Changing radiation dose from diagnostic computed tomography examinations in Saskatchewan

Purpose

Follow-up study to observe if provincial mean effective radiation dose for head, chest, and abdomen-pelvis (AP) computed tomographies (CTs) remained stable or changed since the initial 2006 survey.

Methods

Data were collected in July 2008 from Saskatchewan's 13 diagnostic CT scanners of 3358 CT examinations. These data included the number of scan phases and projected dose length product (DLP). Technologists compared projected DLP with 2006 reference data before scanning. Projected DLP was converted to effective dose (ED) for each head, chest, and AP CT. The total dose that the patients received with scans of multiple body parts at the same visit also was determined.

Results

The mean (± SD) provincial ED was 3.4 ± 1.6 mSv for 1023 head scans (2.7 ± 1.6 mSv in 2006), 9.6 ± 4.8 mSv for 588 chest scans (11.3 ± 8.9 mSv in 2006), and 16.1 ± 9.9 mSv for 983 AP scans (15.5 ± 10.0 mSv in 2006). Single-phase multidetector row CT ED decreased by 31% for chest scans (9.5 ± 3.9 mSv vs 13.7 ± 9.7 mSv in 2006) and 17% for AP scans (13.9 ± 6.0 mSv vs 16.8 ± 10.6 mSv in 2006) and increased by 19% for head scans (3.2 ± 1.2 mSv vs 2.7 ± 1.5 mSv in 2006). The total patient dose was highest (33.8 ± 10.1 mSv) for the 20 patients who received head, neck, chest, and AP scans during a single visit. Because of increased utilisation and the increased CT head dose, Saskatchewan per capital radiation dose from CT increased by 21% between 2006 and 2008 (1.14 vs 1.38 mSv/person per year).

Conclusion

Significant dose and variation reduction was seen for single-phase CT chest and AP examinations between 2006 and 2008, whereas CT head dose increased over the same interval. These changes, combined with increased utilisation, resulted in per capita increase in radiation dose from CT between the 2 studies.     

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.     

Reduction of radiation exposure and image quality using dose reduction tool on computed tomography fluoroscopy

The purpose of our study was to measure the reduction rate of radiation dose and variability of image noise using the angular beam modulation (ABM) on computed tomography (CT) fluoroscopy. The Alderson-Rando phantom and the homemade phantom were used in our study. These phantoms were scanned at on-center and off-center positions at -12 cm along y-axis with and without ABM technique. Regarding the technique, the x-ray tube is turned off in a 100-degree angle sector at the center of 12 o'clock, 10 o'clock, and 2 o'clock positions during CT fluoroscopy. CT fluoroscopic images were obtained with tube voltages, 120 kV; tube current-time product per reconstructed image, 30 mAs; rotation time, 0.5 s/rot; slice thickness, 4.8 mm; and reconstruction kernel B30s in each scanning. After CT scanning, radiation exposure and image noise were measured and the image artifacts were evaluated with and without the technique. The reduction rate for radiation exposure was 75-80% with and without the technique at on-center position regardless of each angle position. In the case of the off-center position at -12 cm, the reduction rate was 50% with and without the technique. In contrast, image noise remained constant with and without the technique. Visual inspection for image artifacts almost have the same scores with and without the technique and no statistical significance was found in both techniques (p>0.05). ABM is an appropriate tool for reducing radiation exposure and maintaining image-noise and artifacts during CT fluoroscopy.     

Virtual computed tomography colonoscopy: artifacts, image quality and radiation dose load in a cadaver study

The purpose of our study was to evaluate the interdependency of spatial resolution, image reconstruction artifacts, and radiation doses in virtual CT colonoscopy by comparing various CT scanning protocols. A pig's colon with several artificial polypoid lesions was imaged after air insufflation with helical CT scanning using 1-, 3-, and 5-mm collimation, and pitch values varying from 1.0 to 3.0. Virtual endoscopic images and “fly through” sequences were calculated on a Sun Sparc 20 workstation (Navigator Software, GE Medical Systems, Milwaukee, Wis.). Several reconstruction artifacts as well as overall image quality were evaluated by three independent reviewers. In addition, radiation doses for the different CT protocols were measured as multiple-scan average dose using a 10-cm ion chamber and a standard Plexiglass body phantom. Generally, image quality and reconstruction artifacts were less affected by pitch values than by beam collimation. Thus, narrow beam collimation at higher pitch values (e. g. 3 mm/2.0) seems to be a reasonable compromise between quality of virtual endoscopic images and radiation dose load. Received: 4 February 1999; Revised: 16 June 1999; Accepted: 17 June 1999     

Effect of radiation dose and adaptive statistical iterative reconstruction on image quality of pulmonary computed tomography

Purpose  

The purpose of this study was to assess the effects of dose and adaptive statistical iterative reconstruction (ASIR) on image quality of pulmonary computed tomography (CT).     

前瞻性心电门控技术在256层CT冠状动脉成像中的应用

目的:比较前瞻性心电门控(前门控)与回顾性心电门控(后门控)螺旋CT冠状动脉成像的图像质量及辐射量,探讨前门控CTA对冠心病的临床应用价值。方法:分析接受前瞻性心电门控冠状动脉检查的109例患者及接受回顾性心电门控冠状动脉检查的99例患者的影像学资料,对其图像质量及辐射量进行评价。结果:前门控与后门控两组图像质量评分分别为4.97±4.78和4.36±0.69,两组间比较差异无统计学意义(P>0.05),前门控与后门控两组有效辐射量分别为(3.13±0.57)mSv和(10.21±2.43)mSv,两组间比较差异有统计学意义(P<0.05)。结论:在一定的心率(<75次/分)范围内,256层螺旋CT前门控冠状动脉成像的图像诊断质量与后门控具有一致性,且前门控明显降低了辐射量。     

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

     

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.     

Image quality and radiation dose in 256-slice cardiac computed tomography: Comparison of prospective versus retrospective image acquisition protocols

Purpose

To assess coronary artery image quality and patient radiation exposure in patients who underwent clinically indicated 256-slice CTA.

Methods

Consecutive patients (n = 193) underwent 256-slice CTA, using (1) retrospective gating without radiation dose modulation, (2) retrospective gating with radiation dose modulation and (3) prospective gating. Image quality was determined by consensus of two experienced observers using a 5-grade scale. The effective dose was calculated.

Results

In all patients, CTA was performed without adverse events. Retrospective CTA was assessed in 39 patients with and 39 without dose modulation, while 115 patients underwent prospective CTA. Heart rate was related to image quality with all protocols (r = 0.46, p < 0.001). Up to a heart rate of 75 bpm no significant difference in overall image quality was observed for all three protocols, while no significant differences could be observed between retrospective CTA with and without dose modulation for any segments or heart rates. Prospective and retrospective CTA with dose modulation showed radiation savings of ∼75% and ∼30%, respectively compared to retrospective CTA without dose modulation (p < 0.001).

Conclusions

In patients with heart rates up to 75 bpm prospective CTA should be the first choice acquisition protocol. For heart rates >75 bpm, retrospective CTA with dose modulation should be considered.     

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).     

Effect of acquisition technique on radiation dose and image quality in multidetector row computed tomography coronary angiography with submillimeter collimation

RATIONALE AND OBJECTIVES: We sought to examine effects of tube voltage and current on radiation dose and image quality for minimally invasive coronary angiography with a 16-slice multidetector row computed tomography (MDCT) scanner. MATERIALS AND METHODS: We scanned the phantom used in the American College of Radiology Computed Tomography Accreditation Program at tube voltages of 80 and 120 kVp at 550, 650, and 750 mAseff, with and without a reduction in radiation dose by electrocardiographically (ECG) controlled tube current modulation (ECG pulsing). RESULTS: Without ECG pulsing, the effective dose was 3 to 13 mSv. On average, a 50% increase in tube voltage led to increased radiation dose (215%), contrast-to-noise ratio (150%), and decreased image noise (-48%). On average, a 17% increase in mAseff led to increased radiation dose (17%) and contrast-to-noise ratio (4%) and decreased image noise (-9%). Dose reduction by ECG pulsing (simulated heart rate, 70 beats per minute) was 28%. With ECG pulsing, noise in images reconstructed during ventricular systole was double that in images reconstructed during ventricular diastole. CONCLUSIONS: These quantitative findings about the relationships among scan acquisition parameters, radiation dose, and image quality have practical implications for using ECG pulsing to reduce radiation doses in MDCT coronary angiography.     

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     

Image quality vs radiation dose of four cone beam computed tomography scanners

OBJECTIVES: To evaluate image quality by examining segmentation accuracy and assess radiation dose for cone beam CT (CBCT) scanners. METHODS: A skull phantom, scanned by a laser scanner, and a contrast phantom were used to evaluate segmentation accuracy. The contrast phantom consisted of a polymethyl methacrylate (PMMA) cylinder with cylindrical inserts of air, bone and PMMA. The phantoms were scanned on the (1) Accuitomo 3D, (2) MercuRay, (3) NewTom 3G, (4) i-CAT and (5) Sensation 16. The structures were segmented with an optimal threshold. Thicknesses of the bone of the mandible and the diameter of the cylinders in the contrast phantom were measured across lines at corresponding places in the CT image vs a ground truth. The accuracy was in the 95th percentile of the difference between corresponding measurements. The correlation between accuracy in skull and contrast phantom was calculated. The radiation dose was assessed by DPI(100,c) (dose profile integral (100,c)) at the central hole of a CT dose index (CTDI) phantom. RESULTS: The results for the DPI(100,c) were 107 mGy mm for (1), 1569 mGy mm for (2), 446 mGy mm for (3), 249 mGy mm for (4) and 1090 mGy mm for (5). The segmentations in the contrast phantom were submillimeter accurate in all scanners. The segmentation accuracy of the mandible was 2.9 mm for (1), 4.2 mm for (2), 3.4 mm for (3), 1.0 mm for (4) and 1.2 mm for (5). The correlation between measurements in the contrast and skull phantom was below 0.37 mm. CONCLUSIONS: The best radiation dose vs image quality was found for the i-CAT.     

两种数字乳腺X射线摄影系统的比较

目的探讨比较全视野数字乳腺X射线摄影系统(FFDM)与计算机乳腺X射线摄影系统(CRM)在影像质量与辐射剂量方面的差异。方法用FFDM对ALVIM乳腺摄影体模TRM进行自动曝光控制(AEC)摄影,再用CRM专用成像板(IP)在同一摄影机上用相同条件对体模摄影。固定AEC摄影时的kV值,选用曝光量数值14、16、18、22和24 mAs,在FFDM机上对模体摄影,记录上述摄影条件和入射皮肤剂量(ESD)及平均腺体剂量(AGD)。由5位影像科资深医师分别在相同条件下对所得影像进行软阅读,按照5分值判断法评判,然后绘制受试者工作特征曲线(ROC)曲线,计算出每种信号的判断概率值(P_det),对所得数据进行统计学分析。结果在辐射剂量均为1.36 mGy时,FFDM对模体内钙化点和肿块灶P_det值比CRM高,尤其是微小钙化点和小肿块灶,微小钙化点最大差值为0.215,小肿块灶最大差值为0.245。在相同的P_det值下,FFDM的辐射剂量比CRM低,ESD的值降低了26%,腺体平均剂量降低了41%。在使用FFDM摄影时,当mAs值超过AEC值时,P_det值没有明显改变。结论在相同曝光条件下,FFDM对乳腺钙化点和肿块灶的检出率高于CRM;在获得相似图像质量时,FFDM的辐射剂量明显低于CRM。     

Attenuation-based kV pair selection in dual source dual energy computed tomography angiography of the chest: impact on radiation dose and image quality

Objectives

The purpose of this study was to evaluate the impact of attenuation-based kilovoltage (kV) pair selection in dual source dual energy (DSDE)-pulmonary embolism (PE) protocol examinations on radiation dose savings and image quality.

Methods

A prospective study was carried out on 118 patients with suspected PE. In patients in whom attenuation-based kV pair selection selected the 80/140Sn kV pair, the pre-scan 100/140Sn CTDIvol (computed tomography dose index volume) values were compared with the pre-scan 80/140Sn CTDIvol values. Subjective and objective image quality parameters were assessed.

Results

Attenuation-based kV pair selection switched to the 80/140Sn kV pair (“switched” cohort) in 63 out of 118 patients (53%). The mean 100/140Sn pre-scan CTDIvol was 8.8 mGy, while the mean 80/140Sn pre-scan CTDIvol was 7.5 mGy. The average estimated dose reduction for the “switched” cohort was 1.3 mGy (95% CI 1.2, 1.4; p?<?0.001), representing a 15% reduction in dose. After adjusting for patient weight, mean attenuation was significantly higher in the “switched” vs. “non-switched” cohorts in all five pulmonary arteries and in all lobes on iodine maps.

Conclusions

This study demonstrates that attenuation-based kV pair selection in DSDE examination is feasible and can offer radiation dose reduction without compromising image quality.

Key Points

? Attenuation-based kV pair selection in dual energy examination is feasible. ? It can offer radiation dose reduction to approximately 50% of patients. ? Approximate 15% reduction in radiation dose was achieved using this technique. ? The image quality is not compromised by use of attenuation-based kV pair selection.

     

Radiation dose optimization in pediatric temporal bone computed tomography: influence of tube tension on image contrast and image quality

Introduction  

The purpose of this experimental study was to investigate the effect of tube tension reduction on image contrast and image quality in pediatric temporal bone computed tomography (CT).