Stereolithographic models simulating trabecular bone and their characterization by thin-slice- and micro-CT

The analysis of bone structure in vivo is an important goal in osteoporosis, because the determination of bone mineral density alone is insufficient to predict whether an individual patient will eventually suffer an osteoporotic fracture or not. An additional structural analysis may significantly improve the statistical assessment of fracture risk. In this study we present a method to generate realistic although enlarged 3D phantoms of trabecular bone. These phantoms are useful in characterizing the potential of in vivo imaging procedures for the analysis of bone structure and to verify textural or structural analysis methods applied to these images. Our phantoms are based on a real trabecular bone specimen that was converted to a plastic model using the technique of stereolithography. The trabecular network is modeled by hydroxyapatite. Limitations of the stereolithographic process prevent the generation of exact 1:1 replicas of the real bone. A histomorphometric analysis of microCT scans of the phantoms showed that an excellent replication of the bone structure could be achieved in phantoms enlarged by a factor of 2.5 with "trabecular" hydroxyapatite concentrations up to 400 mg/cm3. In order to demonstrate the usefulness of our phantoms, we investigated one of them with various thin-slice CT protocols using clinical single- and multi-slice spiral CT scanners. The enlargement of the phantoms limits their use on high spatial resolution CT scanners (resolution >20 lp/cm). The limited hydroxyapatite concentration requires enhanced exposure rates for the phantoms scans to offset the larger impact of noise due to the lower contrast in the phantoms.     

64排CT容积HRCT扫描方案优化的模具研究

目的优化容积HRCT的扫描方案,提高容积HRCT的图像质量。方法应用64排CT对Catphan模具进行扫描,采用螺旋扫描方式,对HRCT的扫描方案进行优化,优化的参数包括：探测器宽度、焦点尺寸、旋转时间、管电压及管电流、扫描孔径、螺距、重建卷积函数、重建模式。结果增加探测器宽度可使噪声降低（t=-4.228,P=0.002）,放射剂量降低,对空间分辨率无明显影响。改变旋转时间对空间分辨率、噪声（F=0.627,P=0.130）均无明显差异。小焦点较大焦点的空间分辨率提高1 LP/cm。增加管电压与管电流可使噪声降低,空间分辨率随之改善,放射剂量增加。不同扫描孔径的放射剂量有所不同。螺距0.5得到最佳的Z轴分辨率12 LP/cm。在3种高分辨率算法中,bone优于bone plus及edge。重建模式plus较full的噪声降低（t=58.234,P〈0.001）,Z轴分辨率也降低。结论采用优化的扫描方案,可以提高容积HRCT的图像质量并控制放射剂量,有助于正确评价容积HRCT的价值。     

高分辨靶重建模式优化宝石CT成像

目的以体模实验为基础,观察高分辨靶重建模式优化宝石CT成像的价值。方法采用宝石CT不同的扫描野(SFOV;50cm vs 32cm)对Catphan 500体模分别进行高分辨和非高分辨模式扫描,并对原始数据以相同大小的显示野(25cm)进行STAND算法重建成像。根据不同成像方式,将所有图像分为SFOV 50cm+非高分辨组(A组)、SFOV50cm+高分辨组(B组)、SFOV 32cm+非高分辨组(C组)和SFOV 32cm+高分辨组(D组),测量并比较各组图像噪声、SNR、CNR、空间分辨率、密度分辨率及CT剂量指数(CTDI)。结果 4组噪声、SNR、CNR、空间分辨率、密度分辨率及CTDI差异均有统计学意义(P均0.05)。C组较A组噪声增加(P0.01);与A组比较,B组空间分辨率提高,D组CNR、SNR均降低(P均0.01),且噪声升高(P0.01)。结论选择高分辨靶重建模式,不增加图像噪声,并可保证对比噪声比和信噪比,提高空间分辨率。     

Effective Dose of CT- and Fluoroscopy-Guided Perineural/Epidural Injections of the Lumbar Spine: A Comparative Study

The objective of this study was to compare the effective radiation dose of perineural and epidural injections of the lumbar spine under computed tomography (CT) or fluoroscopic guidance with respect to dose-reduced protocols. We assessed the radiation dose with an Alderson Rando phantom at the lumbar segment L4/5 using 29 thermoluminescence dosimeters. Based on our clinical experience, 4–10 CT scans and 1-min fluoroscopy are appropriate. Effective doses were calculated for CT for a routine lumbar spine protocol and for maximum dose reduction; as well as for fluoroscopy in a continuous and a pulsed mode (3–15 pulses/s). Effective doses under CT guidance were 1.51 mSv for 4 scans and 3.53 mSv for 10 scans using a standard protocol and 0.22 mSv and 0.43 mSv for the low-dose protocol. In continuous mode, the effective doses ranged from 0.43 to 1.25 mSv for 1–3 min of fluoroscopy. Using 1 min of pulsed fluoroscopy, the effective dose was less than 0.1 mSv for 3 pulses/s. A consequent low-dose CT protocol reduces the effective dose compared to a standard lumbar spine protocol by more than 85%. The latter dose might be expected when applying about 1 min of continuous fluoroscopy for guidance. A pulsed mode further reduces the effective dose of fluoroscopy by 80–90%.     

Which Phantom Is Better for Assessing the Image Quality in Full-Field Digital Mammography?: American College of Radiology Accreditation Phantom versus Digital Mammography Accreditation Phantom

Objective

To compare between the American College of Radiology (ACR) accreditation phantom and digital mammography accreditation phantom in assessing the image quality in full-field digital mammography (FFDM).

Materials and Methods

In each week throughout the 42-week study, we obtained phantom images using both the ACR accreditation phantom and the digital mammography accreditation phantom, and a total of 42 pairs of images were included in this study. We assessed the signal-to-noise ratio (SNR) in each phantom image. A radiologist drew a square-shaped region of interest on the phantom and then the mean value of the SNR and the standard deviation were automatically provided on a monitor. SNR was calculated by an equation, measured mean value of SNR-constant coefficient of FFDM/standard deviation. Two breast radiologists scored visible objects (fibers, specks, and masses) with soft-copy images and calculated the visible rate (number of visible objects/total number of objects). We compared SNR and the visible rate of objects between the two phantoms and calculated the k-coefficient for interobserver agreement.

Results

The SNR of the ACR accreditation phantom ranged from 42.0 to 52.9 (Mean, 47.3 ± 2.79) and that of Digital Phantom ranged from 24.8 to 54.0 (Mean, 44.1 ± 9.93) (p = 0.028). The visible rates of all three types of objects were much higher in the ACR accreditation phantom than those in the digital mammography accreditation phantom (p < 0.05). Interobserver agreement for visible rates of objects on phantom images was fair to moderate agreement (k-coefficients: 0.34-0.57).

Conclusion

The ACR accreditation phantom is superior to the digital mammography accreditation phantom in terms of SNR and visibility of phantom objects. Thus, ACR accreditation phantom appears to be satisfactory for assessing the image quality in FFDM.     

液体流率MR测量实验研究

目的:探讨稳定流动状态下磁共振信号强度与液体流速关系,为横窦血流量测定提供适当方法.材料和方法:在实验水模上放置内径3.4mm塑胶管,用高压注射器以不同的流量向管道内注入水,流量的变化范围从0.1～1.6ml/s.用1.5T超导磁共振仪单个无门控2D PC序列进行扫描,对液体磁共振信号强度和管道内实际流速采用相关回归分析方法进行统计分析.结果:磁共振信号强度(y)和液体速度(x)呈明显线性关系,y=68.914x 357.206,R2=0.998.结论:相位对比法是一种有效的流量测量方法.     

CT图像空间分辨力的实用检测方法

目的:设计应用于检测CT图像空间分辨力的实用方法及体模。方法:检测体模由两块纯有机玻璃中嵌入约0.1 mm厚的铝箔制成,扫描时使之与扫描面垂直,得到系统的冲击响应,即线扩展函数,经相干平均和傅立叶变换等步骤获得系统的调制传输函数,从而评价设备的空间分辨力。受检设备为单层面和多层面CT扫描仪各一台,设置不同扫描条件,共做4组实验。结果:调制传输函数曲线与所采用的扫描条件一致,截止频率与采用国际通用的CAPHAN 500体模测量的结果相当。结论:与线对法相比,通过测量线扩展函数计算调制传输函数来评价CT图像空间分辨力的方法减少了人工干预,结果准确、可靠。     

Analysis of MR phase-contrast measurements of pulsatile velocity waveforms

Errors in the measurement of the mean velocity of pulsatile velocity waveforms with ungated phasecontrast techniques were studied theoretically and experimentally. Waveforms consisting of a constant and two sinusoidal components were analyzed. Variations in magnitude and phase of the vascular magnetic resonance (MR) signal resulted in errors, the severity of which increased when either factor increased. Magnitude variations always resulted in overestimation. The general shape of the waveform greatly influenced the error, with certain waveforms producing greater inherent error than others. Experimental measurements were performed, validating the predicted sensitivity of these errors to changes in imaging parameters, including TR and flow-encoding sensitivity. Errors generally became more severe with increased flow-encoding sensitivity. The theoretical and experimental results suggest that accurate mean velocity measurements in many vessels of the body-with acquisition times of less than 15 seconds-should be attainable with ungated imaging techniques and with careful selection of relevant imaging parameters.     

A phantom for imaging biological fluids by ultrasound and CT scanning

The construction of a phantom for comparative imaging of biological fluids by ultrasonic and computerized tomographic scanning is described. The phantom incorporates a tissue-equivalent gel closely resembling human liver tissue as imaged by these two modalities.     

Anthropomorphic breast phantoms for assessing ultrasonic imaging system performance and for training ultrasonographers: part II

Three prototype anthropomorphic breast phantoms are discussed. The phantoms were constructed using ultrasonically tissue-mimicking materials; these materials mimic various tissue parenchymae in terms of attenuation, speed of sound, density, and scatter level. Realistic artifacts related to refraction and reflection at interfaces between different simulated parenchymae are produced. The phantoms represent premenopausal breasts, and they complement one another. Two of them represent the dense breasts of women under 30 years of age, and one represents that of a woman between 35 and 40 years of age. Of the former two, one produces what is apparently above-average refraction effects in the region of the peripheral fat layer; the other produces more typical refraction effects. Simulated tumors, cysts, and calcifications of various sizes are suspended in the glandular regions. Such phantoms are valuable for use in developmental testing of state-of-the-art ultrasound machines, quality assurance testing of clinical machines, and training of sonographers in breast imaging.