Dose reduction in multislice computed tomography

OBJECTIVE: Evaluation of the attenuation-based on-line modulation of tube current on multislice computed tomography (CT) to explore the potential of this dose-saving technique. METHODS: Fifty-five patients with follow-up CT examinations were scanned without and with a CARE Dose (Siemens Medical Solutions, Erlangen, Germany). The applied dose, image noise, and subjective image quality were evaluated. The reduction in patient exposure was determined by obtaining the effective milliamperes per second for each reconstructed scan and the absolute dosage requirement for the whole scan. RESULTS: The dose reduction achieved by applying the attenuation-based on-line modulation of tube current was 29.4% +/- 3.1% (P=0.002) for all scans, 30.5% +/- 3.2% (P=0.002) for the thorax scans, 29.7% +/- 2.9% (P=0.002) for the abdomen scans, and 28.7% +/- 2.7% (P=0.003) for the thorax and abdomen scans together. No significant restrictions in image quality were observed. CONCLUSIONS: Remarkable dose reduction can be obtained using the attenuation-based on-line modulation of tube current on multislice CT without compromising image quality.     

Dose reduction in computed tomography by individualized scan protocols

PURPOSE: To find a method of adjusting the mAs-value in relation to the size of the patient undergoing computed tomography (CT) examination as a means of minimizing the radiation dose to the patient. MATERIAL AND METHODS: A correction factor to be applied on the tube charge for each patient was calculated using two mathematical methods. This approach was tested on 4 Perspex phantoms of different sizes and geometries. Noise was measured in the images with and without use of the correction factors. Retrospectively, correction factors were calculated for 12 CT examinations of the abdomen and the dose reduction was estimated for these patient studies. RESULTS: The variations in noise measured in the images of the different phantoms were dramatically reduced by both methods. The retrospectively performed patient study showed that the largest correction factor was 7 times greater than the smallest, which means that a dose reduction factor of 7 is possible in the extreme case. CONCLUSION: Our proposed methods of adjusting the applied tube charge (mAs-value) in relation to the size of the patient can be used on the vast majority of CT systems. The potential for dose reduction is great, especially for small patients.     

Dose reduction by automatic exposure control in multidetector computed tomography: comparison between measurement and calculation

The aim of this study was to investigate the potential of dose reduction in multidetector computed tomography (MDCT) by current-modulated automatic exposure control (AEC) and to test the reliability of the dose estimation by the conventional CT dosimetry program CT-EXPO, when an average tube current is used. Phantom measurements were performed at a CT system with 64 detector rows for four representative examination protocols, each without and with current-modulated AEC. Organ and effective doses were measured by thermoluminescence dosimeters (TLD) at an anthropomorphic Alderson phantom and compared with those given by the calculation with CT-EXPO. The application of AEC yielded dose reductions between 27 and 40% (TLD measurements). While good linearity was observed between measured and computed effective dose values both without and with AEC, the organ doses showed large deviations between measurement and calculation. The dose to patients undergoing a MDCT examination can be reduced considerably by applying a current-modulated AEC. Dosimetric algorithms using a constant current-time product provide reliable estimates of the effective dose.     

Dose reduction in computed tomography by attenuation-based on-line modulation of tube current: evaluation of six anatomical regions

This study investigated the potential of attenuation-based on-line modulation of tube current to reduce the dose of computed tomography (in milliamperes) without loss in image quality. The dose can be reduced for non-circular patient cross-sections by reducing the tube current at the angular positions at which the diameter through the patient diameter is smallest. We investigated a new technical approach with attenuation-based on-line modulation of tube current. Computed tomographic projection data were analyzed to determine the optimal milliampere values for each projection angle in real time, instead of performing prior measurements with localizer radiographs. We compared image quality, noise pattern, and dose for standard scans and for scans with attenuation-based on-line modulation of tube current in a group of 30 radiation therapy patients. Six different anatomical regions were examined: head, shoulder, thorax, abdomen, pelvis, and extremities (knee). Image quality was evaluated by four radiologists in a blinded fashion. We found the dose to be reduced typically by 15–50 %. In general, no deterioration in image quality was observed. Thus the dose in computed tomography be reduced substantially by technical measures without sacrificing image quality. Attenuation-based on-line modulation of tube current is an efficient and practical means for this. Received: 15 July 1999; Revised: 22 October 1999; Accepted: 26 October 1999     

X-ray computed tomography in purulent pleurisy

Complementary CT scan imaging during investigation of 18 cases of empyema showed it to be an essential examination, since it established the diagnosis in all cases, determined possible extension of the infectious process and possible causal lesion, defined the most effective approach for percutaneous drainage and evaluated efficacy of the later.     

X-ray computed tomography of extrahepatic cholestasis

Findings in a series of 53 examinations performed in patients with extrahepatic cholestasis demonstrated the value of computed tomography exploration to determine mechanisms and etiology of biliary tract affections. Sensitivity of the CT scan for detection of biliary tract dilatations was equivalent to that obtained by ultrasound, and was even higher for certain types of patient (obese, distended, etc.). Results of this study combined with data in the literature enables precise diagnostic criteria to be established when determining etiology of these dilatations, which require investigation by a CT scan when ultrasound imaging proves unsatisfactory.     

我国CT检查成年人辐射剂量诊断参考水平的建立历程及解读

经过放射诊断专家、影像技术专家、辐射防护专家和专业技术人员10多年的探索,一项基于大规模国内调查数据而建立的CT检查成年人辐射剂量诊断参考水平(diagnostic reference level,DRL)以国家卫生行业标准(WS/T 637-2018)形式发布。其制定原则和方法符合国际惯例和我国的实际情况,基本上涵盖了我国成年人常见CT检查项目,与国外的DRL比较,整体处于一个合理或较低的剂量水平。给出的50%分位数(可能达到水平)和25%分位数(异常低剂量的提示水平)作为辐射剂量优化指导的额外工具。在日常放射诊断活动中,使辐射剂量与图像质量、临床诊断任务相匹配,降低非正当过高或过低剂量的发生频率。     

Comparison of diagnostic value of multidetector computed tomography and X-ray in the detection of body packing

Objective

Radiologists and other clinicians are facing an increasing number of illegal drug-related medical conditions. We aimed to draw attention to this growing global problem and to highlight some of the important points related to diagnosis and follow-up of body packing. We compare the diagnostic performance of unenhanced multidetector CT (MDCT) and abdomen X-ray for the detection of drug-filled packets.

Materials and methods

Sixty-seven suspects, who underwent both CT and X-ray examinations, have been included in the study. All MDCT and X-ray images were independently and retrospectively reviewed by two observers with different degrees of experience in abdomen imaging. Fifty-two of them were identified as body packers finally. Interobserver agreement, sensitivity, specificity, positive and negative predictive value were calculated.

Results

Two types of packets with different characteristics were identified in all body packers. Type 1 packets (solid-state drug) were found in 41 patients and type 2 packets (liquid cocaine) in 11 patients. All statistical analyses concern the detection of any packets. That is, the whole evaluation has been performed per patient. Sensitivity/specificity values of type 1 and type 2 packets for MDCT were 100–98%/100–100% and 100–100%/100–100%, respectively. Besides, sensitivity/specificity values of type 1 and type 2 packets for X-ray were 93–90%/100–91% and 64–45%/73–71%, respectively. In addition, interobserver agreements for detection of any packets were excellent (κ = 0.96) and good (κ = 0.75) for interpretation of MDCT and X-ray, respectively.

Conclusion

Unenhanced MDCT is a fast, accurate and easily used diagnostic tool with high sensitivity and specificity for the exact diagnosis of body packing.     

Use of X-ray computed tomography in cervical infections

Infections of face and neck represent serious and potentially life threatening conditions that are sometimes difficult to differentiate from neoplastic tumours, especially in subacute clinical forms. Conventional radiographic techniques offer interest for cervical masses, except Ultra-Sonographic exam, in sites regarding vascular axes, but carries little value for evaluating their spread into the different cervical spaces. On the other hand, C.T. is valuable to precise the location and the extent and to determine its inflammatory nature by studying the fats and the aponeurosis around it. It help in the analysis of associated adjacent signs: soft tissue swelling, extensive obliteration of adjacent fats, swelling of cervical aponeurosis, thickening of adjacent muscles. These findings are documented by the study of fourteen patients, admitted in St-Antoine hospital. All abscesses, except one, were easy to diagnose because of their low central attenuation. False negative cases are possible and noted by other authors. So, in absence of response to appropriate therapy, surgery is necessary to eliminate a misdiagnosed abscess. Furthermore, it's sometimes possible to suspect an etiology (foreign body, tuberculosis).     

Dose management in multi–slice spiral computed tomography

Dose management is a necessary central issue in multi-slice spiral CT. The concern about patient doses in CT in the medical field, but also in the public, is high, and demands for improved solutions are undeniable. This article presents technical background and basic information on dose measurements, on ways to influence dose and on the dose levels typically encountered in medical CT. A particular focus is put on the outline of new concepts for dose management and optimization. The new approaches are based on tube current modulation. They serve to adapt the tube current intensities automatically and in real time to the anatomy of the specific patient. The end point of these efforts is an automated exposure control for CT.     

X-ray computed tomography in fractures of the acetabulum

Radiographic assessment of these fractures remains difficult. Conventional techniques according to Letournel show the lesions but not to the best advantage, for instance the "congruency" of femoral head with acetabulum. 54 CT scan were performed (1982-1984) every time a doubt was persisting. Incarcerations of fragments, impactions of the acetabulum, sacro-iliac joint disjunctions, congruency and lesions of femoral head are much better seen with scanner. In planing the surgical therapy (or orthopedic), CT scan add a great deal to the information and dramatically improves the results.     

Dose reduction in xeroradiography--application to chest tomography.

Exposure and image quality in xeroradiography were studied in a test object and in patient tomographic examinations of the chest. With increased tube voltage and added copper filtration, skin exposure was reduced up to a factor of 10 without loss of image quality.     

X-ray computed tomography of duodenal lipoma]

Duodenal lipoma is a rare, often asymptomatic tumor; the circumstances of its discovery have become more frequent as CT examinations are more commonly performed. The merits of a CT examination for this condition is to allow both a positive diagnosis and the follow-up of these fatty tumors which have very few clinical expressions, thus avoiding complementary examinations or even useless laparotomies. The authors describe three cases of incidental discovery of duodenal lipomas.     

Limitations of computed tomography for diagnostic Neuroradiology

Summary The limitations of computed tomography for diagnostic Neuroradiology are pointed out. The relation of CT to the classical neuroradiological examinations are discussed.