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Purpose To present a new method, S0 estimation of the free induction decay combined with a single spin echo measurement (SOFIDSE), that enables simultaneous measurements of R2*, R2, and R2′ in order to quantify the local concentration of holmium microspheres (Ho-MS) for radioembolization. Theory and Methods SOFIDSE estimates R2* and the signal magnitude at time point 0, S0, from a multigradient echo readout of the free induction decay and subsequently estimates R2 using S0 and a single spin echo, from which R2′ is deducted. The method was evaluated by comparing SOFIDSE R2 values with values obtained from shifted spin echo (SSE) measurements on a phantom setup containing Ho-MS and from dual spin echo measurements on a healthy volunteer. Results On average, SOFIDSE showed a small overestimation of R2 values compared with SSE independent of the microsphere concentration. R2′ values determined by subtraction of either SOFIDSE R2 or SSE R2 from R2* showed excellent agreement (correlation coefficient = 1; P = 9 · 10−11). The Ho-MS-induced R2′ values obtained by SOFIDSE were insensitive to the R2 value of the tissue in which they resided. Conclusion SOFIDSE enables quantification of Ho-MS, in media with spatially or temporally varying R2 values, in a single acquisition. Magn Reson Med 73:273-283, 2015. © 2014 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Quantitativeperfusion MRI is a promising new technique capable of offering information on cerebral blood flow (CBF), cerebral blood volume (CBV), and mean transit time (MTT). However, it is still unclear how these perfusion parameters relate to the underlying physiological indicators and how they compare to conventional techniques. The purpose of this study was to investigate how quantitative perfusion MRI is related to the cerebrovascular reactivity as measured by transcranial Doppler ultrasonography (TCD) in combination with a CO2 stimulus in patients with a symptomatic occlusion of the internal carotid artery (ICA). Thirty-nine patients with transient or minor disabling retinal or hemispheric ischemic symptoms and an occlusion of the ICA underwent quantitative perfusion MRI and CO2 reactivity measurements by TCD. Perfusion parameters were correlated with cerebrovascular reactivity measurements and compared with measurements of control subjects. The results of this study show a negative correlation between the cerebrovascular reactivity and the time to bolus peak (TBP) both for gray (r = −0.26, P = 0.035) and white matter (r = −0.28, P = 0.026). No correlation between resting CBV, CBF, or MTT and cerebrovascular reactivity was found. Our results indicate that an increase in TBP reflects a poor development of collateral flow, which is supported by a relatively low CO2 reactivity in these patients. [Copyright &y& Elsevier]

Gradient echo techniques are often hampered by signal dephasing due to macroscopic phase perturbations because of system imperfections (shimming) or object induced perturbations of the magnetic field (hemorrhagic lesions, calcified tissue, air-tissue interfaces). Many techniques have been proposed to reduce the effects of macroscopic phase variations. Among these techniques are tuned pulse sequences, fitting techniques and reconstruction algorithms. These methods, however, suffer from one or more of the following drawbacks: they require longer acquisition times, require additional acquisitions, compensate only locally, can only be applied to multi-gradient echo data or may result in inaccurate results. In this work a generally applicable post-processing technique is presented to evaluate and compensate signal alterations invoked by first and second order macroscopic phase incoherences. In this technique, the derivatives of the signal phase are determined by applying the Fourier derivative theorem on the complex data. As a result, the phase derivatives are obtained without phase unwrapping and without compromising the resolution. The method is validated for single and multi-echo acquisitions by experiments on a co-axial cylinder phantom with known macroscopic field disturbances. The potential of the method is demonstrated on a multi-gradient echo acquisition on the head of a human volunteer. In general a first order correction is shown to be sufficient, however higher order correction is found to be beneficial near sharp transitions of the magnetic field., (Copyright © 2011 Elsevier Inc. All rights reserved.)

In this paper the preparation and characterization of holmium-loaded alginate microspheres is described. The rapid development of medical imaging techniques offers new opportunities for the visualisation of (drug-loaded) microparticles. Therefore, suitable imaging agents have to be incorporated into these particles. For this reason, the element holmium was used in this study in order to utilize its unique imaging characteristics. The paramagnetic behaviour of this element allows visualisation with MRI and holmium can also be neutron-activated resulting in the emission of gamma-radiation, allowing visualisation with gamma cameras, and beta-radiation, suitable for therapeutic applications. Almost monodisperse alginate microspheres were obtained by JetCutter technology where alginate droplets of a uniform size were hardened in an aqueous holmium chloride solution. Ho(3+) binds via electrostatic interactions to the carboxylate groups of the alginate polymer and as a result alginate microspheres loaded with holmium were obtained. The microspheres had a mean size of 159 microm and a holmium loading of 1.3 +/- 0.1% (w/w) (corresponding with a holmium content based on dry alginate of 18.3 +/- 0.3% (w/w)). The binding capacity of the alginate polymer for Ho(3+) (expressed in molar amounts) is equal to that for Ca(2+), which is commonly used for the hardening of alginate. This indicates that Ho(3+) has the same binding affinity as Ca(2+). In line herewith, dynamic mechanical analyses demonstrated that alginate gels hardened with Ca(2+) or Ho(3+) had similar viscoelastic properties. The MRI relaxation properties of the microspheres were determined by a MRI phantom experiment, demonstrating a strong R(2)* effect of the particles. Alginate microspheres could also be labelled with radioactive holmium by adding holmium-166 to alginate microspheres, previously hardened with calcium (labelling efficiency 96%). The labelled microspheres had a high radiochemical stability (94% after 48 h incubation in human serum), allowing therapeutic applications for treatment of cancer. The potential in vivo application of the microspheres for a MR-guided renal embolization procedure was illustrated by selective administration of microspheres to the left kidney of a pig. Anatomic MR-imaging showed the presence of holmium-loaded microspheres in the kidney. In conclusion, this study demonstrates that the incorporation of holmium into alginate microspheres allows their visualisation with a gamma camera and MRI. Holmium-loaded alginate microspheres can be used therapeutically for embolization and, when radioactive, for local radiotherapy of tumours., (Copyright 2007 Wiley Periodicals, Inc.)

Aim: To evaluate the value of dynamic contrast enhanced magnetic resonance angiography (CE-MRA) for classification of endoleaks after endovascular aneurysm repair (EVAR)., Materials and Methods: Twenty-eight patients, between 2 days and 54 months after EVAR, were evaluated with CTA, MRI and dynamic CE-MRA. The additional diagnostic value of the dynamic 3D CE-MRA was evaluated by determining the ability of the dynamic series in pinpointing the site of inflow of an endoleak., Results: An endoleak was detected in 23 patients. Seventeen of the 23 dynamic series were technically successful (no disturbing artifacts limiting the diagnostic value). Using MRI our findings were: 2 type I, 6 type II, 1 type III, no type IV endoleaks and in 14 cases classification could not be made. The classification results for MRI plus the dynamic CE-MRA were: 2 type I, 12 type II, 1 type III, no type IV endoleaks and in eight cases classification could not be made. In six cases the dynamic MRA allowed classification of the endoleak, which was not possible with the non-dynamic images alone (p=0.091, Fisher exact)., Conclusion: This pilot study shows that dynamic CE-MRA can have additional value in the classification of endoleaks. Dynamic CE-MRA might obviate the need for diagnostic digital subtraction angiography and aid planning for intervention.

The rapid developments of high-resolution imaging techniques are offering unique possibilities for the guidance and follow up of recently developed sophisticated anticancer therapies. Advanced biodegradable drug delivery systems, e.g. based on liposomes and polymeric nanoparticles or microparticles, are very effective tools to carry these anticancer agents to their site of action. Elements from the group of lanthanides have very interesting physical characteristics for imaging applications and are the ideal candidates to be co-loaded either in their non-radioactive or radioactive form into these advanced drug delivery systems because of the following reasons: Firstly, they can be used both as magnetic resonance imaging (MRI) and computed tomography (CT) contrast agents and for single photon emission computed tomography (SPECT). Secondly, they can be used for radionuclide therapies which, importantly, can be monitored with SPECT, CT, and MRI. Thirdly, they have a relatively low toxicity, especially when they are complexed to ligands. This review gives a survey of the currently developed lanthanide-loaded microparticulate systems that are under investigation for cancer imaging and/or cancer therapy.

The 2003 Nobel Prize for Physiology or Medicine has been awarded to the American physical chemist Paul Lauterbur (1929) and the British physicist Peter Mansfield (1933) for their discoveries in the field of magnetic resonance imaging (MRI). Lauterbur devised a method to encode the nuclear magnetic resonance relaxation information in an object spatially and to reproduce it as an image. Mansfield succeeded in exciting a slice perpendicular to the gradient direction, which enabled him to define a third dimension directly. In addition, he developed methods to enhance the speed of imaging. A third scientist, the physician Raymond Damadian, although equally a pioneer in the field of MRI, was--disputably--not a laureate.

In this review we describe current applications and future perspectives of MR angiography, MR flow quantification, and interventional MRI in hemodialysis access management. Each section starts with a brief overview of the main techniques that are currently available or under development. This is followed by a survey of the pertinent literature. Each section concludes with a discussion of the reported findings and an indication of research opportunities.