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%.     

CT扫描方式对表浅器官辐射剂量测量值变异性的影响

目的 探讨CT扫描中表浅器官剂量测量值和图像噪声的不确定性。方法 使用GE Revolution CT对离体头颅标本分别行逐层和螺旋两种模式20次重复扫描。取GE Revolution CT和Philips Brilliance iCT准直宽度80 mm,Siemens Somatom Definition Flash CT准直宽度40 mm,螺距均为1,对胸部模体进行45次重复扫描。以上扫描中各序列均保持容积CT剂量指数（volume CT dose index,CTDI_vol）不变。用剂量计测量头颅标本右眼晶状体位置和胸部模体右乳腺中心位置剂量,剂量计传感器位置保持不变。重组传感器中心所在层面的5 mm层厚肺/软组织算法横断面图像,测量空气区CT值的标准偏差（图像噪声）。分别计算扫描3、5、10、20、30、45次剂量测量值及CT值标准偏差的平均值（Av）、标准差（SD）、变异系数（CV）和相对极差（RR）。采用Pearson和Spearman相关分析评估CT值标准偏差与剂量测量值之间的相关性。结果 头颅标本逐层扫描时剂量测量值几乎不变,螺旋扫描时测量值变化较大,20次测量RR达到10.67%。3台CT扫描仪重复扫描45次的剂量测量值RR分别达到43.83%、25.31%、14.32%。肺/软组织算法图像空气区CT值标准偏差变化幅度亦较大,但差异与剂量测量值不完全相关。结论 逐层扫描模式时,表浅器官剂量测量值稳定。螺旋扫描时,表浅器官剂量测量值和图像噪声均有较大变化。     

Dose reduction with adaptive statistical iterative reconstruction for paediatric CT: phantom study and clinical experience on chest and abdomen CT

Objectives

To assess the benefit and limits of iterative reconstruction of paediatric chest and abdominal computed tomography (CT).

Methods

The study compared adaptive statistical iterative reconstruction (ASIR) with filtered back projection (FBP) on 64-channel MDCT. A phantom study was first performed using variable tube potential, tube current and ASIR settings. The assessed image quality indices were the signal-to-noise ratio (SNR), the noise power spectrum, low contrast detectability (LCD) and spatial resolution. A clinical retrospective study of 26 children (M:F?=?14/12, mean age: 4 years, range: 1–9 years) was secondarily performed allowing comparison of 18 chest and 14 abdominal CT pairs, one with a routine CT dose and FBP reconstruction, and the other with 30 % lower dose and 40 % ASIR reconstruction. Two radiologists independently compared the images for overall image quality, noise, sharpness and artefacts, and measured image noise.

Results

The phantom study demonstrated a significant increase in SNR without impairment of the LCD or spatial resolution, except for tube current values below 30–50 mA. On clinical images, no significant difference was observed between FBP and reduced dose ASIR images.

Conclusion

Iterative reconstruction allows at least 30 % dose reduction in paediatric chest and abdominal CT, without impairment of image quality.

Key points

? Iterative reconstruction helps lower radiation exposure levels in children undergoing CT. ? Adaptive statistical iterative reconstruction (ASIR) significantly increases SNR without impairing spatial resolution. ? For abdomen and chest CT, ASIR allows at least a 30 % dose reduction.     

Analysis of CT acquisition parameters suitable for use in SPECT/CT: A free-response receiver operating characteristic study

PurposeThis dose optimisation free-response receiver operating characteristic (FROC) study compares the diagnostic performance of 8 CT acquisition parameter settings suitable for use with diagnostic quality SPECT/CT systems. Observers were required to localise simulated pulmonary lesions within an anthropomorphic chest phantom.MethodNine observers of varying CT experience (0–10+ years) reviewed 64 cases from each acquisition protocol. FROC methods were used to provide the area under the ROC curve (AUC) figures of merit for each CT acquisition parameter setting. The American College of Radiologists (ACR) CT accreditation phantom was used to acquire quality control (QC) images at each acquisition parameter setting. Measures of contrast to noise ratio (CNR), spatial (contrast) resolution and uniformity could then be compared to the AUC data. Effective dose (E) was estimated using the ImpaCT tool.ResultsAUC analysis revealed no significant difference (p = 0.866) between CT acquisitions for the detection of simulated pulmonary lesions within a chest phantom. The best observer averaged AUC performance was 0.853 (95% CI 0.803–0.903) at an estimated E of 0.82 mSv. The worst observer averaged AUC was recorded at the lowest estimated E (0.28 mSv) was 0.825 (95% CI 0.766–0.885). No correlation was evident between AUC and measures of CNR, spatial resolution or uniformity.ConclusionOur findings suggest that the lowest dose CT acquisition protocol can be used to accurately localise simulated pulmonary lesions within a chest phantom; suggesting that similar protocols could be used on diagnostic quality SPECT/CT systems to allow low-dose evaluations of lung lesions.     

Comparative study with a moving heart phantom of the impact of temporal resolution on image quality with two multidetector electrocardiography-gated computed tomography units

OBJECTIVE: The objective of this study was to compare the temporal resolution-related image quality of electrocardiography-gated images acquired with two multidetector computed tomography (CT) units with a moving heart phantom, at similar fixed heart rates, using half-scan and multisector acquisition modes. METHODS: An adjustable moving heart phantom (Limbsandthings, Horfield, Bristol, UK) was used. Specific heart rates (47, 55, 64, 66, 69, and 73 beats per minute [bpm]) were chosen. On a General Electric CT unit (LightSpeed Plus; General Electric Medical Systems, Milwaukee, WI), retrospective half-scan and multisector mode protocols were performed. On a Siemens CT unit (Somatom Volume Zoom; Siemens, Forchheim, Germany), a retrospective half-scan mode was performed at 47, 55, and 64 bpm, and a two-sector mode was performed at 66, 69, and 73 bpm. Reformatted maximum intensity projection images were qualitatively compared and related to their temporal resolution. RESULTS: Half-scan mode protocols provided similar good results with both CT units up to 55 bpm. The two-sector mode improved image quality compared with the half-scan mode. High temporal resolution with the multisector mode provided the best results. CONCLUSION: For coronary artery imaging, acquisition protocols that provide the highest temporal resolution are mandatory. The multisector mode is one technique that allows high temporal resolution but may be clinically inappropriate at heart rates below 65 bpm or when heart rate variation is observed during scan time.     

Radiation exposure and image quality in chest CT examinations.

OBJECTIVE: The purpose of this study was to determine how changes in radiographic tube current affect patient dose and image quality in unenhanced chest CT examinations. SUBJECTS AND METHODS: Ten sets of CT images were obtained from patients undergoing CT-guided chest biopsies. For each patient, six images of the same region were obtained at settings between 40 and 280 mAs. CT data were used to reconstruct tomographic sections with a field of view limited to the normal contralateral lung. Images were printed using lung and mediastinal image display settings. Image quality was determined by asking radiologists to assess the perceived level of mottle in CT images. Five chest radiologists ranked the relative image quality of six images. Patient effective doses were computed for chest CT examinations performed at each milliampere-second setting. Radiologists indicated whether any perceived improvement of image quality at the higher radiation exposures was worth the additional radiation dose. RESULTS: The differences in quality of chest CT images generated at greater than or equal to 160 mAs were negligible. Reducing the radiographic technique factor below 160 mAs resulted in a perceptible reduction in image quality. Differences in CT image quality for radiographic techniques between 120 and 280 mAs were deemed to be insufficient to justify any additional patient exposure. However, the use of 40 mAs results in an inferior image quality that would justify increased patient exposure. CONCLUSION: Radiographic techniques for unenhanced chest CT examinations can be reduced from 280 to 120 mAs without compromising image quality.     

Multidetector CT of bronchiectasis: effect of radiation dose on image quality

OBJECTIVE: The purpose of our prospective study was to assess the image quality with respect to the radiation dose incurred by multidetector CT (MDCT) in patients with suspected bronchiectasis. SUBJECTS AND METHODS. Image clusters, composed of nine images, using MDCT (120 kVp, a 2.5-mm collimation, a pitch of 6, and 2.5-mm reconstruction intervals) were obtained at each of two levels-the azygous arch and the right inferior pulmonary vein-at 170, 100, 70, 40, 20, and 10 mA. Independently, two chest radiologists assessed and compared the quality of the images obtained at the six milliamperage exposures. Image quality was graded using a 5-point scale with lung and mediastinal window settings. Radiation doses were measured at each of the six milliamperage settings while scanning the whole lung of a thoracic phantom using MDCT. RESULTS: The mean image quality scores at exposures of 170, 100, 70, 40, 20, 10 mA were as follows: 3.9, 3.7, 3.8, 3.2, 2.5, 1.6 at lung window settings and 4.1, 4.3, 4.0, 3.4, 2.3, 1.3 at mediastinal window settings, respectively. Images obtained at 70 mA were rated significantly better than those obtained at 40 mA or less (p < 0.01). The mean radiation dose at 170, 100, 70, 40, 20, 10 mA was 23.72, 14.39, 10.54, 5.41, 2.74, and 1.50 mGy, respectively. CONCLUSION: With a tube current setting as low as 70 mA, MDCT provides images of acceptable quality and volumetric data sets for the evaluation of bronchiectasis. The trade-off of using MDCT rather than conventional high-resolution CT is that the radiation dose is five times higher with MDCT (10.54 mGy) than with conventional high-resolution CT (2.17 mGy with parameters of 120 kVp, 170 mA, 1-mm collimation, and 10-mm intervals).     

胸部低剂量CT扫描对不同部位结构图像质量的影响

目的:探讨胸部低剂量CT扫描对不同部位结构图像质量的影响。方法:随机对48例来我科作胸部CT检 查者行标准剂量及低剂量扫描,选择主动脉弓下缘层面以及右下肺静脉层面进行图像质量的对比分析,分别评价这两个 层面中末梢肺血管、肺小叶、纵隔及胸背部软组织结构的清晰度。结果:胸部低剂量扫描对主动脉弓层面图像质量的影响 大于右下肺静脉层面,其中对肺血管图像质量的影响最小,对肺小叶的影响次之,对纵隔、肩背部软组织影响最大。结论: 胸部低剂量扫描主要影响胸部密实结构的图像质量,对肺内组织结构图像质量的影响不显著,所以可用于早期肺癌的筛 查。     

In-plane bismuth breast shields for pediatric CT: effects on radiation dose and image quality using experimental and clinical data

OBJECTIVE: The purpose of our study was to evaluate the amount of radiation dose reduction and its effect on image quality when using an in-plane bismuth breast shield for multidetector CT (MDCT) of the chest and abdomen in female pediatric patients. SUBJECTS AND METHODS: Fifty consecutive MDCT examinations (chest, 29; abdomen, 21) of female pediatric patients (mean age, 9 years; range, 2 months-18 years) were performed with a 2-ply (1.7 g of bismuth per square centimeter) bismuth shield (three sizes to accommodate patients of varying sizes) overlying the patient's breasts. MDCT images were evaluated for a perceptible difference in image quality in the lungs at the anatomic level under the shield as compared with nonshielded lung and whether the images were of diagnostic quality. In addition, 2-mm regions of interest were placed in the peripheral anterior and posterior portions of each lung in shielded and nonshielded areas, and noise (standard deviation in Hounsfield units) was measured in the regions. Differences among the regions in noise were compared for shielded versus nonshielded areas (paired t test). To measure differences in actual dose, we also evaluated the breast shield with an infant anthropomorphic phantom using thermoluminescent detectors in the breast tissue. The phantom was imaged with and without the breast shield using identical MDCT parameters. RESULTS: All MDCT scans of patients were of diagnostic quality with no perceptible difference in image quality in shielded versus nonshielded lung. We found no statistically significant difference in noise between the shielded and nonshielded lung regions of interest (shielded: mean noise, 17.3 H; nonshielded: mean noise, 18.8 H; p = 0.5180). Phantom measurements revealed a 29% reduction in radiation dose to the breast when a medium-dose MDCT protocol was used. CONCLUSION: Bismuth in-plane breast shielding for pediatric MDCT decreased radiation dose to the breast without qualitative or quantitative changes in image quality.     

胸部能谱成像模式与常规CT扫描的辐射剂量及图像质量的仿真体模研究

目的 通过仿真胸部体模研究胸部能谱CT不同方案成像模式与常规胸部CT扫描的辐射剂量、图像质量、对比噪声比及主观评分对比,获得最佳能谱扫描参数。方法 对仿真胸部体模分别进行常规胸部CT扫描以及3种不同扫描方式的能谱CT成像。3种能谱模式为宝石能谱CT （GSI）Assist模式（方案A）、管电流平均值时的GSI模式（方案B）及管电流最大值时的GSI模式（方案C）。所有扫描方式分别在噪声指数（NI）=9和11时,螺距0.984∶1,依次扫描。记录辐射剂量,同时测量感兴趣区（ROIs）5个不同层面水平的脂肪和肌肉组织的图像噪声值（SD）以评价图像质量。所有扫描序列由两位资深放射医师对肺窗肺纹理及分支5分制主观评分。结果 NI=9和11时,常规CT平扫与方案A、B、C的有效剂量（E）值分别为（8.0、8.5、6.2、10.4）和（5.3、5.1、4.3、6.2）mSv。NI=9时,常规胸部CT平扫与方案A、C的SD值差异有统计学意义（F=4.496,P<0.05）;NI=11时,方案A、B、C与常规胸部CT平扫SD值差异有统计学意义（F=8.425,P<0.05）;常规胸部CT扫描中,NI分别为9和11时SD值差异有统计学意义（t=－2.570,P<0.05）;在相同能谱扫描模式中,NI不同,SD值差异均无统计学意义（P>0.05）。NI相同扫描模式不同及扫描模式相同NI不同时,CNR及主观评分差异均无统计学意义（P>0.05）。结论 合理的能谱扫描模式与常规扫描的辐射剂量没有明显差异,但能谱扫描模式可以获得较高的图像质量。此外,选择合适的噪声指数在图像质量相仿的同时可以明显降低辐射剂量。综合辐射剂量及图像质量,能谱CT智能模式可以达到辐射剂量及图像质量的双向平衡。     

胸部CT低剂量扫描的图像质量与吸收剂量关系分析

目的　探索多层螺旋CT在胸部低剂量扫描的可能性和合理性。方法　 (1)X线吸收剂量测试 :用 12 0kV、0 75s、分别测试 8与 3mm层厚的 115 0、4 0 0、2 5 0、7 5mAsX线照射剂量。计算吸收剂量指数 ,并加以比较。 (2 )水体模测试CT值的均匀性和噪声水平 :在水体模的同一层面 ,用 12 0kV、 0 75s分别作 8与 3mm层厚的 115 0、4 0 0、2 5 0、7 5mAs扫描。在每幅图像的相同位置测 5个兴趣区 ,作CT值的均匀性和噪声水平比较。 (3)病例CT扫描 :随机选择肺部块影和片状影的患者各 30例。用 12 0kV ,0 75s,8与 3mm层厚在同一层面作 115 0、4 0 0、2 5 0、15 0、7 5mAs扫描。另选 15例作 190、15 0、4 0、2 5、15mAs螺旋扫描。作不同厚度的重建间隔对比和后处理图像最大密度投影 (MIP)、计算机容积摄影 (CVR)、多平面重建 (MPR)、高分辨率CT(HRCT)、三维成像(3D)、仿真支气管镜等效果比较。 (4)图像质量评估 :由 4名CT医生盲法评价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评判每一幅图像 ,进行统计学处理。结果　 (1)X线吸收剂量指数测试表明 ,115 0mAs的X线吸收剂量指数大于 4 0 0、2 5 0、7 5mAs的指数分别在 6 0 %、70 %、85 %以上。 (2 )水模测试结果 ,CT图像的均匀性随CT扫     

Detection of ground-glass opacities by use of hybrid iterative reconstruction (iDose) and low-dose 256-section computed tomography: a phantom study

The detection of ground-glass opacities (GGOs) is an important issue in lung cancer screening with low-dose CT. The iterative reconstruction (IR) technique has the ability to improve the image quality relative to the filtered back projection (FBP) technique with low-dose CT. Our purpose was to investigate the ability to detect GGO in a chest phantom using a low-dose CT and hybrid IR, named iDose. Simulated GGOs in a chest phantom were scanned with 256-section CT at tube current second products of 20, 50, 100, and 200 mAs. Five radiologists visually assessed the detectability of GGOs in the phantom. The contrast-to-noise ratio (CNR) for GGOs was used as an estimate of image quality. Comparison of the detectability and CNR between standard images with 200 mAs-FBP and low-dose images with 20, 50, and 100-mAs FBP/iDose were performed by ANOVA with Dunnett’s and Tukey’s test. The detectability was significantly lower at 20-mAs FBP/iDose and 50-mAs FBP than that at 200-mAs FBP (p < 0.05). There was no significant difference between 50-mAs iDose and 200-mAs FBP and between 100-mAs iDose/FBP and 200-mAs FBP. The CNR was significantly higher on iDose images than that on FBP images at each mAs value. The CNR at 200-mAs FBP was the same as that at 50-mAs iDose (CNR:1.8). The hybrid IR technique and low-dose CT imaging with 50 mAs enabled noise and to maintain the detectability for GGOs in a chest phantom that is equivalent to the reference acquisitions of 200 mAs with FBP.     

中国人仿真胸部体模检测多层螺旋CT扫描组织器官剂量的研究

目的 利用中国人仿真胸部模型来测量不同噪声指数下胸部各组织器官的吸收剂量,计算有效剂量(ED)并对MSCT胸部扫描进行剂量评估.方法 对CDP-1C型中国人仿真胸部体模在CT体层解剖和X线衰减两方面进行等效性论证;通过在体模内布放热释光剂量计(TLD)来测量不同噪声水平下各组织器官的吸收剂量,并记录相应的剂量长度乘积(DLP);将两者分别换算为ED后选择单因素t检验方法进行对比研究,分析自动管电流调制(ATCM)技术时不同噪声指数胸部CT扫描的剂量水平.结果 中国人仿真胸部体模与成人CT胸部图像的结构相似.体模主要器官平均CT值为肺-788.04 HU、心脏45.64 HU、肝脏65.84 HU、脊柱254.32 HU,与成人偏差程度分别为肺0.10%、心脏3.04%、肝脏4.49%、脊柱4.36%.肝脏的平均CT值差异有统计学意义(t=-8.705,P＜0.05);肺、心脏和脊柱平均CT值与人体差异无统计学意义(t值分别为-0.752、-1.219、-1.138,P＞0.05).当噪声指数从8.5逐渐增至22.5时,DLP从393.57 mGy·cm递减至78.75 mGy·cm,各器官吸收剂量呈下降趋势(以肺为例,平均吸收剂量从22.38 mGy递减至3.66 mGy).应用DLP所计算的ED较器官吸收剂量计算的ED偏低(以噪声指数为8.5为例,两种方法的ED分别为6.69和8.77 mSv).结论 应用中国人仿真体模来进行CT剂量评估更为准确;基于ATCM技术的胸部CT扫描噪声指数设定至少应大于8.5.

Abstract：

Objective Using the Chinese anthropomorphic chest phantom to measure the absorbed dose of various tissues and organs under different noise index, and to assess the radiation dose of MSCT chest scanning with the effective dose(ED). Methods The equivalence of the Chinese anthropomorphic chest phantom(CDP-1C) and the adult chest on CT sectional anatomy and X-ray attenuation was demonstrated. The absorbed doses of various tissues and organs under different noise index were measured by laying thermoluminescent dosimeters(TLD) inside the phantom, and the corresponding dose-length products(DLP) were recorded. Both of them were later converted into ED and comparison was conducted to analyze the dose levels of chest CT scanning with automatic tube current modulation (ATCM) under different noise index. Student t-test was applied using SPSS 12.0 statistical software. Results The Phantom was similar to the human body on CT sectional anatomy. The average CT value of phantom are -788.04 HU in lung,45.64 HU in heart,65.84 HU in liver,254.32 HU in spine and the deviations are 0.10%,3.04%, 4.49% and 4.36% respectively compared to humans. The difference of average CT value of liver was statistically significant(t=-8.705,P＜0.05),while the differences of average CT values of lung, heart and spine were not significant(t value were -0.752,-1.219,-1.138,respectively and P＞0.05).As the noise index increased from 8.5 to 22.5, the DLP decreased from 393.57 mGy·cm to 78.75 mGy·cm and the organs dose declined. For example, the average absorbed dose decreased from 22.38 mGy to 3.66 mGy in lung. Compared to ED calculating by absorbed dose, the ED calculating by DLP was lower. The ED values of the two methods were 6.69 mSv and 8.77 mSv when the noise index was set at 8.5. Conclusions Application of the Chinese anthropomorphic chest phantom to carry out CT dose assessment is more accurate. The noise index should be set more than 8.5 during the chest CT scanning based on ATCM technique.     

降低儿童16层螺旋CT检查辐射剂量的研究

目的论证CT扫描参数kVp和mAs与剂量和图像噪声的关系,在不影响临床诊断的基础上,修正并验证一种基于成人扫描参数的安全可行的儿童16层螺旋CT检查的扫描参数。方法利用16层螺旋CT,采用标准CT剂量指数(CTDI)测试仪、100mm笔型电离室,分别测量16cm和32cm直径模体在2mm×5mm准直宽度时不同kVp和mAs的CTDI;采用20cm标准水模,测量单一感兴趣区域(ROI)标准偏差值SD代表噪声水平。以成人扫描参数的不同百分比修正为不同年龄段儿童CT扫描的参数供临床验证。结果随着kVp和mAs的增加,CTDI随之增加,并与mAs呈线性关系;16cm直径模体的表面CTDI要高于32cm模体58%;实际的加权CTDIw值高于CT扫描仪显示的CTDIw;mAs相同时,kVp越高,图像噪声SD值越低,在kVp固定时,随着mAs的增加,图像噪声SD随之减少,当mAs增加到一定程度后,图像噪声趋向平稳。结论在不影响临床诊断的图像噪声水平下,根据年龄和体型特点,儿童16层CT检查mAs可以比成人降低10%～85%。     

Organ-based tube current modulation in chest CT. A comparison of three vendors

IntroductionOrgan-based tube current modulation (OBTCM) is designed for anterior dose reduction in Computed Tomography (CT). The purpose was to assess dose reduction capability in chest CT using three organ dose modulation systems at different kVp settings. Furthermore, noise, diagnostic image quality and tumour detection was assessed.MethodsA Lungman phantom was scanned with and without OBTCM at 80–135/140 kVp using three CT scanners; Canon Aquillion Prime, GE Revolution CT and Siemens Somatom Flash. Thermo-luminescent dosimeters were attached to the phantom surface and all scans were repeated five times. Image noise was measured in three ROIs at the level of the carina. Three observers visually scored the images using a fivestep scale. A Wilcoxon Signed-Rank test was used for statistical analysis of differences.ResultsUsing the GE revolution CT scanner, dose reductions between 1.10 mSv (12%) and 1.56 mSv (24%) (p < 0.01) were found in the anterior segment and no differences posteriorly and laterally. Total dose reductions between 0.64 (8%) and 0.91 mSv (13%) were found across kVp levels (p < 0.00001). Maximum noise increase with OBTCM was 0.8 HU. With the Canon system, anterior dose reductions of 6–10% and total dose reduction of 0.74–0.76 mSv across kVp levels (p < 0.001) were found with a maximum noise increase of 1.1 HU. For the Siemens system, dose increased by 22–51% anteriorly; except at 100 kVp where no dose difference was found. Noise decreased by 1 to 1.5 HU.ConclusionOrgan based tube current modulation is capable of anterior and total dose reduction with minimal loss of image quality in vendors that do not increase posterior dose.Implications for practiceThis research highlights the importance of being familiar with dose reduction technologies.     

Reduced computed tomography radiation dose in HIV-related pneumonia: effect on diagnostic image quality

PURPOSE: The objective of this study was to compare the diagnostic quality of low-dose computed tomography (CT) with that of standard-dose chest CT in the diagnosis of infectious lung diseases. MATERIALS AND METHODS: Thirty chest CT scans [high-resolution computed tomography (HRCT), 15; spiral CT, 15] were performed in HIV-positive patients with an infectious lung disease. Two additional slices were obtained at two lower exposures (HRCT, 120 kV/70 mAs and 120 kV/50 mAs; spiral CT, 100 kV/56 mAs and 100 kV/40 mAs) after chest routine CT. Observers compared the quality of the images obtained at different parameters and image noise. Objective evaluation of image noise was also made. RESULTS: Diagnostic image quality was excellent in 93% of the low-dose HRCT scans and in 86% of the low-dose spiral CT scans, rates that are always acceptable in any case. Significant differences were found in noise levels between the low-dose and reference scans; however, artifacts did not compromise detection of abnormalities. In HRCT, a mean reduction of 77% from the standard technique to the low-dose scan is possible in total and in lung effective doses. In spiral CT, this reduction is lower at 71%. These values can reach a further reduction with ultra-low-dose imaging (84% in HRCT and 80% in spiral CT). CONCLUSIONS: Chest CT image quality appears to be adequate to evaluate pulmonary infectious diseases, even with an effective reduction in radiation dose. Standard-dose CT with a higher patient effective dose may be appropriate for selected cases.     

CARE Dose 4D 技术降低成人胸部扫描剂量的临床价值

目的 探讨CARE Dose 4D技术在成人胸部CT扫描中降低辐射剂量及提高图像质量价值.方法 选取胸部CT扫描病例100例,随机分为低剂量组及对照组各50例,低剂量组使用CARE Dose 4D技术.记录每位患者胸部扫描时自动显示的有效毫安秒(mAs)、容积CT剂量指数(CTDI vol)及剂量长度乘积(DLP)和每幅图像上的mAs值.取每例患者肺尖部、主动脉弓下缘水平、左房中部水平及肺底部4幅图像,共400幅.由两位副主任医师按优、良、差3级双盲法评判,测量相应部位图像噪声.结果 在设置质量参考80 mAs时,低剂量组比对照组最大下降44 mAs,平均下降9.60 mAs(12.0%);CTDIvol值最大下降4.75 mGy,平均下降0.95 mGy(11.0%);DLP值平均下降14.88 mGy·cm(7.5%).图像主观评判低剂量组平均优良率为99.5%,对照组为98.0%;肺尖及肺底水平低剂量组高于对照组,左房中部水平低于对照组,主动脉弓下缘水平两组相近.图像噪声测量结果显示低剂量组肺尖及肺底部低于对照组(t=6.299、2.332,P＜0.05),左房中部水平高于对照组(t=3.078,P＜0.05),主动脉弓下缘水平两组相似(t=1.191,P＞0.05).结论 CARE Dose4D技术具有实时在线调节mAs作用,既可提高射线利用效率、降低辐射剂量,又能提高图像质量,在胸部CT扫描中具有一定临床应用价值.

Abstract：

Objective To investigate the value of CARE Dose 4D technique in decreasing radiation dose and improving image quality of multi-slice spiral CT in adult chest scanning.Methods 100patients of chest CT scanning were equally divided into study group and control group randomly.CARE Dose 4D Technique was used in study group.Effective mAs value,volume CT dose index (CTDIvol) and dose length product (DLP) were displayed automatically in machine while chest scanning; those values and actual mAs value of every image were recorded respectively.The image quality at apex of lung,lower edge of aorta arch,middle area of left atrium and base of lung on every image of 400 images was judged and classified as three level (excellent,good,poor) by two deputy chief physicians with double blind method,the image noise at corresponding parts was measured.Results While setting 80 mAs for quality reference mAs,the effective mAs value in study group most decreased 44 mAs than control group with an average decrease of 9.60( 12.0% ) ,CTDIvol with 4.75 mGy with an average decrease of 0.95 mC y( 11.0% ) ,DLP 99.50% in study group,with 98.0% in control group.But it was higher at apex of lung and base of lung,lower at middle area of left atrium,and similar at lower edge of aorta arch in study group than contrast group.The image noise were lower at apex of lung and base of lung in study group than control group (t =6.299 and 2.332,all P ＜ 0.05 ) ,higher at middle area of left atrium in study group than control group (t=3.078,P ＜0.05) and similar at lower edge of aorta arch in study group than control group (t =1.191,P ＞0.05).Conclusions CARE Dose 4D technique provides a function regulated mAs real-time on line,it not only raises utilization rate of radiation and decreases radiation dose,but also promises and increases image quality in chest CT scanning,and has some clinical significance.     

Evaluation of the efficacy of a bismuth shield during CT examinations

PURPOSE: The purpose of the study was to evaluate the efficacy of a bismuth shield (Attenurad F&L Medical Products, Vandergrift, PA) in reducing the dose to surface organs during Computed Tomography (CT) examinations. The shield was evaluated for reduction of the dose to breast during chest examinations and reduction of the dose to the lens of the eye during brain examinations. MATERIALS AND METHODS: The dose was measured on patients (10 for the eye and 30 for the breast), and on an anthropomorphic phantom (Alderson Rando). The reduction of image quality was evaluated both qualitatively by an expert radiologist, and in terms of increased noise on the phantom images (Rando). RESULTS: The use of the protective device reduced the dose by 34% to the breast and 50% to the lens. These figures are confirmed by the measurements taken both on patients and on the anthropomorphic phantom. The protective device reduced image quality in the regions immediately beneath it, but in the cases considered, those regions were of no diagnostic interest, while in the brain and lung regions, the quality is only slightly reduced, always allowing a correct diagnostic evaluation. Numerical analysis also led to the conclusion that a modest increase in noise is only statistically significant for the anterior portions of the lung. When present, the artifacts appeared outside the field of clinical interest. That is mainly due to the use of a foam pad (0.7 - 1 cm thick) to protect the breast. DISCUSSION AND CONCLUSIONS: The protection proved effective both in the case of breast and of lens, leading to a significant reduction in dose, without excessively affecting image quality. The shield proved easy to use, and did not increase the examination time.     

Quality control within the multicentre perfusion CT study of primary colorectal cancer (PROSPeCT): results of an iodine density phantom study

Objectives

To assess the cross-centre consistency of iodine enhancement, contrast-to-noise ratio and radiation dose in a multicentre perfusion CT trial of colorectal cancer.

Materials and methods

A cylindrical water phantom containing different iodine inserts was examined on seven CT models in 13 hospitals. The relationship between CT number (Hounsfield units, HU) and iodine concentration (milligrams per millilitre) was established and contrast-to-noise ratios (CNRs) calculated. Radiation doses (CTDI_vol, DLP) were compared across all sites.

Results

There was a linear relationship between CT number and iodine density. Iodine enhancement varied by a factor of at most 1.10, and image noise by at most 1.5 across the study sites. At an iodine concentration of 1 mg ml^?1 and 100 kV, CNRs ranged from 3.6 to 4.8 in the 220-mm phantom and from 1.4 to 1.9 in the 300-mm phantom. Doses varied by a factor of at most 2.4, but remained within study dose constraints. Iterative reconstruction algorithms did not alter iodine enhancement but resulted in reduced image noise by a factor of at most 2.2, allowing a potential dose decrease of at most 80 % compared to filtered back projection (FBP).

Conclusions

Quality control of CT performance across centres indicates that CNR values remain relatively consistent across all sites, giving acceptable image quality within the agreed dose constraints.

Key Points

? Quality control is essential in a multicentre setting to enable CT quantification. ? CNRs in a body-sized phantom had the recommended value of at least 1.5. ? CTDIs and DLPs varied by factors of 1.8 and 2.4 respectively.     

自动管电流模式下管电压对CT辐射剂量和影像质量影响的模体研究

目的 探讨自动管电流调制模式下行头颈部和胸部CT扫描时,管电压的改变对辐射剂量及影像质量的影响。方法 自动管电流和自动管电压模式下,对头颈部和胸部模体进行常规CT扫描。自动管电流模式下,管电压分别手动选择70、80、100、120和140 kV,对头颈部和胸部模体进行常规CT扫描。每种管电压下定位像扫描3次,再进行1次螺旋扫描。头颈部模体在眼眶中心及第5颈椎（C5）椎体上缘层面选取感兴趣区（ROI）,胸部模体在肺尖及气管分叉层面选取ROI,测量记录对比噪声比（CNR）。用热释光剂量计（TLD）测量每次扫描时眼晶状体和乳腺的器官剂量（取3次测量的平均值）,计算定位像和螺旋扫描的累积值。记录每次扫描的容积CT剂量指数（CTDI_vol）,并计算CTDI_vol累积值。最后通过计算品质因数（FOM）,找到最优化的管电压值。结果 自动管电流和自动管电压模式时,头颈部自动选择120 kV和108 mAs,胸部自动选择80 kV和167 mAs。自动管电流模式时,手动选择70 kV时眼晶状体辐射剂量和CTDI_vol值最小（分别为0.779和4.070 mGy）,140 kV时眼晶状体辐射剂量和CTDI_vol值最大（分别为2.571和25.670 mGy）。70 kV时乳腺辐射剂量和CTDI_vol值最小（分别为0.698和0.900 mGy）,140 kV时乳腺辐射剂量和CTDI_vol值最大（分别为3.452和7.400 mGy）。CNR值在眼眶和C5椎体上缘层面分别为51.30~118.36和80.78~173.12,在肺尖和气管分叉层面分别为50.15~129.58和49.63~115.40。FOM因子在眼眶层面80 kV最大,在C5椎体上缘层面120 kV最大,在肺尖和气管分叉层面都是70 kV最大。头颈部模体最佳管电压：眼眶层面手动100 kV,颈部层面自动管电压模式（120 kV）。胸部模体最佳管电压：手动100 kV。结论 管电压的选择对CT扫描的辐射剂量和影像质量影响较大。对于常规CT扫描,手动100 kV适合眼眶区域扫描,自动120 kV适合颈部区域扫描,手动100 kV适合胸部扫描。