Detectability of simulated pulmonary nodules on chest radiographs: Comparison between irradiation side sampling indirect flat-panel detector and computed radiography

Objective

To compare the detectability of simulated pulmonary nodules on chest radiographs between an irradiation side sampling indirect flat-panel detector (ISS-FPD) and computed radiography (CR).

Materials and methods

This study was an observer performance study. Simulated pulmonary nodules of 8 mm in diameter were superimposed on an anthropomorphic chest phantom. Chest radiographs were acquired under 2 exposure levels (4 and 3.2 mAs) with the ISS-FPD and the CR. Six thoracic radiologists evaluated all 40 images (10 patterns × 2 different exposure doses × 2 different systems) for the presence or absence of a lesion over each of 12 defined areas on a 3-megapixel monochrome liquid-crystal display. Receiver operating characteristic (ROC) curves were obtained for observation in predefined 480 areas. A jackknife method was used for statistical analysis. Differences with a P value of <0.05 were considered significant.

Results

The analysis of the observer detection of simulated pulmonary nodules showed larger areas under the ROC curve (AUC) by the ISS-FPD than by the CR. There was a statistically significant difference between the two systems at 3.2 mAs (P = 0.0330).

Conclusion

The ISS-FPD was superior to the CR for the detection of simulated pulmonary nodules at 3.2 mAs.     

改进的定位技术在胸部肿瘤穿刺活检中的应用

目的：探索CT-SIM三维定位系统、体模固定技术和PET-CT融合影像导引定位技术在胸部肿瘤经皮穿刺活检中的应用价值。方法：对380例胸部肿瘤患者行改进的CT定位技术下的经皮穿刺活检术。根据肿瘤的大小、深度、毗邻关系、活动度以及患者的心肺功能状态,综合运用CT-SIM系统、体模固定技术和PET-CT融合影像导引技术,为患者进行穿刺前定位。统计穿刺定位时间长度、成功率、确诊率、并发症发生情况,并与210例采用传统铅栅定位下胸部肿瘤穿刺活检的相应资料进行比较。结果：采用改进的CT定位技术的380例患者穿刺定位精确,平均定位时间（9.5 min）较传统方法（16.8 min）缩短7.3 min,活检成功率和确诊率分别是98.7%和95.3%,高于传统定位方法的93.3%和83.3%,两者差异均具有统计学意义（P〈0.05）。穿刺并发症发生率相似,气胸发生率分别为2.8%和2.9%,咯血发生率分别为11%和12.8%。结论：根据患者状态及肿瘤特点,在CT-SIM系统快速精确定位技术的基础上,综合运用体模固定技术和PET-CT融合影像导引技术,能显著缩短经皮穿刺活检的定位时间,提高活检成功率。     

头部体模扫描试验对成人头颅CT低剂量扫描的优化初探

目的：通过对头部体模扫描试验,探讨成人头颅CT低剂量扫描参数。方法：以层厚10 mm,扫描时间为1 s,通过改变mA值,以10 mA为间隔,20-300 mA间29个不同mA条件对头部体模进行轴向扫描,对容积CT剂量指数（CTDIvol）、噪声（SD）和对比-噪声比（CNR）进行客观评价分析与统计学处理,对图像低密度分辨力进行主观评价。结果：①CTDIvol随mAs增大而增大,呈线线关系;与300 mAs的CTDIvol（42 mGy）比较,80-150 mAs的CTDIvol（11-21 mGy）下降73%-50%。②SD值随mAs升高而降低;SD值随mAs变化曲线可分为SD改变非常显著段（20-50 mAs）、显著段（50-80 mAs）、缓坡段（90-150 mAs）和平缓段（160-300 mAs）。③CNR随mAs改变与SD值改变相反。④SD值与CNR统计学处理：20 mAs与30 mAs、30 mAs与50 mAs5、0 mAs与80 mAs、80 mAs与150 mAs、150 mAs与300 mAs的各SD值及CNR有统计学差异（P〈0.05）;160-300 mAs的各SD值与CNR无统计学差异（P〉0.05）。⑤图像LCR主观评价：20-50 mAs,分辨低密度圆柱体困难;50-80 mAs,主观图像质量明显下降,图像对诊断有影响;90-150 mAs主观图像质量有一定改变;160-300 mAs主观图像质量改变不明显。结论：80-150 mAs为低对比要求较高的成人颅脑低剂量平扫可用区间,为临床降低扫描剂量提供了依据。临床患者检查,可以用100 mAs进行平扫,CT剂量指数明显降低。     

符合线路肿瘤显像宽峰采集与常规程序对病灶检出能力比较的模型研究

目的比较符合线路肿瘤显像宽峰采集程序和常规程序对病灶的检出能力。方法用符合线路SPECT宽峰采集和常规程序分别对一系列对比度的模型进行扫描,从视觉观察和L/B值测量两方面比较两种程序对病灶的检出能力。结果视觉观察两种程序对病灶的检出率一致,当对比度2∶1和2.5∶1时直径0.8cm病灶均无法分辨,对比度大于等于15∶1时均出现溢出,常规程序溢出现象更显著;两种程序的L/B值无显著差别,直径2.8cm病灶在对比度10∶1以下L/B值均接近对比度,其余各个病灶的L/B值均显著低于对比度,病灶直径越小低估程度越明显。结论符合线路SPECT宽峰采集程序在不影响对病灶检出的同时能够缩短扫描时间。     

被检体形状及放置对MR线圈信噪比的影响

目的了解被检体、线圈间的耦合与线圈信噪比（SNR）的关系。方法MR扫描时，在头、体线圈中使用不同形状的水模及不同放置，做SNR测量序列扫描，检测SNR。结果扁圆柱体W100水模在头线圈中轴向放置时SNR（55．47±0．69）比径向放置时（46．59±1．36）高（t=16．48，P〈0．01），也比水平向放置时（46．32±0．88）高（t=23．15，P〈0．01），差异有统计学意义；扁圆柱体W100水模在体线圈中轴向放置时SNR（20．35±0．29）比径向放置时（19．52±0．42）高（t=4．60，P〈0．01），也比水平向放置时（19．68±0．46）高（t=3．52，P〈0．01），差异有统计学意义。直径较小的长圆柱体自制水模，中央轴对称放置于头线圈时SNR（27．64±0．83）比侧移或倾斜时（26．32±0．85）高（t=3．30，P〈0．01），差异有统计学意义。结论以线圈中心轴为对称轴放置被检体，可提高线圈SNR。     

Strategies to improve contrast in turboFLASH imaging: reordered phase encoding and k-space segmentation.

TurboFLASH (fast low-angle shot) sequences enable the acquisition of an image in a fraction of a second. However, unique to T1-weighted ultrafast imaging, the magnetization variation during image acquisition can produce artifacts along the phase-encoding direction. In this study, the signal behavior and nature of these artifacts were analyzed with various acquisition schemes to improve image contrast. The magnetization variation during image acquisition and its filtering effect on the image were simulated for three different approaches to T1-weighted turboFLASH imaging: standard turboFLASH with (a) monotonically ascending phase-encoding steps, (b) reordered phase encoding, and (c) k-space segmentation. Each of the modified data acquisition schemes has advantages. However, for subsecond imaging, reordered phase encoding produced improved image contrast over that of standard turboFLASH, and segmented k-space imaging gave superior tissue contrast compared with that of both standard and reordered turboFLASH, with imaging time that permits breath-hold studies.     

Development of whole-body representation and dose calculation in a commercial treatment planning system

For the epidemiological evaluation of long-term side effects of radiotherapy patients, it is important to know the doses to organs and tissues everywhere in the patient. Computed tomography (CT) images of the patients which contain the anatomical information are sometimes available for each treated patient. However, the available CT scans usually cover only the treated volume of the patient including the target and surrounding anatomy. To overcome this limitation, in this work we describe the development of a software tool using the Varian Eclipse Scripting API for extending a partial-body CT to a whole-body representation in the treatment planning system for dose calculation. The whole-body representation is created by fusing the partial-body CT with a similarly sized whole-body computational phantom selected from a library containing 64 phantoms of different heights, weights, and genders. The out-of-field dose is calculated with analytical models from the literature and merged with the treatment planning system-calculated dose. To test the method, the out-of-field dose distributions on the computational phantoms were compared to dose calculations on whole-body patient CTs. The mean doses, D2% and D98% were compared in 26 organs and tissues for 14 different treatment plans in 5 patients using 3D-CRT, IMRT, VMAT, coplanar and non-coplanar techniques. From these comparisons we found that mean relative differences between organ doses ranged from ?10% and +20% with standard deviations of up to 40%. The developed method will help epidemiologists and researchers estimate organ doses outside the treated volume when only limited treatment planning CT information is available.     

Accuracy of ultra-high–resolution computed tomography with a 0.3-mm detector for quantitative assessment of coronary artery stenosis grading in comparison with conventional computed tomography: A phantom study

BackgroundThe development of ultra-high–resolution CT (U-HRCT) is expected to improve the accuracy of coronary stenosis evaluation. This study aimed to evaluate the accuracy of the stenosis severities of coronary artery phantoms estimated using U-HRCT by comparing them to those estimated with conventional CT.MethodsCoronary artery phantoms with non-calcified and calcified lesions were scanned with conventional CT (64-row ?× ?0.625 ?mm) and U-HRCT (32-row ?× ?0.3125 ?mm). The coronary artery phantoms had lumen diameters of 2.0, 3.0, and 4.0 ?mm with non-calcified lesions representing 0%, 25%, 50%, and 75% stenosis and 3.0 and 4.0 ?mm with calcified lesions representing 0%, 25%, 50%, and 75% stenosis. The lumen diameters at the stenotic and non-stenotic regions were measured, and the stenosis severities were compared with the true values.ResultsFor non-calcified lesions, conventional CT significantly underestimated the stenosis severity in the phantom showing 75% stenosis with lumen diameters of 2.0 and 3.0 ?mm (p ?< ?0.05), while the estimated stenosis severities were not significantly different from the true values at all settings with U-HRCT. For the calcified lesions, conventional CT overestimated the stenosis severities at all settings (p ?< ?0.05), while U-HRCT yielded estimations closer to the true values, although still with some overestimation (p ?< ?0.05).ConclusionBy using U-HRCT, the estimated stenosis severities of the coronary artery with non-calcified lesion become almost equal to the true value, while those with calcified lesion are still overestimated although they become closer to the true value.     

Reducing dose in urography while maintaining image quality—a comparison of storage phosphor plates and a flat-panel detector

The introduction of new flat-panel detector technology often forces us to accept too high dose levels as proposed by the manufacturers. We need a tool to compare the image quality of a new system with the accepted standard. The aim of this study was to obtain a comparable image quality for two systems—storage phosphor plates and a flat-panel system using intravenous urography (IVU) as a clinical model. The image quality figure was calculated using a contrast–detail phantom (CDRAD) for the two evaluated systems. This allowed us to set a dose for the flat-panel system that gave equivalent image quality to the storage phosphor plates. This reduced detector dose was used in an evaluation of clinical images to find out if the dose reduction from the phantom study indeed resulted in images of equal clinical image quality. The image quality was assessed using image criteria of the European guidelines for IVU with visual grading analysis. Equivalent image quality in image pairs was achieved at 30% of the dose. The CDRAD contrast–detail phantom makes it possible to find dose levels that give equal image quality using different imaging systems.     

Mechanisms of flow-induced signal loss in MR angiography.

Mechanisms of signal loss in magnetic resonance angiography were studied with a stenotic flow phantom. The results indicate that while signal loss induced by mean fluid motions is localized about the stenosis, the fluctuating component of fluid motion induces signal loss over a much larger region, primarily distal to the stenosis. For both motion components, use of gradient moment nulling (GMN) above first order was found to be an ineffective means of reducing signal loss. In contrast, shortened gradient durations were found to reduce signal loss substantially. However, though a zeroth-order gradient is generally of the shortest duration, use of a slightly longer, first-order gradient was found to be the most robust means of reducing signal loss.