MRI with zero echo time (ZTE) is achieved by 3D radial centre-out encoding and hard-pulse RF excitation while the projection gradient is already on. Targeting short-T(2) samples, the efficient, robust and silent ZTE approach was implemented for high-bandwidth high-resolution imaging requiring particularly rapid transmit-receive switching and algebraic image reconstruction. The ZTE technique was applied to image extracted human teeth at 11.7T field strength, yielding detailed depictions with very good delineation of the mineralised dentine and enamel layers. ZTE results are compared with UTE (ultra-short echo time) MRI and micro-computed tomography (μCT), revealing significant differences in SNR and CNR yields. Compared to μCT, ZTE MRI appears to be less susceptible to artefacts caused by dental fillings and to offer superior sensitivity for the detection of early demineralisation and caries lesions.

Pseudo-continuous ASL at high magnetic field is very sensitive to shim conditions. Label and control radiofrequency phase optimization based on prescans robustly maximizes the ASL signal obtained with unbalanced pCASL and minimizes the asymmetry between hemispheres. Magn Reson Med 79:1314-1324, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Proton MR spectroscopy is useful for in vivo monitoring of metabolic alterations in the brain due to chronic dialysis.

The analysis of myocardial microstructure in vivo is important for the determination of myocardial contractility and function. The purpose of the present study was to demonstrate that high-resolution T* 2 imaging has the potential to visualize the microstructure of beating, isolated rat hearts. To perform T* 2 imaging, a multiple gradient-echo sequence was implemented on an 11.75 Tesla microscopy system. An in-plane resolution of 78 m and a slice thickness of 250 m were achieved in 24 min. In comparison to histological sections, the T* 2 maps showed an excellent spatial correspondence to the myocardial fiber structure. To demonstrate the utility of this technique, morphologic alterations in myocardial microstructure were investigated in hearts with chronic myocardial infarction. Scar tissue and the extent of the infarcted region were clearly visualized and quantified using high-resolution T* 2 imaging. The myofiber structure of the heart plays a critical role in force production and contraction of the heart. Fiber orientation is also an important determinant of myocardial stress and strain, and, consequently, of cardiac perfusion and oxygen consumption (1). Furthermore, the structural fiber arrangement is known to be modified during the time course of different cardiac diseases (2,3).Because molecular movements are strongly influenced by the organization and geometry of the microscopic environment, diffusion-weighted MRI has become a useful tool for investigation of the microstructure of materials and biological tissues. Diffusion tensor imaging (DTI), for example, has so far been used to characterize the fiber architectures of the brain white matter (4), spinal cord (5,6), cartilage (7), myocardium (1,8 -10), and other musculature (11).Because the tissue microstructure of the myocardium may also be characterized by its distribution of field inhomogeneities, this structure should be observable in T* 2 maps. The relative scale of these inhomogeneities compared with an imaging voxel can be divided roughly into two relevant categories (12-14): macroscopic and mesoscopic field inhomogeneities. Macroscopic field inhomogeneities arise from magnet imperfections, imperfect shimming, air-tissue interfaces inside animals, and similar effects. These types of inhomogeneities contain no structural or physiological information. Mesoscopic field inhomogeneities do provide structural information about biological tissue, and have proved to be a useful tool for investigating biological tissue structure and function. The goal of the present study was to demonstrate that the microstructure of biological tissue can be investigated with high-resolution T* 2 imaging. In particular, we show that the fiber orientation in the isolated rat heart can be characterized with T* 2 imaging. Furthermore, scar tissue can be visualized in the chronically infarcted isolated rat heart by T* 2 imaging. METHODS Isolated Heart ModelHearts of male Wistar rats were excised and perfused in the Langendorff mode (15) with oxygenated (95% O 2 and 5% CO 2 ) K...

Our purpose was to study morphological, functional, and metabolic changes induced by chronic ischemia in myocardium supplied by the stenotic vessel and in the remote area by MR techniques. A new technique of image fusion is proposed for analysis of coronary artery stenosis involving coronary MR angiography and spectroscopic imaging. Cine-MRI was performed 2 wk after induction of coronary stenosis. Global heart function and regional wall thickening were determined in 11 Wistar rats with stenosis and compared with 7 control rats. Two weeks after stenosis was induced, spin-labeling MRI for measurement of perfusion was performed in 14 isolated hearts. In eight isolated hearts with coronary stenosis, MR spectroscopy was performed, followed by angiography. 31P metabolite maps were fused with three-dimensional coronary angiograms. Induction of stenosis led to reduced segmental wall thickening (control: 75 +/- 9%, ischemic region: 9 +/- 3%, P < 0.05 vs. control) but also to impaired function of the remote region and lower cardiac output. Perfusion was reduced by 74.9 +/- 4.0% within ischemic segments compared with a septal control region. The phosphocreatine (PCr)/ATP ratio as a marker of ischemia was reduced in the region associated with stenosis (1.09 +/- 0.09) compared with remote (1.27 +/- 0.08) and control hearts (1.43 +/- 0.08; P < 0.05). The histological fraction of fibrosis within the ischemic region (12.8 +/- 1.4%) correlated to ATP signal reduction from remote to the ischemic region (r = 0.71, P < 0.05), but not to reduced wall thickening. Coronary narrowing caused declining function accompanied by diminished PCr/ATP, indicating impaired energy metabolism. Neither decline of function nor PCr signal decline correlated to fraction of fibrosis in histology. In contrast, reduction of ATP correlated to fibrosis and therefore to loss of viability. Impaired function within the ischemic region is associated with decreased PCr. Function of the remote region was affected as well. The fusion of PCr metabolite maps and the coronary angiogram may help to assess coronary morphology and resulting metabolic changes simultaneously.