Sebastian Keil

Image fusion in dual energy computed tomography: effect on contrast enhancement, signal-to-noise ratio and image quality in computed tomography angiography.

Objective:The aim of this study was to evaluate the influence of different weighting factors on contrast enhancement, signal-to-noise ratio (SNR), and image quality in image fusion in dual energy computed tomography (DECT) angiography. Material and Methods:Fifteen patients underwent a CT angiography of the aorta with a SOMATOM Definition Dual Source CT (DSCT; Siemens, Forchheim, Germany) in dual energy mode (DECT) (tube voltage: 80 and 140 kVp; tube current: 297 eff. mA and 70 eff. mA; collimation, 14 × 1.2 mm). Raw data were reconstructed using a soft convolution kernel (D30f). Fused images were calculated using a spectrum of weighting factors (0.0, 0.1, 0.3, 0.5, 0.7, 0.9, and 1.0) generating different ratios between the 80- and 140-kVp images (eg, factor 0.5 corresponds to 50% image information from the 140- and the 80-kVp image). Both CT values and SNR were measured in the descending aorta (levels of celiac trunk, renal arteries, and aortic bifurcation), in the right and left common iliac artery and in paraaortal fat. Image quality was evaluated using a 5-point grading scale. Results were compared using paired t-tests and nonparametric paired Wilcoxon tests. Results:Statistically significant increases in mean CT values were seen in vessels when increasing weighting factors were used (all P ≤ 0.001). For example, mean CT values derived from the aorta at the level of the celiac trunk were 273.8 ± 25.8 Hounsfield units (HU), 304.0 ± 24.3 HU, 361.4 ± 22.5 HU, 418.3 ± 25.8 HU, 477.8 ± 32.2 HU, 536.2 ± 41.2 HU, 564.6 ± 45.3 HU, when the weighting factors 0.0, 0.1, 0.3, 0.5, 0.7, 0.9, and 1.0 were used. The highest SNR values were found in vessels when the weighting factor 0.5 was used. The highest SNR values of the paraaortal fat were obtained for the weighting factors 0.3 and 0.5. Visual image assessment for image quality showed the highest score for the data reconstructed using the weighting factor 0.5. Conclusion:Different weighting factors used to create fused images in DECT cause statistically significant differences in CT value, SNR, and image quality. Best results were obtained using the weighting factor 0.5, which we recommend for image fusion in DECT angiography.

Jugular versus subclavian totally implantable access ports: catheter position, complications and intrainterventional pain perception.

PURPOSE To determine the safest and most tolerable method for totally implantable access ports (TIAPs) particularly in regard to patients pain perception and catheter-related complications. MATERIALS AND METHODS From January 2007 to October 2008 a subcutaneous TIAP (Bardport, Bard Access System, UT, USA) was implanted in 138 oncological patients (60 male, 78 female; 18-85 years old; mean age of 56 ± 6 years) by experienced interventional radiologists. 94 TIAP were implanted through the subclavian vein (subclavian group) and 44 TIAP were implanted through the internal jugular vein (jugular group). Intrainterventional pain perception (visual analogue scale from 1 to 10), postinterventional catheter tip migration and radiation dose were documented for each method and implantation side and differences were compared with Wilcoxon t-test. For ordinal variables, comparison of two groups was performed with the Fishers exact test. RESULTS No severe periinterventional complication occurred. Inadvertent arterial punctures without serious consequences were reported in one case for the jugular group versus four cases in the subclavian group. Significantly (p<0.05) lower pain perception, radiation dose and tip migration rate were observed in the jugular group. Catheter occlusions occurred in 4% (n=4) of the subclavian group versus 2% (n=1) of the jugular group. The corresponding values for vein thrombosis and catheter dislocation were 3% (n=3) and 1% (n=1) in the subclavian group, while none of those complications occurred in the jugular group. CONCLUSION Both techniques, the TIAP implantation via fluoroscopy-guided subclavian vein puncture and via ultrasound-guided jugular vein puncture, are feasible and safe. Regarding intrainterventional pain perception, radiation dose, postinterventional catheter tip position and port function the jugular vein puncture under ultrasound guidance seems to be advantageous.

Semi-automated quantification of hepatic lesions in a phantom.

Purpose:Accurate measurement is crucial for the assessment of tumor dimensions to allow accurate evaluation of tumor response. Thus, the purpose of our study was to assess the accuracy of semi-automated RECIST and volumetric measurements of liver lesions in a liver phantom with different CT acquisition parameters. Materials and Methods:A phantom of the upper abdomen with 14 hepatic lesions of different sizes (diameter: 12.0–40.0 mm), densities (45/180 HU at 120 kV), or alignment (vertical/transverse) was scanned with a 16-slice multidetector row computed tomography using varying tube currents (40/60/80/100/120/165mAseff), reconstruction kernels (Siemens B20/30/40/50/70s), or slice thicknesses (1/2/3/4/5 mm). Longest axial diameter and volume of the 14 lesions were quantified using a semi-automated software tool (SyngoOncology, Siemens Medical Solutions, Forchheim, Germany) and compared with the known real longest axial diameter and volume values of the lesions. Absolute percentage errors (APE) were calculated. Degree of agreement in longest axial diameter and volume between software and real measurements was represented graphically in Bland-Altman plots and by corresponding concordance correlation coefficient. Results:At standard soft tissue reconstruction kernel (Siemens B30s) and slice thickness (3 mm) mean absolute percentage error APE (concordance correlation coefficients) ranged between 6.93 and 14.27 (0.96 and 0.99) for longest axial diameter and between 4.98 and 10.85 (0.99 and 1.00) for volume. At varying reconstruction kernels, APE values (concordance correlation coefficients) ranged between 7.92 and 8.31 (0.98 and 0.99) for longest axial diameter and between 4.95 and 6.93 (1.00) for volume. Applying different slice sections APE values (concordance correlation coefficients) differed from 6.54 to 11.82 (0.97 and 0.99) for longest axial diameter and from 6.93 to 9.17 (1.00) for volume. Conclusions:Software quantification of longest axial diameter and volume of hepatic lesions in a phantom demonstrated a high correlation and accuracy under varying multidetector row computed tomography parameter.

Effect of different saline chaser volumes and flow rates on intravascular contrast enhancement in CT using a circulation phantom

PURPOSE To evaluate the influence of different saline chaser volumes and different saline chaser flow rates on the intravascular contrast enhancement in MDCT. MATERIALS AND METHODS In a physiological flow phantom contrast medium (120 ml, 300 mgI/ml, Ultravist 300) was administered at a flow rate of 6 ml/s followed by different saline chaser volumes (0, 30, 60 and 90 ml) at the same injection rate or followed by a 30-ml saline chaser at different injection rates (2, 4, 6 and 8 ml/s). Serial CT-scans at a level covering the pulmonary artery, the ascending and the descending aorta replica were obtained. Time-enhancement curves were computed and both pulmonary and aortic peak enhancement and peak time were determined. RESULTS Compared to contrast medium injection without a saline chaser the pushing with a saline chaser (30, 60, and 90 ml) resulted in a statistically significant increased pulmonary peak enhancement (all p=0.008) and prolonged peak time (p=0.032, p=0.024 and p=0.008, respectively). Highest aortic peak enhancement values were detected for a saline chaser volume of 30 ml. A saline chaser flow rate of 8 ml/s resulted in the highest pulmonary peak enhancement values compared to flow rates of 2, 4 and 6 ml/s (all p=0.008). Aortic peak enhancement showed the highest values for a flow rate of 6 ml/s. CONCLUSION A saline chaser volume of 30 ml and an injection rate of 6 ml/s are sufficient to best improve vascular contrast enhancement in the pulmonary artery and the aorta in MDCT.

Contrast enhancement in chest multidetector computed tomography: intraindividual comparison of 300 mg/ml versus 400 mg/ml iodinated contrast medium.

RATIONALE AND OBJECTIVES We sought to intraindividually compare intravascular contrast enhancement in multidector computed tomography (MDCT) of the chest using contrast media (CM) containing 300 and 400 mg iodine/ml. MATERIALS AND METHODS Seventy-one patients underwent repeated MDCT scanning of the chest at baseline and follow-up. CM with standard iodine (protocol A: 300 mg iodine/ml; Iopromide 300) and high iodine concentration (protocol B: 400 mg iodine/ml; Iomeprol 400) were used. The iodine delivery rate (1.29 g iodine/s) and total iodine load (37 g iodine) were identical for the two protocols. Contrast enhancement was measured in the right and left ventricles, pulmonary trunk, right and left pulmonary arteries, and ascending and descending aortas. Results were compared using paired t-tests; P values were adjusted using Bonferroni correction (P <or= .005). RESULTS Contrast enhancement values showed no statistically significant differences between the two protocols at all anatomic sites (all P > .005). In the right ventricle, pulmonary trunk, and right and left pulmonary arteries, higher attenuation values for protocol A were detected compared to protocol B (379.0 +/- 110.5 vs. 349.8 +/- 117.6, 354.5 +/- 112.2 vs 330.9 +/- 118.3, 348.6 +/- 106.0 vs. 321.8 +/- 109.9, and 347.9 +/- 102.4 vs. 321.0 +/- 104.9 HU, respectively). After the lung circulation (left ventricle, ascending aorta, and descending aorta), attenuation values were marginally higher for protocol B. Using both protocols resulted in suitable contrast enhancement with a mean pulmonary attenuation higher than 300 HU. CONCLUSIONS Using an adapted injection protocol, the administration of 300 and 400 mg iodine CM resulted in a suitable intravascular contrast enhancement in the chest. The use of 400 mg iodine CM does not lead to a statistically significant improvement in contrast enhancement compared to the 300 mg iodine CM.

Comparison of manual, semi- and fully automated heart segmentation for assessing global left ventricular function in multidetector computed tomography.

Purpose:To evaluate the reliability of global left ventricular (LV) function and mass measurements with the aid of a semi-automated (Circulation; Siemens, Forchheim, Germany) and a new fully automated software (Philips Research Europe, Aachen, Germany) versus an established manual segmentation method (Argus; Siemens). Material and Methods:Forty-one patients (31 men, 10 women; mean age: 62 ± 5 years) with known or suspected coronary heart disease underwent contrast-enhanced Dual-Source computed tomography of the heart (120 kV, 410 mAs/rotation, collimation 2 × 32 × 0.6 mm, gantry rotation time 0.33 milliseconds). Global LV function measurements of end-diastolic volume (EDV), end-systolic volume (ESV), stroke volume, ejection fraction (EF), and LV mass were each assessed with a manual, a semi- and fully automated method. The latter were compared with the manual contour tracing method, which was considered as standard of reference. Postprocessing time for each method was recorded. For statistical analysis, repeated-measures analysis of variance, post hoc t test, and concordance correlation coefficients were calculated. Bland-Altman plots were generated. Results:In general, ESV and EF assessed with the semi-automated and with the fully automated prototype version agreed well with the manual contour tracing method. The mean ESV (±SD) calculated from the manual, the semi-automated, and the fully automated method was 67 ± 43 mL, 74 ± 54 mL, and 75 ± 48 mL, respectively. No statistically significant differences between the methods were found for ESV and EF. In contrast, significant variations (P < 0.05) among the different segmentation methods were shown for EDV, stroke volume, and LV mass. This variation was predominantly due to variation in endocardial delineations among the different techniques. Concordance correlation coefficients demonstrated a better accuracy for the fully automated method than for the semi-automated technique when compared with the manual drawing method. Furthermore, fully automated postprocessing heart segmentation yielded time savings of approximately 80% compared with the manual segmentation tool and 63% compared with the semi-automated technique. Mean postprocessing time (±SD) for the manual, the semi-automated, and the fully automated method was 345 ± 75 seconds, 192 ± 58 seconds, and 72 ± 58 seconds, respectively. Conclusion:LV function and mass analyses using semi- or fully automated segmentation algorithms are feasible even if significant differences in EDV assessment are observed. The fully automated method results in better accuracy and time savings when compared with manual and semi-automated data analysis.

Computed tomography angiography: the effect of different chaser flow rates, volumes, and fluids on contrast enhancement.

Objectives:The aim of this study was to intraindividually compare the effect of different chaser flow rates, volumes, and fluids on contrast enhancement in multidetector-row computed tomography. Materials and Methods:Multidetector-row computed tomography scanning of 5 dogs was performed under standardized conditions using an adapted injection protocol to ensure an identical iodine delivery rate of 1.0 gI/s and a total iodine dose of 300 mg/kg body weight (iopromide 300 and 370). The contrast medium application was followed by a 10-mL saline chaser at different injection rates (0, 2.7, 4, 6, and 8 mL/s) or by different saline chaser volumes (0, 5, 10, and 15 mL) at a flow rate of 4 mL/s. Furthermore, different chaser fluids (NaCl, hydroxyethyl starch 10%, and Dextran 1%) with different viscosities (hydroxyethyl starch 10% and dextran 1%: 3.28 and 5.98 mPa · s at 37°C) were tested (volume: 10 mL; flow rate: 6 mL/s). Each dog was examined with each protocol. The interval between each computed tomography scan session which included 2 measurements was at least 3 days. Dynamic computed tomography scans were acquired at the level of the cephalic vein, cranial vena cava, pulmonary artery, and ascending and descending aorta. Time-enhancement curves were computed, and pulmonary and aortic peak enhancements as well as time-to-peak were analyzed. Results:Increased saline chaser flow rates or increased saline chaser volumes resulted in increased pulmonary and aortic peak contrast enhancement. Peak enhancement was highest and significantly greater compared with no saline chaser for a flow rate of 8 mL/s (pulmonary artery: 816.8 vs. 471.5 HU, P = 0.0079; ascending aorta: 578.7 vs. 384.1 HU, P = 0.0079; descending aorta: 581.4 HU vs. 390.6 HU, P = 0.0159) and a saline volume of 15 mL (pulmonary artery: 670.2 vs. 453.5 HU, P = 0.0079; ascending aorta: 512.1 vs. 370.6 HU, P = 0.0317; descending aorta: 504.0 HU vs. 394.4 HU, P = 0.0159). No significant differences between the peak times for different saline chasers were found. Different chaser fluids did not exhibit significant differences in peak enhancement or peak time. A time-enhancement curve of the cephalic vein showed that the early effects of the saline chaser involved clearing the vein and pushing the contrast medium to the central circulation. Conclusions:Saline chasing increases pulmonary and aortic peak enhancement with increasing flow rates and volumes of the chaser. The use of more viscous chaser fluids does not improve contrast enhancement. The early effects of the saline chaser involve clearing the vein and pushing the contrast medium to the central circulation.

Percutaneous Radiofrequency Ablation for Treatment of Recurrent Retroperitoneal Liposarcoma

Percutaneous CT-guided radiofrequency ablation (RFA) is becoming more and more established in the treatment of various neoplasms, including retroperitoneal tumors of the kidneys and the adrenal glands. We report the case of RFA in a patient suffering from the third relapse of a retroperitoneal liposarcoma in the left psoas muscle. After repeated surgical resection and supportive radiation therapy of a primary retroperitoneal liposarcoma and two surgically treated recurrences, including replacement of the ureter by a fraction of the ileum, there was no option for further surgery. Thus, we considered RFA as the most suitable treatment option. Monopolar RFA was performed in a single session with a 2-cm umbrella-shaped LeVeen probe. During a 27-month follow-up period the patient remained free of tumor.

Introduction of a dedicated circulation phantom for comprehensive in vitro analysis of intravascular contrast material application.

Objectives:To develop a circulation phantom with physiologic circulation parameters, including a pulmonary and a body circulation for the evaluation of intravascular contrast material (CM) application. Materials and Methods:The circulation phantom consists of a low-pressure venous system into which CM is injected, a pulmonary circulation, and high-pressure body circulation with an anthropometric aorta and coronary arteries. The phantom is driven by a pulsatile Harvard heart pump. Venous and arterial pressure were set to physiologic values with heart rate (60 beats/min), stroke volume (60 mL), and ratio of diastole to systole (60/40) also were within physiologic limits. CM with different iodine concentrations (300, 370, and 400 mg iodine/mL) were injected at a flow rate of 4 mL/s (iodine delivery rate: 1.2 g, 1.48 g, and 1.6 g iodine/s, respectively; total iodine load for all protocols: 36 g). Serial computed tomography scans at the level of the pulmonary artery, the ascending and the descending aorta replica were obtained. Dynamic pressure in the phantom and true injection system parameters (flow rate, injection pressure, and CM volume) was continuously monitored. Time-enhancement curves were calculated, and pulmonary and aortic peak time and enhancement were determined. Results were compared using nonparametric unpaired Wilcoxon tests. Results:The pressure in the phantom showed physiologic values for the low (mean pressure: 15 mm Hg) and high pressure part (125/75 mm Hg). Programmed injection values (flow rate, pressure, and volume) were reached for all injections. Using CM with 400 mg iodine/mL, the shortest pulmonary and aortic peak times and the highest pulmonary and aortic peak enhancement values were obtained compared with CM with 300 and 370 mg iodine/mL. Conclusions:We developed a flow phantom with physiologic circulation parameters for measurement of contrast enhancement. The phantom is suitable for further evaluation of CM injection protocols for pulmonary and aortic enhancement.

Semiautomated versus Manual Evaluation of Liver Metastases Treated by Radiofrequency Ablation

PURPOSE To determine the accuracy of semiautomated volume and density measurements of liver metastases from colorectal and breast cancer before and after radiofrequency (RF) ablation compared with manual evaluation. MATERIALS AND METHODS Twenty-five patients (mean age, 63.2 years +/- 10.7) with 50 known liver metastases from underlying primary breast (n = 15) or colorectal cancer (n = 35) underwent triphasic contrast-enhanced multidetector computed tomography (CT) to evaluate hepatic tumor load and localization before RF ablation and for postinterventional follow-up. Each lesion was quantified in terms of volume and CT value (in HU) with a semiautomated software tool and manually by an experienced radiologist before and 4 months after RF ablation. RESULTS Before RF ablation, all 50 liver metastases, and after ablation, 49 of 50 ablation zones (98%), were correctly evaluated by the software. Mean lesion volumes before and after the intervention were 5.5 cm(3) and 22.4 cm(3), respectively. Corresponding concordance correlation coefficients between measurement techniques were 0.98 and 0.99, respectively, for volume; and 0.90 and 0.76, respectively, for CT value. CONCLUSIONS Compared with manual measurements, semiautomated volumetric assessment of liver metastases before and after RF ablation demonstrated a high degree of correlation. Agreement of attenuation was slightly worse, particularly when assessing the postinterventional multidetector CT examination, probably because of the different regions of interest used for manual and semiautomated assessment of CT values.