No abstract

Fast and accurate cardiac T1 mapping is feasible within a single-shot IR experiment.

This work presents a method that allows for the assessment of 3D murine myocardial motion in vivo at microscopic resolution. Phase-contrast (PC) magnetic resonance imaging (MRI) at 17.6 T was applied to map myocardial motion in healthy mice along three gradient directions. High-resolution velocity maps were acquired at three different levels in the murine myocardium with an in-plane resolution of 98 m, a slice thickness of 0.6 mm, and a temporal resolution of 6 ms. The applied PC-MRI method was validated with phantom experiments that confirmed the cor-rectness of the method with deviations of <1.7%. Myocardial in-plane velocities between 0.5 cm/s and 2.2 cm/s were determined for the healthy murine myocardium. Through-plane velocities of 0.1-0.83 cm/s were measured. Velocity data was also used to calculate the myocardial twist angle during systole at different slices in the short-axis view. Magn Reson Med 55: 1058-1064, 2006. In recent years transgenic and knockout mice have gained increasing importance in cardiovascular research. Murine models of cardiovascular disease with gene overexpres-sions, mutations, or knockouts can easily be produced. An examination of the consequences of these modifications adds to our understanding of the function of certain gene products. These facts have been the driving force behind the development of suitable methods for assessing the cardiac function of mice in vivo. Echocardiography and ventriculography have proven to be feasible tools for evaluating heart function in small animals (1-5). However, over the past few years MRI has emerged as the most powerful imaging modality for measuring a broad spectrum of functional parameters and thus allowing for accurate detection of the pathophysiological state of the murine heart (6-8). Traditional cine MRI allows assessment of wall thickening and the ejection fraction. If the entire left ventricle (LV) is imaged by acquiring different slices, global cardiac functional parameters such as LV mass, end-diastolic volume (EDV), and end-systolic volume (ESV) become accessible (9). In combination with spatial modulation of magnetiza-tion (SPAMM), local functional parameters (e.g., myocar-dial motion) can be measured (10,11). By generating a grid of dark bends within an image and thus tracking the deformation of the myocardium during the heart cycle, motion and strain parameters of the myocardium can be calculated. An intrinsic drawback of this method is the large difference between spatial image resolution and the tag spacing, which limits the resolution of motion information. Recently published studies achieved a resolution of 133 267 m in the image plane by applying a tag spacing of 0.7 mm (12). With respect to the size of the murine heart (inner diameter of about 10 mm and myocardial wall thickness on the order of 1-2 mm), the tagged cine MRI approach yields restricted information about local myocar-dial motion. Aletras et al. (20) introduced a combination of SPAMM with an additional unencoding gradient module called displacement encoding wi...

This work introduces an MR-compatible active breathing control device (MR-ABC) that can be applied to lung imaging. An MR-ABC consists of a pneumotachograph for respiratory monitoring and an airway-sealing unit. Using an MR-ABC, the subjects were forced to suspend breathing for short time intervals, which were used in turn for data acquisition. While the breathing flow was stopped, data acquisition was triggered by ECG to achieve simultaneous cardiac and respiratory synchronization and thus avoid artifacts from blood flow or heart movement. The flow stoppage allowed a prolonged acquisition window of up to 1.5 sec. To evaluate the potential of an MR-ABC for segmented k-space acquisition, diaphragm displacement was investigated in five volunteers and compared with images acquired using breath-holding, a respiratory belt, and free breathing. Respiratory movement was comparatively low using the breath-hold approach, a respiratory belt or an MR-ABC. During free-breathing diaphragm displacement was comparatively large. To demonstrate the potential of an MR-ABC, lung MRI was performed using whole-chest 3D gradient-echo imaging, multislice turbo spin-echo (TSE) imaging, and short tau inversion recovery TSE (STIR-TSE). Cardiorespiratory synchronization was used for each sequence. None of the volunteers reported any discomfort or inconvenience when using an MR-ABC. Flow stoppage of up to 2.5 sec per breathing cycle was well tolerated, therefore allowing for a reduction of the total imaging time as compared to usage of a respiratory belt or MR navigator. Magn Reson Med 58:1092-1098, 2007.

No abstract

A short-echo spectroscopic imaging sequence extended with a frequency-selective multiple-quantum- coherence technique (Sel-MQC) is presented. The method enables acquisition of a complete water-suppressed proton spectrum with a short echo time and filtering of the J-coupling metabolite, lactate, from co-resonant lipids in one scan. The purpose of the study was to validate this combined pulse sequence in vitro and in vivo. Measurements on phantoms confirmed the feasibility of the method, and, for a practical in vivo application, experiments were carried out on eight tumors from two different tumor models [UT-SCC-8 (n = 4) and SAS (n = 4)]. T(1)- and T(2)-weighted metabolite and lipid ratios were calculated, and the tumors showed different values in the central and outer regions. The ratio of the lipid methylene peak area (1.30 ppm) to choline peak area (3.20 ppm) was significantly (p < 0.01) different in the central tumor area between the two models, and lactate was detected in only three out of four tumors in the SAS tumor line. The present approach of combining short-echo spectroscopic imaging and lactate editing allows the characterization of tumor-specific metabolites such as choline, lipid methylene and methyl resonances as well as lactate in a single scan.

The selective multiple quantum coherence technique is combined with a read gradient to accelerate the measurement of a specific scalar-coupled metabolite. The sensitivities of the localization using pure phase encoding and localization with the read gradient are compared in experiments at high magnetic field strength (17.6 T). Multiple spin-echoes of the selective multiple quantum coherence edited metabolite are acquired using frequency-selective refocusing of the specified molecule group. The frequency-selective refocusing does not affect the J-modulation of a coupled spin system, and the echo time is not limited to a multiple of 1/J to acquire pure in-phase or antiphase signal. The multiple echoes can be used to accelerate the metabolite imaging experiment or to measure the apparent transverse relaxation T 2 . A simple phase-shifting scheme is presented, which enables the suppression of editing artifacts resulting from the multiple spin-echoes of the water resonance. In 1 H NMR spectroscopy, the spectral overlap of resonances is a common problem when information about a specific metabolite (e.g., lactate [Lac]) is desired in vivo. In the last decades, several types of spectral editing schemes were developed to filter the metabolite of interest from coresonant or overlapping signals (1-4). The class of multiple quantum coherence (MQC) filters using magnetic field gradients for editing provides robust single-shot editing techniques. One of the single-shot editing filters is the frequency selective multiple quantum coherence editing scheme (Sel-MQC) proposed by He et al. (5). This selective MQC filter enables editing of a single scalar-coupled spin system with simultaneous suppression of water and other resonances in one scan.Successful applications of the Sel-MQC editing sequence have been shown in several studies in which the metabolite of interest is overlapped by other spins with a similar chemical shift. For instance, in extracranial tumor tissues, the Lac CH 3 resonance (at 1.33 parts per million [ppm]) has been filtered from overlapping methylene groups of mobile lipids (5,6). A recent preliminary study on healthy and cancerous human breast tissue has shown a robust application of the Sel-MQC editing sequence to detect polyunsaturated fatty acids (PUFA) (7). The olefinic methylene protons of PUFA at 5.3 ppm that are coupled with the allylic methylene protons of unsaturated acyl chains at 2.8 ppm were detected in breast tissue, and the PUFA pattern is sensitive to breast tissue changes, including cancerous alterations. An adiabatic version of the Sel-MQC scheme was used by de Graaf et al. (8) to detect the ␤H1-glucose resonance at 4.63 ppm in rat brain in vivo. Executing the Sel-MQC sequence with adiabatic radiofrequency pulses allows optimal sensitivity when surface coils are used. In recent years, several extensions of the Sel-MQC editing scheme have been developed, such as Hadamard encoding for localization (9,10), multislice selection using spatial-spectral selective pulses (11), T 1 and T 2 relaxation ...

In order to treat degenerative diseases, the importance of advanced therapy medicinal products has increased in recent years. The newly developed treatment strategies require a rethinking of the appropriate analytical methods. Current standards are missing the complete and sterile analysis of the product of interest to make the drug manufacturing effort worthwhile. They only consider partial areas of the sample or product while also irreversibly damaging the investigated specimen. Two-dimensional T1 / T2 MR relaxometry meets these requirements and is therefore a promising in-process control during the manufacturing and classification process of cell-based treatments. In this study a tabletop MR scanner was used to perform two-dimensional MR relaxometry. Throughput was increased by developing an automation platform based on a low-cost robotic arm, resulting in the acquisition of a large dataset of cell-based measurements. Two-dimensional inverse Laplace transformation was used for post-processing, followed by data classification performed with support vector machines (SVM) as well as optimized artificial neural networks (ANN). The trained networks were able to distinguish non-differentiated from differentiated MSCs with a prediction accuracy of 85%. To increase versatility, an ANN was trained on 354 independent, biological replicates distributed across ten different cell lines, resulting in a prediction accuracy of up to 98% depending on data composition. The present study provides a proof of principle for the application of T1 / T2 relaxometry as a non-destructive cell classification method. It does not require labeling of cells and can perform whole mount analysis of each sample. Since all measurements can be performed under sterile conditions, it can be used as an in-process control for cellular differentiation. This distinguishes it from other characterization techniques, as most are destructive or require some type of cell labeling. These advantages highlight the technique’s potential for preclinical screening of patient-specific cell-based transplants and drugs.