Fast Estimation of the Vascular Cooling in RFA Based on Numerical Simulation.

We present a novel technique to predict the outcome of an RF ablation, including the vascular cooling effect. The main idea is to separate the problem into a patient independent part, which has to be performed only once for every applicator model and generator setting, and a patient dependent part, which can be performed very fast. The patient independent part fills a look-up table of the cooling effects of blood vessels, depending on the vessel radius and the distance of the RF applicator from the vessel, using a numerical simulation of the ablation process. The patient dependent part, on the other hand, only consists of a number of table look-up processes. The paper presents this main idea, along with the required steps for its implementation. First results of the computation and the related ex-vivo evaluation are presented and discussed. The paper concludes with future extensions and improvements of the approach.

The value of combined soft-tissue and vessel visualisation before transarterial chemoembolisation of the liver using C-arm computed tomography.

The purpose of the study was to prospectively evaluate intrahepatic vessel depiction on C-arm CT (CACT) and the influence of the additional combined tissue and three-dimensional vessel visualisation on the positioning of the TACE catheter in comparison to DSA alone. Thirty consecutive patients scheduled for their first transarterial chemoembolisation underwent biphasic CACT and DSA of the liver. After assessing the DSA images for procedure planning, the CACT images were reviewed. The number and origin of the tumour-feeding arteries and the ideal position of the catheter for TACE on both DSA and CACT were assessed and correlated. The number of vessels identified as tumour feeders in each patient was significantly higher using additional CACT than on DSA alone (CACT: 4.0 +/- 1.7; DSA: 3.3 +/- 1.4; P = 0.003, t-test). After considering CACT, in 50% of the patients the catheter position was changed for TACE. Segmental portal vein thrombosis was seen in three patients on CACT, but in only one on DSA. As CACT depicts soft tissue and small vessels with high spatial resolution, tumour vessel allocation is facilitated, and ideal catheter position for TACE can be more accurately identified. The high impact of CACT on the TACE procedure suggests the benefits of its routine use for all patients undergoing their first TACE.

Ex situ quantification of the cooling effect of liver vessels on radiofrequency ablation.

PURPOSE: To quantify the cooling effect of hepatic vessels on liver radiofrequency (RF) ablation ex situ. METHODS: Bipolar RF applicators (diameter = 1.8 mm, electrode length = 30 mm) were inserted parallel to perfused glass tubes (diameter = 5 and 10 mm; flow = 250-1,800 ml/min) at distances of 5 and 10 mm in porcine livers ex vivo. RF ablation was performed at 30 W/15 kJ. RF lesions were analyzed by measuring the maximum (r (max)) and minimum radius (r (min)) and the lesion area. RESULTS: Glass tubes without flow showed no influence on RF lesions, whereas perfused glass tubes had a significant cooling effect on lesions. r (min) was reduced to 50% at 5 mm applicator-to-vessel distance and the lesion area was reduced from 407 to 321 mm(2) (p < 0.001). There was no significant influence of glass tube diameter or flow volume on any of the analyzed parameters. CONCLUSIONS: Cooling effects of intrahepatic vessels could be simulated in an ex situ model. Cooling effects should be taken into account in RF ablation within 10 mm distance to major liver vessels regardless of blood flow volume or vessel diameter. Surgical RF ablation with temporary blood flow occlusion should be considered in such constellations.

Magnetic resonance imaging-guided renal artery stent placement in a Swine model: comparison of two tracking techniques.

BACKGROUND: Magnetic resonance (MR)-guided interventions have evolved from a pure research application to a preclinical method over the last decade. Among the device-tracking techniques, susceptibility artifact-based tracking relies on the contrast between the surrounding blood and the device, and radiofrequency coil-based tracking relies on the local gradient field amplification in a resonating circuit attached to the interventional device. PURPOSE: To evaluate the feasibility and precision of susceptibility artifact-based and microcoil-based MR guidance methods for renal artery stent placement in a swine model. MATERIAL AND METHODS: MR imaging-guided renal artery stent placements were performed in six fully anesthetized pigs using a 1.5T short-bore MR scanner. Susceptibility artifact-based tracking with manual scan-plane adjustments and microcoil tracking with automatic scan-plane adjustments were used for renal artery stent placements in three pigs in each group. With both methods, near real-time steady-state free-precession (SSFP) imaging was used. Differences between the two tracking approaches on stenting time, total procedure time, and stent position were measured. RESULTS: The microcoil-based approach yielded a shorter mean procedure time (17 vs. 23 min). There was no relevant difference for the mean stenting time (12 vs. 13 min). The mean stent deviation from the aortic wall with the susceptibility approach was larger than with the microcoil approach (10 vs. 4.0 mm). CONCLUSION: For MRI-guided renal artery stent placement, the microcoil-based technique had a shorter procedure time and a higher stent placement precision than the susceptibility artifact-based approach.

Quantitative and qualitative evaluation of the influence of different table feeds on visualization of peripheral arteries in CT angiography of aortoiliac and lower extremity arteries.

The influence of different table feeds (TF) on vascular enhancement and image quality in patients undergoing lower extremity runoff-CTA for peripheral artery occlusive disease (PAOD), acute ischemia (AI) or abdominal aortic aneurysm (AAA) with PAOD was investigated retrospectively. One hundred eighty-five patients (PAOD: n = 132; AI: n = 40; AAA: n = 13) underwent 16-detector runoff-CTA (120 kV; 140 mAs; rotation time 0.5 s, collimation 16 x 1.5 mm) using different TF (30 mm/s: n = 25; 40 mm/s: n = 91; 48 mm/s: n = 36; 56 mm/s: n = 33). Vascular enhancement of the large arteries was measured every 10 cm along the z-axis from the upper abdomen to the toe. Arterial enhancement in the distal lower leg was compared (ANOVA, Bonferroni post-test). Qualitative assessment of bolus timing was performed independently by two radiologists. The study was IRB approved. In patients with PAOD or AI, enhancement of calf arteries using a TF of 48 mm/s (278 +/- 79 HU) was significantly higher in comparison to two slower TF (30 mm/s: 201 +/- 70 HU, P < 0.001; 40 mm/s: 251 +/- 79 HU, P < 0.05; 56 mm/s: 261 +/- 57 HU, NS) and the fewest noninterpretable arterial segments below the knee were observed with a TF of 48 mm/s (reader 1: 5/121 = 4.1%; reader 2: 4/121 = 3.3%). In patients with AAA, the fewest nondiagnostic segments occurred with a TF of 30 mm/s (2/12 = 17%, both readers) and 40 mm/s (4/24 = 17%, both readers). A TF of 48 mm/s provided the best synchronization of CT data acquisition and contrast bolus propagation and thus the best image quality in patients with PAOD and AI. In patients with AAA, a slower TF of 30 mm/s provided better image quality than faster CT protocols.

[CT-based liver volumetry in a porcine model: impact on clinical volumetry prior to living donated liver transplantation]. / CT-basierte Lebervolumetrie im Tiermodell: Bedeutung für die klinische Volumetrie im Rahmen der Leberlebendspende.

PURPOSE: Exact preoperative determination of the liver volume is of great importance prior to hepatobiliary surgery, especially in living donated liver transplantation (LDLT). In the current literature, a strong correlation between preoperatively calculated and intraoperatively measured liver volumes has been described. Such accuracy seems questionable, primarily due to a difference in the perfusion state of the liver in situ versus after explantation. Purpose of the study was to asses the influence of the perfusion state on liver volume and the validity of the preoperative liver volumetry prior to LDLT. METHODS: In an experimental study, 20 porcine livers were examined. The livers were weighted and their volumes were determined by water displacement prior and after fluid infusion to achieve a pressure physiologically found in the liver veins. The liver volumes in the different perfusion states were calculated based on CT-data. The calculated values were compared with the volume measured by water displacement and the weight of the livers. RESULTS: Assessment of calculated CT volumes and water displacements at identical perfusion states showed a tight correlation and differed on average by 4 +/- 5 %. However, livers before and after fluid infusion showed a 33 +/- 8 % (350 +/- 150 ml) difference in volume. CONCLUSION: CT-volumetry acquires highly accurate data as confirmed by water displacement studies. However, the perfusion state has major impact on liver volume, which has to be accounted for in clinical use.