铋屏蔽对头颈部多层螺旋CT中眼晶状体辐射剂量的降低作用

目的 探讨扫描平面内铋屏蔽在头颈部多层螺旋CT(MSCT)扫描中对影像质量的影响和眼晶状体辐射剂量的降低作用.方法 分别使用颅脑、颞骨和鼻窦临床扫描条件,在无屏蔽、1层、2层和3层铋屏蔽覆盖眼部区域时,对标准水模和离体头颅标本进行扫描,用热释光剂量片测量头颅标本每次扫描时的眼晶状体器官剂量.在屏蔽材料和被扫描体间放置5、10、15和20 mm厚的海绵时,使用鼻窦扫描条件采集影像,并测量眼晶状体的剂量.测量水模影像中与屏蔽物为2、4、6和8 cm距离处的CT值,主观评价头颅标本影像中伪影对解剖结构的影响.结果 颅脑、颞骨和鼻窦CT临床扫描中眼晶状体的器官剂量分别为24.31、27.60和20.01 mGy.使用铋屏蔽时,均使得眼晶状体剂量有显著下降,但下降幅度随着铋屏蔽物的增加而降低.在各种厚度的屏蔽物时,屏蔽物间隙越大,眼晶状体剂量的降低程度越小,测量兴趣区CT值的增加程度也显著降低.颅脑和颞骨CT扫描分别使用2层和3层铋屏蔽,在不影响诊断的前提下,可有效降低眼晶状体剂量分别为47.1%和59.1%;鼻窦CT扫描时,1层屏蔽无间隙、2层屏蔽1.5 cm间隙不影响诊断,可降低眼晶状体剂量分别为31.5%和34.5%.结论 扫描平面内铋屏蔽材料的合理应用,可有效降低头颈部CT扫描中眼晶状体的辐射剂量.     

不同CT值赋值法对脑转移瘤放疗剂量计算影响的研究

目的研究不同CT值赋值法对脑转移瘤放疗计划剂量计算的影响,为基于磁共振(MR)图像进行放疗计划设计提供基础。方法选取35例接受放疗的脑转移瘤患者,每位患者在放疗前同一天分别进行CT和MR模拟定位,基于CT图像制定三维适形放射治疗(3D-CRT)或调强放射治疗(IMRT)计划为原计划Plan1。将CT图像和MR图像刚性配准,在CT和MR图像上勾画主要的组织和器官,计算各组织器官的群体化CT值。基于CT图像,采用3种CT值赋值法生成3组伪CT,分别为:全组织赋予140 HU;空腔、骨骼和软组织分别赋予-700、700和20 HU;不同组织器官分别赋予群体化的CT值。Plan1在3组伪CT上重新计算剂量分布,分别获得Plan2、Plan3、Plan4,然后比较这3组计划和Plan1的剂量学差异。结果骨骼、空腔平均CT值分别为(735.3±68.0)、(-723.9±27.0)HU,软组织的平均CT值基本分布在-70~70 HU。Plan2、Plan3、Plan4相比Plan1的剂量差异依次减小,在剂量指标比较中,眼晶状体最大剂量差异最大,分别可达5.0%以上、1.5%~2.0%、1.0%~1.5%,其余剂量指标差异的95%置信区间上限基本不超过2.0%、1.2%、0.8%。在像素点剂量比较中,局部靶区病例中差异>1%的区域主要分布在靠近射野的皮肤处,而全脑靶区病例中主要分布在骨骼与空腔、软组织交界处,以及靠近射野的皮肤处。此外,CT值赋值法在3D-CRT的剂量学差异大于IMRT,在全脑靶区病例大于局部靶区病例。结论不同CT值赋值法对脑转移瘤放疗计划剂量计算的影响显著,对骨骼、空腔和软组织赋予合适CT值,剂量计算偏差可基本控制于1.2%以内,而对各组织器官赋予群体化的CT值,可进一步将偏差控制于0.8%以内,满足临床要求。     

Dose reduction to radiosensitive tissues in CT. Do commercially available shields meet the users' needs?

AIM: To assess the effectiveness and economy of routinely using commercially available in-plane bismuth shielding during CT scanning of the chest and brain. METHODS AND MATERIALS: Forty patients were scanned with thermoluminescent dosemeters (TLDs) in situ to measure the radiation dose to the thyroid and eye during CT scanning of the brain and chest. Half of the patients had the "AttenuRad" shield in place during scanning. RESULTS: Use of the shielding reduced the mean dose to the eye from 6.0 +/- 0.3 mGy to 4.9 mGy +/- 0.2 mGy and the thyroid dose from 16.4 mGy +/- 1.2 mGy to 7.1 mGy +/- 0.5 mGy. CONCLUSION: Use of the thyroid shield is recommended for all CT scanning of the chest. The eye shield does not produce as marked a reduction in radiation dose to the lens of the eye, when an angled gantry is used, since the eyes are not in the primary beam. Use of the eyeshield is justifiable where irradiation of the orbit is unavoidable, although whether artifacts would be a problem if the shield was used in this way was not assessed.     

Radiation dose to the lens of eye and thyroid gland in paranasal sinus multislice CT

CT has become an established examination in the evaluation of the paranasal sinuses. Until recently this was achieved by the direct coronal technique on conventional and single slice helical scanners. With the advent of multislice technology, thin slice axial CT with excellent coronal and sagittal reconstructions is now the norm. We describe a study designed to evaluate the radiation dose to the lens of the eye and thyroid gland in the axial and coronal planes on a Siemens Volume Zoom quad slice scanner at 140 kV and effective mAs of 100 using 1 mm collimation. Thermoluminescent dosimeters were placed on the eyelid and thyroid gland of 29 patients scanned axially in the supine position and a further 28 patients scanned coronally in the prone position with gantry tilt. The results show mean doses of 35.1 mGy (lens) and 2.9 mGy (thyroid gland) in the coronal plane compared with 24.5 mGy (lens) and 1.4 mGy (thyroid gland) in the axial plane. Results obtained from a head phantom and from using the ImPACT CT dose calculator were comparable. The kV and mAs were then reduced to 120 and 40, respectively, and the axial study repeated using the head phantom and predicted doses using the ImPACT CT dose calculator. The low dose scanning technique revealed a lens dose of 9.2 mGy and thyroid dose of 0.4 mGy. The eye dose on a multislice scanner is still substantially less than the threshold dose of 0.5-2 Gy for detectable lens opacities. These results indicate that, in addition to the established perceived advantages of multislice axial sinus CT, i.e. patient comfort, no artefact from dental amalgam and reproducible true coronal images, should be included a decreased radiation dose to both the eye lens and thyroid gland compared with direct coronal scanning.     

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.     

Dose classification scheme for computed tomography of the paranasal sinuses

PURPOSE: The purpose of this study was to define objective and reproducible standards for the quality of CT images as a function of radiation doses and therapeutic validity. MATERIALS AND METHODS: CT images of the paranasal sinuses of 145 patients (77 female, 68 male; 5-83 years old; mean age, 39.9 years) were classified both subjectively (with a view toward their validity for the planning of functional endoscopic sinus surgery, FESS) and objectively by defining the pixel noise (the standard deviation, STD, of the CT number) in a homogeneous region of interest (ROI), centered on the M. masseter and on the frontal lobe. These measurements were then compared to measurements obtained from scan images of a water-filled Perspex phantom. RESULTS: The pixel noise measured in the phantom images was nearly identical to the respective values on the M. masseter on the patient images. The use of an edge-enhancing reconstruction algorithm and low-dose protocols, with a pixel noise amounting to 70-90 Hounsfield Units (HU), are indicated for children, chronic sinusitis, and septum deviation, while standard protocols, with a pixel noise of 50-70 HU, are recommended for the preoperative planning and postoperative control of FESS. The pixel noise for high-dose protocols is less than 50 HU; nonetheless, such protocols should generally be avoided. CONCLUSION: The pixel noise measured in a water-filled Perspex phantom is indicative of the clinical potential and image quality of paranasal sinus CT scans. Alternatively, the M. masseter can be chosen as an ROI to measure the pixel noise in order to obtain a rough estimate of the image quality or radiation dose class.     

64层CT容积与常规高分辨率CT图像质量的比较

目的 比较容积高分辨率CT(VHRCT)与常规高分辨率CT(CHRCT)的图像质量,探讨VHRCT的可行性.方法 对Catphan 412模具行VHRCT及CHRCT扣描,测量和记录图像的空间分辨率、噪声及放射剂量并进行比较;对32例患者行VHRCT及CHRCT检查,对图像质量进行评分并比较.模具部分采用配对t检验比较噪声的差异;临床部分采用Wilcoxon配对符号秩和检验比较图像质量的差异.结果 模具研究中,VHRCT横断面图像的空间分辨率与CHRCT相同,均为11 LP/cm,其z轴分辨率为12 LP/cm.剂量相近时,VHRCT的噪声为(69.18±2.77)HU,大于CHRCT的噪声(54.62±2.12)HU,(t=-15.929,P＜0.01);噪声相近时,VHRCT的剂量较CHRCT增加19.09 mGy.临床研究中,VHRCT与CHRCT横断面图像的质量评分分别为3.22与3.24,差异无统计学意义(Z=-0.319,P＞0.05),VHRCT与CHRCT冠状面蕈建图像的质量评分分别为3.05与1.88,差异有统计学意义(Z=-5.088,P＜0.01).结论 对于64层CT,VHRCT的横断面图像质量接近CHRCT,多平面重组图像具有高分辨率可广泛应用,其扫描剂量尚有待优化.     

Helical CT scanning of the nose and paranasal sinuses using a low dose protocol: in comparison to conventional CT

Computerized tomography is widely regarded as the optimal imaging technique for the nose and paranasal sinuses. The technique however, involves exposing the lens of the eye to ionizing radiation, risking cataract formation. Accordingly, it is important to minimize the radiation dose, whilst at the same time delivering high quality images. A protocol for scanning the nose and paranasal sinuses is described which produces high quality image data using a relatively low radiation dose. The technique may be readily adapted to produce images suitable for endoscopic sinus surgery or for production of 3-dimensional models of the nasal passages suitable for airflow analysis.     

Dose reduction in computed tomography: the effect of eye and testicle shielding on radiation dose measured in patients with beryllium oxide-based optically stimulated luminescence dosimetry

The aim of this study was to assess the effect of eye and testicle shielding on radiation dose to the lens and the testes of patients undergoing CT examinations. Fifty-one male patients underwent CT twice with identical protocols initially without, the second time with protective garments. Doses to the testes and the lenses were recorded with beryllium oxide-based dosimeters. The dose to the testes and lenses from CT exposure was reduced by 96.2% ± 1.7% and 28.2% ± 18.5%, when testicle and eye shielding was used, respectively. The effect of the eye shielding on the eye lens dose was found to depend on the x-ray tube position when the eye is primarily exposed during the scan. The maximum eye lens dose reduction achieved was found to be 43.2% ± 6.5% corresponding to the anterior position of the tube. A significant correlation between the patient’s body mass index and dose exposure could not be found. Eye and testicle shields, apart from being inexpensive and easy to use, were proven to be effective in reducing eye lens and testicle radiation dose burden from CT exposures.     

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.     

A new low-dose CT examination compared with standard-dose CT in the diagnosis of acute sinusitis

A low-dose CT of the paranasal sinuses was designed with few, thin sections, non-uniform intersection gaps, low milliampere settings and avoidance of direct radiation to the eye lens. The low-dose CT was prospectively compared with standard-dose CT in patients with suspicion of acute sinusitis. Forty-seven patients were examined with low-dose CT immediately after standard-dose CT. The effective dose and the lens dose were calculated and compared. Using standard-dose CT as a gold standard the sensitivity and specificity of low-dose CT was calculated for each sinus group. The effective dose and the lens dose of the low-dose CT were reduced to, respectively, 3 and 2% of the standard-dose CT. The diagnostic yield of the low-dose CT with regard to acute sinusitis was good with a high specificity (≥96%) for all sinus groups. The sensitivity was also high (≥95%) except for the frontal sinus where the sensitivity was 83%. Low-dose CT offers considerable dose reduction and should be the standard for imaging patients with suspected acute inflammatory paranasal disease. Electronic Publication     

能谱纯化联合器官剂量调制技术对婴幼儿头部CT扫描器官剂量及图像质量影响的体模研究

目的探讨能谱纯化技术(SPS)、器官剂量调制技术(OBTCM)以及两者结合对婴幼儿头部CT扫描器官剂量及图像质量的影响。方法利用两个头部仿真体模(CIRS 1岁和5岁), 分别采用参考扫描模式(Reference)、Reference + OBTCM、SPS及SPS+OBTCM 4种模式进行扫描;测量并比较不同体模不同扫描模式眼晶状体、脑部前侧及脑部后侧的辐射剂量, 眼眶和脑实质区域的噪声水平及对比噪声比(CNR)。结果相比Reference模式, 1岁与5岁体模的眼晶状体剂量在Reference + OBTCM模式分别减少约(21.89±0.01)%和(28.33±0.34)%;在SPS模式下, 1岁和5岁体模的眼晶状体剂量减少分别为(71.38±1.30)%和(53.72±2.42)%;SPS+OBTCM模式分别减少约(71.12±2.54)%和(55.73±1.90)%。不同体模不同扫描模式眼眶及脑实质的噪声水平, 差异有统计学意义(F=5.67～85.47, P<0.05);与Reference模式相比, Reference + OBTCM模式的噪声水平在不同体模不同部位...     

双源CT扫描模式对头颈部辐射剂量和影像质量的影响

目的 探讨头颈部CT扫描中,不同扫描模式对辐射剂量和影像质量的影响程度。方法 利用头颈部仿真模体和双源CT,分别使用固定扫描条件120 kV和200 mAs,以及自动管电流调制技术（CARE Dose 4D）、自动管电压调制技术（CARE kV）和部分角度扫描模式（X-CARE）的组合进行成像,分别为120 kV+200 mAs、120 kV+200 mAs+X-CARE、CARE Dose 4D+120 kV、CARE Dose 4D+120 kV+X-CARE、CARE Dose 4D+CARE kV、CARE Dose 4D+CARE kV+X-CARE 6种扫描模式。每次扫描均使用两片热释光剂量片（TLD）分别测量眼晶状体和甲状腺的剂量,两片TLD所测数值取均值。记录以上各种扫描时的容积CT剂量指数（CTDI_vol）和剂量长度乘积（DLP）,测量眼晶状体层面和甲状腺层面影像的对比度噪声比（CNR）。结果 120 kV+200 mAs扫描时,眼晶状体和甲状腺的器官剂量分别为19.8和26.0 mGy,使用120 kV+200 mAs+X-CARE可降低剂量至13.3和22.2 mGy;与CARE Dose 4D+120 kV相比,CARE Dose 4D+CARE kV可使CTDI_vol由13.1降至10.1 mGy,眼晶状体剂量和甲状腺剂量由20.8和23.7 mGy分别降至16.6和19.9 mGy,而使用CARE Dose 4D+CARE kV+X-CARE时,器官剂量又进一步分别降至6.3和11.0 mGy,但影像质量显著降低;与CARE Dose 4D+120 kV相比,使用CARE Dose 4D+120 kV+X-CARE,眼晶状体和甲状腺剂量分别由20.8和23.7 mGy降至9.6和15.1 mGy,同时CTDI_vol由13.1 mGy降至9.3 mGy。使用CARE Dose 4D+CARE kV+X-CARE时,CTDI_vol和器官剂量降至最低,但头颅和颈部CNR也降至最低。结论 颅脑扫描时CARE Dose 4D+120 kV+X-CARE模式、颈部扫描时CARE Dose 4D+CARE kV模式在保持影像质量较好的同时可有效降低辐射剂量。当对影像质量要求不高时可选用CARE Dose 4D+CARE kV+X-CARE模式,从而显著降低辐射剂量。     

CT管电压对鼻窦图像质量和辐射剂量的影响研究

目的探讨CT管电压在鼻窦扫描中对图像质量和辐射剂量的影响。方法利用离体头颅标本,在逐层扫描方式下,分别选择5种不同的管电压(70、80、100、120、140 kV),对鼻窦区域进行扫描。噪声指数(NI)厂家默认为9,自动管电流调制,Smart mA设置为对应管电压下的最大范围。探测器宽度为120 mm。进行骨算法和软组织算法重建,层厚均为0.625 mm。按照临床实践的基线重组横断面、冠状面和矢状面图像,层厚2 mm。在横断面的中心层面上,选择相应的兴趣区测量CT值均值和标准差,计算对比度噪声比(CNR)。同时记录CT容积剂量指数(CTDIvol)和剂量长度乘积(DLP),并计算图像品质因子(FOM)。两名放射诊断医师和1名主管技师采用双盲法对实验所得图像进行主观评价,5分制标准计分。结果实验所得影像质量均满足诊断要求。在骨算法重建下,管电压为100和80 kV的CNR分别为66.98、64.75,高于管电压为70、120、140 kV的CNR值(51.61、61.56、57.76)。CTDIvol最大值为34.11 mGy(140 kV),最小值为17.45 mGy(70 kV)。管电压100 kV时的FOM值为152.26。在软组织算法重建下,管电压为80 kV的CNR为195.62,显著高于管电压为70、100、120、140 kV组(139.46、154.49、148.06、155.58)。管电压80 kV时的FOM值为1273.56,显著高于管电压为70、100、120、140 kV组(1114.56、809.98、735.63、709.62)。结论CT头颅标本鼻窦逐层扫描中,临床怀疑骨质病变时,优先选择骨算法100 kV;临床怀疑软组织病变时,优先选择软组织算法80 kV时,所得的图像质量最佳且受检者辐射剂量较低。     

Radiation doses to the eye lenses in computed tomography of the orbit and the petrous bone

Standard CT examinations of the orbit and the petrous bone were simulated with a tissue-equivalent human skull phantom on a Somatom DR 2 scanner. The orientation of the scan planes and the scan parameters including thickness, number of slices and mAs were varied according to the assumed diagnostic problems. The total radiation doses in the region of the eye lenses were measured with thermoluminescent dosimeters. If the globes are located within the X-ray field, the total radiation doses received by the lenses increased with the number and the thickness of the slices and the mAs. The highest radiation doses were found in contiguous thin-section scans of the orbit in axial (52 mGy) or direct coronal (47 mGy) orientation. In cases where the globes were located outside the X-ray field, the radiation doses received by the eye lenses could be reduced by a factor of 16, resulting in only 3.1-3.4 mGy for a complete axial study of the inner ear. Recommendations are given how to reduce the radiation exposure to the eye lenses without loss of diagnostical information.     

Quantitative assessment of selective in-plane shielding of tissues in computed tomography through evaluation of absorbed dose and image quality

This study aimed at assessment of efficacy of selective in-plane shielding in adults by quantitative evaluation of the achieved dose reduction and image quality. Commercially available accessories for in-plane shielding of the eye lens, thyroid and breast, and an anthropomorphic phantom were used for the evaluation of absorbed dose and image quality. Organ dose and total energy imparted were assessed by means of a Monte Carlo technique taking into account tube voltage, tube current, and scanner type. Image quality was quantified as noise in soft tissue. Application of the lens shield reduced dose to the lens by 27% and to the brain by 1%. The thyroid shield reduced thyroid dose by 26%; the breast shield reduced dose to the breasts by 30% and to the lungs by 15%. Total energy imparted (unshielded/shielded) was 88/86 mJ for computed tomography (CT) brain, 64/60 mJ for CT cervical spine, and 289/260 mJ for CT chest scanning. An increase in image noise could be observed in the ranges were bismuth shielding was applied. The observed reduction of organ dose and total energy imparted could be achieved more efficiently by a reduction of tube current. The application of in-plane selective shielding is therefore discouraged.     

眼眶海绵状血管瘤的CT诊断

目的：研究眼眶海绵状血管瘤的ＣＴ表现及其诊断价值。材料与方法：对５５例眼眶海绵状血管瘤ＣＴ图像进行回顾性分析。结果：４５例肿块位于眼眶肌锥内,２例深达眶尖部;另１０例占据肌锥内外或仅发生于肌锥外。横断面扫描显示３４例肿块位于眼球后,其中２０例紧贴球后壁;冠状位扫描较难分辨眼球与球后肿瘤的前后界限。横断面扫描中,肿瘤与视神经、禄外肌界限不清;但在冠状位可显示两者受压移位。４３例肿瘤为类圆形或椭圆形,边界清晰,１０例呈不规则或闭块状,且边界欠清,另２例两个瘤体呈哑玲状相连。３８例密度不均或欠均,其中６例有高密度斑点或片状阴影,２例为钙化或静脉石。３０例增强后扫描中２０例部分增强明显,且增强后肿瘤的边界、形态、大小更加清楚。结论：横断面在辨别肿瘤与眼眶及眼球的关系,冠状位在区分肿瘤与视神经、眼外肌时各有优势,增强扫描     

Low-dose dental computed tomography: significant dose reduction without loss of image quality

Purpose: To measure and reduce the patient dose during computed tomography (CT) for dental applications. Material and Methods: Lithium fluoride thermoluminescent dosimeters were implanted in a tissue-equivalent humanoid phantom (Alderson-Rando-Phantom) to determine doses to the thyroid gland, the active bone marrow, the salivary glands, and the eye lens. Dental CT was performed with spiral CT and a dental software package. The usual dental CT technique was compared with a new dose-reduced protocol, which delivered best image quality at lowest possible radiation dose, as tested in a preceding study. Image quality was analysed using a human anatomic head preparation. In addition, the radiation dose was compared with panoramic radiography and digital volume tomography (DVT). Eight radiologists evaluated all images in a blinded fashion. A Wilcoxon rank pair test was used for statistical evaluation. Results: Radiation dose could be reduced by a factor of 9 (max.) with the new dose-reduced protocol (e.g. bone marrow dose from 23.6 mSv to 2.9 mSv; eye lens from 0.5 mSv to 0.3 mSv; thyroid gland from 2.5 mSv to 0.5 mSv; parotid glands from 2.3 mSv to 0.4 mSv). Dose reduction did not reduce image quality or diagnostic information. Conclusion: A considerable dose reduction without loss of diagnostic information is achievable in dental CT. As radiation exposure of the presented low-dose protocol is expected to be in the same range as DVT, low-dose dental CT might be superior to DVT, because CT can be used to evaluate soft tissues as well.     

Supplementary CT temporal lobe cuts confer no worthwhile benefit

Summary The value of angled temporal lobe cuts as a supplement to conventional head computed tomography (CT) has been assessed by comparing the diagnostic yield of standard axial and specific temporal lobe images (TLCT) in 62 patients with temporal lobe epilepsy and 87 with Alzheimer-type senile dementia. Fewer than one patient in six had structural abnormality in the temporal lobe most readily demonstrated by axial CT. Five patients with epilepsy and ten with dementia had changes demonstrated only by TLCT, reported on by one or other of a pair of observers. However such changes were of dubious clinical relevance, or arose as a result of artefact. In one patient with epilepsy and underlying neoplasm, axial CT was positive and TLCT false-negative. The routine addition of temporal lobe cuts to a conventional axial examination confers no added benefit to justify the prolonged examination time and increased radiation dose to the lens of the eye.     

Dose reduction in multislice CT by means of bismuth shields: results of in vivo measurements and computed evaluation

Purpose

We investigated the amount of patient dose reduction in the thyroid, lens of the eye and the breast when using bismuth protections in multislice computed tomography (CT) exams as well as their influence on the quality of diagnostic images.

Materials and methods

The radiation dose was measured by using thermoluminescence dosimeters. The study was conducted on the two CT scanners installed in our radiology department (64 and eight slices). The shield effects on the CT image were evaluated by measuring the signal-to-noise ratio in a phantom and in vivo, and by verifying the presence of artefacts on patients’ images. The obtained organ-dose reduction factors were used to evaluate the effects of shielding on the effective dose.

Results

The shielding attenuation ranged from 30% to 60% depending on the CT scan protocols and organs. The difference between shielded and unshielded signal-to-noise ratio was statistically significant but within the standard requirements for quality assurance. Results were in agreement with the radiologists’ perception of image quality. The use of the shields allowed up to 38% reduction of effective dose.

Conclusions

Use of bismuth shields significantly decreases both organ and effective radiation dose, with a consequent reduction in health risk for the patient, quantified in 1.4 fewer cases of radiation-induced tumours every 5 years in our centre (12,100 exams/year), in agreement with the risk factors proposed by Publication 60 of the International Commission on Radiological Protection (ICRP). The relative inexpensiveness of these protections, their easy application and their substantial lack of influence on image quality suggest their massive introduction into routine clinical practice.