Incremental benefit of maximum-intensity-projection images on observer detection of small pulmonary nodules revealed by multidetector CT

OBJECTIVE: Our purpose was to assess the incremental effect of maximum-intensity-projection (MIP) image processing on the ability of various observers to detect small (<1 cm in diameter) central and peripheral lung nodules revealed by multidetector CT. MATERIALS AND METHODS: We retrospectively identified 25 patients with metastatic disease, each having from two to nine nodules that were 3-9 mm in diameter. Two senior and three junior reviewers interpreted all images on a workstation. The observers first reviewed axial images (3.75-mm collimation, 3-mm reconstruction interval, multidetector acquisition) in cine and sequential fashion and recorded the size, lobe, and central or peripheral (within 1 cm of the edge of lung) location of each nodule. MIP images (10-mm slab, 8-mm interval) were then reviewed, and additional nodules detected were recorded. Final counts were established by consensus. RESULTS: The reviewers found 122 nodules (71 peripheral, 51 central) in the 25 patients. The addition of MIP slabs significantly enhanced reviewer detection of central nodules (p < 0.001) and junior reviewer detection of peripheral nodules (p < 0.001). MIP slabs also reduced the effects of reviewer experience, particularly for peripheral nodules. CONCLUSION: MIP processing reduces the number of overlooked small nodules, particularly in the central lung. Observer nodule detection remains imperfect even when lesions are clearly depicted on images.     

Diagnostic accuracy of image postprocessing methods for the detection of coronary artery stenoses by using multidetector CT

PURPOSE: To retrospectively evaluate the diagnostic accuracy of multidetector computed tomography (CT) coronary angiography for detection of hemodynamically significant (>or=50%) stenoses by using various image postprocessing methods, with conventional coronary angiography as the reference standard. MATERIALS AND METHODS: The analysis used data from previous studies, use of which had been approved by the Institutional Review Board. Sixteen-section multidetector CT data sets for 40 patients (30 men, 10 women; mean age 56 years +/- 8; mean heart rate, 61 beats per minute +/- 6) were evaluated. Six independent investigators evaluated the data sets for the presence of stenoses with diameter reduction of 50% or more, by using either exclusively transverse images, free oblique multiplanar reconstructions (MPRs), free oblique maximum intensity projections (MIPs, 5 mm thick), prerendered curved MPRs, prerendered curved MIPs, or prerendered three-dimensional volume rendered reconstructions (VRTs). Evaluation results were compared with conventional coronary angiography for each artery in a blinded fashion (chi(2) test). RESULTS: Overall, 35 coronary artery stenoses were present. Percentage of evaluable arteries and accuracy for detecting stenosis (percentages of accurately classified arteries were, respectively, 99% and 88% for transverse, 99% and 91% for oblique MPR, 94% and 86% for oblique MIP, 94% and 83% for curved MIP, 93% and 81% for curved MPR, and 91% and 73% for VRT). Accuracy was significantly higher for oblique MPR than for curved MPR (P=.01), curved MIP (P=.03), and VRT (P<.001). CONCLUSION: The evaluation of multidetector CT coronary angiography with interactive image display methods, especially interactive oblique MPRs, permits higher diagnostic accuracy than evaluation of prerendered images (curved MPR, curved MIP, or VRT images).     

Evaluation of small pulmonary arteries by 16-slice multidetector computed tomography: Optimum slab thickness in condensing transaxial images converted into maximum intensity projection images

OBJECTIVE: The purpose of this study was to determine the optimal slab thickness for condensing transaxial images into maximum intensity projection (MIP) images in the evaluation of small pulmonary arteries using 16-slice multidetector-row computed tomography (MDCT). METHODS: Helical computed tomography (CT) scans were obtained from lung apices to bases using 16-slice MDCT [120 kV(peak), 180 mA, beam width of 10 mm, beam pitch of 1.375, and reconstruction thickness of 1.25 mm] in 29 patients suspected of having a pulmonary embolism. Four kinds of image series (1.25-mm thick original transaxial source images and 3 kinds of reconstructed images using the MIP technique with slab thicknesses of 2.5 mm, 5 mm, and 10 mm) were obtained from each patient and forwarded to monitors of a picture archiving and communication system for analysis by 2 independent observers. The observers recorded the name of the segmental (20 total; 10 in each lung) and subsegmental (40 total; 20 in each lung) arteries that were traceable in each image series. Image quality of the 4 image types were graded into 5 scales based on their degree of vascular opacification, the sharpness of the vascular margins of the contrast-enhanced CT angiograms, and the visibility of lung parenchyma (excellent [5] to nondiagnostic [1]) and compared. RESULTS: In both the 1.25-mm thick original transaxial and 2.5-mm thick MIP images, a higher percentage of subsegmental arteries was traceable (91.3% [2119/2320 observations] and 87.2% [2023/2320 observations], respectively; P <0.05) than in the 5-mm and 10-mm thick MIP images (66.4% [1540/2320] and 40.5% [940/2320], respectively). No statistically significant difference was observed between the 1.25-mm thick transaxial and 2.5-mm thick MIP images in this respect. Image quality of 2.5-mm thick MIP images was superior to that of the 5-mm and 10-mm thick MIP images (P < 0.0001). No statistically significant difference was found between the scores of the image quality of the 1.25-mm thick original transaxial images and the 2.5-mm thick MIP images. CONCLUSION: After reducing the image number by one half, 2.5-mm thick MIP images using 16-slice MDCT are found to provide satisfactory images, which are comparable to 1.25-mm thick transaxial images for the analysis of subsegmental pulmonary arteries in patients suspected of pulmonary embolism.     

Reduced radiation dose helical chest CT: effect on reader evaluation of structures and lung findings

PURPOSE: To assess, by using computer simulation, the effect of the use of reduced computed tomographic (CT) tube current on reader evaluation of structures and lung findings on images obtained at clinically indicated chest CT examinations. MATERIALS AND METHODS: The noise level in the raw scan data of 150 clinically indicated conventional tube current (200-320-mA) chest CT examinations was modified to simulate tube current reduction to 100 and to 40 mA. A total of 450 image sets were thus available. Four radiologists blinded to the tube current used assessed the image sets in random order for 14 structures and lung findings and ranked subjective image quality by using a five-point scale (1 = nondiagnostic, 2 = inferior, 3 = adequate, 4 = good, 5 = excellent). After a 3-week interval, the 150 conventional tube current image sets were rescored so that intraobserver agreement could be assessed. The McNemar statistic was used to determine whether there were more scoring disagreements between interpretations of the conventional and those of the reduced tube current scans or between the two interpretations of the conventional tube current scans. RESULTS: When overall agreement for 14 structures and lung findings was pooled over four observers, significantly more disagreements (P <.05) were seen when scores were compared between conventional and reduced tube current scans than when scores were compared between repeated interpretations of the conventional tube current scans. There was a significant decrease (P <.05) in the subjective image quality of reduced tube current scans compared with the subjective image quality of conventional tube current scans. CONCLUSION: These data indicate that reduced tube current does affect reader evaluation of structures and lung findings and reduces a reader's subjective assessment of image quality.     

Renal artery stenosis: CT angiography--comparison of real-time volume-rendering and maximum intensity projection algorithms

PURPOSE: To compare results of helical computed tomographic (CT) angiography with real-time interactive volume rendering (VR) to CT angiography with maximum intensity projection (MIP) for the detection of renal artery stenosis. MATERIALS AND METHODS: Twenty-five patients underwent both conventional and CT angiography of the renal arteries. Images were blindly reviewed after rendering with MIP and VR algorithms. MIP images were viewed in conjunction with axial CT images; VR models were evaluated in real time at the workstation without CT images. Findings in 50 main and 11 accessory renal arteries were categorized as normal or by degree of stenosis. RESULTS: All arteries depicted on conventional angiograms were visualized on MIP and VR images. Receiver operating characteristic (ROC) analysis for MIP and VIR images demonstrated excellent discrimination for the diagnosis of stenosis of at least 50% (area under the ROC curve, 0.96-0.99). Although sensitivity was not significantly different for VR and MIP (89% vs 94%, P > .1), specificity was greater with VR (99% vs 87%, P = .008 to .08). Stenosis of at least 50% was overestimated with CT angiography in four accessory renal arteries, but three accessory renal arteries not depicted at conventional angiography were depicted at CT angiography. CONCLUSION: In the evaluation of renal artery stenosis, CT angiography with VR is faster and more accurate than CT angiography with MIP. Accessory arteries not depicted with conventional angiography were depicted with both CT angiographic algorithms.     

Wavelet compression of low-dose chest CT data: effect on lung nodule detection

PURPOSE: To assess the effect of using a lossy Joint Photographic Experts Group standard for wavelet image compression, JPEG2000, on pulmonary nodule detection at low-dose computed tomography (CT). MATERIALS AND METHODS: One hundred sets of lung CT data ("cases") were compressed to 30:1, 20:1, and 10:1 levels by using a wavelet-based JPEG2000 method, resulting in 400 test cases. Each case consisted of nine 1.25-mm sections that had been obtained with 20-40 mAs. Four thoracic radiologists independently interpreted the test case images. Performance was measured by using area under the receiver operating characteristic (ROC) curve (Az) and conventional sensitivity and specificity analyses. RESULTS: There were 51 cases with and 49 without lung nodules. Az values were 0.984, 0.988, 0.972, 0.921, respectively, for original and 10:1, 20:1, and 30:1 compressed images. Az values decreased significantly at 30:1 (P =.014) but not at 10:1 compression, with a trend toward significant decrease at 20:1 (P =.051). Specificity values were unaffected by compression (>98.0% at all compression levels). Sensitivity values were 86.3% (176 of 204 test cases with nodules), 77.9% (159 of 204 cases), 76.5% (156 of 204 cases), and 70.1% (143 of 204 cases), respectively, for original and 10:1, 20:1, and 30:1 compressed images. Results of logistic regression model analysis confirmed the significant effects of compression rate and nodule attenuation, size, and location on sensitivity (P <.05). CONCLUSION: While no reduction in nodule detection at 10:1 compression levels was demonstrated by using ROC analysis, a significant decrease in sensitivity was identified. Further investigation is needed before widespread use of image compression technology in low-dose chest CT can be recommended.     

softMip: a novel projection algorithm for ultra-low-dose computed tomography

Two projection algorithms are currently available for viewing computed tomography (CT) data sets: average projection (AVG) and maximum intensity projection (MIP). Although AVG images feature good suppression of image noise but reduced edge sharpness, MIP images are characterized by good edge sharpness but also amplify image noise. Ultra-low-dose (ULD) CT has very low radiation exposure but has high image noise. Maximum intensity projection images of ULDCT data sets amplify image noise and are therefore unsuitable for image interpretation in the routine clinical setting. We developed a synthesis of both algorithms that tries to unite the respective advantages. The resulting softMip algorithm was implemented in C++ and installed on a workstation. Depending on the settings used, softMip images can represent any graduation between MIP and AVG. The new softMip algorithm was evaluated and compared with MIP and AVG in terms of image noise and edge sharpness in a series of phantom experiments performed on 7 different CT scanners. Furthermore, image quality of the transition from AVG to MIP by means of softMip was compared with the image quality of simply blending AVG and MIP. Images generated with softMip showed less image noise than MIP images (P < 0.0005) and higher edge sharpness than AVG images (P< 0.0005). The softMip transition from AVG to MIP had a better ratio of edge sharpness and image noise than blending (P < 0.0005). Our results suggest that softMip is a very promising projection procedure for postprocessing cross-sectional image data, especially ULDCT data sets.     

CT portography by multidetector helical CT: comparison of three rendering models

PURPOSE: To assess the value of multidetector CT portography in visualizing varices and portosystemic collaterals in comparison with conventional portography, and to compare the visualizations obtained by three rendering models (volume rendering, VR; minimum intensity projection, MIP; and shaded surface display, SSD). METHODS: A total of 46 patients with portal hypertension were examined by CT and conventional portography for evaluation of portosystemic collaterals. CT portography was performed by multidetector CT (MD-CT) scanner with a slice thickness of 2.5 mm and table feed of 7.5 mm. Three types of CT portographic models were generated and compared with transarterial portography. RESULTS: Among the 46 patients, 48 collaterals were identified on CT transverse images, while 38 collaterals were detected on transarterial portography. Forty-four of 48 collaterals identified on CT transverse images were visualized with the MIP model, while 34 and 29 collaterals were visualized by the VR and SSD methods, respectively. The average CT value for the portal vein and varices was 198 HU with data acquisition of 50 sec after contrast material injection. CONCLUSIONS: CT portography by multidetector CT provides excellent images in the visualization of portosystemic collaterals. The images of collaterals produced by MD-CT are superior to those of transarterial portography. Among the three rendering techniques, MIP provides the best visualization of portosystemic collaterals.     

Can maximum intensity projection images with multidetector-row computed tomography help to differentiate between the micronodular distribution of focal and diffuse infiltrative lung diseases?

OBJECTIVE: The objective of this study was to evaluate whether maximum intensity projection (MIP) images increased the ability of experienced and resident radiologists to differentiate between the micronodular distribution of focal and diffuse infiltrative lung diseases. METHODS: The cases used in the study were those of 26 patients with focal or diffuse micronodular lung diseases, including 7 cases of sarcoidosis, 6 of miliary tuberculosis, 3 of pulmonary tuberculosis, 3 of chronic bronchitis, 2 of human T-lymphotropic virus type 1-associated bronchoalveolar disorder, 2 of diffuse aspiration bronchiolitis, 1 of atypical mycobacterial infection, and 1 of lymphangitic carcinomatosis. Scans of the entire lung during a single breath hold at 1.25-2.5 mm thickness and a pitch of 6 were performed using a multidetector-row computed tomography (MDCT) apparatus with a 4-row detector. Additional MIP image slabs were produced from the initial axial images on all study patients on a workstation according to a protocol that incorporated a slab thickness of 10 mm, a reconstructed interval of 10 mm, and a window width of -1500 Hounsfield units. The ability of 10 radiologists (5 board-certified radiologists and 5 radiology residents) to interpret contiguous thin-section CT scans and additional MIP images was then studied in an observer performance study. The results of both sets of observer performances were compared using receiver operating characteristic analysis. RESULTS: In the resident observers, the mean area under the receiver operating characteristic curve (Az) value increased significantly from 0.654 without the MIP images to 0.753 with the MIP images (P < 0.01). In the board-certified radiologists, however, the mean Az values remained unchanged at 0.867 without the MIP images and 0.846 with the MIP images. CONCLUSIONS: This study showed that MIP images may help radiologists in training to differentiate between the micronodular distribution of focal and diffuse infiltrative lung diseases.     

胆囊及胆总管结石MRC:3D原始图与MIP图对比研究

目的 :评价磁共振胆管成像 (MRC)三维原始图 (简称为原始图 )与 3D最大强度投影 (MIP)重建图像 (简称为MIP图 )在胆囊结石及胆总管结石中的应用价值。方法 :对 42例明确诊断为胆囊或胆总管结石的患者行 3DFSE扫描 ,获得原始图后 ,经工作站行靶最大强度投影 (MIP)重建得到三维立体图。两位有经验的放射学医师对图像进行分析 ,在病变的显示与否上取得一致。然后 ,对原始图及MIP图对结石的显示率进行统计学处理。结果 :在胆总管结石的显示上 ,原始图及MIP的显示率分别为 93 .3 3 %和 86.67% ,两者差异无显著性意义 (P >0 .0 5 ) ;而对于胆囊结石 ,显示率分别为97.0 6%和 2 3 .5 3 % ,两者间差异存在显著性意义 (P <0 .0 5 )。结论 :原始图及MIP图在显示胆总管结石上 ,两者具有同样较高的临床价值 ,而在显示胆囊结石上 ,原始图的临床应用价值要明显高于MIP图     

肾移植术后肺巨细胞病毒感染的影像学表现

目的:探讨肾移植术后肺巨细胞病毒感染的CT特点。方法:回顾性分析24例经临床及实验室检查证实的巨细胞病毒感染(CMV)的CT特征。结果:本组24例巨细胞病毒感染患者中有2例CT表现未见明显异常,其余22例均有毛玻璃样阴影改变,其中呈两肺多发、散在分布7例,呈两肺弥漫性分布15例。仅表现为毛玻璃影者4例,伴有小叶间隔增厚10例,伴有实变影者7例,伴有多发小结节影者8例,伴有少量胸腔积液者4例。结论:肾移植术后肺巨细胞病毒感染最常见CT表现为双肺弥漫性分布的毛玻璃样阴影,且常伴有小叶间隔增厚、小结节影、实变影等表现。     

自适应统计迭代重建技术在PET/CT全身扫描中的应用

目的 采用自适应统计迭代重建(ASiR)技术提高PET/CT全身扫描低剂量CT的图像质量。 方法 采用CT性能模型测量CT值准确度和噪声,对模型进行两次扫描,扫描条件分别为:120 kV、120 mA和120 kV、300 mA。另随机选取行PET/CT扫描的受检者30例,按体重静脉注射18F-FDG 3.70 MBq,PET/CT全身扫描条件为:PET采用三维+飞行时间+点扩展函数重建技术,1.5 min/床位;CT采用螺旋扫描,120 kV,自动曝光控制技术(30~210 mA,噪声指数25)。模型图像和患者全身扫描CT图像分别按照常规方法和40% ASiR方法进行重建。 结果 模型和临床研究结果表明,ASiR方法获得的模型CT值标准差较常规CT图像重建方法降低了33.0%(t=27.76,P < 0.01),正常组织(脑、肺、纵隔、肝脏和椎体)和病灶(脑、肺、纵隔、肝脏和椎体)CT值标准差平均分别降低了21.08%(t=23.35,P < 0.01)和24.43%(t=16.15,P < 0.01),而肝脏正常组织和肝脏病灶分别降低了51.33%(t=34.21,P < .01)和49.54%(t=15.21,P < 0.01)。 结论 采用ASiR技术明显降低了PET/CT全身扫描低剂量CT图像的噪音,提高了CT图像质量,使其适用于定量分析研究和临床应用。     

Respiratory Motional Effect on Cone-Beam CT in Lung Radiation Surgery

The cone-beam CT (CBCT), which is acquired using an on-board imager (OBI) attached to a linear accelerator, is used effectively in the verification of setup accuracy for lung radiation surgery. In this study, the respiratory organ motional effect on the CBCT was evaluated with a properly devised phantom system, and the level of possible error in conditions of a real clinical process was assessed. In a comparison study between the CBCT in static status and CBCT images acquired in 20 different motional cases, we confirmed that the image quality and information of CBCT were degraded, with an increase of motional ranges in the region of inhomogeneous structures. The 4D-CT MIP (50～55%) for the planning of lung radiation surgery and the 4D-CT MIP (full phase) were compared with CBCT in the various motional cases for the evaluation of the influence of the motional effect on CBCT in the process of the setup error correction. The average ratio of relative difference between plan CT: 4D-CT MIP (50%～55%) and CBCT was 5.79% and between plan CT: 4D-CT MIP (50%～55%) and 4D-CT MIP (full phase) was 42.95% in the phantom study. In the analysis of clinical cases of lung radiation surgery, the gross tumor volumes were compared in each CT image. The average ratio of relative difference between plan CT: 4D-CT MIP (50～55%) and CBCT was 10.72% and between plan CT: 4D-CT MIP (50～55%) and 4D-CT MIP (full phase) was 28.19%. These results showed that, although a respiratory organ motional effect on CBCT introduced variation in image quality, the error as a result of this variation could be estimated relatively low in the setup error correction for a gated-lung radiation surgery when the planning was performed in 4D-CT MIP (50～55%), which already included a related signal of motional effect.     

Lung nodules: dual-kilovolt peak analysis with CT--multicenter study

PURPOSE: To test the following hypothesis: The greater the increase in the mean computed tomographic (CT) number of a radiologically indeterminate lung nodule from the CT number on a 140-kVp CT image to that on an 80-kVp CT image, the more likely the nodule is benign (ie, contains calcium). MATERIALS AND METHODS: Two hundred forty indeterminate lung nodules were prospectively studied at four institutions: Mayo Clinic Scottsdale, Ariz (n = 160); Mayo Clinic Rochester, Minn (n = 50); Shiga Health Insurance Hospital, Otsu, Japan (n = 25); and Duke University Medical Center, Durham, NC (n = 5). Of the 240 nodules, 157 met the entrance criteria for this study and had a diagnosis. All nodules included were solid, 5-40-mm diameter, relatively spherical, homogeneous, and without visible evidence of calcification or fat. Each nodule was evaluated by using 3-mm-collimation, nonenhanced CT scans with both 140- and 80-kVp x-ray beams. RESULTS: There were 86 (55%) benign and 71 (45%) malignant nodules. The median increase in the nodule mean CT number from the CT number on 140-kVp images to that on 80-kVp images was 2 HU for benign nodules and 3 HU for malignant nodules. This difference was not statistically significant. The area under the receiver operating characteristic curve was 0.505. CONCLUSION: Dual-kilovolt peak analysis with current CT technology does not appear to be helpful in the identification of benign lung nodules.     

Azygos arch valves: prevalence and appearance at contrast-enhanced CT

PURPOSE: To evaluate the prevalence and appearance of azygos arch valves at intravenous contrast material-enhanced computed tomography (CT). MATERIALS AND METHODS: Findings of 309 intravenous contrast-enhanced spiral CT examinations of the chest were retrospectively reviewed. The presence of contrast material reflux into the azygos arch and of a focal bulge in the azygos arch was recorded. An azygos valve was considered present if contrast material with a curvilinear posterior contour was seen in the azygos arch. The chi2 test was used to compare the frequency of contrast material reflux into the azygos vein for high and low rates of contrast material injection and for right and left arm injection. RESULTS: Reflux of contrast material into the azygos arch occurred at 154 (49.8%) of 309 examinations, and valves were seen on images of 105 (68.2%) examinations. A focal bulge was seen in the azygos arch on images of 86 (81.9%) of 105 examinations with an azygos valve. Contrast material refluxed more frequently into the azygos vein in examinations with high rates of injection (83 of 128 examinations, 64.8%) than in those with low rates of injection (71 of 181, 39.2%, P <.001). Among the patients with high rates of injection, contrast material refluxed more frequently into the azygos vein with the right arm injection than with left arm injection (53 of 70, 76% vs 30 of 58, 52%, P <.01). Refluxed contrast material appeared as discrete collections within cusps of the azygos valves on images of 69 (44.8%) of 154 examinations. CONCLUSION: Valves in the azygos arch are common and more frequently seen at CT when high injection rates and right arm injections are used.     

多层螺旋CT冠脉造影的标准体位

目的:探讨建立多层螺旋CT冠脉造影标准体位.材料和方法:对120例临床怀疑冠心病患者进行16层螺旋CT心电门控平扫及增强扫描.所有患者用舒张期增强扫描重建像行最大密度投影(MIP)重建及容积漫游技术(VRT)重建,其中30例与常规冠状动脉造影对照.总结16层螺旋CT心脏冠状动脉造影不同体位的显示情况,得出CT冠状动脉造影统一体位.结果:分别定义了6个MIP重建体位和9个VRT重建体位.结论:多层螺旋CT冠状动脉造影是一种无创、简便、优良的冠状动脉造影方法,建立起标准造影体位有利于对冠脉病变进行更全面评价.     

Postprocessing technique with MDCT data improves the accuracy of the detection of lung nodules

Purpose The aim of this study was to determine whether postprocessing techniques could improve the accuracy of detecting lung nodules. Materials and methods A total of 154 segmented lung volumes of multidetector-row computed tomography (MDCT) data were the subject of the study. Lung nodules were present in 88 volumes and absent in 66 volumes. We prepared four groups: (1) 7- or 10-mm thick-section axial images; (2) 1-mm thin-section axial images; (3) sliding slab maximum intensity projection (MIP) images with a slab thickness of 15 mm; and (4) sliding slab volume rendering (VR) images with a slab thickness of 15 mm. Sixteen physicians reviewed each group in interactive cine mode. The observers’ performance in the detection of lung nodule was evaluated by receiver operating characteristic (ROC) analysis. Results The observers’ performance of the MIP and VR groups was significantly better than in other two groups. There was no significant difference statistically between the thin and thick groups. Conclusion The detectability of lung nodules is improved with the use of sliding slab MIP and VR using thin-section image data. Thin-section volume data are essential for improving diagnostic accuracy, but observation of thin-section images without utilization of image-processing techniques dose not improve diagnostic accuracy. This article was presented at the 2005 Japan Radiological Society annual meeting     

多层螺旋CT诊断气管支气管内膜结核的价值

目的:总结气管支气管内膜结核的多层螺旋CT表现,评价多层螺旋CT在支气管内膜结核诊断中的价值。方法:对36例经纤支镜证实的气管支气管内膜结核患者行多层螺旋CT扫描,结合多种影像后处理技术,分析其影像学表现,重点观察支气管管腔和管壁的形态学改变。结果:多层螺旋CT轴位及其三维重建图像能明确显示支气管管腔变窄、管腔表面不光滑、腔内结节状突起以及管壁增厚、密度增高、僵直和钙化。轴位图像还可显示肺内伴随表现。结论:多层螺旋CT扫描结合多种后处理技术可以有效地提高支气管结核的诊断率,是临床上一种无创性评价气管支气管病变的有效方法。     

Radiation exposure and image quality in chest CT examinations.

OBJECTIVE: The purpose of this study was to determine how changes in radiographic tube current affect patient dose and image quality in unenhanced chest CT examinations. SUBJECTS AND METHODS: Ten sets of CT images were obtained from patients undergoing CT-guided chest biopsies. For each patient, six images of the same region were obtained at settings between 40 and 280 mAs. CT data were used to reconstruct tomographic sections with a field of view limited to the normal contralateral lung. Images were printed using lung and mediastinal image display settings. Image quality was determined by asking radiologists to assess the perceived level of mottle in CT images. Five chest radiologists ranked the relative image quality of six images. Patient effective doses were computed for chest CT examinations performed at each milliampere-second setting. Radiologists indicated whether any perceived improvement of image quality at the higher radiation exposures was worth the additional radiation dose. RESULTS: The differences in quality of chest CT images generated at greater than or equal to 160 mAs were negligible. Reducing the radiographic technique factor below 160 mAs resulted in a perceptible reduction in image quality. Differences in CT image quality for radiographic techniques between 120 and 280 mAs were deemed to be insufficient to justify any additional patient exposure. However, the use of 40 mAs results in an inferior image quality that would justify increased patient exposure. CONCLUSION: Radiographic techniques for unenhanced chest CT examinations can be reduced from 280 to 120 mAs without compromising image quality.     

光谱CT头部虚拟平扫图像:不同单能量图像质量的对比

目的:探讨双层探测器光谱CT不同单能量图像在头部影像诊断中的临床应用效能。方法:回顾性分析2019年6-12月因头晕、晕厥和头痛等临床症状而在本院行光谱CT(IQon Spectral CT)头部CT平扫检查的38例患者的影像资料。从光谱CT扫描中可获取常规混合能量图像和40~120 keV的光谱成像数据,以5 keV为间隔增量将光谱数据重建为17组单能级图像。分别测量每组图像上幕上灰质和白质的CT值和噪声值(SD),并计算信号噪声比(SNR)和对比信噪比(CNR)。同时对常规图像与120 keV单能级图像的伪影区域的脑组织结构(灰、白质)的对比及后颅窝伪影情况进行主、客观评分和比较。采用Bonferroni法进行统计学分析。结果:各组单能图像之间脑灰质CT值(P<0.001)、噪声(P=0.012)和CNR(P<0.001)的差异均有统计学意义,而脑白质CT值的差异无统计学意义(P=0.107)。其中65 keV图像的脑灰质CT值,脑灰、白质的噪声和SNR均高于其它单能级和常规混合能量图像(P<0.05),CNR亦高于其它单能级图像和常规图像(P<0.05)。与常规图像比较,120keV单能级图像上颅底层面伪影区域的脑灰、白质CT值(P=0.046)、噪声(P<0.01)、SNR(P<0.001)和CNR(P<0.001)的差异均具有统计学意义,且图像质量评分(P<0.001)和伪影评分(P<0.001)的差异亦有统计学意义。结论:和常规图像相比,从双层探测器光谱CT重建的单能图像在65 keV灰、白质对比度好,图像噪声降低、软组织分别率提高。120 keV单能级图像在由颅骨引起的X线束硬化伪影方面,能有效还原周围组织结构,提升图像质量。