Omnipaque 350

CTA was performed using a 64-channel multidetector CT scanner (GE Optima CT660, GE Healthcare, USA) with IV bolus administration of a nonionic contrast medium (Omnipaque 350, GE Healthcare, USA). The scanning parameters included collimation of 39.38 × 0.625 mm, a spiral pitch of 0.984, a tube voltage of 120 kV, a tube amperage of 450 mA, a 0.4 s rotation time, and a slice thickness of 0.625 mm. A total of 50 mL of contrast medium followed by 30 mL of saline solution was injected into an antecubital vein at a rate of 4–4.5 mL/sec using a power injection platform (LF OptiVantage DH, USA). CT scanning was triggered by using a Smart Prep protocol, with the region of interest placed in the common carotid artery. Image acquisition started 5 sec after the attenuation reached 100 HU. The scanning time was approximately 4.5–6.0 s.

A 320-row CT system (Aquilion ONE, Toshiba, Otawara, Japan) was used in all patients for CTPA scanning. All the exams were performed with non-ECG-gated helical scan protocol. Patients were positioned supine and feet first into the gantry. Dual scanograms were used for determination of the anatomical coverage. The volume was placed to cover the entire lung fields from the pulmonary apex to the posterior costophrenic angle. Each volume CTPA data acquisition was acquired with a single breath-hold. The CT gantry rotation time was 330 ms. The tube voltage was 100–120 kV; effective tube current was 200–300 mA adjusted by personal body mass index (BMI). The collimation was 0.625 mm; pitch was 0.99. All the data were reconstructed using a standard soft-tissue and lung kernel (FC56). Images were reconstructed with slice thickness of 0.9 mm, interval of 0.45 mm.
A total of 40–50 mL contrast medium (Omnipaque 350, GE Healthcare, Shanghai, China) was intravenously injected by using a dual-head power injector with the injection rate of 3.5–4.5 mL/s adjusted according to BMI and the CT data acquisition time. A saline chaser bolus of 30 mL was injected with the same rate as the contrast medium. A region of interest was placed at the level of the main pulmonary artery for bolus tracking. The exposure was triggered with a 5 s delay after the 150 HU threshold was reached.

After Institutional Animal Care and Use Committee approval, 10 ablations were created in two 45 kg female swine in an operating suite with an incorporated CT (Siemens, Munich, Germany). Pre-procedural contrast-enhanced CT (50 cc/injection, Omnipaque 350 mg/ml, GE Healthcare, Waukesha, WI, USA) was used to visualize the hepatic vasculature and plan multiple ablation sites in the liver at varying proximity to 3 to 10 mm diameter vessels. A 3 cm LeVeen RFA electrode was positioned under CT guidance to obtain non-overlapping ablations. After CT documentation of probe position, the RF power was applied per protocol (Boston Scientific RF 3000 generator) and the power and electrical impedance sampled at 1 second intervals using a laptop PC connected to the RF generator via serial port; data was saved to disk and later fed to the RFA Physics Library to simulate the ablation.
At each site, a post-ablation contrast-enhanced CT scan was acquired, from which the true ablation volume was segmented (Fig 4a). The lesion geometry was segmented manually using ITK-SNAP (http://www.itksnap.org/).

All patients underwent CT of the chest, abdomen, and pelvis to identify metastases. All chest CT examinations were acquired from the lung apices through the lung bases using 8-row detector CT (Eclos; Hitachi Medical Corporation, Tokyo, Japan) or 40-row detector CT (Somatom Definition AS; Siemens Medical Systems, Erlangen, Germany) using the following parameters: section thickness of 2.5 and 3 mm, reconstruction (Bf70 algorithm) 2.5 or 2 mm, gantry rotation time 0.8 or 0.5 s, pitch 0.7 or 0.8, tube potential 120 kV, and mAs setting adjusted for body weight. All patients received intravenous contrast medium (2 mL/kg; flow rate 3 mL/s; Omnipaque 350; GE Healthcare-Milano-Italy).
CT images were reviewed and interpreted by two radiologists (S.E and P.R.) with 3 and 5 years experience of chest CT interpretation. Both specialists were presented with the patients’ clinical history, but were unaware of histological findings. Pulmonary nodules were assessed for size, number, location (upper, middle or lower lobe). Nodule size was defined as the largest diameter measured with electronic calipers on the CT images. Moreover, the nodules were classified according to their size, attenuation (solid or partly solid or ground glass) and growth.

Depending on the site of injection, no smaller than a 20-gauge needle was used to inject 100 cc of the contrast agent Isovue-370 (Bracco Diagnostics Inc, Monroe Township, NJ) or Omnipaque-350 (GE Healthcare, Princeton, NJ) into the antecubital fossa at a rate of 4 cc/s. The first cine image was acquired after an upfront 8-second delay. After the first blush of contrast was observed in the MPA, the CT scan was initiated and the image was acquired during an approximate 3- to 5-second breath-hold. The total delay time before imaging ranged from 13 to 18 seconds.