Volume viewer

CT scans were obtained on a MDCT (LightSpeed VCT XT; GE Healthcare, Milwaukee, WI, USA; or LightSpeed Pro 16; GE Healthcare). The scanners were set to the following parameters: detector collimation, 64 × 0.625 mm and 16 × 1.25 mm; helical pitch, 0.984 and 0.938; section thickness/interval, 3.75/3.75 mm and 3.75/3.75 mm; rotation time, 0.5 seconds; 120 kVp/300-500 mA and 120 Kvp/200-400 mA, respectively. Intravenous contrast (iopromide, Ultravist 370; Bayer Healthcare, Berlin, Germany) was injected at a rate of 3 mL/sec in a total volume of 130 mL through the antecubital vein using a mechanical injector. Bolus tracking was not applied, and scanning started 90 seconds after beginning the contrast injection. No oral contrast agent was used. Scanning regularly covered the region from the dome of the liver to the lower vagina. Coronal reformatted images of 3.0 mm section thickness and 3.0 mm reconstruction intervals were generated using the source CT data set and commercially available console software (Volume Viewer; GE Medical Systems, Waukesha, WI, USA). Radiation dose to the patients was monitored for each examination using the volume CT dose index (CTDI_vol) and dose length product (DLP), which were calculated by the CT scanner and were automatically saved to a dose report. The mean CTDI_vol value was 10.7 ± 2.1 mGy, and the mean DLP value was 530.3 ± 109.1 mGy·cm.

The MRE scan parameters were as follows: spin-echo echo-planar imaging (SE-EPI); TR/TE: 1000 ms/min full; matrix: 64 × 64; FOV: 42 cm × 42 cm; layer thickness: 10 mm; layer spacing: 5 mm; number of layers, 7; number of excitations, 1; bandwidth: ±250 kHz; driver frequency, 60 Hz; amplitude, 70 %; end-expiratory breath-hold scan; and a scanning duration of 17 s.
All acquired MRE images were automatically processed by the postprocessing software Volume Viewer (version 13.0, GE Healthcare) on the MR master computer, and wave images, elastograms, and magnitude images were generated using inversion algorithms. The elastogram forms crossed line regions (low-confidence data regions excluded by the postprocessing algorithm).
Two radiologists (the same two as before) selected the ROI (right branch level of the portal vein) in the right lobe region of the liver, including the two layers above this level and a total of three layers, using a weighted average for the measurements. The physicians drew the ROI to include as much of the liver parenchyma as possible, with a minimum area >3 cm², while avoiding large vessels, bile ducts, and areas in the 1 cm surrounding the liver or in the cross-shadow areas (low-confidence data areas). Two radiologists recorded the postprocessing time for each patient.

We have retrospectively selected the preoperative coronal three-dimensional computed tomography angiography (3D-CTA) images of 44 unruptured cases out of the 81 cases because the morphology of the SDCP was not demonstrated accurately in the cases of subarachnoid hemorrhage. We used the workstation of GE Healthcare (Volume Viewer^Ⓡ) and selected a slice of coronal 3D-CTA images at the site corresponding to the limen insula on a slice of axial 3D-CTA images for each case. These images demonstrated the SDCP well and each width of subarachnoid space between the OG and the PP was measured at the three points as follows: Point A which was the lateral superior subarachnoid space of the SDCP, Point B which was the downward subarachnoid space of the SDCP, and Point C which was the medial inferior subarachnoid space of the SDCP (Fig. 1e).