多层面螺旋CT曝光参数的优化

目的　分析不同曝光参数组合和层厚模式对图像质量及CT剂量指数 (computedtomographydoseindex ,CTDI)的影响 ,探讨多层面螺旋CT优化的曝光参数。资料与方法　设备采用MarconiMx80 0 0型CT机及附带QA体模。在其他扫描条件均相同时 ,实验分 90kV ,12 0kV ,140kV 3组 ,每组与可供选用mAs搭配形成不同的曝光组合和只改变层厚模式 ,应用系统默认曝光参数分别对QA体模进行扫描 ,检测分析不同曝光组合和层厚模式对图像质量及CTDI值的影响。结果　当kV不变时 ,图像的噪声随mAs的增加逐步得到改善 ,高对比分辨率、低对比分辨率相应提高 ,CTDI值也随之加大 ;当mAs不变时 ,图像的噪声随kV的升高也得到改善 ,高对比分辨率、低对比分辨率同样随之提高 ,并且CTDI值也加大。层厚模式的改变 ,图像的噪声随层厚的增加而改善 ,高对比分辨率、低对比分辨率同样随之提高 ,而CTDI值在 4mm× 5mm ,2mm× 8mm及 2mm× 10mm层厚模式中变化幅度不明显 ;此时CTDI值与所选用的Increment密切相关。按照图像质量评价标准 ,符合条件的曝光参数组合为 90kV与 3 0 0mAs、3 75mAs;12 0kV与 15 0mAs、2 0 0mAs、2 5 0mAs、3 0 0mAs ;140kV与 10 0mAs、15 0mAs、2 0 0mAs、2 5 0mAs、3 0 0mAs。结论　当kV为定值时 ,图像质量与mAs、CTDI值     

常规CT 的放射剂量最优化

目的：优化患者CT扫描参数,减少其辐射危害。方法以成人头部,胸部和腹部CT扫描为考察对象,应用CT专用16 cm直径CTDI测量模体,改变kVp和 mAs组合,测量所扫描图像的噪声,高对比分辨率,低对比分辨率等,以此为依据决定图像是否合格,并从合格影像中选出辐射剂量最小的一组kVp/mAs做为最优化结果。结果在噪声,高对比分辨率,低对比分辨率等都合格的情况下,各部位辐射剂量最小的一组kVp/mAs分别是：130/90（成人头部）,110/70（成人胸部）,130/65（成人腹部）。其辐射剂量相对设备预设条件下的辐射剂量下降百分比分别是：25．0％,12．0％和34．3％。结论体模实验证明,合理组合kVp和mAs设置可以在保证图像质量的情况下降低CT辐射剂量,从而为临床实际的CT剂量最优化提供借鉴。     

小儿头部多层螺旋CT检查的放射剂量评价

目的　评价小儿头部低剂量与常规剂量多层螺旋CT检查的放射剂量 ,为小儿头部多层螺旋CT检查提供扫描剂量参数。资料与方法　 (1)按年龄把 12 0例 0～ 6岁小儿分成 2组 ,患儿 <6个月 ,12 0kVp、90mAs扫描 30例 ;6个月～ 6岁 ,12 0kVp ,15 0mAs扫描 30例 ;常规扫描剂量为 12 0kVp、2 6 0mAs,依照上述年龄段各扫描 30例。其余扫描参数为 :准直 1.5mm ,层厚 6mm ,重建间隔 6mm ,床速 11.7mm/r,扫描时间 0 .75s。分别比较 2种扫描剂量产生的有效mAs、CT权重剂量指数 (weightedCTdoseindex ,CTDIw)及剂量长度乘积 (dose lengthproduct,DLP) ,并作 χ2检验。 (2 )由 3名医师盲法评价CT图像。按正常图像、图像有少许伪影、图像有严重伪影的等级对每帧图像进行质量评判 ,并进行统计学处理。结果　 (1)小儿各年龄段低剂量 (90mAs、15 0mAs)扫描的CTDIw为 17.2 8mGy、2 8.8mGy ,分别是常规剂量 (2 6 0mAs)扫描的 34.6 %、5 7.8% ;前者的DLP分别为 2 37mGy·cm、4 2 3mGy·cm ,明显低于后者的 6 83mGy·cm、731mGy·cm(P <0 .0 1)。 (2 ) 98%以上小儿头部低剂量CT图像可满足临床影像诊断需要 ,与常规剂量小儿头部图像相比无显著差异 (P >0 .0 5 )。结论　小儿头部低剂量多层螺旋CT扫描的辐射剂量为常规剂量扫描的 35     

降低新生儿64层螺旋CT颅脑扫描辐射的研究

目的研究64层螺旋CT在新生儿颅脑扫描中可用的最低扫描参数,以达到降低辐射剂量,减少辐射损害的目的。方法用螺旋和切片2种不同扫描方式,采用逐渐降低扫描参数方法,得出新生儿颅脑64层螺旋CT扫描可用的最佳方法和最低扫描参数。固定KVP值120 kV和其他扫描参数,每次降低10 mAs;切片法低剂量组扫描参数从120 kV和60 mAs开始,螺旋法低剂量组扫描参数从120 kV和90 mAs开始。每组扫描20例患儿,每组扫描所得图像由3位高级职称影像诊断专家按图像清晰度、图像层次对比度,脑组织、脑室、脑沟具体解剖结构及病变显示能力标准,将图像质量分为优质、良好、一般、较差、差5个等级,分别被评为5、4、3、2、1分,3分及以上的图像认为满足诊断要求。结果64层螺旋CT螺旋扫描120 kV和60 mAs是可用的最低扫描参数。螺旋扫描120 kV和60 mAs的CT辐射剂量指数（CTDI）7.7 mGy、平均剂量长度体积（DLP）155.1 mGy.cm;切片扫描120 kV和30 mAs是最低参数。切片扫描120 kV和30 mAs的CTDI 5.19 mGy、平均DLP 41.9 mGy.cm。2组最低扫描参数剂量分别是常规螺旋扫描的40%和11%,同时切片扫描是螺旋扫描剂量的27%。由此,切片扫描较螺旋扫描剂量明显减低,约73%。结论64层螺旋CT新生儿颅脑扫描的最佳方法是切片扫描,可用的最低扫描参数是120 kV和30 mAs。     

多层螺旋CT螺距与图像噪声和辐射剂量的关系探讨

目的 探讨多层螺旋CT螺距对CT图像噪声和辐射剂量的影响.方法 利用Philips Brilliance 16螺旋CT机和圆柱体体模(30 cm),使用成人胸部扫描方案,螺距分别使用0.188(准直16×0.75最小螺距 )、0.313、0.438、0.563 、0.688 、0.813 、0.938、1.063、1.188、1.313、1.438、1.563(准直16×0.75最大螺距)等12组进行螺旋扫描,每组取5幅图像,设图像中心为感兴趣区,测量CT值标准差及噪声水平,记录不同螺距下扫描时间、mAs值和容积CT剂量指数(CTDIvol),并进行比较分析.结果 当螺距＜1.188时,CTDIvol无明显变化,螺距＞1.188时,CTDIvol降低较明显.螺距从0.188～1.063逐渐增大过程中,图像噪声水平从0.49%逐渐增加至0.55%,增加幅度不大,而螺距从1.063～1.563时,图像噪声水平增大幅度相对明显,从0.55%逐渐增加至0.66%.但螺距在1.438即约2时,图像噪声水平比其前后2组螺距图像噪声水平有所降低,而此螺距时CTDIvol与最高值相比下降19%.结论 螺旋CT扫描参数螺距设为2左右时是比较适当的,能兼顾扫描剂量和图像质量.     

螺旋CT头颅扫描剂量的合理调整及其防护价值

目的：探讨能充分满足临床诊断需要且符合图像质量标准的CT扫描参数值,降低扫描辐射剂量。方法：①使用260、200、150、100、80mAs 5种剂量对模拟成人头颅的水模进行扫描,对获得的每幅图像选取相同的5个感兴趣区（ROI）测定并记录CT值的标准差,采用ROICT值标准差（SD）评价图像噪声。对各剂量组CT值标准差的均数和标准差作统计学处理;②随机选取来科全颅脑扫描显示颅内病变的10例,常规剂量260mAs扫描后,经患者同意,对病灶中心层面用200mAs加扫一层,对获取的两组图像质量进行盲式评判,评判标准依据空间分辨率、噪声及伪影将图像分为差、一般、较好、好四级。结果：①水模扫描：随着扫描剂量的降低,CTDIw（mGy）值明显下降,200mAs组比260mAs组降低13．34mGy;②图像噪声随着扫描剂量的降低而增加,但常规剂量260mAs组与减低剂量200mAs组间不存在差异（P〉0．05）;③260mAs和200mAs两种剂量的图像质量统计学处理无差异（Х^2=0．313,P=0．576）。结论：200mAs扫描剂量图像质量不受剂量降低而影响,但能降低辐射剂量,是可以实施调整的扫描参数,具有积极的放射防护意义。     

多排螺旋CT低剂量扫描在小儿胸部的应用

目的评估低剂量扫描在小儿胸部的应用。方法水模测试:在水体模的同一层面做3mm层厚的150、80、50、35、15mAs扫描。在每幅图像的5个相同感兴趣区测CT值,做CT值的均匀性和噪声水平比较。病例扫描:随机选择肺部感染的患儿40例,先行常规剂量(150mAs)扫描以确定感染部位,再在感染局部做低剂量扫描(50,35mAs及15mAs)。其他参数为:120kV,床进28.8mm/圈,0.5s/圈,16×1.5mm准直,重建层厚及间隔均为3mm。比较不同剂量的CT权重剂量指数(CTDIw)及剂量长度乘积(DLP);由2位高年资医师按优、良、合格及不合格的等级盲法评价不同剂量的图像质量,结果进行统计学处理。结果CT图像的均匀性随着扫描剂量的减少而变差,图像噪声水平随扫描剂量的减少而增高。小儿胸部150、50、35、15mAs的CTDIw分别为:10.0、3.3、2.3、1.0mGy,其DLP分别为:117.8、39.3、27.5和11.8;150、50、35mAs的符合临床诊断图像(包括优,良,合格3个等级)所占比例,肺窗和纵隔窗均不小于90%,而15mAs的不合格图像所占比例为20%。结论在保证图像质量的前提下,多排螺旋CT小儿胸部检查采用35mAs的扫描条件较为适宜。     

64层螺旋CT噪声测试及其影响因素分析

目的测试和评价64层螺旋CT图像噪声及其影响因素。方法对SOMATOM Sensation 64层螺旋CT，使用临床常用的腹部扫描模式，采用不同直径的模体，不同层厚、毫安秒（mAs）、管电压（kV）、重建算法、视野和螺距等扫描参数，分别进行螺旋扫描和断面扫描，测量其图像中心感兴趣区内的标准差并进行分析。结果160mAs时，标称层厚10、7、5、3、1和0.6mm的噪声分别是8.4、9.3、10.7、13.0、21.8、28.3；120kV时，重建算法为B30 smooth、B40 smooth、B60 sharp、B70 sharp时的噪声分别是8.4、9.5、41.4、44.5；对于标称层厚5mm时，螺距为0.5、0.75、1、1.25、1.5时噪声为10．6、11、10．7、10．5、10．9；随着模体直径的增加，螺旋扫描和断面扫描时的噪声均增大；视野为200mm×200mm、150mm×150mm、100mm×100mm时的图像噪声是7．83、8．10、10．47。结论64层螺旋CT图像噪声随mAs、层厚、kV、视野的增大而减少，随模体直径的增加和高分辨率算法而增大，但不随螺距和扫描方式的改变而改变。     

MSCT扫描参数对图像质量影响的实验研究

目的:探讨MSCT扫描参数对图像质量的影响。方法:通过固定扫描条件对含有不同密度材料的QCT体模分别进行常规轴面扫描和螺旋扫描,并在体模图像的不同密度材料的中心区域,分别选取一个相同大小的感兴趣区(ROI)进行CT值(-x±SD)测量,观察两种扫描方式下图像的CT值变化;然后在其它条件不变的情况下,改变其中1个扫描条件(层厚,电压,曝光量,螺距)再对体模各扫描3次,测量并比较各条件下各材料的CT值。结果:常规扫描和螺旋扫描对应体模CT图像各材料的x-接近,随材料密度的增加以及螺距的增大,图像的x-和SD增大更明显。在其他条件不变的情况下,随曝光量、层厚的增加,体模CT图像对应各材料的x-无明显变化,而SD明显减小;随着管电压的升高,体模CT图像对应各材料的-x和SD明显减小;随螺距的增大,体模CT图像对应各材料的-x无明显变化,而SD明显增加。结论:CT扫描参数的变化对图像质量有直接的影响,各扫描参数对图像质量影响的大小又有差异。     

螺旋CT胸部低剂量参数优化

目的 探讨螺旋CT胸部低剂量扫描优化参数.方法 通过在不同扫描参数下对检测模体进行常规剂量及低剂量螺旋CT扫描,评定不同扫描条件下模体辐射剂量及采集图像的空间分辨力、密度分辨力、噪声水平和均匀度,选择最佳扫描参数.扫描参数: 120 kV,0.75 s,Pitch 1.0,FOV 360,重建模式RF3(标准滤过),选取不同层厚和不同管电流分别扫描并记录各组结果,对所有数据进行统计学处理.结果 160 mA常规剂量之CTDI与低剂量各组(30 mA、50 mA、70 mA、90 mA)值比较差异有显著性差异,30 mA与50 mA之间、50 mA与70 mA之间CTDI值无显著性差异;层厚1 mm及管电流10 mA的图像噪声与其它各组层厚及管电流参数有非常显著性差异;空间分辨率和低对比分辨率随着管电流的增加而提高,在50 mA处低对比分辨率有较明显的拐点,即当管电流降低至30 mA时,低对比分辨率显著降低.结论 50 mA、层厚5 mm是单螺旋CT胸部低剂量扫描的最佳参数,适用于CT普查和早期肺癌的筛查.     

Dosimetry and adequacy of CT-based attenuation correction for pediatric PET: phantom study

PURPOSE: To evaluate the dose from the computed tomographic (CT) portion of positron emission tomography (PET)/CT to determine minimum CT acquisition parameters that provide adequate attenuation correction. MATERIALS AND METHODS: Measurements were made with a PET/CT scanner or a PET scanner, five anthropomorphic phantoms (newborn to medium adult), and an ionization chamber. The CT dose was evaluated for acquisition parameters (10, 20, 40, 80, 160 mA; 80, 100, 120, 140 kVp; 0.5 and 0.8 second per rotation; 1.5:1 pitch). Thermoluminescent dosimetry was used to evaluate the germanium 68/gallium 68 rod sources. A phantom study was performed to evaluate CT image noise and the adequacy of PET attenuation correction as a function of CT acquisition parameters and patient size. RESULTS: The volumetric anthropomorphic CT dose index varied by two orders of magnitude for each phantom over the range of acquisition parameters (0.30 and 21.0 mGy for a 10-year-old with 80 kVp, 10 mAs, and 0.8 second and with 140 kVp, 160 mAs, and 0.8 second, respectively). The volumetric anthropomorphic CT dose index for newborn phantoms was twice that for adult phantoms acquired similarly. The rod source dose was 0.03 mGy (3-minute scan). Although CT noise varied substantially among acquisition parameters, its contribution to PET noise was minimal and yielded only a 2% variation in PET noise. In a pediatric phantom, PET images generated by using CT performed with 80 kVp and 5 mAs for attenuation correction were visually indistinguishable from those generated by using CT performed with 140 kVp and 128 mAs. With very-low-dose CT (80 kVp, 5 mAs) for the adult phantom, undercorrection of the PET data resulted. CONCLUSION: For pediatric patients, adequate attenuation correction can be obtained with very-low-dose CT (80 kVp, 5 mAs, 1.5:1 pitch), and such correction leads to a 100-fold dose reduction relative to diagnostic CT. For adults undergoing CT with 5 mAs and 1.5:1 pitch, the tube voltage needs to be increased to 120 kVp to prevent undercorrection.     

儿童CT检查中扫描参数的优化

目的 了解儿童CT检查扫描条件选择及其所致辐射剂量的相关性,以期通过适当调节mAs、扫描长度等参数,降低儿童CT检查患者受照剂量。方法 比较江苏省7家医院不同年龄组（<1岁、1~5岁、6~10岁和11~15岁）儿童头颅、胸部、腹部多排螺旋CT检查主要扫描参数的差异。选用相同的检查参数在TM160剂量模体上测量CTDI₁₀₀,计算DLP,并通过经验加权因子,估算出不同部位检查的有效剂量（E）。对mAs、扫描长度和DLP进行多元线性回归分析,比较两家典型医院由于选择扫描条件不同所导致的剂量差异。结果 儿童头颅、胸部、腹部CT检查所致患者的有效剂量均值分别为2.46、5.69、11.86 mSv,各部位检查DLP与mAs、扫描长度均呈正相关（r=0.81、0.81、0.92,P<0.05）。较高的mAs选择,致使本研究各年龄组儿童胸腹部CT检查有效剂量是德国Galanski等研究的1.2~3.0倍;B医院各年龄组腹部检查选择了较高的扫描长度,以致其所致有效剂量均高于本研究均值。结论 建议通过合理优化儿童不同部位CT检查mAs、扫描长度等扫描参数,降低受检者所受辐射风险。     

Effects of patient size on radiation dose reduction and image quality in low-kVp CT pulmonary angiography performed with reduced IV contrast dose

The purpose of the study is to evaluate image quality and radiation exposure as a function of patient size for CT pulmonary angiography (CTPA) performed at reduced tube voltage and reduced intravenous (IV) contrast dose. We reviewed consecutive CTPAs performed between 9/1/2010 and 10/31/2010 on a 128-slice Siemens AS+ scanner using automated tube current modulation with quality reference mAs 200 and IV contrast concentration 370 mg I/ml followed by a saline flush: 99 scans at 120 kVp using 75 ml of contrast at 5 ml/s and 53 scans on patients lighter than 175 lbs at 100 kVp using 50 ml of contrast at 4 ml/s. We measured patient size (mean water-equivalent diameter) using a topogram analysis tool, signal (mean CT density) and noise (standard deviation) in the main pulmonary artery (MPA) on axial images, and calculated local CTDI(vol) from the kVp and mAs. Linear regression models were created for dependent variables ln(CTDI(vol)), signal, noise, and signal to noise ratio (SNR) as a function of independent variables size, age, gender, and kVp. After controlling for other variables, scanning at 100 kVp yielded CTDI(vol) reduction of 33 % (p?相似文献   

Patient-circumference-adapted dose regulation in body computed tomography. A practical and flexible formula

PURPOSE: To illustrate that the attenuation formula based on monochromatic radiation in homogeneous objects may be used for dose regulation in body computed tomography (CT) based on patient circumference and using a simple cloth measuring tape. MATERIAL AND METHODS: Based on the attenuation formula for monochromatic radiation the following Microsoft Excel equation was derived: mAs(x) = mAs(n)*EXP((0.693/ HVT)*(O(x)-O(n))/PI()), where mAs(x) (milliampere second) in a patient with circumference O(x) is calculated based on the nominal mAs(n) set for a reference patient with the circumference O(n) with regard to indication, scan protocol, and available CT scanner. The HVT = half-value thickness (object thickness change in cm affecting mAs setting by a factor of 2) resulting in the least mAs difference compared with published studies investigating the mAs needed for constant image noise in abdominal CT phantoms at 80-140 kVp was evaluated. Clinically recommended HVT values were applied to 20 patients undergoing abdominal CT using 130 effective mAs and 94 cm circumference as nominal settings, and an HVT of 9 cm. RESULTS: The object-sized dependent mAs for constant image noise at 80-140 kVp in 10-47 cm diameter abdominal phantoms (31-148 cm in circumference) differed, with few exceptions, by no more than 10% from those obtained with our formula using an HVT of 3.2-3.8 cm. An HVT of 9 cm in the patient study resulted in the same image noise-patient circumference relation as a phantom study using a "clinically adapted mAs" resulting in an acceptable noise according to diagnostic requirements. Clinical experiences recommend an HVT of about 8 cm for abdominal CT and 12 cm in thoracic CT. Changing the kVp from 120 to 80, 100, or 140 requires a mAs change roughly by factors of 4, 2, and 0.6, respectively, for constant image noise. CONCLUSION: Until fully automatic automatic exposure control systems have been introduced, applying the formula in a computer program provides the radiologist with an easy, quick, flexible, and practical instrument for reasonably good patient-sized adjusted exposure levels in clinical practice.     

Optimisation of the AP abdomen projection for larger patient body thicknesses

IntroductionThis study aims to identify optimal exposure parameters, delivering the lowest radiation dose while maintaining images of diagnostic quality for the antero-posterior (AP) abdomen x-ray projection in large patients with an AP abdominal diameter of >22.3 cm.MethodologyThe study was composed of two phases. In phase 1, an anthropomorphic phantom (20 cm AP abdominal diameter) was repetitively radiographed while adding 3 layers (5 cm thick each) of fat onto the phantom reaching a maximum AP abdominal diameter of 35 cm. For every 5 cm thickness, images were taken at 10 kVp (kilovoltage peak) intervals, starting from 80 kVp as the standard protocol currently in use at the local medical imaging department, to 120 kVp in combination with the use of automatic exposure control (AEC). The dose area product (DAP), milliampere-second (mAs) delivered by the AEC, and measurements to calculate the signal to noise ratio (SNR) and contrast to noise ratio (CNR) were recorded. Phase 2 included image quality evaluation of the resultant images by radiographers and radiologists through absolute visual grading analysis (VGA). The resultant VGA scores were analysed using visual grading characteristics (VGC) curves.ResultsThe optimal kVp setting for AP abdominal diameters at: 20 cm, 25 cm and 30 cm was found to be 110 kVp increased from 80 kVp as the standard protocol (with a 56.5% decrease in DAP and 76.2% in mAs, a 54.2% decrease in DAP and 76.2% decrease in mAs and a 29.2% decrease in DAP and 59.7% decrease in mAs, respectively). The optimal kVp setting for AP abdominal diameter at 35 cm was found to be 120 kVp increased from 80 kvp as the standard protocol (with a 50.7% decrease in DAP and 73.4% decrease in mAs). All this was achieved while maintaining images of diagnostic quality.ConclusionTailoring the exposure parameters for large patients in radiography of the abdomen results in a significant reductions in DAP which correlates to lower patient doses while still maintaining diagnostic image quality.Implications for clinical practiceThis research study and resultant parameters may help guide clinical departments to optimise AP abdomen radiographic exposures for large patients in the clinical setting.     

Radiation dose reduction and image quality in pediatric abdominal CT with kVp and mAs modulation and an iterative reconstruction technique

ObjectiveThe objective of this study was to compare the radiation dose and image quality of pediatric abdominal computed tomography (CT) using a protocol reconstructed with filtered back projection (FBP) and a protocol with both kVp and mAs modulation and sinogram-affirmed iterative reconstruction (SAFIRE).Materials and methodsWe retrospectively reviewed pediatric abdominal CT examinations performed with both kVp and mAs modulation. These raw data were reconstructed with SAFIRE at different strengths from 2 to 4 (SAFIRE groups 2–4). Another set of age/sex-matched pediatric abdominal CT examinations were also reviewed, which were performed during the same period with only mAs modulation and FBP (control group). The radiation dose and image quality were compared between groups. The image quality was objectively evaluated as the noise measured in the liver, aorta, and spleen at the level of the main portal vein and the image quality was subjectively reviewed by two radiologists for diagnostic acceptability using a four-point scale (0: unacceptable; 1: worse than the control group, but acceptable; 2: comparable with the control group; and 3: better than the control group). An independent t test was used in order to compare the radiation dose. An independent t test with Bonferroni correction and generalized estimating equations were used for the comparison of the objective and subjective image quality, respectively.ResultsTwenty-nine patients (M:F=19:10; mean age, 10.0 years) were enrolled in each group. The SAFIRE group, using the size-specific dose estimates calculation method showed a 64.2% radiation dose reduction (from 8.1 to 2.9 mGy, P< .05), compared with the results of the control group. The objective image noise of the SAFIRE groups 2 and 3 was comparable to that of the control group. The subjective image quality was the best in SAFIRE group 3 [odds ratio (OR) 3.015, P< .001 when comparing to SAFIRE group 0; OR 1.513, P< .001 when comparing to SAFIRE group 2].ConclusionsImage acquisition with both kVp and mAs modulation and iterative reconstruction using SAFIRE with strength 3 can preserve the objective and subjective image quality of pediatric abdominal CT scans with less than half the radiation dose.     

肺部容积高分辨CT低剂量扫描方案的体模与临床应用研究

目的 研究肺部容积高分辨CT(volumetric high-resolution CT,VHRCT)的低剂量扫描方案,评价其诊断价值.方法 采用120 kV和10～250 mAs对Catphan 500体模行VHRCT扫描,层厚0.625 mm,记录图像的空间分辨力、密度分辨力、噪声及扫描剂量,制定低剂量VHRCT的扫描方案;105例在本院行常规剂量VHRCT检查的肺弥漫病变患者,复诊时行低剂量VHRCT,比较常规剂量与低剂量VHRCT对于肺弥漫病变的显示情况.结果 体模研究中,管电压120 kV,管电流120～250 mAs时,VHRCT图像的空间分辨力均为9 LP/cm;低于120 mAs时,随着管电流降低,VHRCT图像的空间分辨力和密度分辨力下降而噪声增加.临床研究中,对于肺弥漫病变各种征象的显示,低剂量VHRCT(120 kV,120 mAs)与常规剂量VHRCT(120 kV,250 mAs)比较差异无统计学意义(P＞0.05).扫描剂量较常规VHRCT降低52％.结论 采用120 kV和120 mAs行低剂量VHRCT,可以在保持图像的分辨能力及诊断价值的前提下显著降低放射剂量,其取代常规剂量VHRCT具有可行性.     

基于蒙特卡罗数学模型两种脊柱全景X射线成像技术受检者辐射剂量的对比研究

目的 比较两种脊柱全景X射线成像技术对受检者产生的辐射剂量。方法 使用仿真体模进行实验,摸索出该体模在日本岛津Sonialvision safire17设备Slot scan脊柱全景成像的适宜成像条件,然后在GE Discovery XR650型DR系统上对该体模进行不同曝光条件的DR脊柱全景成像,3位有经验的放射科医生对两种成像技术的图像进行评分,选择图像质量评分均值最接近的对应成像参数为实验成像参数。将相关成像参数及X射线机信息输入PCXMC 2.0软件,计算受检者脊柱全景成像的器官吸收剂量和有效剂量。结果 Slot scan脊柱全景成像的适宜成像条件为高质量全景成像模式(HQ模式)、SID 150 cm、100 kVp和2 mAs, DR手动曝光模式脊柱全景成像相当图像质量的成像条件为SID 200 cm、100 kVp和3.2 mAs。Slot scan HQ模式、DR手动曝光模式和DR自动曝光模式脊柱全景成像的有效剂量(E)分别为(0.118 7±0.001 4)、(0.084 7±0.000 8)和(0.158 0±0.001 5) mSv,DR手动曝光模式的有效剂量明显低于其余2种模式(F=3 007.293,P<0.05);除乳腺以外,DR手动曝光模式的器官剂量均低于Slot scan HQ模式的器官剂量(P<0.05);除甲状腺、食管、肺以外,DR自动曝光模式的器官剂量均高于另外两种成像方式的器官剂量(P<0.05)。结论 两种手动全景成像技术的辐射剂量均处于较低水平,合理选择全景成像技术的曝光参数和模式可实现低剂量全景X射线成像。     

Strategies for formulating appropriate MDCT techniques when imaging the chest, abdomen, and pelvis in pediatric patients

OBJECTIVE: Our aim was to formulate appropriate MDCT chest and abdominopelvic CT scan protocols for pediatric patients. MATERIALS AND METHODS: Surface radiation dose measurements from a set of anthropomorphic phantoms (nominal 1 year old, 5 year old, and 10 year old) and an adult phantom were compared with standard CT dose index measurements. Image-noise values on axial 5-mm-thick anthropomorphic phantom images were obtained as a measure of image quality. RESULTS: Peripheral CT dose index values obtained with the standard 16-cm acrylic phantom were within approximately 10% of the CT surface dose measurements for the pediatric anthropomorphic phantoms for both chest and abdominopelvic scan protocols. The noise value for the adult phantom image acquired using a typical clinical CT technique was identified, and targeting this level of noise for pediatric CT examinations resulted in a decrease in dose of 60-90%. Initially, 80 kVp was selected for use with very small children; however, beam-hardening artifacts were severe enough to cause us to abandon this option. Current pediatric protocols at M. D. Anderson Cancer Center rely on 100- and 120-kVp settings. The display field-of-view parameter can be used as a surrogate for patient size to develop clinical pediatric CT protocol charts. CONCLUSION: CT dose index measurements obtained using the 16-cm standard acrylic phantom are sufficiently accurate for estimating chest and abdominopelvic CT entrance exposures for pediatric patients of the same approximate size as the anthropomorphic phantoms used in this study. Image-noise measurements can be used to adjust chest and abdominopelvic CT techniques for pediatric populations, resulting in a decrease in measured entrance dose by 60-90%.