Design and application of a four-channel transmit/receive surface coil for functional cardiac imaging at 7T

Purpose

To design and evaluate a four‐channel cardiac transceiver coil array for functional cardiac imaging at 7T.

Materials and Methods

A four‐element cardiac transceiver surface coil array was developed with two rectangular loops mounted on an anterior former and two rectangular loops on a posterior former. specific absorption rate (SAR) simulations were performed and a B calibration method was applied prior to obtain 2D FLASH CINE (mSENSE, R = 2) images from nine healthy volunteers with a spatial resolution of up to 1 × 1 × 2.5 mm³.

Results

Tuning and matching was found to be better than 10 dB for all subjects. The decoupling (S₂₁) was measured to be >18 dB between neighboring loops, >20 dB for opposite loops, and >30 dB for other loop combinations. SAR values were well within the limits provided by the IEC. Imaging provided clinically acceptable signal homogeneity with an excellent blood‐myocardium contrast applying the B calibration approach.

Conclusion

A four‐channel cardiac transceiver coil array for 7T was built, allowing for cardiac imaging with clinically acceptable signal homogeneity and an excellent blood‐myocardium contrast. Minor anatomic structures, such as pericardium, mitral, and tricuspid valves and their apparatus, as well as trabeculae, were accurately delineated. J. Magn. Reson. Imaging 2011;. © 2011 Wiley‐Liss, Inc.     

Impact of HMG-CoA reductase inhibition on brain pathology

Over the past two decades, 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors (HMGCRIs), originally designed to lower cholesterol blood levels, have been found to affect GTPase signaling during normal intracellular tasks. This finding has prompted use of these drugs in pathological situations, where such signaling processes need to be manipulated. Here, we review recent progress on the outcome of modulating GTPase signaling after inhibition of protein prenylation by HMGCRIs. We also discuss current controversies over the direct implications of these cholesterol-lowering agents on cholesterol-rich membrane lipid rafts and associated signaling. By reviewing these two different cellular events and the evidence from clinical studies, an overall assessment can be made of the concept of interfering with the HMG-CoA reductase pathway in different brain pathologies. We thereby provide a rational link between the benefit of applying HMGCRIs in brain pathologies, such as multiple sclerosis, Alzheimer's disease and stroke, and the impact on signaling in specific cell types crucial to disease pathogenesis.     

The clinical value of therapeutic plasma exchange in multifocal motor neuropathy

OBJECTIVE: Although there is evidence for a pathogenic role of humoral factors in multifocal motor neuropathy (MMN), plasma exchange (PE) is assumed to be an ineffective treatment. We set out to elucidate possible reasons for this apparent contradiction. METHODS: A retrospective analysis of seven patients with MMN, who underwent 4 to 18 sessions of PE. Clinical response, electrophysiological parameter and anti-ganglioside antibody titers were reviewed. RESULTS: Two patients, who had anti-ganglioside antibodies, exhibited transient clinical responses to PE, manifested by improved neurological function. Whereas electrophysiological parameters continued to worsen in all patients, anti-ganglioside antibody titers declined during PE, but increased after PE. CONCLUSION: PE is of limited therapeutic value in patients with MMN, who do not respond to established treatment options. It may only be useful as an adjunctive treatment in a subset of patients. The transient decrease of anti-ganglioside-antibodies titers suggests that pathogenic humoral factors in MMN are only temporarily reduced. Further, PE treatment alone is insufficient to prevent axons from continuing degeneration, which may explain the failure of PE to substantially influence the disease course of patients with MMN.     

Autoimmune diseases of the peripheral nervous system

Autoimmune-mediated diseases targeting the peripheral nerve represent a group of disorders often associated with high clinical disability. At present, therapeutic options are limited. The application of innovative and cutting-edge technologies to the study of immune-mediated disorders of the peripheral nervous system (PNS) have generated a better understanding of underlying principles of the organization of the immune network present in the peripheral nerve and its dialogue with the systemic immune system. These insights may foster the development of specific and highly effective therapies for autoimmune diseases of the peripheral nerve. Of great interest in this context is the application of monoclonal antibodies, such as rituximab or alemtuzumab, which in small observational studies provided promising clinical results. But also other immunomodulatory or immunosuppressive drugs used in other indications currently find their way to PNS autoimmunity. Clearly, prospective controlled clinical trials are warranted before making firm conclusions on the feasibility of these innovative therapeutic approaches for treating immune-mediated disease of the peripheral nerve.     

Multiband diffusion‐weighted MRI of the eye and orbit free of geometric distortions using a RARE‐EPI hybrid

Diffusion‐weighted imaging (DWI) provides information on tissue microstructure. Single‐shot echo planar imaging (EPI) is the most common technique for DWI applications in the brain, but is prone to geometric distortions and signal voids. Rapid acquisition with relaxation enhancement [RARE, also known as fast spin echo (FSE)] imaging presents a valuable alternative to DWI with high anatomical accuracy. This work proposes a multi‐shot diffusion‐weighted RARE‐EPI hybrid pulse sequence, combining the anatomical integrity of RARE with the imaging speed and radiofrequency (RF) power deposition advantage of EPI. The anatomical integrity of RARE‐EPI was demonstrated and quantified by center of gravity analysis for both morphological images and diffusion‐weighted acquisitions in phantom and in vivo experiments at 3.0 T and 7.0 T. The results indicate that half of the RARE echoes in the echo train can be replaced by EPI echoes whilst maintaining anatomical accuracy. The reduced RF power deposition of RARE‐EPI enabled multiband RF pulses facilitating simultaneous multi‐slice imaging. This study shows that diffusion‐weighted RARE‐EPI has the capability to acquire high fidelity, distortion‐free images of the eye and the orbit. It is shown that RARE‐EPI maintains the immunity to B₀ inhomogeneities reported for RARE imaging. This benefit can be exploited for the assessment of ocular masses and pathological changes of the eye and the orbit.     

The subpopulation of microglia expressing functional muscarinic acetylcholine receptors expands in stroke and Alzheimer’s disease

Microglia undergo a process of activation in pathology which is controlled by many factors including neurotransmitters. We found that a subpopulation (11 %) of freshly isolated adult microglia respond to the muscarinic acetylcholine receptor agonist carbachol with a Ca²⁺ increase and a subpopulation of similar size (16 %) was observed by FACS analysis using an antibody against the M3 receptor subtype. The carbachol-sensitive population increased in microglia/brain macrophages isolated from tissue of mouse models for stroke (60 %) and Alzheimer’s disease (25 %), but not for glioma and multiple sclerosis. Microglia cultured from adult and neonatal brain contained a carbachol-sensitive subpopulation (8 and 9 %), which was increased by treatment with interferon-γ to around 60 %. This increase was sensitive to blockers of protein synthesis and correlated with an upregulation of the M3 receptor subtype and with an increased expression of MHC-I and MHC-II. Carbachol was a chemoattractant for microglia and decreased their phagocytic activity.