Minimal vascular flows cause strong heat sink effects in hepatic radiofrequency ablation ex vivo.

BACKGROUND: The present paper aims to assess the lower threshold of vascular flow rate on the heat sink effect in bipolar radiofrequency ablation (RFA) ex vivo. METHODS: Glass tubes (vessels) of 3.4 mm inner diameter were introduced in parallel to bipolar RFA applicators into porcine liver ex vivo. Vessels were perfused with flow rates of 0 to 1,500 ml/min. RFA (30 W power, 15 kJ energy input) was carried out at room temperature and 37°C. Heat sink effects were assessed in RFA cross sections by the decrease in ablation radius, area and by a high-resolution sector planimetry. RESULTS: Flow rates of 1 ml/min already caused a significant cooling effect (P ≤ 0.001). The heat sink effect reached a maximum at 10 ml/min (18.4 mm/s) and remained stable for flow rates up to 1,500 ml/min. CONCLUSIONS: Minimal vascular flows of ≥1 ml/min cause a significant heat sink effect in hepatic RFA ex vivo. A lower limit for volumetric flow rate was not found. The maximum of the heat sink effect was reached at a flow rate of 10 ml/min and remained stable for flow rates up to 1,500 ml/min. Hepatic inflow occlusion should be considered in RFA close to hepatic vessels.

Hepatic transit time analysis using contrast enhanced MRI with Gd-BOPTA: A prospective study comparing patients with liver metastases from colorectal cancer and healthy volunteers.

PURPOSE: To find out if the hepatic transit time (HTT) shortening, which was already proven in patients with liver metastases by other modalities, can also be detected with MRI. MATERIALS AND METHODS: The Patient group consisted of 20 subjects with liver metastases from colorectal cancer and the control group of 21 healthy subjects. Baseline and post contrast images were acquired before and after administration of Gd-BOPTA, using a T1-weighted bolus test sequence. Arrival times (AT) of the contrast agent for the aorta, the hepatic artery, the portal vein and one hepatic vein were determined. Based on arrival time measurements HTT were calculated. RESULTS: All analyses showed significantly shorter HTT in patients with metastases compared with healthy volunteers (P < 0.05). There were no false positives using a threshold of 10.4 s for arterial to venous HTT. For aortal to venous and portal to venous HTT a threshold of 12.5 s and 4 s was calculated, respectively. No significant correlation between HTT and involved liver segments, overall volume of metastases or subject age was found. CONCLUSION: We conclude that HTT measurements using contrast enhanced MRI with Gd-BOPTA can detect hemodynamic changes due to metastatic liver disease from colorectal cancer.

Gadofluorine M-enhanced magnetic resonance imaging of inflammatory bowel disease: quantitative analysis and histologic correlation in a rat model.

OBJECTIVES: : To determine the colonic mural enhancement in a rat model of inflammatory bowel disease (IBD) using gadofluorine M- and diethylenetriamine pentaacetic acid (Gd-DTPA)-enhanced magnetic resonance (MR) imaging, and to correlate the degree of enhancement with the histopathologic severity of the disease. MATERIALS AND METHODS: : This study was approved by our hospital's institutional animal care and use committee. A total of 44 rats with 2 grades (mild, n = 17; and severe, n = 27) of dinitrobenzene sulfonic acid (DNBS)-induced IBD and 13 rats without IBD, were examined using a 2.4-T, small animal MR scanner. T2- and T1-weighted MR images were acquired, and sequential T1-weighted MR imaging was then performed immediately and again 15, 45, 60, and 90 minutes, and 24 hours after intravenous -injection of either gadofluorine M- or Gd-DTPA (0.1 mmol Gd/kg body weight). The signal-to-noise ratios and enhancement ratios (ER) of the colon wall were measured. For paired and group comparisons of the histopathology and MR imaging data, the Wilcoxon- and the Mann-Whitney U tests were used, and the multifactorial analysis of variance test was used to compare the time courses of the ERs. RESULTS: : Gadofluorine M injection resulted in significant differences in the ER of noninflamed, mildly inflamed, and severely inflamed colon wall at any time up to 24 hours after contrast injection (ER at 24 hours 2.0 ± 1.2; 10.1 ± 4.3; and 49.7 ± 10.8, respectively; P < 0.01). After Gd-DTPA injection, significant differences were observed in the ER of inflamed and noninflamed bowel at 15, 45, and 60 minutes (P < 0.01); however, no significant differences in mildly and severely inflamed bowel were observed at any time. In contrast to Gadofluorine M, there was no prolonged contrast enhancement in the inflamed colon wall after intravenous injection of Gd-DTPA (ER at 24 hours 1.6 ± 1.3; 3.4 ± 2.7; and 3.3 ± 1.6, respectively; n.s.). CONCLUSIONS: : Gadofluorine M-enhanced MR imaging shows a higher correlation of the wall enhancement and histopathology grading in an IBD rat model than does Gd-DTPA-enhanced imaging.

Qualitative and quantitative evaluation of hepatocellular carcinoma and cirrhotic liver enhancement using Gd-EOB-DTPA.

OBJECTIVE: The objective of our study was to prospectively evaluate quantitatively and qualitatively the enhancement patterns of cirrhotic liver tissue and hepatocellular carcinoma (HCC) after administration of the hepatocyte-specific contrast agent gadolinium ethoxybenzyl diethylenetriamine pentaacetic acid (Gd-EOB-DTPA) on dynamic MRI and to determine the time point of maximum liver-to-lesion contrast. SUBJECTS AND METHODS: Twenty-five patients with HCC in liver cirrhosis underwent 1.5-T MRI. T2-weighted turbo spin-echo and T1-weighted 3D gradient-echo sequences before and between 15 seconds and 20 minutes after the injection of 10 mL of Gd-EOB-DTPA were performed. Signal-to-noise ratios (SNRs) of liver parenchyma and liver-to-lesion contrast-to-noise ratios (CNRs) were calculated and plotted over time. Enhancement patterns of HCC were characterized qualitatively by two radiologists. RESULTS: The SNR of liver parenchyma increased significantly at 15 seconds and 60 seconds after contrast injection and remained stable thereafter. HCC showed positive CNR during the arterial phase and increasingly negative CNR during the further time course (p < 0.05). The maximum absolute CNR was found at 20 minutes after contrast injection. There was no correlation between the degree of enhancement at any time point and tumor grade. On qualitative evaluation, 16 HCCs showed arterial enhancement with early washout, and five showed arterial enhancement with late washout. In the remaining four HCCs, enhancement persisted until 20 minutes. Lesion conspicuity at 20 minutes after contrast injection was at least equal to or higher than it was on the remaining sequences in 19 of the 25 patients. CONCLUSION: After Gd-EOB-DTPA injection, most HCCs showed typical arterial enhancement with early washout. Liver-to-lesion contrast was best at 20 minutes.

Hepatic transit time analysis using contrast-enhanced ultrasound with BR1: A prospective study comparing patients with liver metastases from colorectal cancer with healthy volunteers.

We prospectively compared hepatic transit time (HTT) measurements in subjects with liver metastases from colorectal cancer (group a) and healthy volunteers (group b) using contrast-enhanced ultrasound with BR1. The purpose of this study was to verify our hypothesis that the hemodynamic changes of the liver, which occur during metastasis seeding, would shorten the HTT, and we expect that such changes could be used for the detection of occult liver metastases from colorectal cancer in the future. The study had institutional review board approval and all subjects gave informed written consent. Group a and group b consisted of 22 subjects each. Baseline and post contrast images were acquired starting 10 s before and ending 40 s after administration of BR1, using nonlinear imaging at a frame rate of 5/s. The baseline images were used to determine the signal intensity without contrast enhancement as the reference signal. Arrival times (AT) of the contrast agent for the hepatic artery, the portal vein and one hepatic vein were determined using (i) quantitative analysis and (ii) subjective analysis by two blinded readers. HTT was calculated based on arrival time measurements. Quantitative and subjective analysis showed significantly shorter arterial to venous and portal to venous HTT in group a compared with group b (p < 0.001). Arterial to venous HTT (quantitative analysis) was < or = 9 s in 19 of 22 subjects of group a and >9 s in 18 of 22 subjects of group b (sensitivity 86%, specificity 82%, positive predictive value 83%, negative predictive value 86%, area under the curve [AUC] 0.87). Portal to venous HTT (quantitative analysis) was < 7 s in 21 of 22 subjects of group a and > 7s in 15 of 22 subjects of group b (sensitivity 95%, specificity 68%, PPV 75%, NPV 94%, AUC 0.85). There was an inverse relation with number of liver segments involved for arterial to venous and portal to venous HTT in group a (p < 0.05), but no correlation between HTT and overall volume of metastases (group a) or subject age (group b). From the results of our study, we conclude that HTT measurements using contrast-enhanced ultrasound with BR1 can detect hemodynamic changes caused by metastatic liver disease from colorectal cancer. However, comparison with the literature suggests that the use of other contrast agents might provide better results. Comparison of different contrast agents for the purpose of transit time analysis would therefore be useful before embarking on a prospective trial looking at the detection of occult liver metastases in patients with colorectal cancer. (E-mail: jhohmann@uhbs.ch).

Magnetic resonance imaging of experimental inflammatory bowel disease: quantitative and qualitative analyses with histopathologic correlation in a rat model using the ultrasmall iron oxide SHU 555 C.

OBJECTIVES: To quantitatively and qualitatively characterize the MR findings of inflammatory bowel disease in a rat model after i.v. injection of the reticuloendothelial system cell specific ultrasmall iron oxide SHU 555 C. MATERIALS AND METHODS: Colitis was induced in 15 rats using dinitrobenzene sulfonic acid instillation. Five rats served as controls. T1- and T2-weighted spin-echo- and T2*-weighted gradient-echo-sequences were acquired at 2.4 Tesla before and immediately, 15, 45, 60, and 90 minutes, and 24 hours after i.v.-injection of SHU 555 C (0.1 mmol Fe/kg). MR images were evaluated quantitatively regarding thickness and signal-to-noise ratio (SNR) of the bowel wall and qualitatively regarding overall bowel wall signal intensity and the occurrence of bowel wall ulcerations. MR findings were correlated to histology. RESULTS: The inflamed bowel wall was significantly thicker than the noninflamed bowel wall and 90 minutes after contrast injection it showed a significant reduction of SNR in T1- (94 +/- 27 vs. 61 +/- 29; P < 0.01), T2- (67 +/- 26 vs. 28 +/- 17; P < 0.05), and T2*- (92 +/- 57 vs. 10 +/- 7; P < 0.05) weighted images as compared with unenhanced images. At 24 hours, the respective SNR values remained significantly reduced. The signal loss was homogeneous in 12 and focal in 3 of the 15 rats with colitis. Nine rats showed colonic wall ulcerations. In all but one animal (missed focal ulceration) MR findings correlated to the histologic findings. CONCLUSIONS: SHU 555 C leads to a significant signal intensity loss of the inflamed bowel wall in T1-, T2- and T2*-weighted images. SHU 555 C enhanced MRI findings correlate well with histologic findings.

Electromagnetic field-based navigation for percutaneous punctures on C-arm CT: experimental evaluation and clinical application.

The aim of this study was to prospectively evaluate the needle visualization and placement error and use of an electromagnetic field-based tracking navigation device for puncture procedures based on C-arm CT (CACT) images. A commercially available navigation device was mounted on an angiographic X-ray system setup for CACT. After the target was defined, needle placement was performed under real-time visualization of the virtual needle in CACT images. The final, real needle position was assessed by CACT. Punctures were performed in phantoms (n = 76) and in twelve patients (eight biopsies, three drainages, one injection). Procedure times, system error, user error and total error were assessed. In phantoms, mean total error was 2.3 +/- 0.9 mm, user error was 1.4 +/- 0.8 mm and system error was 1.7 +/- 0.8 mm. In the patient study, the targeted puncture was successful in all twelve cases. The mean total error was 5.4 mm +/- 1.9 mm (maximum 8.1 mm), user error was 3.7 +/- 1.7 mm, system error was 3.2 +/- 1.4 mm and mean skin-to-target time was less than 1 min. The navigation device relying on CACT was accurate in terms of needle visualization and useful for needle placement under both experimental and clinical conditions. For more complex procedures, electromagnetic field-based tracking guidance might be of help in facilitating the puncture and reducing both the puncture risk and procedure time.

Portal vein segmentation of a 3D-planning system for liver surgery--in vivo evaluation in a porcine model.

BACKGROUND: Computer systems allow the planning of complex liver operations. The segmentation of intrahepatic vessels builds the basis for the calculation of liver segments and resection proposals. For surgical use, it is essential to know the capabilities and limitations of the segmentation. The aim of this study was to determine the sensitivity and precision of the portal vein segmentation of a computer planning system for liver surgery in vivo. METHODS: Segmentations were performed with the software system HepaVision on computed tomography (CT) scan data of domestic pigs. An in situ corrosion cast of the portal vein served as the gold standard. The segmentation results of the portal vein and the corrosion cast were compared with regard to sensitivity, precision, and amount of short-circuit segmentations. RESULTS: The methodology demonstrated high resolution ex situ. The in vivo sensitivity of the portal vein segmentation was 100% for vessels of more than 5 mm in diameter and 82% for vessels of 3-4 mm. All segment branches were detected as well as 84% of the first subsegment branches with a diameter of more than 3 mm. The precision of the system was 100% for segment branches and 89% for the first subsegment vessels. The amount of internal short-circuit segmentations was less than 3.0%. No external short-circuits were found. CONCLUSION: The system has a high precision and sensitivity under clinical conditions. The segmentation is suitable for portal vein branches of the first and second order and for vessels of >/=3 mm in diameter.

Visualization of hypervascular liver lesions During TACE: comparison of angiographic C-arm CT and MDCT.

OBJECTIVE: The purpose of our study was to evaluate the diagnostic accuracy and scan coverage of flat-detector C-arm CT compared with that of biphasic MDCT for depicting malignant hepatic lesions in patients with hypervascular liver tumors before they undergo transarterial chemoembolization (TACE). MATERIALS AND METHODS: Fifteen patients with either hepatocellular carcinoma (HCC, n = 8) or hypervascular liver metastases from uveal melanoma (n = 7) underwent arterial and portal venous C-arm CT of the liver using intraarterial contrast media administration directly before TACE. The number and location of their hepatic malignancies were compared with those on MDCT. The scan coverage was documented and the liver diameter measured on MDCT. RESULTS: Compared with MDCT, the sensitivity and specificity for segmental tumor involvement were 97% (76/78) and 85% (28/33), respectively, for reader 1, and 99% (77/78) and 79% (24/29), respectively, for reader 2. Complete scan coverage of the liver was obtained in five of the 15 patients with C-arm CT. In patients with incomplete scan coverage on C-arm CT, the craniocaudal liver diameter was significantly larger than in those patients with complete scan coverage (mean [95% CI], 22.7 [19.5-25.9] cm vs 20.2 [15.4-25.0] cm, p = 0.0193). CONCLUSION: Biphasic arterial and portal venous C-arm CT showed a high sensitivity for the detection of malignant liver lesions. However, the liver could not be visualized completely in two thirds of the patients. Therefore, the current scan range limitations need to be overcome to make C-arm CT a valuable adjunct to MDCT for preprocedure evaluation and postprocedure follow-up imaging.

Influence of intrahepatic vessels on volume and shape of percutaneous thermal ablation zones: in vivo evaluation in a porcine model.

OBJECTIVES: Aim of the study was to evaluate the precise influence of different intrahepatic vessels, vessel sizes, and distances from the applicator on volume and shape of hepatic laser ablation zones in an in vivo porcine model. MATERIALS AND METHODS: The study was approved by the institutional animal care and use committee. Eighteen computed tomography-guided Nd:YAG laser ablations were performed in the livers of 10 pigs at varying distances from hepatic veins and portal fields. After hepatectomy the livers were cut into 2-mm slices perpendicular to the laser applicator axes. For each ablation zone the maximum achievable (ideal) volume, the segmented (real) volume, the maximum radius, and the radius at the position of adjacent hepatic vessels were determined. The shapes of the ablation zones were evaluated qualitatively. Comparative statistics using the unpaired t test and a multiple linear regression analysis were performed. RESULTS: Ideal and real ablation zone volumes differed by 27.3% (8.6 +/- 1.5 mL vs. 6.4 +/- 1.1 mL; P < 0.0001). Thirty-eight of 60 (63%) hepatic veins versus 28 of 31 (90%) portal veins within the central slices of the 18 ablation zones led to a reduction of the ablation zone's radius, depending on the distance between the vessel and the applicator and the vessel type. Portal fields revealed stronger effects than hepatic veins. The vessel diameter showed no independent effect (P > 0.05). When influencing, all hepatic veins showed a focal indentation whereas portal fields always showed broad flattening of the ablation zone. CONCLUSIONS: Portal fields lead to more heat sink than hepatic veins. The effects decreased with the distance between vessel and applicator tip, but less so for portal fields. The 2 vessel types induced considerably different shape alterations of the ablation zones. These results were not dependent on vessel size. This should be considered in the planning of thermal tumor ablations.

MRI of the thorax during whole-body MRI: evaluation of different MR sequences and comparison to thoracic multidetector computed tomography (MDCT).

PURPOSE: To evaluate the accuracy of four MR sequences used as part of a whole-body MRI protocol to detect pulmonary lesions in cancer patients. MATERIALS AND METHODS: A total of 31 oncology patients were imaged in a 1.5T MR scanner (Magnetom Avanto; Siemens Medical Solutions, Germany) for whole-body staging. MR chest imaging included: axial and coronal T2-weighted (T2w)-short-tau inversion-recovery (STIR), axial T2w turbo spin-echo (TSE), and contrast-enhanced (CE) three-dimensional (3D) volumetric interpolated breathhold examination (VIBE). Multidetector computed tomography (MDCT) of the thorax served as the reference standard. The MDCT and MR images were evaluated independently by two radiologists. Comparative analysis was performed per lesion, per lobe, and per patient. Sensitivity, specificity, and predictive values were determined. RESULTS: Compared to MDCT that detected 268 pulmonary lesions ranging from 2 to 75 mm in diameter, the MR sensitivities were 91.1%, 92.5%, 90.8%, and 87.3% for the coronal STIR, the axial STIR, the axial T2w-TSE, and the axial CE 3D-VIBE, respectively. Undetected pulmonary lesions were either calcified or smaller than 10 mm in the axial diameter. With coronal STIR, six false-positive findings were detected; with axial STIR, 14 were detected; with axial T2w-TSE, 10 were detected; and with 3D-VIBE, seven were detected. CONCLUSION: Pulmonary MRI is feasible as part of a whole-body MRI protocol. In our study, STIR images achieved high accuracy compared to chest MDCT for pulmonary lesions of 3 mm in size or larger.

Preoperative volume calculation of the hepatic venous draining areas with multi-detector row CT in adult living donor liver transplantation: Impact on surgical procedure.

OBJECTIVE: The purpose was to assess the volumes of the different hepatic territories and especially the drainage of the right paramedian sector in adult living donor liver transplantation (ALDLT). METHODS: CT was performed in 40 potential donors of whom 28 underwent partial living donation. Data sets of all potential donors were postprocessed using dedicated software for segmentation, volumetric analysis and visualization of liver territories. During an initial period, volumes and shapes of liver parts were calculated based on the individual portal venous perfusion areas. After partial hepatic congestion occurring in three grafts, drainage territories with special regard to MHV tributaries from the right paramedian sector, and the IRHV were calculated additionally. Results were visualized three-dimensionally and compared to the intraoperative findings. RESULTS: Calculated graft volumes based on hepatic venous drainage and graft weights correlated significantly (r = 0.86, P < 0.001). Mean virtual graft volume was 930 ml and drained as follows: RHV: 680 ml, IRHV: 170 ml (n = 11); segment 5 MHV tributaries: 100 ml (n = 16); segment 8 MHV tributaries: 110 ml (n = 20). When present, the mean aberrant venous drainage fraction of the right liver lobe was 28%. CONCLUSION: The evaluated protocol allowed a reliable calculation of the hepatic venous draining areas and led to a change in the hepatic venous reconstruction strategy at our institution.

Multipolar radiofrequency ablation of hepatic tumors: initial experience.

Institutional review board approval and patient informed consent were obtained. Use of a multipolar radiofrequency (RF) ablation device in patients with hepatic malignancy was prospectively evaluated with regard to feasibility, achieved ablation zone size and shape, technical effectiveness, and complications. Nineteen malignant liver tumors were treated with the multipolar resistance-controlled RF ablation system, with which up to three internally cooled bipolar coagulation electrodes can be operated simultaneously. Postinterventional imaging was performed with dynamic contrast material-enhanced magnetic resonance (MR) imaging and MR imaging-based three-dimensional planimetry. Complete tumor destruction was achieved in 18 of 19 tumors. Mean ablation zone volume was 52 mL +/- 45 (standard deviation). Thirteen patients were treated with a percutaneous approach; six, with an intraoperative approach. Maximum ablation size was 91 x 62 x 79 mm with the percutaneous and 73 x 98 x 74 mm with the intraoperative approach. Of the 18 completely evaluable ablation zones, 13 were concentric, two were moderately eccentric, two were eccentric, and one was wedge-shaped. The multipolar RF ablation device achieves large ablation zones and has high technical effectiveness in treating hepatic tumors.

3D CT modeling of hepatic vessel architecture and volume calculation in living donated liver transplantation.

The aim of this study was to evaluate a software tool for non-invasive preoperative volumetric assessment of potential donors in living donated liver transplantation (LDLT). Biphasic helical CT was performed in 56 potential donors. Data sets were post-processed using a non-commercial software tool for segmentation, volumetric analysis and visualisation of liver segments. Semi-automatic definition of liver margins allowed the segmentation of parenchyma. Hepatic vessels were delineated using a region-growing algorithm with automatically determined thresholds. Volumes and shapes of liver segments were calculated automatically based on individual portal-venous branches. Results were visualised three-dimensionally and statistically compared with conventional volumetry and the intraoperative findings in 27 transplanted cases. Image processing was easy to perform within 23 min. Of the 56 potential donors, 27 were excluded from LDLT because of inappropriate liver parenchyma or vascular architecture. Two recipients were not transplanted due to poor clinical conditions. In the 27 transplanted cases, preoperatively visualised vessels were confirmed, and only one undetected accessory hepatic vein was revealed. Calculated graft volumes were 1110 +/- 180 ml for right lobes, 820 ml for the left lobe and 270 +/- 30 ml for segments II+III. The calculated volumes and intraoperatively measured graft volumes correlated significantly. No significant differences between the presented automatic volumetry and the conventional volumetry were observed. A novel image processing technique was evaluated which allows a semi-automatic volume calculation and 3D visualisation of the different liver segments.