心包窦和心包隐窝的螺旋CT表现及其解剖学基础

目的 在横断面解剖学的基础上，评价心包窦、隐窝的横断面螺旋CT表现及其影像学意义。资料与方法 复习52例心包积液（按中－大量组和少量组）和146例无心包疾病（正常对照组）病例纵隔螺旋CT影像，并对照2例尸体横断面解剖，描述心包窦、隐窝在5个主要横断面的显示率，并进行统计学分析。结果 心包各窦、隐窝的显示率均大于40％。心包少量积液组与中－大量积液组心各包窦与隐窝的显示率，以及病例组与对照组间PCR、RPR、pSAR的显示率无显著性差异（P＞0．05）；而病例组与对照组间其余心包各窦与隐窝的显示率有显著性差异（P＜0．05）。结论 心包窦、隐窝在螺旋CT上易于显示。其定位诊断需依靠断层解剖学知识，并应与邻近正常结构及其病变相区别。     

高位心包上隐窝的CT表现

为评价高位心包上隐窝的CT特点与发生率,作者回顾性评价了1998年12月-1999年3月除外心包积液的276例284次连续胸部CT扫描。 心包横窦分为主动脉上下隐窝和左右肺隐窝,主动脉上隐窝进一步分为前、后及右侧部分。该文中的心包上隐窝特指心包主动脉上隐窝的后侧部分,把高位心包上隐窝定义为头臂血管与气管间的气管     

100名正常成人右中叶嵴、左舌叶嵴的CT表现

目的 提高对右中叶嵴、左舌叶嵴CT表现的认识.资科与方法复习100名正常成人胸部CT扫描片,观察右中叶嵴、左舌叶嵴的形态、大小、边缘和位置.为了探讨其诊断意义,分析30例原发性肺结核患者的CT资料.结果 两侧叶嵴形态分别为三角形、喇叭形、菱形、类圆形和不规则形.正常右中叶嵴的前后径平均为(17.8±2.2)mm,左右径平均为(17.3±2.1)mm,嵴角平均为(73.8±7.8)°;正常左舌叶嵴的前后径平均为(18.2±2.2)mm,左右径平均为(17.6±2.1)mm,嵴角平均为(66.0±9.6)°.叶嵴的外缘均显示凹入或平直.右中叶嵴位置较左舌叶嵴稍靠前靠下.在30例原发性肺结核CT片上,右中叶嵴增大主要是右肺门叶间下组及右下叶外侧组淋巴屯结增大;左舌叶嵴增大主要是左肺门叶间下组及左下叶外侧组淋巴结增大.30例中,19例(63.3%)伴有纵隔淋巴结增大,以右气管旁组(14例),右气管支气管组(12例)和隆突下组(17例)多见.增强扫描片上,淋巴结呈环状强化14例(46.6%),不均匀强化11例(36.7%),均匀强化5例(16.7%).结论 熟悉右中叶嵴、左舌叶嵴正常和异常的CT表现,有助于对肺门淋巴腺病的诊断与鉴别诊断.     

64层螺旋CT左心房和肺静脉成像在心房颤动射频消融术中的价值及应用

目的 应用64层螺旋CT(MSCT)对左心房和肺静脉进行形态学分析,用以指导心房颤动(简称房颤)环肺静脉线性消融术,并评估预后.方法 对232例患者(房颤组146例,对照组86例)行64层MSCT左心房和肺静脉成像,比较房颤组及对照组肺静脉解剖学变异的发生率,测量各支肺静脉开口的径线及形态,观察左心房的大小及左心房耳部的形态.结果 64层MSCT左心房和肺静脉成像可以提供详细的左心房与肺静脉连接方式及肺静脉解剖学变异,肺静脉解剖变异占总样本数的16.8%(39/232).各组肺静脉开口均呈上下径大于前后径的椭圆形.房颤组及对照组中左心房的内径差异存在统计学意义[房颤组:(39.47±8.98)mm;对照组:(36.94±5.49)mm;P=0.02],而2组患者肺静脉开口的径线差异无统计学意义[房颤组肺静脉上下径:左上(18.15±1.35)mm,左下(16.96±1.18)mm,右上(17.50±1.12)mm,右下(17.65±0.94)mm;对照组肺静脉上下径:左上(18.07±0.94)mm,左下(17.50±0.57)mm,右上(18.03±1.02)mm,右下(17.94±0.76)mm,P值均＞0.05;房颤组肺静脉前后径:左上(12.26±1.89)mm,左下(11.96±0.61)mm,右上(12.32±1.08)mm,右下(12.39±0.95)mm;对照组肺静脉前后径:左上(12.74±1.03)mm,左下(12.23 ±0.75)mm,右上(12.64±0.87)mm,右下(12.72±0.67)mm,P值均＞0.05].结论 64层MSCT左心房和肺静脉成像不仅可以了解环肺静脉线性消融术前肺静脉及左心房解剖变异的情况,而且可以进一步评价心房功能和风险,对介入治疗具有重要的指导意义.     

CT肺动脉阻塞指数对肺栓塞治疗效果的定量评估

目的 评估Qanadli等提出的CT阻塞指数在定量分析肺动脉栓塞(pulmonary embolism,PE)患者治疗效果中的价值.资料与方法 经多层螺旋CT血管成像(CTA)确诊、经溶栓或(及)抗凝治疗并治疗后以CTA随访的患者55例,随访时间为1-6周.治疗前后采用Qanadli栓塞指数评价PE程度,并采用Spearman等级相关系数评价其与临床指征(血氧饱和度及肺动脉压)恢复的相关性.结果 55例患者中,51例经溶栓或(及)抗凝治疗后临床指征明显改善,血氧饱和度由(83.52±4.461)%上升到(94.76±3.532)% (P <0.001),肺动脉压力由(31.17±5.892) mmHg(1mmHg=0.133kPa)下降至(19.83±4.804) mmHg (P<0.001);Qanadli栓塞指数从治疗前的(45.09±18.22)%降至治疗后的(10.86±10.29)%(P<0.001).4例临床指征改善不明显,Qanadli栓塞指数治疗前后差异无显著统计学意义(P=0.080).治疗前后Qanadli栓塞指数与血氧饱和度、肺动脉压力的差异度均存在良好相关性(r值分别为0.934,0.813 ).结论 Qanadli栓塞指数可准确用于PE治疗效果的定量评估,对临床治疗方案的制定有指导作用.     

心脏粘液瘤瘤体大小与患者心功能、肺动脉压及血管栓塞关系

目的探讨心脏粘液瘤患者的瘤体大小与心功能、肺动脉压及血管栓塞的关系。方法选取自2015年6月至2018年6月在辽宁省肿瘤医院诊治的63例心脏粘液瘤患者作为研究对象,按照纽约心脏协会(NYHA)心功能分级将患者分为Ⅰ级(n=10)、Ⅱ级(n=21)、Ⅲ级(n=24)和Ⅳ级(n=8)4组,测定各组患者术前血管栓塞发生情况、手术前后肺动脉压水平及术后肿瘤大小,分析患者瘤体大小与心功能分级、肺动脉血压及血管栓塞的关系。结果心功能Ⅰ级、Ⅱ级、Ⅲ级和Ⅳ级患者血管栓塞发生率分别为0、4.8%(1/21)、12.5%(3/24)和25.0%(2/8),各组患者心脏粘液瘤的质量分别为(23.6±4.3)g、(30.2±4.1)g、(42.5±5.2)g、(76.4±6.8)g,随心功能分级的增高,粘液瘤质量及血管栓塞发生率呈现升高趋势,差异均有统计学意义(P<0.05)。Ⅰ级、Ⅱ级、Ⅲ级和Ⅳ级患者术前肺动脉压为(1.6±0.6)kPa、(3.9±1.1)kPa、(5.5±1.4)kPa、(7.1±2.3)kPa,随着心功能分级的增高,患者术前肺动脉压水平显著升高(P<0.05);而粘液瘤切除后各组患者肺动脉压降为(2.0±0.7)kPa、(2.3±0.7)kPa、(3.0±0.9)kPa、(3.4±0.7)kPa,差异有统计学意义(P<0.05)。相关性分析发现,心脏粘液瘤患者的瘤体质量与患者心功能分级、肺动脉压水平及发生血管栓塞均呈显著正相关,相关系数分别为0.416、0.532和0.518(P<0.05)。结论心脏粘液瘤患者瘤体大小与其心功能、肺动脉压水平及发生血管栓塞密切相关。     

64排CT评估肺动脉栓塞严重程度的价值

目的:探讨64排螺旋CT定量评估肺动脉栓塞(PE)严重程度的价值.材料和方法:根据临床的严重性和治疗方法的选择,将95例怀疑PE的患者分为3组:严重肺动脉栓塞(SPE)组、非严重肺动脉栓塞(NSPE)组、无肺动脉栓塞(WPE)组.分别阅读各组的CTPA图像,采用CT动脉阻塞指数定量分析栓塞肺动脉的范围及程度,测量舒张期左、右心室短轴最大径及中央肺动脉直径,并观察室间隔形态.结果:与肺动脉严重程度显著相关的因素有:血管阻塞指数(SPE组:74.7;NSPE组:23.0;WPE组:0)、左室短轴最大径(SPE组:31.2mm;NSPE组:35.3mm;WPE组:36.6mm)、右室/左室短轴比(SPE组:1.24;NSPE组:1.04;WPE组:0.93)、中央肺动脉直径(SPE组:31.8mm;NSPE组:28.1mm;WPE组:25.9mm)和1、2级室间隔(SPE组:53.3%,13.3%;NSPE组:16.3%,0%).结论:64排螺旋CT不仅能正确诊断可疑的PE,而且能定量评估PE的严重程度,从而为临床治疗提供更多的信息.     

MR三维成像在高度近视中的应用探讨

目的:采用MR三维成像比较高度近视眼和正视眼的眼球径线和容积,探讨高度近视眼球的径线、容积与屈光度的相关性.方法:研究对象为高度近视眼40例共80眼(患者组)和正视眼40例共80眼(对照组).所有受试者均行MR三维成像检查,测量并比较2组受试者的眼球径线及眼球容积.结果:所有受试者的眼球三维MR图像清晰.高度近视眼球呈不同程度扩张,80眼中57眼可见后巩膜葡萄肿形成.患者组眼球前后径、左右径、上下径及容积分别为(29.38±2.31)、(25.58±1.80)和(24.94±1.49) mm及(10.78±1.91) cm3,对照组分别为(22.98±0.66)、(22.59±0.62)和(23.17±1.04) mm及(7.57±0.70) cm3,两组间差异均有统计学意义(P＜0.05),其中以前后径的差值最大.高度近视眼球的径线、容积与屈光度均呈正相关(r值0.383～0.542,P＜0.001).结论:高度近视眼球的径线及容积较正视眼明显增大.MR三维成像可以清晰显示眼球的形态,高度近视眼球的径线及容积与屈光度间有一定相关性.     

心包隐窝(或窦)的影像学表现

心包为一坚韧的纤维浆膜层,包裹在心脏及大血管根部外面,起着保护和防止它们过度扩张的作用。当脏层心包由心脏表面上升至大血管根部并折返至壁层心包时,完全包绕了升主动脉,覆盖了肺动脉主干及其分支的纵隔内部分,并部分覆盖了上腔静脉。这种发生在大血管之间的心包反折,形成了心包腔内的各种隐窝(recess)或窦(sinus),其中形同管道状者称之为窦,不规则形者称为隐窝。它们包括上隐窝(superiorpericardialrecess)、横窦(transversesinus)、左肺隐窝(leftpulmonicrecess)、斜窦(obliquesinus)、肺静脉隐窝(pulmonaryvenousrecess)及腔静脉后隐…     

急性肺动脉栓塞患者CT阻塞指数与缺氧严重程度的相关性研究

目的:评价急性肺动脉栓塞患者CT阻塞指数(CTOI)与缺氧严重程度的相关性。方法:对24例急性肺动脉栓塞患者(栓塞组)的CT肺动脉造影(CTPA)资料进行回顾性分析,了解肺动脉CTOI与血氧饱和度(SO2)的相关性;以30例无栓塞的患者作为对照组,了解栓塞患者及无栓塞患者的SO2是否有差异;以SO2值94%为标准,将肺动脉栓塞患者分为缺氧组(<94%)和非缺氧组(≥94%),了解引起缺氧的肺动脉栓塞程度。结果:肺动脉栓塞组和对照组的SO2分别为:(89.96±7.68)%和(97.53±5.26)%,肺动脉栓塞组的SO2明显低于对照组(P<0.05);CTOI与SO2之间呈明显负相关(r=0.45,P=0.03),随着CTOI的增加,SO2降低越明显;肺动脉栓塞患者中,非缺氧组CTOI值的95%可信区间为0%～49.20%,缺氧组CTOI值的95%可信区间为39.88%～100%,CTOI值为40%～50%时,患者处于氧供不足的临界状态。结论:急性肺动脉栓塞患者CTOI与缺氧严重程度具有相关性,SO2值低于94%时,提示肺动脉栓塞超过约50%。     

Pericardial "sleeve" recess of right inferior pulmonary vein mimicking adenopathy: computed tomography findings

OBJECTIVE: The purpose of this study was to assess the computed tomography (CT) features of the pericardial "sleeve" recess of the right inferior pulmonary vein misinterpreted as adenopathy. METHOD: Six patients with fluid in the pericardial sleeve recess mistaken for adenopathy were retrospectively identified. The following CT features were assessed: location of fluid in relation to the vein, size, shape, attenuation, and mass effect on the inferior pulmonary vein. RESULTS: The most common presentation was fluid inferior and posterior to the vein. The anterior and posterior components are typically spindle shaped, whereas the superior and inferior components are ovoid. The attenuation values of the fluid ranged from 2-32 H (mean = 13 H). None of the fluid collections exerted mass effect on the right inferior pulmonary vein. CONCLUSION: Although fluid in the right pulmonary venous sleeve pericardial recess can mimic adenopathy, this accumulation has a characteristic appearance, and knowledge of this normal variant is useful in preventing misinterpretation.     

Pericardial sinuses and recesses: findings at electrocardiographically triggered electron-beam CT.

PURPOSE: To evaluate the appearance of the pericardial sinuses and recesses at electrocardiographically triggered electron-beam computed tomography (CT). MATERIALS AND METHODS: Findings in 100 patients without known pericardial disease were reviewed. The patients underwent electron-beam CT of the heart because of suspected coronary arterial disease. Incremental electrocardiographically triggered images were obtained with a 100-msec exposure time and 1.5-mm section thickness after intravenous administration of contrast material. The appearance of the pericardial sinuses and recesses was determined. RESULTS: In each patient, at least one of the sinuses was visible at CT. The transverse and oblique sinuses (or one of their recesses) were depicted in 95 and 89 patients, respectively. The left pulmonic recess was depicted in 81 patients; inferior aortic recess, 80 patients; posterior pericardial recess, 67 patients; left pulmonic vein recess, 60 patients; right pulmonic recess, 51 patients; superior aortic recess, 47 patients; right pulmonic vein recess, 29 patients; and postcaval recess, 23 patients. CONCLUSION: Pericardial sinuses and recesses are frequently depicted on electrocardiographically triggered electron-beam CT images. Knowledge of their locations is helpful in the differentiation of normal pericardium from pericardial effusions and mediastinal processes such as lymph nodes.     

心包隐窝的MRI所见与解剖对照研究

目的：熟悉正常心包隐窝的ＭＲＩ表现，对诊断与鉴别诊断具有重要的临床应用价值。材料与方法：选用胸部断解剖标本４例，心包完整离体心脏标本２例。搜集经ＭＲＩ检查无心包病变患者图像２１例。结合解剖，分析ＭＲＩ上正常心包各隐窝的形态、位置、毗邻关系和出现率。结果：（１）主动脉上窦：ＭＲＩ显示２０例，占９５％，其形态有半圆形、三角形、新月形和不规则形。（２）横窦：７１．４％病例ＭＲＩ显示横窦，呈弧线或菱形腔隙     

CT阻塞指数对肺栓塞的评价及其与D-二聚体相关性分析

目的：探讨肺动脉CT阻塞指数对肺栓塞(PE)高危性的评价及其与D-二聚体之间的关系。方法收集经 CT肺动脉成像(CTPA)及D-二聚体检查的125例PE病例。将其分为高危PE组和非高危PE组,比较分析2组在 CT阻塞指数、D-二聚体、主肺动脉直径间的差异,以及肺动脉 CT 阻塞指数与 D-二聚体、主肺动脉直径之间的相关性(Spearman相关性评价)。结果高危PE组的CT阻塞指数明显高于非高危PE组(P=0.000),高危PE组主肺动脉直径较非高危PE组增粗,差异有统计学意义(P=0.000),而高危PE组和非高危PE组D-二聚体差异无统计学意义(P=0.103)。CT阻塞指数与D-二聚体无相关性(P=0.71)。结论血浆D-二聚体指标可以提示PE,不能评价PE的高危性;肺动脉CT阻塞指数在一定程度上可以反映PE的严重性,其与 D-二聚体间无相关性。     

16层螺旋CT肺血管造影对亚段肺栓塞诊断的成像技术探讨

目的:研究16层螺旋CT肺血管造影在急性肺动脉栓塞(PE)诊断中的应用价值。着重探讨亚段水平周围型肺栓塞的适宜扫描参数及显示方法。方法:应用16层螺旋CT扫描机(GE ligtspeed 16)对临床拟诊肺栓塞的42例患者进行前瞻性研究。依据患者屏气时间长短,设定3组扫描参数。结果:CT诊断肺栓塞31例。中央型22例,周围型9例。3组扫描参数均可清晰显示亚段水平肺动脉栓子。高质量扫描模式肺动脉CTA成像质量最高,常规扫描模式次之,高速扫描模式再次之。结论:16层螺旋CT肺血管造影快速、无创、敏感性、特异性高。选择适宜扫描参数及显示方法,急性肺栓塞诊断可以达到亚段水平。2组常规扫描模式更为适宜PE患者。     

Computed tomography in pulmonary artery sarcoma: distinguishing features from pulmonary embolic disease

OBJECTIVE: The purpose of this study was to present the computed tomography (CT) findings of pulmonary artery sarcoma in 7 patients with a focus on the distinguishing features of pulmonary embolic disease. METHODS: For the 9 years from December 1993 to November 2002, we treated 7 patients with pathologically proven pulmonary artery sarcoma, and during the 2 years from December 2000 to November 2002, we treated 40 patients with acute (n = 33) or chronic (n = 7) pulmonary embolism. In these patients, pulmonary embolism was diagnosed from serial CT or clinical findings. Two chest radiologists, blinded to the diagnoses, independently reviewed the scans of all 47 patients in random order, and the so-documented CT features of sarcoma and pulmonary embolism were compared by using Fisher exact test or the generalized estimating equations test. RESULTS: The two most frequent CT findings of pulmonary artery sarcomas were a low-attenuation filling defect occupying the entire luminal diameter of the main (n = 1) or proximal (n = 6) pulmonary artery and an expansion of any segment of the pulmonary artery with extensive intraluminal filling defect, as observed in six (86%) of 7 patients. In contrast, the finding of a lesion occupying the entire luminal diameter at the level of proximal pulmonary arteries was absent in all 40 patients with pulmonary embolism (P < 0.0001) (kappa = 0.9111). Expansion of the pulmonary arteries was seen in one (3%) of 40 patients with pulmonary embolism (P < 0.0001) (kappa = 0.9108). Extraluminal extension was observed in 5 of 7 (71%) patients with sarcoma, but in no patient with an embolism (P < 0.0001) (kappa = 0.8773). CONCLUSION: CT can help differentiate pulmonary artery sarcoma from pulmonary embolism by indicating a low-attenuation filling defect occupying the entire luminal diameter of the proximal or main pulmonary artery, expansion of the involved arteries, or extraluminal tumor extension.     

肺栓塞的螺旋CT诊断(附15例分析)

目的:探讨螺旋CT对肺栓塞的诊断价值。方法:回顾性分析15例肺栓塞患者CT平扫及增强扫描表现。结果:15例平扫显示片状实变影、磨玻璃影、楔型影、“马赛克”征等。增强扫描中央型肺栓塞12例,周围型肺栓塞3例;中央肺动脉扩张10例;右心室增大7例;支气管动脉显示15例,其中扩张6例;支气管静脉显示并扩张1例;根据肺动脉内栓子形态分4类。结论:CT对肺动脉栓塞具有较高的诊断价值。     

Deep venous thrombosis: detection by using indirect CT venography. The Pulmonary Angiography-Indirect CT Venography Cooperative Group

PURPOSE: To assess the clinical benefits of performing indirect computed tomographic (CT) venography after pulmonary CT angiography to detect deep venous thrombosis (DVT) in patients suspected of having a pulmonary embolism. MATERIALS AND METHODS: The authors prospectively enrolled 541 consecutive patients who underwent pulmonary CT angiography for suspected pulmonary embolism at seven institutions. Using a protocol that optimizes venous enhancement without additional contrast material injection, the authors obtained contiguous images from the pelvis to the popliteal fossa. Ultrasonography (US) also was performed in 116 patients. RESULTS: DVT was found at indirect CT venography in 45 (8%), and pulmonary embolism was found at pulmonary CT angiography in 91 (17%) of 541 patients. Among the 45 patients with DVT, DVT occurred in 16 patients who had no pulmonary embolism at pulmonary CT angiography, which increased the diagnosis of thromboembolic disease by 18%. Among 116 patients who underwent US and indirect CT venography, 15 had DVT at US, and in all 15, DVT also was seen at indirect CT venography. In four additional cases, DVT was seen at only indirect CT venography. CONCLUSION: Among patients suspected to have pulmonary embolism, a substantial number had DVT in the absence of pulmonary embolism. Combined pulmonary CT angiography-indirect CT venography can depict these cases with accuracy comparable to that of US and thus could have a significant effect on patient care.     

Helical CT as preferred imaging modality in the diagnosis of pulmonary embolism]

PURPOSE: We investigated the role of Helical Computed Tomography (CT) as primary screening imaging modality in the diagnosis of pulmonary embolic disease. MATERIAL AND METHODS: We retrospectively reviewed the CT examinations, resulted positive for pulmonary embolism, performed in 134 patients (69 men and 65 women, ranging in age 23-83 years) from June 1998 to June 1999. CT was performed with a helical unit (thickness 3 mm, reconstruction interval 2 mm, pitch 1.5) after intravenous contrast agent (120 mL) rapid infusion (4 mL/s, 15s acquisition delay from bolus starting) and using a power injector. The spiral acquisition was performed from the apex of the pulmonary trunk to the diaphragm. Pulmonary embolism was considered as complete when a filling defect was present in a main pulmonary artery, as moderate when a filling defect was observed in an interlobar pulmonary artery and as very small when a filling defect was identified in a segmental pulmonary artery. RESULTS: Helical CT allowed us to identify the presence of a filling defect in the main pulmonary artery in 60.4% of cases (complete pulmonary embolism), in an interlobar pulmonary artery in 27.6% of cases (moderate pulmonary embolism) and in a segmental pulmonary artery in 11.9% of cases (very small pulmonary embolism). At helical CT study, pulmonary embolus was identified as complete filling defect (92.5% of cases), thromboembolic mass floating freely in the lumen (28.3%) and partial filling defect (19.4%). Pleural effusion and pulmonary infarction were associated in 46.2% and 20.1% respectively. DISCUSSION AND CONCLUSIONS: Pulmonary embolic disease continues to be a major cause of morbidity and mortality. The clinical diagnosis of pulmonary embolism remains an important challenge: among the different imaging modalities, contrast-enhanced helical CT can be used as primary screening imaging modality in the diagnosis of pulmonary embolism, allowing us to detect the presence of pulmonary embolus in the main, lobar and segmental artery, as demonstrated in our experience.     

Clinical validity of helical CT being interpreted as negative for pulmonary embolism: implications for patient treatment.

OBJECTIVE: The purpose of our study was to assess the clinical usefulness of helical CT findings that are interpreted as negative for pulmonary embolism. MATERIALS AND METHODS: One hundred twenty-six patients underwent 132 helical CT examinations and 352 patients underwent ventilation-perfusion scanning for suspected acute pulmonary embolism over a 17-month period at a single institution. Findings from clinical follow-up at a minimum of 6 months were assessed, with a special focus on the presence of recurrent thromboembolism and mortality in 78 consecutive patients in whom helical CT findings were interpreted as negative for pulmonary embolism and anticoagulant therapy was not administered (group I). During the same 17-month period, 46 patients underwent ventilation-perfusion scanning that was interpreted as normal (group II), and 132 patients underwent ventilation-perfusion scanning that was interpreted as showing a very low to low probability for pulmonary embolism (group III). Patients in groups II and III did not undergo helical CT or pulmonary angiography and did not receive anticoagulant therapy. However, clinical follow-up was solicited. Patients from groups II and III were used as control subjects. RESULTS: Nine patients in group I died, one of whom was found to have a microscopic pulmonary embolism at autopsy. In group II, four patients died, none of whom were shown to have a missed or recurrent pulmonary embolism. Of the 18 patients in group III who died, three had a recurrent or missed pulmonary embolism (mean interval, 9 days), and two were found to have deep vein thrombosis on sonography of the leg (mean interval, 12 weeks). Negative predictive values for helical CT, normal lung scanning, and low-probability ventilation-perfusion scanning were 99%, 100%, and 96%, respectively (p = .299). CT provided either additional findings or an alternate diagnosis in 42 (53.8%) of the 78 patients in whom helical CT findings had been interpreted as negative for pulmonary embolism. CONCLUSION: A helical CT scan can be effectively used to rule out clinically significant pulmonary emboli and may prevent further investigation or unnecessary treatment of most patients.