Wolfram Stiller

Publications of Wolfram Stiller

• Computed tomography perfusion analysis of pancreatic carcinoma.

  Authors: Miriam Klau, Wolfram Stiller, Franziska Fritz, Meinhard Kieser, Jens Werner, Hans-Ulrich Kauczor, Lars Grenacher

  Journal of computer assisted tomography. 03/2012; 36(2):237-42.

  The purpose of this study was to evaluate CT perfusion of pancreatic carcinomas using the Patlak model for assessing perfusion, permeability, and blood volume. A total of 25 patients with pancreaticThe purpose of this study was to evaluate CT perfusion of pancreatic carcinomas using the Patlak model for assessing perfusion, permeability, and blood volume. A total of 25 patients with pancreatic carcinoma were examined prospectively with a 64-slice computed tomography (CT) using a dynamic sequence after intravenous injection of 80-mL contrast material (370 mg/mL; flow rate, 5 mL/s). Eighty-kilovolt (peak) perfusion acquisitions were evaluated for estimating perfusion parameters for carcinoma and healthy tissue using a 2-compartment model (Patlak model). Twenty patients had hypodense tumors; in 5 patients, the tumor could not be delineated in contrast-enhanced CT. All carcinomas could be identified clearly in the color-coded perfusion maps. Perfusion, permeability, and blood volume values were significant lower in pancreatic carcinomas compared to healthy pancreatic tissue (0.27 ± 0.20 vs 0.89 ± 0.19 min, P < 0.0001; 0.43 ± 0.20 vs 0.75 ± 0.16 × 0.5 min, P < 0.0001; and 38.9 ± 20.7 vs 117.8 ± 46.9 mL/100 mL, P < 0.0001). Computed tomographic perfusion of the pancreas using a 2-compartment perfusion model is feasible. Color-coded perfusion maps could be a helpful tool to delineate pancreatic carcinomas even if they are not visible in contrast-enhanced CT.

• Reduction of radiation exposure and improvement of image quality with BMI-adapted prospective cardiac computed tomography and iterative reconstruction.

  Authors: Waldemar Hosch, Wolfram Stiller, Dirk Mueller, Gitsios Gitsioudis, Johanna Welzel, Monika Dadrich, Sebastian J Buss, Evangelos Giannitsis, Hans U Kauczor, Hugo A Katus, Grigorios Korosoglou

  European journal of radiology. 07/2011;

  PURPOSE: To assess the impact of body mass index (BMI)-adapted protocols and iterative reconstruction algorithms (iDose) on patient radiation exposure and image quality in patients undergoingPURPOSE: To assess the impact of body mass index (BMI)-adapted protocols and iterative reconstruction algorithms (iDose) on patient radiation exposure and image quality in patients undergoing prospective ECG-triggered 256-slice coronary computed tomography angiography (CCTA). METHODS: Image quality and radiation exposure were systematically analyzed in 100 patients. 60 Patients underwent prospective ECG-triggered CCTA using a non-tailored protocol and served as a 'control' group (Group 1: 120kV, 200mAs). 40 Consecutive patients with suspected coronary artery disease (CAD) underwent prospective CCTA, using BMI-adapted tube voltage and standard (Group 2: 100/120kV, 100-200mAs) versus reduced tube current (Group 3: 100/120kV, 75-150mAs). Iterative reconstructions were provided with different iDose levels and were compared to filtered back projection (FBP) reconstructions. Image quality was assessed in consensus of 2 experienced observers and using a 5-grade scale (1=best to 5=worse), and signal- and contrast-to-noise ratios (SNR and CNR) were quantified. RESULTS: CCTA was performed without adverse events in all patients (n=100, heart rate of 47-87bpm and BMI of 19-38kg/m(2)). Patients examined using the non-tailored protocol in Group 1 had the highest radiation exposure (3.2±0.4mSv), followed by Group 2 (1.7±0.7mSv) and Group 3 (1.2±0.6mSv) (radiation savings of 47% and 63%, respectively, p<0.001). Iterative reconstructions provided increased SNR and CNR, particularly when higher iDose level 5 was applied with Multi-Frequency reconstruction (iDose5 MFR) (14.1±4.6 versus 21.2±7.3 for SNR and 12.0±4.2 versus 18.1±6.6 for CNR, for FBP versus iDose5 MFR, respectively, p<0.001). The combination of BMI adaptation with iterative reconstruction reduced radiation exposure and simultaneously improved image quality (subjective image quality of 1.4±0.4 versus 1.9±0.5 for Group 2 reconstructed using iDose5 MFR versus Group 1 reconstructed using FBP, p<0.05). CONCLUSIONS: Prospective ECG-triggered 256-slice CCTA allows for visualization of the coronary artery tree with high image quality within a wide range of heart rates and BMIs. The combination of BMI-adapted protocols with iterative reconstruction algorithms can reduce radiation exposure for the patients and simultaneously improve image quality.

• Iodine removal in intravenous dual-energy CT-cholangiography: Is virtual non-enhanced imaging effective to replace true non-enhanced imaging?

  Authors: Christof M Sommer, Christoph B Schwarzwaelder, Wolfram Stiller, Sebastian T Schindera, Ulrike Stampfl, Nadine Bellemann, Maria Holzschuh, Jan Schmidt, Juergen Weitz, Lars Grenacher, Hans U Kauczor, Boris A Radeleff

  European journal of radiology. 02/2011;

  PURPOSE: To evaluate whether virtual non-enhanced imaging (VNI) is effective to replace true non-enhanced imaging (TNI) applying iodine removal in intravenous dual-energy CT-cholangiography.PURPOSE: To evaluate whether virtual non-enhanced imaging (VNI) is effective to replace true non-enhanced imaging (TNI) applying iodine removal in intravenous dual-energy CT-cholangiography. MATERIALS AND METHODS: From April 2009 until February 2010, fifteen potential donors for living-related liver transplantation (mean age 37.6±10.8 years) were included. Potential donors underwent a two-phase CT-examination of the liver. The first phase consisted of a single-energy non-enhanced CT-acquisition that provided TNI. After administration of hepatobiliary contrast agent, the second phase was performed as a dual-energy cholangiographic CT-acquisition. This provided VNI. Objective image quality (attenuation values [bile ducts and liver parenchyma] and contrast-to-noise ratio) and subjective overall image quality (1 - excellent; 5 - non diagnostic) were evaluated. Effective radiation dose was compared. RESULTS: For TNI and VNI, attenuation values for bile ducts were 16.8±11.2HU and 5.5±17.0HU (p<0.05) and for liver parenchyma 55.3±8.4HU and 58.1±10.6HU (n.s.). For TNI and VNI, contrast-to-noise ratio was 2.6±0.6HU and 6.9±2.1HU (p<0.001). For VNI, subjective overall image quality was 1 in ten datasets, 2 in four datasets and 3 in one dataset. Effective radiation dose for the dual-energy cholangiographic CT-acquisition was 3.6±0.9mSv and for two-phase single-energy CT-cholangiography 5.1±1.3mSv (p<0.001). CONCLUSION: In this study on iodine removal in intravenous dual-energy CT-cholangiography, subjective image quality is equivalent, contrast-to-noise ratio is improved and effective radiation dose is reduced when VNI is performed. The differences between TNI and VNI with respect to attenuation values seem to have limited clinical relevance and therefore we consider VNI as effective to replace TNI.

• Dual-energy computed-tomography cholangiography in potential donors for living-related liver transplantation: initial experience.

  Authors: Christof M Sommer, Christoph B Schwarzwaelder, Wolfram Stiller, Sebastian T Schindera, Tobias Heye, Ulrike Stampfl, Stefanie Ramsauer, Nadine Bellemann, Juergen Weitz, Jan Schmidt, Lars Grenacher, Hans U Kauczor, Boris A Radeleff

  Investigative radiology. 07/2010; 45(7):406-12.

  To report our initial experience with dual-energy computed-tomography (CT) cholangiography in potential donors for living-related liver transplantation. Seventeen potential donors for living-relatedTo report our initial experience with dual-energy computed-tomography (CT) cholangiography in potential donors for living-related liver transplantation. Seventeen potential donors for living-related liver transplantation (6 women and 11 men; average age 37.8 +/- 10.4 years) underwent contrast-enhanced dual-energy CT cholangiography. A dual-energy CT scan of the liver was carried out with acquisition of 2 raw datasets at tube currents of 140 and 80 kV, respectively. A third weighted average dataset were obtained (weighting ratio: 70% 140 kV, 30% 80 kV). Pure iodine images (fourth dataset) and contrast-optimized images (fifth dataset) were reconstructed. Analysis of all datasets comprised determination of bile duct visualization scores (on a scale of 1 to 4: 1, not visualized; 2, faintly seen; 3, identified but the origin or portions of the duct are not visualized; and 4, excellent visualization from origin to branches), maximum bile duct diameters, bile duct attenuation, and liver parenchyma attenuation as well as image noise, signal-to-noise ratio, and contrast-to-noise ratio. Highest maximum bile duct diameters were detected for optimized-contrast images and the 80 kV dataset, intermediate for pure iodine images and the weighted average dataset and lowest for the 140 kV dataset with significant differences. Highest bile duct attenuation was detected for optimized-contrast images (535.7 +/- 148.3 HU) and the 80 kV dataset (533.7 +/- 145.9 HU) with significant differences compared with pure iodine images (344.9 +/- 106.5 HU) and the weighted average dataset (355.5 +/- 87.6 HU) (P < 0.001). Highest image noise was detected for the 80 kV dataset (39.3 +/- 5.4 HU) with significant differences compared with the optimized-contrast images (31.5 +/- 4.0) (P < 0.001). Highest signal-to-noise ratio and contrast-to-noise ratio were detected for pure iodine images (18.3 +/- 7.1 and 17.6 +/- 7.0) and optimized-contrast images (17.3 +/- 5.8 and 14.8 +/- 5.5) with significant differences compared with the 80 kV dataset (14.0 +/- 5.2 and 11.8 +/- 4.8) and the weighted average dataset (15.1 +/- 4.4 and 12.1 +/- 4.1) (P < 0.001 and P < 0.01). Dual-energy CT cholangiography in potential donors for living-related liver transplantation is remarkable. Pure iodine images and contrast-optimized images allow precise analysis of the biliary system with increased image quality compared with conventional images. Contrast-optimized images should be used for detection and localization of the bile ducts and pure iodine images for quantitative description of the anatomic dimensions of the biliary segments.

• Motion characterization of aortic wall and intimal flap by ECG-gated CT in patients with chronic B-dissection.

  Authors: Maria-Katharina Ganten, Tim F Weber, Hendrik von Tengg-Kobligk, Dittmar Böckler, Wolfram Stiller, Philipp Geisbüsch, Günter W Kauffmann, Stefan Delorme, Michael Bock, Hans-Ulrich Kauczor

  European journal of radiology. 08/2008;

  RATIONALE AND OBJECTIVES: To evaluate whether dynamic computed tomography (CT)-imaging can provide functional vessel information in patients with chronic aortic dissection type Stanford-B (ADB).RATIONALE AND OBJECTIVES: To evaluate whether dynamic computed tomography (CT)-imaging can provide functional vessel information in patients with chronic aortic dissection type Stanford-B (ADB). MATERIALS AND METHODS: In 32 patients, ECG-gated CT-angiography images were obtained. Cross-sectional area change and wall distensibility were investigated by semiautomatic vessel area segmentation at the end of aortic arch. Significance of distensibility differences was tested with regard to the aortic diameter, and the oscillation of the intimal flap was analyzed. RESULTS: The aorta could be segmented successfully in all patients. These were separated into three subgroups: (A) 6 patients with an aortic diameter <4cm and without a visible intimal flap, (B) 9 patients with an aortic diameter <4cm, and (C) 17 individuals with an aortic diameter >/=4cm; (B) and (C) having a visible intimal flap. Differences in distensibility between the subgroups were not significant. Overall mean distensibility was D(tot)=(1.3+/-0.6)x10(-5)Pa(-1). Analysis of intimal flap oscillation showed a pulsatile short axis diameter decrease of the true lumen of up to 29%. CONCLUSION: Dynamic, ECG-gated CT-angiography can demonstrate pulsatile changes in aortic area and a highly variable motion of the intimal flap. Aortic distensibility appears independent of diameter or presence of a intimal flap. Follow-up studies may show correlation with possible complications.

• Intrinsic respiratory gating in small-animal CT.

  Authors: Soenke H Bartling, Julien Dinkel, Wolfram Stiller, Michael Grasruck, Ijad Madisch, Hans-Ulrich Kauczor, Wolfhard Semmler, Rajiv Gupta, Fabian Kiessling

  European radiology. 08/2008; 18(7):1375-84.

  Gating in small-animal CT imaging can compensate artefacts caused by physiological motion during scanning. However, all published gating approaches for small animals rely on additional hardware toGating in small-animal CT imaging can compensate artefacts caused by physiological motion during scanning. However, all published gating approaches for small animals rely on additional hardware to derive the gating signals. In contrast, in this study a novel method of intrinsic respiratory gating of rodents was developed and tested for mice (n=5), rats (n=5) and rabbits (n=2) in a flat-panel cone-beam CT system. In a consensus read image quality was compared with that of non-gated and retrospective extrinsically gated scans performed using a pneumatic cushion. In comparison to non-gated images, image quality improved significantly using intrinsic and extrinsic gating. Delineation of diaphragm and lung structure improved in all animals. Image quality of intrinsically gated CT was judged to be equivalent to extrinsically gated ones. Additionally 4D datasets were calculated using both gating methods. Values for expiratory, inspiratory and tidal lung volumes determined with the two gating methods were comparable and correlated well with values known from the literature. We could show that intrinsic respiratory gating in rodents makes additional gating hardware and preparatory efforts superfluous. This method improves image quality and allows derivation of functional data. Therefore it bears the potential to find wide applications in small-animal CT imaging.

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• Quantification of aortic distensibility in abdominal aortic aneurysm using ECG-gated multi-detector computed tomography.

  Authors: Maria-Katharina Ganten, Ute Krautter, Hendrik von Tengg-Kobligk, Dittmar Böckler, Hardy Schumacher, Wolfram Stiller, Stefan Delorme, Hans-Ulrich Kauczor, Günter W Kauffmann, Michael Bock

  European radiology. 05/2008; 18(5):966-73.

  RATIONALE AND OBJECTIVES: To detect distensibility changes that might be an indicator for an increased risk of rupture, cross-sectional area changes of abdominal aortic aneurysms (AAA) have beenRATIONALE AND OBJECTIVES: To detect distensibility changes that might be an indicator for an increased risk of rupture, cross-sectional area changes of abdominal aortic aneurysms (AAA) have been determined using ECG-gated CT. MATERIALS AND METHODS: Distensibility measurements of the aorta were performed in 67 patients with AAA. Time-resolved images were acquired with a four detector-row CT system using a modified CT-angiography protocol. Pulsatility-related cross-sectional area changes were calculated above and at AAA level by semiautomatic segmentation; distensibility values were obtained using additional systemic blood pressure measurements. Values were compared for small Ø<5 cm (n=44) and large Ø>5 cm (n=23) aneurysms. RESULTS: The aorta could be segmented successfully in all patients. Upstream AAA distensibility D was significantly higher than at AAA level for both groups: means above AAA (at AAA) D(above)=(1.3+/-0.8) x 10(-5) Pa(-1) (D(AAA )=(0.6+/-0.5) x 10(-5) Pa(-1)) t-test p(D)<0.0001. Differences of the distensibility between smaller and larger aneurysms were not found to be significant. CONCLUSION: Distensibility can be measured non-invasively with ECG-gated CT. The reduction of distensibility within aneurysms compared to normal proximal aorta is subtle; the lack of difference between both small and large aneurysms suggests that this reduction occurs early in the aneurysm's development. Hence, reduced distensibility might be a predictive parameter in patients with high risk of aortic disease.

• Radiation dose reduction in chest CT: a review.

  Authors: Takeshi Kubo, Pei-Jan Paul Lin, Wolfram Stiller, Masaya Takahashi, Hans-Ulrich Kauczor, Yoshiharu Ohno, Hiroto Hatabu

  AJR. American journal of roentgenology. 03/2008; 190(2):335-43.

  OBJECTIVE: This article aims to summarize the available data on reducing radiation dose exposure in routine chest CT protocols. First, the general aspects of radiation dose in CT and radiation riskOBJECTIVE: This article aims to summarize the available data on reducing radiation dose exposure in routine chest CT protocols. First, the general aspects of radiation dose in CT and radiation risk are discussed, followed by the effect of changing parameters on image quality. Finally, the results of previous radiation dose reduction studies are reviewed, and important information contributing to radiation dose reduction will be shared. CONCLUSION: A variety of methods and techniques for radiation dose reduction should be used to ensure that radiation exposure is kept as low as is reasonably achievable.

• Retrospective motion gating in small animal CT of mice and rats.

  Authors: Soenke H Bartling, Wolfram Stiller, Michael Grasruck, Bernhard Schmidt, Peter Peschke, Wolfhard Semmler, Fabian Kiessling

  Investigative radiology. 11/2007; 42(10):704-14.

  OBJECTIVES: Implementation and evaluation of retrospective respiratory and cardiac gating of mice and rats using a flat-panel volume-CT prototype (fpVCT). MATERIALS AND METHODS: Respiratory andOBJECTIVES: Implementation and evaluation of retrospective respiratory and cardiac gating of mice and rats using a flat-panel volume-CT prototype (fpVCT). MATERIALS AND METHODS: Respiratory and cardiac gating was implemented by equipping a fpVCT with a small animal monitoring unit. ECG and breathing excursions were recorded and 2 binary gating signals derived. Mice and rats were scanned continuously over 80 seconds after administration of blood-pool contrast media. Projections were chosen to reconstruct volumes that fall within defined phases of the cardiac/respiratory cycle. RESULTS: Multireader analysis indicated that in gated still images motion artifacts were strongly reduced and diaphragm, tracheobronchial tract, heart, and vessels sharply delineated. From 4D series, functional data such as respiratory tidal volume and cardiac ejection fraction were calculated and matched well with values known from literature. DISCUSSION: Implementation of retrospective gating in fpVCT improves image quality and opens new perspectives for functional cardiac and lung imaging in small animals.

• Small Animal Computed Tomography Imaging

  Authors: Soenke H. Bartling, Wolfram Stiller, Wolfhard Semmler, Fabian Kiessling

  Current Medical Imaging Reviews. 02/2007; 3.

  Micro Computed Tomography (micro-CT) was suggested in biomedical research to investigate tissues and small animals. Its use to characterize bone structures, vessels (e.g. tumor vascularization),Micro Computed Tomography (micro-CT) was suggested in biomedical research to investigate tissues and small animals. Its use to characterize bone structures, vessels (e.g. tumor vascularization), tumors and soft tissues such as lung parenchyma has been shown. When co-registered, micro-CT can add structural information to other small animal imaging modalities. However, due to fundamental CT principles, high-resolution imaging with micro-CT demands for high x-ray doses and long scan times to generate a sufficiently high signal-to-noise ratio. Long scan times in turn make the use of extravascular contrast agents difficult. Recently introduced flat-panel based mini-CT systems offer a valuable trade-off between resolution (~200 µm), scan time (0.5 s), applied x-ray dose and scan field-of-view. This allows for angiography scans and follow-up examinations using iodinated contrast agents having a similar performance compared to patient scans. Furthermore, dynamic examinations such as perfusion studies as well as retrospective motion gating are currently implemented using flat-panel CT. This review summarizes applications of experimental CT in basic research and provides an overview of current hardware developments making CT a powerful tool to study tissue morphology and function in small laboratory animals such as rodents.