Bashar Issa

Magnetic Nanoparticles: Surface Effects and Properties Related to Biomedicine Applications

Due to finite size effects, such as the high surface-to-volume ratio and different crystal structures, magnetic nanoparticles are found to exhibit interesting and considerably different magnetic properties than those found in their corresponding bulk materials. These nanoparticles can be synthesized in several ways (e.g., chemical and physical) with controllable sizes enabling their comparison to biological organisms from cells (10–100 μm), viruses, genes, down to proteins (3–50 nm). The optimization of the nanoparticles’ size, size distribution, agglomeration, coating, and shapes along with their unique magnetic properties prompted the application of nanoparticles of this type in diverse fields. Biomedicine is one of these fields where intensive research is currently being conducted. In this review, we will discuss the magnetic properties of nanoparticles which are directly related to their applications in biomedicine. We will focus mainly on surface effects and ferrite nanoparticles, and on one diagnostic application of magnetic nanoparticles as magnetic resonance imaging contrast agents.

In vivo measurement of the apparent diffusion coefficient in normal and malignant prostatic tissues using echo-planar imaging

To measure for the first time the apparent diffusion coefficient (ADC) values in anatomical regions of the prostate for normal and patient groups, and to investigate its use as a differentiating parameter between healthy and malignant tissue within the patient group.

Magnetic Properties of Magnetic Nanoparticles for Efficient Hyperthermia

Localized magnetic hyperthermia using magnetic nanoparticles (MNPs) under the application of small magnetic fields is a promising tool for treating small or deep-seated tumors. For this method to be applicable, the amount of MNPs used should be minimized. Hence, it is essential to enhance the power dissipation or heating efficiency of MNPs. Several factors influence the heating efficiency of MNPs, such as the amplitude and frequency of the applied magnetic field and the structural and magnetic properties of MNPs. We discuss some of the physics principles for effective heating of MNPs focusing on the role of surface anisotropy, interface exchange anisotropy and dipolar interactions. Basic magnetic properties of MNPs such as their superparamagnetic behavior, are briefly reviewed. The influence of temperature on anisotropy and magnetization of MNPs is discussed. Recent development in self-regulated hyperthermia is briefly discussed. Some physical and practical limitations of using MNPs in magnetic hyperthermia are also briefly discussed.

PEG coating reduces NMR relaxivity of Mn0.5Zn0.5Gd0.02Fe1.98O4 hyperthermia nanoparticles

To investigate both T1 and T2 MR relaxation enhancement of Gd substituted Zn‐Mn ferrite magnetic nanoparticles. Both uncoated and polyethylene glycol (PEG) coated particles were used.

NMR relaxation in systems with magnetic nanoparticles: A temperature study

To measure and model nuclear magnetic resonance (NMR) relaxation enhancement due to the presence of gadolinium (Gd)‐substituted Zn‐Mn ferrite magnetic nanoparticles (MNP) at different temperatures.

Temperature Dependence of Saturation Magnetization and Coercivity in Mn0.5Zn0.5Gd0.02Fe1.98O4 Ferrite Nanoparticles

The influence of temperature on coercivity, Hc and saturation magnetization, Ms were investigated experimentally in Mn0.5Zn0.5Gd0.02Fe1.98O4 ferrite nanoparticles (average size 35 nm). Isothermal magnetization curves M (H) were obtained in the field range from -5 kOe to +5 kOe at different temperatures after the zero field cooling (ZFC) process. The temperature dependence of the coercivity, Hc(T) deviated slightly from the classical Knellers law. The temperature dependence of saturation magnetization, Ms(T) was found to have an excellent agreement with the Blochs law. These results are discussed in terms of several factors such as the size and size distribution of the particles, inter-particle interactions and the surface spin.

Medical Physics Education and Training: Regional and International Challenges

Due to recent fast technical developments and the ever increasing demands for better health services and living standards, increasing demands are witnessed for a larg- er number of better qualified medical physicists. Pressures are mounting on educational institutes to come up with the appro- priate balance among background teaching material, skills, and practical training. The widening spectrum of new teaching courses possible for addition to the university curriculum presents a non-trivial program structure problem. In addition to more financial and hardware demands, it requires careful tailoring of the educational process (teaching material and skills, timing and delivery methods, program structure) ac- cording to the particular goals of the program and the profes- sional needs of the geographic location. We highlight some of the difficulties experienced locally in both medical physics (MP) education and profession and compare them with vari- ous regions of the globe. Finally, we propose some suggestions to alleviate them. In particular we emphasize the importance of acquiring programming skills at an early stage of the educa- tional process. This is so not only because it is a skill, but also because it can be developed into a teaching tool itself through the solving of many MP problems by modeling and simulation.

Design of self-refocused pulses under short relaxation times

The effect of using self-refocused RF pulses of comparable duration to relaxation times is studied in detail using numerical simulation. Transverse magnetization decay caused by short T2 and longitudinal component distortion due to short T1 are consistent with other studies. In order to design new pulses to combat short T1 and T2 the relaxation terms are directly inserted into the Bloch equations. These equations are inverted by searching the RF solution space using simulated annealing global optimization technique. A new T2-decay efficient excitation pulse is created (SDETR: single delayed excursion T2 resistive) which is also energy efficient. Inversion pulses which improve the inverted magnetization profile and achieve better suppression of the remaining transverse magnetization are also created even when both T1 and T2 are short. This is achieved, however, on the expense of a more complex B1 shape of larger energy content.

Improved discrimination of breast lesions using selective sampling of segmented MR images

Objective: The aim of this work is to examine if the specificity of differentiation between malignant and benign tumours can be improved by retrospectively examining lesion-extracted distributions. A semi-automated method for selecting a region-of-interest (ROI) is described. A new histogram segmentation approach for sampling pharmacokinetic breast maps of transfer uptake is defined in order to assign classification variables for the lesion. Method: Fifty exchange rate parameter maps were extracted from 49 subjects and retrospectively analysed. Distributions obtained from semi-automatically delineated ROIs were subdivided into ten overlapping segments. Parameters were extracted from each segment which effectively presents a new pixel intensity sampling strategy. Mann–Whitney non-parametric tests and ROC curves were generated. Results: Correlation exists between mean parameter values drawn from semi-automatically or manually drawn ROIs. However, the former yield higher specificity values as applied to this subset of enhancing benign lesions. Segmenting the exchange rate parameter histogram allows the identification of which part of the distribution correlates most with tumour type. Significantimprovement in specificity is obtained when using half the pixels within the ROI. Conclusion: Improved specificity values are obtained by a new method of selecting the differentiation parameters which relies on intensity rather than spatial segmentation. Only half the pixels available within the ROI contributed to the measured classification parameters

MRI Simulation Study Investigating Effects of Vessel Topology, Diffusion, and Susceptibility on Transverse Relaxation Rates Using a Cylinder Fork Model

Brain vasculature is conventionally represented as straight cylinders when simulating blood oxygenation level dependent (BOLD) contrast effects in functional magnetic resonance imaging (fMRI). In reality, the vasculature is more complicated with branching and coiling especially in tumors. Diffusion and susceptibility changes can also introduce variations in the relaxation mechanisms within tumors. This study introduces a simple cylinder fork model (CFM) and investigates the effects of vessel topology, diffusion, and susceptibility on the transverse relaxation rates R2* and R2. Simulations using Monte Carlo methods were performed to quantify R2* and R2 by manipulating the CFM at different orientations, bifurcation angles, and rotation angles. Other parameters of the CFM were chosen based on physiologically relevant values: vessel diameters (~2‒10u2009µm), diffusion rates (1u2009×u200910−11‒1u2009×u200910−9u2009m2/s), and susceptibility values (3u2009×u200910−8–4u2009×u200910−7 cgs units). R2* and R2 measurements showed a significant dependence on the bifurcation and rotation angles in several scenarios using different vessel diameters, orientations, diffusion rates, and susceptibility values. The angular dependence of R2* and R2 using the CFM could potentially be exploited as a tool to differentiate between normal and tumor vessels. The CFM can also serve as the elementary building block to simulate a capillary network reflecting realistic topological features.