Cone-beam CT (CBCT) is an imaging technique used in conjunction with radiation therapy. For example CBCT is used to verify the position of lung cancer tumours just prior to radiation treatment. The accuracy of the radiation treatment of thoracic and upper abdominal structures is heavily affected by respiratory movement. Such movement typically blurs the CBCT reconstruction and ideally should be removed. Hence motion-compensated CBCT has recently been researched for correcting image artefacts due to breathing motion. This paper presents a new dual-modality approach where CBCT is aided by using electrical impedance tomography (EIT) for motion compensation. EIT can generate images of contrasts in electrical properties. The main advantage of using EIT is its high temporal resolution. In this paper motion information is extracted from EIT images and incorporated directly in the CBCT reconstruction. In this study synthetic moving data are generated using simulated and experimental phantoms. The paper demonstrates that image blur, created as a result of motion, can be reduced through motion compensation with EIT.

The use of computed tomography (CT) scanning has been growing steadily. Therefore, CT dose measurement is becoming increasingly important for patient protection and optimization. A phantom is an important tool for dose measurement. This paper focuses on the evaluation of a CT dosimetry phantom made from nylon, instead of the standard polymethyl methacrylate (PMMA), which is not readily available or is too expensive in some countries. Comparison between phantoms made from the two materials is made in terms of measurements of the CT dose indices (CTDI). These were measured for four different beam widths and kVp settings at the center and periphery in head and body phantoms made from both materials and weighted CTDIs (CTDIw) were calculated. CT numbers along the z-axis of the phantom were also measured at the center and four peripheral positions of each scanned slice to check phantom homogeneity. Results showed that values for the CTDIw measured in the nylon phantoms were slightly higher than those from the PMMA while CT numbers for nylon were lower than those of PMMA. This is because the mass attenuation coefficient of the nylon is higher. Nylon could be used as a substitute material for CT dosimetry phantom to enable measurements and adjustment factors are given which could be used to estimate PMMA values for making comparisons with displayed values.

Automatic tube current modulation (ATCM) systems to aid in optimizing dose and image noise have become standard on computed tomography (CT) scanners over the last decade. ATCM systems of the main vendors modulate tube current in slightly different ways, with some using a control parameter related to image noise (e.g. Toshiba, GE) while others use a quality reference image mAs (e.g. Siemens). The translation of clinical protocols including ATCM operation between CT scanners from different manufacturers in order to obtain similar levels of image quality with optimized exposure variables has become an important issue. In this study, cylindrical phantoms of different sizes representing small, average and large patients, have been combined into one phantom, which has been scanned on Siemens, Toshiba and GE CT scanners with the full ranges of ATCM image quality settings. The volume weighted CT dose index (CTDI) and image noise over each section of the phantom were recorded for every setting. Relationships between the image quality level settings, and CTDI and measured image noise were analysed in order to investigate ATCM performance. Equations were developed from fits of the data to enable CTDI and image noise to be expressed in terms of the image quality parameters for different size phantoms on each scanner. The Siemens scanner protocol was chosen as the reference, as it avoided high doses for large patients, while allowing full modulation of tube current for patients of all sizes, and so was considered to provide optimized performance. The equations derived were used to equate the noise parameters on Toshiba and GE scanners to the quality reference mAs on the Siemens scanner, so that clinical protocols incorporating similar levels of optimization could be obtained on the three CT scanners.

No abstract

No abstract