LIVIVO - Search results -

Search results

Result 1 - 10 of total 20

Search options

Article ; Online: Accuracy of CT numbers and electron density calibration for mixtures of materials with low and high-atomic number

Ese Zehra / Erni Daniel / Zylka Waldemar

Current Directions in Biomedical Engineering, Vol 9, Iss 1, Pp 411-

2023 Volume 414

Abstract: In computed tomography (CT) materials with high-atomic number Z cause image artefacts, thus, errors in CT numbers given in Hounsfield Units (HU). Also, the conventional HU scale (CHU) implemented in CT scanners is truncated, i.e., it does not cover high- ... ...

Abstract	In computed tomography (CT) materials with high-atomic number Z cause image artefacts, thus, errors in CT numbers given in Hounsfield Units (HU). Also, the conventional HU scale (CHU) implemented in CT scanners is truncated, i.e., it does not cover high-Z materials. These restrictions lead to incorrect mapping of CT numbers to electron density, which are used in radiotherapy (RT) treatment planning systems (TPS). Even analytical conversion methods are only permissible for tissue-equivalent materials. In terms of HU-to-density conversion in RT TPS, we investigated the CT numbers of material mixtures up to Z<29 at the CHU and an extended-HU (EHU) scale, respectively, and quantify the systematic errors of image artefacts. In [1] the feasibility of a stoichiometric analytical calibration method were analyzed for metals and adapted for higher accurcy, for energies of 80 kV and 120 kV. In this work, we add results for 100 kV and 140 kV to cover the wide diagnostic range. The CT numbers are effected by physical and machine-based properties and depend strongly on the energy, e.g., for Cu a HU difference of 6 171HU at 80 kV and 140 kV occured. The analytical calibration parameters change with energy by a factor between 2 and 10 depending on the physical process. Although for high- Z materials our calibration procedure remains in conflict with rigorous physics [2], it offers an improved and a practical way to predict electron densities from CT numbers.
Keywords	computed-tomography calibration ; extended hounsfield scale ; stoichiometric calibration ; radiotherapy ; Medicine ; R
Subject code	600
Language	English
Publishing date	2023-09-01T00:00:00Z
Publisher	De Gruyter
Document type	Article ; Online
Database	BASE - Bielefeld Academic Search Engine (life sciences selection)

Full text online

Full text

Inter-library loan at ZB MED

Your chosen title can be delivered directly to ZB MED Cologne location if you are registered as a user at ZB MED Cologne.

Article ; Online: Reducing dose of Cone-Beam CT used for patient positioning in radiooncology

Gorges Verena / Zylka Waldemar

Current Directions in Biomedical Engineering, Vol 7, Iss 2, Pp 227-

2021 Volume 230

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 ... ...

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 Smári. 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. A more patientspecific uptake protocol for patients with laterally located tumor was created which allows a dose reduction of 54%.
Keywords	cone-beam ; computer tomography ; dose ; reduction ; patient position ; radiooncology ; Medicine ; R
Subject code	610
Language	English
Publishing date	2021-10-01T00:00:00Z
Publisher	De Gruyter
Document type	Article ; Online
Database	BASE - Bielefeld Academic Search Engine (life sciences selection)

Full text online

Full text

Inter-library loan at ZB MED

Your chosen title can be delivered directly to ZB MED Cologne location if you are registered as a user at ZB MED Cologne.

Article ; Online: Extension of the Stoichiometric Calibration of CT Hounsfield values to Metallic Materials

Ese Zehra / Zylka Waldemar

Current Directions in Biomedical Engineering, Vol 6, Iss 3, Pp 526-

2020 Volume 529

Abstract: Nowadays, patients with metallic implants undergoing radiotherapy may suffer from inaccuracy in the treatment plan caused by the implant. To ensure a precise plan an accurate relation between Hounsfield values of the computer tomographic (CT) images and ... ...

Abstract	Nowadays, patients with metallic implants undergoing radiotherapy may suffer from inaccuracy in the treatment plan caused by the implant. To ensure a precise plan an accurate relation between Hounsfield values of the computer tomographic (CT) images and the electron density of the elements and material mixtures is indispensable. In order to extend the stoichiometric calibration approach known for tissues to the regime of metallic materials, the basic physical equations as well as approximations in the parametrization and fitting are carefully reviewed. CT images of a standard calibration phantom and pure metallic samples up to the atomic number Z = 29 were acquired for various energies. Hounsfield values were determined on an extended Hounsfield scale which allows the mapping of material having high atomic number Z. It is found that from basic physics an empirical factorization of the cross-sections into a function of Z and a function of photon energy E is not allowed over a wide range of Z. Specifically, the parameterization for tissue like materials cannot be prolonged to materials with high-Z. Thus, the calibration is subdivided into regions of materials and its accuracy is quantified in each region. It depends, among others, on the knowledge of the X-ray photon spectra, the segmentation of the material samples and the empirical parameterization of the linear-attenuation coefficient.
Keywords	computed tomography ; calibration ; extended hounsfield units ; stoichiometric calibration ; electron density ; radio therapy ; Medicine ; R
Subject code	600
Language	English
Publishing date	2020-09-01T00:00:00Z
Publisher	De Gruyter
Document type	Article ; Online
Database	BASE - Bielefeld Academic Search Engine (life sciences selection)

Full text online

Full text

Inter-library loan at ZB MED

Your chosen title can be delivered directly to ZB MED Cologne location if you are registered as a user at ZB MED Cologne.

Article ; Online: 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

Ese Zehra / Zylka Waldemar

Current Directions in Biomedical Engineering, Vol 5, Iss 1, Pp 597-

2019 Volume 600

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 ... ...

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.
Keywords	computed tomography ; radiotherapy ; primo ; monte carlo simulation ; Medicine ; R
Language	English
Publishing date	2019-09-01T00:00:00Z
Publisher	De Gruyter
Document type	Article ; Online
Database	BASE - Bielefeld Academic Search Engine (life sciences selection)

Full text online

Full text

Inter-library loan at ZB MED

Your chosen title can be delivered directly to ZB MED Cologne location if you are registered as a user at ZB MED Cologne.

Article ; Online: Design and Development of a Bioreactor System for Mechanical Stimulation of Musculoskeletal Tissue

Bartel Theresa / Mortimer Jeremy W. / Zylka Waldemar / Paxton Jennifer Z. / Vorstius Jan

Current Directions in Biomedical Engineering, Vol 9, Iss 1, Pp 122-

2023 Volume 125

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 ... ...

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. The bioreactor reported here can now be implemented in tissue engineering applications including tissue specimen.
Keywords	tissue engineering ; bioreactor ; rapid prototyping ; enthesis tissue ; Medicine ; R
Subject code	670
Language	English
Publishing date	2023-09-01T00:00:00Z
Publisher	De Gruyter
Document type	Article ; Online
Database	BASE - Bielefeld Academic Search Engine (life sciences selection)

Full text online

Full text

Inter-library loan at ZB MED

Your chosen title can be delivered directly to ZB MED Cologne location if you are registered as a user at ZB MED Cologne.

Article ; Online: Investigation of avascular tumor–immune system interactions using a CA–PDE model

Zylka Waldemar / Waßenberg Jörg

Current Directions in Biomedical Engineering, Vol 4, Iss 1, Pp 615-

2018 Volume 619

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 ... ...

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.
Keywords	avascular tumor ; mathematical model ; specific immune system ; tumor-immune system interactions ; cellular automata ; Medicine ; R
Language	English
Publishing date	2018-09-01T00:00:00Z
Publisher	De Gruyter
Document type	Article ; Online
Database	BASE - Bielefeld Academic Search Engine (life sciences selection)

Full text online

Full text

Inter-library loan at ZB MED

Your chosen title can be delivered directly to ZB MED Cologne location if you are registered as a user at ZB MED Cologne.

Article ; Online: Validation of iterative CT reconstruction by inter and intra observer performance assessment of artificial lung foci

König Britta / Guberina Nika / Kühl Hilmar / Zylka Waldemar

Current Directions in Biomedical Engineering, Vol 6, Iss 3, Pp 534-

2020 Volume 537

Abstract: We investigate the suitability of statistical and model-based iterative reconstruction (IR) algorithm strengths and their influence on image quality and diagnostic performance in low-dose computer tomography (CT) protocols for lung-cancer screening ... ...

Abstract	We investigate the suitability of statistical and model-based iterative reconstruction (IR) algorithm strengths and their influence on image quality and diagnostic performance in low-dose computer tomography (CT) protocols for lung-cancer screening procedures. We evaluate the inter- and intra-observer performance for the assessment of iterative CT reconstruction. Artificial lung foci shaped as spheres and spicules made from material with calibrated Hounsfield units were pressed within layered granules in lung lobes of an anthropomorphic phantom. Adaptively, a soft-tissue- and fat- extension ring were attached. The phantom with foci was scanned using standard high contrast, low-dose and ultra lowdose protocols. For reconstruction the IR algorithm ADMIRE at four different strength levels were used. Two ranking tests and Friedman statistics were performed. Fleiss k and modified Cohen’s kneywere used to quantify inter- and intra-observer performance. In conjunction with the standard lung kernel BL75 radiologists evaluated medium to high IR strength, with preference to S4, as suitable for lung foci detection. When varying reconstruction kernels the ranking became more random than with varying phantom diameter. The inter-observer reliability shows poor to slight agreement expressed by k<0 and k=0-0.20 . For the intra-observer reliability non- agreement with kney=0-0.20and moderate agreement with kney=0.60-0.79 for the first ranking test, and almost perfect agreement with kney>0.90 for the second ranking test was observed. In conclusion, our validation suggests radiological preference of medium to high iteration strengths, especially S4, for lung foci detection. An investigation of the correlation between diagnostic experience and the subjective perception of IR reconstructed CT images still needs to be investigated.
Keywords	ct ; iterative reconstruction ; lung nodule detection ; inter- and intra-observer reliability ; low-dose ; image quality ; phantom ; Medicine ; R
Subject code	610
Language	English
Publishing date	2020-09-01T00:00:00Z
Publisher	De Gruyter
Document type	Article ; Online
Database	BASE - Bielefeld Academic Search Engine (life sciences selection)

Full text online

Full text

Inter-library loan at ZB MED

Your chosen title can be delivered directly to ZB MED Cologne location if you are registered as a user at ZB MED Cologne.

Article ; Online: Design and first results of a phantom study on the suitability of iterative reconstruction for lung-cancer screening with low-dose computer tomography

König Britta / Guberina Nika / Kühl Hilmar / Zylka Waldemar

Current Directions in Biomedical Engineering, Vol 5, Iss 1, Pp 593-

2019 Volume 596

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 ... ...

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 strength levels were used. Volume CT dose index (CTDIvol) and dose-length product were recorded. Radiologists assessed subjective image quality using a six-point Likert scale by reading all image series in terms detectability of lung nodules. As a measurable objective image quality parameter signal-to-noise ratios (SNR) were investigated. The CTDIvol decreases by more than 70% for all protocols and nodules compared to diagnostic reference value for chest CT (p<0.00001). The evaluation of image quality parameters, i.e. SNR, indicates that LD and ULD protocols in conjunction with IR assert high quality lung-nodule detection. The results reveal that IR algorithm with moderate to high strength is an indispensable alternative to FBP in low-dose scanning, thus, potentially suitable for lung-tumour screening.
Keywords	ct ; iterative reconstruction ; fbp ; low-dose ; image quality ; phantom study ; lung nodule detection ; Medicine ; R
Subject code	610
Language	English
Publishing date	2019-09-01T00:00:00Z
Publisher	De Gruyter
Document type	Article ; Online
Database	BASE - Bielefeld Academic Search Engine (life sciences selection)

Full text online

Full text

Inter-library loan at ZB MED

Your chosen title can be delivered directly to ZB MED Cologne location if you are registered as a user at ZB MED Cologne.

Article ; Online: Thermal measurements of a muscle-mimicking phantom during ultra-high field magnetic resonance imaging

Garcia Maíra M. / Oliveira Tiago R. / Chaim Khallil T. / Otaduy Maria C. G. / Bruns Christian / Svejda Jan T. / Bernarding Johannes / Erni Daniel / Zylka Waldemar

Current Directions in Biomedical Engineering, Vol 9, Iss 1, Pp 319-

2023 Volume 322

Abstract: At ultra-high field MRI (Bo>7T) it is crucial to predict and control the patient safety. Commonly patient safety is controlled by the power deposited in the tissue (specific absorption rate - SAR). However, temperature distributions do not always ... ...

Abstract	At ultra-high field MRI (Bo>7T) it is crucial to predict and control the patient safety. Commonly patient safety is controlled by the power deposited in the tissue (specific absorption rate - SAR). However, temperature distributions do not always correlate directly with SAR distributions, which makes temperature control also a crucial parameter to guarantee patient safety. In this work, temperature changes were accessed by MR thermometry, specifically by the proton resonance frequency shift technique (PRF). A phantom mimicking muscle tissue was used to evaluate the temperature rise caused by the radiofrequency (RF) absorption during 7T MRI, applied through a commercial birdcage head coil. A pulse-sequence protocol was implemented for both, the generation of temperature increase and the MR thermometry. To control the temperature, a digital thermometer was used, and oil tubes were utilized to dismiss the drift effects for PRF. Measurements of the phantom’s dielectric characteristics, i.e. conductivity and permittivity, were in good agreement with the literature values for muscle. Spatio-temporal evaluations showed a temperature increase in time via RF exposure and the feasibility of measuring temperature maps using the PRF shift method. The accuracy of the PRF shift method increased when the drift effects were quantified and dismissed, indicating a PRF reading accuracy differing less than 0.5 °C from the thermometer. Results also validate our heating and temperature imaging protocol. This study is a valuable contribution to the evaluation of heating effects caused by RF absorption and demonstrates potential impact on future thermal investigations, which may use different heating sources, as well validate thermal simulations.
Keywords	mr thermometry ; 7t mri ; mri safety ; proton resonance frequency (prf) ; temperature mapping ; Medicine ; R
Subject code	600
Language	English
Publishing date	2023-09-01T00:00:00Z
Publisher	De Gruyter
Document type	Article ; Online
Database	BASE - Bielefeld Academic Search Engine (life sciences selection)

Full text online

Full text

Inter-library loan at ZB MED

Your chosen title can be delivered directly to ZB MED Cologne location if you are registered as a user at ZB MED Cologne.

Article ; Online: Numerical examinations of simplified spondylodesis models concerning energy absorption in magnetic resonance imaging

Hadert Nicole / Liu Qi / Zylka Waldemar

Current Directions in Biomedical Engineering, Vol 2, Iss 1, Pp 653-

2016 Volume 658

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 ...

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.
Keywords	sar ; mri ; osteosynthesis implants ; numerical simulation ; Medicine ; R
Subject code	600
Language	English
Publishing date	2016-09-01T00:00:00Z
Publisher	De Gruyter
Document type	Article ; Online
Database	BASE - Bielefeld Academic Search Engine (life sciences selection)

Full text online

Full text

Inter-library loan at ZB MED

Your chosen title can be delivered directly to ZB MED Cologne location if you are registered as a user at ZB MED Cologne.

To top

Full text online

More links

Kategorien

Inter-library loan at ZB MED

Full text online

More links

Kategorien

Inter-library loan at ZB MED

Full text online

More links

Kategorien

Inter-library loan at ZB MED

Full text online

More links

Kategorien

Inter-library loan at ZB MED

Full text online

More links

Kategorien

Inter-library loan at ZB MED

Full text online

More links

Kategorien

Inter-library loan at ZB MED

Full text online

More links

Kategorien

Inter-library loan at ZB MED

Full text online

More links

Kategorien

Inter-library loan at ZB MED

Full text online

More links

Kategorien

Inter-library loan at ZB MED

Full text online

More links

Kategorien

Inter-library loan at ZB MED