the novel mixed SPECT/CT device shortens the duration of image acquisition and provides precise attenuation correction and fusion imaging, which provides a scientific basis for rational selection of treatment regimens in clinical practice. This review describes the advances in clinical application of SPECT/CT.
Keyword:Single-photon emission computed tomography; Computed tomography; Standard uptake value; Nuclear medicine; Clinical application;
单光子发射计算机断层成像(SPECT)是一种常见诊断方法,用于肿瘤精准诊断、器官或器官系统三维(3D)成像以及体内血流和新陈代谢检查,该技术需要将发射γ的放射性核素注射到患者血液中[1]。SPECT经常被用于确认131I、90Y或177Lu 标记抗体治疗下所需的示踪剂分布或进行疾病诊断,这一过程受到光子散射、光子衰减和部分体积伪影的影响,放射性物质需SPECT进行绝对定量[2]。传统SPECT与计算机断层扫描(CT)结合使用构成核医学成像适用于各种临床疾病的诊断应用[3]。采用新型混合SPECT/CT设备的可用性越来越高,这为缩短采集时间并提供精确的衰减校正和融合成像提供了机会。SPECT/CT 的主要优点表现为更好的衰减校正、更高的特异性以及准确描述疾病的定位和邻近组织的可能受累[4]。通过SPECT/CT准确定位和表征用于内分泌肿瘤、孤立性肺结节、肺癌、脑肿瘤、淋巴瘤、前列腺癌、恶性和良性骨病变等[5,6]。此外,混合SPECT/CT成像特别适合支持微创手术日益增长的应用,以及精准定义心血管患者诊断和预后特征,SPECT/CT对其他临床疾病或恶性肿瘤的应用目前正在进行广泛研究,其诊断准确性进一步得到提高。
1 SPECT/CT在乳腺癌诊疗中的应用
乳腺癌是女性患者最常见的癌症之一,发病率为11.7%,约有的50%~75%乳腺癌患者发生骨转移[7]。早期发现骨转移并使用分子成像技术(如SPECT/CT)将其与退行性病变区分开来,对于治疗乳腺癌患者随访具有重要作用。SPECT/CT在检测骨转移性病变方面的敏感性在89%~95%,特异性为82%~95%[8]。对转移性骨病乳腺癌患者SPECT/CT数据进行定量分析所得最大标准摄取值(SUV),有助于鉴别退行性骨病变的活动性骨转移,根据获得的图像明确诊断,从而提高诊断准确性和患者的临床管理,定量分析可以提供更标准化骨扫描[9]。
SPECT/CT可以确定乳腺癌进展的视觉和定量评估之间的方法间一致性程度,时以绝对单位报告放射性示踪剂的摄取,Kaneta等[10]定量分析计算70名患者,评估的转移性病变数量显着减少,平均SUV值为20.4±20.8。Gherghe等[11]报道退行性骨病变和转移性骨病变之间的最大SUV值存在显著差异,为了评估区分退行性病变和转移性病变的诊断准确性,ROC曲线下AUC具有0.974的高值(95%CI 0.95-0.98),其中转移性病变的数值更高,这种差异的机制可能为转移性乳腺癌细胞可以改变参与骨重塑。
Quah等[12]对SPECT/CT数据的定量分析可以提高区分退行性骨病变和转移性病变的准确性,通过ROC曲线分析获得的SUV最大临界值为16.6 g/mL,有助于区分乳腺癌患者的转移性和退行性病变,敏感性为91.5%、特异性为93.3%。SPECT/CT SUV值有益于治疗效果评估、患者随访和患者间比较。
2 SPECT/CT在前列腺癌诊疗中的应用
前列腺癌(PCa)是老年男性泌尿系统中最常见的癌症,也是癌症相关死亡的第六大原因之一,骨骼是前列腺癌中最常见的远处器官转移部位,8%~35%的患者在诊断时已经出现远处转移[13]。前列腺癌的骨转移可通过CT和MRI监测溶骨性和混合型骨转移,溶骨性转移瘤通常没有明确的边界,因此很难在CT或MRI图像上精确确定其大小,99TcmTc-PSMA-T4 是一种新的放射性药物(Polatom),用于对前列腺癌患者的局部区域转移和/或局部复发进行成像,通过SPECT / CT图像可以评估前列腺癌患者骨转移的治疗效果,其相应敏感性范围为63%~95%[14]。转移性前列腺癌到骨骼通常以整个骨骼的广泛疾病为特征,在影像学检查中≥ 50 个病变的患者通常被认为在骨扫描时有超扫描,SPET/CT 定量评估限制在超级扫描中每个解剖部位一个病变15或为每个患者选择最多5个病变[15]。
Harmon等[16]测量活动性骨转移负荷的总骨摄取量计算为使用骨SPECT / CT在躯干中[作为标准化摄取值获得的平均摄取值]×(病变体积)的总和,比较了61例有骨转移的前列腺癌患者和69例没有骨转移的前列腺癌患者的骨转移和非转移区域,骨转移患者非转移部位的摄取显著低于无转移的患者。Abbasi等[17]骨转移的前列腺癌患者SPECT / CT诊疗在敏感性和特异性分析显示,平均摄取值 7.0为阈值水平,在9名患者中,有两名患者总骨摄取量和骨扫描指数变化之间存在差异,其中总骨摄取量变化与视觉判断相关,但骨扫描指数变化没有,在两名患者中,骨扫描指数在整个病程中接近0,但总骨摄取量呈阳性并发生变化,尽管变化不大。因此,常规SPECT/CT在典型前列腺癌形态学影像学表现和放射性示踪剂摄取模式的情况下,可以诊断出转移性病变。
3 SPECT/CT在骨关节损伤诊疗中的应用
距骨骨软骨损伤在大多数情况下因为早期无症状损伤很容易被忽视,25%~-50%的踝关节扭伤患者在初始损伤(扭伤)后数年内会出现慢性长期踝关节疼痛,研究发现由于踝关节不稳定导致距骨慢性损伤的发生率高达50%[18]。SPECT/CT是一种针对距骨囊性病变患者的新型多模态成像方法,其应用可以实时评估距骨骨软骨损伤的血流动力学代谢状态。软骨下骨囊性病变及其周围区域表现出最高的活动,而距骨的其余部分呈现出正常的生理骨代谢区,硬化区位于病变区和正常组织的交界处显示出活跃的骨代谢,示踪剂浓度明显位于胫骨穹窿前部和胫骨臼骨关节背伸的应力点,其中硬化区最集中,骨代谢最活跃,血流最丰富[18]。Hamilton等[19]报道病理学显示与SPECT / CT结果显示曲折的纤维囊壁,致密成纤维细胞增殖多,胶原纤维丰富囊壁周围的肉芽组织和炎性细胞聚集,软骨发生坏死病变周围有骨化和活动成骨,活性软骨发生和骨化SPECT / CT静态融合图像上显示囊性腔中示踪剂的异常浓度。囊性病变内成骨修复活动的存在继发于损伤,腭骨损伤的局灶性坏死与明显的充血和炎症反应、活动性纤维和骨修复以及囊性病变周围快速形成保护性新骨的硬化性外壳同时发生,在相当大的应力下保持距骨关节表面的整体完整性和正常形态[20,21]。
内侧隔室骨关节炎 (OA)易引起膝关节内翻畸形,临床症状为膝关节疼痛,多发年轻患者,内侧开口楔形高位胫骨截骨术 (MOWHTO)治疗为主可减轻膝关节内侧隔室的负荷。99Tcm羟亚甲基二膦酸盐(HDP)SPECT/CT是一种常用来确定退行性膝关节内侧隔室骨关节炎的进展程度和临床症状的方法,且其使用量逐渐增加[22]。Kim等[23]研究了接受胫骨截骨术的患者在SPECT / CT上的摄取变化,结果显示术后12个月和24个月膝关节内侧隔室放射性示踪剂摄取显着减少以及骨关节炎指数 评分的显着改善。Hopwood等[24,25]在SPECT / CT分析中观察到最小的临床重要差异组的胫骨前外侧室有显着改善,治疗可能导致侧支室超负荷,因为在楔形高位胫骨截骨术之后,承重线从内侧转移到外侧隔室,这会导致膝关节外侧的承重增加并恶化该区域的放射性示踪剂摄取。SPECT/ CT 的定量评估在近些年越来越被临床认可,通过定量分析进行相对或绝对的数值评估,分析图像数据客观,诊断准确性进一步得到提高。
4 SPECT/CT在甲状腺疾病诊疗中的应用
甲状腺疾病的发病率逐年上升,甲状腺产生左旋甲状腺素(T4)和三碘甲状腺原氨酸(T3)调节新陈代谢,甲状腺激素不足可能导致甲状腺功能减退和甲状腺功能亢进[26]。甲状腺摄取百分比的测量已经在核医学领域使用多年,鉴别诊断甲状腺功能改变的疾病,定量 SPECT/CT 在测量甲状腺摄取百分比方面比传统方法更准确。
Dong等[27]报道在50例患者中,46例甲状腺刺激素(TSH)水平低于正常,T3或游离T4水平升高或正常,之前经实验室使用放射免疫测定法(RIA)或酶联免疫吸附测定进行确诊,患者通过定量SPECT/CT观察甲状腺摄取百分比差异显著,Graves患者的数值最高(5.28±5.19)%,其次是甲状腺功能正常患者(0.78±0.50)%和是甲状腺炎患者(0.33±0.40)%。Shao等[28]报道SPECT/CT观察标准化摄取值在Graves病患者中最大为83.77±52.53,其次是甲状腺功能正常和甲状腺炎患者分别为33.51±23.54和11.34±13.72。SPECT/CT可以评估甲状腺疾病复发危险度,给临床制定个体化治疗方案提供指导,以减少并发症的发生。
5 小结
SPECT/CT是一种核医学影像方法,经过近年发展,可以提供自动化图像分析,且图像质量和诊断可信度有了显著提高,如混合SPECT/CT设备的实现、衰减校正的实现和迭代重建技术,由多个连续床位采集的全身SPECT/CT图像已经开始增加。在未来,将出现具有更高光子灵敏度的新准直器和探测器,如在SPECT/CT中使用迭代CT重建,可为新的自动化图像分析方法奠定基础,并有助于临床诊断和SPECT/CT图像解释的标准化。
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