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Functional magnetic resonance imaging (fMRI) has become a powerful and influential method to non-invasively study neuronal brain activity. For this purpose, the blood oxygenation level-dependent (BOLD) effect is most widely used. T2* weighted echo planar imaging (EPI) is BOLD sensitive and the prevailing fMRI acquisition technique. Here, we present an alternative to its standard Cartesian recordings, i.e. k-space density weighted EPI, which is expected to increase the signal-to-noise ratio in fMRI data. Based on in vitro and in vivo pilot measurements, we show that fMRI by k-space density weighted EPI is feasible and that this new acquisition technique in fact boosted spatial and temporal SNR as well as the detection of local fMRI activations. Spatial resolution, spatial response function and echo time were identical for density weighted and conventional Cartesian EPI. The signal-to-noise ratio gain of density weighting can improve activation detection and has the potential to further increase the sensitivity of fMRI investigations.

Abstract??ObjectiveDensity weighted phase-encoding has proven to be a highly efficient method fork-space sampling as it improves the localization properties and increases the signal-to-noise ratio for extended samples at the same time. But either density weighted imaging lengthens the minimum scan time or, if the Nyquist criterion is violated in parts of the sampledk-space, undersampling artefacts occur. Purpose of this work was to combine density weighted imaging and parallel imaging techniques to improve the spatial response function and consequently the signal-to-noise ratio without spoiling image quality by undersampling artefacts.Materials and MethodsImages were acquired with parallel acquisition for effective density weighted imaging (PLANED imaging) and compared to results sampled with conventional Cartesian phase-encoding with the same spatial resolution and the same number of excitations.ResultsBoth in vivo and phantom measurements recorded with the PLANED method revealed a considerable enhancement of the signal-to-noise ratio and a remarkable reduction of Gibbs artefacts compared to standard Cartesian imaging.ConclusionIt has been demonstrated that PLANED improves image quality by suppressing truncation artefacts and increasing the SNR without lengthening the measurement time. [ABSTRACT FROM AUTHOR]

To show the application of auto-sensitivity encoding (SENSE)—a self-calibrating parallel imaging technique—to first pass perfusion imaging of the whole human heart. The self-calibrating parallel imaging method auto-SENSE was implemented for a saturation recovery turbo-fast low-angle shot (FLASH) sequence on a 1.5-T scanner using a standard four-element body phased array coil. By reducing the acquisition time per slice by a factor of two compared to conventional turbo FLASH imaging, the number of imaged slices could be doubled to six to ten with an unchanged temporal resolution of one image per heartbeat. This technique has been tested in eight healthy volunteers for contrast-enhanced heart perfusion imaging. Auto-SENSE heart perfusion imaging with improved coverage of the human heart could be performed successfully in all volunteers. A first quantitative comparison of perfusion values between the auto-SENSE and the non-SENSE techniques shows good agreement. Auto-SENSE allows perfusion imaging of the whole human heart without gaps. J. Magn. Reson. Imaging 2003;18:702–708. © 2003 Wiley-Liss, Inc. [ABSTRACT FROM AUTHOR]

Malignant hyperthermia (MH) is a metabolic myopathy with an abnormal release of calcium by the sarcoplasmic reticulum (SR), triggered by volatile anesthetics and succinylcholine. Similarly, caffeine enhances Ca2+release by the SR in vitro. In a prospective, randomized study, high-energy phosphates were studied by intramuscular 31-phosphorus magnetic resonance spectroscopy (31P-MRS) in 10 MH-susceptible (MHS) and 7 MH-nonsusceptible (MHN) subjects before and after injection of 0.5 ml caffeine (20 mM). Intramuscular energy balance, measured by the ratios of Pi/PCr and Pi/γ-ATP, did not differ between MHS and MHN patients before and after intramuscular caffeine injection. However, within each group, Pi/PCr and Pi/γ-ATP increased significantly only in the MHS group. Intramuscular caffeine injection seemed to impair the metabolic balance in MHS individuals. This may reflect a local calcium overload leading to consumption of high-energy phosphates and increase of inorganic phosphate. Intramuscular stimulation by caffeine and 31P-MRS may provide a valuable tool to investigate MH-related metabolic disturbances. Muscle Nerve 28: 353–358, 2003 [ABSTRACT FROM AUTHOR]

To evaluate the sodium longitudinal relaxation (T1) characteristics for myocardium and blood in humans. Eleven healthy volunteers were examined by using a 23Na heart surface coil at a 1.5 T clinical scanner equipped with a broadband spectroscopy option. 23Na MR measurements were performed by using a three-dimensional spoiled gradient echo sequence (in-plane resolution, 3.5 mm × 7 mm; slice thickness, 24 mm; TE, 3.1 msec; bandwidth, 65 Hz/pixel; TR, 21 to 150 msec). Longitudinal T1 relaxation time components were 31.6±7.0 msec and 31.1±7.5 msec for myocardium and blood, respectively. 23Na T1 relaxation times of myocardium and blood can be determined in humans. The results are in agreement with values obtained from animal studies. J. Magn. Reson. Imaging 2003;17:726–729. © 2003 Wiley-Liss, Inc. [ABSTRACT FROM AUTHOR]