ABSTRACT PURPOSE Measurement of organ and effective doses during angiographic CT (ACT) examinatio... more ABSTRACT PURPOSE Measurement of organ and effective doses during angiographic CT (ACT) examinations of head and heart in a pedeatric anthropomorphic phantom with thermoluminiscent dosimeters (TLD). METHOD AND MATERIALS ACT is a cross-sectional imaging modality for soft-tissue structures using C-arm-fluoroscopy with flat-panel detectors (FPD). ACT is utilized in children to guide interventional procedures in congenital heart defects or cerebral vascular malformations. To measure the organ and effective doses during head- and brain-examinations, a pediatric anthropomorphic phantom (ATOM, CIRS, Norfolk, VA, USA), representing a five year-old boy, was equipped with 132 TLD in 44 different positions representing relevant organs regarding ICRP-recommendations. The examinations were performed with an angiographic C-arm-system (Axiom Artis Dyna-CT, Siemens, Forchheim, Germany) with a 20 x 20cm FPD. Two different standard protocols recommended by the vendor were used to examine the head (70kV, 0.36µGy/frame, 126 frames) and the heart (70kV, 0.54µGy/frame, 126 frames). The TLD wear read out immediately after each examination. Organ and effective doses were calculated regarding ICRP-recommendations and compared to known dose values of matching standard MSCT-scans of the head and the heart. RESULTS The measured effective doses amounted to 0.11 mSv for the head and 0.46 mSv for the heart. The effective doses of the ACT-examinations were noticeably lower than the comparable MSCT-doses (1.8 mSv head, 9 mSv heart). CONCLUSION ACT-examinations have even lower doses than comparable MSCT-examinations. Further dose reduction ACT of the heart can be expected using an ecg-triggered protocol. CLINICAL RELEVANCE/APPLICATION ACT is a promising imaging technique for interventional procedures in children with an effective dose comparable to MSCT examinations.
This paper presents a speaker localization system usinga microphone array. The array is operated ... more This paper presents a speaker localization system usinga microphone array. The array is operated as a steeredlter-and-sum beamformer implemented as a summedcorrelator. In particular, we emphasize the use of aspeech pause detector to improve the robustness of thespeaker localization system by avoiding erroneous positionestimates when no speech signal is present. Simulationresults and measurements show that speech pausedetection improves the overall
PURPOSE To investigate dose distribution and image quality in 3D images reconstructed from projec... more PURPOSE To investigate dose distribution and image quality in 3D images reconstructed from projections acquired on a flat-panel C-arm system. METHOD AND MATERIALS A Siemens AXIOM Artis dTA C-arm system was used to acquire 2D projections. Using a CTDI phantom (16 cm diam, 14 cm length) and a 0.6 cc Farmer chamber, the exposure was measured at the center of the phantom and at 12 points around the periphery at 70, 81 and 109 kVp during a partial circle-scan over 200 degrees. Images of the low-contrast insert of the CatPhan phantom (16-cm diameter) were also obtained for two dose settings (dose to detector 0.36 uGy and 1.2 uGy), for the same kVp range. Volume data sets were reconstructed using enhanced C-arm 3D reconstruction software (DynaCT). Contrast-to-noise ratio (CNR) was calculated for the 10HU 10-mm-diameter disk using a region of interest (ROI) in the disk and an equivalent ROI in the background at the same radius (to ensure that uncorrected cupping due to scatter did not affec...
ABSTRACT PURPOSE Measurement of organ and effective doses during angiographic CT (ACT) examinatio... more ABSTRACT PURPOSE Measurement of organ and effective doses during angiographic CT (ACT) examinations of head and heart in a pedeatric anthropomorphic phantom with thermoluminiscent dosimeters (TLD). METHOD AND MATERIALS ACT is a cross-sectional imaging modality for soft-tissue structures using C-arm-fluoroscopy with flat-panel detectors (FPD). ACT is utilized in children to guide interventional procedures in congenital heart defects or cerebral vascular malformations. To measure the organ and effective doses during head- and brain-examinations, a pediatric anthropomorphic phantom (ATOM, CIRS, Norfolk, VA, USA), representing a five year-old boy, was equipped with 132 TLD in 44 different positions representing relevant organs regarding ICRP-recommendations. The examinations were performed with an angiographic C-arm-system (Axiom Artis Dyna-CT, Siemens, Forchheim, Germany) with a 20 x 20cm FPD. Two different standard protocols recommended by the vendor were used to examine the head (70kV, 0.36µGy/frame, 126 frames) and the heart (70kV, 0.54µGy/frame, 126 frames). The TLD wear read out immediately after each examination. Organ and effective doses were calculated regarding ICRP-recommendations and compared to known dose values of matching standard MSCT-scans of the head and the heart. RESULTS The measured effective doses amounted to 0.11 mSv for the head and 0.46 mSv for the heart. The effective doses of the ACT-examinations were noticeably lower than the comparable MSCT-doses (1.8 mSv head, 9 mSv heart). CONCLUSION ACT-examinations have even lower doses than comparable MSCT-examinations. Further dose reduction ACT of the heart can be expected using an ecg-triggered protocol. CLINICAL RELEVANCE/APPLICATION ACT is a promising imaging technique for interventional procedures in children with an effective dose comparable to MSCT examinations.
This paper presents a speaker localization system usinga microphone array. The array is operated ... more This paper presents a speaker localization system usinga microphone array. The array is operated as a steeredlter-and-sum beamformer implemented as a summedcorrelator. In particular, we emphasize the use of aspeech pause detector to improve the robustness of thespeaker localization system by avoiding erroneous positionestimates when no speech signal is present. Simulationresults and measurements show that speech pausedetection improves the overall
PURPOSE To investigate dose distribution and image quality in 3D images reconstructed from projec... more PURPOSE To investigate dose distribution and image quality in 3D images reconstructed from projections acquired on a flat-panel C-arm system. METHOD AND MATERIALS A Siemens AXIOM Artis dTA C-arm system was used to acquire 2D projections. Using a CTDI phantom (16 cm diam, 14 cm length) and a 0.6 cc Farmer chamber, the exposure was measured at the center of the phantom and at 12 points around the periphery at 70, 81 and 109 kVp during a partial circle-scan over 200 degrees. Images of the low-contrast insert of the CatPhan phantom (16-cm diameter) were also obtained for two dose settings (dose to detector 0.36 uGy and 1.2 uGy), for the same kVp range. Volume data sets were reconstructed using enhanced C-arm 3D reconstruction software (DynaCT). Contrast-to-noise ratio (CNR) was calculated for the 10HU 10-mm-diameter disk using a region of interest (ROI) in the disk and an equivalent ROI in the background at the same radius (to ensure that uncorrected cupping due to scatter did not affec...
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