Ladislav Valkovič

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.

Effects of carnosine supplementation on glucose metabolism: Pilot clinical trial

Carnosine is a naturally present dipeptide in humans and an over‐the counter food additive. Evidence from animal studies supports the role for carnosine in the prevention and treatment of diabetes and cardiovascular disease, yet there is limited human data. This study investigated whether carnosine supplementation in individuals with overweight or obesity improves diabetes and cardiovascular risk factors.

Fully adiabatic 31P 2D-CSI with reduced chemical shift displacement error at 7 T--GOIA-1D-ISIS/2D-CSI.

A fully adiabatic phosphorus (31P) two‐dimensional (2D) chemical shift spectroscopic imaging sequence with reduced chemical shift displacement error for 7 T, based on 1D‐image‐selected in vivo spectroscopy, combined with 2D‐chemical shift spectroscopic imaging selection, was developed. Slice‐selective excitation was achieved by a spatially selective broadband GOIA‐W(16,4) inversion pulse with an interleaved subtraction scheme before nonselective adiabatic excitation, and followed by 2D phase encoding. The use of GOIA‐W(16,4) pulses (bandwidth 4.3–21.6 kHz for 10–50 mm slices) reduced the chemical shift displacement error in the slice direction ∼1.5–7.7 fold, compared to conventional 2D‐chemical shift spectroscopic imaging with Sinc3 selective pulses (2.8 kHz). This reduction was experimentally demonstrated with measurements of an MR spectroscopy localization phantom and with experimental evaluation of pulse profiles. In vivo experiments in clinically acceptable measurement times were demonstrated in the calf muscle (nominal voxel volume, 5.65 ml in 6 min 53 s), brain (10 ml, 6 min 32 s), and liver (8.33 ml, 8 min 14 s) of healthy volunteers at 7 T. High reproducibility was found in the calf muscle at 7 T. In combination with adiabatic excitation, this sequence is insensitive to the B1 inhomogeneities associated with surface coils. This sequence, which is termed GOIA‐1D‐ISIS/2D‐CSI (goISICS), has the potential to be applied in both clinical research and in the clinical routine. Magn Reson Med, 2013.

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

Dynamic 31P–MRSI using spiral spectroscopic imaging can map mitochondrial capacity in muscles of the human calf during plantar flexion exercise at 7 T

Phosphorus MRSI (31P–MRSI) using a spiral‐trajectory readout at 7 T was developed for high temporal resolution mapping of the mitochondrial capacity of exercising human skeletal muscle.

Dynamic PCr and pH imaging of human calf muscles during exercise and recovery using (31) P gradient-Echo MRI at 7 Tesla.

Simultaneous acquisition of spatially resolved 31P‐MRI data for evaluation of muscle specific energy metabolism, i.e., PCr and pH kinetics.

Dynamic 31P MR spectroscopy of plantar flexion: Influence of ergometer design, magnetic field strength (3 and 7 T), and RF‐coil design

PURPOSE Dynamic phosphorus magnetic resonance spectroscopy ((31)P MRS) during and after acute exercise enables the noninvasive in vivo determination of the mitochondrial capacity of skeletal muscle. Nevertheless, the lack of standardization in experimental setups leads to significant variations in published values of maximal aerobic capacity, even in the population of healthy volunteers. Thus, in this study, we aimed to assess the impact of the ergometer type (pneumatic and mechanical resistance construction), radiofrequency (RF)-coil diameter, and different magnetic field strengths (3 and 7 T) on the metabolic parameters measured by dynamic (31)P MRS during a plantar flexion isotonic exercise protocol within the same group of healthy volunteers. METHODS Dynamic (31)P MRS measurements of the calf muscle in 11 volunteers (mean age, 36  ±  13 yrs; mean BMI, 23.5 ± 2.5 kg/m(2)), on a 3 T MR system with a custom-made mechanical ergometer in the first research laboratory (RL1) and on 3 and 7 T MR systems equipped with a commercial pneumatic ergometer in the second research laboratory (RL2), were performed at three different workloads. RF-coils differed slightly between the sites and MR systems used. The repeatability of the experimental protocol was tested in every setup. The basal concentrations of phosphocreatine (PCr), exercise-induced depletion of PCr (ΔPCr), initial PCr resynthesis rate (VPCr), and mitochondrial capacity (Qmax) were calculated and compared between the research sites and field strengths. RESULTS High repeatability of the measurement protocol was found in every experimental setup. No significant differences at any workload were found in these metabolic parameters assessed at different magnetic field strengths (3 T vs 7 T), using the same ergometer (in RL2) and a similar RF-coil. In the inter-research laboratory comparison at the same field strength (3 T), but with using different ergometers and RF-coils, differences were found in the concentration of PCr measured at rest and in the drop in PCr signal intensity. These differences translated into difference in the value of mitochondrial capacity at a workload of 15% of maximal voluntary contraction (MVC) force (0.45 ± 0.16 mM/s vs 0.31 ± 0.08 mM/s, in the RL1 and RL2, respectively). CONCLUSIONS Metabolic parameters measured during exercise challenge by dynamic (31)P MRS do not depend upon the magnetic field strength used. For multicenter studies with different ergometers, it is important to set the same workload, measurement, and evaluation protocols, especially when the effects of very mild exercise (15% MVC) are to be compared. However, a higher workload (24% MVC) decreases the influence of imperfections and intersite differences for the assessed value of maximal mitochondrial capacity.

Investigating the prediction value of multiparametric magnetic resonance imaging at 3 T in response to neoadjuvant chemotherapy in breast cancer

AbstractObjectiveTo explore the predictive value of parameters derived from diffusion-weighted imaging (DWI) and contrast-enhanced (CE)-MRI at different time-points during neoadjuvant chemotherapy (NACT) in breast cancer.MethodsInstitutional review board approval and written, informed consent from 42 breast cancer patients were obtained. The patients were investigated before and at three different time-points during neoadjuvant chemotherapy (NACT) using tumour diameter and volume from CE-MRI and ADC values obtained from drawn 2D and segmented 3D regions of interest. Prediction of pathologic complete response (pCR) was evaluated using the area under the curve (AUC) of receiver operating characteristic analysis.ResultsThere was no significant difference between pathologic complete response and non-pCR in baseline size measures (p > 0.39). Diameter change was significantly different in pCR (p < 0.02) before the mid-therapy point. The best predictor was lesion diameter change observed before mid-therapy (AUC = 0.93). Segmented volume was not able to differentiate between pCR and non-pCR at any time-point. The ADC values from 3D-ROI were not significantly different from 2D data (p = 0.06). The best AUC (0.79) for pCR prediction using DWI was median ADC measured before mid-therapy of NACT.ConclusionsThe results of this study should be considered in NACT monitoring planning, especially in MRI protocol designing and time point selection.Key Points• Mid-therapy diameter changes are the best predictors of pCR in neoadjuvant chemotherapy. • Volumetric measures are not strictly superior in therapy monitoring to lesion diameter. • Size measures perform as a better predictor than ADC values.

In-vivo31P-MRS of skeletal muscle and liver: A way for non-invasive assessment of their metabolism

In addition to direct assessment of high energy phosphorus containing metabolite content within tissues, phosphorus magnetic resonance spectroscopy (31P-MRS) provides options to measure phospholipid metabolites and cellular pH, as well as the kinetics of chemical reactions of energy metabolism in vivo. Even though the great potential of 31P-MR was recognized over 30 years ago, modern MR systems, as well as new, dedicated hardware and measurement techniques provide further opportunities for research of human biochemistry. This paper presents a methodological overview of the 31P-MR techniques that can be used for basic, physiological, or clinical research of human skeletal muscle and liver in vivo. Practical issues of 31P-MRS experiments and examples of potential applications are also provided. As signal localization is essential for liver 31P-MRS and is important for dynamic muscle examinations as well, typical localization strategies for 31P-MR are also described.