Automa

Antemortem CT scans were performed for reasons of clinical necessity such as for diagnosis or to ascertain the condition of hospitalized patients. All scans included at least the chest; patients were not excluded from the study if other regions of the body were scanned.
All antemortem CT studies were performed on 64-detector-row helical CT scanners (Aquilion 64, Toshiba Medical Systems Corporation, Ohtawara, Japan; Discovery CT750 HD and LightSpeed VCT, GE Healthcare, Buckinghamshire, UK) in the craniocaudal direction with the patient in the supine position with both arms raised. The scan parameters were as follows: slice thickness, 5 mm; slice interval, 5 mm; rotation time, 0.5 s; and tube voltage, 120 kVp. AutomAtic tube current modulation was performed by Volume EC (Toshiba) and AutomA (GE). Images were reconstructed at 0.5 mm intervals with a 350 mm field of view and a 512×512 image matrix.

All patients were scanned with a 64-slice, high-definition CT scanner (Discovery HD 750, General Electric Healthcare). The scan range covered the whole lung, from the level of the pulmonary apex to the liver dome. All patients were required to hold their breath during the examination. Image acquisition parameters included collimation, 64×0.625 mm; slice thickness, 5 mm; pitch, 0.984; rotation time, 0.5 s; table speed, 78.75 mm/s; tube voltage, 100 kVp. Tube current modulation in the x, y, and z axes (Auto mA, GE Healthcare) was used, with a tube current range of 10–400 mA. The NI was set at 15 for group 1 as the standard protocol for a chest scan in our department. The NIs were set at 20, 30, and 40 for groups 2, 3, and 4, respectively. After each examination for the patients using NI = 40, images reconstructed with 30% ASIR were immediately reviewed by a radiologist on the operator console for image quality. If non-diagnostic images were obtained, a new study using NI = 30 was subsequently performed. This fact was mentioned in the informed consent.
A set of mixed reconstruction images with different levels of ASIR and FBP were generated, namely, 0% ASIR, 30% ASIR, 50% ASIR and 80% ASIR, in which 0% ASIR means 0% ASIR blended with 100% FBP, 30% ASIR means 30% ASIR blended with 70% FBP, etc. Therefore, each acquisition set had 4 series of images with different ASIR levels.

Acquisitions were performed on a 64-detector row CT scanner (Revolution GSI, GE Medical Systems). This scanner is equipped with OTCM (ODM, GE Medical Systems). OTCM constitutes a tube current modulation mode that reduces the mA when the tube travels across the anterior arch of the patient’s circumference without increasing it over the remaining lateral and posterior arches. To enable OTCM, the AutomAtic tube current modulation (ATCM) system (AutomA and SmartmA, GE Medical Systems) needs also to be activated. In head, the mA is reduced by up to 30% across 90° anterior projections, while in body, the mA is reduced by up to 40% across 180° anterior projections (Fig. 1) [18 ].Fig. 1

A graphical illustration of the configuration setup used in the MC simulation experiments showing the positioning of the phantom with regard to the angle of OTCM mA reduction. For head, the mA was reduced by 30% in 9 out of 36 tube positions, while for body, the mA was reduced by 40% in 18 out of 36 tube positions

PET acquisition started 60 min after intravenous injection of 370 MBq ¹⁸F-labelled Na F (IASOflu-IASON GmbHGraz, Austria) and included 10–12 bed positions. All PET scans were acquired in 3D mode (3 min emissions per bed position) and were reconstructed by using an iterative reconstruction algorithm. CT acquisition data were optimized to obtain diagnostic CT images also with small image reconstruction thickness using the following data: 120 kV, 120–400 mA with an automatic system of dose optimisation (Auto-mA, General Electric Medical Systems), tube rotation time 0.5 s, 16 mm × 1.25 mm detector configuration, and table feed 13.75 mm per rotation. Overall, we acquired only one CT scan, obtaining two image reconstruction thicknesses 3.75 mm (for attenuation correction and anatomic localization) and 1.25 mm (for multiplanar reconstruction). No iodinated contrast medium was injected. CT acquisition was performed from the skull vertex to the distal femur, with the same field of view used for ¹⁸F-Fluoride-PET.

The CT imaging procedures were described previously [16 (link)]. Briefly, two 64-detector-row CT scanners with the same specifications (Optima CT 660 Discovery Edition; GE Healthcare, Milwaukee, WI, USA) were used. After acquiring posteroanterior and lateral localizer images, axial CT images parallel to the orbitomeatal line were obtained in non-helical mode, covering the posterior fossa and the top of the brain. Tube current was determined by automatic exposure control (AEC) software—i.e., Auto mA and Smart mA (GE Healthcare)—to modulate radiation exposure according to the X-ray attenuation for each patient and at each imaging location [17 (link)]. The noise index was set to 4. Organ dose modulation was applied to the orbital region to reduce the radiation dose to the eye lens. [18 (link),19 (link)]. Other imaging parameters were as follows: tube voltage, 120 kV; rotation time, 1 s; beam width, 10 mm; slice thickness, 5 mm; and slice increment, 5 mm. The volume CT dose index (CTDIvol) provided by the CT scanner mentioned above was recorded and analyzed as an index of the radiation dose.

The imaging procedures were as described previously [21 (link)]. Briefly, two 64-detector-row CT scanners with the same specifications (Optima CT 660 Discovery Edition; GE Healthcare, Milwaukee, WI, USA) were used. After obtaining posteroanterior and lateral localizer images, axial CT images parallel to the orbitomeatal line were acquired in axial mode from the inferior margin of the posterior fossa to the top of the brain. The tube current was determined using AEC software (Auto mA and Smart mA; GE Healthcare), with a noise index of 4 [13 (link)]. Organ dose modulation was applied over the orbit to reduce the radiation dose to the eye lens [24 (link),25 (link)]. The other imaging parameters were as follows: tube voltage, 120 kV; rotation time, 1 s; beam collimation, 0.625 mm × 16; slice thickness, 5 mm; slice increment, 5 mm.