GE AMX-4Plus移动X射线机的数字化X射线摄影改造

目的为了提高床旁X射线摄片的图像质量,对现有移动X射线机GEAMX-4Plus进行数字化X射线摄影（DR）改造,由原来影像板（IP）成像再行计算机X射线摄影（CR）扫描获得图像的方式改为DR直接摄片。方法以移动X射线机为基础．配置Pixium3543无线平板系统．设计基于该平板的数字摄影操作平台系统和曝光同步控制系统。结果DR改造后,移动X射线机可以正常使用,性能稳定,图像质量较以前CR模式得到大幅提高,获得临床认可。结论数字化x射线摄影改造既使原有移动X射线机得到充分的利用,也使床旁摄片质量、临床诊断及时性、准确度等方面得到大幅提高。     

DR组织均衡技术在低剂量鼻骨侧位X射线摄影中的应用

目的探寻在鼻骨侧位X射线摄影中利用数字化X射线摄影(DR)组织均衡技术获取满足诊断需要的图像并降低患者辐射剂量的研究。方法利用人体模型进行常规的鼻骨侧位摄影,然后固定千伏值,在原有的mAs值上分别降低0.4、0.8、1.2 mAs进行摄片,再将降低剂量的图像采用DR组织均衡技术进行处理,比较不同图像对于满足诊断的需要和患者所接受的辐射剂量。结果常规摄影技术得到的图像需反复调节不同的窗宽、窗位才能显示密度、厚度不同的鼻骨与软组织;降低0.4、0.8 mAs,虽然图像的空间分辨率降低,但是采用DR组织均衡技术可在同一幅图像上清晰显示鼻骨与邻近软组织结构,同时降低患者的辐射剂量;降低1.2 mAs,不但图像的空间分辨率降低,而且无法采用DR组织均衡技术使图像达到满足诊断需要。结论采用DR组织均衡技术不仅能将密度、厚度不同的鼻骨及邻近软组织在同一副图像上清晰显示,而且能够有效降低患者的辐射剂量。     

数字摄影如何降低受检者辐射剂量

在计算机X射线摄影（computed radiography,CR）、数字化X射线摄影（digitalradiography,DR）技术广泛应用的今天,这些新技术给人们的健康作出贡献的同时,也给受检者带来辐射剂量的增加,这对受检者的潜在危害也越来越大。那么,探索如何尽量减少受检者辐射剂量,仍然是放射技术人员应当关注的问题。     

高千伏胸部摄影在DR系统的应用

目的探讨DR高千伏胸部摄影的条件,评价DR胸部影像. 方法①选择5种体型人体(特瘦、瘦、中等、胖、特胖)各10人,将KV固定为125KV,按7种不同档次的mAs进行正侧位投照.②选取最佳成像的摄影条件,按此条件对1000例患者进行摄影.③对1000例DR胸部影像进行质量评定. 结果①高千伏投照5种体型最佳成像的mAs范围,正位2.0～6.4mAs,侧位4.0～10.0mAs.②1000例DR胸部影像甲级片占50.6%,乙级片占38.5%,丙级片占10.9%,无废片影像. 结论高千伏DR胸部摄影可代替高千伏屏-胶胸部摄影,并具有更多的优越性.     

高千伏胸部摄影在DR系统的应用

目的：探讨DR高千伏胸部摄影的条件，评价DR胸部影像。方法：①选择5种体型人体（特瘦、瘦、中等、胖、特胖）各10人，将KV固定为125KV，按7种不同档次的mAs进行正侧位投照。②选取最佳成像的摄影条件，按此条件对1000例患者进行摄影。③对1000例DR胸部影像进行质量评定。结果：①高千伏投照5种体型最佳成像的mAs范围，正位2．0－6．4mAs，侧位4．0－10．0mAs。②1000例DR胸部影像甲级片占50．6％，乙级片占38．5％，丙级片占10．9％，无废片影像。结论：高千伏DR胸部摄影可代替高千伏屏－胶胸部摄影，并具有更多的优越性。     

医用X射线摄影所致受检者体表剂量估算方法进展

目的:探讨医用X射线摄影所致受检者入射体表剂量的估算模式,为掌握受检者与患者的剂量水平提供技术支持,并为制定相应的防护措施提供理论依据。方法:对目前已有的普通X射线摄影和数字X射线摄影两大类医用X射线装置中涉及到受检者入射体表剂量估算的研究论文进行归纳和总结,并对相应方法的原理和应用进行探讨,比较各类方法的优点和缺点。结果:普通X射线摄影估算模式的数学模型简单,计算便捷,但相应的曝光参数获取不易,且由于模型相对简化,可能因机型、照射野、受检者及其他摄影条件的差异,导致估算时产生较大的偏差。数字X射线摄影估算模式则不需要进行多余的测量及记录,可根据每次摄影后系统给出的曝光指示值或者DAP值来推算出受检者的入射体表剂量,但在该类方法中,受检部位厚度的不确定性会致使结果存在较大差异。结论:目前现存的用于估算医用X射线摄影所致受检者入射体表剂量的模型仍存在较大差异和不足,其中数字X射线摄影估算方法有较大应用前景,仍有待进一步发展和探索。     

数字化X射线摄影术曝光指数与曝光参数关系的实验研究

目的 探讨数字化X射线摄影术(DR)曝光指数(EI)与曝光参数之间的关系、曝光参数值的改变对EI值的影响,以便利用EI来指导DR摄影时曝光参数值的合理选择.方法 选择28 cm×28 cm大小和9.0、10.8 cm厚聚甲基丙烯酸甲酯(PMMA)板.西门子公司AXIOM Luminos dRF多功能数字化X射线机,配备...     

婴幼儿胸部DR摄影源像距与辐射剂量和图像质量的相关性研究

目的 探讨婴幼儿胸部数字X射线摄影(DR)的源像距(SID)与图像质量及辐射剂量的相关性.方法 先进行仿真胸部体模(成都剂量体模)实验性曝光,采用同一管电压(65 kVp)和不同SID进行曝光组合,记录每次曝光的毫安秒(mAs)、单位面积剂量:在实验的基础上进行婴幼儿胸部DR,收集2008年5月～2010年5月初次人院的50例婴幼儿行胸部DR(其中男性28例,女性22例;年龄5个月～2岁,平均年龄10个月),住院期间复查1次作为对照,初检组均使用110cmSID,复检组均使用90cmSID进行DR胸部摄影.由3名资深影像学专家对获取的100幅图像质最进行评判,评判结果运用统计学软件SPSS 13.0进行分析,使用接受者操作特征曲线(ROC)分析和t检验.结果 100例初检及复查婴幼儿的图像质量均符合诊断要求(P>0.05);而不同的SID曝光的面积剂量差异有统计学意义(P<0.05).结论 婴幼儿胸部DR的不同SID,其辐射剂量差异具有统计学意义,且图像质量均能满足诊断要求,90cmSID在婴幼儿胸部DR中值得提倡.     

数字化X射线摄影图像显示器配置对X射线摄影剂量的影响

目的:研究数字化X射线摄影系统图像获取工作站显示器配置不同对图像质量的影响及对被检者照射剂量的影响.材料与方法:应用对比度细节体模CDRAD2.0影像,以图像质量因子IQF作为图像质量评价标准,计算不同照射剂量下两种图像显示条件下图像质量及照射剂量的差别.结果:所研究的普通显示器与高分辨率、高亮度显示器在不同照射剂量条件下显示的图像质量因子显著不同(p＜0.000).结论:应用高亮度、高分辨率显示器作为图像获取工作站显示器可显著降低体模照射剂量.     

X射线摄影效应测定尺的研发与应用

目的探讨X射线摄影测量出现误差的原因,提高X射线测量的准确性。方法自行研制X射线摄影效应尺,由底尺、高度尺和活动尺三大部分构成,分别刻以灌注铅胶的刻度,用于实际测量。检测焦片距100cm、物片距20cm时显示图像尺寸与实际尺寸的大小。结果各公司平板显示范围未能达到所标识的43 cm×43 cm,Kodak 7500、GE、佳能、西门子4家公司实际显示范围分别为41.5 cm、40.5 cm、42.5 cm、41.0 cm。而焦片距100 cm、物体厚度20 cm进行曝光时,底尺显示43.0 cm时,实际物体尺寸仅有36.0 cm,7.0 cm的物体盲区未被显示。结论为避免图像放大引起的失真,摄影时使用X射线摄影效应测定尺即可进行准确测量,减少误差。     

Experimental investigation of the dose and image quality characteristics of a digital mammography imaging system

Our purpose in this study was to investigate the image quality and absorbed dose characteristics of a digital mammography imaging system with a CsI scintillator, and to identify an optimal x-ray tube voltage for imaging simulated masses in an average size breast with 50% glandularity. Images were taken of an ACR accreditation phantom using a LORAD digital mammography system with a Mo target and a Mo filter. In one experiment, exposures were performed at 80 mAs with x-ray tube voltages varying between 24 and 34 kVp. In a second experiment, the x-ray tube voltage was kept constant at 28 kVp and the technique factor was varied between 5 and 500 mAs. The average glandular dose at each x-ray tube voltage was determined from measurements of entrance skin exposure and x-ray beam half-value layer. Image contrast was measured as the fractional digital signal intensity difference for the image of a 4 mm thick acrylic disk. Image noise was obtained from the standard deviation in a uniformly exposed region of interest expressed as a fraction of the background intensity. The measured digital signal intensity was proportional to the mAs and to the kVp5.8. Image contrast was independent of mAs, and dropped by 21% when the x-ray tube voltage increased from 24 to 34 kVp. At a constant x-ray tube voltage, image noise was shown to be approximately proportional to (mAs)(-05), which permits the image contrast to noise ratio (CNR) to be modified by changing the mAs. At 80 mAs, increasing the x-ray tube voltage from 24 to 34 kVp increased the CNR by 78%, and increased the average glandular dose by 285%. At a constant lesion CNR, the lowest average glandular dose value occurred at 27.3 kVp. Increasing or decreasing the x-ray tube voltage by 2.3 kVp from the optimum kVp increased the average glandular dose values by 5%. These results show that imaging simulated masses in a 4.2 cm compressed breast at approximately 27 kVp with a Mo/Mo target/filter results in the lowest average glandular dose.     

Evaluation of radiation dose and image quality following changes to tube potential (kVp) in conventional paediatric chest radiography

Purpose

A study of radiation dose and image quality following changes to the tube potential (kVp) in paediatric chest radiography.

Materials and Method

A total of 109 patients ranging from 1 month to 15 years were included in two phases of the study. Phase 1 investigated the range of entrance surface air kerma (ESAK) values received from patients exposed to the existing exposure factors. In the second phase, new exposure factors using recommended values of tube potential (kVp) with reduced mAs were used. ESAK values were measured using thermoluminescent dosemeters (TLDs). Image quality in both phases was evaluated using image quality criteria proposed by the Council of the European Communities (CEC). Results of both techniques were analysed for any differences.

Results

The overall mean ESAK before the changes was 0.22 mGy (range: 0.05-0.43) Following changes in tube potential, the overall mean reduced to 0.15 mGy (range: 0.03-0.38), a significant reduction by 34%. The interquartile range was reduced from 45% to 40%. However, doses to those below a year in age still remained high. Assessment of image quality was found to have no significant differences as far as the two techniques used were concerned. However, higher image scores were achieved using higher kVps.

Conclusion

Significant dose reduction was achieved through appropriate changes in tube potential and reduction of mAs without any loss in image quality.     

Technique factors and their relationship to radiation dose in pendant geometry breast CT

The use of breast computed tomography (CT) as an alternative to mammography in some patients is being studied at several institutions. However, the radiation dosimetry issues associated with breast CT are markedly different than in the case of mammography. In this study, the spectral properties of an operational breast CT scanner were characterized both by physical measurement and computer modeling of the kVp-dependent spectra, from 40 to 110 kVp (Be window W anode with 0.30 mm added Cu filtration). Previously reported conversion factors, normalized glandular dose for CT-DgN(ct), derived from Monte Carlo methods, were used in concert with the output spectra of the breast scanner to compute the mean glandular dose to the breast based upon different combinations of x-ray technique factors (kVp and mAs). The mean glandular dose (MGD) was measured as a function of the compressed breast thickness (2-8 cm) and three different breast compositions (0%, 50%, and 100% glandular fractions) in four clinical mammography systems in our institution. The average MGD from these four systems was used to compute the technique factors for breast CT systems that would match the two-view mammographic dose levels. For a 14 cm diameter breast (equivalent to a 5 cm thick compressed breast in mammography), air kerma levels at the breast CT scanner's isocenter (468 mm from the source) of 4.4, 6.4, and 9.0 mGy were found to deliver equivalent mammography doses for 0%, 50%, and 100% glandular breasts (respectively) at 80 kVp. At 80 kVp (where air kerma was 11.3 mGy/100 mAs at the isocenter), 57 mAs (integrated over the entire scan) was required to match the mammography dose for a 14 cm 50% glandular breast. At 50 kVp, 360 mAs is required to match mammographic dose levels. Tables are provided for both air kerma at the isocenter and mAs for 0%, 50%, and 100% glandular breasts. Other issues that impact breast CT technique factors are also discussed.     

Dual-energy cardiac imaging: an image quality and dose comparison for a flat-panel detector and x-ray image intensifier

This study presents a comparison of dual-energy imaging with an x-ray image intensifier and flat-panel detector for cardiac imaging. It also investigates if the wide dynamic range of the flat-panel detector can improve dual-energy image quality while reducing patient dose. Experimental contrast-to-noise (CNR) measurements were carried out in addition to simulation studies. Patient entrance exposure and system tube loading were also recorded. The studied contrast objects were calcium and iodine. System performance was quantified with a figure-of-merit (FOM) defined as the image CNR(2) over patient entrance exposure. The range of thickness studied was from 10 to 30 cm of Lucite (PMMA). Detector dose was initially set to 140 nGy (16 microR)/frame. The high-energy 120 kVp beam was filtered by an additional 0.8 mm silver filter. Keeping the same filament current, the kVp for the low-energy beam was adjusted as a function of thickness until 140 nGy was achieved. System performance was found to be similar for both systems, with the x-ray image intensifier performing better at lower thicknesses and the flat-panel detector performing better at higher thicknesses. This requirement of fixed detector entrance exposure was then relaxed and the kVp for the low-energy beam was allowed to vary while the mAs of the x-ray tube remained fixed to study changes in dual-energy image quality, patient dose and FOM with the flat-panel detector. It was found that as the kVp for the low-energy beam was reduced, system performance would rise until reaching a maximum while simultaneously lowering patient exposure. Suggested recommendations for optimal dual-energy imaging implementation are also provided.     

Grid removal and impact on population dose in full-field digital mammography

The study purpose was to determine the impact of anti-scatter grid removal on patient dose, in full field digital mammography. Dose saving, phantom based, was evaluated with the constraint that images acquired with and without grid would provide the same contrast-to-noise ratio (CNR). The digital equipment employed a flat panel detector with cesium iodide for x-ray to light conversion, 100 microm pixel size; the x-ray source was a dual-track tube with selectable filtration. Poly(methyl-emathocrylate) (PMMA) layers in the range 20-70 mm were used to simulate the absorption of different breast thickness, while two Al foils, 0.1 and 0.2 mm thick were used to provide a certain CNR. Images with grid were acquired with the same beam quality as selected in full automatic exposure mode and the mAs levels as close as possible, and the CNR measured for each thickness between 20 and 70 mm. Phantom images without grid were acquired in manual exposure mode, by selecting the same anode/filter combination and kVp as the image with grid at the same thickness, but varying mAs from 10 to 200. For each thickness, an image without aluminum was acquired for each mAs value, in order to obtain a flat image to be used to subtract the scatter nonuniformity from the phantom images. After scatter subtraction, the CNR was measured on images without grid. The mAs value that should be set to acquire a phantom image without grid so that it has the same CNR as the corresponding grid image was calculated. Therefore, mAs reduction percentage was determined versus phantom thickness. Results showed that dose saving was lower than 30% for PMMA equivalent breast thinner than 40 mm, decreased below 10% for intermediate thickness (45-50 mm), but there was no dose gain for thickness beyond 60 mm. By applying the mAs reduction factors to a clinical population derived from a data base of 4622 breasts, dose benefit was quantified in terms of population dose. On the average, the overall dose reduction was about 8%. It was considered small, not sufficient to justify a clinical implementation, and the anti-scatter grid was maintained.     

Effective doses to patients undergoing thoracic computed tomography examinations

The purpose of this study was to investigate how x-ray technique factors and effective doses vary with patient size in chest CT examinations. Technique factors (kVp, mAs, section thickness, and number of sections) were recorded for 44 patients who underwent a routine chest CT examination. Patient weights were recorded together with dimensions and mean Hounsfield unit values obtained from representative axial CT images. The total mass of directly irradiated patient was modeled as a cylinder of water to permit the computation of the mean patient dose and total energy imparted for each chest CT examination. Computed values of energy imparted during the chest CT examination were converted into effective doses taking into account the patient weight. Patient weights ranged from 4.5 to 127 kg, and half the patients in this study were children under 18 years of age. All scans were performed at 120 kVp with a 1 s scan time. The selected tube current showed no correlation with patient weight (r2=0.06), indicating that chest CT examination protocols do not take into account for the size of the patient. Energy imparted increased with increasing patient weight, with values of energy imparted for 10 and 70 kg patients being 85 and 310 mJ, respectively. The effective dose showed an inverse correlation with increasing patient weight, however, with values of effective dose for 10 and 70 kg patients being 9.6 and 5.4 mSv, respectively. Current CT technique factors (kVp/mAs) used to perform chest CT examinations result in relatively high patient doses, which could be reduced by adjusting technique factors based on patient size.     

Patient dose in digital mammography

In the present investigation, we analyze the dose of 5034 patients (20,137 images) who underwent mammographic examinations with a full-field digital mammography system. Also, we evaluate the system calibration by analyzing the exposure factors as a function of breast thickness. The information relevant to this study has been extracted from the image DICOM header and stored in a database during a 3-year period (March 2001-October 2003). Patient data included age, breast thickness, kVp, mAs, target/filter combination, and nominal dose values. Entrance surface air kerma (ESAK) without backscatter was calculated from the tube output as measured for each voltage used under clinical conditions and from the tube loading (mAs) included in the DICOM header. Mean values for the patient age and compressed breast thickness were 56 years (SD: 11) and 52 mm (SD: 13), respectively. The majority of the images was acquired using the STD (for standard) automatic mode (98%). The most frequent target/filter combination automatically selected for breast smaller than 35 mm was Mo/Mo (75%); for intermediate thicknesses between 35 and 65 mm, the combinations were Mo/Rh (54%) and Rh/Rh (38.5%); Rh/Rh was the combination selected for 91% of the cases for breasts thicker than 65 mm. A wide kVp range was observed for each target/filter combination. The most frequent values were 28 kVp for Mo/Mo, 29 kVp for Mo/Rh, and 29 and 30 kV for Rh/Rh. Exposure times ranged from 0.2 to 4.2 s with a mean value of 1.1 s. Average glandular doses (AGD) per exposure were calculated by multiplying the ESAK values by the conversion factors tabulated by Dance for women in the age groups 50 to 64 and 40 to 49. This approach is based on the dependence of breast glandularity on breast thickness and age. The total mean average glandular dose (AGD(T)) was calculated by summing the values associated with the pre-exposure and with the main exposure. Mean AGD(T) per exposure was 1.88 mGy (CI 0.01) and the mean AGD(T) per examination was 3.8 mGy, with 4 images per examination on average. The mean dose for cranio-caudal view (CC) images was 1.8 mGy, which is lower than that for medio-lateral oblique (MLO) view because the thickness for CC images was on average 10% lower than that for MLO images. Mean AGD(T) for the oldest group of women (1.90) was 3% higher than the AGD(T) for the younger group (1.85) due to the larger compressed breast thickness of women in the older group (10% on average). Differences between the corresponding AGD(T) values of each age group were lowest for breast thicknesses in the range 40-60 mm, being slightly higher for the women in the older group.     

Effect of radiographic techniques (kVp and mAs) on image quality and patient doses in digital subtraction angiography

We investigated how varying the x-ray tube voltage and image receptor input exposure affected image quality and patient radiation doses in interventional neuroradiologic imaging. Digital subtraction angiography (DSA) images were obtained of a phantom with 1 mm diameter vessels containing iodine at concentrations between 4.5 and 50 mg/cc. The detection threshold concentration of iodine was determined by inspecting DSA images obtained at a range of x-ray tube voltages and input exposure levels. Surface doses were obtained from measured x-ray tube output data, and corresponding values of energy imparted were determined using the exposure-area product incident on the phantom. In one series of experiments, the air kerma at the image intensifier (X) was varied between 0.44 microGy per frame and 8.8 microGy per frame at a constant x-ray tube voltage of 70 kVp. In a second series of experiments, the tube voltage was varied between 50 and 100 kVp, and the mAs adjusted to maintain a constant exposure level at the input of the image intensifier. At a constant x-ray tube voltage, the surface dose and energy imparted were directly proportional to the input exposure per frame used to acquire the DSA images. On our DSA system operated below 2.2 microGy per frame, the threshold iodine concentration was found to be proportional to X(-0.57), which is in reasonable agreement with the theoretical prediction for a quantum noise limited imaging system. Above 2.2 microGy per frame, however, the threshold iodine concentration was proportional to X(-0.26), indicating that increasing the input exposure above this value will only achieve modest improvements in image quality. At a constant image intensifier input exposure level, increasing the x-ray tube voltage from 50 kVp to 100 kVp reduced the surface dose by a factor of 6.1, and the energy imparted by a factor of 3.5. The detection threshold iodine concentration was found to be proportional to kVp(n), where n was 2.1 at 1.1 microGy per frame, and 1.6 at 3.9 microGy per frame. For clinical situations that can be modeled by a uniform phantom, reducing the x-ray tube voltage rather than increasing the exposure level would best achieve improvements on our DSA imaging system performance.     

Patient dose from kilovoltage cone beam computed tomography imaging in radiation therapy

Kilovoltage cone-beam computerized tomography (kV-CBCT) systems integrated into the gantry of linear accelerators can be used to acquire high-resolution volumetric images of the patient in the treatment position. Using on-line software and hardware, patient position can be determined accurately with a high degree of precision and, subsequently, set-up parameters can be adjusted to deliver the intended treatment. While the patient dose due to a single volumetric imaging acquisition is small compared to the therapy dose, repeated and daily image guidance procedures can lead to substantial dose to normal tissue. The dosimetric properties of a clinical CBCT system have been studied on an Elekta linear accelerator (Synergy RP, XVI system) and additional measurements performed on a laboratory system with identical geometry. Dose measurements were performed with an ion chamber and MOSFET detectors at the center, periphery, and surface of 30 and 16-cm-diam cylindrical shaped water phantoms, as a function of x-ray energy and longitudinal field-of-view (FOV) settings of 5,10,15, and 26 cm. The measurements were performed for full 360 degrees CBCT acquisition as well as for half-rotation scans for 120 kVp beams using the 30-cm-diam phantom. The dose at the center and surface of the body phantom were determined to be 1.6 and 2.3 cGy for a typical imaging protocol, using full rotation scan, with a technique setting of 120 kVp and 660 mAs. The results of our measurements have been presented in terms of a dose conversion factor fCBCT, expressed in cGy/R. These factors depend on beam quality and phantom size as well as on scan geometry and can be utilized to estimate dose for any arbitrary mAs setting and reference exposure rate of the x-ray tube at standard distance. The results demonstrate the opportunity to manipulate the scanning parameters to reduce the dose to the patient by employing lower energy (kVp) beams, smaller FOV, or by using half-rotation scan.