Multislice Helical Scans Research Articles

Трудности диагностики центральной эндофитной опухоли легкого, возникшей на фоне туберкулеза

Актуальность. Проблема раннего выявления рака легких, возникшего на фоне специфического процесса, является чрезвычайно актуальной и сложной. Целью работы стало изучение роли рентгенологических и бронхоскопических методов исследования в диагностике центральной эндофитной опухоли легкого у больных туберкулезом легких. Материалы и методы. Анализ литературы, клинический случай. Результаты. Такие рентгенологические методы исследования, как обзорная рентгенограмма, информативны на поздних стадиях развития эндофитной опухоли легкого. Самым информативным методом на ранних стадиях является многосрезовое спиральное сканирование, особенностью которого является изотропность изображений (равное качество во всех плоскостях). Приведен клинический случай развития центральной эндофитной опухоли легкого у больного мультирезистентным туберкулезом легких. Выводы. Необходимо сочетание таких инструментальных методов исследования, как рентгенологические и фибробронхоскопия (с исследованием аспирата из бронхов), что дает в совокупности значительный объем информации о развитии у больного туберкулезом центральной эндофитной опухоли легкого.

Chest circumference as a predictive parameter of computed tomography coronary angiography radiation doses from dual-source computed tomography.

Our aim in this study was to determine the relationship between chest circumference and the radiation doses received by breast tissues during Dual-Source Computed Tomography (DSCT) cardiac scans. Routine cardiac DSCT examinations with similar exposure lengths were applied to 30 female patients. The scanogram image, multi-slice helical scan x-ray tube voltage and anode-cathode current were adjusted automatically according to attenuation for each patient during the scanogram acquisition. The standard protocol was otherwise applied to all patients. The 30 patients had an average weight of 67.8±15.3 kg, and the average length of the scanned region was 278.0±11.6 mm. Radiation doses were calculated from the dose-length product (DLP) and the computed tomography dose index (CTDI) scanner data values. The correlations between radiation dose and chest circumference were investigated. The level of significance was set at p<0.05. For routine cardiac DSCT scans, the average values were as follows: total DLP: 715.54±317.01 mGycm, CTDIvol: 40.79±19.41 mGy, and effective dose (ED): 17.89±7.93 mSv. The chest circumference of patients correlates well with their radiation exposure (p<0.01). The distribution of different tissues throughout the human body may vary among races and genders. Because of this, many researchers use body mass index (BMI) to set image quality and predict the radiation dose distribution from general computed tomography (CT) examinations. Additional anthropomorphic phantom studies should be conducted to determine more accurate conversion factors and, hence, better ED predictions.

TU-D-304A-08: A Novel Boundary Tracking Method for Metal Artifact Suppression in Helical CT Imaging

Purpose: One of the major challenges for metal artifact suppression in CT lies in the accurate detection of metal regions either in image space or projection space. In this work, we proposed a novel, semi-automatic boundary tracking scheme based on dual-front active contour models and boundary mapping strategy to detect the metal regions on reformatted projection data, and to effectively suppress metal artifacts on reconstructed images. Methods and Materials: We first created reformatted projections from multi-slice helical scan by combining data at the same angle view over the full longitudinal scan range. The shapes, locations, and number of metal objects can be easily identified from every single reformatted projection. Since the shape of the metal projections only changes slightly between adjacent projections, the segmented boundary from the first reformatted projections can be mapped to the next projection, and used as the initialization of the dual-front active contour model to find the actual metal object boundary in the current projection within only a couple of iterations with an automatic stop criterion. After detecting the metal implants on all the reformatted projections, a Delaunay triangulation was applied to fill the metal shadows. Finally, the image was reconstructed using commercially available reconstruction algorithms for multi-slice helical CT. Results: Patient studies were performed to evaluate the proposed method. Four cases were corrected, including three abdominal exams with hip prosthesis, and one musculoskeletal exam with shoulder prosthesis. The results demonstrated that the proposed method can suppress metal artifacts efficiently and effectively. Conclusions: A novel boundary tracking method was proposed for metal artifact suppression in multi-slice helical CT. This method incorporates the information of shape and location of metal implants into the boundary tracking procedure, which can handle multiple metal implants with various sizes and shapes, and can improve the segmentation accuracy and artifact suppression.

平成15年度後期国際研究集会派遣会員報告書(学術交流委員会だより)

With multi-slice helical scanning, increasing helical pitch causes changes in the effective slice sensitivity profile and thus in a thickening of the effective slice thickness. However, the increase in helical pitch alters the time sensitivity profile, thereby decreasing the effective scan time. In this paper we report the results of our research concerning the setting of optimum conditions to resolve this issue. The experiment was conducted with a moving phantom. The movement showed a variety of changes. When the subject was not in motion, increases in helical pitch resulted in deterioration in the image quality of the CT image. However, when the subject was in motion increases in helical pitch improved image quality. The general belief until now has been that helical pitch should be decreased in order to improve CT image quality. However, in the case of a moving subject, reduced helical pitch leads to deterioration in the time resolution and thus to a deterioration in the image quality. Through this study we have acquired an understanding of which helical pitch value is optimal in terms of the subject's rate of movement.

Algorithm for image reconstruction in multi-slice helical CT.

Efforts are being made to develop a new type of CT system that can scan volumes over a large range within a short time with thin slice images. One of the most promising approaches is the combination of helical scanning with multi-slice CT, which involves several detector arrays stacked in the z direction. However, the algorithm for image reconstruction remains one of the biggest problems in multi-slice CT. Two helical interpolation methods for single-slice CT, 360LI and 180LI, were used a starting points and extended to multi-slice CT. The extended methods, however, had a serious image quality problem due to the following three reasons: (1) excessively close slice positions of the complementary and direct data, resulting in a larger sampling interval; (2) the existence of several discontinuous changeovers in pairs of data samples for interpolation; and (3) the existence of cone angles. Therefore we have proposed a new algorithm to overcome the problem. It consists of the following three parts: (1) optimized sampling scan; (2) filter interpolation; and (3) fan-beam reconstruction. Optimized sampling scan refers to a special type of multi-slice helical scan developed to shift the slice position of complementary data and to acquire data with a much smaller sampling interval in the z direction. Filter interpolation refers to a filtering process performed in the z direction using several data. The normal fan-beam reconstruction technique is used. The section sensitivity profile (SSP) and image quality for four-array multi-slice CT were investigated by computer simulations. Combinations of three types of optimized sampling scan and various filter widths were used. The algorithm enables us to achieve acceptable image quality and spatial resolution at a scanning speed that is about three times faster than that for single-slice CT. The noise characteristics show that the proposed algorithm efficiently utilizes the data collected with optimized sampling scan. The new algorithm allows suitable combinations of scan and filter parameters to be selected to meet the purpose of each examination.