Biplane interventional pediatric system with cone‐beam CT: dose and image quality characterization for the default protocols

Abstract

The aim of this study was to assess image quality and radiation dose of a biplane angiographic system with cone‐beam CT (CBCT) capability tuned for pediatric cardiac procedures. The results of this study can be used to explore dose reduction techniques. For pulsed fluoroscopy and cine modes, polymethyl methacrylate phantoms of various thicknesses and a Leeds TOR 18‐FG test object were employed. Various fields of view (FOV) were selected. For CBCT, the study employed head and body dose phantoms, Catphan 504, and an anthropomorphic cardiology phantom. The study also compared two 3D rotational angiography protocols. The entrance surface air kerma per frame increases by a factor of 3–12 when comparing cine and fluoroscopy frames. The biggest difference in the signal‐to‐noise ratio between fluoroscopy and cine modes occurs at FOV 32 cm because fluoroscopy is acquired at a 1440×1440 pixel matrix size and in unbinned mode, whereas cine is acquired at 720×720 pixels and in binned mode. The high‐contrast spatial resolution of cine is better than that of fluoroscopy, except for FOV 32 cm, because fluoroscopy mode with 32 cm FOV is unbinned. Acquiring CBCT series with a 16 cm head phantom using the standard dose protocol results in a threefold dose increase compared with the low‐dose protocol. Although the amount of noise present in the images acquired with the low‐dose protocol is much higher than that obtained with the standard mode, the images present better spatial resolution. A 1 mm diameter rod with 250 Hounsfield units can be distinguished in reconstructed images with an 8 mm slice width. Pediatric‐specific protocols provide lower doses while maintaining sufficient image quality. The system offers a novel 3D imaging mode. The acquisition of CBCT images results in increased doses administered to the patients, but also provides further diagnostic information contained in the volumetric images. The assessed CBCT protocols provide images that are noisy, but with very good spatial resolution.PACS number(s): 87.59.‐e, 87.59.‐C, 87.59.‐cf, 87.59.Dj, 87.57. uq

Assessment of volumetric absorbed dose for mobile fluoroscopic 3D image acquisition

“…For a rotation of less than 360°, however, it is questionable whether four positions are sufficient, since either one or two of the measurement points may be outside the beam depending on the relative positions of the x‐ray tube arc and dosimeter. Previous studies have employed the use of four and eight measurement points, but they did not compare the accuracy of differing numbers of points. A study using a fixed c‐arm with 200° rotation found a variation of up to 10% in the CTDI W calculated when measurements were acquired at the four cardinal positions and when they were rotated by 45° …”

“…The traditional pencil chamber is insufficient to measure the entire beam in these scanners. Although alternate measurement techniques have been proposed to better measure wide beams, at this time, most clinical physicists do not have the equipment necessary to follow these recommendations. The International Atomic Energy Agency (IAEA) released a report in 2011 detailing a technique to calculate a CTDI for wide beam scanners using the standard 100‐mm pencil chamber and 32‐cm acrylic phantom, which was based on recommendations from the International Electrotechnical Commission and recommended for use by the wide‐beam CT dosimetry working party of the Institute of Physics and Engineering in Medicine .…”