Sixteen-detector row CT of abdomen and pelvis: study for optimization of Z-axis modulation technique performed in 153 patients

PURPOSE: To retrospectively determine the optimal noise indexes required to obtain diagnostically acceptable computed tomographic (CT) images of the abdomen and pelvis with z-axis modulation. MATERIALS AND METHODS: Ninety-five patients underwent 16-section multi-detector row CT of the abdomen and pelvis with z-axis modulation at noise indexes of 10.5, 11.0, 11.5, and 12.0 HU with 10-380 mA. Subsequently, 58 patients were scanned at noise indexes of 12.5 and 15.0 HU with 75-380 mA. The weights of all subjects were recorded, and transverse and anteroposterior diameters were measured. The CT images were evaluated for abnormalities and graded for image quality in terms of noise and diagnostic acceptability by using a five-point scale. Objective noise in the liver parenchyma was measured, and the tube current was recorded at each section in all 153 patients. Statistical analyses were performed to determine the appropriate noise index and to assess the effect of patient weight and abdominal diameters on image noise and diagnostic acceptability at different noise indexes. Tube current-time products (in milliampere seconds) at various noise indexes were compared with those at CT previously performed without z-axis modulation. RESULTS: No significant difference in subjective image noise or diagnostic acceptability was found at noise indexes of 10.5-15.0 HU (P =.14), and objective noise was significantly inferior only at a noise index of 15.0 HU (P =.009). Compared with CT scanning at a 10.5-HU noise index, CT scanning at 12.5- and 15.0-HU noise indexes yielded, respectively, 10.0% and 41.3% reductions in radiation exposure. Patient weight and abdominal diameters affected subjective image quality. CONCLUSION: Use of a 15.0-HU noise index at 75-380 mA results in acceptable subjective image noise and diagnostic acceptability but significantly greater objective image noise at routine abdominal-pelvic CT. For greater image quality demands, a noise index of 12.5 HU results in acceptable image quality and a 19.6% reduction in radiation exposure.     

Chest CT performed with z-axis modulation: scanning protocol and radiation dose

Institutional review board approval of the study protocol and waiver of informed consent were obtained. This study was compliant with the Health Insurance Portability and Accountability Act. The purpose of this study was to retrospectively assess the scanning protocol and radiation dose associated with z-axis automatic tube current modulation in multi-detector row CT scanning of the chest. Fifty-three patients (mean age, 54 years; age range, 26-77 years; 25 men, 28 women) underwent 16-detector row chest CT with z-axis modulation and noise indexes of 10.0, 12.5, and 15.0 HU. Two radiologists independently compared images acquired with z-axis modulation and fixed tube current (180-300 mA) techniques for image noise, diagnostic acceptability, and depiction of peripheral bronchovascular markings. Tube current-time product was calculated for each study. There was good interobserver agreement between the two readers (kappa = 0.72). Compared with the fixed tube current technique, z-axis modulation provides acceptable image noise for chest CT, with an 18% and 26% reduction in tube current-time product at 10.0- and 12.5-HU noise indexes, respectively.     

Comparison of Z-axis automatic tube current modulation technique with fixed tube current CT scanning of abdomen and pelvis

PURPOSE: To compare image quality, diagnostic acceptability, and radiation exposure associated with 16-section multi-detector row computed tomographic (CT) examinations of abdomen and pelvis performed with z-axis modulation technique of automatic tube current modulation and with manual selection of fixed tube current. MATERIALS AND METHODS: Sixty-two consecutive subjects (mean age, 60 years; age range, 19-84 years; male-to-female ratio, 35:27) underwent follow-up CT of abdomen and pelvis with use of a 16-section multi-detector row scanner and z-axis modulation technique (10.5-12.0-HU noise index, 10-380 mA). Scanning parameters included 140 kVp, 0.5-1.0-second gantry rotation time, 0.938:1 beam pitch, and 5-mm reconstructed section thickness. For each subject, images obtained with z-axis modulation were compared with previous images obtained with fixed tube current (200-300 mA) and with other parameters identical. Images were compared for noise and diagnostic acceptability by two subspecialty radiologists using a five-point scale (1, unacceptable; 3, acceptable; 5, excellent) at five levels: upper liver at diaphragm, porta hepatis, right kidney hilum, iliac crest, and upper margin of acetabulum. Tube current and gantry rotation time used for acquisitions at these levels were recorded. Data were analyzed with parametric and nonparametric statistical tests. RESULTS: Although no significant differences were found (P =.34), images acquired with z-axis modulation at the levels of the upper liver (diaphragm) and acetabulum had a higher noise and lower diagnostic quality, compared with images acquired with fixed tube current. Compared with fixed tube current, z-axis modulation resulted in tube current-time product reduction in 54 (87%) of 62 examinations (mean reduction, 71.2 mAs) and increase in eight (13%) (mean increase, 17.0 mAs). CONCLUSION: Compared with manually selected fixed tube current, z-axis automatic tube current modulation resulted in reduced tube current-time product and similar image noise and diagnostic acceptability at CT of abdomen and pelvis.     

Optimised low-dose multidetector CT protocol for children with cranial deformity

Objective

To present an optimised low-dose multidetector computed tomography (MDCT) protocol for the study of children with cranial deformity.

Methods

Ninety-one consecutive MDCT studies were performed in 80 children. Studies were performed with either our standard head CT protocol (group 1, n?=?20) or a low-dose cranial deformity protocol (groups 2 and 3). Group 2 (n?=?38), initial, and group 3 (n?=?33), final and more optimised. All studies were performed in the same 64-MDCT equipment. Cranial deformity protocol was gradationally optimised decreasing kVp, limiting mA range, using automatic exposure control (AEC) and increasing the noise index (NI). Image quality was assessed. Dose indicators such us CT dose index volume (CTDIvol), dose-length product (DLP) and effective dose (E) were used.

Results

The optimised low-dose protocol reached the following values: 80 kVp, mA range: 50–150 and NI?=?23. We achieved a maximum dose reduction of 10-22 times in the 1- to 12-month-old cranium in regard to the 2004 European guidelines for MDCT.

Conclusion

A low-dose MDCT protocol that may be used as the first diagnostic imaging option in clinically selected patients with skull abnormalities.

Key Points

? MDCT is a very useful tool in the study of skull lesions ? Low-dose MDCT minimises child exposure to ionising radiation while maintaining image quality ? Low-dose MDCT should be considered as the first imaging option in selected patients     

Detection of urinary tract stones at low-radiation-dose CT with z-axis automatic tube current modulation: phantom and clinical studies

PURPOSE: To evaluate depiction of urinary tract calculi at computed tomography (CT) with a z-axis modulation technique at various noise indexes to reduce radiation dose and preserve image quality. MATERIALS AND METHODS: Sixteen radiopaque kidney stones (2.5-19.2 mm in diameter) were embedded in the collecting systems of two bovine kidneys immersed in a water bath. A kidney phantom was made by placing the kidneys in an elliptical Plexiglas phantom (32 x 20 x 20 cm) filled with physiologic saline. The phantom was scanned at 16-detector row CT with a fixed tube current (300 mA) and z-axis modulation at noise indexes of 14, 20, 25, 35, and 50; remaining imaging parameters were held constant. Two abdominal radiologists reviewed images from most to least noisy. Images were evaluated for presence of stones and size, site, and attenuation value of each stone. Readers also graded conspicuity and margins of each stone on a five-point scale. In addition, follow-up studies of 22 patients (mean age, 46 years; range, 26-57 years; male-female ratio, 14:8) with kidney and ureteral stones who underwent CT with z-axis modulation (noise index, 14 and 20) were evaluated in the same manner. Statistical analysis was performed with the Student t test, Wilcoxon signed rank test, and kappa test of interobserver agreement. Institutional review board approval was obtained, and informed consent was not needed. RESULTS: In the phantom study, all 16 stones were identified on images obtained with a fixed tube current and z-axis modulation at noise indexes of 14, 20, and 25 (with a reduction in radiation dose of up to 77% compared with that of fixed tube current scanning). Three stones (<5 mm) were not visualized with z-axis modulation at noise indexes of 35 and 50. No significant difference was shown for conspicuity of kidney stones in 22 patients who underwent CT with z-axis modulation (with a 43%-66% reduction in radiation dose) when compared with results of previous fixed tube current studies (P > .05). CONCLUSION: Kidney stones (< or =2.5 mm) can be adequately depicted with the z-axis modulation technique, with a 56%-77% reduction in radiation dose. In patients with urinary tract stones, the technique results in a 43%-66% reduction in radiation dose at noise indexes of 14 and 20 without compromising stone depiction.     

多层螺旋CT自动毫安技术对腰椎患者扫描剂量减少的可行性研究

目的 探讨MSCT Z轴自动毫安(ATCM)调制扫描技术对患者腰椎CT扫描剂量减少的可行性.方法 对48例腰椎间盘突出症患者分椎间盘介入术前检查及术后复查2组,进行L3～S1相同覆盖范围MSCT检查.术前检查组采用常规固定320 mAs(FM组),术后复查组采用噪声指数为12.0 HU的Z轴ATCM技术(ATCM组).分别选择L3～4、L4～5、L5～S1椎间盘平面作为观察平面,对2种毫安技术的图像质量、图像噪声和辐射剂量进行统计学分析.图像质量评分、辐射剂量比较采用配对t检验,图像噪声比较采用单因素方差分析.结果 FM组的剂量长度乘积(DLP)平均为(273.4±45.4)mGy·cm,ATCM组为(187.9±66.4)mGy·cm,ATCM组比FM组降低31.3%(t=8.205,P<0.05);FM组的3个椎间盘平面图像噪声变异分别为(9.8±2.4)、(9.9±2.4)、(11.5±3.2)HU,ATCM组分别为(12.0±0.8)、(11.7±0.6)、(11.7±1.4)HU,ATCM组的图像噪声变异小于FM组(F=23.31,P<0.05);FM组3个椎间盘平面的图像质量评分分别为(4.7±0.3)、(4.5±0.2)、(4.5±0.2)分,ATCM组分别为(4.6±0.3)、(4.5±0.2)、(4.5±0.2)分,两组图像质量评分差异无统计学意义(t=1.000,P>0.05).结论 使用噪声指数为12.0 HU的ATCM技术,在保证图像质量的情况下可以降低辐射剂量约31.3%.     

64层螺旋CT自动毫安技术对降低下肢动脉 血管成像辐射剂量的研究

目的 探讨64层螺旋CT自动毫安技术(ATCM)对降低下肢动脉血管成像辐射剂量的可行性。方法 通过预实验改变噪声指数(NI)调节管电流,得出NI值为10 HU时图像质量与辐射剂量匹配较佳。搜集52例疑有下肢动脉闭塞糖尿病及高血压病患者病例,随机分为实验组和对照组行自肾下腹主动脉至足底的CT容积扫描,每组病例26例。对照组采用常规固定300 mA(FM组),实验组采用NI为10 HU的自动毫安(ATCM组)技术。分别选择肾下腹主动脉、髋关节水平股动脉、 NFDB1 动脉及踝关节胫前动脉平面作为观察平面,对两种毫安技术的图像质量、图像噪声和辐射剂量均采用 t 检验方法进行统计学分析。结果 FM组的辐射剂量CTDI_vol为10.81 mGy,平均DLP为(1280.4±124.7)mGy·cm,ATCM组的平均CTDI_vol为(5.14±1.23)mGy,平均DLP为(582.86±150.41)mGy·cm,比FM组降低约54.4%,两组差异有统计学意义(CTDI_vol、DLP的 t 值分别为13.13、17.36, P 值均<0.05)。FM组的4个选取平面图像噪声分别为13.8±4.04、14.53±2.79、5.69±1.38、(4.75±1.38) HU。ATCM组分别为10.76±2.11、12.13±2.96、10.47±2.96、(6.17±1.53) HU,两组差异有统计学意义( t 值分别为2.911、3.038、7.287及3.186, P 值均<0.05),ATCM组肾下腹主动脉、髋关节水平股动脉层面的图像噪声较FM组的低,而 NFDB1 动脉、踝关节胫前动脉层面的图像噪声较FM组的高,ATCM组图像噪声变异度小,图像更加均匀。FM组图像质量评分平均为2.654±0.562,ATCM组图像评分平均为2.462±0.582,两组图像质量评分差异无统计学意义( t =1.21, P ＞0.05)。结论 使用噪声指数为10的下肢动脉ATCM技术,在保证图像质量的情况下可以降低辐射剂量约54.4%。     

64层螺旋CT心脏成像获得一致噪声及控制辐射剂量的个体化管电流选择方法

目的 探讨根据患者个体差异调整管电流(mA),获得一致64层螺旋CT冠状动脉血管成像(CTCA)的图像噪声,进而控制辐射剂量的方法.方法 (1)80例患者作为固定mA组(650 mA)以一致的扫描条件进行64层螺旋CTCA检查.2名医师用5分法评价固定mA组的噪声水平以确定诊断图像质量所需要的噪声水平标准差(SD)SD.值,并建立一个少量对比剂团注探测循环时间扫描(TB)噪声SDTB值和心脏扫描(CA)达到SD0水平所需mA的关系式.(2)80例64层螺旋CTCA检查根据个体差异调整扫描mA,作为个体mA调制组与固定mA组进行比较,分析该方法的可操作性和辐射剂量的控制,两组均数比较用独立样本t检验.结果 (1)固定mA组的TB和CA的噪声SD呈线性相关(r2=0.994);(2)根据主观评价的结果将SD0定为28 HU可获得满意的图像质量;(3)个体mA调制组噪声平均值28.97 HU,SD为1.93,小于固定mA组的5.14,但质量评分(4.27±0.68)与固定mA组(4.03±0.93)差异无统计学意义(P＞0.05);(4)个体mA调制组63例调整后＜650 mA,平均CT剂量指数(CTDIvol)为58.32 mGy,比固定mA组(85.94 mGy)减少了32.1%,其中1例患者仪使用160 mA,CTDIvol=19.27 mGy,是固定mA组平均剂量的22.4%.结论 通过个体的TB噪声SD调整mA可获得一致心脏扫描噪声水平,是有效的实用的保证成像质量又对个体辐射剂量进行控制的方法.     

自动管电流调节技术对主动脉夹层术后的评价及其辐射剂量的研究

目的探讨64排螺旋CT(MSCT),采用固定噪声指数(NI)的Z轴自动管电流调节(ATCM)技术在主动脉夹层术后CT造影中对图像质量及辐射剂量的影响。资料与方法随机将本院主动脉夹层术后的患者100例分为2组,每组50例。A组采用固定管电流扫描技术,均采用280 mA。B组采用Z轴ATCM扫描技术,管电流为100～350 mA,根据体重指数(BMI)不同分为两组:BMI>25 kg/m2者,NI=10;BMI<25 kg/m2者,NI=12,其余扫描参数均一致。将所有图像均传输至ADW 4.3工作站,进行三维及二维后处理,同时记录机器自动生成的CT剂量指数(CTDlvol)、相应剂量长度乘积(DLP)。结果 B组在不影响诊断的情况下,辐射剂量较A组CTDlvol降低了28.3%、DLP降低了30.4%。A组CTDIvol均值为(19.13±1.94)mGy;DLP均值为(1205.59±197.12)mGy.cm,B组BMI>25 kg/m2者CTDIvol均值为(14.82±2.97)mGy;DLP均值为(887.6±177.51)mGy.cm,BMI<25kg/m2者CTDIvol均值为(12.61±2.17)mGy;DLP均值为(789.86±139.33)mGy.cm,所有图像均能满足诊断需要。结论 64排螺旋CT采用固定NI的ATCM技术在主动脉夹层CT造影中可获得较好图像质量,在满足诊断需求的同时降低了患者辐射剂量。     

ASIR或MBIR算法重建颈肩部CT图像质量总是优于FBP吗？

目的 比较滤过反向投影（filtered back projection,FBP）,自适应迭代重建技术（adaptive statistical iterative reconstruction,ASIR）,基于模型的迭代重建（model-based iterative reconstruction,MBIR）三种算法重建颈肩部CT平扫和增强图像质量.方法 对20例患者颈肩部进行相对低剂量CT平扫及增强扫描,采用FBP,ASIR（权重50％）,MBIR三种算法重建出颈肩部CT图像,测量甲状腺,腋下脂肪、锁骨下动脉及周围肌肉的CT值,采用方差分析比较三种重建算法图像的对比噪声比（contrast noise ratio,CNR）及噪声指数（noise index,NI）.同时,两名医生对图像进行主观评价,采用卡方检验比较三种重建算法的主观评级.结果 颈肩部CT平扫和增强图像,MBIR和ASIR的CNR显著高于FBP,NI显著低于FBP. MBIR的CNR显著高于ASIR,NI显著低于ASIR.主观图像噪声和胸廓入口处射线硬化伪影,MBIR和ASIR显著优于FBP;主观图像对比,FBP显著优于MBIR和ASIR;小结构可视程度、主观视觉病灶可信度与诊断信心,三者不存在显著性差异.结论 在相对低剂量扫描条件下,MBIR和ASIR能够显著降低颈肩部的主观和客观图像噪声,显著提高CNR.但是由于图像面貌的改变导致的主观图像对比的下降,未能显著提高小结构可视程度,主观视觉病灶可信度与诊断信心.     

64层螺旋CT 的自动管电流调制技术（ATCM）的控制参数和辐射剂量的胸部模体实验研究

目的：通过胸部模体扫描探讨影响自动管电流技术的控制参数及影响因素对管电流mA调制效果和辐射剂量以及图像噪声的影响。方法使用GE lightspeed VCT 对模拟胸部模体进行扫描,实验组使用不同的噪声指数（noise index ,NI）,调制方法,扫描层厚,定位像,管电压等组合扫描,并记录CTDIvol值以及测量图像的中心,右侧和体前空气的感兴趣区的标准差（standard deviation ,SD）值。对照组使用固定管电流200mA扫描,比较各种组合的辐射剂量和成像噪声。结果对照组的 CTDIvol 为10．07mGy ,实验组 A ,B ,C ,D ,E 的 CTDIvol 分别为18．58mGy ,24．56mGy ,14.98mGy ,12.46mGy ,11．49mGy均大于对照组。使用smartmA进行角度调制的C组比A组的CTDIvol降低约15％;而使用侧位定位像扫描的实验组D的辐射剂量也与使用正位像的实验组C辐射剂量不同;使用相同的NI值扫描,层厚越薄,调制的管电流越大,辐射剂量越大。图像中心区域的噪声（6．12±0．85）H U的变化要比体侧和体前的噪声（6．73±1．78）HU ,（7．29±1．23）HU的变化小,各层的一致性要好于体侧和体前的噪声。但由于有最大mA调制800mA的限制,在实验组B的肩部几乎都是最大mA扫描,而最后的CTDIvol为31．76mGy。使用联合调制后,各层的平均mA明显减少,而图像噪声的没有统计学改变;NI值升高,辐射剂量减少;管电压改变,辐射剂量改变,但图像噪声不变。结论ATCM技术可以通过实时调整管电流获得各层图像一致的噪声水平。联合调制比Z轴调制更有效的控制辐射剂量而不会带来图像质量的损失。定位像的选择,NI值的设定,扫描层厚的选择,最大mA的设定会影响辐射剂量。     

64层螺旋CT自动管电流调节技术在婴幼儿胸部低剂量CT扫描中应用的可行性研究

目的 探讨应用64层螺旋CT(MSCT),采用适宜噪声指数的Z轴自动管电流调节技术获得稳定的婴幼儿胸部CT扫描图像,并降低射线剂量的可行性研究.方法 选取100例根据临床需要行64层MSCT胸部扫描的3岁以下婴幼儿患儿,按年龄和体重用随机数字表法分为2组,每组各50例.对照组(中位年龄1.7岁)采用固定管电流扫描技术:1岁以下120 mA,≥1岁者150 mA;研究组(中位年龄1.4岁)采用z轴自动管电流调节扫描技术:1岁以下预设噪声指数为8,≥1岁为9,毫安设置范围为10～250 mA,其余扫描参数条件2组一致.记录2组CT剂最指数(CTDIvol)值.2名医师独立对图像质量采用5分制进行评估,＞13分被认为符合临床诊断要求.采用Kappa方法评价不同观察者评定结果间的一致性.结果 对照组的平均客观噪声和CTDIvol分别为(4.78 4±0.58)和(6.68±0.62)mGy,研究组的平均客观噪声和CTDIvol分别是(7.84±0.66)和(2.34±0.71)mGy;研究组和对照组的平均管电流分为(41.6 4±11.6)和(99.2±7.7)mAs.研究组的平均CTDIvol较对照组下降了 65%.研究组和对照组平均图像质量评分分别为(3.46±0.40)和(4.65±0.46)分,所用图像均获得了满意的临床诊断要求,2名医师的评估结果获得了中等一致性(Kappa值分别为0.474和0.536).结论 64层MSCT自动管电流调节技术应用于婴幼儿胸部扫描时可以在降低射线剂量的基础卜获得稳定的图像质量,噪声指数设定在8或9较为适宜.     

Impact of image noise levels, scout scan dose and lens shield on image quality and radiation exposure in z-axis dose-modulated neck MSCT on 16- and 64-slice Toshiba Aquilion scanners

Objective

Assessing the impact of image noise (IN) levels, scout scan dose and lens shield use on image quality and radiation exposure in neck multislice CT (MSCT) when using z-axis dose modulation (DM).

Methods

Neck MSCT phantom studies with/without z-axis DM were performed by using different IN levels (S.D. 7.5-30 HU) and scout scan tube currents (7.5-50 mA) on Toshiba Aquilion scanners (16-/64-slice). Image quality indices were evaluated by two radiologists and radiation exposure parameters calculated. Cadaveric phantom measurements elucidated lens shield interactions with DM efficacy. The lowest dose scan protocol with diagnostic image quality was introduced into the clinical imaging routine and retrospectively evaluated in 20 age-matched patients undergoing neck MSCT with/without DM.

Results

The highest image noise level in DM neck studies with comparable image quality to standard neck CT amounted to 20 HU, resulting in a mean tube current of 50 mAs (CTDI_w 6.3 mGy). DM reduced effective dose by 35% and organ dose figures (lens, thyroid) by 33%. Scout scan dose lowering to 20 mA resulted in an effective dose (ED) decrease of 0.06 mSv (5%). Avoiding lens shield placement during scout scan effected an organ dose decrease of 20%. Overall contour sharpness and image contrast did not differ significantly (DM/without DM) whereas image noise was rated higher in DM neck CT studies (p < 0.05).

Conclusions

z-Axis dose modulation, as assessed on 16- and 64-slice Toshiba Aquilion scanners, is effective and mandatory in neck MSCT. DM efficacy can be enhanced by optimising scout scan doses and lens shield use.     

Radiation dose and image quality in pediatric CT: effect of technical factors and phantom size and shape

PURPOSE: To evaluate effects of varying tube current and voltage on radiation dose, image noise, and image contrast with different phantom sizes and shapes. MATERIALS AND METHODS: Four round lucite phantoms with 8-32-cm diameters were scanned with multi-detector row computed tomography (CT) and 80-120 kVp. Radiation dose was based on CT dose index, image noise, and iodine contrast and measured with constant and variable tube currents that were age appropriate for each tube voltage. Radiation dose and image noise and contrast were compared in round and oval 24-cm phantoms. For various combinations of technical factors and phantom sizes and shapes, percentage differences were calculated for radiation dose and image noise and contrast. Associations between tube voltage and radiation dose, image noise, and image contrast in round and oval phantoms were determined by fitting second-degree polynomials to data. Differences in radiation dose and image noise and contrast, which were attributable to differences in tube voltage, were tested with paired t tests. RESULTS: With 165-mAs tube current, radiation doses with 140- and 80-kVp tube voltages were 103% ([41.9 mGy - 20.6 mGy]/20.6 mGy) and 58% ([10.2 mGy - 4.2 mGy]/10.1 mGy) higher in the 8-cm phantom than in the 32-cm phantom. When tube current was adapted for phantom size, radiation dose at 80 kVp in the 8-cm phantom was reduced by 82% ([10.1 mGy - 1.8 mGy]/10.1 mGy). In the 8-cm phantom, tube voltage was decreased from 120 to 80 kVp and tube current remained at 165 mAs, resulting in a 68% noise increase ([3.1 HU - 1.8 HU]/1.8 HU). With variable tube current, 80-kVp tube voltage in the 8-cm phantom led to a 138% noise increase ([7.3 HU - 3.1 HU]/3.1 HU). With reduced tube voltage, image contrast increased. In the 8-cm phantom, with a constant 165-mAs tube current and a decrease in tube voltage from 120 to 80 kVp, there was a 35% ([333 HU - 217 HU]/333 HU) increase in contrast. No difference was noted in radiation dose or noise between round and oval phantoms (P = .604 and P = .06, respectively), but a small statistically significant difference (1%) in contrast attenuation was demonstrated (P = .025). CONCLUSION: Reduced tube voltage for pediatric contrast material-enhanced CT reduces radiation dose and maintains image contrast. Image noise increases, but the effect is minimal in smaller phantoms. An additional reduction in tube current further reduces radiation dose.     

多层螺旋CT低剂量扫描技术在甲状腺增强扫描中的临床应用

目的：探讨多层螺旋 CT 低剂量扫描技术在甲状腺增强扫描中的临床应用价值。方法80例患者随机分为4组(每组各20例),4组分别为：A 组,120 kV、180 mA;B 组,120 kV、100 mA;C 组,100 kV、180 mA;D 组,100 kV、100 mA。主观评价图像质量并评分,统计甲状腺 CT 值、图像背景噪声(N)、图像信噪比(SNR)、CT 剂量指数(CTDIvol)、剂量长度乘积(DLP)、有效辐射剂量(ED)并进行对比分析。结果4组图像主观评分为3.90±0.31、3.75±0.44、3.70±0.47、3.60±0.60,SNR 为26.34±3.13、25.08±1.87、25.86±2.38、24.87±2.20,四者无统计学差异(P >0.05);甲状腺 CT 值为(168.55±13.39)HU、(170.70±11.34)HU、(185.20±22.35)HU、(190.55±21.38)HU,N 为(6.48±0.84)HU、(6.83±0.45)HU、(7.19±0.86)HU、(7.66±1.01)HU, CTDIvol 为(10.95±0.00)mGy、(6.08±0.00)mGy、(6.59±0.00)mGy、(3.66±0.00)mGy,DLP 为(145.67±8.79)mGy·cm、(84.58±4.94)mGy·cm、(89.86±3.26)mGy·cm、(50.20±1.89)mGy·cm,ED 为(0.73±0.04)mSv、(0.42±0.03)mSv、(0.45±0.03)mSv、(0.25±0.01)mSv,四者有统计学差异(P <0.05)。结论多层螺旋 CT 低剂量扫描技术既能保证图像质量又能有效降低甲状腺增强 CT 检查的辐射剂量。     

Z轴自动管电流调制技术在头颈部CT扫描血管成像中对甲状腺剂量的降低

目的 评价在进行头颈部CT扫描血管成像时,Z轴自动管电流调制技术(ATCM)对减少甲状腺的辐射剂量的作用及对图像噪声的影响。方法 回顾性地分析140例头颈部CT增强血管成像的病例,其中用固定管电流技术和 Z 轴自动管电流调节技术各70例,观察其成像质量,记录其客观噪声水平(由CT图像衰减值的标准差进行评估),并比较其单次扫描的加权CT剂量指数CTDI_w,管电流mA及剂量长度乘积DLP。结果 在扫描范围、扫描参数(管电压、螺距、准直器厚度等)、造影剂注射速率和注射部位完全相同的情况下,固定管电流技术和 Z 轴自动管电流调节技术的图像质量相同,甲状腺图像噪声分别为10.14和13.64 HU。单次扫描的加权CT剂量指数CTDI_w(mGy)分别为(43.22±1.42)和(35.99±1.31) mGy。剂量长度乘积分别为(1514.45±5.56)和(1121.39±5.51)mGy·cm, 剂量长度乘积降低约25.95%。结论 Z 轴自动管电流调节技术能有效降低总曝光量和累计剂量长度乘积,可以有效地降低患者的辐射剂量,特别是像甲状腺和眼晶体等射线敏感组织器官的辐射剂量降低,减少其辐射危害,但是图像噪声略有增加。     

自适应迭代重建技术对儿童低剂量胸部CT图像质量的优化

目的比较应用自适应迭代重建技术（adaptive statistical iterative reconstruction,ASIR）儿童低剂量胸部CT与传统的滤过反向投影（filteredbackprojection,FBP）的图像质量、噪声和放射剂量。方法回顾性分析80例应用自动管电流调节技术（ATCM）扫描的胸部CT检查作为试验组,年龄29天～16岁（中位年龄3．3岁）,检查时根据年龄分为4组,o～12月预设噪声指数11HU,1～3岁预设噪声指数13HU,4～6岁预设噪声指数15Hu,7～17岁预设噪声指数17HU,将所有图像经ASIR30％重建;对照组选取同时期80例经ATCM扫描的儿童胸部CT检查,1～7岁预设噪声指数8HU,7～17岁预设噪声指数12HU,未经ASIR技术重建图像。测量所有病例左心室及同层面图像的背部肌肉客观噪声值,由两位医师分别用5分制主观评价图像质量和噪声程度,并用kappa检验评价观察者间的一致性。同时记录CT剂量指数（CTDIv01）及剂量长度乘积（DLP）。结果试验组客观噪声平均值为10．49±1．65,对照组客观噪声9．16±1．52,无统计学差异,同时,试验组和对照组的主观图像质量接受率为3．90和3．98,所有图像合乎诊断要求,观察者间的评估具有一致性（k=0．64）;试验组和对照组间的CTDIv01分别为（1.19±0．78）mGy和（2．62±0．93）mGy,试验组CT-DIvol比对照组降低了54．6％,两者间差异明显（Pd0．001）。结论应用ASIR技术可获得稳定图像质量,满足诊断的前提下,可以能进一步有效减低射线剂量。     

Measurement of radiation dose in cerebral CT perfusion study

PURPOSE: To evaluate radiation dose in cerebral perfusion studies with a multi-detector row CT (MDCT) scanner on various voltage and current settings by using a human head phantom. MATERIALS AND METHODS: Following the CT perfusion study protocol, continuous cine scans (1 sec/rotation x60 sec) consisting of four 5-mm-thick contiguous slices were performed three times at variable tube voltages of 80 kV, 100 kV, 120 kV, and 140 kV with the same tube current setting of 200 mA and on variable current settings of 50 mA, 100 mA, 150 mA, and 200 mA with the same tube voltage of 80 kV. Radiation doses were measured using a total of 41 theroluminescent dosimeters (TLDs) placed in the human head phantom. Thirty-six TLDs were inside and three were on the surface of the slice of the X-ray beam center, and two were placed on the surface 3 cm caudal assuming the lens position. RESULTS: Average radiation doses of surface, inside, and lens increased in proportion to the increases of tube voltage and tube current. The lowest inside dose was 87.6+/-15.3 mGy, and the lowest surface dose was 162.5+/-6.7 mGy at settings of 80 kV and 50 mA. The highest inside dose was 1,591.5+/-179.7 mGy, and the highest surface dose was 2,264.6+/-123.7 mGy at 140 kV-200 mA. At 80 kV-50 mA, the average radiation dose of lens was the lowest at 5.5+/-0.0 mGy. At 140 kV-200 mA the radiation dose of lens was the highest at 127.2+/-0.6 mGy. CONCLUSION: In cerebral CT perfusion study, radiation dose can vary considerably. Awareness of the patient's radiation dose is recommended.     

噪声关联Z轴管电流调制技术降低多层CT胸部扫描辐射剂量的作用

目的 评价噪声关联z轴管电流调制技术降低多层CT胸部扫描的辐射剂量、提高图像质量(信噪比水平)的效果.方法 连续200名CT定位像未显示明显胸部异常的受检者,按前瞻性的研究方法 进行分组,根据检查顺序的单双数随机分为z轴管电流调制组(单数者为试验组)和管电流固定组(双数者为对照组),每组100名.试验组的目标噪声水平设置为10.0 HU,扫描设备根据定位像扫描时获取的胸部密度信息自动设置扫描时的动态管电流值;对照组的管电流设置为200 mA,其他扫描参数与试验组完全相同.分别记录2组的最大管电流、CT剂量容积(CTDIv01)、剂量长度乘积(DLP)和女性乳房最大层面的管电流值;测量肺尖、主动脉弓、左心房和肺底层面的图像噪声.图像质量分3级(优、良、差),由2名有经验的CT技师采用双盲法评价.计数资料采用成组设计的x2检验,计量资料采用成组设计的t检验,P<0.05为差异有统计学意义.结果 试验组的最大管电流、CTDIvol、DLP和乳房最大层面管电流的平均值分别为(178.5±125.6)mA、(10.5±3.8)mGy、(231.6±24.3)mGy/cm和(116.0±22.5)mA;对照组的分别为200.0 mA、12.8 mCy、(274.7±18.4)mGy/cm和200.0 mA,试验组较对照组分别降低10.8%、19.9%、15.7%和42.0%,两组差异有统计学意义(P值均<0.05).试验组肺尖和肺底层面的图像噪声分别为10.5和10.4 HU,明显低于对照组的15.3和15.6 HU;图像质量优的数量大幅增加.结论 噪声关联z轴管电流调制技术实现了受检者个性化适应性曝光,在胸部扫描时可明显降低受检者的整体辐射剂量,并提高图像质量.     

多模型自适应统计迭代重建算法对鼻窦CT图像质量和辐射剂量影响的实验研究

目的探讨鼻窦CT扫描中,前置和后置自适应统计迭代重建算法(ASiR-V)对图像质量和辐射剂量的影响,并寻找最佳的迭代组合。方法以1具离体头颅标本为研究对象,采用临床鼻窦CT常规扫描条件[噪声指数(NI)=8],以及前置ASiR-V的不同等级(0~100%,间隔为10%)进行螺旋扫描,所得原始数据使用后置ASiR-V的不同等级(0~100%,间隔为10%)进行骨算法和标准算法重建,共获得242个鼻窦薄层图像序列。选择特定的感兴趣区(ROI)测量CT值,并计算图像对比噪声比(CNR)和品质因子(FOM)。记录容积CT剂量指数(CTDIvol)和智能毫安(Smart mA)值。采用线性回归分析对ASiR-V各等级与对应的CTDIvol、Smart mA、CNR、FOM进行比较分析。采用配对t检验对相同后置不同前置ASiR-V骨算法和标准算法图像的CNR进行分析比较。主观评价采用双盲法由3名高年资放射诊断医师以4分法(4分为最佳)进行图像质量评分。结果随着前置ASiR-V等级(0~100%)的增加,Smart mA、CTDIvol均减低,呈线性负相关(r分别为-0.981、-0.976,P均<0.001);Smart mA降幅为72.05%,CTDIvol降幅为71.22%。前置ASiR-V相同,随后置ASiR-V等级增加,骨算法和标准算法图像对应的CNR呈上升趋势,呈正相关(骨算法图像:R2分别为0.976、0.992、0.982、0.982、0.975、0.975、0.979、0.996、0.952、0.978、0.965;标准算法图像:R2分别为0.944、0.990、0.988、0.993、0.996、0.987、0.984、0.996、0.996、0.990、0.965);后置ASiR-V相同,随前置ASiR-V等级增加,骨算法和标准算法图像对应的FOM呈波动变化(骨算法图像:R2分别为0.335、0.341、0.344、0.364、0.385、0.405、0.418、0.429、0.455、0.474、0.516;标准算法图像:R2分别为0.223、0.278、0.327、0.285、0.309、0.329、0.325、0.346、0.360、0.390、0.380)。以上各种前置和后置迭代等级组合所得图像主观评价均可满足诊断要求(评分≥3)。结论当NI=8时,骨算法最佳前置和后置迭代等级组合为80%和100%;标准算法最佳迭代等级组合为100%和100%。鼻窦CT扫描中,选择恰当的前置和后置迭代等级组合,能够在图像质量满足诊断要求的前提下,有效降低辐射剂量。