Computed tomography (CT) is one of the most important modalities in a radiological department, which produces images with high diagnostic confidence, but in some cases contributes to a high radiation dose to the patient. The radiation dose can be reduced by the use of advanced image reconstruction algorithms. This study was done on a Philips Brilliance iCT with iterative reconstruction iDose4 and model-based iterative reconstruction IMR. The purpose was to investigate the effect on the image quality with thin slice images reconstructed with IMR, compared to standard slice thickness reconstructed with iDose4. Objective measurements of noise and contrast-to-noise ratio were performed using an image quality phantom, an anthropomorphic phantom and clinical cases. Subjective evaluations of low-contrast resolution were performed by observers using an image quality phantom. IMR gives strong noise reduction and enhanced low-contrast and thereby enable selection of thinner slice thickness. Objective evaluation of image noise shows that thin slices reconstructed with IMR provides lower noise than thicker slice images reconstructed with iDose4. With IMR the slice thickness is of less importance for the noise. With thinner slices the partial volume artefacts becomes less pronounced. In conclusion, we have shown that IMR enables reduction of the slice thickness and at the same time maintain or even reduce the noise level compared to iDose4 reconstruction with standard slice thickness. This will subsequently result in an improvement of image quality for images reconstructed with IMR.
The O-arm system is a mobile intraoperative imaging system that is comprised of fluoroscopy and cone beam CT. The
configuration of the O-arm system with absence of patient table and a broad beam width (165 mm in isocenter) brings
new practical and physical requirements on how to perform dose measurements. The purpose of this study was to
describe a method that overcomes this and makes it possible to characterize the radiation output from the O-arm system.
A holder with a clamp and a flexible ball joint that can orientate the radiation detector support and the Mover that can be
adjusted to hold the dose detector in a horizontal position was used. Evaluation of the dose response for three different
dose detectors of different active length (0.3, 23.1 and 100 mm) was made for three different beam qualities.
Furthermore the dose profile free in air to control the possible heel effect and width of the x-ray field during rotation was
measured and the dose rate waveform was analyzed. The FWHM of the dose profile was 162 mm. The dose response of
the three detectors is reported. The average dose response was lower for the detector with longer active length due to the
influence of the dose profile shape. From dynamic measurement total exposure time, pulse width, and the number of
pulses were verified. In conclusion, an external horizontal hanging holder with mover option helps to assist to make dose
measurement easier and enables characterize the radiation output from the O-arm system.
The motivation of this study is the general lack of knowledge regarding the efficiency and the appropriate use of the
adaptation strengths of Siemens automatic exposure control system CARE Dose 4D. The purpose was to evaluate the
effect on radiation absorbed dose using different adaptation strengths of CARE Dose 4D in three routine pediatric CT
protocols. A pediatric anthropomorphic whole body phantom was used to simulate a 4 year old patient. CT scans were
performed with a Siemens SOMATOM Definition Flash using three different pediatric protocols: neck, thorax, and
abdomen. The characteristic of the tube current modulation was similar for all adaptation strengths. The difference is the
extent of decrease in tube current. The degree of dose reduction using CARE Dose 4D and CARE kV compared using a
fix effective mAs was 34-57%, 51-88%, and 56-91% for neck, thorax, and abdomen protocol, respectively. Accordingly,
there is a large difference in radiation dose dependent on the adaptation strength: a factor of 1.5, 4.5, and 4.6 for neck,
thorax, and abdomen protocol, respectively. The adaptation strengths can be used to obtain user-specified modifications
of image quality or radiation dose to the patient. Radiologists and medical physicists need to be aware of the large
differences between the adaptation strengths, and such differences are useful when attempting strategies to optimize CT
radiation dose.
The purpose of this study was to estimate organ and effective dose to the patient during spinal surgery with a cone-beam
O-arm system. The absorbed dose to radiosensitive organs and effective dose were calculated on mathematically
simulated phantom corresponding to a 15-year-old patient using PCXMC 2.0. Radiation doses were calculated at every
15° of the x-ray tube projection angle at two regions: thoracic spine and lumbar spine. Two different scan settings were
investigated: 120 kV/128 mAs (standard) and 80 kV/80 mAs (low-dose). The effect on effective dose by changing the
number of simulated projection angles (24, 12 and 4) was investigated. Estimated effective dose with PCXMC was
compared with calculated effective dose using conversion factors between dose length product (DLP) and effective dose.
The highest absorbed doses were received by the breast, lungs (thoracic spine) and stomach (lumbar spine). The effective
doses using standard settings were 5 times higher than those delivered with low-dose settings (2-3 scans: 7.9-12 mSv
versus 1.5-2.4 mSv). There was no difference in estimated effective dose using 24 or 12 projection angles. Using 4
projection angles at every 90° was not enough to accurate simulate the x-ray tube rotating around the patient. Conversion
factors between DLP and effective dose were determined. Our conclusion is that the O-arm has the potential to deliver
high radiation doses and consequently there is a strong need to optimize the clinical scan protocols.
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