Abstract
Since the introduction of flat panel detector-equipped C-arms, the use of flat panel detector CT (FPCT) in the neuroradiologic angiography suite has become more frequent. This examination implicates its own specific radiation exposure. We used the CT dose index (CTDI) concept and adapted it to the special FPCT geometry to provide a consistent comparison with multisection head CT (cCT). Exposure data obtained for routine scanning during a period of 1 year were used to assess a specific dose of a total of 217 rotational scans performed in 105 patients. One hundred seventy-two scans were 3D digital subtraction angiography (DSA) scans. There were 45 scans that were performed to achieve high-quality, soft-tissue resolution. Dose measurements in cylindrical polymethylmethacrylate (PMMA) phantoms were used to determine the CTDI value and to compare it with the reference values for cCT. In addition, the dose-area product (DAP) was registered and correlated with the CTDI and corresponding dose-length product (DLP) values. Exposure data and dose values were compared with cCT. Mean-weighted CTDI value of 3D-DSA was approximately 9 mGy per scan. High-quality, soft-tissue resolution FPCT scans, comparable with cCT, revealed a mean dose value of 75 mGy (reference value for cCT, CTDI(w) approximately 60 mGy). The high-speed scans used for 3D-DSA revealed a significantly lower CTDI(w) and DLP compared with clinical CT. The high-quality FPCT protocol resulted in a higher dose and should therefore be limited to acute cases, when patient transfer to a CT scanner is considered to be a disadvantage for patient management.
Highlights
AND PURPOSE: Since the introduction of flat panel detector– equipped C-arms, the use of flat panel detector CT (FPCT) in the neuroradiologic angiography suite has become more frequent
The high-speed scans used for 3D-digital subtraction angiography (DSA) revealed a significantly lower CTDIw and dose-length product (DLP) compared with clinical CT
The high-quality FPCT protocol resulted in a higher dose and should be limited to acute cases, when patient transfer to a CT scanner is considered to be a disadvantage for patient management
Summary
Exposure data obtained for routine scanning during a period of 1 year were used to assess a specific dose of a total of 217 rotational scans performed in 105 patients. Exposure data and dose values were compared with cCT. Detruncation software is included by the manufacturer to correct for respective artifacts.[2] The system uses an automatic exposure control (AEC), which modulates the exposure settings (exposure time, tube current, and tube voltage) with respect to the detector entrance dose (DED).[2] The modulation method is attenuation based, and large differences are expected for different body regions or patient cross-sections. The mAs level (tube current ϫ exposure time per pulse) is changed; in a second step, with a lower priority, the tube voltage is adapted if the desired DED cannot be achieved with the mAs-modulation only
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