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.     

肺动脉CT三维血管成像低剂量扫描的应用

目的 探索肺动脉三维血管成像多层螺旋CT低剂量扫描的可行性,以及肺动脉容积三维处理(VR)图像的质量与平扫SD值的关系。方法 选取行肺动脉CT检查的受检者87人。选取志愿者63人为低剂量组,其余24人采用常规剂量扫描作为常规组。两者平扫均采用常规剂量150 mAs,低剂量肺动脉增强扫描采用60 mAs。图像进行VR后处理后,按A、B、C 3个等级进行评定,两组VR图像进行质量等级比较。低剂量组平扫图像测量CT值的标准差SD值, 与增强的VR图像质量等级关系进行受试者操作特性曲线(ROC)分析。结果 常规剂量组VR图像等级为A级的达到100%,在低剂量组VR图像等级为A级的达到85.7%。平扫SD值与肺动脉VR图像的质量相关性分析,ROC曲线下面积为0.906.结论 肺动脉三维血管成像的低剂量扫描切实可行。     

Low-dose whole-body CT using deep learning image reconstruction: image quality and lesion detection

Objectives:To evaluate image quality and lesion detection capabilities of low-dose (LD) portal venous phase whole-body computed tomography (CT) using deep learning image reconstruction (DLIR).Methods:The study cohort of 59 consecutive patients (mean age, 67.2 years) who underwent whole-body LD CT and a prior standard-dose (SD) CT reconstructed with hybrid iterative reconstruction (SD-IR) within one year for surveillance of malignancy were assessed. The LD CT images were reconstructed with hybrid iterative reconstruction of 40% (LD-IR) and DLIR (LD-DLIR). The radiologists independently evaluated image quality (5-point scale) and lesion detection. Attenuation values in Hounsfield units (HU) of the liver, pancreas, spleen, abdominal aorta, and portal vein; the background noise and signal-to-noise ratio (SNR) of the liver, pancreas, and spleen were calculated. Qualitative and quantitative parameters were compared between the SD-IR, LD-IR, and LD-DLIR images. The CT dose-index volumes (CTDI_vol) and dose-length product (DLP) were compared between SD and LD scans.Results:The image quality and lesion detection rate of the LD-DLIR was comparable to the SD-IR. The image quality was significantly better in SD-IR than in LD-IR (p < 0.017). The attenuation values of all anatomical structures were comparable between the SD-IR and LD-DLIR (p = 0.28–0.96). However, background noise was significantly lower in the LD-DLIR (p < 0.001) and resulted in improved SNRs (p < 0.001) compared to the SD-IR and LD-IR images. The mean CTDI_vol and DLP were significantly lower in the LD (2.9 mGy and 216.2 mGy•cm) than in the SD (13.5 mGy and 1011.6 mGy•cm) (p < 0.0001).Conclusion:LD CT images reconstructed with DLIR enable radiation dose reduction of >75% while maintaining image quality and lesion detection rate and superior SNR in comparison to SD-IR.Advances in knowledge:Deep learning image reconstruction algorithm enables around 80% reduction in radiation dose while maintaining the image quality and lesion detection compared to standard-dose whole-body CT.     

Bayesian statistical reconstruction for low-dose X-ray computed tomography using an adaptive-weighting nonlocal prior

How to reduce the radiation dose delivered to the patients has always been a important concern since the introduction of computed tomography (CT). Though clinically desired, low-dose CT images can be severely degraded by the excessive quantum noise under extremely low X-ray dose circumstances. Bayesian statistical reconstructions outperform the traditional filtered back-projection (FBP) reconstructions by accurately expressing the system models of physical effects and the statistical character of the measurement data. This work aims to improve the image quality of low-dose CT images using a novel AW nonlocal (adaptive-weighting nonlocal) prior statistical reconstruction approach. Compared to traditional local priors, the proposed prior can adaptively and selectively exploit the global image information. It imposes an effective resolution-preserving and noise-removing regularization for reconstructions. Experimentation validates that the reconstructions using the proposed prior have excellent performance for X-ray CT with low-dose scans.     

Low-dose multidetector dynamic CT in the breast: preliminary study

This study investigated the feasibility of using low-dose multidetector dynamic computed tomography (CT) scan for imaging breast. We measured the radiation dose using a phantom at low- and standard-dose CT. To compare the image quality at low- and standard-dose CT, we evaluated normal breasts in 57 cases. In 44 cases with breast cancer, we assessed the staging and time-enhancement curves of breast cancer. In conclusion, the low-dose multidetector dynamic CT scan is feasible for the evaluation of the breast, with reduced radiation dose and with similar image quality when compared with standard-dose CT scan. In breast cancers, low-dose dynamic CT could be used for the staging of breast cancer before surgery.     

Low-dose CT urography using deep learning image reconstruction: a prospective study for comparison with conventional CT urography

Objectives:To compare the image quality of low-dose CT urography (LD-CTU) using deep learning image reconstruction (DLIR) with conventional CTU (C-CTU) using adaptive statistical iterative reconstruction (ASIR-V).Methods:This was a prospective, single-institutional study using the excretory phase CTU images for analysis. Patients were assigned to the LD-DLIR group (100kV and automatic mA modulation for noise index (NI) of 23) and C-ASIR-V group (100kV and NI of 10) according to the scan protocols in the excretory phase. Two radiologists independently assessed the overall image quality, artifacts, noise and sharpness of urinary tracts. Additionally, the mean CT attenuation, signal-to-noise ratio (SNR) and contrast-to-noise (CNR) in the urinary tracts were evaluated.Results:26 patients each were included in the LD-DLIR group (10 males and 16 females; mean age: 57.23 years, range: 33–76 years) and C-ASIR-V group (14 males and 12 females; mean age: 60 years, range: 33–77 years). LD-DLIR group used a significantly lower effective radiation dose compared with the C-ASIR-V group (2.01 ± 0.44 mSv vs 6.9 ± 1.46 mSv, p < 0.001). LD-DLIR group showed good overall image quality with average score >4 and was similar to that of the C-ASIR-V group. Both groups had adequate and similar attenuation value, SNR and CNR in most segments of urinary tracts.Conclusion:It is feasibility to provide comparable image quality while reducing 71% radiation dose in low-dose CTU with a deep learning image reconstruction algorithm compared to the conventional CTU with ASIR-V.Advances in knowledge:(1) CT urography with deep learning reconstruction algorithm can reduce the radiation dose by 71% while still maintaining image quality.     

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.     

Radiation dose reduction in hepatic multidetector computed tomography with a novel adaptive noise reduction filter

Purpose The aim of this study was to optimize a novel adaptive noise reduction filter based on patient body weight and to investigate its utility for improving the image quality of low-dose hepatic computed tomography (CT) scans. Materials and methods The tube current-time product was changed from 140 to 180 and from 60 to 100 mAs at standard-and low-dose CT, respectively, based on the body weights of 45 patients. Unenhanced and two-phase contrast-enhanced helical scans were obtained at the standard dose during the hepatic arterial and equilibrium phases. During the equilibrium phase, we obtained low-dose scans of the liver immediately after standard-dose scans. The low-dose CT images were postprocessed with the filter. Two radiologists visually evaluated artifacts in the liver parenchyma and its graininess, the sharpness of the liver contour, tumor conspicuity, homogeneity of the enhancement of the portal vein, and overall image quality. Results There was no statistically significant difference between standard and filtered low-dose images with respect to artifacts in the liver, the graininess of the liver parenchyma, tumor conspicuity, homogeneity of enhancement of the portal vein, or overall image quality. Conclusion The adaptive noise reduction filter effectively reduced image noise. We confirmed the effectiveness of the filter by examining clinical hepatic images obtained at low-dose CT.     

Standard chest CT using combined automated tube potential selection and iterative reconstruction: image quality and radiation dose reduction

ObjectiveTo evaluate the image quality and radiation dose reduction of chest computed tomography (CT) using combined automated tube potential selection (ATPS) and iterative reconstruction (IR).Materials and MethodsImage quality and radiation dose were compared between conventional contrast-enhanced chest CT using 120 kVp and filtered back projection (Protocol A) and CT using ATPS and IR (Protocol B) in 43 patients.ResultsThe effective radiation dose was 3.6±0.4 mSv for Protocol A and 2.2±0.6 mSv for Protocol B (mean dose reduction, 39.7%). Protocol B showed diagnostic image quality in all patients.ConclusionATPS and IR allows for radiation dose reduction while maintaining diagnostic image quality.     

SR-NLM: A sinogram restoration induced non-local means image filtering for low-dose computed tomography

Radiation dose has raised significant concerns to patients and operators in modern X-ray computed tomography (CT) examinations. A simple and cost-effective means to perform a low-dose CT scan is to lower the milliampere-seconds (mAs) as low as reasonably achievable in data acquisition. However, the associated image quality with lower-mAs scans (or low-dose scans) will be unavoidably degraded due to the excessive data noise, if no adequate noise control is applied during image reconstruction. For image reconstruction with low-dose scans, sinogram restoration algorithms based on modeling the noise properties of measurement can produce an image with noise-induced artifact suppression, but they often suffer noticeable resolution loss. As an alternative technique, the noise-reduction algorithms via edge-preserving image filtering can yield an image without noticeable resolution loss, but they often do not completely eliminate the noise-induced artifacts. With above observations, in this paper, we present a sinogram restoration induced non-local means (SR-NLM) image filtering algorithm to retain the CT image quality by fully considering the advantages of the sinogram restoration and image filtering algorithms in low-dose image reconstruction. Extensive experimental results show that the present SR-NLM algorithm outperforms the existing methods in terms of cross profile, noise reduction, contrast-to-ratio measure, noise-resolution tradeoff and receiver operating characteristic (ROC) curves.     

Optimisation of multislice computed tomography protocols in angio–CT examinations

PURPOSE: The aim of this paper is to explain a general procedure for the optimisation of multislice computed tomography (MSCT) protocols. MATERIALS AND METHODS: Four angio-CT protocols with a GE LightSpeed Plus 4-slice CT scanner were considered. Effective doses were computed for a sample of patients. First the dose was optimised for arterial-phase scans on a standard patient and adapted to the weight of individual patients with a scaling factor. RESULTS: The mean effective dose for an angio-CT examination ranged from 18.8 mSv to 28.8 mSv, depending on the protocol adopted. Following the optimisation procedure, we drew up a table indicating tube current values for each patient weight. Calculation of the effective dose before and after the optimisation procedure revealed a dose reduction of about 40%. CONCLUSIONS: Angio-CT examinations deliver high doses, but these doses can be reduced without affecting image quality.     

肺动脉CT三维血管成像低剂量扫描的应用

目的 探索肺动脉三维血管成像多层螺旋CT低剂量扫描的可行性,以及肺动脉容积三维处理(VR)图像的质量与平扫SD值的关系.方法 选取行肺动脉CT检查的受检者87人.选取志愿者63人为低剂量组,其余24人采用常规剂量扫描作为常规组.两者平扫均采用常规剂量150 mAs,低剂量肺动脉增强扫描采用60 mAs.图像进行VR后处理后,按A、B、C 3个等级进行评定,两组VR图像进行质量等级比较.低剂量组平扫图像测量CT值的标准差SD值,与增强的VR图像质量等级关系进行受试者操作特性曲线(ROC)分析.结果 常规剂量组VR图像等级为A级的达到100%,在低剂量组VR图像等级为A级的达到85.7%.平扫SD值与肺动脉VR图像的质量相关性分析,ROC曲线下面积为0.906.结论 肺动脉三维血管成像的低剂量扫描切实可行.     

肺动脉CT三维血管成像低剂量扫描的应用

目的 探索肺动脉三维血管成像多层螺旋CT低剂量扫描的可行性,以及肺动脉容积三维处理(VR)图像的质量与平扫SD值的关系.方法 选取行肺动脉CT检查的受检者87人.选取志愿者63人为低剂量组,其余24人采用常规剂量扫描作为常规组.两者平扫均采用常规剂量150 mAs,低剂量肺动脉增强扫描采用60 mAs.图像进行VR后处理后,按A、B、C 3个等级进行评定,两组VR图像进行质量等级比较.低剂量组平扫图像测量CT值的标准差SD值,与增强的VR图像质量等级关系进行受试者操作特性曲线(ROC)分析.结果 常规剂量组VR图像等级为A级的达到100%,在低剂量组VR图像等级为A级的达到85.7%.平扫SD值与肺动脉VR图像的质量相关性分析,ROC曲线下面积为0.906.结论 肺动脉三维血管成像的低剂量扫描切实可行.     

Low-dose CT of the thorax in cancer follow-up

PURPOSE: To evaluate the quality of low-dose computed tomography (CT) images in the follow-up of cancer patients. MATERIALS AND METHODS: We selected patients with urogenital (n = 7) or esophageal cancer (n = 13) who were attending routine follow-up between April and July 2001. After water and chest phantom studies to decide the scan parameters, postcontrast low-dose CT scans were obtained at 60 mA (45 mA s) with a smoothing kernel. Three radiologists reviewed the CT scans of the thorax independently for overall image quality and anatomic detail in both mediastinal and lung windows. They subjectively rated the images on a four-point scale (0: poor, 1: fair, 2: good, 3: excellent) according to graininess and sharpness. RESULTS: The average score of the low-dose CT for the lung window was 2.85, which was equivalent to control images. The average score for the mediastinal window was 1.77, which was lower than that of the control CT scan (2.62, P < 0.001) and almost identical to that of the chest phantom experiment. Nine of the 20 cases had abnormal findings; low-dose CT scans depicted them well and offered sufficient information for diagnosis. The radiation exposure was reduced by about half. CONCLUSION: The image quality of low-dose thoracic CT was satisfactory for both mediastinal and lung windows in the follow-up of cancer patients.     

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%。     

Biological effects of low-dose radiation from computed tomography scanning

Abstract

Purpose: With the widespread use of computed tomography (CT), the risks of low-dose radiation from CT have been increasingly highlighted. This study aims to illustrate the CT-induced biological effects and analyze the potential beneficial or harmful outcomes so as to provide radiologists with reasonable advice on CT usage.

Materials and methods: The related literature was analyzed according to the topics of stochastic effect, hereditary effect, deterministic effect, accumulative injuries, hormesis and adaptive response; population epidemiology data were also analyzed.

Results: CT accounts for 9% of X-ray examinations and approximately 40–67% of medical-related radiation, the dose is within the range of low-dose radiation (LDR). Two opposite viewpoints exist nowadays regarding the biological effects of CT scanning: They are either harmful or harmless. Approximately 0.6% and 1.5% of the cumulative cancer risk could be attributed to diagnostic X-rays in the UK and Germany, respectively. The probability of CT scans induced-cancer is about 0.7% and CT angiography's risk is around 0.13%. It is estimated that approximately 29,000 cancers could be related to CT scans in the USA every year. Meanwhile, another investigation of 25,104 patients who underwent 45,632 CT scans in 4 years showed that the majority of CT-induced cancers were accidents rather than certainties of frequent CT scans.

Conclusion: Although the LDR effects of CT are still controversial, the current problems include the high frequency-use and abuse of CT scans, the increase of radiation dose and accumulative dose in high-accuracy CT, and the poor understanding of carcinogenic risks. The underlying biological basis needs further exploring and the ratio of risks and benefits should be considered.     

State of the art of coronary computed tomography angiography

ObjectivesThe aim of this paper is to evaluate contrast media (CM) bolus geometry and opacification patterns in the coronary arteries with particular focus on patient, scanner and safety considerations during coronary computed tomography angiography (CCTA).Key findingsThe rapid evolution of computed tomography (CT) technology has seen this imaging modality challenge conventional coronary angiography in the evaluation of coronary artery disease. Increases in spatial and temporal resolutions have enabled CCTA to become the modality of choice when evaluating the coronary vascular tree as an alternative in the diagnostic algorithm for acute chest pain. However, these new technologic improvements in scanner technology have imposed new challenges for the optimisation of CM delivery and image acquisition strategies.ConclusionUnderstanding basic CM-imaging principles is essential for designing optimal injection protocols according to each specific clinical scenario, independently of scanner technology.Implications for practiceWith rapid advances in CT scanner technology including faster scan acquisitions, the risk of poor opacification of coronary vasculature increases significantly. Therefore, awareness of CM delivery protocols is paramount to consistently provide optimal image quality at a low radiation dose.     

深度学习重建算法改善颅脑低剂量CT图像质量的可行性研究

目的探讨深度学习重建算法(DLIR)较自适应统计迭代重建(ASIR-V)算法在改善颅脑低剂量CT图像质量方面的效果。方法回顾性纳入2021年11月至2022年8月在解放军总医院第二医学中心接受颅脑CT检查的患者, 对所有患者的低剂量CT采用4种不同算法重建:获得30%强度ASIR-V(ASIR-V-30%)图像、低强度DLIR(DLIR-L)图像、中等强度DLIR(DLIR-M)图像和高强度DLIR(DLIR-H)图像。在4组图像的表浅白质、表浅灰质、深部白质和深部灰质内选取感兴趣区并测量其CT值, 计算信噪比(SNR)和对比噪声比(CNR)。由3名神经影像医师按照Likert 5分量表对图像质量进行主观评分。对4组图像的客观、主观评分进行分析, 若总体存在差异, 则进行组内两两比较。结果共纳入109例患者, 男104例、女5例, 年龄65～110岁, 平均(89.16±9.53)岁。颅脑CT低剂量扫描的辐射剂量为(0.93±0.01)mSv, 显著低于常规扫描(2.92±0.01)mSv(t = 56.15, P < 0.05 )。颅脑低剂量CT的4组图像的SNR深部灰质、SN...     

Optimized control of X-ray exposure and image noise using a particular multislice CT scanner

Patient dose reduction in computed tomography (CT) always results in a trade off between radiation exposure and image quality. There are few reports that estimate the relationship between image quality and X-ray exposure in CT examinations as one optimal index. The purpose of this study was to determine the optimal parameter settings enabling a low radiation exposure without compromising image quality using a particular 4-row multislice CT (MSCT) scanner (Aquilion VZ 4-slice CT scanner, Toshiba Medical Systems Corporation, Otawara, Tochigi, Japan). Normalized dose divided by image noise for helical pitches (nDNR: normalized dose to noise ratio) were calculated in consideration of beam collimation and tube current-time product. Optimal tube current-time product was calculated using the nDNR for the helical pitches based on user-defined standards of quality of the CT image. As a result, the nDNR proved to be well-supported to decrease the patient exposure in various exposure conditions of MSCT scans; however, the dose and image noise did not show a linear relation to the helical pitch. In conclusion, nDNR can be applied to patient dose reduction while keeping an acceptable image quality using a particular 4-row MSCT scanner.     

低浓度等渗对比剂结合低管电压在兔肝脏CT灌注成像中的可行性研究

目的 探讨低管电压和低浓度等渗对比剂结合迭代算法在家兔肝脏CT灌注成像应用的可行性。方法 健康新西兰大白兔15只,每只兔子分别进行两次肝脏CT灌注检查,两次检查间隔时间为24 h。第1次扫描作为常规组,使用100 kV和370 mg I/ml对比剂,传统滤过反投影法（FBP）重建图像;第2次扫描作为双低组,采用低管电压80 kV和270 mg I/ml对比剂,并采用第3代适应性迭代降噪（AIDR-3D）重建图像。两名医师对获得的肝脏灌注图进行双盲法评分,并比较观察者评分的一致性。对两组的灌注参数值包括肝动脉灌注量（HAP）、门静脉灌注量（PVP）、肝灌注指数（HPI）及全肝灌注量（TLP）值和腹主动脉平均CT值、图像噪声（N）、信噪比（SNR）、对比信噪比（CNR）、图像优良指数（FOM）进行配对样本t检验。计算和比较不同条件下的有效剂量E和碘的摄入量。结果 两组肝灌注图像的主观评分分别为（4.0±0.76）、（4.3±0.62）分,差异无统计学意义（P>0.05）。两名医师评分的一致性良好（Kappa=0.81,P<0.05）。两组中的PVP、HAP、HPI及TLP值差异无统计学意义（P>0.05）。双低组剂量E为19.85 mSv,较常规组的32.43 mSv降低38.79%。双低组总碘量较常规组减低27.03%。结论 使用等渗低浓度对比剂结合低管电压肝脏灌注检查可以在不降低图像质量的前提下明显减低辐射剂量和碘摄入量。