Bengel F M, Ziegler S I, Avril N, Weber W, Laubenbacher C, Schwaiger M
Department of Nuclear Medicine, Technische Universität München, Munich, Germany.
Eur J Nucl Med. 1997 Sep;24(9):1091-8. doi: 10.1007/BF01254239.
The clinical need for attenuation correction of whole-body positron emission tomography (PET) images is controversial, especially because of the required increase in imaging time. In this study, regional tracer distribution in attenuation-corrected and uncorrected images was compared in order to delineate the potential advantages of attenuation correction for clinical application. An ECAT EXACT scanner and a protocol including five to seven bed positions, emission scans of 9 min and post-injection transmission scans of 10 min per bed position were used. Uncorrected and attenuation-corrected images were reconstructed by filtered backprojection. In total, 109 areas of focal fluorine-18 fluorodeoxyglucose (FDG) uptake in 34 patients undergoing PET for the staging of malignancies were analysed. To measure focus contrast, a ratio of focus (target) to background average countrates (t/b ratio) was obtained from transaxial slices using a region of interest technique. Calculation of focus diameters by a distance measurement tool and visual determination of focus borders were performed. In addition, images of a body phantom with spheres to simulate focal FDG uptake were acquired. Transmission scans with and without radioactivity in the phantom were used with increasing transmission scanning times (2-30 min). The t/b ratios of the spheres were calculated and compared for the different imaging protocols. In patients, the t/b ratio was significantly higher for uncorrected images than for attenuation-corrected images (5.0+/-3.6 vs 3.1+/-1.4; P<0.001). This effect was independent of focus localization, tissue type and distance to body surface. Compared with the attenuation-corrected images, foci in uncorrected images showed larger diameters in the anterior-posterior dimension (27+/-14 vs 23+/-12 mm; P<0.001) but smaller diameters in the left-right dimension (19+/-11 vs 21+/-11 mm; P<0.001). Phantom data confirmed higher contrast in uncorrected images compared with attenuation-corrected images. It is concluded that, although distortion of foci was demonstrated, uncorrected images provided higher contrast for focal FDG uptake independent of tumour localization. In most clinical situations, the main issue of whole-body PET is pure lesion detection with the highest contrast possible, and not quantification of tracer uptake. The present data suggest that attenuation correction may not be necessary for this purpose.
全身正电子发射断层扫描（PET）图像衰减校正的临床需求存在争议，尤其是因为成像时间需要增加。在本研究中，比较了衰减校正图像和未校正图像中的区域示踪剂分布，以阐明衰减校正对于临床应用的潜在优势。使用了一台ECAT EXACT扫描仪和一个包括五到七个床位的方案，每个床位进行9分钟的发射扫描和10分钟的注射后透射扫描。通过滤波反投影重建未校正和衰减校正的图像。总共分析了34例因恶性肿瘤分期而接受PET检查的患者中109个氟-18氟脱氧葡萄糖（FDG）摄取灶区域。为了测量病灶对比度，使用感兴趣区域技术从横断面切片中获得病灶（目标）与背景平均计数率的比值（t/b比值）。使用距离测量工具计算病灶直径并目视确定病灶边界。此外，采集了带有球体的体模图像以模拟局灶性FDG摄取。使用体模中有放射性和无放射性的透射扫描，并增加透射扫描时间（2 - 30分钟）。计算并比较不同成像方案下球体的t/b比值。在患者中，未校正图像的t/b比值显著高于衰减校正图像（5.0±3.6对3.1±1.4；P<0.001）。这种效应与病灶定位、组织类型和到体表的距离无关。与衰减校正图像相比，未校正图像中的病灶在前后维度上显示出更大的直径（27±14对23±12毫米；P<0.001），但在左右维度上显示出更小的直径（19±11对21±11毫米；P<0.001）。体模数据证实未校正图像比衰减校正图像具有更高的对比度。结论是，尽管显示出病灶有畸变，但未校正图像为局灶性FDG摄取提供了更高的对比度，且与肿瘤定位无关。在大多数临床情况下，全身PET的主要问题是尽可能高对比度地单纯检测病变，而不是示踪剂摄取的定量。目前的数据表明，为此目的可能不需要进行衰减校正。
