@article{HadertLiuZylka2016, author = {Hadert, Nicole and Liu, Qi and Zylka, Waldemar}, title = {Numerical examinations of simplified spondylodesis models concerning energy absorption in magnetic resonance imaging}, series = {Current Directions in Biomedical Engineering}, volume = {2}, journal = {Current Directions in Biomedical Engineering}, number = {1}, pages = {653 -- 658}, year = {2016}, abstract = {Metallic implants in magnetic resonance imaging (MRI) are a potential safety risk since the energy absorption may increase temperature of the surrounding tissue. The temperature rise is highly dependent on implant size. Numerical examinations can be used to calculate the energy absorption in terms of the specific absorption rate (SAR) induced by MRI on orthopaedic implants. This research presents the impact of titanium osteosynthesis spine implants, called spondylodesis, deduced by numerical examinations of energy absorption in simplified spondylodesis models placed in 1.5 T and 3.0 T MRI body coils. The implants are modelled along with a spine model consisting of vertebrae and disci intervertebrales thus extending previous investigations [1, 2]. Increased SARvalues are observed at the ends of long implants, while at the center SAR is significantly lower. Sufficiently short implants show increased SAR along the complete length of the implant. A careful data analysis reveals that the particular anatomy, i.e. vertebrae and disci intervertebrales, has a significant effect on SAR. On top of SAR profile due to the implant length, considerable SAR variations at small scale are observed, e.g. SAR values at vertebra are higher than at disc positions.}, subject = {Kernspintomografie}, language = {en} } @article{HadertLiuZylka2016, author = {Hadert, Nicole and Liu, Qi and Zylka, Waldemar}, title = {Numerical examinations of simplified spondylodesis models concerning energy absorption in magnetic resonance imaging}, series = {Current Directions in Biomedical Engineering}, volume = {2}, journal = {Current Directions in Biomedical Engineering}, number = {1}, issn = {2364-5504}, doi = {10.1515/cdbme-2016-0143}, pages = {653 -- 658}, year = {2016}, abstract = {Metallic implants in magnetic resonance imaging (MRI) are a potential safety risk since the energy absorption may increase temperature of the surrounding tissue. The temperature rise is highly dependent on implant size. Numerical examinations can be used to calculate the energy absorption in terms of the specific absorption rate (SAR) induced by MRI on orthopaedic implants. This research presents the impact of titanium osteosynthesis spine implants, called spondylodesis, deduced by numerical examinations of energy absorption in simplified spondylodesis models placed in 1.5 T and 3.0 T MRI body coils. The implants are modelled along with a spine model consisting of vertebrae and disci intervertebrales thus extending previous investigations [1], [2]. Increased SAR values are observed at the ends of long implants, while at the center SAR is significantly lower. Sufficiently short implants show increased SAR along the complete length of the implant. A careful data analysis reveals that the particular anatomy, i.e. vertebrae and disci intervertebrales, has a significant effect on SAR. On top of SAR profile due to the implant length, considerable SAR variations at small scale are observed, e.g. SAR values at vertebra are higher than at disc positions.}, language = {en} } @article{KochSchaefersZylka2011, author = {Koch, Christian and Schaefers, Gregor and Zylka, Waldemar}, title = {A novel phantom design to reduce thermal losses during radio frequency (RF) induced heating testing according to ASTM F2182-09 standard}, series = {ISRMRM - Proceedings of the International Society for Magnetic Resonance in Medicine}, volume = {19}, journal = {ISRMRM - Proceedings of the International Society for Magnetic Resonance in Medicine}, issn = {1065-9889}, pages = {3775}, year = {2011}, language = {en} } @article{BertschMelzerZylkaetal.2001, author = {Bertsch, Thomas and Melzer, Andreas and Zylka, Waldemar and Schaefers, Gregor and Busch, Martin}, title = {A prototype of an expandable active MRI stent (aMRIs)}, series = {International Congress Series}, volume = {1230}, journal = {International Congress Series}, doi = {10.1016/S0531-5131(01)00215-1}, pages = {1088 -- 1093}, year = {2001}, language = {en} } @article{BartelMortimerZylkaetal.2023, author = {Bartel, Theresa and Mortimer, Jeremy M and Zylka, Waldemar and Paxton, Jennifer and Vorstius, Jan Bernd}, title = {Design and Development of a Bioreactor System for Mechanical Stimulation of Musculoskeletal Tissue}, series = {Current Directions in Biomedical Engineering}, volume = {9}, journal = {Current Directions in Biomedical Engineering}, number = {1}, doi = {https://doi.org/10.1515/cdbme-2023-1031}, pages = {122 -- 125}, year = {2023}, abstract = {We report on the development of a bioreactor system for mechanical stimulation of musculoskeletal tissues. The ultimate object is to improve the quality of medical treatment following injuries of the enthesis tissue. To this end, the tissue formation process through the effect of mechanical stimulation is investigated. A six-well system was designed, 3D printed and tested. An integrated actuator creates strain by applying a force. A contactless position sensor monitors the travels. An electronic circuit controls the bioreactor using a microcontroller. An IoT platform connects the microcontroller to a smartphone, enabling the user to alter variables, trigger actions and monitor the system. The system was stabilised by implementing two PID controllers and safety measures. The results show that the bioreactor design is suited to execute mechanical stimulation and to investigate the tissue formation and regeneration process …}, language = {en} } @article{GarciaOliveiraPapotietal.2019, author = {Garcia, Ma{\´i}ra M. and Oliveira, Tiago R. and Papoti, Daniel and Chaim, Khallil T. and Otaduy, Maria C. G. and Erni, Daniel and Zylka, Waldemar}, title = {Experimental and numerical investigations of a small animal coil for ultra-high field magnetic resonance imaging (7T)}, series = {Current Directions in Biomedical Engineering}, volume = {5}, journal = {Current Directions in Biomedical Engineering}, number = {1}, issn = {2364-5504}, doi = {10.1515/cdbme-2019-0132}, pages = {525 -- 528}, year = {2019}, abstract = {The purpose of this work was to develop and investigate a radiofrequency (RF) coil to perform image studies on small animals using the 7T magnetic resonance imaging (MRI) system, installed in the imaging platform in the autopsy room (Portuguese acronym PISA), at the University of Sao Paulo, Brazil, which is the unique 7T MRI scanner installed in South America. Due to a high demand to create new specific coils for this 7T system, it is necessary to carefully assess the distribution of electromagnetic (EM) fields generated by the coils and evaluate the patient/object safety during MRI procedures. To achieve this goal 3D numerical methods were used to design and analyse a 8-rungs transmit/receive linearly driven birdcage coil for small animals. Calculated magnetic field (B 1) distributions generated by the coil were crosschecked with measured results, indicating good confidence in the simulated results.}, language = {en} } @article{KoenigGuberinaKuehletal.2019, author = {K{\"o}nig, Britta and Guberina, Nika and K{\"u}hl, Hilmar and Zylka, Waldemar}, title = {Design and first results of a phantom study on the suitability of iterative reconstruction for lung-cancer screening with low-dose computer tomography}, series = {Current Directions in Biomedical Engineering}, volume = {5}, journal = {Current Directions in Biomedical Engineering}, number = {1}, issn = {2364-5504}, doi = {10.1515/cdbme-2019-0149}, pages = {593 -- 596}, year = {2019}, abstract = {In this research computer tomography (CT) iterative reconstruction (IR) algorithms are investigated, specifically the impact of their statistical and model-based strength on image quality in low-dose lung screening CT protocols in comparison to filtered back projection (FBP). It has been probed whether statistical, model-based IR in conjunction with low-dose, and ultra-low-dose protocols are suitable for lungcancer screening. To this end, artificial lung nodules shaped as spheres and spicules made from material with calibrated Hounsfield units (HU) were attached on marked positions in the lung structure of an anthropomorphic phantom. Nodule positions were selected by distinguished radiologists. The phantom with nodules was scanned on a CT Scanner using standard high contrast (SHC), low-dose (LD) and ultra low-dose (ULD) protocol. For reconstruction FBP and the IR algorithm ADMIRE at three different …}, language = {en} } @article{EseZylka2019, author = {Ese, Zehra and Zylka, Waldemar}, title = {Influence of 12-bit and 16-bit CT values of metals on dose calculation in radiotherapy using PRIMO, a Monte Carlo code for clinical linear accelerators}, series = {Current directions in biomedical engineering}, volume = {5}, journal = {Current directions in biomedical engineering}, number = {1}, issn = {2364-5504}, doi = {10.1515/cdbme-2019-0150}, pages = {597 -- 600}, year = {2019}, abstract = {In this paper, the effect of computed tomography (CT) values of metals in 12-bit and 16-bit extended Hounsfield Unit (EHU) scale on dose calculations in radiotherapy treatment planning systems (TPS) were quantified. Dose simulations for metals in water environment were performed with the software PRIMO in 6MV photon mode. The depth dose profiles were analysed and the relative dose differences between the metals determined with 12-bit and 16-bit CT imaging, respectively, were calculated. Maximum dose differences of ΔAl= 3.0\%, ΔTi= 4.5\%, ΔCr= 6.2\% and ΔCu= 11.6\% were measured. In order to increase the accuracy of dose calculation on patients with implants, CT imaging in the EHU scale is recommended.}, language = {en} } @inproceedings{KoenigGuberinaKuehletal.2019, author = {K{\"o}nig, Britta and Guberina, Nika and K{\"u}hl, Hilmar and Zylka, Waldemar}, title = {Design and first results of a phantom study on the suitability of iterative reconstruction for lung-cancer screening with low-dose computer tomography}, series = {Konferenz: YRA -Young Researchers AcademyMedTech in NRW. 3rd YRA MedTech Symposium, 24.05.2019 in Aachen}, booktitle = {Konferenz: YRA -Young Researchers AcademyMedTech in NRW. 3rd YRA MedTech Symposium, 24.05.2019 in Aachen}, isbn = {978-3-940402-22-6}, doi = {10.17185/duepublico/48750}, pages = {29 -- 30}, year = {2019}, language = {en} } @inproceedings{NguyenKoenigZylka2019, author = {Nguyen, Hoai Thu and K{\"o}nig, Britta and Zylka, Waldemar}, title = {Establishment of a 4-Alternative-Forced-Choice test to evaluate the radiological performance of iterative reconstruction in computer tomography images}, series = {Konferenz: YRA -Young Researchers AcademyMedTech in NRW. 3rd YRA MedTech Symposium, 24.05.2019 in Aachen}, booktitle = {Konferenz: YRA -Young Researchers AcademyMedTech in NRW. 3rd YRA MedTech Symposium, 24.05.2019 in Aachen}, isbn = {978-3-940402-22-6}, doi = {10.17185/duepublico/48750}, pages = {31 -- 32}, year = {2019}, language = {en} } @inproceedings{GarciaOliveiraPapotietal.2019, author = {Garcia, Ma{\´i}ra M. and Oliveira, Tiago R. and Papoti, Daniel and Chaim, Khallil T. and Erni, Daniel and Zylka, Waldemar}, title = {Numerical evaluation of small animal warming potential when using a birdcage coil for 7T magnetic resonance imaging}, series = {Konferenz: YRA -Young Researchers AcademyMedTech in NRW. 3rd YRA MedTech Symposium, 24.05.2019 in Aachen}, booktitle = {Konferenz: YRA -Young Researchers AcademyMedTech in NRW. 3rd YRA MedTech Symposium, 24.05.2019 in Aachen}, isbn = {978-3-940402-22-6}, doi = {10.17185/duepublico/48750}, pages = {33 -- 34}, year = {2019}, language = {en} } @inproceedings{EseErniZylka2019, author = {Ese, Zehra and Erni, Daniel and Zylka, Waldemar}, title = {The influence of CT tube current and voltage on extended Hounsfield unit values}, series = {Konferenz: YRA -Young Researchers AcademyMedTech in NRW. 3rd YRA MedTech Symposium, 24.05.2019 in Aachen}, booktitle = {Konferenz: YRA -Young Researchers AcademyMedTech in NRW. 3rd YRA MedTech Symposium, 24.05.2019 in Aachen}, isbn = {978-3-940402-22-6}, doi = {10.17185/duepublico/48750}, pages = {27 -- 28}, year = {2019}, language = {en} } @inproceedings{HadertZylka2016, author = {Hadert, Nicole and Zylka, Waldemar}, title = {Numerical examinations of energy absorption in simplified spondylodesis models}, series = {1st YRA MedTech Symposium 2016. April 8th / 2016 / University of Duisburg-Essen}, booktitle = {1st YRA MedTech Symposium 2016. April 8th / 2016 / University of Duisburg-Essen}, editor = {Erni, Daniel}, isbn = {978-3-940402-10-3}, doi = {10.17185/duepublico/40821}, pages = {14 -- 15}, year = {2016}, abstract = {A simplified model for spondylodesis, ie fixation of vertebrae by osteosynthesis, is developed for virtual magnetic resonance imaging (MRI) examinations to numerically calculate energy absorption. This paper presents results of calculated energy absorption in body tissue surrounding titanium rod implants. In general each wire or rod behaves like an antenna in electromagnetic fields. The specific absorption rate (SAR) profile describes dependence of implant size. SAR hotspots appear near the rod edges. Depending of the size of implant fixation SAR is 62\%(small fixation) up to 90.95\%(large fixation) higher than without implants. In addition, local SAR profile displays local dependency on tissue: SAR is lower between the vertebrae.}, language = {en} } @inproceedings{LuebeckDemirelRiesenbecketal.2011, author = {L{\"u}beck, Robin and Demirel, Cengiz and Riesenbeck, Dorothea and Reimann, Petra and Zylka, Waldemar}, title = {Intensit{\"a}ts-Modulierte-Strahlentherapie (IMRT) und 3D-Planung im Vergleich bei Prostatakrebs-Patienten mit beidseitiger H{\"u}ftgelenksprothese}, series = {Konferenz: 17. Jahrestagung der Deutschen Gesellschaft f{\"u}r Radioonkologie, 2.-5. Juni 2011 in Wiesbaden}, booktitle = {Konferenz: 17. Jahrestagung der Deutschen Gesellschaft f{\"u}r Radioonkologie, 2.-5. Juni 2011 in Wiesbaden}, year = {2011}, language = {en} } @inproceedings{SchmitjansVorstiusZylka2017, author = {Schmitjans, Michael and Vorstius, Jan Bernd and Zylka, Waldemar}, title = {Upgrade of Bioreactor System Providing Physiological Stimuli to Engineered Musculoskeletal Tissues}, series = {2nd YRA MedTech Symposium 2017. June 8th - 9th / 2017 / Hochschule Ruhr-West}, booktitle = {2nd YRA MedTech Symposium 2017. June 8th - 9th / 2017 / Hochschule Ruhr-West}, editor = {Erni, Daniel and Fischerauer, Alice and Himmel, J{\"o}rg and Seeger, Thomas and Thelen, Klaus}, isbn = {978-3-940402-10-3}, doi = {10.17185/duepublico/43984}, pages = {45 -- 46}, year = {2017}, abstract = {A novel central control interface (CCI) is developed to improve the modular bioreactor system with regard to extendability and modifiability in Tissue Engineering (TE) applications. This paper presents the results developed in the project with open-source hardware and the graphical programming system LabVIEW. A new platform independent User Interface was further developed to contribute to the new flexibility of the device.}, language = {en} } @article{KoenigKuehlZylka2021, author = {K{\"o}nig, Britta and K{\"u}hl, Hilmar and Zylka, Waldemar}, title = {Computed tomography lung-cancer screening: does iterative reconstruction matter?}, series = {Shanghai Chest}, volume = {5}, journal = {Shanghai Chest}, number = {October}, issn = {2521-3768}, doi = {10.21037/shc-21-9}, pages = {Artikelnr. 35}, year = {2021}, abstract = {Background: By reviewing image quality and diagnostic perception, the suitability of a statistical model-based iterative reconstruction algorithm in conjunction with low-dose computed tomography for lung cancer screening is investigated. Methods: Artificial lung nodules shaped as spheres and spiculated spheres made from material with calibrated Hounsfield units were attached on marked positions in the lung structure of anthropomorphic phantoms. The phantoms were scanned using standard high contrast, and two low-dose computed tomography protocols: low-dose and ultra-low-dose. For the reconstruction, the filtered back projection and the iterative reconstruction algorithm ADMIRE at different strength levels (S1-S5) and the kernels Bl57, Br32, Br69 were used. Expert radiologists assessed image quality by performing 4-field-ranking tests and reading all image series to examine the aptitude for the detectability of lung nodules. Signal-to-noise ratio was investigated as objective image quality parameter. Results: In ranking tests for lung foci detection expert radiologists prefer medium to high iterative reconstruction strength levels. For the standard clinical kernel Bl57 and varying phantom diameter, a noticeable preference for S4 was detected. Experienced radiologists graded filtered back projection reconstructed images with the highest perceptibility. Less experienced readers assessed filtered back projection and iterative reconstruction equally with the highest grades for the Bl57 kernel. Independently of the dose protocol, the signal-to-noise ratio increases with the iterative reconstruction strength level, specifically for Br69 and Bl57. Conclusions: Subjective image perception does not significantly correlate with the experience of the radiologist, which presumably mirrors reader's training and accustomed reading adjustments. Regarding signal-to-noise ratio, iterative reconstruction outperforms filtered back projection for spheres and spiculated spheres. Iterative reconstruction matters. It promises to be an alternative to filtered back projection allowing for lung-cancer screening at markedly decreased radiation exposure but comparable or even improved image quality.}, language = {en} } @article{GorgesZylka2021, author = {Gorges, Verena and Zylka, Waldemar}, title = {Reducing dose of Cone-Beam CT used for patient positioning in radiooncology}, series = {Current Directions in Biomedical Engineering}, volume = {7}, journal = {Current Directions in Biomedical Engineering}, number = {2}, issn = {2364-5504}, doi = {10.1515/cdbme-2021-2058}, pages = {227 -- 230}, year = {2021}, abstract = {Cone-Beam computed tomography (CBCT) has become the most important component of modern radiotherapy for positioning tumor patients directly before treatment. In this work we investigate alternations to standard acquisition protocol, called preset, for patients with a tumor in the thoracic region. The effects of the changed acquisition parameters on the image quality are evaluated using the Catphan Phantom and the image analysis software Sm{\´a}ri. The weighted CT dose index (CTDIW) is determined in each case and the effects of the different acquisition protocols on the patient dose are classified accordingly. Additionally, the clinical suitability of alternative presets is tested by investigating correctness of image registration using the CIRS thorax phantom. The results show that a significant dose reduction can be achieved. It can be reduced by 51\% for a full rotation by adjusting the gantry speed.}, language = {en} } @inproceedings{QamhiyehKhouyaZylkaetal.2021, author = {Qamhiyeh, Sima and Khouya, A. and Zylka, Waldemar and Stuschke, M. and P{\"o}ttgen, C.}, title = {Vergleich der interfraktionellen Variation der Zwerchfell-Position im atemgetriggerten CBCT mit dem Planungs-4D-CT als Basis f{\"u}r das Atemcoaching und f{\"u}r die Dosisakkumulation}, series = {Strahlentherapie und Onkologie. Journal of radiation oncology, biology, physics}, volume = {197}, booktitle = {Strahlentherapie und Onkologie. Journal of radiation oncology, biology, physics}, number = {Supplement 1}, issn = {0179-7158}, doi = {10.1007/s00066-021-01791-4}, pages = {S39 -- S40}, year = {2021}, language = {de} } @inproceedings{KoenigGernhardtGuberinaetal.2020, author = {K{\"o}nig, Britta and Gernhardt, C. and Guberina, Nika and K{\"u}hl, Hilmar and Forsting, Michael and Zylka, Waldemar}, title = {Suitability of iterative reconstruction for lung-cancer screening with low-dose computer tomography: First results of a phantom study.}, series = {European Congress of Radiology 2020}, booktitle = {European Congress of Radiology 2020}, doi = {10.26044/ecr2020/C-02150}, pages = {C-02150}, year = {2020}, language = {en} } @article{BosKoenigBlexetal.2021, author = {Bos, Denise and K{\"o}nig, Britta and Blex, Sebastian and Zensen, Sebastian and Opitz, Marcel and Maier, Sandra and Forsting, Michael and Zylka, Waldemar and K{\"u}hl, Hilmar and Wetter, Axel and Guberina, Nika}, title = {Experimental examination of radiation doses from cardiac and liver CT perfusion in a phantom study as a function of organ, age and sex}, series = {Journal of Radiological Protection}, volume = {41}, journal = {Journal of Radiological Protection}, number = {3}, issn = {0952-4746}, doi = {10.1088/1361-6498/abf71f}, pages = {512}, year = {2021}, abstract = {Cardiac and liver computed tomography (CT) perfusion has not been routinely implemented in the clinic and requires high radiation doses. The purpose of this study is to examine the radiation exposure and technical settings for cardiac and liver CT perfusion scans at different CT scanners. Two cardiac and three liver CT perfusion protocols were examined with the N1 LUNGMAN phantom at three multi-slice CT scanners: a single-source (I) and second- (II) and third-generation (III) dual-source CT scanners. Radiation doses were reported for the CT dose index (CTDIvol) and dose-length product (DLP) and a standardised DLP (DLP10cm) for cardiac and liver perfusion. The effective dose (ED10cm) for a standardised scan length of 10 cm was estimated using conversion factors based on the International Commission on Radiological Protection (ICRP) 110 phantoms and tissue-weighting factors from ICRP 103. The proposed total lifetime attributable risk of developing cancer was determined as a function of organ, age and sex for adults. Radiation exposure for CTDIvol, DLP/DLP10 cm and ED10 cm during CT perfusion was distributed as follows: for cardiac perfusion (II) 144 mGy, 1036 mGy·cm/1440 mGy·cm and 39 mSv, and (III) 28 mGy, 295 mGy·cm/279 mGy·cm and 8 mSv; for liver perfusion (I) 225 mGy, 3360 mGy·cm/2249 mGy·cm and 54 mSv, (II) 94 mGy, 1451 mGy·cm/937 mGy·cm and 22 mSv, and (III) 74 mGy, 1096 mGy·cm/739 mGy·cm and 18 mSv. The third-generation dual-source CT scanner applied the lowest doses. Proposed total lifetime attributable risk increased with decreasing age. Even though CT perfusion is a high-dose examination, we observed that new-generation CT scanners could achieve lower doses. There is a strong impact of organ, age and sex on lifetime attributable risk. Further investigations of the feasibility of these perfusion scans are required for clinical implementation.}, language = {en} } @article{BosKoenigBlexetal.2021, author = {Bos, Denise and K{\"o}nig, Britta and Blex, Sebastian and Zensen, Sebastian and Opitz, Marcel and Maier, Sandra and Forsting, Michael and Zylka, Waldemar and K{\"u}hl, Hilmar and Wetter, Axel and Guberina, Nika}, title = {Experimental Examination of Radiation Doses Of Dual-and Single-Energy Computed Tomography in Chest And Upper Abdomen in a Phantom Study}, series = {Radiation Protection Dosimetry}, volume = {193}, journal = {Radiation Protection Dosimetry}, number = {3-4}, issn = {0144-8420}, doi = {10.1093/rpd/ncab052}, pages = {237 -- 246}, year = {2021}, abstract = {The aim of this phantom study is to examine radiation doses of dual- and single-energy computed tomography (DECT and SECT) in the chest and upper abdomen for three different multi-slice CT scanners. A total of 34 CT protocols were examined with the phantom N1 LUNGMAN. Four different CT examination types of different anatomic regions were performed both in single- and dual-energy technique: chest, aorta, pulmonary arteries for suspected pulmonary embolism and liver. Radiation doses were examined for the CT dose index CTDIvol and dose-length product (DLP). Radiation doses of DECT were significantly higher than doses for SECT. In terms of CTDIvol, radiation doses were 1.1-3.2 times higher, and in terms of DLP, these were 1.1-3.8 times higher for DECT compared with SECT. The third-generation dual-source CT applied the lowest dose in 7 of 15 different examination types of different anatomic regions.}, language = {en} } @article{KoenigGuberinaKuehletal.2020, author = {K{\"o}nig, Britta and Guberina, Nika and K{\"u}hl, Hilmar and Zylka, Waldemar}, title = {Eignet sich die statistische modellbasierte iterative Rekonstruktion mit low-dose Protokollen der Computertomografie f{\"u}r Lungenkrebs-Screening? Erste Ergebnisse einer Phantomstudie.}, series = {R{\"o}Fo. Fortschritte auf dem Gebiet der R{\"o}ntgenstrahlen und der bildgebenden Verfahren}, volume = {192}, journal = {R{\"o}Fo. Fortschritte auf dem Gebiet der R{\"o}ntgenstrahlen und der bildgebenden Verfahren}, number = {S01}, issn = {1438-9010}, doi = {10.1055/s-0040-1703452}, pages = {110}, year = {2020}, language = {de} } @article{KoenigGuberinaKuehletal.2020, author = {K{\"o}nig, Britta and Guberina, Nika and K{\"u}hl, Hilmar and Zylka, Waldemar}, title = {Validation of iterative CT reconstruction by inter and intra observer performance assessment of artificial lung foci}, series = {Current Directions in Biomedical Engineering}, volume = {6}, journal = {Current Directions in Biomedical Engineering}, number = {3}, issn = {2364-5504}, doi = {10.1515/cdbme-2020-3137}, pages = {4}, year = {2020}, language = {en} } @incollection{EseQamhiyehKreutneretal.2018, author = {Ese, Zehra and Qamhiyeh, Sima and Kreutner, Jakob and Schaefers, Gregor and Erni, Daniel and Zylka, Waldemar}, title = {CT Extended Hounsfield Unit Range in Radiotherapy Treatment Planning for Patients with Implantable Medical Devices}, series = {World Congress on Medical Physics and Biomedical Engineering 2018. June 3-8, 2018, Prague, Czech Republic (Vol.3)}, booktitle = {World Congress on Medical Physics and Biomedical Engineering 2018. June 3-8, 2018, Prague, Czech Republic (Vol.3)}, editor = {Lhotska, Lenka and Sukupova, Lucie and Lacković, Igor and Ibbott, Geoffrey S.}, publisher = {Springer}, address = {Singapore}, isbn = {978-981-10-9022-6}, doi = {10.1007/978-981-10-9023-3_111}, publisher = {Westf{\"a}lische Hochschule Gelsenkirchen Bocholt Recklinghausen}, pages = {599 -- 603}, year = {2018}, abstract = {Radiotherapy (RT) treatment planning is based on computed tomography (CT) images and traditionally uses the conventional Hounsfield unit (CHU) range. This HU range is suited for human tissue but inappropriate for metallic materials. To guarantee safety of patient carrying implants precise HU quantification is beneficial for accurate dose calculations in planning software. Some modern CT systems offer an extended HU range (EHU). This study focuses the suitability of these two HU ranges for the quantification of metallic components of active implantable medical devices (AIMD). CT acquisitions of various metallic and non-metallic materials aligned in a water phantom were investigated. From our acquisitions we calculated that materials with mass-density ρ > 3.0 g/cm3 cannot be represented in the CHU range. For these materials the EHU range could be used for accurate HU quantification. Since the EHU range does not effect the HU values for materials ρ < 3.0 g/cm3, it can be used as a standard for RT treatment planning for patient with and without implants.}, language = {en} } @article{EseKressmannKreutneretal.2018, author = {Ese, Zehra and Kressmann, Marcel and Kreutner, Jakob and Schaefers, Gregor and Erni, Daniel and Zylka, Waldemar}, title = {Influence of conventional and extended CT scale range on quantification of Hounsfield units of medical implants and metallic objects}, series = {Technisches Messen (tm). Plattform f{\"u}r Methoden, Systeme und Anwendungen der Messtechnik}, volume = {85}, journal = {Technisches Messen (tm). Plattform f{\"u}r Methoden, Systeme und Anwendungen der Messtechnik}, number = {5}, issn = {0171-8096}, doi = {10.1515/teme-2017-0122}, pages = {343 -- 350}, year = {2018}, abstract = {We report on the suitability of two different ranges of Hounsfield units (HU) in computed tomography (CT) for the quantification of metallic components of active implantable medical devices (AIMD). The conventional Hounsfield units (CHU) range, which is traditionally used in radiology, is well suited for tissue but suspected inappropriate for metallic materials. Precise HU values are notably beneficial in radiotherapy (RT) for accurate dose calculations, thus for the safety of patient carrying implants. Some of today's CT machines offers an extended Hounsfield units (EHU) range. This study presents CT acquisitions of a water phantom containing various metallic discs and an implantable-cardioverter defibrillator (IPG). We show that the comparison of HU values at EHU and CHU ranges clearly reveals the superiority and accuracy of EHU. Some geometrical discrepancies perpendicular to slices are observed. At EHU metal artifact reduction algorithms (MAR) underestimates HU values rendering MAR potentially inappropriate for RT.}, language = {en} } @article{RoqueZylka2016, author = {Roque, Tha{\´i}s and Zylka, Waldemar}, title = {Modelling the Growth and Treatment of Tumours}, series = {GIT laboratory journal Europe}, volume = {3-4}, journal = {GIT laboratory journal Europe}, issn = {1611-6038}, pages = {34 -- 36}, year = {2016}, abstract = {Cancer is a leading cause of morbidity and mortality worldwide, with approximately 14 million new cases and 8.2 million cancer related deaths in 2012 [1]. Moreover, the global cancer burden is expected to exceed 20 million new cancer cases by 2025. Understanding the spatial and temporal behaviour of cancer is a crucial precondition to achieve a successful treatment. Because no two cancer cases are the same, every patient should receive a treatment plan designed specifically for her case, in order to improve the patient's survival chances.}, language = {en} } @inproceedings{EseTumaQamhiyehetal.2018, author = {Ese, Zehra and Tuma, Lara and Qamhiyeh, Sima and Kreutner, Jakob and Schaefers, Gregor and Erni, Daniel and Zylka, Waldemar}, title = {Extended CT Hounsfield values scale as a method to improve radiotherapy for patients with active and metallic implants}, series = {Biomedical engineering = Biomedizinische Technik. Joint journal of the German Society for Biomedical Engineering in VDE and the Austrian and Swiss Societies for Biomedical Engineering}, volume = {63}, booktitle = {Biomedical engineering = Biomedizinische Technik. Joint journal of the German Society for Biomedical Engineering in VDE and the Austrian and Swiss Societies for Biomedical Engineering}, number = {S1}, issn = {0013-5585}, doi = {10.1515/bmt-2018-6051}, pages = {303}, year = {2018}, language = {en} } @inproceedings{WassenbergZylka2016, author = {Wassenberg, J{\"o}rg and Zylka, Waldemar}, title = {Modeling of avascular tumor growth by reaction-diffusion equations and cellular automata}, series = {1st YRA MedTech Symposium 2016. April 8th / 2016 / University of Duisburg-Essen}, booktitle = {1st YRA MedTech Symposium 2016. April 8th / 2016 / University of Duisburg-Essen}, editor = {Erni, Daniel}, isbn = {978-3-940402-10-3}, doi = {10.17185/duepublico/40821}, pages = {56}, year = {2016}, language = {en} } @incollection{EutingAraujoMoreiraZylka2012, author = {Euting, Stephan and Ara{\´u}jo-Moreira, Fernando M. and Zylka, Waldemar}, title = {Magnetic Particle Imaging Using Ferromagnetic Magnetization}, series = {Magnetic Particle Imaging. A Novel SPIO Nanoparticle Imaging Technique}, booktitle = {Magnetic Particle Imaging. A Novel SPIO Nanoparticle Imaging Technique}, editor = {Buzug, Thorsten M. and Borgert, J{\"o}rn}, publisher = {Springer}, address = {Berlin}, isbn = {978-3-642-24132-1}, doi = {10.1007/978-3-642-24133-8_3}, publisher = {Westf{\"a}lische Hochschule Gelsenkirchen Bocholt Recklinghausen}, pages = {15 -- 20}, year = {2012}, abstract = {Nanofluids, defined as fluids containing suspended solid nanoparticles, are potential systems for utilization in biomedical applications. Magnetic Particle Imaging (MPI) uses superparamagnetic nanofluids, e.g. a colloidal suspension of iron oxide particles. In this work a new biocompatible nanofluid based on pure and stable ferromagnetic carbon is investigated. Although this material has a relatively small value of coercive magnetic field, it does exhibit a true ferromagnetic behavior up to 300 K. We present results obtained from numerical investigations performed to calculate the impact of a ferromagnetic magnetization to the MPI signal chain. Moreover, by modeling ferromagnetic magnetization we prove here the general suitability of ferromagnetic materials for MPI. Due to the low saturation magnetization, however, MPI for ferromagnetic carbon will be possible only in the near future when realistic concentrations of the nanofluid ferromagnetic carbon will be experimentally obtainable.}, language = {en} } @article{ZylkaWassenberg2018, author = {Zylka, Waldemar and Wassenberg, J{\"o}rg}, title = {Investigation of avascular tumor-immune system interactions using a CA-PDE model}, series = {Current directions in biomedical engineering}, volume = {4}, journal = {Current directions in biomedical engineering}, number = {1}, issn = {2364-5504}, doi = {10.1515/cdbme-2018-0148}, pages = {615 -- 619}, year = {2018}, abstract = {We report on investigations that illustrate the interaction between the specific immune system and a young avascular tumor growing due to a diffusive nutrient supply. We formulate a hybrid cellular automata-partial differential equation (CA-PDE) model which includes cell cycle dynamics and allows for tracking the spatial and temporal evolution of this elaborate biological system. We present results of two dimensional numerical simulations that, specifically in this work, include special cases of the spherical and papillary tumor growth, the infiltration of immune system cells into the tumor and the escape of tumor cells from the regime of the immune cells.}, language = {en} } @article{GalonskeThieleErnstetal.2017, author = {Galonske, Kirsten and Thiele, Martin and Ernst, Iris and Lehrke, Ralph and Zylka, Waldemar}, title = {Comparison of treatment plans calculated by Ray Tracing and Monte Carlo algorithms for head and thorax radiotherapy with Cyberknife}, series = {Current directions in biomedical engineering}, volume = {3}, journal = {Current directions in biomedical engineering}, number = {2}, issn = {2364-5504}, doi = {10.1515/cdbme-2017-0136}, pages = {647 -- 650}, year = {2017}, abstract = {This study investigates differences between treatment plans generated by Ray Tracing (RT) and Monte Carlo (MC) calculation algorithms in homogeneous and heterogeneous body regions. Particularly, we focus on the head and on the thorax, respectively, for robotic stereotactic radiotherapy and radiosurgery with Cyberknife. Radiation plans for tumors located in the head and in the thorax region have been calculated and compared to each other in 47 cases and several tumor types.}, language = {en} } @article{RoqueKalkanZylka2012, author = {Roque, Tha{\´i}s and Kalkan, Zehra and Zylka, Waldemar}, title = {Biological effectiveness in hypofractionation: Modeling tumor survival probability for large doses with a stochastic cell-cycle model}, series = {Biomedical engineering = Biomedizinische Technik. Joint journal of the German Society for Biomedical Engineering in VDE and the Austrian and Swiss Societies for Biomedical Engineering}, volume = {57}, journal = {Biomedical engineering = Biomedizinische Technik. Joint journal of the German Society for Biomedical Engineering in VDE and the Austrian and Swiss Societies for Biomedical Engineering}, number = {SI-1-Track-O}, doi = {https://doi.org/10.1515/bmt-2012-4111}, pages = {202 -- 205}, year = {2012}, language = {en} } @inproceedings{GalonskeThieleZylka2017, author = {Galonske, Kirsten and Thiele, Martin and Zylka, Waldemar}, title = {Monte Carlo and Ray Tracing Algorithm for treatment planning in clinical applications with Cyberknife}, series = {2nd YRA MedTech Symposium 2017. June 8th - 9th / 2017 / Hochschule Ruhr-West}, booktitle = {2nd YRA MedTech Symposium 2017. June 8th - 9th / 2017 / Hochschule Ruhr-West}, editor = {Erni, Daniel and Fischerauer, Alice and Himmel, J{\"o}rg and Seeger, Thomas and Thelen, Klaus}, isbn = {978-3-940402-10-3}, doi = {10.17185/duepublico/43984}, pages = {16 -- 17}, year = {2017}, language = {en} } @inproceedings{EseQamhiyehKreutneretal.2018, author = {Ese, Zehra and Qamhiyeh, Sima and Kreutner, Jakob and Schaefers, Gregor and Erni, Daniel and Zylka, Waldemar}, title = {Erweiterte CT Hounsfield Werte Skala als eine Methode zu Verbesserung der Strahlentherapie f{\"u}r Patienten mit aktiven und metallischen Implantaten}, series = {Konferenz: 49. Jahrestagung der DGMP und 21. Jahrestagung der Deutschen Sektion der ISMRM, 19.-22. September 2018 in N{\"u}rnberg}, booktitle = {Konferenz: 49. Jahrestagung der DGMP und 21. Jahrestagung der Deutschen Sektion der ISMRM, 19.-22. September 2018 in N{\"u}rnberg}, year = {2018}, language = {de} } @article{OttoZylkaKloska2017, author = {Otto, Heinz and Zylka, Waldemar and Kloska, Jenny}, title = {MTRA-Mangel entgegenwirken - Erste Absolventen des Studienganges „Medizinische Radiologietechnologie" in Deutschland}, series = {Der Radiologe. Zeitschrift f{\"u}r diagnostische und interventionelle Radiologie, Radioonkologie, Nuklearmedizin}, volume = {57}, journal = {Der Radiologe. Zeitschrift f{\"u}r diagnostische und interventionelle Radiologie, Radioonkologie, Nuklearmedizin}, number = {8}, issn = {0033-832X}, doi = {10.1007/s00117-017-0293-0}, pages = {684 -- 685}, year = {2017}, language = {de} } @article{RoqueGarciaOtaduyZylka2013, author = {Roque, Tha{\´i}s and Garcia Otaduy, Maria Concepcion and Zylka, Waldemar}, title = {Integration of Patient Specific MRI Imaging Data Into a Stochastic Low-Grade Glioma Model}, series = {Biomedical Engineering. Biomedizinische Technik}, volume = {58}, journal = {Biomedical Engineering. Biomedizinische Technik}, number = {SI-1-Track-N}, issn = {0013-5585}, doi = {10.1515/bmt-2013-4342}, pages = {2}, year = {2013}, language = {en} } @article{KalkanZylka2013, author = {Kalkan, Zehra and Zylka, Waldemar}, title = {Protraction Effects in a Stochastic Cell-Cycle Tumor Model Exposed to Fractionated Radiotherapy}, series = {Biomedical Engineering. Biomedizinische Technik}, volume = {58}, journal = {Biomedical Engineering. Biomedizinische Technik}, number = {SI-1-Track-N}, issn = {0013-5585}, doi = {10.1515/bmt-2013-4340}, pages = {2}, year = {2013}, language = {en} } @article{BreeuwerHoldenZylka2001, author = {Breeuwer, Marcel M. and Holden, Mark and Zylka, Waldemar}, title = {Detection and correction of geometric distortion in 3D MR images}, series = {Proceedings Volume 4322, Medical Imaging 2001: Image Processing}, journal = {Proceedings Volume 4322, Medical Imaging 2001: Image Processing}, doi = {10.1117/12.430986}, year = {2001}, abstract = {Three-dimensional magnetic resonance medical images may contain scanner- and patient-induced geometric distortion. For qualitative diagnosis, geometric errors of a few millimeters are often tolerated. However, quantitative applications such as image-guided neurosurgery and radiotherapy can require an accuracy of a millimeter or better. We have developed a method to accurately measure scanner-induced geometric distortion and to correct the MR images for this type of distortion. The method involves a number of steps. First, a specially designed phantom is scanned that contains a large number of reference structures on positions with a manufacturing error of less than 0.05 mm. Next, the positions of the reference structures are automatically detected in the scanned images and a higher-order polynomial distortion-correction transformation is estimated. Then the patient is scanned and the transformation is applied to correct the patient images for the detected distortion. The distortion-correction method is explained in detail in this paper. The accuracy of the method has been measured with synthetically generated phantom scans that contain an exactly-known amount and type of distortion. The reproducibility of the method has been measured by applying it to a series of consecutive phantom scans. Validation results are briefly described in this paper, a more-detailed description is given in another submission to SPIE Medical Imaging 2001.}, language = {en} } @article{ZylkaSabczynski1999, author = {Zylka, Waldemar and Sabczynski, J{\"o}rg}, title = {Effect of Localization Devices and Registration Methods on the Accuracy of Stereotactic Frame Systems Predicted by the Gaussian Approach}, series = {Computer Aided Surgery}, volume = {4}, journal = {Computer Aided Surgery}, number = {2}, issn = {1092-9088}, doi = {10.3109/10929089909148162}, pages = {77 -- 86}, year = {1999}, abstract = {A qualitative work-flow analysis of a neurosurgical procedure indicates that the resolution of the image used to plan the intervention is the major source of inaccuracy. Quantitative experimental measurements confirm this observation. They fail, however, to explain the relationship between the accuracy of the frame components involved in a stereotactic procedure and the overall application accuracy. This investigation shows that the novel Gaussian approach is a flexible framework for the calculation of the application accuracy of frame systems. Therefore, the Gaussian approach provides a detailed understanding of the interplay between the various factors affecting accuracy. The basic ideas and limitations of the Gaussian approach are briefly explained. The effect of fiducial marker distribution and registration is investigated and shown to introduce a spatial dependence to the accuracy. The results of the Gaussian approach are compared with experimental data for three stereotactic frame devices: Leksell G, Cosman-Roberts-Wells, and Brown-Roberts-Wells. Although the Gaussian approach is an approximation, it reproduces the accuracy measured in the experiment within the statistical error of that experiment. Comp Aid Surg 4:77-86 (1999). © 1999 Wiley-Liss, Inc.}, language = {en} } @article{GarciaChaimOtaduyetal.2020, author = {Garcia, Maira M. and Chaim, Khallil T. and Otaduy, Maria C. G. and Rennings, Andreas and Erni, Daniel and Vatanchi, Maryam and Zylka, Waldemar}, title = {Investigating the influence of dielectric pads in 7T magnetic resonance imaging - simulated and experimental assessment}, series = {Current Directions in Biomedical Engineering}, volume = {6}, journal = {Current Directions in Biomedical Engineering}, number = {3}, issn = {2364-5504}, doi = {10.1515/cdbme-2020-3007}, pages = {4}, year = {2020}, language = {en} } @inproceedings{SmajicPeimannEutingKotracheetal.2010, author = {Smajic-Peimann, Sylvia and Euting, Stephan and Kotrache, Sami and Zylka, Waldemar}, title = {Simulation of SAR and temperature distributions for human organs with two different Birdcage designs at 42,6MHz and 127,8MHz}, series = {Konferenz: Jahrestagung der DGBMT und 3-L{\"a}nder-Tagung D-A-CH, 05.-08. Oktober 2010 in Rostock}, booktitle = {Konferenz: Jahrestagung der DGBMT und 3-L{\"a}nder-Tagung D-A-CH, 05.-08. Oktober 2010 in Rostock}, year = {2010}, language = {en} } @article{SchaefersZylkaBuschetal.2001, author = {Schaefers, Gregor and Zylka, Waldemar and Busch, Martin and Melzer, Andreas}, title = {Wireless application of an intravascular resonator within the Vena Cava for MRI}, series = {International Congress Series}, volume = {1230}, journal = {International Congress Series}, number = {June}, doi = {10.1016/S0531-5131(01)00227-8}, pages = {1094 -- 1099}, year = {2001}, language = {en} } @inproceedings{KochSchaefersZylka2010, author = {Koch, Christian and Schaefers, Gregor and Zylka, Waldemar}, title = {Heating of Fractured Stent in MRI at 64 \& 128 MHZ: A Numerical Study}, series = {Konferenz: ISMRM Workshop on MR Safety: RF Heating of the Human in MRI, 15.-17. Oktober 2010 in Stillwater, Minnesota (USA)}, booktitle = {Konferenz: ISMRM Workshop on MR Safety: RF Heating of the Human in MRI, 15.-17. Oktober 2010 in Stillwater, Minnesota (USA)}, year = {2010}, language = {en} } @article{EseZylka2020, author = {Ese, Zehra and Zylka, Waldemar}, title = {Extension of the Stoichiometric Calibration of CT Hounsfield values to Metallic Materials}, series = {Current Directions in Biomedical Engineering}, volume = {6}, journal = {Current Directions in Biomedical Engineering}, number = {3}, issn = {2364-5504}, doi = {10.1515/cdbme-2020-3135}, pages = {4}, year = {2020}, language = {en} } @inproceedings{Zylka2010, author = {Zylka, Waldemar}, title = {Auf dem Weg zur Beherrschung der Gefahren - Simulation der Wechselwirkungen des HF-Feldes mit Implantaten}, series = {Konferenz: 14. Fortbildungsseminar der Arbeitsgemeinschaft Physik und Technik der Deutschen R{\"o}ntgengesellschaft, 18.-19. Juni 2010 in M{\"u}nster}, booktitle = {Konferenz: 14. Fortbildungsseminar der Arbeitsgemeinschaft Physik und Technik der Deutschen R{\"o}ntgengesellschaft, 18.-19. Juni 2010 in M{\"u}nster}, year = {2010}, language = {de} } @article{ZylkaSabczynskiSchmitz1999, author = {Zylka, Waldemar and Sabczynski, J{\"o}rg and Schmitz, Georg}, title = {A Gaussian approach for the calculation of the accuracy of stereotactic frame systems}, series = {Medical Physics}, volume = {26}, journal = {Medical Physics}, number = {3}, doi = {10.1118/1.598529}, pages = {381 -- 391}, year = {1999}, abstract = {Stereotactic frame systems are widely used in neurosurgery. The accuracy of frame devices is considered as a gold standard to which the accuracy of new frameless stereotactic navigation systems is compared. The purpose of this study is to develop a general approach for the prediction of the application accuracy of stereotactic systems. The approach will be applied to the frame-based biopsy performed with three frame devices: Leksell G, Cosman-Roberts-Wells (CRW), and Brown-Roberts-Wells (BRW). A work-flow analysis will be carried out demonstrating that the accuracy relevant for a clinical application comprises several error sources including imaging, target and entry point selection, image to frame coordinates registration, and the setting of mechanical parameters of the frame. These error sources will be postulated to obey a Gaussian distribution probability density. The linear, i.e., Gaussian, error propagation, will be used to link all error contributions thus to calculate the cumulative accuracy of the frame used in the application. Although the Gaussian approach is an approximation, it allows for an analytical treatment of the accuracy. Both the accuracy at the target point and the accuracy of the probe needle guidance along the planned trajectory have been investigated. Of great significance is the relationship found between accuracy, pixel dimension, and image slice thickness, the latter being the dominant factor for slices of more than 1.5 mm thickness, yielding inaccuracies larger than 1.5 mm. For target points the predictions for the application accuracy have been compared to the results of measurements, showing good agreement with the experimental data.}, language = {en} } @inproceedings{EseKressmannKreutneretal.2017, author = {Ese, Zehra and Kressmann, Marcel and Kreutner, Jakob and Douiri, Amin and Scholz, Stefan and G{\"o}rtz, Wolfgang and Schaefers, Gregor and Erni, Daniel and Zylka, Waldemar}, title = {A comparison of CT Hounsfield units of medical implants and their metallic and electrical components determined by a conventional and an extended CT-scale}, series = {2nd YRA MedTech Symposium 2017. June 8th - 9th / 2017 / Hochschule Ruhr-West}, booktitle = {2nd YRA MedTech Symposium 2017. June 8th - 9th / 2017 / Hochschule Ruhr-West}, editor = {Erni, Daniel and Fischerauer, Alice and Himmel, J{\"o}rg and Seeger, Thomas and Thelen, Klaus}, isbn = {978-3-940402-10-3}, doi = {10.17185/duepublico/43984}, pages = {12 -- 13}, year = {2017}, language = {en} } @inproceedings{RudigkeitGouveaSantosRoqueetal.2011, author = {Rudigkeit, Nina and Gouv{\^e}a Santos, Bruno and Roque, Tha{\´i}s and Zylka, Waldemar}, title = {Modeling Tumor Growth and Treatment using Imaging Data}, series = {Konferenz: 45. Jahrestagung der DGBMT, 27.-30. September 2011 in Freiburg}, booktitle = {Konferenz: 45. Jahrestagung der DGBMT, 27.-30. September 2011 in Freiburg}, year = {2011}, language = {en} }