Enlarged longitudinal dose profiles in cone-beam CT and the need for modified dosimetry

In order to examine phantom length necessary to assess radiation dose delivered to patients in cone-beam CT with an enlarged beamwidth, we measured dose profiles in cylindrical phantoms of sufficient length using a prototype 256-slice CT-scanner developed at our institute. Dose profiles parallel to the rotation axis were measured at the central and peripheral positions in PMMA (polymethylmethacrylate) phantoms of 160 or 320 mm diameter and 900 mm length. For practical application, we joined unit cylinders (150 mm long) together to provide phantoms of 900 mm length. Dose profiles were measured with a pin photodiode sensor having a sensitive region of approximately 2.8 x 2.8 mm2 and 2.7 mm thickness. Beamwidths of the scanner were varied from 20 to 138 mm. Dose profile integrals (DPI) were calculated using the measured dose profiles for various beamwidths and integration ranges. For the body phantom (320-mm-diam phantom), 76% of the DPI was represented for a 20 mm beamwidth and 60% was represented for a 138 mm beamwidth if dose profiles were integrated over a 100 mm range, while more than 90% of the DPI was represented for beamwidths between 20 and 138 mm if integration was carried out over a 300 mm range. The phantom length and integration range for dosimetry of cone-beam CT needed to be more than 300 mm to represent more than 90% of the DPI for the body phantom with the beamwidth of more than 20 mm. Although we reached this conclusion using the prototype 256-slice CT-scanner, it may be applied to other multislice CT-scanners as well.     

A new CT scan method for measuring the tibial tubercle trochlear groove distance in patellar instability

Patellar malalignment leading to objective or potential patella instability can be caused by tibial tuberosity lateralisation. This can be treated with a tuberosity medialisation. CT scan measurements are needed to assess the tibial tubercle trochlear groove distance. When using the previously described methods to determine this distance it can be difficult to determine the anatomical structures on the maximum intensity projection images, and this can lead to measurement error. This study was designed to compare the reliability of a new computer based CT measurement to the previously described method to determine the tibial tubercle trochlear groove distance. For each method, four observers measured each of 50 knees twice. The inter- and intra-observer variability for the conventional method and a new method were determined. Using the conventional method, the number of knees for which the difference between the aggregate mean of all eight measurements and the mean of duplicate measurements per observer greater than 2 mm varied among the observers between 7 and 24 for the 50 knees, while this variation between four and seven for the same 50 knees using the new method. The limits of reproducibility based on measurements from the four different observers improved by 25%, indicating that the measurement error is considerably smaller with the new method. We advise using this more accurate method to improve the selection of patients for a tuberosity medialisation.     

Physical evaluation of CT scan methods for radiation therapy planning: comparison of fast, slow and gating scan using the 256-detector row CT scanner

Although slow-rotation CT scanning (slow-scan CT: SSCT) has been used for radiation therapy planning, based on the rationale that the average duration of the human respiratory cycle is 4 s, a number of physical and quantitative questions require answering before it can be adopted for clinical use. This study was performed to evaluate SSCT physically in comparison with other scan methods, including respiratory-gated CT (RGCT), and to develop procedures to improve treatment accuracy. Evaluation items were geometrical accuracy, volume accuracy, water equivalent length and dose distribution using the 256-detector row CT with three scan methods. Fast-scan CT (FSCT) was defined as obtaining all respiratory phases in cine scan mode at 1.0 s per rotation. FSCT-ave was the averaged FSCT images in all respiratory phases, obtained by reconstructing short time intervals. SSCT has been defined as scanning with slow gantry rotation to capture the whole respiratory cycle in one rotation. RGCT was scanned at the most stable point in the respiratory cycle, which provides the same image as that by FSCT at the most stable point. Results showed that all evaluation items were dependent on motion characteristics. The findings of this study indicate that 3D planning based solely on SSCT under free breathing may result in underdosing of the target volume and increase toxicity to surrounding normal tissues. Of the three methods, RGCT showed the best ability to significantly increase the accuracy of dose distribution, and provided more information to minimize the margins. FSCT-ave is a satisfactory radiotherapy planning alternative if RGCT is not available.     

图像域迭代重建算法对腹部CT平扫图像质量和辐射剂量的影响

目的:探讨图像域迭代重建算法对腹部CT平扫图像质量及辐射剂量的影响。 方法:以辽阳市中心医院2017年1月~2018年4月行腹部CT平扫的150例患者为研究对象,依据就诊先后顺序随机将其分为观察组与对照组,各75例。均行自动毫安控制技术扫描,管电压均为130 kV。观察组预设图像质量参考毫安秒150 mAs,行图像域迭代重建算法重建;对照组预设图像质量参考毫安秒250 mAs,行滤波反投影重组。通过CT值、图像噪声SD、图像信噪比、对比噪声比评价两组图像客观质量,并行图像质量主观评价,记录两组CT剂量容积指数。 结果:观察组肝脏、脾脏的图像噪声SD均显著低于对照组,图像信噪比均显著高于对照组,差异有统计学意义（P<0.05）;CT值、对比噪声比、主观整体质量评分两组比较差异均无统计学意义（P>0.05）;观察组CT剂量容积指数为（10.02±2.85） mGy,显著低于对照组的（15.68±4.36） mGy,差异有统计学意义（P<0.05）。 结论:图像域迭代重建算法不仅能保证腹部CT平扫图像质量,而且能有效减少辐射剂量。     

Real-time multiprocessing of slit scan chromosome profiles

The multiprocessor NERV and its application to slit scan flow cytometry is described. Up to 320 processors and 640 MBytes of RAM may be used in one VME crate, providing a computing power of ≤ 1300 MIPS. The multiprocessor is controlled by a host computer that provides a friendly user interface and comfortable program development tools. All hardware and software has been tested on a prototype NERV system with 5 processors. For a real-time classification/detection of normal and aberrant chromosomes, the centromeric index or the number of centromeres are computed or specifically labeled DNA sequences are detected. The program is partitioned into 60 tasks that can be executed concurrently. A total analysis time of < 600 μs including system overhead will be achieved according to timing measurements which have been done for all individual tasks.     

鼻部外伤中X线侧位片与CT冠状和横断扫描的应用对比

目的通过三种影像学方法的研究,确定合理的鼻部外伤影像学检查方法。方法对106例鼻部外伤者同时作X线鼻骨侧位像、冠状和横断CT扫描。以冠状 横断CT扫描的结果为准,比较了各种检查方法之间对鼻部外伤影像学征象的检出率。结果两种CT扫描合用的诊断效果最好。X线鼻骨侧位片仅能检出70.76%的鼻骨骨折,对上颌骨骨折等其他鼻部外伤均不能诊断。在鼻骨或/和上颌骨额突骨折的诊断中冠状CT扫描均显著优于横断CT扫描,而在鼻泪管骨折、骨颌缝分离、鼻骨间缝增宽的诊断上则横断CT扫描均要显著优于冠状CT扫描。结论在鼻部外伤的影像学检查中仅作鼻骨X线侧位片是不够的;为了解有无鼻骨/或上颌骨突骨折应首先作鼻部冠状CT扫描,如经济条件许可,可加作鼻骨横断扫描。     

Determination of the urethral dose in prostate brachytherapy when the urethra cannot be visualized in the postimplant CT scan

This study investigates the feasibility of locating the urethra at the geometric center of peripherally loaded 125I prostate implant when a urinary catheter is not utilized for the postimplant CT scan. Twenty postimplant CT scans utilizing a urinary catheter were randomly selected. The urethra was localized in each study and, in addition, a surrogate urethra was localized at the geometric center of the prostate. Dose-volume histograms of the urethra and surrogate urethra were compiled and compared. The values obtained for the urethra D10, D25, and D50 were in good agreement and demonstrate that the urethral dose can be determined reliably by locating a surrogate urethra at the geometric center of the prostate in a peripherally loaded implant when the urethra cannot be visualized.     

CT结肠成像技术扫描体位的优化

目的探讨不同部位的结直肠癌病变或结直肠癌术后吻合口显示清晰程度与扫描体位（仰卧位/俯卧位）的关系,为优化CT结肠成像（CTC）技术提供理论依据。方法选择32例临床病理确诊为结直肠癌患者,其中男性22例,女性10例;年龄30～73岁,平均年龄50.6岁。行CTC检查,体位采用仰卧位及俯卧位,将CTC结果与纤维肠镜和手术病理结果对照。同时有20例术后吻合口（直肠为保肛患者）患者获得复查。结果 52例次患者中,病灶及吻合口位于直肠27例次,肛管3例次,乙状结肠9例次,降结肠3例次,横结肠4例次,升结肠6例次,均为单发病灶。位于直肠与乙状结肠的病变或吻合口：直肠25/27（92.59%,χ2=32.72,P﹤0.05）,乙状结肠9/9（100%,χ2=8.42,P﹤0.05）。俯卧位上肠管充气明显,病变显示清晰,优于仰卧位,差异具有统计学意义;位于横结肠的病变或吻合口4/4（100%,χ2=4.5,P﹤0.05）,仰卧位肠管充气明显,病变显示清晰,优于俯卧位,差异具有统计学意义。升降结肠病变或吻合口在仰卧位9/9（100%）及俯卧位9/9（100%）上肠管充气效果相同,均显示清晰,差异无统计学意义。肛管癌在仰卧位（0/3）及俯卧位（0/3）上均显示欠佳,由于病例数少,不具有统计学意义。结论 CTC中不同体位上不同位置的结直肠肠管充气效果不同,根据病变或吻合口的位置,采取最佳单体位,可使患者接受的射线剂量减半,而肠管的充气效果最佳,有利于显示病变及判定吻合口有无复发。     

Neuropsychological deficits and CT scan changes in elderly depressives

A number of computerized tests were used to study visual attention, memory and learning in elderly depressed patients. Impairment was found in approximately 70% of depressed patients and was seen particularly in memory and in measures of latency. Depressed patients showed equivalent impairment in short-term memory but less impairment in conditional associative learning compared to a group of patients with early dementia of the Alzheimer-type (DAT), matched for age and pre-morbid IQ. With respect to qualitative differences between depression and DAT, depressed patients showed a different pattern of errors and a consistently prolonged latency of response which was independent of delay in a delayed matching-to-sample test. On recovery from depression, although improvement was seen in most test scores, performance in measures of latency and in a number of tests of memory and learning failed to reach the level seen in a group of matched control subjects and approximately 35% of patients continued to show impairment. For the depressed patients, ventricular brain ratio (VBR) correlated with measures of slowing. In addition, in the 'recovered-depressives', VBR correlated with poor performance at high levels of task difficulty. These findings are discussed with respect to previous literature on the pattern of cognitive impairment and CT scan findings in depression.     

Comparison of the Batho, ETAR and Monte Carlo dose calculation methods in CT based patient models

This paper shows the contribution that Monte Carlo methods make in regard to dose distribution calculations in CT based patient models and the role it plays as a gold standard to evaluate other dose calculation algorithms. The EGS4 based BEAM code was used to construct a generic 8 MV accelerator to obtain a series of x-ray field sources. These were used in the EGS4 based DOSXYZ code to generate beam data in a mathematical water phantom to set up a beam model in a commercial treatment planning system (TPS), CADPLAN V.2.7.9. Dose distributions were calculated with the Batho and ETAR inhomogeneity correction algorithms in head/sinus, lung, and prostate patient models for 2 x 2, 5 x 5, and 10 X 10 cm2 open x-ray beams. Corresponding dose distributions were calculated with DOSXYZ that were used as a benchmark. The dose comparisons are expressed in terms of 2D isodose distributions, percentage depth dose data, and dose difference volume histograms (DDVH's). Results indicated that the Batho and ETAR methods contained inaccuracies of 20%-70% in the maxillary sinus region in the head model. Large lung inhomogeneities irradiated with small fields gave rise to absorbed dose deviations of 10%-20%. It is shown for a 10 x 10 cm2 field that DOSXYZ models lateral scatter in lung that is not present in the Batho and ETAR methods. The ETAR and Batho methods are accurate within 3% in a prostate model. We showed how the performance of these inhomogeneity correction methods can be understood in realistic patient models using validated Monte Carlo codes such as BEAM and DOSXYZ.     

右肺下叶段支气管CT显示的应用解剖

目的：为给ＣＴ对右肺下叶作斜位扫描提供倾斜角度及对诊断提供参考数据。方法：以３０例标本制成支气管树和１３例ＣＴ影像观测叶、段支气管内径、段支气管与叶支气管的夹角。结果：叶支气管内径５．０±０．２ｍｍ。相邻底段支气管内径无显著差别。ＢⅥ、ＢⅦ、ＢⅧ、ＢⅨ和ＢⅩ的夹角分别为８８．１°±１．７°、１８．２°±３．５°、２０．２°±２．８°、１５．８°±２．６°和１６．７°±３．６°。结论：叶段支气管内径、管壁厚度可为ＣＴ诊断增加一个以数据为依据确定管腔狭窄或管壁增厚的方法以提高中心型肺癌的正确诊断率，依段支气管的倾斜角度将ＣＴ机架和体位作相应的倾斜和偏移使扫描层面与段支气管垂直可提高其ＣＴ显示率。     

Solid state line scan cameras for measuring strain in soft tissues and implants

The line scan camera, or LSC, is an inexpensive and easily applied technique for optical strain measurement of soft biomaterials. The LSC is based on a linear array of photodiodes; in gauging applications, where measurements between dark/light interfaces are important, the digital nature of the array can be exploited. Advantages of the LSC include low cost, high frequency response, applicability to front- or backlighted samples, insensitivity to stray and nonuniform lighting as well as to accidental overexposure, ease and linearity of calibration, and lack of temperature sensitivity. With the 1024 element arrays used herein, the relative resolution is theoretically limited to 1 part in 1024, or 0.1%; in practice, the relative resolution is somewhat poorer. LSCs have been successfully used in mechanical tests to measure the diameter of arteries and compliant vascular grafts, the longitudinal strain of vascular grafts, and the dynamic diameter of elastic tube models of graft/artery systems in pulsatile flow visualization experiments.     

Comparison of the plaque assay and 50% tissue culture infectious dose assay as methods for measuring filovirus infectivity

Two common methods of quantifying filovirus infectivity, a plaque assay and 50% cell culture infectious dose (TCID₅₀) endpoint dilution assay, were compared. The two assays were performed side by side using the same virus stock sample to determine the correlation between the results of the two assays. The TCID₅₀ assay appeared to be more sensitive but slightly more variable, and there was a tenfold difference in the numerical results of these methods of enumeration. The advantages and disadvantages of both assays are discussed. Both methods are useful and practicable in filovirus research, and this comparison will be hugely beneficial to the filovirus research community as it seeks to become more united. Further work in this area should be performed to ensure consistency in filovirus research.     

Estimating thyroid dose in pediatric CT exams from surface dose measurement

The purpose of this study was to investigate the possibility of estimating pediatric thyroid doses from CT using surface neck doses. Optically stimulated luminescence dosimeters were used to measure the neck surface dose of 25 children ranging in ages between one and three years old. The neck circumference for each child was measured. The relationship between obtained surface doses and thyroid dose was studied using acrylic phantoms of various sizes and with holes of different depths. The ratios of hole-to-surface doses were used to convert patients' surface dose to thyroid dose. ImPACT software was utilized to calculate thyroid dose after applying the appropriate age correction factors. A paired t-test was performed to compare thyroid doses from our approach and ImPACT. The ratio of thyroid to surface dose was found to be 1.1. Thyroid doses ranged from 20 to 80 mGy. Comparison showed no statistical significance (p = 0.18). In addition, the average of surface dose variation along the z-axis in helical scans was studied and found to range between 5% (in 10?cm diameter phantom/24?mm collimation/pitch 1.0) and 8% (in 16?cm diameter phantom/12?mm collimation/pitch 0.7). We conclude that surface dose is an acceptable predictor for pediatric thyroid dose from CT. The uncertainty due to surface dose variability may be reduced if narrower collimation is used with a pitch factor close to 1.0. Also, the results did not show any effect of thyroid depth on the measured dose.