64层螺旋CT机架旋转时间对图像质量的影响探讨

目的研究不同机架旋转时间对64层螺旋CT图像质量的影响。方法使用SOMATOM Sensation 64层螺旋CT。把del-ta模体沿Z轴固定于CT机架的中心,使用腹部螺旋扫描模式,进行扫描和重建,然后制作各位置图像序列的层敏感度曲线(SSP),并对各图像序列的SSP进行傅里叶变换得到调制传递函数(MTF)。后用腹部螺旋扫描模式对CT质控模体Catphan500进行扫描和重建,分别记录图像的最大线对数及其能分辨的各级对比度的最小目标的尺寸。结果0.5s组和1s组的MTF曲线几乎重合,5%MTF值分别为11.3LP/cm和11.9LP/cm;其空间分辨率和低对比度分辨率也完全相同。结论机架旋转时间0.5s组和1s组图像质量无差别。为缩短扫描时间,消除呼吸伪影,我们建议在腹部螺旋扫描时,机架旋转时间0.5作为常规应用。     

多层螺旋CT各向同性成像参数的优化选择研究

目的:通过客观评价方法研究多层螺旋CT实现各向同性成像的可行性及参数优化选择。方法:应用PhilipsMx8000四层螺旋CT对国际通用Catphan500CT模体内一个直径0.28mm的钨质小球进行扫描。采用内耳模式,成像参数:120kV,150mAs,准直2×0.5mm,FOV180mm,重建矩阵512×512,重建间隔0.3mm,分别使用不同的螺距、重建层厚、螺旋插值法、滤过。应用采集到的原始数据进行图像重建并分别测试点扩散函数在x、y和z轴的半高宽(以此作为空间分辨率)。结果:采用180°线性插值法、重建层厚0.6mm、螺距0.875、filter=D、重建间隔0.3mm的参数组合,在x轴、y轴和z轴三个方向的空间分辨率分别为0.9、0.9、0.9mm。结论:采用180°线性插值法、重建层厚0.6mm、螺距0.875、filter=D、重建间隔0.3mm的参数组合可以实现各向同性成像,推荐临床使用。     

低mAs-CT低分辨率水模图像质量的实验研究

目的:探讨CT检查中低管电流-时间乘积技术低分辨率水模图像质量.方法:设置多种管电流-时间乘积,5和10mm层厚,多种重建算法,对Catphan 500模型进行CT扫描,记录CT值,SD值,并计算CNR值.同时运用统计学方法和Excel表格对获得的数据进行统计分析.结果:管电流-时间乘积、射线剂量、层厚和图像质量成正比关系,不同的重刎建算法对图像质量会产生不同的影响.结论:低管电流-时间乘积能够降低射线剂量,但是剂量减少会增加图像噪声,影响图像质量,增加层厚和使用soft重建算法可以达到降低图像噪声的目的.     

改变扫描野及矩阵对肺结节CT图像质量影响的体模研究

目的：探讨在多排螺旋 CT 扫描中改变扫描野(FOV)和矩阵(matrix)对体模中纯磨玻璃结节(pGGN)的 CT 图像质量的影响。方法应用 Philips Brilliance 128排螺旋 CT 在3种不同 FOV(50 mm、150 mm、300 mm)条件下对含有 pGGN(直径均≥5 mm)的胸部仿真体模进行扫描,分别用标准分辨率(512×512)和高分辨率(1024×1024)矩阵进行重建(标准算法),记录体模中每个结节及其邻近组织在不同条件下的 CT 值和及其标准差(SD),通过公式计算各条件下图像的平均标准差(MSD)、对比噪声比(CNR)及信噪比(SNR),比较不同条件下各项指标的差异;再由2名医师采取盲法对不同条件下结节的可见度进行评分,用 Kappa 检验评价观察者间的一致性。结果2名观察者的一致性为中等或较好。当矩阵不变时,不同 FOV 条件下各 pGGN 的 MSD、CNR 及 SNR均无明显统计学差异,但结节的可见度评分随着 FOV 的减小而提高;而当 FOV 不变时,不同矩阵条件下 pGGN 的 MSD、CNR 及SNR 均存在统计学差异,高分辨率矩阵的 MSD 高于标准分辨率矩阵,CNR 和 SNR 低于标准分辨率矩阵,且对于结节的可见度评分,高分辨率矩阵较标准分辨率矩阵相比并无明显提高。结论对直径≥5 mm 的 pGGN,在矩阵相同的条件下,缩小 FOV,并不会对 CT 图像的质量造成影响,但能够提高结节的可见度评分;而当 FOV 保持不变,高分辨率矩阵的图像的 MSD 更大,SNR 及CNR 更小,且高分辨率矩阵对结节的可见度并无明显提高。     

CT机质量控制检测的探讨

目的:CT机质量控制检测方法的探讨及应用。方法:用美国模体实验室的Catphan 500模体和瑞典奥利科公司的Solidose 400剂量仪检测CT机扫描架的定位光精度、扫描床运动精度、层厚、CT值线性、视野均匀性、噪声、高对比度分辨率、低对比度分辨率和CT剂量指数(CTDI)。结果:所检测CT机作为整机均合格,但部分指标不合格。结论:通过对噪声、CT线性、对比度分辨率等图像性能参数的检测,可有效保证系统性能良好和维持最优化的图像质量;对CTDI的检测,可及时了解辐射危险水平,进而优化扫描方案,在保证诊断的前提下降低病人受照剂量。     

双源CT脑静脉造影扫描技术探讨

目的:选择脑双源CT静脉造影(CTV)的最佳扫描时相及重建层厚,以获得良好的脑静脉图像。方法:①11例志愿者行同层动态增强扫描,以探讨团注追踪触发技术的理论阈值。以理论阈值为中心,将45例志愿者随机分为3组探讨团注追踪触发技术的应用阈值。②将扫描所获得原始数据以0.75mm和1.50mm层厚重建,比较2组层厚重建的三维血管图像质量,进行统计分析。结果:触发阈值100HU组,靶血管全程显示良好;采用0.75mm层厚重建的三维血管图像质量优于1.50mm层厚(P<0.05)。结论:采用100HU阈值进行静脉触发扫描和0.75mm层厚重建血管可以获得良好的脑CTV图像。     

幼猪头颅低剂量螺旋CT扫描参数优化研究

目的 以幼猪头颅模拟婴幼儿头颅,探求最合适的婴幼儿头颅低剂量螺旋CT扫描参数.方法 选取幼猪5只,在固定其他参数的情况下,先行常规400 mAs CT扫描,再行300、250、200、150、100 mAs低剂量扫描,每只猪每个条件扫描12次,各获得960幅图像,测量实验动物的CT剂量指数(CT dose index,CTDI).扫描均采用脑组织算法,将获得图像由3名医师进行双盲法阅片,使用4分制评分,对6组图像的清晰度进行质量评分,比较各组间图像质量评分及CTDI的差异性.CTDI及评分结果的比较采用方差分析和卡方检验.结果 管电流400、300、250、200、150、100 mAs时CTDI分别为(55.5±0.1)、(41.9±0.0)、(34.7±0.0)、(27.8±0.0)、(20.9±0.0)、(12.2±0.0)mgy,差异有统计学意义(F=214872.0,P<0.05).常规400 mAs扫描及低剂量300、250、200、150 mAs扫描图像总评分分别为(3.7±0.5)、(3.7±0.5)、(3.6±0.3)、(3.6±0.5)、(3.6±0.5)分,评分均在3分以上,可达到诊断要求,而100 mAs扫描图像总评分为(2.1±0.5)分,<3分,图像不能达到诊断要求.100 mAs时,960幅图像中>3分215幅,<3分745幅,与常规剂量400 mAs组(960幅图像评分均>3分者934幅)图像质量比较差异有统计学意义(χ~2=3289.9,P<0.05).结论 在其他参数不变情况下,利用150 mAs低剂量对幼儿头颅进行螺旋CT扫描,图像质量能够满足临床要求,而辐射剂量大幅下降.     

iDose 6迭代重建在降低盆腔CT扫描辐射剂量中的应用

目的 :探讨应用iDose 6迭代重建在获得高质量CT图像前提下,能否降低盆腔CT扫描的辐射剂量。方法 :选择57例行盆腔CT增强扫描的患者作为研究对象,均行常规剂量(120 kV,200 mAs)及低剂量(120 kV,60 mAs)CT扫描。低剂量扫描分别行滤波反投影(FBP)重建、iDose 6迭代重建作为观察组;常规剂量扫描图像行FBP重建作为对照组。由2位医师观察记录2组的辐射剂量及图像质量评价的主客观指标。结果:观察组辐射剂量为对照组的25.71%;观察组iDose 6迭代重建图像主客观指标与对照组差异均无统计学意义(均P0.05)。结论:iDose 6迭代重建技术可显著提高CT图像质量,有助于降低盆腔CT扫描的辐射剂量。     

腹部水模不同管电压、管电流CT扫描的研究

目的通过不同的管电压、管电流(m As)对水模反复扫描,探索最适腹部低剂量图像的扫描条件。方法将碘剂、生理盐水按比例配制成实验水模,固定于CT质量确认模上,置于扫描床中心。选择人体腹部扫描条件,固定扫描条件(层厚、螺距、FOV等)不变,仅改变m As或管电压,对配有不同碘浓度的七只试管进行扫描,测量CT图像的一定感兴趣区(ROI)的CT值(x珋±SD,SD表示噪声值),计算得出SNR,并将常规扫描得到的CT值、图像噪声、SNR与改变扫描条件后的进行比较。观察不同管电压、管电流对CT值、图像噪声值及SNR的影响。结果 1)管电压为120k V时,管电流降到60m As时,图像质量明显下降,达不到临床诊断标准;管电压为100k V,管电流降到120m As时,图像质量明显下降,达不到临床诊断标准;管电压为80k V,管电流为200m As或低于200m As时,图像质量达不到临床诊断标准;管电压为70k V,管电流为200m As或低于200m As时,图像质量达不到临床诊断标准;2)CT值、SNR值均随对比剂碘浓度的升高而升高;CT值随电压升高而降低,而电压为100k V时,SNR值最大。结论腹部低剂量检查时,推荐扫描条件100k V,150m As,既能降低辐射剂量,也能得到接近管电压120k V、200m As图像质量的图像。     

不同探测器宽肺部低剂量CT影像的对照分析

目的 比较16层螺旋CT 2种不同探测器宽肺部低量扫描的影像质量,为肺部低剂量检查提供最佳扫描参数.方法 对100例采用1.5 mm×16(24 mm)宽探测器行肺部低剂量体检时有肺结节发现者,再采用0.75 mm×16(12 mm)宽探测器对肺结节进行局部扫描,其它扫描条件均相同,再分别重建5 mm及重叠50%的 2 mm及1 mm的最薄层图像用于三维后处理用,对照分析其影像及后处理重建图像的质量.结果 2种扫描检查对病灶的显示均无明显差异,图像质量优良.结论 肺部低剂量16层螺旋CT扫描可采用宽(1.5 mm)探测器进行扫描,能提供与较窄探测器相近的诊断信息.     

64层螺旋CT检测泌尿系结石低kV扫描的优化选择及临床应用

目的：探讨64层螺旋CT检测泌尿系结石低kV扫描方案的优化及临床应用。方法：132例泌尿系结石患者随机分成6组（每组22名患者）：Ⅰ组（80kV～200mAs组）、Ⅱ组（80kV～300mAs组）、Ⅲ组（100kV～100mAs组）、Ⅳ组（100kV～150mAs组）、Ⅴ组（100kV～200mAs组）、Ⅵ组（120kV～200mAs组）。Ⅵ组为对照组。扫描层厚5mm,层间距5mm,螺距0.984;扫描结束后将获得的扫描原始数据（5mm图像）重建成1.25mm图像。测量5mm图像和1.25mm图像的肾实质的CT值及SD值,计算信噪比（SNR）,测量1.25mm层厚图像结石的最大CT值及最大横径,计数结石检出数,对图像进行主观评分并统计优、良、合格及不合格图像的例数。记录各组的辐射剂量指标CTDIvol。结果：测量5mm层厚图像,Ⅲ组的SD值为18.20,Ⅰ组的SD值为17.84,其扫描图像主观评分均合格（〉6分）,X线辐射剂量比对照组降低了69.01%。5mm图像重建成1.25mm图像后,图像噪声显著增大,与对照组相比,Ⅴ组的噪声增加率仅为28.60%,信噪比降低率仅为11.11%,X线辐射剂量降低了38.02%,其他各实验组与对照组相比噪声增加率均超过了35%。结论：在降低X线照射剂量的情况下,腹部低kVCT扫描（100kV～100mAs,80kV～200mAs）图像质量符合诊断要求,可以作为检查泌尿系结石MSCT扫描的优化条件。     

Is targeted reconstruction necessary for evaluating contrast-enhanced chest computed tomography using a liquid crystal display monitor?

Purpose  The aim of this study was to examine whether 20-cm field-of-view (FOV) targeted reconstruction (TR) on contrast-enhanced (CE) chest computed tomography (CT) might improve the diagnostic value compared with simple zooming (SZ) from whole-thorax FOV images using a 2 million (2M)-pixel liquid crystal display (LCD) monitor. Materials and methods  We prospectively evaluated 44 patients. SZ images were magnified from a FOV of 26–34 cm (mean 29.7 cm). Parameters were 512 × 512 matrix and 3 mm thickness and interval. Images were reconstructed using a soft-tissue kernel. Three radiologists evaluated contour, spiculation, notch, pleural tag, invasion, and internal characteristics of the lesions using 5-scale scores. We also performed a phantom study to evaluate the spatial resolution of images. Results  The diagnostic value of the TR images was similar to that of the SZ images, with the findings identified in 88%–100% of the cases. Artifacts from highdensity structures deteriorated the image quality in six (14%), and the SZ images were judged to be preferable in five of them. In the phantom study, there was little difference in spatial resolution between the two images. Conclusion  The SZ images from whole-thorax FOV on CE chest CT were similar in quality to TR images using a 2M-pixel LCD monitor.     

Spatial variation of resolution and noise in multi-detector row spiral CT

RATIONALE AND OBJECTIVES: The authors performed this study to evaluate an approach for measuring the variations of three-dimensional spatial resolution and image noise throughout a field of view imaged with multi-detector row spiral computed tomographic (CT) scanners. MATERIALS AND METHODS: The authors designed a phantom (diameter, 320 mm) that contained 37 metallic spheres (diameter, approximately 0.8 mm) positioned between two disks made of a material with attenuation being that of water. One sphere was located at the isocenter of the phantom, and the rest were evenly spaced in three concentric rings with diameters of 100, 200, and 300 mm, respectively. The phantom was imaged with two widely used multi-detector row CT scanners by using a standard protocol and four variations of that protocol. Because a recently developed theory holds that image resolution should be proportional to the square root of the trace of the covariance matrix of a point spread function, the authors developed a software package to segment high-attenuation spheres from the CT image volume and compute point spread functions from blurred images of the spheres. Three-dimensional spatial resolution and image noise were calculated as a function of radial distance within the field of view. RESULTS: Resolution and noise were quantified in the resultant CT image volumes and found to be nonisotropic, with worse resolution and less noise occurring at the periphery of the field of view. CONCLUSION: The method enabled measurement of variations in spatial resolution and of their distribution on images obtained with multi-detector row CT scanners. These findings may contribute to the development of an improved algorithm for image reconstruction.     

16层螺旋CT的z轴空间分辨力测试

目的：采用主客观两种方法评价16层螺旋Cr系统的z轴空间分辨力,分析16层螺旋CT的螺距（Pitch）对z轴空间分辨力的影响。方法：把Catphan500模体的CTP528模块水平放置在检查床面上,使用Somatom Cardiac16层CT机和腹部螺旋扫描模式：准直宽度0．75nma×16,重建间隔0．1mm,重建层厚0．75mm,不同螺距进行扫描,然后重建图像。在后处理工作站对各Pitch的序列图像进行冠状位多平面重组后目测图像上z轴方向可识别的线对测试卡的最大线对数。使用上述扫描条件,对Delta模体进行扫描,制作不同螺距的MTF曲线。结果：采用线对测试卡测试的Pitch分别为0．75、1．00、1．25的z轴空间分辨力是10、9、9LP／cm。采用MTF方法测试的相对信号强度2％的空间分辨力分别是11．31、9．51、9．70LP／cm。结论：Somatom Cardiac16层螺旋CT机具有比较高的z轴空间分辨力。对于该机型,Pitch的变化对z轴空间分辨力的影响非常小。     

Optimization of the technique of virtual colonoscopy using a multislice spiral computerized tomography

PURPOSE: To optimize scanning parameters for virtual colonoscopy utilizing a multislice Helical CT scanner in an in vitro study (using a homemade colonic phantom) and in a preliminary clinical study. MATERIAL AND METHODS: A colonic phantom was built using a plastic tube and 12 plastiline polyps were placed inside. The colonic phantom was studied with a multislice Helical CT scanner. Axial images were obtained with the phantom parallel to the long axis of the moving table (in order to simulate the evaluation of ascending and descending colon): oblique images were acquired with the phantom at 45 degrees relative to the long axis of the moving table (in order to simulate the evaluation of sigmoid colon and colonic flexures). Four different scanning protocols were tested: 1) slice collimation, 5 mm; slice width, 7 mm; table speed, 25 mm; reconstruction index, 5 mm; 2) slice collimation, 2.5 mm; slice width, 3 mm; table speed, 15 mm; reconstruction index, 3 mm; 3) slice collimation, 1 mm; slice width, 1.25 mm; table speed, 5 mm; reconstruction index, 1 mm; 4) slice collimation, 1 mm; slice width, 1.25 mm; table speed, 4 mm; reconstruction index, 1 mm. Quantitative analysis consisted in evaluation of the number of identified polyps and polyp size along the longitudinal axis. Qualitative analysis consisted in the evaluation of image artifacts and quality of 3D reconstructed images (step artifacts and polyp geometry distortion). This preliminary clinical study was performed in 12 patients (7 men and 5 women) who underwent multislice Helical CT colonography. We selected patients with clinical indications for conventional colonoscopy or after unsuccessful conventional colonoscopy. RESULTS: Multislice Helical CT colonography was 100% sensitive in the detection of all polyps and in all scanning protocols. With oblique scans, only a 3-mm polyp was missed during protocol 1 (sensitivity: 92%). Polyp geometry distortion was observed on longitudinal reconstructions, whereas no distortion was seen on axial images. Image quality was graded as optimal for protocols 2, 3, and 4; protocol 1 was graded as good on transverse scans and as poor on oblique scans. In our preliminary clinical study, two colonic carcinomas and three polyps were identified. CONCLUSIONS: At present, the introduction of multislice technology in virtual colonoscopy permits to improve spatial resolution and image definition. The actual clinical advantage, in terms of increased diagnostic accuracy, needs further investigation in larger clinical studies.     

Effects of scanning and reconstruction parameters on image quality in electron-beam CT angiography: coronary artery phantom study

RATIONALE AND OBJECTIVES: This study compared the image quality obtained with different scanning and reconstruction parameters for electron-beam computed tomographic (CT) angiography and sought optimal methods for visualizing the coronary artery lumen. MATERIALS AND METHODS: Electron-beam CT angiography with contrast material enhancement was used to image 35 branches of fresh postmortem swine coronary arteries. Different collimation widths, fields of view (FOVs), reconstruction kernels, and algorithms were employed to reconstruct the acquired raw data into CT angiographic images. Image quality was compared and analyzed. RESULTS: The contrast-to-noise ratios (C/Ns) for 1.5-, 2-, and 3-mm section thickness were 28.4 +/- 15.2, 31.9 +/- 9.3, and 33.8 +/- 14.5, respectively (P < .05). The lengths of visualized coronary artery lumina were significantly longer for 1.5-mm scanning (71.6 mm +/- 4.3) than for 2-mm (58.3 mm +/- 5.5) and 3-mm scanning (59.0 mm +/- 8.0) (P < .01). The C/Ns for 12.7-, 18.0-, and 26.0-cm FOV reconstruction were 32.8 +/- 9.9, 28.9 +/- 8.2, and 27.1 +/- 8.2, respectively (not significant), and the visualized luminal lengths were 76.1 mm +/- 12.5, 71.7 mm +/- 14.6, and 65.4 mm +/- 13.1, respectively (not significant). The highest C/N (48.2 +/- 13.3) was achieved with smooth kernels and a cone-beam algorithm, and the lowest (14.7 +/- 3.4) with very sharp kernels and a normal algorithm. Cone-beam algorithm images had significantly higher C/Ns than did normal algorithm images (P < .001), and they demonstrated longer coronary artery lumina (P < .01). CONCLUSION: Collimation width, FOV, reconstruction kernels, and algorithms are important in the processing of high-quality electron-beam coronary angiograms. A 1.5-mm collimation width, 12.7-cm FOV, cone-beam reconstruction algorithm, and very sharp kernels should help in obtaining the best image quality and depicting the longest segments of coronary artery lumen.     

Evaluation of CRT images of digitized film angiographs

X-ray sheet film images of the test chart, the vascular phantom and angiography were digitized at sampling pitch of 0.2 mm and 0.15 mm using film digitizer TFR-01 (Toshiba) and transferred to a device for image storage and display system with 1635-line display monitor (TDF-500AS, Toshiba). Comparison of image qualities between film- and CRT-images was performed in fundamental and clinical studies. Resolution of the test chart image of conventional radiography was worse on CRT than on the original film, although it was improved when film image was digitized at resolution of 0.15 mm/pixel in comparison with that at resolution of 0.2 mm/pixel. Moiré stripes which occurred due to interference were found on CRT images taken using a grid technique. On CRT images of X-ray sheet film using direct magnification technique moiré stripes were not produced because of non grid technique, and the resolution approached that of the original film. In the study using vascular phantom, the optimal image on CRT could be obtained by various image processing procedures, and image quality on CRT with resolution of 0.15 mm approached that of original film. In case of direct magnification CRT images were superior to film images. Subtraction image of the vascular phantom at resolution of 0.2 mm/pixel was obtained on CRT and compared with film subtraction image. On conventional subtraction CRT image moiré stripes impaired the image quality in comparison with the film subtraction. However, magnification subtraction image of the vascular phantom on CRT was superior to the film subtraction. The results obtained in the test chart studies and phantom studies were also confirmed in clinical studies using various kind of angiograms. In addition, ROC study using clinical angiograms showed no significant statistical differences between the original film and CRT image even with 0.2 mm matrix size. Angiographic image on CRT at resolution of 0.15 mm/pixel or less is available for clinical use in place of conventional film image.     

Semi-automatic measurement of the airway dimension by computed tomography using the full-width-half-maximum method: a study on the measurement accuracy according to the CT parameters and size of the airway.

OBJECTIVE: To assess the influence of variable factors such as the size of the airway and the CT imaging parameters such as the reconstruction kernel, field-of-view (FOV), and slice thickness on the automatic measurement of airway dimension. MATERIALS AND METHODS: An airway phantom was fabricated that contained eleven poly-acryl tubes of various lumen diameters and wall thicknesses. The measured density of the poly-acryl wall was 150 HU, and the measured density of the airspace filled with polyurethane foam was -900 HU. CT images were obtained using a 16-MDCT (multidetector CT) scanner and were reconstructed with various reconstruction kernels, thicknesses and FOV. The luminal radius and wall thickness were measured using in-house software based on the full-width-half-maximum method. The measured values as determined by CT and the actual dimensions of the tubes were compared. RESULTS: Measurements were most accurate on images reconstructed with use of a standard kernel (mean error: -0.03 +/- 0.21 mm for wall thickness and -0.12 +/- 0.11 mm for the luminal radius). There was no significant difference in accuracy among images with the use of variable slice thicknesses or a variable FOV. Below a 1-mm threshold, the measurement failed to represent the change of the real dimensions. CONCLUSION: Measurement accuracy was strongly influenced by the specific reconstruction kernel utilized. For accurate measurement, standardization of the imaging protocol and selection of the appropriate anatomic level are essential.