In human heart failure due to DCM, both PCr and ATP are significantly reduced. Ratios of PCr to ATP underestimate changes of high-energy phosphate levels.

A new approach for utilizing conjugate k-space symmetry for improved parallel MRI performance is presented. By generating virtual coils containing conjugate symmetric k-space signals from actual coils, additional image-and coil-phase information can be incorporated into the reconstruction process for parallel acquisition techniques. In that way the reconstruction conditions are improved, resulting in less noise enhancement. In particular in combination with generalized autocalibrating partially parallel acquisitions (GRAPPA), the virtual coil concept represents a practical approach since no explicit spatial phase information is required. In addition, the influence of phase variations originating from the complex receiver coils as well as from the background is investigated. Many strategies for reducing the scan time of MRI experiments work by collecting only a fraction of the data required for an artifact-free image. In the phase-constrained or partial-Fourier approach for Cartesian MRI, the k-space is sampled asymmetrically along the phase-encoding (PE) direction with full sampling density. While one-half of k-space is fully Fourier-encoded, only a portion of the other half of k-space is covered. Dedicated reconstruction algorithms recover the missing data by exploiting conjugate symmetry properties of k-space (1-3).Alternative approaches for scan time reductions include the parallel MRI (pMRI) methods (for example (4 -6)). The basic idea of Cartesian pMRI is to cover the entire span of k-space, but skip a fraction of the PE steps. In that way the Nyquist criterion is violated along the PE dimension, resulting in aliasing artifacts. Parallel MRI algorithms use spatial information inherent in an array of multiple receiver coils to either recover missing data in k-space or remove aliasing artifacts in the image domain. Cartesian sensitivity encoding (SENSE) (5) is a widespread imagedomain pMRI technique that unfolds superimposed pixels by incorporating spatial coil sensitivity information. However, for nonideal coil configurations noise enhancement occurs as a result of ill-conditioning of the inverse solution. The noise enhancement varies within the field of view (FOV) and can be analytically described by the geometry factor (g-factor). In addition to SENSE, the k-space domain "generalized autocalibrating partially parallel acquisitions" (GRAPPA) (6) technique is widely used. In GRAPPA, missing k-space lines in a single coil are approximated by a linear combination of measured k-space lines from all coils. To calculate the reconstruction coefficients, additional Nyquist sampled k-space lines (autocalibration signal, ACS) have to be measured. Equivalent to SENSE, noise enhancement occurs depending on the coil sensitivity profiles. However, in contrast to SENSE an analytical prediction of the noise enhancement is not trivial for GRAPPA. Both SENSE and GRAPPA are successfully applied in daily clinical routine.Several approaches for combining partial-Fourier acquisitions with parallel MRI have been presented to achi...

The purpose of this study was to present the prebolus technique for quantitative multislice myocardial perfusion imaging. In quantitative MR perfusion studies the maximum contrast agent dose is limited by the requirement to determine the arterial input function (AIF). The prebolus technique consists of two consecutive contrast agent administrations. The AIF is determined from a first low-dose bolus, while a second, high-dose bolus allows the measurement of the myocardium with improved signal increase. The results of the prebolus technique using a multislice saturation recovery trueFISP sequence in healthy volunteers are presented. In comparison to a standard dose of 3 ml Gd-DTPA, perfusion values are maintained while the signal increase in the concentration time courses was considerably improved, accompanied by reduced standard deviations of the obtained perfusion values (0.72 ؎ 0.13 ml/g/min for 1 ml/8 ml and 0.67 ؎ 0.10 ml/g/min for 1 ml/12 ml Gd-DTPA, respectively The clinical practicability of first-pass contrast-enhanced myocardial perfusion MRI has been improved in the last years by a number of technical changes of the acquisition sequences (1). Consequently, clinical first-pass perfusion studies could be performed for the primary diagnosis of coronary artery disease, as well as for the detection of myocardial viability (2,3). Different strategies to determine quantitative values of myocardial perfusion in humans have been proposed (4 -9) and normal values for healthy human volunteers have been reported (5-9). A prerequisite for perfusion quantification is the determination of the arterial input function (AIF). But saturation effects allow the determination of the AIF only for low concentrations of contrast agent (10), while a high dose leads to improved signal-to-noise ratio (SNR) in the myocardium (11). The combination of the advantages of both doses has been shown in an animal study (12). In this work the prebolus technique was applied to humans. A multislice version using a saturation recovery technique was implemented for quantitative measurement of myocardial perfusion in healthy volunteers. MATERIALS AND METHODS In Vivo Perfusion ImagingThis study was approved by our institution's Ethics Committee and written informed consent was obtained from all 11 volunteers (eight male, three female, age 24 Ϯ 4 years). All measurements were carried out on a clinical 1.5 T whole-body scanner (Magnetom Symphony, Siemens Medical Solutions, Erlangen, Germany) using a 12-element body phased array coil. First-pass perfusion images were acquired with an arrhythmia-insensitive multislice, saturation recovery trueFISP imaging technique (13). The following sequence parameters were chosen: repetition time 2.6 ms, echo time 1.1 ms, delay between saturation and sampling of center of k-space 110 ms, flip angle 50°, threequarters Fourier acquisition, number of phase encoding lines 60, FOV 340 mm with reduction to 3/4, i.e., 255 mm, in phase-encoding direction, slice thickness 8 mm. Forty consecutive images were acquired for ea...

Clinical and histopathological findings hint at regional differences in the brain's sensitivity to metabolic changes in cirrhosis. The aim of the present study was to examine regional differences in cerebral ammonia metabolism in patients with cirrhosis and grade 0-to-I hepatic encephalopathy (HE). 13 N-ammonia, 15 O-water positron emission tomography (PET) and magnetic resonance imaging (MRI) were performed. Quantitative values of cerebral blood flow (CBF) and the initial cerebral ammonia uptake rate (K1) were derived for several regions of interest from images of the desired parameters after interactive coregistration with the patients' MRI-studies. CBF (mL/mL/min), K1 (mL/mL/min), and the ammonia extraction fraction (K1/CBF) showed marked regional variance with the highest levels in the thalamus, the lenticular nucleus, and the cerebellum. In conclusion, the regional differences in cerebral ammonia uptake correspond to the distribution of histopathological H epatic encephalopathy (HE) is characterized by distinct clinical findings: patients display motor disturbances even at the lower grades of HE. Patients' faces are without expression, their movements are very slow, and muscle tone may be rigid. In some patients, body position is similar to Parkinson's disease, and posture reflexes are abnormal. Several patients present with tremor or asterixis. 1 With regard to cognition, deficits in attention, visual perception, visuospatial orientation, and visual construction predominate. 2,3 Thus, clinical and neuropsychological findings hint at a special sensitivity of distinct cerebral regions for toxic substances active in HE. Recent 18 F-fluorodeoxyglucose PET studies of cerebral glucose metabolism in patients with cirrhosis and minimal encephalopathy support this assumption. It has been shown that in such patients with HE, glucose utilization is decreased in the cingulum and frontal and parieto-occipital cortex and increased in the basal ganglia, cerebellum, and temporomesial structures, compared to healthy controls and patients with cirrhosis and no HE. [4][5][6] The mechanisms responsible for these differences are unknown. Regional differences in ammonia metabolism could be one possible cause.Ammonia is regarded as playing a major role in the pathophysiology of HE. Recent studies have shown that hyperammonemia affects GABAergic and glutamatergic neurotransmission and induces astrocytic swelling, considered to be major pathophysiological mechanisms in the development of HE. [7][8][9] The aim of the present study was to analyze cerebral ammonia metabolism in patients with cirrhosis, examining regional differences and their relationship to the grade of encephalopathy and the grade of liver dysfunction.The results of this study have been presented, in part, in abstract form. 10 Patients and Methods

Obtaining functional information on the human lung is of tremendous interest in the characterization of lung defects and pathologies. However, pulmonary ventilation and perfusion maps usually require contrast agents and the application of electrocardiogram (ECG) triggering and breath holds to generate datasets free of motion artifacts. This work demonstrates the possibility of obtaining highly resolved perfusion-weighted and ventilation-weighted images of the human lung using proton MRI and the SElf-gated Non-Contrast-Enhanced FUnctional Lung imaging (SENCEFUL) technique. The SENCEFUL technique utilizes a two-dimensional fast low-angle shot (FLASH) sequence with quasi-random sampling of phase-encoding (PE) steps for data acquisition. After every readout, a short additional acquisition of the non-phase-encoded direct current (DC) signal necessary for self-gating was added. By sorting the quasi-randomly acquired data according to respiratory and cardiac phase derived from the DC signal, datasets of representative respiratory and cardiac cycles could be accurately reconstructed. By application of the Fourier transform along the temporal dimension, functional maps (perfusion and ventilation) were obtained. These maps were compared with dynamic contrast-enhanced (DCE, perfusion) as well as standard Fourier decomposition (FD, ventilation) reference datasets. All datasets were additionally scored by two experienced radiologists to quantify image quality. In addition, one initial patient examination using SENCEFUL was performed. Functional images of healthy volunteers and a patient diagnosed with hypoplasia of the left pulmonary artery and left-sided pulmonary fibrosis were successfully obtained. Perfusion-weighted images corresponded well to DCE-MRI data; ventilation-weighted images offered a significantly better depiction of the lung periphery compared with standard FD. Furthermore, the SENCEFUL technique hints at a potential clinical relevance by successfully detecting a perfusion defect in the patient scan. It can be concluded that SENCEFUL enables highly resolved ventilation- and perfusion-weighted maps of the human lung to be obtained using proton MRI, and might be interesting for further clinical evaluation.

Exciting multiple slices at the same time, ''controlled aliasing in parallel imaging results in higher acceleration'' (CAIPIRI-NHA) and ''phase-offset multiplanar'' have shown to be very effective techniques in 2D multislice imaging. Being provided with individual rf phase cycles, the simultaneously excited slices are shifted with respect to each other in the FOV and, thus, can be easily separated. For SSFP sequences, however, similar rf phase cycles are required to maintain the steady state, impeding a straightforward application of phase-offset multiplanar or controlled aliasing in parallel imaging results in higher acceleration. In this work, a new flexible concept for applying the two multislice imaging techniques to SSFP sequences is presented. Linear rf phase cycles are introduced providing both in one, the required shift between the slices and steady state in each slice throughout the whole measurement. Consequently, the concept is also appropriate for realtime and magnetization prepared imaging. Steady state properties and shifted banding behavior of the new phase cycles were investigated using simulations and phantom experiments. Moreover, the concept was applied to perform whole heart myocardial perfusion SSFP imaging as well as real-time and cine SSFP imaging with increased coverage. Showing no significant penalties in SNR or image quality, the results successfully demonstrate the general applicability of the concept. Magn Reson Med 65:157-164,

A reconstruction technique called Model-based Acceleration of Parameter mapping (MAP) is presented allowing for quantification of longitudinal relaxation time and proton density from radial single-shot measurements after saturation recovery magnetization preparation. Using a mono-exponential model in image space, an iterative fitting algorithm is used to reconstruct one well resolved and consistent image for each of the projections acquired during the saturation recovery relaxation process. The functionality of the algorithm is examined in numerical simulations, phantom experiments, and in-vivo studies. MAP reconstructions of single-shot acquisitions feature the same image quality and resolution as fully sampled reference images in phantom and in-vivo studies. The longitudinal relaxation times obtained from the MAP reconstructions are in very good agreement with the reference values in numerical simulations as well as phantom and in-vivo measurements. Compared to available contrast manipulation techniques, no averaging of projections acquired at different time points of the relaxation process is required in MAP imaging. The proposed technique offers new ways of extracting quantitative information from single-shot measurements acquired after magnetization preparation. The reconstruction simultaneously yields images with high spatiotemporal resolution fully consistent with the acquired data as well as maps of the effective longitudinal relaxation parameter and the relative proton density.

DWI facilitates fast, accurate and comprehensive workup in Crohn disease without the need for intravenous administration of contrast medium. Contrast-enhanced MRI is superior in terms of spatial resolution and multiplanar acquisition.