Fetal radiation dose from CT pulmonary angiography in late pregnancy: a phantom study

Pulmonary embolism (PE) is the leading direct cause of maternal mortality in the UK. Accurate diagnosis is important but, even though CT pulmonary angiography (CTPA) is the recommended imaging modality for PE in the general population, there is limited guidance for pregnant patients. Knowledge of the radiation doses to both the mother and the fetus is therefore important in the justification of CTPA in this situation. Dose measurements were made on three helical CT scanners, with an anthropomorphic phantom representing the chest and abdomen in late gestation. Estimated fetal doses from CT scans of the maternal chest were in the range of 60-230 microGy. Fetal dose reduction strategies (mA modulation, shielding with a lead coat, and a 5 cm shorter scan length) were investigated. These reduced the fetal dose by 10%, 35% and 56%, respectively. Fetal doses from a scan projection radiograph (SPR) of the maternal chest were insignificant when compared with the dose from a CT scan. However, if the SPR was not stopped before the "fetus" was directly irradiated, the dose measured on one scanner was 20 microGy.     

Female breast radiation exposure during CT pulmonary angiography

OBJECTIVE: The objective of our study was to estimate the effective radiation dose to the female breast during CT pulmonary angiography compared with other routine diagnostic imaging techniques. MATERIALS AND METHODS: We retrospectively reviewed the demographic data of patients who underwent CT pulmonary angiography between May 2000 and December 2002, the diagnostic yield of those studies, and the estimated effective radiation dose to the breast incurred during CT. The estimated effective radiation dose was calculated using the ImPACT CT (Impact Performance Assessment of CT) dosimetry calculator and the CT dose index (CTDI) and was compared with the average glandular dose for two-view screening mammography. RESULTS: During the study period, 1,325 CT pulmonary angiograms were obtained. Sixty percent (797) of the scans were obtained on female patients. The mean age of scanned females was 52.5 years (range, 15-93 years). Of the studies performed in females, 401 (50.31%) were negative, 151 (18.95%) were nondiagnostic, and 245 (30.74%) were positive for pulmonary thromboembolism. The calculated effective minimum dose to the breast of an average 60-kg woman during CT was 2.0 rad (20 mGy) per breast compared with an average glandular dose of 0.300 rad (3 mGy) for standard two-view screening mammography. CONCLUSION: CT pulmonary angiography delivers a minimum radiation dose of 2.0 rad (20 mGy) to the breasts of an average-sized woman. This greatly exceeds the American College of Radiology recommendation of < or = 0.300 rad (3 mGy) or less for standard two-view mammography. The potential latent carcinogenic effects of such radiation exposure at this time remain unknown. We encourage the judicious use of CT pulmonary angiography and lower doses and nonionizing radiation alternatives when appropriate.     

Reducing radiation exposure from survey CT scans

OBJECTIVE: The purpose of this study was to focus attention on the technique factors commonly used in survey CT scans (e.g., scout, topogram, or pilot scans) to measure the radiation exposure from typical survey CT scans, to compare their exposure to that of typical chest radiographs, and to explore methods for radiation exposure reduction. MATERIALS AND METHODS: The default survey CT scans on 21 CT scanners, representing three different vendors and 11 different models, were investigated. Exposure measurements were obtained with an ion chamber at isocenter and adjusted to be consistent with standard chest radiographic exposure measurement methods (single posterior-anterior projection). These entrance exposures were compared with those of typical chest radiographs, for which the mean for average-sized adults is 16 mR (4.1 x 10(-6) C/kg). RESULTS: The entrance exposures of the default survey CT scans ranged from 3.2 to 74.7 mR (0.8 to 19.3 x 10(-6) C/kg), which is equivalent to approximately 0.2 to 4.7 chest radiographs. By changing the default scan parameters from 120 kVp to 80 kVp and the tube position from 0 degrees (tube above table) to 180 degrees (tube below table), the entrance exposure for the survey CT scan was reduced to less than that of one chest radiograph for all CT scanners. CONCLUSION: For institutions at which the interpreting radiologists do not rely heavily on the appearance of the survey CT image, we recommend adjusting the technique parameters (kilovoltage and X-ray tube position) to decrease radiation exposure, especially for vulnerable patient populations such as children and young women.     

A prospective,comparative study of ventilation-perfusion scintigraphy and clinical evaluation versus digital subtraction angiography in acute pulmonary thromboembolism

Patients with symptoms of acute pulmonary thromboembolism (APE) of short duration were investigated with digital subtraction angiography (DSA) and ventilation/perfusion lung scintigraphy (V/Q scan), and a standardised clinical evaluation was performed. Forty-six angiograms (96%) were diagnostic at the segmental level and were used as reference. In all V/Q scans classified as normal or of high probability for APE, a complete agreement with DSA was found. In scan categories with low or intermediate probability, where the incidence of APE was 32%, there was considerable inter-observer disagreement. Clinical assessment alone was of limited value, but in patients with low clinical suspicion no APE was found. The results indicate that normal and high probability V/Q scans are very reliable for excluding and identifying APE, respectively, but also that fairly large APE cannot be diagnosed with lung scanning. Subdivision of V/Q scans into more than three categories (normal, high probability and inconclusive) seems to be of no practical value. Using a pulsed sequence technique, high frame rate and central injection, DSA is a valuable clinical tool for diagnosing APE down to the segmental level. Correspondence to: B. Hedlund     

肺灌注显像与磁共振肺血管成像对急性肺栓塞诊断价值的比较研究

目的 对比研究单光子发射计算机断层显像(SPECT)和磁共振肺血管成像(MRPA)评估对急性肺栓塞(APE)的临床诊断价值.方法 检索Cochrane图书馆、Medline数据库、Springerlink数据库及ovid循证医学数据库2004-2013年的英文文献,以及中国期刊网包括中国知网、万方医学数据库以及Google学术搜索2004 2013年的中文文献,按照cochrane协作网推荐的诊断实验纳入标准筛选文献,提取纳入研究的诊断信息(真阳性值、假阳性值、真阴性值、假阴性值).采用Stata12软件和Meta-disc1.4软件对纳入文献行统计学处理,包括异质性检验,计算灵敏度和特异度及其95％可信区间,并选择相应的效应模型予以加权定量合并,绘制汇总工作特征曲线(SROC),最后行敏感性分析.结果 按照纳入标准共获取文献16篇,其中纳入SPECT诊断肺栓塞(PE)文献9篇,MRPA文献7篇.都满足诊断性研究质量评价工具(QUADAS) 14条目中的10条以上,按照随机效应模型对纳入文献进行汇总分析.结果显示,以多排CT(MDCT)为金标准,SPECT诊断PE的敏感度、特异度和95％可信区间分别为0.86(0.83～0.88)和0.94(0.93～0.95),MRPA为0.85(0.80～0.89)和0.98(0.97～0.99),SROC曲线下面积(AUC)分别为96％和99％.结论 基于CTPA诊断PE为辐射暴露检查方法,汇总分析非辐射暴露检查SPECT和MRPA评估PE的诊断价值,二者诊断PE的灵敏度及特异度均很高,其诊断价值无明显差异,SPECT和MRPA检查方法可作为PE诊断辐射暴露禁忌的重要替代检查.     

Prospectively ECG gated CT pulmonary angiography versus helical ungated CT pulmonary angiography: impact on cardiac related motion artifacts and patient radiation dose

Objective

To compare prospectively ECG gated CT pulmonary angiography (CTPA) with routine helical ungated CTPA for cardiac related motion artifacts and patient radiation dose.

Subjects and methods

Twenty patients with signs and symptoms suspicious for pulmonary embolism and who had a heart rate below 85 were scanned with prospectively ECG gated CTPA. These gated exams were matched for several clinical parameters to exams from twenty similar clinical patients scanned with routine ungated helical CTPA. Three blinded independent reviewers subjectively evaluated all exams for overall pulmonary artery enhancement and for several cardiac motion related artifacts, including vessel blurring, intravascular shading, and double line. Reviewers also measured pulmonary artery intravascular density and image noise. Patient radiation dose for each technique was compared. Fourteen clinical prospectively ECG gated CTPA exams from a second institution were evaluated for the same parameters.

Results

Prospectively ECG gated CTPA resulted in significantly decreased motion-related image artifact scores in lung segments adjacent to the heart compared to ungated CTPA. Measured image noise was not significantly different between the two types of CTPA exams. Effective dose was 28% less for prospectively ECG gated CTPA (4.9 mSv versus 6.8 mSv, p = 0.02). Similar results were found in the prospectively ECG gated exams from the second institution.

Conclusion

Compared to routine helical ungated CTPA, prospectively ECG gated CTPA may result in less cardiac related motion artifact in lung segments adjacent to the heart and significantly less patient radiation dose.     

Multiphase CT angiography versus single-phase CT angiography: comparison of image quality and radiation dose

BACKGROUND AND PURPOSE: Conventional CT angiography (CTA) is acquired during only a short interval in the arterial phase, which limits its ability to evaluate the cerebral circulation. Our aim was to compare the image quality and radiation dose of conventional single-phase CTA (SP-CTA) with a multiphase CTA (MP-CTA) algorithm reconstructed from a perfusion CT (PCT) dataset.MATERIALS AND METHODS: Fifty consecutive patients undergoing head CTA and PCT in 1 examination were enrolled. The PCT dataset was obtained with 40.0-mm-detector coverage, 5.0-mm axial thickness, 80 kilovolt peak (kVp), 180 mA, and 30 mL of contrast medium. MP-CTA was reconstructed from the same PCT dataset with an axial thickness of 0.625 mm by using a new axial reconstruction algorithm. A conventional SP-CTA dataset was obtained with 0.625-mm axial thickness, 120 kVp, 350 mA, and 60 mL of contrast medium. We compared image quality, vascular enhancement, and radiation dose.RESULTS: SP-CTA and MP-CTA of 50 patients (male/female ratio, 31/19; mean age, 59.25 years) were analyzed. MP-CTA was significantly better than SP-CTA in vascular enhancement (P = .002), in the absence of venous contamination (P = .006), and was significantly higher in image noise (P < .001). MP-CTA used less contrast medium than SP-CTA and could demonstrate hemodynamic information. The effective dose of MP-CTA was 5.73 mSv, which was equal to that in conventional PCT, and it was 3.57 mSv in SP-CTA.CONCLUSION: It is feasible that MP-CTA may provide both CTA and PCT results. Compared with SP-CTA, MP-CTA provides comparable image quality, better vascular enhancement, hemodynamic information, and more noise with less detail visibility with a lower tube voltage. The radiation dose of MP-CTA is higher than that of SP-CTA, but the dose can be reduced by altering the sampling interval.

Cerebral CT angiography (CTA) is a well-established minimally invasive diagnostic procedure used to detect cerebral aneurysms, acute vascular occlusions, or vasospasms and even predicts hematoma expansion in acute intracerebral hemorrhage.^1–6 Cerebral perfusion CT (PCT) is an important tool to evaluate cerebral ischemia, infarction, cerebral vascular reserve, and microvascular permeability of intracranial neoplasms.⁷ With PCT, the linear relationship between contrast concentration and pixel intensity lends itself more readily to quantification of blood flow values, compared with bolus contrast MR perfusion imaging.^8,9 PCT generates parametric maps of blood flow, including cerebral blood flow (CBF), cerebral blood volume (CBV), and mean transit time (MTT), by using complex deconvolution algorithms.⁷ In a systematic review, the authors concluded that the most accurate assessment of the site of occlusion, infarct core, salvageable brain tissue, and collateral circulation in patients suspected of acute stroke is by a combination of PCT and CTA.¹⁰ Compared with the dose used for single-detector-row CT, thin-section, multidetector CT (MDCT) requires an increased radiation dose for both CTA and PCT examinations.^11–13 To attain an “as low as reasonably achievable radiation dose,” many techniques have been tried to optimize radiation-dose levels in MDCT CTA.Currently, most commercialized CT scanners provide axial scanning in maximum z-axis coverage of 40-mm (2.5 mm × 16) sections; thin-thickness reconstruction modes can be scanned in 20-mm (0.625 mm × 32) sections. During acquisition of conventional CTA, only a short interval in the arterial phase is taken for reconstruction. We call this “single-phase CTA” (SP-CTA). During PCT examinations, to evaluate the area of attenuation change, we acquired axial scans of sequential images at the same level in a fixed or variable time interval (ie, multiphase mode). With the increasing scanning speed of CT, the time interval can be reduced to 0.5 second in state-of-the-art MDCT. Scanning coverage is still a problem because of the cone beam geometry in current MDCT. The fully sampled region, the region covered by every view in the scanning, is less than the cylinder, with a height equal to the detector isocenter coverage.^14,15 To overcome this problem, we used extrapolation during the back projection process. The cone beam effect increases farther away from the isocenter and becomes more prominent with a larger FOV. Under such conditions, a novel vendor reconstruction algorithm has been developed to solve the cone beam effect, conducting a 40-mm beam of 64i × 0.625 mm in an axial scanning. We can then obtain raw data of thin-section PCT and perform postprocessing to reconstruct CTA from this thin-section PCT. Because such CTA images contain data from different time points, we call the technique “multiphase CTA” (MP-CTA), in contrast to conventional single-phase (SP-CTA). This study was designed to compare the image quality and radiation dose of MP-CTA by using the novel thin-reconstruction algorithm from the PCT dataset with the SP-CTA data from the same patient.     

肺通气/灌注显像与HCTPA诊断肺动脉栓塞的价值

目的　评价核素肺通气 灌注(V Q)显像、螺旋CT肺动脉造影(HCTPA)及血浆D 二聚体在诊断肺动脉血栓中的作用。方法　临床疑为肺动脉栓塞(PE)患者4 2例,男2 6例,女16例,平均年龄( 4 9 18±16 5 6 )岁,均行核素肺V Q显像、HCTPA及血浆D 二聚体测定。其中32例患者在行肺灌注显像时,选择双足背静脉注射肺灌注显像剂,同时完成双下肢静脉显像。结果　4 2例患者中34例经临床诊断为PE ,肺V Q显像诊断PE的灵敏度、准确性和阳性预测值分别为94 12 %、90 4 8%和94 12 % ,HCTPA分别为85 2 9%、83 33%和93 5 5 % ,D 二聚体分别为5 2 94 %、5 7 14 %和90 0 0 %。32例行下肢深静脉显像的PE患者中2 0例有下肢静脉血栓。结论　肺V Q显像无创、安全、简便,诊断PE的灵敏度、准确性高。核素肺显像诊断亚肺段水平PE的能力明显高于HCTPA。     

Diagnosis of pulmonary embolism: ventilation perfusion scintigraphy versus helical computed tomography pulmonary angiography

The present study compared the accuracy of ventilation perfusion scintigraphy (VQS) and CT pulmonary angiography (CTPA) for the diagnosis of pulmonary embolism. This was a prospective observational study of 112 patients with suspected pulmonary embolism (PE) who could be studied with both investigations within 24 h. Results were compared to final diagnosis at completion of 6-month follow up, using receiver operating characteristic (ROC) analysis. Pulmonary embolism was diagnosed in 27 referred patients (24%). The sensitivity and specificity of VQS and CTPA were similar to that reported from the literature. A normal VQ scan had the highest negative predictive value (100%), while a high-probability VQ scan had the highest positive predictive value (92%). There was no overall difference (area under the ROC curve (AUC)) between VQS (AUC (95% CI) = 0.82 (0.75,0.89)) and CTPA (AUC = 0.88 (0.81,0.94)) for the diagnosis of PE. Among patients with abnormal chest X-rays, CTPA (AUC 0.90 (0.83,0.97)) appeared somewhat better than VQS (AUC 0.78 (0.68,0.88)) but this difference did not reach statistical significance. In this instance, CTPA is at least as accurate as VQS and may provide an opportunity to make alternative diagnoses.     

Quality of CT pulmonary angiography for suspected pulmonary embolus in pregnancy

The main objective of this study was to assess the quality of CT pulmonary angiography (CTPA) for suspected pulmonary embolus (PE) in the pregnant population. We retrospectively identified 40 consecutive pregnant patients who underwent CTPA from January 2005 to December 2006. Forty consecutive age-matched non-pregnant women were used as a control group. Studies were subjectively graded according to overall image quality by two readers in consensus, in randomised and blinded manner. Moreover, contrast enhancement of pulmonary arteries was subjectively and objectively evaluated. The proportion of sub-optimal studies was more than three times higher in the pregnant group (27.5%, n = 11) compared with the non-pregnant group (7.5%, n = 3; p = 0.015). Mean contrast enhancement was consistently higher in the non-pregnant group compared with pregnant group, both subjectively and objectively. The percentage of inadequately opacified vascular segments was more than two times higher in the pregnant group (28.7%, n = 264) than in the non-pregnant group (13.3%, n = 122; p = 0.0001). The incidence of sub-optimal CTPA studies is higher in pregnancy when compared with an age-matched non-pregnant control group. In addition to radiation issues, this should also be considered when implementing diagnostic strategies for suspected PE in pregnancy.     

Pulmonary lymphangioleiomyomatosis: correlation of ventilation-perfusion scintigraphy, chest radiography, and CT with pulmonary function tests

PURPOSE: To determine the findings on ventilation-perfusion (V-P) scintigrams, computed tomographic (CT) scans, and chest radiographs and correlate them with pulmonary function test results in patients with lymphangioleiomyomatosis. MATERIALS AND METHODS: V-P scintigraphy, chest radiography, conventional and thin-section CT, and pulmonary function tests were performed in 39 patients. The images were graded on a scale of 0 (normal) to 3 (severely abnormal). RESULTS: Imaging abnormalities were found on 92% of ventilation scintigrams, 92% of perfusion scintigrams, 79% of chest radiographs, 100% of CT scans, and 100% of thin-section CT scans. On ventilation scintigrams, 28 (72%) patients demonstrated a speckling pattern. On CT scans, all patients had pulmonary cysts. Univariate analysis showed that extent of disease on chest radiographs and CT scans, cyst size, V-P abnormalities, and degree of speckling were inversely correlated with forced expiratory volume in one second (FEV(1)), diffusing capacity of lung for carbon monoxide, and the ratio of FEV(1) to forced vital capacity (FVC) (P <.01) but not with FVC and total lung capacity. Larger cyst size correlated with extent of disease at CT, but not significantly (P =.056). CONCLUSION: Scintigraphic and radiologic abnormalities are seen in a majority of patients with lymphangioleiomyomatosis. On ventilation scintigrams, a frequently seen speckling pattern may be related to accumulation of radionuclide in pulmonary cysts-a hallmark of the disease at CT. Findings with each imaging modality correlate with certain pulmonary functions.     

肺灌注/通气显像与螺旋CT肺动脉造影诊断肺栓塞的对比研究

目的评价肺灌注/通气显像与螺旋CT肺动脉造影诊断肺栓塞各自的敏感性。方法以肺动脉造影为金标准,并按不同栓塞部位分为叶及段肺动脉、亚段肺动脉两组;按肺动脉狭窄程度分为严重狭窄(超过50%)和轻度狭窄(少于50%)两组。对40例疑肺栓塞患者先后行肺核素显像和螺旋CT肺动脉造影检查,根据分组分别比较两种方法的敏感性。结果①肺动脉造影共确定叶及段肺动脉栓塞102支。其中,肺灌注/通气显像显示86处叶及段性肺灌注/通气不匹配,敏感性为84.3%;螺旋CT肺动脉造影示98支,敏感性为96.1%;②肺动脉造影共确定140支亚段肺动脉栓塞,其中肺灌注/通气显示120处,敏感性为85.7%;螺旋CT肺动脉造影显示115支,敏感性为82.1%;③肺动脉狭窄程度>50%时,通气/灌注显示109处,螺旋CT肺动脉造影显示97支;肺动脉狭窄程度<50%时,通气/灌注显示91处,螺旋CT肺动脉造影显示121支。结论对叶及段肺动脉栓塞,两种方法敏感性基本相同;对亚段肺动脉栓塞,肺灌注/通气显像略高;肺血管轻度栓塞时,螺旋CT肺动脉造影略高。     

Technegas versus (81m)Kr ventilation-perfusion scintigraphy: a comparative study in patients with suspected acute pulmonary embolism.

81mKr is widely used as a ventilation agent to diagnose pulmonary embolism (PE). However, (81m)Kr is expensive, which limits its continuous availability. Technegas can be an alternative ventilation agent with the advantage of being less expensive and available daily. The aim of this study was to compare the value of technegas with that of (81m)Kr in the detection of PE. METHODS: Ninety-two consecutive patients (29 men; mean +/- SD, 53 +/- 17 y old) with at least one segmental perfusion defect (Hull criteria) were studied prospectively. Perfusion and ventilation (V/Q) lung scintigraphy with both technegas and (81m)Kr were performed within 24 h on all patients. V/Q lung scan results were classified as high probability for PE (normal ventilation study) or nondiagnostic (abnormal ventilation study). All V/Q lung scans were read by two experienced nuclear physicians in consensus. For the intra- and interobserver variabilities, two experienced observers independently read the V/Q lung scans. RESULTS: (81m)Kr and technegas showed a good agreement (kappa, 0.68; 95% confidence interval [CI], 0.53-0.82). However, technegas significantly increased the number of nondiagnostic V/Q lung scans (P: = 0.035). In 15 patients, a discrepancy was found between (81m)Kr and technegas. False-positive V/Q lung scan results occurred in 4 of 12 patients (33%) with (81m)Kr and in 2 of 3 patients (66%) with technegas. The intra- and interobserver variabilities were 0.71-0.88 (95% CI, 0.56-1.0) for perfusion/(81m)Kr and 0.74-0.96 (95% CI, 0.58-1.0) for perfusion/technegas. CONCLUSION: In comparison with (81m)Kr, technegas does not result in more false-positive V/Q lung scan results. The use of technegas, however, increases the number of nondiagnostic V/Q lung scan results, which would increase the demand for further additional testing to confirm or refute PE.     

Diagnosis of acute pulmonary embolism in outpatients: comparison of thin-collimation multi-detector row spiral CT and planar ventilation-perfusion scintigraphy

PURPOSE: To compare multi-detector row computed tomography (CT) and ventilation-perfusion (V-P) scintigraphy in the diagnosis of acute pulmonary embolism (PE) in outpatients who were cared for in the emergency department. MATERIALS AND METHODS: Ninety-four nonconsecutive patients, in whom acute PE was suspected, underwent thin-collimation multi-detector row CT (collimation, 4 x 1 mm; pitch, 1.25; scanning time, 0.5 second) and V-P scintigraphy. Concordance between CT and scintigraphic images was used in the diagnosis of PE. Pulmonary angiography was performed within 24 hours if interpretations of V-P and spiral CT images were inconclusive or discordant. Sensitivity and specificity values were calculated for V-P scintigrams and CT scans of the lungs. The rates of conclusive results for scintigraphy and CT were compared. RESULTS: The sensitivity of thin-collimation multi-detector row CT and V-P scintigraphy for the detection of PE was 96% (27 of 28; CI: 82%, 99%) and 98% (65 of 66; CI: 92%, 99%), respectively. The specificity of CT and V-P scintigraphy was 86% (24 of 28; CI: 67%, 96%) and 88% (58 of 66; CI: 77%, 94%), respectively. Seven V-P scintigrams were of intermediate probability, and one spiral CT study was indeterminate. Examinations with spiral CT yielded conclusive results more often than examinations with planar V-P scintigraphy (P <.05). Five V-P scintigrams and spiral CT scans were discordant. Twelve pulmonary angiographic examinations were performed. Angiographic findings were concordant in 10 (91%) of 11 patients with conclusive CT scans in whom pulmonary angiography was attempted. CT was used to establish an alternative diagnosis in 19 (29%) of 66 patients in whom PE was excluded. CONCLUSION: Thin-collimation multi-detector row CT is more accurate than V-P scintigraphy in the diagnosis of acute PE in outpatients. Furthermore, CT provides alternative diagnoses for patients without PE on high-quality transverse or near-isotropic reformatted images.