Philipp Bruners

A feasibility study of contrast enhancement of acute myocardial infarction in multislice computed tomography: comparison with magnetic resonance imaging and gross morphology in pigs.

Introduction:Late enhancement magnetic resonance imaging (MRI) of myocardial infarction (MI) is clinically established. There are no reports on MI assessment using state-of-the-art multislice CT technology. For this reason, animal experiments were conducted to examine the applicability of contrast-enhanced ECG-gated multislice computed tomography (MSCT) for the detection of acute MI. The results were correlated with MRI and postmortem tissue staining. Material and Methods:Acute MI was induced in 14 pigs by balloon occlusion of the LAD. In 8 animals, the LAD was reperfused after 45 minutes. In 6 animals, the LAD was permanently blocked. MR imaging was performed 15 minutes after the administration of 0.2 mmol Gd-DTPA/kg/bodyweight. Subsequently, 16-slice MSCT was performed at various timepoints after injecting 120 mL of iodinated contrast medium. 2,3,5-Triphenyltetrazolin-chloride (TTC) staining was acquired for all hearts investigated. Correlation analysis was applied to compare the area of MI derived from MRI, MSCT, and TTC. The reperfused infarcts were compared with the nonreperfused infarcts using an unpaired t test. Results:Mean infarct area as measured by TTC staining was 18.3% ± 7.8% of the left ventricular area. Good correlation of the spatial extent of the infarcted area was found for TTC and MRI as well as for TTC and MSCT data obtained 5 minutes postcontrast injection. MSCT imaging demonstrated a significant difference in density (P < 0.001) between nonreperfused (47.0 ± 6.6 HU) and reperfused (116.4 ± 19.8 HU) infarction. Conclusion:In our pilot study, contrast-enhanced MSCT was feasible to assess myocardial viability in pigs. MSCT also affords differentiation of nonreperfused and reperfused acute MI. MI sizes derived from MSCT imaging correlate well to those obtained with MRI and TTC.

Low tube voltage improves computed tomography imaging of delayed myocardial contrast enhancement in an experimental acute myocardial infarction model.

Objective:We sought to evaluate the influence of tube voltage on the visualization of acute myocardial infarction (MI) in cardiac multislice spiral computed tomography (MSCT). Materials and Methods:Acute MI was induced in 12 domestic pigs by a 45-minute balloon occlusion of the left anterior descending artery. Delayed enhancement magnetic resonance imaging was performed 15 minutes after the injection of 0.2 mmol/kg Gd-DTPA. On the same day, retrospectively ECG-gated MSCT was performed at 120, 100, and 80 kV (16 × 0.75mm, 550mAseff.) 15 minutes after the injection of 140 mL of iopromide (1 g/iodine/kg). The pigs were killed and the hearts were excised and stained with 2,3,5-triphenyltetrazolium chloride. The area of acute MI, contrast-to-noise ratio (CNR), and percent signal difference were compared among the different imaging techniques by applying Bland-Altman plots and 2-way analysis of variance. Results:On MSCT at 120, 100, and 80 kV, the respective mean acute MI sizes were 18.4 ± 11.4%, 19.3 ± 11.5%, and 20.5 ± 11.6%. The mean MI sizes were 20.8 ± 12.2% and 20.1 ± 12.4% on magnetic resonance imaging and 2,3,5-triphenyltetrazolium chloride staining. Analysis of variance did not show any statistically significant differences between the different techniques with respect to the size of acute MI (P = 0.9880). Comparing the different kV settings on MSCT, the highest percent signal difference (74.7 ± 12.1%) and the highest CNR (6.7 ± 1.8) between infarcted and healthy remote myocardium were achieved at 80 kV. Conclusions:When compared with routine scan protocols, low tube voltage MSCT allows for the assessment of the MI size with an improved CNR and contrast resolution. This technique appears to be advantageous for assessing myocardial viability from contrast enhanced late-phase MSCT.

Left ventricular function can reliably be assessed from dual-source CT using ECG-gated tube current modulation.

Purpose:The aim of this study was to assess the reliability of global left ventricular (LV) function analysis using dual source CT (DSCT) with and without ECG-gated tube current modulation in comparison with magnetic resonance (MR) imaging. Methods and Materials:In 7 pigs with myocardial infarction retrospectively ECG-gated DSCT (2 × 64 × 0.6 mm; 120kV; 380mAsrot.) with and without tube current modulation (gating window: 40%–75%) as well as cine MR imaging of the heart were performed on the same day. From DSCT data 6 mm double-oblique short axis images were computed. DSCT as well as MR images were analyzed using Simpson method. LV volumes, ejection fraction and, myocardial mass were calculated. Wall motion was assessed visually. Standard deviations of attenuation values measured in the LV cavity were assigned to image noise and compared using Wilcoxon test. LV volumes were compared with Lin concordance-correlation coefficient (&rgr;c). Regional wall motion was analyzed with weighted kappa statistics. Results:Both, DSCT with (DSCTDM) and without (DSCTnorm) dose modulation were in good agreement with MR imaging. For ejection fraction, there was an excellent concordance-correlation comparing DSCTnorm with DSCTDM (&rgr;c = 0.9749), DSCTnorm with MR imaging (&rgr;c = 0.9435), and DSCTDM with MR imaging (&rgr;c = 0.9612). The corresponding kappa values comparing regional wall motion were &kgr; = 0.988, &kgr; = 0.901, and &kgr; = 0.888, respectively. During end-systole there was no significant difference in the image noise between DSCTnorm and DSCTDM techniques (P = 0.8750), but the difference became significant when comparing end-diastolic DSCT images (P = 0.0156). Conclusions:ECG-gated tube-current modulation does not hamper the quantitative assessment of global and regional LV function using DSCT.

Dual-source computed tomography for assessing cardiac function: a phantom study.

Purpose:To investigate the influence of heart rate and temporal resolution on the assessment of global ventricular function with dual-source computed tomography (DSCT). Materials and Methods:A dynamic cardiac phantom was repeatedly scanned with a DSCT scanner applying a standardized scan protocol at different heart rates, ranging from 40 to 140 bpm. Images were reconstructed with monosegmental and bisegmental algorithms using data from a single source and from both sources. Ventricular volumes and ejection fraction (EF) were computed by semiautomated analysis. Results were compared with the phantoms real volumes. Interscan, intraobserver, and interobserver variability were calculated. Results:For single-source data reconstruction temporal resolution was fixed to 165 milliseconds, whereas dual-source image reconstructions resulted in a temporal resolution of 83 milliseconds (monosegmental) and 67.7 ± 14.2 milliseconds (bisegmental), respectively. In general, deviation from the phantoms real volumes was less with dual-source data reconstruction when compared with single-source data reconstruction. Comparing dual-source data reconstruction with single-source data reconstruction, the percent deviation from the phantoms real volumes for EF was 0.7% (monosegmental), 0.7% (bisegmental), and 4.3% (single source), respectively. There was no correlation between heart rate and EF for dual-source data reconstruction (r = −0.168; r = −0.157), whereas a relevant correlation was observed for single-source data reconstruction (r = −0.844). Interscan, intraobserver, and interobserver variability for EF were 1.4%, 0.9%, and 0.3%, respectively. Conclusions:DSCT allows reliable quantification of global ventricular function independent of the heart rate. Multisegmental image reconstruction is not needed for DSCT assessment of global ventricular function.

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.

Local Ablative Therapies in HCC: Percutaneous Ethanol Injection and Radiofrequency Ablation

Hepatocellular carcinoma (HCC) is the most common primary hepatic malignancy. Surgery and transarterial chemoembolization have for many years dominated the local treatment of HCC. The introduction of image-guided percutaneous techniques for local tumor ablation changed the treatment of liver cancer. Percutaneous ethanol injection (PEI) and radiofrequency ablation (RFA) have both successfully been employed in the treatment of HCC. In current guidelines both techniques are recommended as standard therapy in limited liver cancer. From the current literature both techniques have to be considered safe and effective in the treatment of HCC. Several randomized trials showed RFA to be superior to PEI for treating small HCC. Moreover, several studies analyzed survival after PEI or RFA in comparison with surgery, proving interventional therapy to be a serious competitor of resection. With introduction of combined interventional therapies including transarterial chemoembolization, PEI and RFA survival was improved further. In this article, we provide an insight into the technical basics of PEI and RFA and review the clinical results and indications of these interventional techniques in the treatment of HCC.

Dual energy CT with nonlinear image blending improves visualization of delayed myocardial contrast enhancement in acute myocardial infarction.

ObjectivesThe objective of this study was to evaluate the effect of, and optimal parameters for, nonlinear image blending compared with linear image blending in the late-phase dual energy computed tomography (DECT) for the visualization of delayed myocardial contrast enhancement in acute myocardial infarction (MI). Materials and MethodsAcute reperfused MI was induced in 7 pigs by temporary occlusion of the left anterior descending or the left circumflex artery. Two hours after the reperfusion, a contrast-enhanced, late-phase DECT (80 kV/140 kV) scanning was performed. The DECT data were postprocessed with linear and nonlinear image blending techniques. Contrast and percentage signal differences between healthy and infarcted myocardium as well as the blood pool of the left ventricle were computed for the linear and nonlinear techniques and the low- and high-kilovolt images. Data were compared using repeated-measures analysis of variance and post hoc t tests. ResultsThe nonlinear blending showed the highest signal differences for all contrasts and analyses. Repeated-measures ANOVA results confirmed that the differences were statistically significant for the different postprocessing techniques (P value ranging from <0.001–0.003). Paired-samples post hoc t tests proved the significance of these results (P value ranging from <0.001–0.037). The ideal settings for the nonlinear image blending can thus be deduced from the computed tomographic values of the regions of interest in the linearly blended images with the weighting factor 0.3. ConclusionsNonlinear image blending improves the visualization of acute MI in the late-phase DECT. It is superior to linearly blended images and source images obtained at 80 or 140 kV.

Perkutane Radiofrequenzablation von Osteoidosteomen: Technik und Ergebnisse

PURPOSE Osteoid osteoma is a benign primary bone tumor that typically occurs in children and young adults. Besides local pain, which is often worse at night, prompt relief due to medication with acetylsalicylic acid (ASS) is characteristic for this bone lesion. Because long-term medication with ASS does not represent an alternative treatment strategy due to its potentially severe side effects, different minimally invasive image-guided techniques for the therapy of osteoid osteoma have been developed. In this context radiofrequency (RF) ablation in particular has become part of the clinical routine. The technique and results of image-guided RF ablation are compared to alternative treatment strategies. MATERIALS AND METHODS Using this technique, an often needle-shaped RF applicator is percutaneously placed into the tumor under image guidance. Then a high-frequency alternating current is applied by the tip of the applicator which leads to ionic motion within the tissue resulting in local heat development and thus in thermal destruction of the surrounding tissue including the tumor. RESULTS The published primary and secondary success rates of this technique are 87 and 83 %, respectively. Surgical resection and open curettage show comparable success rates but are associated with higher complication rates. In addition image-guided RF ablation of osteoid osteomas is associated with low costs. CONCLUSION In conclusion image-guided RF ablation can be considered the gold standard for the treatment of osteoid osteoma.

Assessment of global left and right ventricular function using dual-source computed tomography (DSCT) in comparison to MRI: an experimental study in a porcine model.

Objective:We sought to evaluate the ability of retrospectively ECG-gated dual-source computed tomography (DSCT) to assess left (LV) and right ventricular (RV) functional parameters in comparison to 1.5 T magnetic resonance imaging (MRI). Materials and Methods:Ten domestic pigs (60 kg) underwent both contrast-enhanced cardiac DSCT and cardiac MRI using standardized examination protocols under general anesthesia. From manually drawn endocardial and epicardial contours, LV and RV end-systolic (ESV) and end-diastolic volume (EDV), stroke volume (SV), ejection fraction (EF), myocardial mass (MM), peak filling rate (PFR), peak ejection rate (PER), time to peak ejection (TPE), and time to peak filling (TPF) were calculated by means of dedicated analysis software. LV and RV functional parameters were analyzed using Bland-Altman plots, Student t test, and Pearsons correlation coefficient. Results:Both left and right ESV and EDV, SV and EF determined with DSCT correlated well with MR imaging results (left, r = 0.98/0.92/0.82/0.98; right, r = 0.90/0.94/0.96/0.94). PER, PFR, TPE, TPF, and MM showed only a moderate to low correlation (left, r = 0.67/0.37/0.23/0.35/0.57; right, r = 0.78/0.69/0.12/0.11/0.44). PER and PFR were significantly underestimated by DSCT when compared with MRI. Conclusions:Retrospectively ECG-gated DSCT correctly depicts end-systole and can accurately determine LV and RV volumes, SV, and EF in comparison to MRI. DSCT showed a significant underestimation of PER and PFR in comparison to MRI.

Fluid-Modulated Bipolar Radiofrequency Ablation: An Ex-Vivo Evaluation Study

Background: The effect of radiofrequency ablation (RFA) can be modulated by fluid injection. Purpose: To evaluate the potential of different fluids to modulate the effect of bipolar RFA in an ex-vivo liver model. Material and Methods: A bipolar RFA system with an internally cooled needle-shaped applicator (20-mm active tip) was used to induce coagulation lesions in ex-vivo porcine liver. Prior to the ablation procedure, 1-ml samples of seven different fluids were injected (0.9% saline, gadopentetate dimeglumine, ioxithalamate, 10% hydroxyethyl starch, 5% glucose, 95% ethanol, distilled water). Each fluid was used for five RF ablations. During the procedure, applied energy, impedance, and time were recorded. Additionally, temperature was measured at a fixed distance of 0.5 and 1.0 cm from the RF probe. Generator output was set to 20 W, as recommended by the vendor. Five ablation procedures without fluid injection served as the reference standard. The lesion diameters were measured, and volume and an efficiency index (coagulation volume/procedure duration) calculated and compared (ANOVA, Student-Newman-Keuls test). Results: In comparison to the reference standard, fluid injection resulted in an enlargement of mean coagulation volume for all fluids. In comparison to RF ablation alone (1.42±0.33 cm3), significant increase (P<0.001) of lesion size was found using gadopentetate dimeglumine, hydroxyethyl starch, glucose, and ethanol. The largest lesions were generated using preinjection of hydroxyethyl starch. Most energy could be applied after injection of glucose. Comparing the efficiency index, no statistically significant differences were found. Conclusion: Besides the modulation of the electrical conductivity, the increase in thermal conductivity also contributes to the enhancement of RFA by the injection of the tested fluids. Further studies are needed to evaluate this effect for larger injection volumes under in-vivo conditions.