Relative to common clinical magnetic field strengths, higher fields benefit functional brain imaging both by providing additional signal for high-resolution applications and by improving the sensitivity of endogenous contrast due to the blood oxygen level dependent (BOLD) mechanism, which has limited detection power at low magnetic fields relative to the use of exogenous contrast agent. This study evaluates the utility of iron oxide contrast agent for gradient echo functional MRI at 9.4 T in rodents using cocaine and methylphenidate as stimuli. Relative to the BOLD method, the use of high iron doses and short echo times provided a roughly twofold global increase in functional sensitivity, while also suppressing large vessel signal and reducing susceptibility artifacts. MRI is widely used to assess brain function in humans and animals due to a powerful combination of capabilities, including high spatiotemporal resolution, volumetric coverage, and the potential for noninvasive, longitudinal studies. Many of the target applications for fMRI in animal models are inherently challenging in terms of sensitivity. For instance, functional signals often are attenuated in disease or recovery states, such as the evolution of neuronal plasticity during recovery from stroke (1-3). Pharmacological stimuli can produce widespread, graded, dosedependent changes in local brain function; low-field blood oxygen level dependent (BOLD) signal is simply inadequate for detecting changes in many brain regions without averaging results from a very large number of animals (4,5).High magnetic field strengths provide numerous advantages for fMRI, as well as challenges (6). Sample polarization increases with magnetic field, providing additional signal that can be traded for higher spatial resolution. Functional changes in the BOLD relaxation rate also increase with field strength (7), making BOLD detection power more competitive with that provided by an exogenous agent (8). Moreover, paramagnetic deoxyhemoglobin shortens blood relaxation times at high field strengths, which should decrease spatially nonspecific signal associated with draining vessels. However, the time scale for relaxation of transverse magnetization using gradient echoes (T 2 *) becomes progressively shorter and more heterogeneous, especially in regions near magnetic susceptibility interfaces that arise at air-tissue and bone-tissue interfaces. Signal dropout and image distortion reduce some of the theoretical advantages of BOLD fMRI at high fields by forcing a choice between increased image artifacts or the reduced sensitivity that accompanies short gradient echo times or spin echo methods.Because of the limitations of BOLD sensitivity, many fMRI applications in animal models have employed exogenous contrast agents (1-3,9 -11), which experimentally have been shown to markedly improve fMRI sensitivity at magnetic field strengths up to 4.7 T (4,5,8,12-14). The use of exogenous agents with very long blood half lives for fMRI has been termed IRON fMRI (5), to denote the increas...

We present the long-term clinical and angiographic follow-up results of 100 consecutive intracranial aneurysms treated with Onyx liquid embolic system (MTI, Irvine, Calif.), either alone or combined with an adjunctive stent, in a single center. A total of 100 aneurysms in 94 patients were treated with endosaccular Onyx packing. Intracranial stenting was used adjunctively in 25 aneurysms including 19 during initial treatment and 6 during retreatment. All aneurysms except two were located in the internal carotid artery. Of the 100 aneurysms, 35 were giant or large/wide-necked, and 65 were small. Follow-up angiography was performed in all 91 surviving patients (96 aneurysms) at 3 and/or 6 months. Follow-up angiography was performed at 1, 2, 3, 4 and 5 years in 90, 41, 26, 6 and 2 patients, respectively. Overall, aneurysm recanalization was observed in 12 of 96 aneurysms with follow-up angiography (12.5%). All 12 were large or giant aneurysms, resulting in a 36% recanalization rate in the large and giant aneurysm group. One aneurysm out of 25 treated with the combination of a stent and Onyx showed recanalization. There was also no recanalization in the follow-up of small internal carotid artery aneurysms treated with balloon assistance only. At final follow-up, procedure- or device-related permanent neurological morbidity was present in eight patients (8.3%). There were two procedure-related and one disease-related (subarachnoid hemorrhage) deaths (mortality 3.2%). Delayed spontaneous asymptomatic occlusion of the parent vessel occurred in two patients, detected on routine follow-up. Onyx provides durable aneurysm occlusion with parent artery reconstruction resulting in perfectly stable 1-year to 5-year follow-up angiography both in small aneurysms treated with balloon assistance only (0% recanalization rate) and large or giant aneurysms treated with stent and Onyx combination (4% recanalization rate). Endosaccular Onyx packing with balloon assistance may not be adequate for stable long-term results in those with a large or giant aneurysm. However, the recanalization rate of 36% in these aneurysms is better than the reported results with other techniques, i.e., coils with or without adjunctive bare stents.

No abstract

No abstract

No abstract