帕金森病脑部葡萄糖代谢和脑多巴胺转运体PET显像特点的临床研究

目的 探讨18F-FDG脑代谢联合11C-甲基-N-2β-甲基酯-3β（4-F苯基）托烷（11C-CFT）脑多巴胺转运体（DAT）PET双显像在帕金森病（PD）诊断与病情严重程度评估中的应用价值。 方法 对55例不同严重程度的PD患者及30名健康对照者分别行18F-FDG脑代谢显像和11C-CFT脑DAT PET显像检查,通过勾画ROI,比较PET图像中不同严重程度的PD患者与健康对照者中脑基底节区葡萄糖代谢及DAT分布的差异,分析18F-FDG PET、11C-CFT PET显像在不同严重程度PD评估中的作用及特点。 结果 与健康对照者相比,18F-FDG PET显像中PD患者脑葡萄糖代谢改变主要为双侧基底节区壳核对称性代谢增高,同时部分患者伴有大脑皮质不同程度代谢减低;11C-CFT PET显像中PD患者双侧尾状核、壳核前、中、后部表现为DAT分布不同程度减低。单侧症状者或双侧症状者均以患侧对侧基底节区壳核DAT分布减低明显,并以壳核后部DAT分布减低为著。 结论 18F-FDG PET联合11C-CFT PET双显像在PD诊断及病情严重程度评估中有应用价值。     

不同显像时间窗对11C-CFT PET/CT显像测多巴胺转运蛋白分布半定量值的影响

目的 通过11C-甲基-N-2β-甲基酯-3β-(4-氟苯基)托烷(CFT) PET/CT显像,观察不同显像时间窗基底节区DAT分布的半定量值,寻找最佳显像时间窗并分析不同年龄和性别间的DAT分布差异.方法 将31名[男20名,女11名,平均年龄(55.7±2.3)岁]知情同意的健康受试者按随机区组法分为年龄匹配的3组,分别在注射11 C-CFT后40～60 min、60～ 80 min和80～100 min进行PET/CT静态显像,计算机自动勾画ROI,获得不同显像时间窗内尾状核及壳核DAT分布的半定量值(尾状核或壳核放射性计数/顶枕叶放射性计数-1),使用单因素方差分析及最小显著差异t检验对不同脑区半定量值进行比较.采用两独立样本t检验比较不同年龄(≥60岁和＜60岁)和性别患者最佳显像时间窗内尾状核及壳核半定量值的差异.结果 左侧尾状核(2.08±0.06、1.75±0.07和1.77±0.12)、右侧壳核前部(2.33±0.06、1.95±0.09和2.08±0.12)、双侧壳核后部(左:1.88±0.06、1.55±0.88和1.72±0.09,右:1.98±0.07、1.61±0.09和1.69±0.12)的DAT分布半定量值在3个时间窗内的差异具有统计学意义(F=3.588、3.345、4.479和3.557,均P＜0.05).其中,40 ～ 60 min显像与60～80 min相比,左侧尾状核、右侧壳核前部、双侧壳核后部半定量值差异具有统计学意义(均P＜0.05);与80～100 min相比,左侧尾状核半定量值差异具有统计学意义(P＜0.05).而60～ 80 min与80～ 100 min显像差异均不具有统计学意义(均P＞0.05).＜60岁的健康人尾状核、壳核DAT分布半定量值高于≥60岁者(t值分别为-3.260、-3.090、-3.270、-3.190、-2.270及-3.110,均P＜0.05);不同性别尾状核及壳核DAT分布差异均无统计学意义(t值分别为0.367、0.522、0.144、0.524、0.166及0.004,均P＞0.05).结论 脑内11C-CFT在注射后60 min达到稳定,11 C-CFT PET/CT显像检测DAT分布的最佳显像时间窗为注射后60～80 min;≥60岁和＜60岁健康人的DAT分布有差异.显像时间窗的统一和不同年龄段的半定量正常值的建立,有助于11C-CFT PET/CT显像在PD诊断方面的临床应用.     

帕金森患者脑多巴胺转运体11C-CFT PET/CT显像特点的分析

目的 探讨帕金森病（PD）患者11C-2β-甲氧甲酰-3β-（4-氟苯基）托烷（CFT）脑多巴胺转运体（DAT）PET/CT显像的特点,分析其对PD的临床诊断价值。 方法 回顾性分析2018年8月至2021年2月于贵州医科大学附属医院行11C-CFT PET/CT脑显像且经临床确诊的41例原发性PD患者的临床资料和影像学资料,其中男性21例、女性20例,年龄34~81岁（57.6±12.2）岁。根据Hoehn-Yahr（H-Y）分级将PD患者分为早期PD组（19例）和晚期PD组（22例）。同时纳入与PD组患者年龄匹配的8名健康受检者作为正常对照组,其中男性4名、女性4名,年龄42~72（61.0±9.8）岁。通过勾画感兴趣区（ROI）得到双侧尾状核、壳核及小脑3个层面的11C-CFT摄取值,按相应公式计算双侧尾状核、壳核、新纹状体的11C-CFT摄取值和不对称指数、壳核与尾状核摄取值的比值。计量资料的比较采用两独立样本t检验;计数资料的比较采用卡方检验;采用Pearson相关性分析评价PD患者新纹状体及各亚区DAT分布与各临床指标之间的相关性。 结果 在11C-CFT PET/CT脑显像中,PD组双侧尾状核放射性分布呈稍降低但尚均匀,双侧壳核放射性分布呈不同程度的降低或稀疏缺损。其中,早期PD组患者双侧壳核放射性分布呈不对称性降低或缺损;晚期PD组患者双侧壳核放射性分布呈较对称性稀疏缺损。与正常对照组比较,PD组新纹状体11C-CFT摄取值减低,且差异有统计学意义（12.29±2.75 对 7.69±2.42,t=4.818,P<0.01）;PD组不对称指数增高,且在壳核中表现最显著,差异有统计学意义（0.06±0.08 对 0.14±0.09,t=2.184,P<0.05）;PD组壳核与尾状核摄取值的比值降低,且差异有统计学意义（1.13±0.13 对 0.74±0.21,t=4.929,P<0.01）。与早期PD组比较,晚期PD组在新纹状体的摄取值降低最明显,且差异有统计学意义（8.50±1.77 对 6.99±2.71,t=2.070,P<0.05）,晚期PD组在尾状核、壳核不对称指数之间的差异均有统计学意义（0.06±0.06 对 0.11±0.08、0.18±0.10 对 0.11±0.07,t=2.251、2.858,均P<0.05）。PD患者新纹状体11C-CFT摄取值与年龄、起病年龄、H-Y分级均呈负相关（r=?0.444、?0.514、?0.426,均P<0.01）,与壳核11C-CFT摄取不对称指数呈正相关（r=0.331,P<0.05）。PD患者尾状核11C-CFT摄取值与年龄、起病年龄、H-Y分级均呈负相关（r=?0.537、?0.581、?0.380,均P<0.05）,与壳核不对称指数呈正相关（r=0.410,P<0.01）;PD患者壳核11C-CFT摄取值与起病年龄、H-Y分级均呈负相关（r=?0.353、?0.453,均P<0.05）,与病程、壳核与尾状核摄取值的比值均呈正相关（r=0.322、0.396,均P<0.05）。 结论 PD患者DAT在11C-CFT PET/CT脑显像上主要表现为双侧尾状核及壳核的放射性分布降低,11C-CFT PET/CT脑DAT显像有助于PD的诊断及其严重程度的评估。     

SPECT图像重建方法对Hoffmann模型图像质量的影响

目的探讨SPECT显像不同断层重建方法对Hoffmann模型图像质量的影响。方法采用放射性线源及Hoffmann模型,进行SPECT配平行孔低能高分辨准直器断层采集。对线源图像和Hoffmann模型图像均用滤波反投影（FBP）法和有序子集最大期望值迭代（OSEM）法进行断层重建。对线源重建图像计算2种重建算法的半高宽（FWHM）值,视觉评价2种方法重建的Hoffmann模型图像,并比较2种重建方法的重建时间和模型特定感兴趣区（ROI）。采用SPSS15．0软件,2种重建方法的脑叶及基底节ROI与小脑ROI计数比值行两独立样本t检验。结果平行孔低能高分辨准直器采集的线源断层图像经FBP法和OSEM法重建,FWHM值分别为18．77mm,12．62mm。OSEM法重建所得Hoffmann模型总的图像质量、基底节区的显示以及核团分辨程度均优于FBP法。FBP法和OSEM法重建时间分别为80s和100s,均在临床允许范围之内。OSEM迭代与FBP法脑叶及基底节ROI与小脑ROI比值差异无统计学意义（t=-0．332,P=0．750）。结论在现有软硬件技术条件下,平行孔低能高分辨准直器配合OSEM法优于FBP法,可获得空间分辨率和图像质量较好的Hoffmann模型重建图像。     

多巴胺转运蛋白PET成像诊断帕金森病

目的探讨多巴胺转运蛋白(DAT)显像诊断帕金森病的价值.材料和方法对18例正常人、31例晚期帕金森病(PD)患者分别进行11C-β-CFT PET显像,采用感兴趣区(ROI)及统计参数图(SPM)进行分析,比较正常组与PD组之间的差异.结果ROI显示PD组尾状核及壳核各区域DAT摄取明显低于对照组,重侧基底节DAT减少较对侧明显,重侧的尾状核头、体及壳核前、中、后的区域内CFT摄取值分别为轻侧的94.6%、87.0%、89.6%、91.8%、95.4%.SPM图像显示DAT减低区域主要集中在两侧尾状核、壳核区域,以壳核中后部减低为著,重侧DAT减低区域明显大于轻侧.结论11C-β-CFT PET显像能够客观显示帕金森病DAT不对称性代谢改变的区域,有助于帕金森病的诊断和疗效评价.SPM分析为一种更全面、准确的统计方法.     

基于Talairach图谱的脑18F-FDG PET图像基底节区的自动勾画

目的建立自动勾画基底节区的方法,并测定健康人的半定量值.方法通过非线性空间变换将PET图像经图像配准和图像形变2个步骤,归一化到Talairach坐标系,根据图谱中脑功能区的坐标,在三维图像中提取相应的基底节区,计算经大脑归一化后尾状核和壳核的半定量值.结果基于Talairach图谱可自动勾画尾状核和壳核,左侧尾状核头、体、尾部的正常值分别为1.02±0.04、0.92±0.07和0.71±0.03,右侧分别为0.98±0.03、0.87±0.04和0.71±0.01,左、右侧壳核的正常值分别为1.20±0.06和1.20±0.04,左右侧半定量值差异无显著性(P＞0.05).结论基于Talairach图谱自动勾画尾状核和壳核的方法有效.     

飞行时间、点扩散函数和高斯滤波对18F-FDG PET/CT肺结节SUV和SNR的影响

目的：探讨飞行时间(TOF)、点扩展函数(PSF)和高斯滤波(GF)对肺结节的标准化摄取值(SUV)和信噪比(SNR)的影响，为肺结节患者提供最佳的PET重建算法。方法：回顾性分析2020年12月至2022年3月在安徽医科大学第一附属医院行全身¹⁸F-FDG PET/CT检查的38例肺结节患者的PET/CT图像。采用滤波反投影(FBP)、有序子集最大期望值(OSEM)、OSEM+TOF、OSEM+PSF、OSEM+TOF+PSF和OSEM+TOF+PSF+GF [GF的半高宽(FWHM)分别为2、4、6、8和10 mm]重建算法进行图像重建，通过视觉评估PET图像质量和半定量方法分析肺结节的SNR和SUV。分别采用Holm-Sidak检验和Friedman检验分析不同重建算法间SUV和SNR的差异。结果：相比于FBP组，OSEM+TOF+PSF组SUVmax、SUVpeak、SUVmean和SNR分别提高8.02%(P>0.05)、10.72%(P<0.000 1)、19.05%(P<0.000 1)和688.89%(P<0.000 1)；...     

基于体素分析技术在肝豆状核变性病变MRI研究中的应用价值

目的：探讨基于体素分析（voxel-based analysis,VBA）图像方法在肝豆状核变性（Wilson’s disease,WD）MRI研究中的应用价值。方法：通过34例WD患者和30例健康志愿者的定量磁化率成像（quantitative susceptibility mapping,QSM）和DTI数据的VBA组间比较,检出WD患者大脑铁沉积及各向异性指数（FA）值异常的脑区,分析这种方法与常规基于ROI方法研究的优势与不足。结果：WD患者较正常人,双侧丘脑、双侧豆状核、双侧尾状核、双侧红核、双侧黑质、双侧颞叶、右侧岛叶和左侧顶下小叶等脑区的铁沉积含量增加,部分白质等脑区的铁沉积含量减少;双侧丘脑的背外侧核和腹外侧核、双侧豆状核、双侧尾状核及双侧红核等脑区的FA值升高,双侧丘脑内侧核及白质等脑区的FA值降低。结论：VBA图像方法具有能够发现未知区域病变、病变区域精确定位,以及研究客观等方面的优势,是一种很有价值的WD的MRI研究方法。     

统计参数图和ROI联合应用在多巴胺转运蛋白PET显像分析中的价值

目的 探讨联合应用统计参数图(SPM)和感兴趣区(ROI)方法在帕金森病(PD)患者多巴胺转运蛋白(DAT)PET图像分析中的价值.方法 临床确诊的41例PD患者,其中23例早期(Hoehn-Yahr Ⅰ～Ⅱ级),年龄(56.2±8.1)岁;18例晚期(Hoehn-Yahr Ⅲ～Ⅳ级),年龄(59.1±7.6)岁.健康对照组12名,年龄(58.84±7.2)岁.分别进行18F-N-(3-氟丙基)-2β-甲酯基-3β-(4'-碘苯基)去甲基托烷(FP-β-CIT)PET显像,对所获得的脑PET图像分别进行ROI及SPM分析.结果 应用ROI方法,与健康对照组相比,在23例早期PD患者中,尾状核、前壳核和后壳核的DAT分别减少29.1%、53.2%和76.0%;18例晚期PD患者的尾状核、前壳核和后壳核的DAT分别减少48.0%、65.5%和83.5%.SPM分析可直观显示,早期和晚期PD双侧壳核DAT较健康对照组减少,尤其是患肢的对侧壳核和后壳核区域.结论 PD患者纹状体内18F-FP-CIT的摄取显著降低,尤以患肢的对侧壳核最为明显;联合应用SPM和ROI方法有助于DAT PET图像的综合分析.     

滤波反投影法和OSEM重建图像测量心功能参数的比较

目的比较静息门控心肌显像滤波反投影法（FBP）和OSEM重建图像后用定量门控心肌断层显像（QGS）、四维模型心肌断层显像（4D—MSPECT）、爱莫瑞心脏工具箱（ECToolbox）软件测量的心功能参数。方法临床疑诊或确诊冠心病患者144例,均行^99Tc^m-MIBI静息门控心肌SPECT显像,所有患者均用FBP和OSEM重建图像,用QGS、4D—MSPECT、ECToolbox软件计算心功能参数LVEF,EDV和ESV,采用Bland—Altman法检验2种重建方法的一致性,配对t检验方法检验心功能参数差异,相关性分析用直线回归分析。结果FBP和OSEM重建测量的心功能参数一致性和相关性好（r均〉0．93,P均〈0．001）。QGS软件FBP重建测得的EDV低于OSEM重建测得的EDV,其他2种软件为FBP高于OSEM[QGS：（82．2±39．1）ml和（83．5±40．8）ml,t=-2．53,P〈0．05;4D—MSPECT：（93．5±46．9）ml和（88．8±45．2）ml,t=5．95,P〈0．01;ECToolbox：（106．4±51．1）ml和（100．8±49．0）ml,t=3．99,P〈0．01]。对于ESV,4D-MSPECT软件FBP测量值高于OSEM[（37．5±41．4）ml和（34．8±37．6）ml,t=3．92,P〈0．01]。QGS软件FBP测得的LVEF低于OSEM测得的LVEF[（62．1±16．9）％和（63．1±16．1）％,t=-3．14,P〈0．01]。ECToolbox软件FBP测得的LVEF高于用OSEM测得的LVEF[（74．1±18．8）％和（71．3±17．1）％,t=5．28,P〈0．01]。结论2种重建方法所测量的心功能参数虽然相关性和一致性很好,但某些参数值差异有统计学意义。     

Is iterative reconstruction an alternative to filtered backprojection in routine processing of dopamine transporter SPECT studies?

In general, striatal dopamine transporter (DAT) binding is assessed by use of data reconstructed by filtered backprojection (FBP). The aim of this study was to investigate whether the use of an iterative reconstruction algorithm (ordered-subset expectation maximization [OSEM]) may provide results comparable to or even better than those obtained by standard FBP. METHODS: In 50 patients with parkinsonian syndromes, SPECT scans were acquired 4 h after injection of 185 MBq of (123)I-fluoropropyl-2beta-carbomethoxy-3beta-(4-iodophenyl)tropane ((123)I-FP-CIT) by use of a triple-head gamma-camera fitted with low-energy, high-resolution fanbeam collimators. After reconstruction by FBP and OSEM, data were filtered with a Butterworth filter and corrected for attenuation. Patient studies were automatically fitted to a mean template with a corresponding 3-dimensional (3D) volume-of-interest map covering the striatum, caudate, and putamen as well as an occipital reference region to calculate specific DAT binding. In addition, studies with an anthropomorphic 3D striatal phantom were performed to mimic different pathologies. RESULTS: Visual assessment of phantom and patient data suggested a better separation between the caudate and the putamen in studies reconstructed by OSEM than in those reconstructed by FBP. There was an excellent correlation between specific DAT binding assessed by OSEM and that assessed by FBP (R(2) values: striatum, 0.999; caudate, 0.998; putamen, 0.998). Mean specific striatal binding obtained by OSEM was approximately 6% lower than that obtained by FBP. In no case was diagnostic information from OSEM inferior to that from FBP. CONCLUSION: Iterative reconstruction of (123)I-FP-CIT SPECT studies for the assessment of DAT is feasible in routine clinical practice. A close correlation between FBP and OSEM data suggested that the latter also allow reliable quantification of DAT binding. Because of a better separation between the caudate and the putamen in the visual evaluation, as suggested by phantom and patient studies, OSEM may even be considered the preferable approach.     

Effects of image reconstruction algorithm on neurotransmission PET studies in humans: Comparison between filtered backprojection and ordered subsets expectation maximization

OBJECTIVES: Both reconstruction algorithms, filtered backprojection (FBP) and ordered subsets expectation maximization (OSEM), are widely used in clinical positron emission tomography (PET) studies. Image reconstruction for most neurotransmission PET scan data is performed by FBP, while image reconstruction for whole-body [18F]FDG scan data is usually performed by OSEM. Although several investigators have compared FBP and OSEM in terms of the quantification of regional radioactivity and physiological parameters calculated from PET data, only a few studies have compared the two reconstruction algorithms in PET studies that estimate neurotransmission, i.e., neuroreceptor and neurotransporter binding. In this study we compared mean regional radioactivity concentration in the late phase and binding potential (BP) between FBP and OSEM algorithms in neurotransmission PET studies for [11C]raclopride and [11C]DASB. METHODS: Dynamic PET scans with [11C]raclopride in 3-dimensional mode were performed on seven healthy subjects. Dynamic PET scans with [11C]DASB in 2-dimensional mode were performed on another seven subjects. OSEM images were post-filtered so that its transverse spatial resolution became similar to that of FBP with the same Hanning filter (Kernel FWHM 6 mm). In both PET studies we calculated the BP of [11C]raclopride and [11C]DASB by a reference tissue model for each ROI (region of interest). RESULTS: There was no significant difference in mean regional radioactivity concentration between FBP and OSEM for [11C]raclopride and [11C]DASB. Only +2.4 - +3.2%, but still a significant difference in BP of [11C]raclopride between FBP and OSEM was observed in the striatum. There was no significant difference in BP between FBP and OSEM in other than the striatum for [11C]raclopride and in all regions for [11C]DASB. In addition, there was no significant difference in root mean square error between FBP and OSEM when BP was calculated. CONCLUSIONS: The BP values were similar between FBP and OSEM algorithms with [11C]raclopride and [11C]DASB. This study indicates that OSEM can be used for human neurotransmission PET studies for calculating BP although OSEM was not necessarily superior to FBP in the present study.     

Effects of iterative reconstruction on image contrast and lesion detection in gamma camera coincidence imaging in lung and breast cancers.

To investigate the effects of iterative reconstruction in 18F-fluorodeoxyglucose (FDG) gamma camera coincidence imaging (GCI), image contrast and visual detection obtained by using the iterative ordered-subsets expectation maximization (OSEM) reconstruction, in a phantom and in patients with lung cancer and breast cancer, were compared with those obtained by using the conventional filtered backprojection (FBP) reconstruction. Images of a cylindrical phantom containing hot spheres of various sizes (10-38 mm) were acquired by positron emission tomography (PET) and GCI at various sphere-to-background activity ratios. Forty-one consecutive patients with biopsy-proven cancer of lung (n = 20) and breast (n = 21) underwent PET and GCI on the same day after intravenous injection of 370 MBq of FDG. GCI images reconstructed by the OSEM and the FBP were compared. FDG PET was considered as the standard of reference. In GCI phantom images, OSEM yielded better contrast and signal-to-noise ratio (SNR) than FBP over the range of sphere sizes. Attenuation correction improved both the image measures and sphere detection obtained by the OSEM in GCI. In the study involving patients, FDG PET depicted 41 primary tumours and 25 metastatic lymph nodes. All of the tumours >2 cm in diameter (n = 25), six of the nine tumours 1.5-2.0 cm in diameter (67%), two of seven tumours <1.5 cm in diameter (29%), and 20 metastatic lymph nodes (80%) were detected in attenuation uncorrected GCI reconstructed by the OSEM as well as the FBP. The undetected lesions in GCI were identical between the OSEM and the FBP reconstructions. OSEM yielded significantly greater tumour-to-background (T/B) ratios and lower noise than FBP in GCI (T/B ratios, 4.1+/-3.2 vs 3.7+/-2.7, P = 0.02; noise, 0.09+/-0.04 vs 0.14+/-0.05, P<0.0001). In conclusion, OSEM yielded better image contrast and less noise than the FBP in GCI, but the lesion detection obtained by the OSEM and the FBP in attenuation uncorrected GCI in patients with lung cancer and breast cancer were similar. Phantom data suggest the potential of OSEM for improving lesion detection in GCI after attenuation correction.     

人脑标本不同区域多巴胺转运体分布的免疫放射自显影研究

目的 定量分析人脑标本不同区域多巴胺转运体(DAT)的免疫反应强度,为神经影像检查DAT变化的参照区选择提供依据.方法 取自8例男性尸脑标本的脑组织块经石蜡包埋切片后,以免疫放射自显影显示黑质、壳及尾状核、扣带回、额叶、枕叶和小脑皮质的DAT免疫反应强度.结果 所观察的脑区中,DAT免疫反应强标记主要分布在黑质、尾状核及壳,小脑皮质标记最弱.定量分析发现,小脑皮质的DAT免疫反应强度分别为额叶、扣带回及枕叶的1/3.50、1/3.72、1/1.28,仅为黑质、尾状核、壳的1/8.33、1/11.67、1/8.56.结论 小脑皮质在所检脑区中DAT含量最低,可作为神经影像检查DAT变化的参照区.     

Preliminary evaluation of image reconstruction by ordered-subset expectation maximization in thallium-201 lung scintigraphy

OBJECTIVES: We observed whether clearer tumor delineation and greater tumor to non-tumor (T/N) count ratios could be obtained using an iterative ordered-subsets expectation maximization (OSEM) algorithm than conventional filtered-back projection algorithm (FBP) in the image reconstruction of thallium-201 (201Tl) lung scintigraphy. METHODS: In 29 patients with lung cancer and phantom studies, tomograms were reconstructed using FBP and OSEM algorithms, with and without a prefilter (Butterworth filter: BW), whose cut-off frequencies were 0.10 cycles/pixel for FBP and 0.10 and 0.17 cycles/pixel for OSEM. Visual interpretation and tumor to non-tumor (T/N) count ratios were obtained and compared. RESULTS: Without a prefilter, T/N ratios from OSEM and FBP were 1.89 +/- 0.31 (early) and 2.00 +/- 0.54 (late) for OSEM, 1.90 +/- 0.33 (early) and 2.05 +/- 0.59 (late) for FBP, respectively. The OSEM reconstruction without prefiltering showed clearer tumor contours than FBP without a prefilter. Incorporation of BW showed visually low-noised images but decreased T/N ratios in both reconstructions with BW (0.10 cycles/pixel). No greater T/N ratios were obtained by OSEM than FBP, with or without prefiltering. With BW with a cut-off frequency of 0.17 cycles/pixel, the same T/N ratios as those without BW were obtained. The tumor model sized 0.9 cm in the phantom study was invisible in both OSEM and FBP reconstructions without a prefilter, but visible with a prefilter. The influence of prefiltering on T/N ratios was also observed in phantom studies. CONCLUSIONS: Visually improved tumor delineation could be obtained in OSEM reconstruction without a prefilter as compared to FBP reconstruction without a prefilter for tumors greater than 2 cm. Prefiltering should be incorporated into OSEM reconstruction in diagnosing small tumors. However, the influence of prefilter (BW) setting on semi-quantitative interpretation needs further discussion.     

Effect of reconstruction algorithms on myocardial blood flow measurement with 13N-ammonia PET.

Filtered backprojection (FBP) is the traditional method for 13N-NH3 PET studies. Ordered-subsets expectation maximization (OSEM) is popular for PET studies because of better noise properties. Scant data exist on the effect of reconstruction algorithms on quantitative myocardial blood flow (MBF) estimation. METHODS: Twenty patients underwent dynamic acquisition rest/stress 13N-NH3 studies. In Part 1, 19 rest/stress image pairs were reconstructed by FBP (10-mm Hanning filter) and by OSEM with 28 subsets and 2 (OSEM2), 6 (OSEM6), or 8 iterations (OSEM8), and a 10-mm postreconstruction smoothing gaussian filter. In Part 2, 9 image pairs were reconstructed by FBP (10-mm Hanning filter) and by OSEM with 28 subsets, 8 iterations, and a gaussian 5-, 10-, or 15-mm postreconstruction smoothing filter. Average MBF (mL/min/mL of myocardium) was calculated using a 3-compartment model. RESULTS: Part 1: For rest MBF, the correlations between FBP and each of the OSEM algorithms were r2 = 0.71, 0.73, and 0.77, respectively. MBF by OSEM6 (0.98 +/- 0.48 [mean +/- SD]) and OSEM8 (0.96 +/- 0.46) was not significantly different from FBP (1.02 +/- 0.39), but OSEM2 (0.80 +/- 0.37) was significantly lower (P < 0.0003). With stress, the correlations were high between FBP and OSEM6 and OSEM8 (r2 = 0.85 and 0.90), and MBF by OSEM6 and OSEM8 was not significantly different from FBP. Part 2: Resting MBF correlated well between FBP and all OSEM smoothing filters (r2 = 0.82, 0.85, and 0.88). Rest MBF using postsmoothing 5- or 10-mm filters was not different from FBP but was significantly lower with the 15-mm filter (P < 0.05). With stress, the correlations were good between FBP and OSEM regardless of smoothing (r2 = 0.76, 0.77, and 0.79). However, MBF with postsmoothing 10- and 15-mm filters was significantly lower than by FBP (P < 0.05). CONCLUSION: Reconstruction algorithms significantly affect the estimation of quantitative blood flow data and should not be assumed to be interchangeable. Although aggressive smoothing may produce visually appealing images with reduced noise levels, it may cause an underestimation of absolute quantitative MBF. In selecting a reconstruction algorithm, an optimal balance between noise properties and diagnostic accuracy must be emphasized.     

Experimental and clinical evaluation of iterative reconstruction (OSEM) in dynamic PET: quantitative characteristics and effects on kinetic modeling.

The purpose of this study was to investigate the quantitative properties and effects of ordered-subset expectation maximization (OSEM) on kinetic modeling compared with filtered backprojection (FBP) in dynamic PET studies. Both phantom and patient studies were performed. METHODS: For phantom studies dynamic two-dimensional emission scans with 10-min frames and 20-min scan intervals were acquired over a 14-h period using an HR+ PET scanner. Various phantoms were scanned: 2-, 5-, 10-, and 20-cm-diameter phantoms filled with an 18F solution (300 kBq/mL) and a NEMA phantom filled with an 18F background (40 kBq/mL) and a cold or 11C insert (450 kBq/mL). Transmission (Tx) scans of 5-60 min were acquired. Data were reconstructed using FBP Hanning 0.5 and OSEM with 2-12 iterations and 12 or 24 subsets. Quantitative accuracy and noise characteristics were assessed. For patient studies, five cardiac, three oncologic, and three brain dynamic 18F-FDG scans were used. Five reconstructions were performed: FBP Hanning 0.5, and OSEM 2 x 12 and OSEM 4 x 16 with and without 5-mm full width at half maximum smoothing. Time-activity curves were calculated using volumes of interest. The input function was derived from arterial sampling. Metabolic rate of glucose (MRglu) was calculated with a standard two-tissue compartment model and Patlak analysis. RESULTS: Contribution of Tx noise to the reconstructed image was smaller for OSEM than for FBP. Differences in signal-to-noise ratio between FBP and OSEM depended on number of iterations and phantom size. Bias with OSEM was observed for regions enclosed within a 5- to 10-fold hotter background. For cardiac studies OSEM 2 x 12 and OSEM 4 x 16 resulted in 13% and 21% higher pixel values and 9% and 15% higher MRglu values compared with FBP. Smoothing decreased all these values to 2%. Similar results were found for most tumor studies. For brain studies MRglu of FBP and OSEM 4 x 16 agreed within 2%. Use of OSEM image-derived input functions for cardiac PET studies resulted in a decrease in calculated MRglu of about 15%. CONCLUSION: For most PET studies OSEM has equal quantitative accuracy as FBP. The higher pixel and MRglu values are explained by the better resolution of OSEM. However, OSEM does not provide accurate image-derived input functions for FDG cardiac PET studies because of bias in regions located within a hotter background.