This article presents a novel approach to passive tracking of paramagnetic markers during endovascular interventions, exploiting positive contrast of the markers to their background, so-called "white marker tracking." The positive contrast results from dephasing of the background signal with a slice gradient, while near the marker the signal is conserved because a dipole field induced by the marker compensates the dephasing gradient. Theoretical investigation shows that a local gradient induced by the local dipole field will nearly always cancel the dephasing gradient somewhere, regardless of marker composition, gradient strength, orientation, and acquisition parameters. The actual appearance of the white marker is determined by the marker strength, echo-time, slice thickness, and gradient strength, as shown both theoretically and experimentally In endovascular interventional MRI, consistent and reliable tracking of the inserted devices is one of the major requirements for the success of an MR-guided endovascular intervention. In the past, several methods have been suggested and shown valuable. In the active approach a combination of small catheter mounted receiver coils and readout-gradients along the coordinate axes can be used to determine the actual position of the coil (1). This method is very time-efficient because only three readouts are needed for coil localization. However, a significant drawback of this active approach is the yet unsolved problem of unacceptable potential heating of long connecting signal cables (2).Passive tracking is not subject to heating problems. In this approach, small paramagnetic rings are mounted as markers on catheters and guidewires (3). These paramagnetic rings produce local field distortions, which show up as areas of signal loss in gradient-echo (GE) imaging. A disadvantage of passive tracking is that it is image-based, resulting in a relatively time-consuming tracking scheme. Furthermore, this tracking method is often hampered by the need for subtraction due to weak negative contrast of the passive markers to their background, especially if thick imaging slices are used. This subtraction leads to an undesired increased sensitivity to motion and flow artifacts.The passive tracking approach would significantly improve if the described disadvantages could be overcome. In this article, we present a novel approach to passive tracking using positive contrast of the markers to their background, so-called "white marker tracking." The positive contrast results from dephasing the background signal with a slice gradient, while near the marker the signal is conserved because the dipole field induced by the marker compensates the dephasing gradient. The idea of local gradient compensation is well known in the literature (4 -6) and has mostly been used in functional MRI experiments to recover signal loss in brain regions that suffer from global field inhomogeneities due to air cavities. In this article, the idea of gradient compensation is exploited for the depiction and tracking of p...

Epilepsy surgery requires precise localization of the epileptic source. EEG-correlated functional MRI (EEG-fMRI) is a new technique showing the haemodynamic effects of interictal epileptiform activity. This study assesses its potential added value in the presurgical evaluation of patients with complex source localization. Adult surgical candidates considered ineligible because of an unclear focus and/or presumed multifocality on the basis of EEG underwent EEG-fMRI. Interictal epileptic discharges (IEDs) in the EEG during fMRI were identified by consensus between two observers. Topographically distinct IED sets were analysed separately. Only patients with significant, positive blood oxygen level-dependent (BOLD) responses that were topographically related to the EEG were re-evaluated for surgery. Forty-six IED sets from 29 patients were analysed. In eight patients, at least one BOLD response was significant, positive and topographically related to the IEDs. These patients were rejected for surgery because of an unclear focus (n = 3), presumed multifocality (n = 2) or a combination of both (n = 3). EEG-fMRI improved localization in four out of six unclear foci. In patients with presumed multifocality, EEG-fMRI advocated one of the foci in one patient and confirmed multifocality in four out of five patients. In four patients EEG-fMRI opened new prospects for surgery and in two of these patients intracranial EEG supported the EEG-fMRI results. In these complex cases, EEG-fMRI either improved source localization or corroborated a negative decision regarding surgical candidacy. It is thus a valuable tool in the presurgical evaluation of patients. Guidelines for the use of EEG-fMRI in clinical practice are proposed.

Purpose:To study 3T compared to 1.5T phased array magnetic resonance imaging (MRI) in the presurgical work-up of patients with epilepsy with complex focus localization. Materials and Methods:In all, 37 patients (Ͼ10 years) in preoperative work-up for epilepsy surgery were offered 3T in addition to 1.5T MRI if ambiguity existed about the epileptic focus. Scans were randomly reviewed by two observers, blinded for prior imaging, patient-identifying information, and each other's assessments, followed by a consensus meeting. The number of abnormal scans, detected lesions, and interobserver agreement were calculated and compared. The final consensus was compared to original scan reports. Results:One observer identified 22 lesions in both 3 and 1.5T scans, while the second identified more lesions in 1.5T scans (28 vs. 20). 3T MRI had better interobserver agreement. 3T revealed more dysplasias, while 1.5T revealed more tissue loss and mesial temporal sclerosis (MTS). The final consensus yielded 29 lesions, whereas original reports identified only 17 lesions. Conclusion:The 3T scans revealed different lesions compared to 1.5T. Patients can benefit most from 3T scans when a dysplasia is suspected. Reevaluation by another experienced neuroradiologist is advised in case of negative or equivocal MRIs.

Ho-PLLA-MS used for internal radionuclide therapy can be imaged clearly in vivo with MR imaging.

Noninvasive imaging techniques like magnetic resonance imaging (MRI), computed tomography (CT) and single photon emission computed tomography (SPECT) play an increasingly important role in the diagnostic workup and treatment of cancerous disease. In this context, a distinct trend can be observed towards the development of contrast agents and radiopharmaceuticals that open up perspectives on a multimodality imaging approach, involving all three aforementioned techniques. To promote insight into the potentialities of such an approach, we prepared an overview of the strengths and limitations of the various imaging techniques, in particular with regard to their capability to quantify the spatial distribution of a multimodal diagnostic agent. To accomplish this task, we used a two-step approach. In the first step, we examined the situation for a particular therapeutic anti-cancer agent with multimodal imaging opportunities, viz. holmium-loaded microspheres (HoMS). Physical phantom experiments were performed to enable a comparative evaluation of the three modalities assuming the use of standard equipment, standard clinical scan protocols, and signal-known-exactly conditions. These phantom data were then analyzed so as to obtain first order estimates of the sensitivity and detection limits of MRI, CT and SPECT for HoMS. In the second step, the results for HoMS were taken as a starting point for a discussion of the factors affecting the sensitivity and detection limits of MRI, CT and SPECT for multimodal agents in general. In this, emphasis was put on the factors that must be taken into account when extrapolating the findings for HoMS to other diagnostic tasks, other contrast agents, other experimental conditions, and other scan protocols.