Perfusion imaging by a flow-sensitive alternating inversion recovery (Fair) technique: Application to functional brain imaging

Perfusion is a crucial physiological parameter for tissue function. To obtain perfusion-weighted images and consequently to measure cerebral blood flow (CBF), a newly developed flow-sensitive alternating inversion recovery (FAIR) technique was used. Dependency of FAIR signal on inversion times (TI) was examined; signal is predominantly located in large vessels at short TI, whereas it is diffused into gray matter areas at longer TI. CBF of gray matter areas in the human brain is 71 ± 15 SD ml/100 g/min (n = 6). In fMRI studies, micro- and macrovessel inflow contributions can be obtained by adjusting TIs. Signal changes in large vessel areas including the scalp were seen during finger opposition at a TI of 0.4 s; however, these were not observed at a longer TI of 1.4 s. To compare with commonly used BOLD and slice selective inversion recovery techniques, FAIR and BOLD images were acquired at the same time during unilateral finger opposition. Generally, activation sites determined by three techniques are consistent. However, activation of some areas can be detected only by FAIR, not by BOLD, suggesting that the oxygen consumption increase couples with the CBF change completely. Relative and absolute CBF changes in the contralateral motor cortex are 53 ± 17% SD (n = 9) and 27 ± 11 SD ml/100 g/min (n = 9), respectively.     

A Holographic Augmented Reality Interface for Visualizing of MRI Data and Planning of Neurosurgical Procedures

Journal of Digital Imaging - The recent introduction of wireless head-mounted displays (HMD) promises to enhance 3D image visualization by immersing the user into 3D morphology. This work...     

Fast anatomical imaging of the heart and assessment of myocardial perfusion with arrhythmia insensitive magnetization preparation

A new contrast preparation based on modified driven equilibrium Fourier transfer is introduced and evaluated for generation of T₁-weighted images for assessment of the myocardial perfusion with contrast agent first-pass kinetics. The new preparation scheme produces T₁ contrast with insensitivity to arrhythmias in prospectively triggered sequential imaging thereby eliminating one of the major sources of problems in potential patient studies with previously employed contrast preparations schemes.     

Dynamic imaging of contrast-enhanced coronary vessels with a magnetization prepared rotated stripe keyhole acquisition

PURPOSE: To evaluate dynamic coronary imaging based on a magnetization prepared contrast-enhanced (CE) rotated stripe keyhole acquisition scheme. MATERIALS AND METHODS: Background suppression of long T(1) tissue was used so that the k-space would be selectively dominated by the contribution of the CE vessel. The phase-encoding axis was then adjusted parallel to the long axis of the vessel to sample the significant power spectrum of the vessel. The performance of this approach was evaluated by means of computer simulations and experimental studies on phantoms and a pig model instrumented with an intracoronary catheter for infusion of contrast media. RESULTS: Computer simulations and phantom studies demonstrated that by rotating the gradient axes to match the k-space pattern of the frequency spectrum, one can reduce the keyhole band to 20% of the full k-space while preserving the structure's lumen width and sharpness. In vivo studies validated those findings, and dynamic angiograms of the CE coronary arteries were obtained as rapidly as 140 msec per image, with an in-plane spatial resolution of 1.5 mm. CONCLUSION: With efficient background suppression, a rotated stripes keyhole acquisition can efficiently acquire the significant k-space of a CE vessel, and provide improved vessel definition with a reduced acquisition matrices scheme.     

Cerebellar activation during copying geometrical shapes

We studied functional MRI activation in the cerebellum during copying 9 geometrical shapes (equilateral triangle, isosceles triangle, square, diamond, vertical trapezoid, pentagon, hexagon, circle, and vertical lemniscate). Twenty subjects were imaged during 3 consecutive 45-s periods (rest, visual presentation, and copying). First, there was a positive relation between cerebellar activation and the peak speed of individual movements. This effect was strongest in the lateral and posterior ipsilateral cerebellum but it was also present in the paramedian zones of both cerebellar hemispheres and in the vermis. A finer grain analysis of the relations between the time course of the blood oxygenation level-dependent activation and movement parameters revealed a significant relation to hand position and speed but not to acceleration. Second, there was a significant relation between the intensity of voxel activation during visual presentation and the speed of the upcoming movement. The spatial distribution of these voxels was very similar to that of the voxels activated during copying, indicating that the cerebellum might be involved in motor rehearsal, in addition to its role during movement execution. Finally, a factor analysis of the intensity of activated voxels in the ipsilateral cerebellum during copying (adjusted for the speed effect) extracted 3 shape factors. Factor 1 reflected "roundness," factor 2 "upward pointing," and factor 3 "pointing (up or down) and elongation." These results link cerebellar activation to more global, spatial aspects of copying.     

Logarithmic transformation for high-field BOLD fMRI data

Parametric statistical analyses of BOLD fMRI data often assume that the data are normally distributed, the variance is independent of the mean, and the effects are additive. We evaluated the fulfilment of these conditions on BOLD fMRI data acquired at 4 T from the whole brain while 15 subjects fixated a spot, looked at a geometrical shape, and copied it using a joystick. We performed a detailed analysis of the data to assess (a) their frequency distribution (i.e. how close it was to a normal distribution), (b) the dependence of the standard deviation (SD) on the mean, and (c) the dependence of the response on the preceding baseline. The data showed a strong departure from normality (being skewed to the right and hyperkurtotic), a strong linear dependence of the SD on the mean, and a proportional response over the baseline. These results suggest the need for a logarithmic transformation. Indeed, the log transformation reduced the skewness and kurtosis of the distribution, stabilized the variance, and made the effect additive, i.e. independent of the baseline. We conclude that high-field BOLD fMRI data need to be log-transformed before parametric statistical analyses are applied.     

Quantitative measurements of cerebral blood flow in rats using the FAIR technique: Correlation with previous lodoantipyrine autoradiographic studies

Flow-sensitive alternating inversion recovery (FAIR) is a recently introduced MRI technique for assessment of perfusion that uses blood water as an endogenous contrast agent. To characterize the FAIR signal dependency on spin tagging time (inversion time (Tl)) and to validate FAIR for cerebral blood flow (CBF) quantification, studies were conducted on the rat brain at 9.4 T using a conventional gradient-recalled echo sequence. The 7¹, of cerebral cortex and blood was found to be 1.9 and 2.2 s, respectively, and was used for CBF calculations. At short Tls (<0.8 s), the FAIR signal originates largely from vascular components with fast flows, resulting in an overestimation of CBF. For Tl > 1.5 s, the CBF calculated from FAIR is independent of the spin tagging time, suggesting that the observed FAIR signal originates predominantly from tissue/capillary components. CBF values measured by FAIR with Tl of 2.0 s were found to be in good agreement with those measured by the iodoantipyrine technique with autoradiogra-phy in rats under the same conditions of anesthesia and arterial pCO₂. The measured pCO₂ index on the parietal cortex using the FAIR technique was 6.07 ml/100 g/min per mmHg, which compares well with the pCO₂ index measured by other techniques. The FAIR technique was also able to detect the regional reduction in CBF produced by middle cerebral artery occlusion in rats.     

Perioperative administration of parenteral fish oil supplements in a routine clinical setting improves patient outcome after major abdominal surgery

BACKGROUND & AIMS: It is hypothesized that provision of pre- and/or postoperative omega-3 fatty acids to surgical patients in clinical routine improves clinical outcome. METHODS: Retrospective evaluation of a 2-year-longitudinal data base of ICU patients (n=249) elected for major abdominal surgery. Group I (n=110): postoperative standard parenteral nutrition (1.2 g amino acids, 0.3 g glutamine dipeptide, 0.6 g lipids, 4 g/kg glucose; energy ratio glucose to lipid 2:1); group II (n=86): part of postoperative lipid emulsion replaced by fish oil; group III (n=53): in addition 2-3 days preoperative fish oil supplementation (max. 100 ml/d). RESULTS: A decrease in mortality was observed in group III compared to group I (P=0.02). The number of patients requiring mechanical ventilation was lower with perioperative fish oil (n=34 in groups I and II. 10 in III, P<0.05). The number of days in ICU was not different (group I: 7.6 days, group II: 7.0, group III: 7.3), the length of hospital stay was shorter in group I (group I: 29.2 days, group II: 24.9, group III: 22.2, P<0.05 vs I). CONCLUSIONS: In a retrospective evaluation, perioperative provision of parenteral fish oil (ca. 10 g/day) beneficially influences patient outcome probably by modulating the immune response.