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MEDICAL PHYSICS IN THE BALTIC STATES 7 (2009) Proceedings of International Conference “Medical Physics 2009” 8 - 10 October 2009, Kaunas, Lithuania DOSE REDUCTION AND IMAGE QUALITY EVALUATIONS OF AUTOMATIC EXPOSURE CONTROL SYSTEMS FROM FOUR DIFFERENT CT MANUFACTURERS Marcus SÖDERBERG, Mikael GUNNARSSON Department of Medical Radiation Physics, Malmö, Lund University, Malmö University Hospital, SE-205 02 Malmö, Sweden Purpose: To evaluate automatic exposure control (AEC) systems from four different CT scanner manufacturers: General Electric (GE), Philips, Siemens, and Toshiba, considering their potential for reducing radiation exposure to the patient while maintaining adequate image quality. Material and Methods: An anthropomorphic chest phantom was used to simulate an adult patient. Measurements were performed using 16-slice and 64-slice CT-scanners from each manufacturer with the AEC system activated and inactivated. The adaptation of the tube current along the longitudinal axis of the phantom and the potential for reducing radiation dose were evaluated using parameters in the DICOM image information. The image quality was evaluated based on image noise (standard deviation of CT numbers), calculated in 0.5-cm 2 circular regions of interest, situated throughout the spine region of the chest phantom. Results: The tube current modulation dynamics were similar among the different AEC systems, especially between GE and Toshiba systems and between Philips and Siemens systems. The AEC systems resulted in a considerable reduction in radiation dose, ranging from approximately 30% to 60%. The image noise increased when the AEC systems were used, especially in regions where the tube current was greatly decreased, such as the lung region. However, the image noise in different anatomical regions of the chest phantom became more uniform when using the AEC systems compared to fixed mAs scans. Conclusion: The use of AEC systems available in modern CT scanners can significant reduce the radiation exposure to the patient and the variation in image noise among images can be lower. 15
MEDICAL PHYSICS IN THE BALTIC STATES 7 (2009) Proceedings of International Conference “Medical Physics 2009” 8 - 10 October 2009, Kaunas, Lithuania DIAGNOSTICS OF CANCEROUS PROSTATE TISSUE BY MEANS OF INFRARED SPECTROSCOPICAL IMAGING Daiva LEŠČIŪTĖ*, Valdas ŠABLINSKAS*, Valdemaras ALEKSA*, Arūnas MARŠALKA*, Feliksas JANKEVIČIUS** *Dept. of General Physics and Spectroscopy, Faculty of Physics, Vilnius University; ** Dept. of Physiology, Biochemistry and Laboratory Medicine, Faculty of Medicine, Vilnius University; ***Centre of Urology, Vilniaus University Hospital Santariskių klinikos, Faculty of Medicine, Vilnius University Abstract: Method of Fourier transform infrared microscopy (FTIR-MC) for the first time is applied for studies of prostate cancerous tissue. The chemical images are obtained by combining mapping technique with imaging with focal plane array (FPA) MCT detector. It is shown that ratio of intensity of amide I and amide II spectral absorption bands can be used for distinguishing cancerous tissue from healthy one. By combining infrared spectral images with optical ones it is shown that infrared imaging is preferable method for defining edges of cancerous tissue of prostate samples compared to the method of conventional histological imaging. It is shown that infrared images allow to define such edges with 10 microns lateral resolution. Keywords: FTIR-MC, FPA detector, prostate, cancer 1. Introduction Modern infrared spectroscopy combined with infrared microscopy allows investigate features of samples in micrometric scale. Just recently this method was started to be applied for studies of biological tissues. Determination of spatial distribution of different chemical components in biological tissues is even possible by using this method. Sensitivity of the method enables to identify tumors even in very early stage of this disease. Early diagnosis of the tumor is very important for its prevention or successful curing of the patient. Tumor formation can be caused by very different reasons such as some genetic miss functioning or some cancerous substances which can present in our surrounding or can be taken in to the body by breathing or with food. Biochemical changes in various tumors usually are very different [1]. FTIR method supplies very useful information about molecular structure of biological tissue. Chemical information obtained by means of infrared spectroscopical microscopy is molecular level information taken from volume of the sample sized to micrometric scale [2]. 2.1 Focal plane array detector For any optical imaging some multichannel detector is needed. Focal plane Mercury Cadmium Telurate (FPA 16 MCT) detector is detector of choice in case of infrared imaging. A FPA MCT detector consists from many small single detectors sized to 6 - 10 μm 2 . Every single detector in the array collects the spectral information from different parts of the sample. Set of spectra obtained by different single detectors of the array can be used for constructing of infrared image of the sample in desired spectral window located in infrared spectral region from 500 to 4000 cm -1 . Such image is considered to be chemical image of the sample when the spectral windows coincide with spectral band specific to one of chemical components of the sample [3]. At present stage of technology the FPA MCT detectors consist from 4096 single detectors, which form 64 × 64 matrix. In such a way 4096 spectra are captured at a time. Infrared imaging becomes rather fast by using such a detector. Sensitivity is another feature of this technology. Lateral resolution obtained with use of such detectors can be achieved as high as size of biological cells. Due to this fact this technology is preferable compare to other imaging technologies which are in use in medical laboratories or operational rooms. It is notable, that in order to extract chemical information from infrared microscopical images some statistical analysis of the images should be applied, including principal component analysis (PCA) and some other unsupervised or supervised statistical methods. Basically, processing of spectral information from the FPA detector is rather complicated. A set of interferograms is primary spectral information, obtained
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