| Summary: | 碩士 === 國立陽明大學 === 生物醫學影像暨放射科學系 === 101 === Background:
The flat-panel detector (FD), for its unique advantages of high detective quantum efficiency (DQE), high frame rates and spatial resolution, and wider dynamic range, has replaced traditional X-ray film in most clinical imaging procedures. Angiographic suites equipped with the FD providing one-stop imaging service (OSIS) is becoming potentially feasible in management of cerebral neurovascular diagonosis. In OSIS procedure, cerebral hemodynamic information (i.e. cerebral circulation time and parenchymal blood volume, PBV) is obtained in one imaging session, but radiation dose and hazard relevant to the OSIS remains one of the major clinical concerns before it can be adopted as a standard imaging strategy.
Purpose:
The aim of our study was to estimate the effective organ doses and their related cancer risks involved in assessing cerebral perfusion examinations between using flat detector computed tomography (FDCT) and 256-slice CT.
Materials and Methods:
In our study, the absorbed organ dose measurements using FDCT and 256-slice CT with an anthropomorphic phantom and thermo-luminescence dosimeters (TLDs) were performed. In 8cm and 16cm wide cerebral parenchymal blood volume (PBV) measurements, we used one standard digital subtraction angiography (DSA) imaging protocol (one 8-second rotational mask, run with 60 frames/second followed by another 8-second rotational contrast medium filled, run with same frame rate) was used. The scanning parameters in the 8cm PBV exam were: 73 kV, 486 mA, 4.0 ms, 48cm×48cm field-of-view (FOV), and in 16cm PBV exam, they were: 72 kV, 540 mA, 4.1 ms, 48cm×48cm FOV. The scanning ranges in 8cm and 16cm exams were from sella turcica to convexity and whole brain coverage, respectively. Eighty TLDs divided into 20 sets were subsequently placed into different organs of the Rando phantom, from the head to the pelvis. In the use of 256-slice CT to measure CT perfusion (CTP), the scanning coverage was identical to that of the 8cm PBV exam, and its scanning parameters were: 5 mm slice thickness, 64×1.25mm collimation, 20cm×20cm FOV, 80 kV, 250 mA, 100 mAs, 0.4 second tube rotation and exposure time, scan interval of 1.5 seconds and lasted for 1 minute. In effective organ doses calculation, we employed the report no. 103 guidelines of the International Commission on Radiological Protection (ICRP-103), and adopted the guidelines of Biological Effects of Ionizing Radiation (BEIR) report VII for related cancer risk assessments.
Results:
In our study, we found that the effective doses were 0.87 ± 0.55 and 3.91 ± 0.78 mSv, respectively for PBV_8cm and PBV_16cm protocols in FDCT exams, and the effective dose in CTP_8cm measured was 2.77 ± 1.59 mSv using the 256-slice CT. Potential cancer risks for organs within the primary radiation beam (e.g., brain) were higher than those outside the primary beam (e.g., thyroid). Nevertheless, the potential cancer risk of PBV_8cm in the FDCT was relatively less, comparing with a head scan of a conventional 256-slice CT.
Conclusions:
Our study concluded that cerebral PBV measurement using the FDCT was dose-saving and with advantages of high reproducibility and reliability. The effective organ doses were lower than those involved in CT perfusion study using 256-slice CT. Moreover, the OSIS procedure can save time on patient transportation and shorten scanning time in PBV measurement, making the FDCT be a potential recommended for cerebral neurovascular diagnosis.
Keywords:
flat detector computed tomography (FDCT), 256-slice CT, parenchymal blood volume (PBV), computed tomography perfusion (CTP), effective dose, risk assessment
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