Abstract
The assessment of intracranial aneurysms is increasingly performed using three‐dimensional cone‐beam rotational angiography (3D CBRA). To reduce the dose to the patient during 3D CBRA procedures, filtered region‐of‐interest imaging (FROI) is presented in literature to be an effective technique as the dose in regions of low interest is reduced, while high image quality is preserved in the ROI. The purpose of this study was to quantify the benefit of FROI imaging during a typical 3D CBRA procedure in a patient's head region. A cone‐beam rotational angiography unit (Infinix) was modeled in GMctdospp, an EGSnrc‐based Monte Carlo software, which calculates patient dose distributions in rotational computed tomography. Kodak Lanex, a gadolinium compound, was chosen to be the ROI filter material. The adult female ICRP reference phantom was integrated in GMctdospp to calculate organ and effective doses in simulations of FROI‐CBRA examinations. During the Monte Carlo simulations, different parameters as the ROI filter thickness, the ROI opening size, the tube voltage, and the isocenter position were varied. The results showed that the reduction in dose clearly depends on these parameters. Comparing the reduction in organ dose in standard 3D CBRA and FROI‐CBRA, a maximum reduction of about 60%–80% could be achieved with a small sized ROI filter and about 40%–70% of the dose could be saved using a ROI filter with a large opening. Further we could show that dose reduction strongly depends on filter thickness, the location of the organ in the radiated area, and the position of the isocenter. As a consequence, dose reduction partially differs from theoretically calculated values by a factor up to 1.6. The effective dose could be reduced to a minimum of about 40%. Due to the fact that standard 3D CBRA is only used for the assessment of aneurysms at present and, thus, most of the patient dose originates from the aneurysm treatment (with 2D techniques) itself, the dose reduction effect of ROI filtering in 3D CBRA tends to be much smaller, if the patient dose of a whole aneurysm treatment procedure is considered.PACS numbers: 87.59.DJ, 87.55.kh
Highlights
Three-dimensional cone-beam rotational angiography (3D CBRA) is frequently used in modern neuroradiology, as it facilitates diagnosis and planning treatment of intracranial aneurysms.[1]
Apart from tube current modulation or peak kilovoltage optimization, which is good practice in rotational cone-beam CTs, a number of authors investigated the feasibility of filtered region of interest (ROI) imaging.[9,10,11] In many procedures the region of interest, such as the area of the intervention, the location of the aneurysm or the position of stents and coils, is considerably smaller than the detectors field of view (FOV)
In this study we quantitatively evaluated the potential dose savings of region-of-interest imaging applied to a typical neuroradiological investigation
Summary
Three-dimensional cone-beam rotational angiography (3D CBRA) is frequently used in modern neuroradiology, as it facilitates diagnosis and planning treatment of intracranial aneurysms.[1]. Apart from tube current modulation or peak kilovoltage optimization, which is good practice in rotational cone-beam CTs, a number of authors investigated the feasibility of filtered region of interest (ROI) imaging.[9,10,11] In many procedures the region of interest, such as the area of the intervention, the location of the aneurysm or the position of stents and coils, is considerably smaller than the detectors field of view (FOV). On the other hand artifacts occur in the reconstruction process as soon as the adjusted FOV does not include the entire body structure in each projection. For this reason filtered ROI (FROI) imaging was introduced to attenuate the X-ray beam substantially (but not completely) to preserve sufficient attenuation data for 3D image reconstruction
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