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.     

Evaluation of variations in sinonasal region with computed tomography

AIM: To investigate the frequency of anatomical variations in sinonasal region and association of these variations with mucosal diseases.METHODS: The study included 400 cases (191 female and 209 male) who were considered to have preliminary diagnoses of sinonasal pathology and who had paranasal sinus computed tomography (CT) examination in axial plane. Reformatted CT images were studied in all planes.RESULTS: Age range of the patients was 20-83 (mean 40.26 ± 14.85). Most commonly detected anatomical variation was Agger nasi cell (74.8%). There was a significant association between clinoid process pneumatization and protrusion of internal carotid arteries and optic nerves into sphenoid sinus (P < 0.001). Besides, the relationships between pterygoid process pneumatization and protrusion of vidian nerve into sphenoid sinus, and between pneumatization of large sphenoid wing and protrusion of maxillary nerves into sphenoid sinus were also significant (P < 0.001). Uncinate bulla and giant ethmoid bulla were found to be significantly associated with sinonasal mucosal diseases (P = 0.004 and P = 0.002, respectively).CONCLUSION: Sinonasal region has a great number of variations, and some of them have been determined to be associated with sinonasal mucosal disease. It is necessary to know that some of these variations are associated with protrusion of significant structures such as carotid artery or optic nerve into the sinus and care should be observed in surgeries on patients carrying these variations.     

Dual-source cardiac computed tomography: image quality and dose considerations

Computed tomography (CT) imaging of the heart, most prominently coronary CT angiography, is currently subject to intense interest and is increasingly incorporated into clinical decision-making. In spite of tremendous progress in CT technology over the past decade, the limited temporal resolution has remained one of the most severe problems, especially for cardiac imaging. The novel design concept of dual-source CT (DSCT) allows for an effective scan time of 83 ms independent of heart rate. While large trials are still missing, initial studies have shown improved image quality, especially for visualizing the coronary arteries and detecting coronary artery stenoses. Further investigations have shown that routine beta blockade to lower the heart rate is not necessary to reliably achieve diagnostic image quality. Other applications that may particularly benefit from increased temporal resolution are the analysis of ventricular function and of the cardiac valves. Dose issues which are of interest for cardiac CT in general are discussed in some detail, including a quantitative analysis of dose values and three-dimensional dose distributions. Various strategies to lower radiation exposure are available today, and DSCT offers specific potential for this.     

Paediatric and adult computed tomography practice and patient dose in Australia

The current practice for CT scanning of paediatric patients in Australia has been assessed through a survey sent to the site of all CT scanners licensed in New South Wales and all dedicated children's hospitals in Australia. The survey addressed demographic details, CT scanner details and scanning parameters for four imaging scenarios (brain CT, chest CT, abdomen/pelvis CT and high-resolution chest CT for three different age groups (8 weeks, 5-7 years and adult patients). The effective dose for each imaging scenario and age group was calculated and compared for 52 sites representing 53 CT scanners. For any age group and imaging scenario, there was a large spread of effective dose. For comparable CT examinations, the effective dose varied by up to 36-fold between centres. There was a clear trend for centres that frequently carry out CT scans on paediatric patients to have the lowest radiation doses. Four age group/imaging scenarios showed significantly lower effective doses for hospital-based CT than for nonhospital sites. There was also a trend for doses to be lower at dedicated paediatric centres. Effective dose was closely associated with mAs, with most centres using lower mAs for younger patients, but few centres reduced the kVp for paediatric patients. The results of the survey emphasize the need for continuing education and protocol review, particularly in paediatric CT examinations, in a complex and fast changing environment.     

Evaluation of patient absorbed dose management system in percutaneous coronary intervention

The angiography equipment Infinix Celeve of Toshiba Corp. is a system that estimates patient absorbed dose at the skin by using a dose area product meter. This system performs incidence area compensation, which corresponds to the changes of I.I. size, FID, and FTD. We evaluated the clinical usefulness of patient entrance skin dose management by the dose area product meter of Celeve by verifying the effects of various clinical parameters on absorbed dose. We determined compensation according to the various angles usually used by clinicians, and estimated the absorbed peak dose at the skin. By using the angle compensation of the C arm, the displayed values on the dose area product meter of Celeve could be used for skin doses as they were. The skin absorbed dose was 3.0 Gy or more in 33 of the 332 examples.     

A 2D multiresolution image reconstruction method in X-ray computed tomography

We propose a multiresolution X-ray imaging method designed for non-destructive testing/evaluation (NDT/NDE) applications which can also be used for small animal imaging studies. Two sets of projections taken at different magnifications are combined and a multiresolution image is reconstructed. A geometrical relation is introduced in order to combine properly the two sets of data and the processing using wavelet transforms is described. The accuracy of the reconstruction procedure is verified through a comparison to the standard filtered backprojection (FBP) algorithm on simulated data.     

Study of improvement in X-ray computed tomography images with a radiation treatment planning system: image noise and slice thickness

In radiotherapy, dose distribution and calculation of dose monitor units (DMU) are generally performed by a radiation treatment planning system using CT images. Therefore, differences in calculation can arise as a result of the quality of the CT image data. The quality of CT images involves contrast resolution, resolution, noise, slice thickness, and other factors. Among these factors, we examined noise and slice thicknesses. Results demonstrated that, even if noise increased, CT value did not change, and, therefore, did not influence DMU. Examination of slice thickness showed that, when the radiation field was rectangular, it was not influenced by slice thickness. However, when a multi-leaf collimator (MLC) was used, if slice thickness was thicker than the size of the MLC, a difference arose in the position of the MLC, and, therefore, some difference arose in dose. Therefore, slice thickness should be thinner than the size of the MLC.     

Radiation dose reduction in paediatric coronary computed tomography: assessment of effective dose and image quality

Objectives

To assess the impact of different protocols on radiation dose and image quality for paediatric coronary computed tomography (cCT).

Materials and methods

From January-2012 to June-2014, 140 children who underwent cCT on a 64-slice scanner were included. Two consecutive changes in imaging protocols were performed: 1) the use of adaptive statistical iterative reconstruction (ASIR); 2) the optimization of acquisition parameters. Effective dose (ED) was calculated by conversion of the dose-length product. Image quality was assessed as excellent, good or with significant artefacts.

Results

Patients were divided in three age groups: 0–4, 5–7 and 8–18 years. The use of ASIR combined to the adjustment of scan settings allowed a reduction in the median ED of 58 %, 82 % and 85 % in 0–4, 5–7 and 8–18 years group, respectively (7.3?±?1.4 vs 3.1?±?0.7 mSv, 5.5?±?1.6 vs 1?±?1.9 mSv and 5.3?±?5.0 vs 0.8?±?2.0 mSv, all p?<?0,05). Prospective protocol was used in 51 % of children. The reduction in radiation dose was not associated with reduction in diagnostic image quality as assessed by the frequency of coronary segments with excellent or good image quality (88 %).

Conclusions

cCT can be obtained at very low radiation doses in children using ASIR, and prospective acquisition with optimized imaging parameters.

Key points

? Using ASIR allows 25?% to 41?% reduction in the ED.? Prospective protocol is used up to 51?% of children after premedication.? Low dose is possible using ASIR and optimized prospective paediatric cCT

     

Influence of rotation speed of X-ray computed tomography on image quality

The rotation speed of X-ray CT is known to influence the quality of images. We examined changes in imaging characteristics according to various physical characteristics. The physical characteristic of rotation speed (1.0, 0.8, 0.7, 0.6, 0.5 sec/rot) was evaluated at the FOV center (isocenter) and 90 mm outside the center (off-center). The items of evaluation included low contrast resolution, high contrast resolution, noise, definition, and artifacts. High contrast resolution and definition declined at a rotation speed of 0.6 sec/rot or less at off-center. An increase in shower artifact and change in the shape of the wire section were found at a rotation speed of 0.6 sec/rot or less at off-center. It was determined that image quality was especially influenced in terms of definition characteristics when the speed of rotation was high. A decrease in the number of views can be considered the main cause; that is, the use of high-speed rotation degrades image quality. Therefore, it is important to consider proper usage as it corresponds with purpose.     

利用噪声等价图像和深度学习方法对低剂量CT降噪

目的:研究在常规剂量扫描情况下模拟低剂量CT图像的方法,以此生成训练数据集中与常规剂量CT具有对应关系的低剂量CT图像,并建立深度学习模型,用于低剂量CT图像的降噪。方法:使用Philip Brilliance CT Big Bore模拟定位机,其不同算法重建的CT图像具有不同的噪声水平,其中iDose4算法噪声较大,...     

Advanced computed tomography technology and patient dose: a literature review

Cumulative patient radiation dose is a hot topic making headlines today. Responsible for almost two thirds of the medical radiation dose given to patients, computed tomography (CT) has been the major target of these news articles. Through this review of peer reviewed publications, an examination of the relationship between the advancement of technology in CT equipment and the increasing patient dose areexplored. Discussion includes CT scan protocols, demands of physicians, equipment capabilities, and possible solutions to address the problem. Although most of these issues are well known in the imaging community, a few of the results are somewhat surprising. The information disclosed will help form a path to a future with lowerradiation doses received by all patients.     

Optimization of patient dose and image quality with z-axis dose modulation for computed tomography (CT) head in acute head trauma and stroke

The purpose of this study is to retrospectively analyze the effect of z-axis modulation for CT head protocols on patient dose and image quality in patients with acute head trauma and stroke. The study was approved by the Institutional Review Board. We retrospectively evaluated the effect of dose modulation on unenhanced CT head examinations in patients with acute head trauma and stroke. Two series of 100 consecutive studies were reviewed: 100 studies performed without dose modulation, 100 studies performed with z-axis dose modulation. Multidetector 16-section CT was performed sequentially and axial 5-mm-thick slices were obtained from base of skull to vertex. With z-axis dose modulation, the same tube current range was maintained, but a computer algorithm altered the tube current applied to each CT section. For each examination, the weighted volume CT dose index (CTDI (vol)) and dose-length product (DLP) were recorded and noise was measured. Each study was also reviewed for image quality by two independent, blinded readers. The variables (CTDI (vol) and DLP, image quality, and noise) in the two groups were compared by using student t test and Wilcoxon rank-sum test. For unenhanced CT head examinations, the CTDI (vol) and DLP, respectively, were reduced by 35.8% and 35.2%, respectively, by using z-axis dose modulation. Image quality and noise were unaffected by the use of this dose modulation technique (P?<?0.004). Utilization of z-axis modulation technique for CT head examination in patients with acute head trauma and stroke offers significant radiation dose reduction while image quality is optimally maintained.     

Management of patient dose and image noise in routine pediatric CT abdominal examinations

The aim was to propose a strategy for finding reasonable compromises between image noise and dose as a function of patient weight. Weighted CT dose index (CTDI_w) was measured on a multidetector-row CT unit using CTDI test objects of 16, 24 and 32 cm in diameter at 80, 100, 120 and 140 kV. These test objects were then scanned in helical mode using a wide range of tube currents and voltages with a reconstructed slice thickness of 5 mm. For each set of acquisition parameter image noise was measured and the Rose model observer was used to test two strategies for proposing a reasonable compromise between dose and low-contrast detection performance: (1) the use of a unique noise level for all test object diameters, and (2) the use of a unique dose efficacy level defined as the noise reduction per unit dose. Published data were used to define four weight classes and an acquisition protocol was proposed for each class. The protocols have been applied in clinical routine for more than one year. CTDI_vol values of 6.7, 9.4, 15.9 and 24.5 mGy were proposed for the following weight classes: 2.5–5, 5–15, 15–30 and 30–50 kg with image noise levels in the range of 10–15 HU. The proposed method allows patient dose and image noise to be controlled in such a way that dose reduction does not impair the detection of low-contrast lesions. The proposed values correspond to high- quality images and can be reduced if only high-contrast organs are assessed.     

Radiation dose and image quality of X-ray volume imaging systems: cone-beam computed tomography, digital subtraction angiography and digital fluoroscopy

Objective

Radiation dose and image quality estimation of three X-ray volume imaging (XVI) systems.

Methods

A total of 126 patients were examined using three XVI systems (groups 1–3) and their data were retrospectively analysed from 2007 to 2012. Each group consisted of 42 patients and each patient was examined using cone-beam computed tomography (CBCT), digital subtraction angiography (DSA) and digital fluoroscopy (DF). Dose parameters such as dose–area product (DAP), skin entry dose (SED) and image quality parameters such as Hounsfield unit (HU), noise, signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were estimated and compared using appropriate statistical tests.

Results

Mean DAP and SED were lower in recent XVI than its previous counterparts in CBCT, DSA and DF. HU of all measured locations was non-significant between the groups except the hepatic artery. Noise showed significant difference among groups (P?<?0.05). Regarding CNR and SNR, the recent XVI showed a higher and significant difference compared to its previous versions. Qualitatively, CBCT showed significance between versions unlike the DSA and DF which showed non-significance.

Conclusion

A reduction of radiation dose was obtained for the recent-generation XVI system in CBCT, DSA and DF. Image noise was significantly lower; SNR and CNR were higher than in previous versions. The technological advancements and the reduction in the number of frames led to a significant dose reduction and improved image quality with the recent-generation XVI system.

Key Points

? X-ray volume imaging (XVI) systems are increasingly used for interventional radiological procedures. ? More modern XVI systems use lower radiation doses compared with earlier counterparts. ? Furthermore more modern XVI systems provide higher image quality. ? Technological advances reduce radiation dose and improve image quality.     

单层与多层螺旋CT所致儿童受检者辐射剂量研究

目的 研究和评价儿童受检者在单层与多层螺旋CT扫描中所受到的辐射剂量。方法 测试21台CT机的头部和体部剂量指数,并结合0～1岁组、5岁组、10岁组儿童和成年人的头部和胸部常规扫描条件,计算CTDI_w、CTDI_vol、DLP值,再由DLP与有效剂量转换系数计算头部和胸部常规扫描所致各年龄组儿童和成年人的有效剂量。 结果 单位mAs的头部CTDI大于体部CTDI;在头部常规扫描中,0～1岁组、5岁组、10岁组儿童受到的有效剂量分别为2.2、1.3、1.1 mSv;在胸部常规扫描中,0～1岁组、5岁组、10岁组儿童受到的有效剂量分别为5.3、3.1、3.4 mSv;每单位mAs所致儿童有效剂量平均比成人高1.8倍;多层CT的儿童头部CTDI_vol、DLP、有效剂量值均大于单层与双层CT,多层与双层CT的儿童胸部CTDI_vol、DLP、有效剂量值均小于单层CT。 结论 与成年人相比,儿童在CT检查中可能受到更大辐射危害,应严格遵循儿童CT检查适应证,并合理选择CT扫描参数,尽可能降低儿童受到的辐射剂量。     

Image quality and dose in computed tomography

Radiation exposure to the patient during CT is relatively high, and it is therefore important to optimize the dose so that it is as low as possible but still consistent with required diagnostic image quality. There is no established method for measuring diagnostic image quality; therefore, a set of image quality criteria which must be fulfilled for optimal image quality was defined for the retroperitoneal space and the mediastinum. The use of these criteria for assessment of image quality was tested based on 113 retroperitoneal and 68 mediastinal examinations performed in seven different CT units. All the criteria, except one, were found to be usable for measuring diagnostic image quality. The fulfilment of criteria was related to the radiation dose given in the different departments. By examination of the retroperitoneal space the effective dose varied between 5.1 and 20.0 mSv (milli Sievert), and there was a slight correlation between dose and high percent of “yes” score for the image quality criteria. For examination of the mediastinum the dose range was 4.4–26.5 mSv, and there was no significant increment of image quality at high doses. The great variation of dose at different CT units was due partly to differences regarding the examination procedure, especially the number of slices and the mAs (milli ampere second), but inherent dose variation between different scanners also played a part. Received 30 August 1995; Revision received 27 December 1995; Accepted 24 January 1995