Ivan Frollo

Regional variations of T₂* in healthy and pathologic achilles tendon in vivo at 7 Tesla: preliminary results.

The aim of this study was to investigate T  2* in the Achilles tendon (AT), in vivo, using a three‐dimensional ultrashort time echo (3D‐UTE) sequence, to compare field strength differences (3 and 7 T) and to evaluate a regional variation of T  2* in healthy and pathologic tendon. Ten volunteers with no history of pain in the AT and five patients with chronic Achilles tendinopathy were recruited. 3D‐UTE images were measured with the following echo times, at echo time = [0.07, 0.2, 0.33, 0.46, 0.59, 0.74, 1.0, 1.5, 2.0, 4.0, 6.0, and 9.0 ms]. T  2* values in the AT were calculated by fitting the signal decay to biexponential function. Comparing volunteers between 3 and 7 T, short component T  2s* was 0.71 ± 0.17 ms and 0.34 ± 0.09 ms (P < 0.05); bulk long component T  2l* was 12.85 ± 1.87 ms and 10.28 ± 2.28 ms (P < 0.05). In patients at 7 T, bulk T  2s* was 0.53 ± 0.17 ms (P = 0.045, compared to volunteers), T  2l* was 11.49 ± 4.28 ms (P = 0.99, compared to volunteers). The results of this study suggest that the regional variability of AT can be quantified by T  2* in in vivo conditions. Advanced quantitative imaging of the human AT using a 3D‐UTE sequence may provide additional information to standard clinical imaging. Finally, as the preliminary patient data suggest, T  2s* may be a promising marker for the diagnosis of pathological changes in the AT. Magn Reson Med, 2012.

Time-resolved phosphorous magnetization transfer of the human calf muscle at 3 T and 7 T: A feasibility study

Phosphorous ((31)P) magnetization transfer (MT) experiments enable the non-invasive investigation of human muscle metabolism in various physiological and pathological conditions. The purpose of our study was to investigate the feasibility of time-resolved MT, and to compare the results of MT experiments at 3 T and 7 T. Six healthy volunteers were examined on a 3T and a 7 T MR scanner using the same setup and identical measurement protocols. In the calf muscle of all volunteers, four separate MT experiments (each ∼10 min duration) were performed in one session. The forward rate constant of the ATP synthesis reaction (kATP) and creatine kinase reaction (kCK), as well as corresponding metabolic fluxes (FATP, FCK), were estimated. A comparison of these exchange parameters, apparent T₁s, data quality, quantification precision, and reproducibility was performed. The data quality and reproducibility of the same MT experiments at 7 T was significantly higher (i.e., kATP 2.7 times higher and kCK 3.4 times higher) than at 3 T (p<0.05). The values for kATP (p=0.35) and kCK (p=0.09) at both field strengths were indistinguishable. Even a single MT experiment at 7 T provided better data quality than did a 4 times-longer MT experiment at 3T. The minimal time-resolution to reliably quantify both FATP and FCK at 7 T was ∼6 min. Our results show that MT experiments at 7 T can be at least 4 times faster than 3 T MT experiments and still provide significantly better quantification. This enables time-resolved MT experiments for the observation of slow metabolic changes in the human calf muscle at 7 T.

Interrelation of 31P-MRS metabolism measurements in resting and exercised quadriceps muscle of overweight-to-obese sedentary individuals

Phosphorus magnetic resonance spectroscopy (31P‐MRS) enables the non‐invasive evaluation of muscle metabolism. Resting Pi‐to‐ATP flux can be assessed through magnetization transfer (MT) techniques, and maximal oxidative flux (Qmax) can be calculated by monitoring of phosphocreatine (PCr) recovery after exercise. In this study, the muscle metabolism parameters of 13 overweight‐to‐obese sedentary individuals were measured with both MT and dynamic PCr recovery measurements, and the interrelation between these measurements was investigated. In the dynamic experiments, knee extensions were performed at a workload of 30% of maximal voluntary capacity, and the consecutive PCr recovery was measured in a quadriceps muscle with a time resolution of 2 s with non‐localized 31P‐MRS at 3 T. Resting skeletal muscle metabolism was assessed through MT measurements of the same muscle group at 7 T. Significant linear correlations between the Qmax and the MT parameters kATP (r = 0.77, P = 0.002) and FATP (r = 0.62, P = 0.023) were found in the study population. This would imply that the MT technique can possibly be used as an alternative method to assess muscle metabolism when necessary (e.g. in individuals after stroke or in uncooperative patients). Copyright

Depth-resolved surface coil MRS (DRESS)-localized dynamic (31) P-MRS of the exercising human gastrocnemius muscle at 7 T.

Dynamic 31P‐MRS with sufficiently high temporal resolution enables the non‐invasive evaluation of oxidative muscle metabolism through the measurement of phosphocreatine (PCr) recovery after exercise. Recently, single‐voxel localized 31P‐MRS was compared with surface coil localization in a dynamic fashion, and was shown to provide higher anatomical and physiological specificity. However, the relatively long TE needed for the single‐voxel localization scheme with adiabatic pulses limits the quantification of J‐coupled spin systems [e.g. adenosine triphosphate (ATP)]. Therefore, the aim of this study was to evaluate depth‐resolved surface coil MRS (DRESS) as an alternative localization method capable of free induction decay (FID) acquisition for dynamic 31P‐MRS at 7 T. The localization performance of the DRESS sequence was tested in a phantom. Subsequently, two dynamic examinations of plantar flexions at 25% of maximum voluntary contraction were conducted in 10 volunteers, one examination with and one without spatial localization. The DRESS slab was positioned obliquely over the gastrocnemius medialis muscle, avoiding other calf muscles. Under the same load, significant differences in PCr signal drop (31.2 ± 16.0% versus 43.3 ± 23.4%), end exercise pH (7.06 ± 0.02 versus 6.96 ± 0.11), initial recovery rate (0.24 ± 0.13 mm/s versus 0.35 ± 0.18 mm/s) and maximum oxidative flux (0.41 ± 0.14 mm/s versus 0.54 ± 0.16 mm/s) were found between the non‐localized and DRESS‐localized data, respectively. Splitting of the inorganic phosphate (Pi) signal was observed in several non‐localized datasets, but in none of the DRESS‐localized datasets. Our results suggest that the application of the DRESS localization scheme yielded good spatial selection, and provided muscle‐specific insight into oxidative metabolism, even at a relatively low exercise load. In addition, the non‐echo‐based FID acquisition allowed for reliable detection of ATP resonances, and therefore calculation of the specific maximum oxidative flux, in the gastrocnemius medialis using standard assumptions about resting ATP concentration in skeletal muscle. Copyright

Measurement and imaging of planar electromagnetic phantoms based on NMR imaging methods

Measurement and Imaging of Planar Electromagnetic Phantoms Based on NMR Imaging Methods Planar electromagnetic phantom design for measurement and imaging using NMR has been performed. Electromagnetic phantom computation and testing on a NMR 0.178 Tesla Esaote Opera imager were accomplished. The classical geometrical and chemical phantoms are generally used for testing of NMR imaging systems. They are simple cylindrical or rectangular objects with different dimensions and shapes with holes filled with specially prepared water solutions. In our experiments a homogeneous phantom (reference medium) - a container filled with water - was used. The resultant image represents the magnetic field distribution in the homogeneous phantom. An image acquired by this method is actually a projection of the sample properties onto the homogeneous phantom. The goal of the paper is to map and image the magnetic field deformation using NMR imaging methods. We are using a double slender rectangular vessel with constant thickness filled with specially prepared water solution in our experiments. For detection a carefully tailored gradient-echo imaging method, susceptible to magnetic field homogeneity, was used.

Magnetic Field Distribution Measurement by the Modified FLASH Method

Abstract Magnetic field inhomogeneities cause blurring and distortion of images gained by nuclear magnetic resonance. In order to adjust the magnetic coils finely, a precise and rapid method for measuring the magnetic field is needed. We describe a gradient echo technique of the FLASH version for mapping static magnetic fields.

One-dimensional image-selected in vivo spectroscopy localized phosphorus saturation transfer at 7T.

To evaluate the feasibility of a one‐dimensional image‐selected in vivo spectroscopy (1D‐ISIS) saturation transfer (ST) sequence at 7T for localized in vivo measurements of energy metabolism in different tissues in clinically reasonable examination times.

Skeletal muscle alkaline Pi pool is decreased in overweight-to-obese sedentary subjects and relates to mitochondrial capacity and phosphodiester content

Defects in skeletal muscle energy metabolism are indicative of systemic disorders such as obesity or type 2 diabetes. Phosphorus magnetic resonance spectroscopy (31P-MRS), in particularly dynamic 31P-MRS, provides a powerful tool for the non-invasive investigation of muscular oxidative metabolism. The increase in spectral and temporal resolution of 31P-MRS at ultra high fields (i.e., 7T) uncovers new potential for previously implemented techniques, e.g., saturation transfer (ST) or highly resolved static spectra. In this study, we aimed to investigate the differences in muscle metabolism between overweight-to-obese sedentary (Ob/Sed) and lean active (L/Ac) individuals through dynamic, static, and ST 31P-MRS at 7T. In addition, as the dynamic 31P-MRS requires a complex setup and patient exercise, our aim was to identify an alternative technique that might provide a biomarker of oxidative metabolism. The Ob/Sed group exhibited lower mitochondrial capacity, and, in addition, static 31P-MRS also revealed differences in the Pi-to-ATP exchange flux, the alkaline Pi-pool, and glycero-phosphocholine concentrations between the groups. In addition to these differences, we have identified correlations between dynamically measured oxidative flux and static concentrations of the alkaline Pi-pool and glycero-phosphocholine, suggesting the possibility of using high spectral resolution 31P-MRS data, acquired at rest, as a marker of oxidative metabolism.

Hypergravity‐induced Increase in Plasma Catecholamine and Corticosterone Levels in Telemetrically Collected Blood of Rats during Centrifugation

Rats subjected to various accelerations (+G) exhibited increased levels of plasma epinephrine (EPI), norepinephrine (NE), and corticosterone. However, the collection of blood was performed after a centrifugation finished, and therefore the levels could be affected by the process of deceleration. The aim of this study was to evaluate plasma EPI, NE, and corticosterone levels in blood collected directly during centrifugation after reaching different G (2–6), using newly developed remote‐controlled equipment. Animals placed into the centrifuge cabins had inserted polyethylene tubing in the tail artery, which was connected with a preprogrammed device for blood withdrawals. Plasma EPI, NE, and corticosterone levels were measured at different time intervals of hypergravity of 2–6G. Plasma EPI levels showed a huge, hypergravity‐level–dependent increase. After the last blood collection was completed during hypergravity, the centrifuge was turned off and another blood sampling was performed immediately after the centrifuge stopped (10 min). In these samples, plasma EPI showed significantly lower levels compared to centrifugation intervals. Plasma NE levels were significantly increased after 6G only. The increase in plasma corticosterone was dependent on level of G, however after the centrifuge stopped, corticosterone levels remained elevated. Thus, our data show that hypergravity highly activates the adrenomedullary and hypothalamo‐pituitary‐adrenocortical systems, whereas the sympathoneural system is activated only at high hypergravity. Immediately after centrifugation is over, EPI levels quickly return to control values. Our technique of blood collection during centrifugation allows assessment of the real hormonal levels at the particular hypergravity value.

Parallel plane gradient system for NMR experiments

A multiconductor parallel plane gradient system has been designed and constructed for the purpose of magnetic resonance experiments. The stress is laid upon the analysis of the optimal geometrical configuration of the parallel conductive strips, the four‐conductor back current pass and the introduction of basic equations for the multiconductor gradient system calculation. The influence of the length and the number of conductors on the linearity of the gradient magnetic field contours have been discussed. The proposed gradient system was used in experimental MR equipment for the imaging of small biological objects.