Right ventricular dysfunction secondary to acute massive pulmonary embolism detected by helical computed tomography pulmonary angiography

OBJECTIVE: Acute massive pulmonary embolism causes abrupt pulmonary arterial hypertension and right ventricular dysfunction (RVD). Patients with RVD have a worse prognosis than those with normal right ventricular function. Consequently, recognizing the RVD at the time of pulmonary embolism is useful for risk stratification and enables more aggressive therapy. The study compared the accuracy of helical computed tomographic (CT) scans with echocardiography in the detecting of RVD in patients with acute massive pulmonary embolism. MATERIALS AND METHODS: Specifically, this work reviewed the CT pulmonary angiograms of 14 patients who were positive for acute massive pulmonary embolism during a 52-month period. CT scans were reviewed for findings indicating RVD. Scans were considered positive for RVD if the right ventricle was dilated or there was leftward shift of the interventricular septum. Echocardiographic reports serving as the reference standard for the diagnosis of RVD were also reviewed. CT study results were then correlated with echocardiography results. RESULTS: Among 14 patients with massive pulmonary embolism, echocardiography identified 12 patients having RVD, whereas the remaining two patients were negative for RVD. Meanwhile, CT correctly identified 11 of 12 patients as having RVD, and was negative for RVD in the remaining 3 patients. Correlated with echocardiography, CT scan for RVD detection had a sensitivity of 91.6% and a specificity of 100%. CONCLUSIONS: CT can accurately detect RVD in patients with acute massive pulmonary embolism. However, this result requires confirmation using a larger prospective cohort study.     

Detection of central pulmonary embolism on computed tomography densitometry images before computed tomography pulmonary angiography

OBJECTIVE: The purpose of this article is to describe the imaging findings of acute central pulmonary embolism on computed tomography (CT) densitometry images performed before contrast-enhanced CT pulmonary angiography. METHODS: A retrospective review was conducted of reports from all CT pulmonary angiograms performed at our institution, and cases of acute central pulmonary embolism, defined as those with clot in the main, left, or right pulmonary arteries, were identified. Images of positive studies were reviewed on a picture archiving and communications system (PACS) workstation. RESULTS: A total of 1282 CT pulmonary angiograms were obtained for evaluation of possible acute pulmonary embolism, and 1 combined CT aortogram and pulmonary angiogram was performed for aortic dissection and acute pulmonary embolism. Two hundred fourteen (16.7%) examinations positive for acute pulmonary embolism were identified, 26 (12.1%, 2.0% of total examinations) of which had central clots. Of the 26 patients with central acute pulmonary embolism, 12 (46.1%, 5.6% of all positive studies and 0.9% of all CT pulmonary angiograms) had clots that were visible on the densitometry images. CONCLUSION: Although an uncommon finding, acute central pulmonary embolism can be detected on CT densitometry performed to optimize opacification of the pulmonary arteries for CT pulmonary angiography and may prove useful in selected clinical situations.     

Fatal paradoxical pulmonary air embolism complicating percutaneous computed tomography-guided needle biopsy of the lung

A 63-year-old man with left upper zone haziness on chest X-ray and an infiltrative lesion with a pleural mass in the left upper lobe on CT scan was scheduled for CT-guided percutaneous trans-thoracic needle biopsy. During the procedure, the patient had massive haemoptysis and cardiorespiratory arrest and could not be revived. Post-mortem CT showed air in the right atrium, right ventricle, pulmonary artery and also in the left atrium and aorta. A discussion on paradoxical air embolism following percutaneous trans-thoracic needle biopsy is presented.     

64层螺旋CT肺血管造影在肺栓塞诊疗中的应用价值

目的 探讨64层螺旋CT在肺栓塞诊断及治疗中的指导作用。方法 63例患者均行64层螺旋CT肺血管造影(CTPA),并进行多种形式的图像重建结合轴位图像分析。结果 64层螺旋CTPA对63例患者肺动脉各级管腔内的栓子均明确显示,共累及肺动脉303支;图像分析结果伞部显示肺栓塞的直接征象为:主肺动脉和(或)左右肺叶、段、亚段血管腔内充盈缺损和血管阻塞;部分显示肺栓塞的间接征象为:马赛克征、右心房及右心室肥厚及扩张、肺动脉扩张、胸腔积液、肺不张及实变(肺梗死)等。62例患者经溶栓治疗后复查CTPA,其中,栓子完全消失者47例,栓子明显缩小者11例,溶栓治疗效果差者3例,考虑为慢性肺栓塞。结论 64层螺旋CTPA是临床最有效的诊断肺栓塞及溶栓后疗效评价的无创性方法之一。     

64层螺旋CT肺血管造影在肺栓塞诊疗中的应用价值

目的 探讨64层螺旋CT在肺栓塞诊断及治疗中的指导作用.方法 63例患者均行64层螺旋CT肺血管造影(CTPA),并进行多种形式的图像重建结合轴位图像分析.结果 64层螺旋CTPA对63例患者肺动脉各级管腔内的栓子均明确显示,共累及肺动脉303支;图像分析结果伞部显示肺栓塞的直接征象为:主肺动脉和(或)左右肺叶、段、亚段血管腔内充盈缺损和血管阻塞;部分显示肺栓塞的间接征象为:马赛克征、右心房及右心室肥厚及扩张、肺动脉扩张、胸腔积液、肺不张及实变(肺梗死)等.62例患者经溶栓治疗后复查CTPA,其中,栓子完全消失者47例,栓子明显缩小者11例,溶栓治疗效果差者3例,考虑为慢性肺栓塞.结论 64层螺旋CTPA是临床最有效的诊断肺栓塞及溶栓后疗效评价的无创性方法之一.     

Role of helical CT in detecting right ventricular dysfunction secondary to acute pulmonary embolism

OBJECTIVE: The purpose of this study was to evaluate the role of helical CT in detecting right ventricular dysfunction (RVD) after acute pulmonary embolism (PE). METHODS: This was a retrospective study consisting of 25 patients with CT scans positive for acute pulmonary embolism who had either follow-up echocardiography (23 patients) or pulmonary angiography (2 patients). CT scans were reviewed for findings suggestive of RVD. Scans were considered positive for RVD if the right ventricle (RV) was dilated or if the interventricular septum was deviated towards the left ventricle. Results were then correlated with the results of echocardiography or pulmonary angiography to estimate the sensitivity and specificity of CT in detecting RVD associated with PE. RESULTS: Within this group of 25 patients with PE, CT demonstrated sensitivity of 78% (7/9), specificity of 100% (16/16), and positive predictive value of 100% (7/7) in detection of RVD. CONCLUSION: CT may be useful in detecting RVD in patients with acute PE.     

Compression of the Right Pulmonary Artery by a Massive Descending Aortic Aneurysm Causing Bilateral Perfusion Defects on Pulmonary Scintigraphy

A 67-year-old woman, who presented with a 2 month history of dyspnea, had a ventilation and perfusion lung scan that showed absent perfusion of the entire right lung with normal ventilation, as well as a rounded matched defect in the left lower lung adjacent to midline, suspicious for an aortic aneurysm or dissection. CT pulmonary angiography revealed a massive descending aortic aneurysm compressing the right pulmonary artery as well as the left lung parenchyma, accounting for the bilateral perfusion scan defects. We present the Xe-133 ventilation, Tc-99m MAA perfusion and CT pulmonary angiography imaging findings of this rare case.     

20例肺动脉栓塞螺旋CT增强扫描的影像分析

目的:研究肺动脉栓塞螺旋CT增强扫描的影像表现,充分认识肺栓塞的CT征象,提高肺栓塞的诊断水平。方法:共20例,男14例,女6例。使用东芝Xpress/SXCT扫描机作造影增强螺旋CT扫描。统计分析肺叶及肺叶以上肺动脉栓塞CT增强的综合表现。结果:肺动脉栓塞原发病以下肢深静脉血栓形成最为多见,有7例。下肢深静脉血栓有2例是由桑拿浴引起。将肺栓塞的程度分为轻度栓塞、中度栓塞、重度栓塞和完全栓塞。轻度栓塞为栓塞面占肺动脉管径<30%;中度栓塞为栓塞面30%～50%;重度栓塞为栓塞面>50%,周围仍见对比剂显影或通过;完全栓塞的栓塞面周边无对比剂显影通过。肺动脉栓塞直接征象是栓塞部位不强化,呈充盈缺损改变。此外,还见9个继发征象:肺动脉总干增宽,右心室和右心房增大。肺叶透亮度增加,肺血管纹理稀疏、细小。肺静脉变小,基底静脉变小,边缘不整,呈干藤样改变。左心房变小。左心室亦变小,室间隔向左后移位。肺组织实变,呈三角形。胸腔积液和心包积液。结论:肺动脉栓塞胸部螺旋CT增强扫描的表现是一组综合征象,笔者称为肺栓塞10联征。充分认识10联征,能大大提高肺栓塞的诊断水平。肺动脉栓塞有多种原发病,以下肢深静脉血栓形成最多见,桑拿浴可引起下肢深静脉血栓,可能是肺栓塞的一个诱因。     

Pulmonary Bone Cement Embolism: CT Angiographic Evaluation with Material Decomposition Using Gemstone Spectral Imaging

We report a case of pulmonary bone cement embolism in a female who presented with dyspnea following multiple sessions of vertebroplasty. She underwent spectral CT pulmonary angiography and the diagnosis was made based on enhanced visualization of radiopaque cement material in the pulmonary arteries and a corresponding decrease in the parenchymal iodine content. Here, we describe the CT angiography findings of bone cement embolism with special emphasis on the potential benefits of spectral imaging, providing additional information on the material composition.     

慢性心力衰竭的CT表现

目的:探讨慢性心力衰竭的CT表现。材料和方法:回顾性分析28例慢性心力衰竭的CT表现。结果:左心室增大16例、右心室增大8例、左心房增大6例、右心房增大4例,左、右心房增大3例,肺水肿24例、胸腔积液25例、肺动脉扩张3例、升主动脉扩张5例和冠状动脉钙化7例。左心衰CT示肺水肿、左心室扩大和胸腔积液。右心衰CT示右心室扩大、主肺动脉扩张和胸腔积液。全心衰竭CT示左右心室扩大,肺水肿和双侧胸腔积液。结论:CT可显示心脏各房室扩大、大动脉扩张、肺水肿、胸腔和心包积液以及冠状动脉钙化,为诊断原发心脏疾病及慢性心力衰竭提供重要依据。     

Clinical usefulness of imaging performed after CT angiography that was negative for pulmonary embolus in a high-risk oncologic population

OBJECTIVE: The purpose of our study was to determine the prevalence and types of additional imaging examinations that were performed, and whether anticoagulation therapy was started or continued, after CT angiography showed no pulmonary embolus in a high-risk oncologic population. MATERIALS AND METHODS: We reviewed the radiology report for each CT angiogram that was obtained for clinically suspected pulmonary embolism at our institution (a tertiary cancer center) during a 25-month period. The radiology information system was then searched for any additional confirmatory radiologic examinations performed within 2 days after a negative finding on CT angiography. Medical records were reviewed to determine whether anticoagulation therapy was started or continued despite a negative finding on CT angiography. RESULTS: Two hundred seventy-six CT angiograms were obtained in 260 oncology patients who were clinically suspected of having pulmonary embolism. The findings from 203 CT angiograms (74%) were interpreted as negative; 56 (20%), as positive; and 17 (6%), as equivocal for pulmonary embolism. Fifty-eight patients (21%) with negative findings on CT angiography subsequently underwent additional imaging, the results of which were potentially clinically important in 6% of the patients. Six patients began to receive and two continued to undergo anticoagulation therapy despite negative findings on CT angiography; three of the six patients received anticoagulation for new-onset atrial fibrillation. CONCLUSION: Negative results of CT angiography for pulmonary embolism did not deter referring physicians from ordering other confirmatory imaging tests in 21% of patients in a high-risk oncologic population. Those additional tests rarely revealed results that might have been clinically important.     

Valor pronóstico de la tomografía computarizada en la tromboembolia pulmonar aguda

In addition to being the standard reference for the diagnosis of acute pulmonary thromboembolism, CT angiography of the pulmonary arteries can also provide valuable information about the patient's prognosis. Although which imaging findings are useful for prognosis remains controversial, signs of right ventricular dysfunction on CT are now included in clinical algorithms for the management of pulmonary thromboembolism. However, the optimal method for obtaining these measurements while maintaining a balance between the ease of use necessary to include their evaluation in our daily activity and the loss of precision in its predictive capacity remains to be determined. Moreover, other variables associated with pulmonary thromboembolism that often go unobserved can complement the prognostic information we can offer to clinicians. This review aims to clarify some of the more controversial aspects related to the prognostic value of CT in patients with pulmonary embolisms according to the available evidence. Knowing which variables are becoming more important in the prognosis, how to detect them, and why it is important to include them in our reports will help improve the management of patients with pulmonary embolism.     

MRI of the pulmonary veins: comparison between 3D MR angiography and T1-weighted spin echo

OBJECTIVE: The purpose was to determine the ability of three-dimensional (3D) magnetic resonance (MR) angiography to depict normal pulmonary veins in comparison with spin-echo MR imaging. MATERIALS AND METHODS: MR imaging of 40 patients with cardiovascular disease were reviewed. Patients with known pulmonary venous abnormalities were excluded. Using a standard GE 1.5-T magnet, axial T1-weighted spin-echo 5-mm-thick contiguous slices and 3D MR angiography (contiguous slice thickness of 2.5-3.5 mm, 20-30 c.c. of gadolinium bolus at 1-1.5 c.c./sec, 32-43-second breath-hold, coronal and sagittal plane acquisition) were evaluated retrospectively on separate occasions by two experienced radiologists. Multiplanar imaging projection was used for the identification of pulmonary veins. Each lung was considered to have two drainage veins: a superior vein and an inferior vein. Identification of a pulmonary vein was made by visualizing a connection with the left atrium. RESULTS: 143 pulmonary veins (87.5% +/-5.2) were identified at the level of the left atrium on T1-weighted spin-echo images, and 157 (98.1% +/-1.9) were identified on 3D MR angiography (p<0.01). Overall we identified by T -weighted spin-echo imaging 36 right upper, 38 right lower, 27 left upper, and 38 left lower pulmonary veins. By 3D MR angiography, we identified 38 right upper, 40 right lower, 39 left upper, and 40 left lower pulmonary veins. All four pulmonary veins were detected in 22 patients on spin-echo imaging (55%) and in 37 patients (92.5%) on 3D MR angiography (chi = 3.81, p<0.05). CONCLUSION: A significant difference is demonstrated between 3D MR angiography and spin-echo MR imaging in identifying normal pulmonary veins. MR angiography provides a complete view of normal pulmonary venous anatomy and could be a valuable tool for the assessment of abnormal pulmonary venous drainage.     

Pulmonary embolism, right ventricular strain, and intracardiac thrombus-in-transit: Evaluation using comprehensive cardiothoracic computed tomography

A 67-year-old woman presented with symptoms of exertional chest discomfort and dyspnea that had been progressive over the past few days. Her initial evaluation was significant of a mildly elevated troponin-T level and T-wave inversion in leads V₁-V₂ on an electrocardiogram (ECG). Initial suspicion was for acute coronary syndrome. However, a transthoracic echocardiogram showed normal left ventricular systolic function, moderate right ventricular enlargement with moderate decrease in systolic function, possible left atrial mass or thrombus, and a possible right atrial mass or thrombus versus a prominent Chiari network. ECG-gated comprehensive cardiothoracic computed tomography (CT) with a 64-slice multidetector CT was done to assess for pulmonary embolism or acute coronary syndrome and to further evaluate the possible right and left atrial masses. This showed large bilateral pulmonary embolism, interatrial thrombus in transit through a patent foramen ovale, and minimal coronary atherosclerosis. Dynamic imaging showed right ventricular enlargement with severe systolic dysfunction. The patient underwent successful pulmonary thromboembolectomy, removal of intracardiac thrombus, and closure of patent foramen ovale.     

Role of a quantitative D-dimer assay in determining the need for CT angiography of acute pulmonary embolism

OBJECTIVE: Our goal was to use the results of a quantitative D-dimer assay to determine the need for pulmonary CT angiography in patients suspected of having acute pulmonary embolism. MATERIALS AND METHODS: From July 2001 to December 2002, 755 patients underwent pulmonary CT angiography for the evaluation of acute pulmonary embolism. A rapid, fully automated quantitative D-dimer assay was obtained in more than half the patients. The electronic medical records of the patients were subsequently reviewed to analyze the negative predictive value of the D-dimer assay in the diagnostic workup of acute pulmonary embolism and to determine the outcome of the patients who had negative findings on both D-dimer assay and pulmonary CT angiography at 3-month follow-up. RESULTS: Of the 755 patients who underwent pulmonary CT angiography, 666 (88.2%) had negative findings, 73 (9.7%) had positive findings, and 16 (2.1%) were indeterminate. A total of 426 patients underwent both pulmonary CT angiography and D-dimer level evaluation, and 84 of these had negative findings (< 0.4 microg/mL) on D-dimer assay. Eighty-two of the 84 patients with negative findings on D-dimer assay had negative findings on pulmonary CT angiography; two were indeterminate and both subsequently had low-probability ventilation-perfusion studies. Among patients with positive D-dimer assays, no one with a level between 0.4 and 1.0 microg/mL had pulmonary CT angiography with findings positive for pulmonary embolism. CONCLUSION: A quantitative D-dimer assay was effective in excluding the need for pulmonary CT angiography and had high negative predictive value when the D-dimer level was less than 1.0 microg/mL.     

Reformatted Four-Chamber and Short-Axis Views of the Heart Using Thin Section (</=2 mm) MDCT Images

RATIONALE AND OBJECTIVES: In cardiovascular computed tomography (CT), thin collimation results in a large number of images per examination. Moreover, interpretation relies on multiplanar reformatted images. MATERIALS AND METHODS: Although many strategies for approaching cardiac reformations have been described, as CT use increases, so does the importance of simple and reproducible postprocessing algorithms. The clinical importance of reformations has recently extended beyond the left ventricle to include the right ventricular in patients with pulmonary embolism. RESULTS: This work illustrates an algorithm to reformat two of the most important views in cardiovascular CT: the four-chamber and short axis views. CONCLUSIONS: The illustration is performed in the context of two cardiovascular examinations: cardiac CT and CT pulmonary angiography.     

New CT index to quantify arterial obstruction in pulmonary embolism: comparison with angiographic index and echocardiography

OBJECTIVE: This study was designed to define and evaluate a specific index to quantify arterial obstruction with helical CT in acute pulmonary embolism. MATERIALS AND METHODS: Fifty-four patients (mean age, 56 years) with proven pulmonary emboli among 158 consecutive patients, who had undergone both CT and pulmonary angiography for clinically suspected pulmonary embolism, were eligible for the study. The CT obstruction index was defined as (n. d) (n, value of the proximal clot site, equal to the number of segmental branches arising distally; d, degree of obstruction scored as partial obstruction [value of 1] or total obstruction [value of 2]). We compared the CT obstruction index with pulmonary arterial obstruction on angiography (assessed by the Miller index), using linear regression, and correlated it with findings on echocardiography. Interobserver variability was determined for both CT and pulmonary angiography indexes. RESULTS: The CT obstruction index (29% +/- 17%) and the Miller index (43% +/- 25%) were well correlated (r = 0.867, p < 0.0001) with an excellent concordance between investigators for both the CT index (r = 0.944, p < 0.0001) and the Miller index (r = 0.904, p < 0.0001). A CT obstruction index greater than 40% identified more than 90% of patients with right ventricular dilatation. CONCLUSION: The degree of arterial obstruction in pulmonary embolism may be quantified by a specific CT index that appears reproducible and highly correlated to the previously described index with pulmonary angiography. Further evaluations are needed to investigate the usefulness of the CT obstruction index for stratification of patient risk and determining therapeutic options.     

CT imaging of acute pulmonary embolism

CT pulmonary angiography (CTPA) has become the de facto clinical "gold standard" for the diagnosis of acute pulmonary embolism (PE) and has replaced catheter pulmonary angiography and ventilation-perfusion scintigraphy as the first-line imaging method. The factors underlying this algorithmic change are rooted in the high-sensitivity and specificity, cost-effectiveness, and 24-hour availability of CTPA. In addition, CTPA is superior to other imaging methods in its ability to diagnose and exclude, in a single examination, a variety of diseases that mimic the symptoms of PE. This article reviews the current role of CTPA in the diagnosis of acute PE as well as more recent developments, such as the use of CT parameters of right ventricular dysfunction for patient prognostication and the assessment of lung perfusion with CT.     

Dual-energy CT pulmonary angiography in patients with suspected pulmonary embolism: value for the detection and quantification of pulmonary venous congestion

Objective:

To evaluate if vascular and pulmonary parenchymal enhancement values in dual-energy (DE) CT pulmonary angiography (CTPA) can suggest the diagnosis of pulmonary congestion.

Methods:

DE-CTPA images of 90 out of 1321 patients negative for pulmonary embolism showed signs of congestive heart failure. We measured DE-derived pulmonary parenchymal [perfused blood volume (PBV)], pulmonary artery (PA) and left atrium (LA) enhancement values in these patients and in 142 control patients. Enhancement values were compared between the populations and correlated with serum values of B-type natriuretic peptide (BNP) and proBNP, where available.

Results:

No significant difference of PBV but significant differences of mean PA and LA enhancement and individual enhancement differences (PA − LA) were found between the populations. PA − LA was higher in patients with elevated BNP and proBNP and was positively correlated with these values. Receiver operating characteristic analysis revealed a moderate discriminatory power of the PA − LA difference for the presence of cardiac biomarker elevations.

Conclusion:

PBV in DE-CTPA is not altered in patients with signs of congestive heart failure. However, differences in enhancement values in the pre- and post-pulmonary vessels were found in comparison with the control population.

Advances in knowledge:

Altered pulmonary vascular haemodynamics in pulmonary venous congestion are not reflected in dual-energy-derived PBV maps. In the diagnosis of left heart failure in patients with chest pain and dyspnoea, density measurements in the pulmonary artery and in the left atrium in CTPA images may be a helpful diagnostic tool.In the diagnostic algorithms for patients with acute dyspnoea, CT pulmonary angiography (CTPA) plays a major role, specifically in cases when pulmonary embolism (PE) is suspected. Whenever no PE can be detected, radiologists face the challenge to detect alternative pathological thoracic findings. An undiagnosed acute or chronic left heart failure with pulmonary congestion can be an alternative cause of acute dyspnoea. Although there are some direct and indirect CT criteria that suggest the diagnosis of congestive heart failure with pulmonary venous hypertension (e.g. dilated pulmonary veins with a blurry appearance of the vessel walls, thickening of the interlobular septal lines, ground-glass opacities/alveolar oedema, pleural effusions and an enlargement of the left atrium and/or ventricle), the diagnosis of left heart failure on the basis of CT findings is often equivocal and rather rater dependent. For suspected left heart failure, chest radiography represents the primary diagnostic tool rather than CT. Still, if CTPA is performed in chest pain workup, an improved, more objective diagnosis of congestive heart failure would be desirable.Dual-energy CTPA (DE-CTPA) can quantify the iodine-related pulmonary beam absorption and thus allow an automated, reader-independent, software-based quantification of the pulmonary content of iodinated contrast material [termed “perfused blood volume” (PBV)].¹ Based on the assumption that an impaired left heart function leads to variances in the pulmonary blood content and in the dynamics of the pulmonary passage of the contrast bolus, we tried to find out if measured absorption values in iodine-enhanced DE-CTPA, that is, DE-based pulmonary PBV values as well as density measurements in the pulmonary trunk and the left atrium, can be helpful in the diagnosis of pulmonary congestion.For this purpose, we retrospectively compared pulmonary parenchymal, pulmonary artery (PA) and left atrium (LA) enhancement values in patients with CT signs of pulmonary congestion with those from patients with no detectable cardiopulmonary pathologies in DE-CTPA and correlated those values with serum levels of established left heart insufficiency markers [cardiac peptides: B-type natriuretic peptide (BNP) and proBNP].     

多层螺旋CT在肺动脉栓塞诊断中的应用(附27例报告)

目的:探讨多层螺旋CT肺动脉成像(CTPA)对肺动脉栓塞的诊断价值.方法:对27例经MSCT确诊肺动脉栓塞患者进行回顾性分析.结果:多发肺动脉栓塞18例,其中双侧多发15例,左侧多发1例,右侧多发2例;单发9例,其中肺动脉干4例,叶动脉1例,段动脉4例.肺动脉栓塞的直接征象包括肺动脉主干或其分支的充盈缺损及肺动脉段面细小及管腔内不均匀密度减低;间接征象可以有肺内"马赛克征"、楔形影或索条状影,胸腔积液或胸膜肥厚.结论:CTPA对肺动脉栓塞的检查是一种价格便宜,无创伤的检查,诊断结果可靠,可作为急诊和普通临床工作中怀疑本病时首选的影像学检查方法.