18F-FMISO在肺癌模型小鼠体内的生物分布及PET显像研究

目的 评价乏氧显像剂18F-硝基咪唑丙醇(18F-FMISO)在肺腺癌动物模型中的诊断价值.方法 荷肺腺癌T739小鼠经尾静脉注入18F-FMISO后不同时间(30、60、90、120 min)处死,测量18F-FMISO的生物分布,并行PET显像.对照组小鼠在注入18F-氟脱氧葡萄糖(18F-FDG)后行PET显像.结果 荷瘤鼠肿瘤PET显像清晰.生物分布研究表明肿瘤有明显的放射性摄取.在肾脏和肝脏有较高的放射性分布.肿瘤对血和肌肉的T/NT比值均大于2.结论 肺部恶性肿瘤组织中18F-FMISO摄取高于正常组织,可通过PET清晰显像,为进一步临床应用于肿瘤的乏氧诊断提供了依据.     

Micro PET/CT显像评价裸鼠MDA-MB231乳腺癌乏氧与增殖状态的研究

目的 探讨18F-FMISO、18F-FDG micro PET/CT显像评价裸鼠MDA-MB231乳腺癌移植瘤中肿瘤乏氧与增殖状态的可行性.方法 16只裸鼠MDA-MB231乳腺癌移植瘤模型先后进行18F-FDG及18F-FMISO PET/CT显像并采集肿瘤最大标准化摄取值[SUVmax (FDG)、SUVmax(FMISO)],所有模型显像结束后立即处死,取肿瘤组织行HIF-1α及Ki67免疫组织化学染色,将SUVmax值与HIF-1α、Ki67的表达水平进行相关性分析.结果 18F-FMISO平均SUVmax值1.69,18F-FDG平均SUVmax值5.80.SUVmax(FMISO)与HIF-1α、Ki67的表达均呈正相关性(r=0.74、0.52,P＜0.05).SUVmax (FDG)与Ki67的表达呈正相关性(r=0.86,P＜0.05),与HIF-1α表达无相关性.HIF-1α与Ki67蛋白的表达呈正相关性(r=0.60,P＜0.05).结论 18F-FMISO PET/CT显像可同时对活体肿瘤进行乏氧及增殖的可视化监测,18F-FDG可提供有效的肿瘤增殖显像,但不能作为有效的肿瘤乏氧显像剂.     

18F-FMISO乏氧显像剂在临床上的应用与进展研究

肿瘤乏氧是癌症病人预后不良的重要原因。乏氧可能是恶性肿瘤对治疗产生耐受的主要机制,而且乏氧会使肿瘤侵袭性增加。所以检测肿瘤细胞乏氧至关重要,它会为临床上的治疗和肿瘤病人的愈后提供线索。目前检测乏氧方法很多,但是应用于临床上的少之又少。其中核医学(PET/SPECT)分子显像技术在临床上应用最为广泛。乏氧显像剂能够选择性聚集在肿瘤乏氧区域,然后通过核医学(PET/SPECT)进行乏氧的显像。乏氧显像剂分为硝基咪唑类和非硝基咪唑类,临床上和基础实验研究中以前者为主。而_¹⁸F-FMISO是第一代硝基咪唑类乏氧显像剂,目前临床上应用广泛。这篇文章将会对_¹⁸F-FMISO的最新实验及临床研究进展及目前存在的问题等进行综述。     

用反应堆生产~(18)F-2-氟-2-去氧-D-葡萄糖

~(18)F-2-氟-2-去氧-D-葡萄糖(简称~(18)F-2FDG)是当前最重要的放射性药物之一。它与PET配合,可测定细胞的代谢功能,把脏器功能显像进一步推进到细胞代谢显像,对大脑和心脏,不论是从生理研究,还是从临床研究局部大脑葡萄糖代谢、诊断癫痫和早老性痴呆等疾病,具有其它方法所不具备的独到之处。甚至有人把揭开     

PET显像剂18F-AlF-NOTA-PRGD2的肿瘤靶向性

目的研究新型PET受体靶向显像剂18F-AlF-NOTA-PRGD2用于肿瘤显像的可行性。方法18F-AlF-NOTA-PRGD2采用
18 氟-氟化铝（18F-AlF）与NOTA-PRGD2在100 ℃下通过鳌合反应标记制备而得。荷脑胶质瘤U87MG裸鼠经尾静脉注射
18F-AlF-NOTA-PRGD2后行体内放射性生物学分布和PET/CT、microPET/CT显像研究。结果18F-AlF-NOTA-PRGD2采用一步
法成功标记,反应时间15~20 min,标记产率为17%~25%。体内放射性生物学研究显示该显像剂能靶向肿瘤病灶,静脉注射后
1 h和2 h肿瘤摄取量分别达4.14±1.44、2.80±1.18% ID/g（t=1.910,P=0.070）,肿瘤/脑比值分别达2.95±0.61、5.21±2.62（t=-1.686,
P=0.167）。PET/CT和microPET/CT显像均可清楚显示该显像剂在荷瘤鼠体内的放射性分布情况,肿瘤显像清楚,体内分布良
好,但microPET/CT图像质量明显优于PET/CT。结论18F-AlF-NOTA-PRGD2标记简单、易行,在荷瘤鼠体内具有优良的肿瘤靶
向性,可发展成为PET肿瘤显像剂。     

~(11)C-胆碱与~(18)氟去氧葡萄糖PET/CT显像在肺癌诊断中的对比研究

目的:通过11C-胆碱(11C-choline)与18氟去氧葡萄糖(18FDG) PET/CT显像对肺癌的对比研究,探讨11C-胆碱PET/CT显像对肺癌的诊断价值,并对其相关性进行研究.方法:21例肺癌患者行11C-胆碱及18FDG PET/CT显像,分别分析11C-胆碱及18FDG PET/CT图像,计算标准摄取值(SUV)、瘤/非瘤(T/N)组织,对11C-胆碱及18FDG PET/CT显像参数进行统计学分析.结果:21例肺癌患者中,17例11C-胆碱及18FDG PET/CT显像表现为代谢增高(80.9%).11C-胆碱PET/CT显像中病灶SUV、T/N值明显低于18FDG PET/CT显像结果(P＜0.05);11C-胆碱PET/CT显像中病灶SUV、T/N值与18FDG PET/CT显像呈正相关关系(r=0.57和0.52,P=0.007和0.016); 11C-胆碱PET/CT显像中SUV、T/N与病灶大小呈正相关关系(r=0.99、0.45 ,P=0.008 4、0.039),18FDG PET/CT显像中SUV与病灶大小呈正相关关系(r=0.68 ,P=0.000 7),而18FDG PET/CT显像T/N与病灶大小相关,但无统计学意义.结论:11C-胆碱反映肿瘤细胞细胞膜的合成情况,在肺癌的诊断中有一定价值.     

18F-FLT与18F-FDG评估白血病荷瘤裸鼠模型肿瘤增殖的研究

目的对比研究3’-脱氧-3’-18F-氟代胸苷(18F-FLT)和18F-氟代脱氧葡萄糖(18F-FDG)在评估慢性髓性白血病(K562细胞株)荷瘤裸鼠模型肿瘤增殖中的应用价值。方法合成放射性显像剂18F-FLT,常规体外培养K562细胞株,分别于加入18F-FLT和18F-FDG后15、30、60和120 min,测定细胞对18F-FLT与18F-FDG的摄取率。将K562细胞株接种于裸鼠肩部皮下建立白血病荷瘤裸鼠模型,并经鼠尾静脉注射18F-FLT和18F-FDG,分别于注射后30、60和120 min,行正电子发射型计算机断层显像(PET),计算靶/非靶(T/NT)比值。结果所合成的18F-FLT经高效液相色谱纯化,放置6 h内放射化学纯度>95%。病理学检查显示经皮下接种K562细胞株可以成功建立白血病荷瘤裸鼠模型;体外细胞摄取试验结果显示:不同时间点K562细胞对18F-FLT的摄取率均显著高于对18F-FDG的摄取率(P<0.05);PET显像示:不同显像时间K562移植瘤18F-FLT PET显像组T/NT比值分别高于18F-FDG PET显像组T/NT比值(P<0.05)。结论与显像剂18F-FDG相比较,18F-FLT能更好地反映白血病荷瘤裸鼠模型移植肿瘤的增殖情况。     

人肝细胞癌HepG2细胞荷瘤裸鼠18F⁃乙基胆碱、11C⁃胆碱、18F⁃FDG生物分布和PET肿瘤显像

目的 单一18 F?FDG PET显像对高分化HCC诊断敏感低,因而探讨荷人肝细胞癌HepG2细胞裸鼠中18 F?乙基胆碱、11 C?胆碱、18 F?FDG的活体生物学分布以及18 F?乙基胆碱(18 F?FECh)、11 C?胆碱、18 F?FDG microPET显像检测荷瘤鼠肿瘤的价值. 方法 荷人肝癌细胞Hep...     

18F-FLT与18F-FDG评估白血病荷瘤裸鼠模型肿瘤增殖的研究

目的 对比研究3’-脱氧-3’-18F-氟代胸苷(18F-FLT)和18F-氟代脱氧葡萄糖(18F-FDG)在评估慢性髓性白血病(K562细胞株)荷瘤裸鼠模型肿瘤增殖中的应用价值.方法 合成放射性显像剂18F-FLT,常规体外培养K562细胞株,分别于加入18F-FLT和18F-FDG后15、30、60和120 min,测定细胞对18F-FLT与18F-FDG的摄取率.将K562细胞株接种于裸鼠肩部皮下建立白血病荷瘤裸鼠模型,并经鼠尾静脉注射18F-FLT和18F-FDG,分别于注射后30、60和120 min,行正电子发射型计算机断层显像(PET),计算靶/非靶(T/NT)比值.结果 所合成的18F-FLT经高效液相色谱纯化,放置6h内放射化学纯度＞95％.病理学检查显示经皮下接种K562细胞株可以成功建立白血病荷瘤裸鼠模型;体外细胞摄取试验结果显示:不同时间点K562细胞对18F-FLT的摄取率均显著高于对18F-FDG的摄取率(P＜0.05);PET显像示:不同显像时间K562移植瘤18F-FLT PET显像组T/NT比值分别高于18F-FDG PET显像组T/NT比值(P＜0.05).结论 与显像剂18F-FDG相比较,18F-FLT能更好地反映白血病荷瘤裸鼠模型移植肿瘤的增殖情况.     

~(18)氟去氧葡萄糖PET显像在脑胶质瘤中的研究进展

18氟去氧葡萄糖(18FDG)是目前最常用的正电子示踪剂,18FDG PET显像在脑胶质瘤的诊断、分级、预后评估、穿刺定位、放疗计划的制订及脑放射性坏死和肿瘤复发的鉴别中起着越来越重要的作用.文中综述了18FDG PET显像在脑胶质瘤中应用的最新进展.     

Association of posttherapy positron emission tomography with tumor response and survival in cervical carcinoma

Context  Retrospective studies have demonstrated that the use of positron emission tomography (PET) with F-18 fluorodeoxyglucose (FDG) in the posttherapy evaluation of patients with cervical carcinoma is predictive of survival outcome. Objective  To validate the association between the metabolic response on the 3-month posttherapy FDG-PET and long-term survival outcome. Design, Setting, and Patients  A prospective cohort study designed to validate our previous finding that the results of a 3-month posttherapy FDG-PET are predictive of long-term clinical outcome. A total of 92 women were treated with external irradiation, brachytherapy, and concurrent chemotherapy from January 2003 through September 2006. Posttherapy whole-body FDG-PET was performed 2 to 4 months (mean, 3 months) after completion of therapy. Main Outcome Measures  The primary outcome end points were metabolic response, progression-free survival, and cause-specific survival. Results  Posttherapy FDG-PET showed a complete metabolic response in 65 patients (70%), a partial metabolic response in 15 (16%), and progressive disease in 12 (13%). Their 3-year progression-free survival rates were 78%, 33%, and 0%, respectively (P < .001). Multivariate analysis demonstrated that the hazard ratio (HR) for risk of recurrence based on the posttherapy metabolic response showing progressive disease was 32.57 (95% confidence interval [CI], 10.22-103.82). A partial metabolic response had an HR of 6.30 (95% CI, 2.73-14.56). These were more predictive of survival outcome than the pretreatment lymph node status (HR, 3.54; 95% CI, 1.54-8.09). Conclusion  In this single-site study population of women with cervical cancer, 3-month posttherapy FDG uptake, as detected by whole-body PET, was predictive of survival.      

阿尔茨海默病大鼠模型PET在体成像研究

目的研究18F-FDG及Aβ蛋白显像剂(4’-schiff-O[11CH3])PET成像技术在判别阿尔茨海默病大鼠模型中的作用。方法对10只注射Aβ1～40复制阿尔茨海默模型大鼠及10只注射生理盐水对照大鼠行HE染色及刚果红染色,检测大鼠脑内病理学改变。用18F-FDG及4’-schiff-O[11CH3]PET显像技术在体观察2组大鼠脑内Aβ蛋白分布及葡萄糖代谢情况。结果模型组大鼠海马出现神经元减少并形成淀粉样斑块。模型组PET显像可见注射侧海马葡萄糖代谢减低及4’-schiff-O[11CH3]摄取增加。对照组仅见轻微神经元损伤,PET显示葡萄糖代谢轻度减低。结论18F-FDG及4’-schiff-O[11CH3]PET显像结合行为学及病理学观察可作为检测模型成功与否的方法之一。     

^18F—FDG PET的临床初步应用

目的：评价国产ＰＥＴ－Ｂ０１和国产＾１８Ｆ－ＦＤＧ的临床应用价值。方法：应用国产ＰＥＴ－Ｂ０１和国产＾１８Ｆ－ＦＤＧ对１８例患者进行ＰＥＴ显像，所有患者均先行透射扫描后再行相同部位发射扫描，部分心肌扫描于注射前１ｈ口服葡萄糖５０ｇ，其余患者均禁食〉６ｈ后进行ＰＥＴ检查。结果：４例发作间期癫痫患儿中，３例可见局部皮质代谢减低区；２例脑血管患者均见和体征相关部位皮质代谢减低；４例糖负荷心肌显像中，心动     

18F-氟代乙酸盐自动化合成及其动物实验研究

【目的】 研究肿瘤显像剂18F-氟代乙酸盐(18F-FAC)的自动化合成工艺及其临床前肿瘤显像评价&#65377;【方法】 以溴代乙酸苄酯为前体,一种方法是应用商用PET-MF-2V-IT-I型氟-18多功能自动化合成仪,采用在柱水解法,经亲核氟化&#65380;在柱水解及Sep-Pak小柱分离纯化制备18F-FAC注射液;另一种方法,采用“一锅法”在同一反应瓶中经亲核氟化&#65380;NaOH水解两步反应及Sep-Pak分离纯化制备18F-FAC注射液&#65377;对荷肝细胞癌小鼠进行18F-FAC和18F-FDG PET显像&#65377;【结果】 两种方法制备的18F-FAC注射液放化纯度均大于95%&#65377;采用在柱水解法自动化合成18F-FAC,未校正放化产率为50% ~ 60%,总合成时间约28 min&#65377;采用“一锅法”自动化合成18F-FAC,未校正放化产率为15% ~ 25%(n = 5),总合成时间约26 min&#65377;荷肝细胞癌小鼠PET显像结果表明,18F-FAC静脉注射1 h后肿瘤对18F-FAC的摄取明显高于周围的正常组织,肿瘤对18F-FAC的摄取明显高于18F-FDG&#65377;【结论】 采用在柱水解法自动化合成18F-FAC注射液,操作简便,能满足科研和临床正电子发射断层显像的需要&#65377;生产的18F-FAC有助于对肝细胞癌的诊断&#65377;     

Pre-clinical evaluation of a new indirectly labeled 99mTc-6-hydrazinopyridine-3-carboxylic acid (HYNIC)-depreotide with HYNIC as bifunctional chelator

Background  Technetium-99m or ^99mTc is widely used for labeling peptide in nuclear medicine. Somatostatin and its analog can inhibit tumor cell growth after binding with its receptor. This research was to study the preclinical effect of a new ^99mTc-6-hydrazinopyridine-3-carboxylic acid (HYNIC)-depreotide, indirect ^99mTc labeling of depreotide using HYNIC as a bifunctional chelator.

Methods  The cyclopeptide, cyclo-[(N-Me) Phe-Tyr-D-Trp-Lys-Val-Hcy], the linear peptide, and [ClCH₂-CO×b-Dap-Lys- Cys-Lys×amide] were synthesized by Fmoc solid-phase synthesis. The cyclopeptide and the linear peptide were linked by liquid-phase synthesis. The product depreotide was isolated and purified by high performance liquid chromatography and was confirmed by mass spectrography. Depreotide was labeled with ^99mTc through a direct labeling method, using HYNIC as a bifunctional chelator. Paper chromatography method was used to calculate the labeling rate, and through the comparative analysis selected the best mark conditions. The new ^99mTc-HYNIC-depreotide was tested by high-performance liquid chromatography (HPLC). The internalization and externalization rates of the new ^99mTc-HYNIC-depreotide were studied in A549 cells. Furthermore, biodistribution of the radiopeptide was studied in nude mice, bearing tumors from human lung carcinoma cells SPC-A1.

Results  The molecular of synthesize depreotide was 1358, and the purity of it was 95.29%. The labeling efficiency of ^99mTc-HYNIC-depreotide was highest at pH 6.0 and 15°C, about (70.95±0.84)%. The labeling rate of the new ^99mTc-HYNIC-depreotide rose to a peak of (20.75±0.48)% at 60 minutes in A549 cells at 37°C and decreased slightly later, while it elevated gradually during the time course at 4°C and 25°C. The internalization rate of the new ^99mTc-HYNIC-depreotide at 37°C increased gradually and reached the peak of 84.4% in 120 minutes, while the externalization rate of the new ^99mTc-HYNIC-depreotide was always less than 20%. In mice bearing the experimental SPC-A1 tumor, the new ^99mTc-HYNIC-depreotide demonstrated a high tumor uptake of (4.05±0.04)% ID/g at 1.5 hpi and remained high ((2.51±0.06)% ID/g) at 4 hpi. The tumor-to-lung activity concentration ratio (T/Lu) was very high for the new ^99mTc-HYNIC-depreotide at all time points. So did the tumor-to-muscle activity (T/Mu) and tumor-to-blood activity concentration ratios (T/Bl).

Conclusion  The findings suggested that the new ^99mTc-HYNIC-depreotide might be a promising candidate radiopharmaceutical for imaging somatostatin receptor positive lung cancer.     

Intravenous tissue-type plasminogen activator for treatment of acute stroke: the Standard Treatment with Alteplase to Reverse Stroke (STARS) study

Context  Tissue-type plasminogen activator (tPA) is the only therapy for acute ischemic stroke approved by the Food and Drug Administration. Objective  To assess the safety profile and to document clinical outcomes and adverse events in patients treated with intravenous tPA for acute stroke in clinical practice. Design and Setting  Prospective, multicenter study of consecutive patients enrolled between February 1997 and December 1998 at 57 medical centers in the United States (24 academic and 33 community). Intervention  Intravenous tPA (recombinant alteplase). Patients  Three hundred eighty-nine patients with a mean age of 69 years (range, 28-100 years); 55% were men. Main Outcome Measures  Time intervals between stroke symptom onset, hospital arrival, and treatment with tPA; pretreatment computed tomographic scan results, intracerebral hemorrhage, and major systemic bleeding. The modified Rankin Scale score was used to assess clinical outcomes at 30 days. Results  Median time from stroke onset to treatment was 2 hours 44 minutes, and the median baseline National Institutes of Health Stroke Scale score was 13. The 30-day mortality rate was 13%. At 30 days after treatment, 35% of patients had very favorable outcomes (modified Rankin score, 0-1) and 43% were functionally independent (modified Rankin score, 0-2). Thirteen patients (3.3%) experienced symptomatic intracerebral hemorrhage, including 7 who died. Twenty-eight patients (8.2%) had asymptomatic intracerebral hemorrhage within 3 days of treatment with tPA. Protocol violations were reported for 127 patients (32.6%), and included treatment with tPA more than 3 hours after symptom onset in 13.4%, treatment with anticoagulants within 24 hours of tPA administration in 9.3%, and tPA administration despite systolic blood pressure exceeding 185 mm Hg in 6.7%. A multivariate analysis found predictors of favorable outcome to be a less severe baseline National Institutes of Health Stroke Scale score, absence of specific abnormalities (effacement or hypodensity of >33% of the middle cerebral artery territory or a hyperdense middle cerebral artery) on the baseline computed tomographic scan, an age of 85 years or younger, and a lower mean arterial pressure at baseline. Conclusions  This study, conducted at multiple institutions throughout the United States, suggests that favorable clinical outcomes and low rates of symptomatic intracerebral hemorrhage can be achieved using tPA for stroke treatment.      

Regional brain metabolic correlates of alpha-methylparatyrosine-induced depressive symptoms: implications for the neural circuitry of depression

Context  We previously used positron emission tomography (PET) measurement of brain metabolism with ¹⁸fluorodeoxyglucose to show that patients receiving selective serotonin reuptake inhibitors (SSRIs) who have a tryptophan depletion–induced return of depressive symptoms have an acute decrease in metabolism in orbitofrontal cortex, dorsolateral prefrontal cortex, and thalamus. Many patients with depression in remission while taking norepinephrine reuptake inhibitors (NRIs) (but not SSRIs) experience a return of depressive symptoms with depletion of norepinephrine and dopamine using -methylparatyrosine (AMPT). Objective  To assess brain metabolic correlates of AMPT administration in patients with depression in remission while receiving NRIs. Design, Setting, and Participants  Randomized, controlled, double-blind trial in which 18 patients recruited in 1997-2000 from the general community who had depression in remission while taking NRIs had PET imaging in a psychiatric research unit following AMPT and placebo administration. Interventions  After initial medication with desipramine and follow-up until response, patients underwent active AMPT (five 1-g doses administered orally over 28 hours) and placebo (diphenhydramine hydrochloride, five 50- mg doses administered similarly) catecholamine depletion challenges in randomized order of assignment, after which PET imaging was performed on day 3 of each condition. Both study conditions were performed 1 week apart. Main Outcome Measures  Regional brain metabolism rates in patients with and without AMPT-induced return of depressive symptoms. Results  AMPT-induced return of depressive symptoms was experienced by 11 of the 18 patients and led to decreased brain metabolism in a number of cortical areas, with the greatest magnitude of effects in orbitofrontal (P = .002) and dorsolateral prefrontal (P = .03) cortex and thalamus (P = .006). Increased resting metabolism in prefrontal and limbic areas predicted vulnerability to return of depressive symptoms. Conclusions  Different neurochemical systems that mediate depression may have effects on a common brain circuitry. Baseline metabolism in successfully treated depressed patients may predict vulnerability to future episodes of depression.      

Clinical validity of a negative computed tomography scan in patients with suspected pulmonary embolism: a systematic review

Context  The clinical validity of using computed tomography (CT) to diagnose peripheral pulmonary embolism is uncertain. Insufficient sensitivity for peripheral pulmonary embolism is considered the principal limitation of CT. Objective  To review studies that used a CT-based approach to rule out a diagnosis of pulmonary embolism. Data Sources  The medical literature databases of PubMed, MEDLINE, EMBASE, CRISP, metaRegister of Controlled Trials, and Cochrane were searched for articles published in the English language from January 1990 to May 2004. Study Selection  We included studies that used contrast-enhanced chest CT to rule out the diagnosis of acute pulmonary embolism, had a minimum follow-up of 3 months, and had study populations of more than 30 patients. Data Extraction  Two reviewers independently abstracted patient demographics, frequency of venous thromboembolic events (VTEs), CT modality (single-slice CT, multidetector-row CT, or electron-beam CT), false-negative results, and deaths attributable to pulmonary embolism. To calculate the overall negative likelihood ratio (NLR) of a VTE after a negative or inconclusive chest CT scan for pulmonary embolism, we included VTEs that were objectively confirmed by an additional imaging test despite a negative or inconclusive CT scan and objectively confirmed VTEs that occurred during clinical follow-up of at least 3 months. Data Synthesis  Fifteen studies met the inclusion criteria and contained a total of 3500 patients who were evaluated from October 1994 through April 2002. The overall NLR of a VTE after a negative chest CT scan for pulmonary embolism was 0.07 (95% confidence interval [CI], 0.05-0.11); and the negative predictive value (NPV) was 99.1% (95% CI, 98.7%-99.5%). The NLR of a VTE after a negative single-slice spiral CT scan for pulmonary embolism was 0.08 (95% CI, 0.05-0.13); and after a negative multidetector-row CT scan, 0.15 (95% CI, 0.05-0.43). There was no difference in risk of VTEs based on CT modality used (relative risk, 1.66; 95% CI, 0.47-5.94; P = .50). The overall NLR of mortality attributable to pulmonary embolism was 0.01 (95% CI, 0.01-0.02) and the overall NPV was 99.4% (95% CI, 98.7%-99.9%). Conclusion  The clinical validity of using a CT scan to rule out pulmonary embolism is similar to that reported for conventional pulmonary angiography.