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Item type:Publication, Access status: with files , Saline bolus for negative contrast perfusion imaging in magnetic particle imaging(IOP Publishing, 2023-09-07); ; ; ; Objective. Magnetic particle imaging (MPI) is capable of high temporal resolution measurements of the spatial distribution of magnetic nanoparticles and therefore well suited for perfusion imaging, which is an important tool in medical diagnosis. Perfusion imaging in MPI usually requires a fresh bolus of tracer material to capture the key signal dynamics. Here, we propose a method to decouple the imaging sequence from the injection of additional tracer material, without further increasing the administered iron dose in the body with each image. Approach. A bolus of physiological saline solution without any particles (negative contrast) diminishes the steady-state concentration of a long-circulating tracer during passage. This depression in the measured concentration contributes to the required contrast dynamics. The presence of a long-circulating tracer is therefore a prerequisite to obtain the negative contrast. As a quantitative tracer based imaging method, the signal is linear in the tracer concentration for any location that contains nanoparticles and zero in the surrounding tissue which does not provide any intrinsic signal. After tracer injection, the concentration over time (positive contrast) can be utilized to calculate dynamic diagnostic parameters like perfusion parameters in vessels and organs. Every acquired perfusion image thus requires a new bolus of tracer with a sufficiently large iron dose to be visible above the background. Main results. Perfusion parameters are calculated based on the time response of the proposed negative bolus and compared to a positive bolus. Results from phantom experiments show that normalized signals from positive and negative boli are concurrent and deviations of calculated perfusion maps are low. Significance. Our method opens up the possibility to increase the total monitoring time of a future patient by utilizing a positive-negative contrast sequence, while minimizing the iron dose per acquired image.Publicationtype: Journal ArticleScopus© Citations 1 12 25 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Using negative bolus in dynamic MPI(Infinite Science Publishing, 2023-03-19); ; ; ; In Magnetic Particle Imaging, the spatial distribution of a tracer is measured and depicted with a concentration dependent signal intensity for any location that contains particles, whereas surrounding tissue does not provide any signal. After tracer injection, the signal over time (positive contrast) can be utilized as a transient response to calculate dynamic diagnostic parameters like perfusion parameter maps. In this work, a bolus of physiological saline solution without any particles (negative contrast) is proposed, where the remaining steady state concentration contributes to the image contrast. This opens up the possibility to stretch the total monitoring time of a patient by utilizing a positive-negative contrast sequence, while keeping the total iron dose constant in the subject. Resulting time responses show that normalized signals from positive and negative boli are concurrent in the phantom experiments, indicating identical diagnostic parameters for in-vivo use.Publicationtype: Journal ArticleScopus© Citations 1 36 118 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Perfusionsbildgebung anhand positiver und negativer Bolusanwendung in der Magnetpartikelbildgebung(2022-07-01); Real-time perfusion imaging is a potential application of magnetic particle imaging. It is used to assess the vascular system and the perfusion of organs and tissues. The intravenous injection of a tracer bolus causes concentration-time curves in a volume of interest. Based on this, various perfusion parameters can be assessed and visualized in perfusion maps, e.g. time to peak, mean transit time, blood volume and blood flow. At certain diseases the consistent monitoring of the perfusion of certain organs is required. Until the reach of a steady state (when the concentration-time curves do not show a profile anymore), the injected particles spread in the patient’s blood. Thus, the injection of another bolus is necessary for every image acquisition. The maximum amount of tracer that may be injected to a patient in a certain time frame is limited. Additionally, the concentration of the tracer in the blood is increased by every bolus. Though, the change of concentration might not be detectable anymore. In this work a possible approach to this problem is considered. Therein, the form of the injection for the acquisition of a new perfusion image is inverted by the use of a water or NaCl bolus (negative bolus) instead of a tracer bolus (positive bolus). On the basis of a phantom of a rat’s heart that is connected to a pump, it is investigated if negative boluses might also be used for perfusion imaging as positive boluses to obtain the same results for the calculation of perfusion parameters. The concentration-time curves of the negative boluses necessarily need to be normalized to the positive ones. For this study, optical experiments were performed by use of ink and water as well as MPI measurements by use of tracer and water for the positive and negative boluses, respectively. Based on these experiments, time-curves were derived and assessed concerning their possibility of normalization. Besides, perfusion maps were calculated and compared quantitatively. As can be seen from the experiments, positive and negative boluses of identic size can be normalized to each other.Publicationtype: Master Thesis31 44 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , 3D printed anatomical model of a rat for medical imaging(De Gruyter, 2019-09-18); ; ; ; For medical research, approximately 115 million animals are needed every year. Rodents are used to test possible applications and procedures for the diagnosis of anatomical and physiological diseases. However, working with living animals increases the complexity of an experiment. Accurate experimental planning is essential in order to fulfill the 3R rules (replace, reduce and refine). Especially in tracer-based imaging modalities, such as magnetic particle imaging (MPI), where only nanoparticles give a positive contrast, the anatomical structure of the rodent is not visible without co-registration with another imaging modality. This leads to problems in the experimental planning, as parameters, such as field of view, rodent position and tracer concentration, have to be determined without visual feedback. In this work, a 3D CAD rat model is presented, which can be used to improve the experiment planning and thus reduce the number of animals required. It was determined using an anatomy atlas and 3D printed with stereolithography. The resulting model contains the most important organs and vessels as hollow cavities. By filling these with appropriate tracer materials, the phantom can be used in different imaging modalities such as MPI, magnetic resonance imaging (MRI) or computed tomography (CT). In a first MPI measurement, the phantom was filled with superparamagnetic nanoparticles. Finally, a successful visualization of all organs and vessels of the phantom was possible. This enables the planning of the experiment and the optimization of experimental parameters for a region of interest, where certain organs in a living animal are localized.Publicationtype: Journal ArticleScopus© Citations 8 602 568