乳腺非介入管电压影响因素研究

目的:参照IEC 61676标准,研究随着管电压的增加,距离、过滤条件和阳极角等影响因素在两种乳腺辐射场（Mo/Mo和W/Rh）中的改变引起Fluke X2和RTI piranha 657两类非接入测量仪器测量结果的变化及差异。方法:利用介入法测量确定管电压稳定性,在两种乳腺辐射场情况下改变距离、过滤条件和阳极角进行非介入管电压测量,根据测量结果计算两种辐射场和两类仪器测量结果的变化趋势,并用蒙特卡罗模拟获得两种辐射场条件下因为过滤变化达到仪器的计数比值差异（R值变化率）并分析原因。结果:在W/Rh辐射场下,即使距离和阳极角差异较大、过滤条件发生微小变化,对两类仪器测量结果的影响符合IEC 61676的要求,都在0.5 kV以内;但是在Mo/Mo辐射场下,同样过滤条件变化引起的两类仪器测量结果差异较大,其中Fluke X2测量结果最大变化甚至达到了1.6 kV。结论:当对乳腺非介入管电压测量仪器进行校准时,各个实验室应该考虑确立统一的校准距离、球管阳极角和过滤要求作为重要的参考条件,特别是在Mo/Mo辐射场下对过滤的限制异常重要,以减少对非介入管电压平均峰值电压测量结果的影响,保证各个校准实验室间结果的一致性,提高可比性;建议进行乳腺非介入管电压测量的时候尽量不使用平均峰值电压来反应测量结果,而应使用实用峰值电压。     

X射线发生器实际峰值电压的测量

目的初步分析X射线发生器实际峰值电压(PPV)的测量误差及其测量差异。方法采用PPV测量方法对不同X射线成像设备进行测量。结果平均峰值电压的测量误差为-1.4～+1.7kV,最大峰值电压测量变化为-0.9～+2.2kV,PPV测量偏差为-3.7～-0.8kV。结论由于计算方法的不同,PPV测量值普遍低于设定电压值和平均值,因而总体测量误差高于平均值和最大峰值电压的测量误差。     

80kVp管电压联合自动管电流调节腹主动脉及双下肢动脉CTA扫描图像质量的评价

目的通过比较80 k Vp与120 k Vp管电压下双下肢CT血管成像(CTA)扫描的辐射剂量、图像质量,评价低管电压下腹主动脉及下肢动脉CTA扫描的可行性。方法回顾性研究40例患者,随机分成两组,每组20人,分别使用80 k Vp或120 k Vp管电压进行腹主动脉及双下肢动脉CTA扫描,通过定性和定量评价轴位、三维重建图像,并进行Shapiro-Wilk Normal分布检验和独立样本t检验。通过测量腹主动脉、双侧髂总动脉、股总动脉、股浅动脉、腘动脉和胫腓干的CT值并计算对比噪声比(CNR),并评价图像质量。结果 80 k Vp管电压组的血管CT值在538 HU至605 HU,高于120 k Vp管电压组。两组之间的CNR和定性评价没有差异。80 k Vp管电压组的DLP为(203±22)m Gy·cm,120 k Vp管电压组为(780±85)m Gy·cm,有效剂量下降了74%。结论低管电压联合自动管电流调节技术进行腹主动脉及双下肢动脉CTA扫描时可以在降低辐射剂量的同时保证图像质量。     

降低儿童X射线CT检查辐射剂量的研究进展

目的：归纳总结减少儿童X射线CT检查所致受检者辐射剂量的方法,为降低儿童接受X射线CT检查的辐射危害风险提供参考。方法：针对X射线CT检查所致儿童的辐射剂量,通过调研相关文献,基于各自研究的目的和原理,归纳总结降低儿童受照剂量的方法。结果：自动管电流调制技术能根据儿童受检者体型自行改变管电流,自动管电压选择技术能根据预先设定的影像质量水平并结合X射线在受检者的衰减自动选择管电压,这两种技术均能自动降低个体的受照剂量;先进的影像重建技术可减少低剂量扫描影像的噪声,间接起到降低个体和群体的受照剂量;非扫描区的合理屏蔽也能有效降低个体和群体的受照剂量;制定剂量参考水平有助于优化X射线CT检查扫描参数,起到降低群体受照剂量的作用。结论：可结合儿童受检者的体型、扫描部位以及X射线CT机的性能,综合运用自动管电流或管电压调制技术、影像重建技术以及屏蔽防护等多种方法,可最大限度地降低儿童X射线CT检查的受照剂量。     

小剂量造影剂联合不同电压对CT肺动脉造影图像质量的影响

目的:观察小剂量造影剂联合不同电压对CT肺动脉造影（CTPA）图像质量的影响。方法:选取2016年1月至2018年5月在滦州市人民医院就诊高度怀疑为肺动脉栓塞患者90例,拟行CTPA明确诊断,以随机数字表法分为A、B、C组,造影剂、电压不同。A组电压为120 kV,造影剂剂量为50 mL;B组电压为100 kV,造影剂剂量为50 mL;C组电压为80 kV,造影剂剂量为30 mL。3组均基于自动管电流调制技术设置管电流,其他参数一致。对比各组图像质量及辐射剂量。结果:B、C组肺动脉主干、左右肺动脉、肺段动脉CT值均明显高于A组,信噪比与对比噪声比均明显低于A组（P<0.05）。3组患者的图像质量主观评分均能达到3~6分,且评分未见统计学差异（P>0.05）。B、C组扫描后实际容积CT剂量指数、扫描长度与剂量长度之积及有效剂量明显低于A组（P<0.05）。结论:与传统扫描条件比较,小剂量造影剂联合低管电压（80 kV）扫描条件下行CTPA检查可在明显降低造影剂剂量的同时保证图像质量,有效减少辐射剂量。     

Varian Edge加速器射野外辐射剂量水平与铅防护用品的防护效果

目的:研究Varian Edge加速器不同工作状态下射野外辐射剂量水平以及铅防护用品的防护效果。方法:利用实验测量的方法，研究加速器在不同工作能量、不同线束均整状态、使用不同防护用品，测量距射野边缘不同距离及不同深度下辐射剂量水平的变化情况。结果:射野外辐射剂量随距射野边缘距离增加（5~40 cm）近似呈指数规律下降，距射野边缘20 cm范围内低能量射束（6 MV、6 MV FFF）的辐射剂量低于高能射束（10 MV、10 MV FFF）的辐射剂量，且随测量深度增加（1~2 cm）而降低。非均整模式下射野外剂量测量结果低于均整模式射束。在相同能量条件下，铅防护用品的防护效果与线束的均整状态无关。对高能射束的防护效果要优于低能射束且随深度增加防护效果迅速下降。深度为1 cm，射束能量10 MV FFF，距射野边缘5~30 cm条件下，防护效果最强，射野外辐射剂量水平降低50%以上。测量深度为2 cm，射束能量为6 MV FFF，距离射野边缘5~30 cm的条件下，防护效果最差，仅能降低10%以下。结论:在实现临床目标的前提下，治疗过程中若无铅防护用品进行保护，推荐采用低能非均整模式进行计划设计；若使用铅防护用品进行保护，可以采用高能非均整模式射束，此时铅防护用品效果最佳，射野外浅层器官所受剂量最低，可有效降低二次肿瘤发生几率。     

逆向拟合法量化测定X线与物质相互作用后的强度变化规律

目的:使用X线衍射仪、自制载物台逆向拟合法量化分析X射线与不同物质相互作用后的强度变化规律及影响因素。 方法:实验使用逆向拟合法验证朗伯比尔定律,列举可能影响穿过物质层后的X射线强度的若干因素（管电压、管电流、距离、物质原子序数和物质层厚度等）,设计多组实验样本,通过各组对各种因素的实验验证,逆向说明影响因素与穿过物质层后X射线强度的关系。 结果:在实验设备有效量程范围内,管电流、物质层厚度和原子序数与穿过物质层的X射线强度呈线性关系;而管电压和X射线发射器与接收器间的距离与穿过物质层的X射线强度呈非线性关系,即当管电压发生线性变化时,穿过物质层后的X射线强度在10~25 kV范围内的管电压下缓慢增加,在25~35 kV范围内时X射线强度迅速增大,X射线强度∝kV2;当X射线发射器与接收器间距离发生线性变化时,穿过物质层的X射线强度在9.00~13.00 cm距离范围内变化显著,而在13.00~17.00 cm距离范围内变化不明显,X射线强度∝1/r2。通过以上关系验证了朗伯比尔定律及其普适性,并探讨利用模拟人进行深入实验验证。 结论:该方法简单直观,可快速测定X射线与不同物质相互作用后的强度变化规律,验证相关影响因素,可用于相关医学物理实验教学。     

电子射野影像系统在加速器辐射野测量中的应用探讨

目的:探讨电子射野影像系统(EPID)在加速器辐射野与灯光野一致性测量中的应用。方法:使用Varian 600CD医用电子直线加速器,6MV X射线能量,使用水平尺,确认机架位于0°,准直器0°,提前校准照射野中心和投影十字线,将厂家自带的金属点十字影子板插在加速器机头上,金属点十字影子板上两金点之间在SSD=100cm处的投影距离为1cm,调整机头十字线与金属十字线投影重合;打开EPID测量板,在SSD=100cm条件下,灯光野分别开到标准野(10×10)cm,(15×15)cm,(20×20)cm,(25×25)cm,剂量率100MU/M,曝光5MU;得到各标准野的辐射野,两金属点之间标准距离1cm,使用测量软件分别分别测量辐射野各方向距离。结果:辐射野各方向偏差较小,均小于±2mm。结论:EPID射野影像检测方式适合于临床质控检验,可用于加速器辐射野与灯光野一致性的质控测量,减少工作量。     

60Co重过滤低剂量率照射剂量学

目的:探讨低剂量60Coγ射线照射由于照射物理条件不同剂量学参数的变化.材料和方法:在常规照射和低熔点铅(LML)重过滤初始γ束条件下,用三维水箱自动测量装置和剂量仪分别测量PDD、OAR和绝对剂量定标后的K修正系数.结果:60Co γ射线初始束经重过滤后PDD在人体脾脏靶区深度5 cm～11cm区域平均降低1.2个百分点,OAR较常规60Co OAR圆弧化,绝对剂量较常规实际减弱80倍,并给出了治疗时间公式.讨论:对60Co γ射线的重过滤,是采用常规60Co γ射线治疗机实现低剂量辐射照射脾脏的最佳方法.     

动脉导管未闭与肺动脉狭窄介入诊疗中的辐射剂量分析

目的了解小儿先天性心脏病(先心病)介入诊疗中受检者的辐射剂量,以便有效开展和加强受检者医疗照射的防护,降低受检者的辐射剂量。方法158例介入治疗患儿,其中男性77例,女性81例;年龄3个月～13岁,平均年龄4岁;体质量5.7～42.0 kg,平均体质量14.2 kg。动脉导管未闭(PDA)封堵术118例,肺动脉狭窄(PS)球囊扩张术40例。采用数字减影血管造影,电影采集模式为小儿心血管模式(ped CARD);帧频控制30 f/s;透视模式为脉冲控制,4 f/s;根据年龄不同选择管电压在60～70 kV,管电流自动调节;对比剂为非离子型370 mgI/mL碘普罗胺。回顾性分析不同术式、不同年龄患儿进行透视时间、皮肤辐射剂量。结果PDA透视时间(4.66±3.59)min,PS(5.62±2.79)min,两种手术透视时间差异无统计学意义(P>0.05);但在同一种手术中透视时间差异较大。皮肤辐射剂量范围1.20~107.00 mGy,平均皮肤辐射剂量22.45 mGy;PDA患儿诊疗时,透视+电影采集总皮肤辐射剂量为(20.24±13.52)mGy;PS患儿诊疗时,透视+电影采集总皮肤辐射剂量为(41.88±29.24)mGy;两组患儿皮肤辐射剂量比较,差异有统计学意义(P<0.05)。不同年龄的皮肤辐射剂量比较,差异有统计学意义(P<0.05);不同体质量的皮肤辐射剂量比较,差异有统计学意义(P<0.05)。结论不同种类手术透视时间的长短与年龄、体质量关系不大,造成透视时间差异显著的主要原因是患儿病变的部位、性质、形态、大小及手术操作者的操作技术和防护意识,要降低辐射剂量,就要缩短透视时间,提高手术操作者的操作技术和防护意识是至关重要。     

Problem of Determination of the First Half-Value Layer of X-Ray Radiation

The methods for determination of the first half value layer of X-ray radiation are analyzed. The organized comparison revealed significant scatter from different sources of the first half value layer for identical conditions. The analytical expression was derived for calculation of the first half value layer based on the measured value and total filtering of the X-ray radiation and anode voltage of the X-ray tube. The results of comparison with experimental data provided a basis for this study.     

Optimization of x-ray spectra in digital mammography through Monte Carlo simulations

In this work, a Monte Carlo code was used to investigate the performance of different x-ray spectra in digital mammography, through a figure of merit (FOM), defined as FOM = CNR2/(ˉ)D(g), with CNR being the contrast-to-noise ratio in image and [Formula: see text] being the average glandular dose. The FOM was studied for breasts with different thicknesses t (2 cm ≤ t ≤ 8 cm) and glandular contents (25%, 50% and 75% glandularity). The anode/filter combinations evaluated were those traditionally employed in mammography (Mo/Mo, Mo/Rh, Rh/Rh), and a W anode combined with Al or K-edge filters (Zr, Mo, Rh, Pd, Ag, Cd, Sn), for tube potentials between 22 and 34 kVp. Results show that the W anode combined with K-edge filters provides higher values of FOM for all breast thicknesses investigated. Nevertheless, the most suitable filter and tube potential depend on the breast thickness, and for t ≥ 6 cm, they also depend on breast glandularity. Particularly for thick and dense breasts, a W anode combined with K-edge filters can greatly improve the digital technique, with the values of FOM up to 200% greater than that obtained with the anode/filter combinations and tube potentials traditionally employed in mammography. For breasts with t < 4 cm, a general good performance was obtained with the W anode combined with 60 μm of the Mo filter at 24-25 kVp, while 60 μm of the Pd filter provided a general good performance at 24-26 kVp for t = 4 cm, and at 28-30 and 29-31 kVp for t = 6 and 8 cm, respectively.     

Scatter/primary ratios for x-ray spectra modified to enhance iodine contrast in screen-film mammography

Contrast mammography to detect the uptake of iodine-containing contrast material may be enhanced by spectral modification of the x-ray beam. Luminance scatter-to-primary ratios were measured for three candidate x-ray tube anode/filter combinations (Mo/Mo, W/Ce, and Ce/Ce). Results show that scattered radiation is significant for all tubes, is lowest for the Mo/Mo system and is essentially the same for the tungsten and cerium anode systems.     

A new method for experimental characterisation of scattered radiation in 64-slice CT scanner

Purpose:

The consummate 64-slice CT scanner that spawns a new generation of non-invasive diagnostic tool, however revolutionary, brings with it the incidental by-product that is scattered radiation. The extended detector aperture capability in the 64-slcie CT scanner allows the effects of scattered radiation to be more pronounced and therefore demands that the magnitude and spatial distribution of scatter component be addressed during the imaging process. To this end, corrective algorithms need to be formulated on a basis of a precise understanding of scatter distribution. Relative to a 64-slice CT scanner, here now a unique solution is based upon dedicated blockers operative within various detector rows, calculating scatter profiles and scatter to primary ratios (SPR).

Materials and methods:

A single dimension blocker array was installed beneath the collimator, and the extrapolated shadow area on the detectors revealed the scatter radiation after exposure. The experiment was conducted using a 64-slice CT scanner manufactured by GE Healthcare Technologies.

Results:

Variables such as tube voltage, phantom size and phantom-off centring on the scatter profile and the SPR was measured using the dedicated blocker method introduced above. When tube voltage is increased from 80kVp to 140kVp in a 21.5 cm water phantom, the SPR is found to reduce from 219.9 to 39.9 respectively.

Conclusion:

The method developed within this study is applicable to any measurement and is direct with minimal complexity.     

A search for optimal x-ray spectra in iodine contrast media mammography

The aim of this work was to search for the optimal x-ray tube voltage and anode-filter combination in digital iodine contrast media mammography. In the optimization, two entities were of interest: the average glandular dose, AGD, and the signal-to-noise ratio, SNR, for detection of diluted iodine contrast medium. The optimum is defined as the technique maximizing the figure of merit, SNR2/AGD. A Monte Carlo computer program was used which simulates the transport of photons from the x-ray tube through the compression plate, breast, breast support plate, anti-scatter grid and image detector. It computes the AGD and the SNR of an iodine detail inside the compressed breast. The breast thickness was varied between 2 and 8 cm with 10-90% glandularity. The tube voltage was varied between 20 and 55 kV for each anode material (Rh, Mo and W) in combination with either 25 microm Rh or 0.05-0.5 mm Cu added filtration. The x-ray spectra were calculated with MCNP4C (Monte Carlo N-Particle Transport Code System, version 4C). A CsI scintillator was used as the image detector. The results for Rh/0.3 mmCu, Mo/0.3 mmCu and W/0.3 mmCu were similar. For all breast thicknesses, a maximum in the figure of merit was found at approximately 45 kV for the Rh/Cu, Mo/Cu and W/Cu combinations. The corresponding results for the Rh/Rh combination gave a figure of merit that was typically lower and more slowly varying with tube voltage. For a 4 cm breast at 45 kV, the SNR2/AGD was 3.5 times higher for the Rh/0.3 mmCu combination compared with the Rh/Rh combination. The difference is even larger for thicker breasts. The SNR2/AGD increases slowly with increasing Cu-filter thickness. We conclude that tube voltages between 41 and 55 kV and added Cu-filtration will result in significant dose advantage in digital iodine contrast media mammography compared to using the Rh/Rh anode/filter combination at 25-32 kV.     

X-ray spectroscopy applied to radiation shielding calculation in mammography

The protective shielding design of a mammography facility requires the knowledge of the scattered radiation by the patient and image receptor components. The shape and intensity of secondary x-ray beams depend on the kVp applied to the x-ray tube, target/filter combination, primary x-ray field size, and scattering angle. Currently, shielding calculations for mammography facilities are performed based on scatter fraction data for Mo/Mo target/filter, even though modern mammography equipment is designed with different anode/filter combinations. In this work we present scatter fraction data evaluated based on the x-ray spectra produced by a Mo/Mo, Mo/Rh and W/Rh target/filter, for 25, 30 and 35 kV tube voltages and scattering angles between 30 and 165 degrees. Three mammography phantoms were irradiated and the scattered radiation was measured with a CdZnTe detector. The primary x-ray spectra were computed with a semiempirical model based on the air kerma and HVL measured with an ionization chamber. The results point out that the scatter fraction values are higher for W/Rh than for Mo/Mo and Mo/Rh, although the primary and scattered air kerma are lower for W/Rh than for Mo/Mo and Mo/Rh target/filter combinations. The scatter fractions computed in this work were applied in a shielding design calculation in order to evaluate shielding requirements for each of these target/filter combinations. Besides, shielding requirements have been evaluated converting the scattered air kerma from mGy/week to mSv/week adopting initially a conversion coefficient from air kerma to effective dose as 1 Sv/Gy and then a mean conversion coefficient specific for the x-ray beam considered. Results show that the thickest barrier should be provided for Mo/Mo target/filter combination. They also point out that the use of the conversion coefficient from air kerma to effective dose as 1 Sv/Gy is conservatively high in the mammography energy range and overestimate the barrier thickness.     

Ambient dose equivalent and effective dose from scattered x-ray spectra in mammography for Mo/Mo, Mo/Rh and W/Rh anode/filter combinations

In this study, scattered x-ray distributions were produced by irradiating a tissue equivalent phantom under clinical mammographic conditions by using Mo/Mo, Mo/Rh and W/Rh anode/filter combinations, for 25 and 30 kV tube voltages. Energy spectra of the scattered x-rays have been measured with a Cd(0.9)Zn(0.1)Te (CZT) detector for scattering angles between 30 degrees and 165 degrees . Measurement and correction processes have been evaluated through the comparison between the values of the half-value layer (HVL) and air kerma calculated from the corrected spectra and measured with an ionization chamber in a nonclinical x-ray system with a W/Mo anode/filter combination. The shape of the corrected x-ray spectra measured in the nonclinical system was also compared with those calculated using semi-empirical models published in the literature. Scattered x-ray spectra measured in the clinical x-ray system have been characterized through the calculation of HVL and mean photon energy. Values of the air kerma, ambient dose equivalent and effective dose have been evaluated through the corrected x-ray spectra. Mean conversion coefficients relating the air kerma to the ambient dose equivalent and to the effective dose from the scattered beams for Mo/Mo, Mo/Rh and W/Rh anode/filter combinations were also evaluated. Results show that for the scattered radiation beams the ambient dose equivalent provides an overestimate of the effective dose by a factor of about 5 in the mammography energy range. These results can be used in the control of the dose limits around a clinical unit and in the calculation of more realistic protective shielding barriers in mammography.     

Radiation probe for indirect evaluation of the high-voltage waveform of a Mo anode mammography unit

A radiation probe was designed for indirectly determining the high voltage of a Mo anode mammography unit. The real time processing of the probe outputs yields exposure time, voltage waveform, kVp, and ripple in the range 24-40 kVp useful for screen-film mammography. The probe, connected to a portable computer, will be employed in a survey of radiation dose and image quality in mammography as part of an ongoing program in Italy.