Assessment of diffusion tensor imaging indices in calf muscles following postural change from standing to supine position

Object

To investigate whether postural change from erect to recumbent position affects calf muscle water diffusivity.

Materials and methods

Ten healthy adults (27.2 ± 4.9 years, 3 females) were imaged at baseline (following assumption of recumbent position), and after 34 min (session 2) and 64 min (session 3) of laying supine within a 3T MRI scanner. Diffusion tensor imaging (DTI) eigenvalues, fractional anisotropy (FA) and apparent diffusion coefficient (ADC) were evaluated in five calf muscles (anterior and posterior tibialis and triceps surae) during each of the three imaging sessions.

Results

Significant decreases were observed in all of the eigenvalues and ADC in each of the muscles with postural change. These reductions ranged from 3.2 to 6.7 % and 3.4 to 7.5 % for the various DTI metrics, following 34 and 64 min of supine rest, respectively (P < 0.05). No significant differences were noted in ADC or eigenvalues between the second and third imaging sessions for any muscle. FA did not change significantly with postural manipulation in any muscle compartment.

Conclusion

Diffusion tensor imaging indices were altered with postural change. As differences were not apparent between the latter two imaging sessions, we suggest that a short supine resting period (~34 min) is sufficient for muscle diffusivity to stabilize prior to quantitative MR imaging in healthy young adults.     

Diffusion property differences of the lower leg musculature between athletes and non-athletes using 1.5T MRI

Object

To compare the differences in diffusion properties—namely fractional anisotropy (FA), three eigenvalues of the diffusion tensor (λ1, λ2, and λ3), and apparent diffusion coefficient (ADC)—between athletically-trained and untrained lower leg musculature.

Materials and methods

Twelve athletes (Group A) and 11 non-athletes (Group B) were recruited. All were females in their 20s. We scanned diffusion tensor images of both calves and compared FA, the three eigenvalues, and ADC in the gastrocnemius medialis, gastrocnemius lateralis, soleus (SOL), and anterior tibialis muscles between Groups A and B, and between the right and left sides, using two-factor fractional ANOVA.

Results

In all muscles of bilateral calves, all three eigenvalues and ADC were lower in Group A than in Group B, with statistically significant differences in all muscles for λ1, λ2, and λ3 and ADC, with a P value of <0.01. Moreover, statistical differences were also found between right and left for λ1, λ2, and λ3 (P?P?Conclusions Our results indicate that training causes a decrease of the three eigenvalues and ADC, which we hypothesize is due to an increase of density of myofilaments in the intracellular space, and deformation of the cell induced by enlargement of extracellular components.     

Quantitative breast MRI: 2D histogram analysis of diffusion tensor parameters in normal tissue

Object

Diffusion tensor imaging (DTI) of the breast may provide a powerful new approach for the detection of intraductal processes. The aim of this investigation was to characterize the relation between diffusion tensor parameters [fractional anisotropy (FA), mean diffusivity (MD)] in normal breast tissue to obtain information on the microenvironment of the diffusing water molecules and to provide a systematic approach for DTI analysis.

Materials and methods

Seven female, healthy volunteers underwent prospective double-spin-echo prepared echo-planar diffusion-weighted sequence (TR/TE 8,250 ms/74 ms, b values 0 and 500 s/mm (2), six encoding directions, 12 averages, 35 slices) in 4 consecutive weeks (3.0 T). Quantitative maps of diffusion tensor parameters were computed offline with custom routines. The interdependence of MD and FA in different voxels was analysed by linear and exponential regression.

Results

All MD and FA maps were of excellent quality. A consistent pattern was observed in that lower fractional anisotropy values were more likely associated with higher mean diffusivity values. The dependence exhibited an exponential behavior with a correlation coefficient R = 0.60 (R linear = 0.57).

Conclusion

The likelihood with which FA and MD values are observed in a voxel within normal breast tissue is characterized by a specific pattern, which can be described by an exponential model. Moreover, we could show that the proposed technique does not depend on the menstrual cycle.     

High resolution morphologic imaging and T2 mapping of cartilage at 7 Tesla: comparison of cartilage repair patients and healthy controls

Object

Our objective was to use 7 T MRI to compare cartilage morphology (thickness) and collagen composition (T2 values) in cartilage repair patients and healthy controls.

Materials and methods

We scanned the knees of 11 cartilage repair patients and 11 controls on a 7 T MRI scanner using a high-resolution, gradient-echo sequence to measure cartilage thickness and a multi-echo spin-echo sequence to measure cartilage T2 values. We used two-tailed t tests to compare cartilage thickness and T2 values in: repair tissue (RT) versus adjacent cartilage (AC); RT versus healthy control cartilage (HC); AC versus HC.

Results

Mean thickness in RT, AC, HC were: 2.2 ± 1.4, 3.6 ± 1.1, 3.3 ± 0.7 mm. Differences in thickness between RT–AC (p = 0.01) and RT–HC (p = 0.02) were significant, but not AC–HC (p = 0.45). Mean T2 values in RT, AC, HC were: 51.6 ± 7.6, 40.0 ± 4.7, 45.9 ± 3.7 ms. Differences in T2 values between RT–AC (p = 0.0005), RT-HC (p = 0.04), and AC–HC (p = 0.004) were significant.

Conclusion

7 T MRI allows detection of differences in morphology and collagen architecture in: (1) cartilage repair tissue compared to adjacent cartilage and (2) cartilage repair tissue compared to cartilage from healthy controls. Although cartilage adjacent to repair tissue may be normal in thickness, it can demonstrate altered collagen composition.     

Effect of motion on the ADC quantification accuracy of whole-body DWIBS

Background and methods

Diffusion-weighted whole-body imaging with background body signal subtraction was introduced as a qualitative approach to detecting metastases in the body. A liver-mimicking phantom with embedded tumours that could be moved to replicate respiratory motion was developed to assess its ability to accurately quantify ADC values.

Results

Mean tumour ADC values were unaltered by the motion; however, a significant (p?Conclusions These findings may be of significance in cancer therapy monitoring where subtle changes in ADC histograms may reveal changes in tumour heterogeneity.     

Orientational dependent sensitivities of T2 and T1ρ towards trypsin degradation and Gd-DTPA2? presence in bovine nasal cartilage

Objective

To study the orientational dependencies of T₂ and T_1ρ in native and trypsin-degraded bovine nasal cartilage, with and without the presence of 1?mM Gd-DTPA^2?.

Materials and methods

Sixteen specimens were prepared in two orthogonal fibril directions (parallel and perpendicular), treated using different protocols (native, Gd treated, trypsin-treated, and combination), and imaged using μMRI at 0° and 55° (the magic angle) fibril orientations with respect to the magnetic field B₀. Two-dimensional (2D) T₂ and T_1ρ images were then calculated quantitatively.

Results

Without Gd, native perpendicular tissues demonstrated significant T_1ρ dispersion (including T₂ at the zero spin-lock field) at 0° and less dispersion at 55°, while native parallel specimens exhibited smaller T_1ρ dispersion at both 0° and 55°. Trypsin degradation caused a minimum 50% increase in T_1ρ. With Gd, trypsin degradation caused significant reduction in T_1ρ values up to 60%.

Conclusion

The collagen orientation in nasal cartilage can influence T₂ and T_1ρ MRI of cartilage. Without Gd, T_1ρ was sensitive to the proteoglycan content and its sensitivity was nearly constant regardless of fibril orientation. In comparison, the T₂ sensitivity to proteoglycan was dependant upon fibril orientation, i.e., more sensitive at 55° than 0°. When Gd ions were present, both T₂ and T_1ρ became insensitive to the proteoglycan content.     

Quantitative liver ADC measurements using diffusion-weighted MRI at 3 Tesla: evaluation of reproducibility and perfusion dependence using different techniques for respiratory compensation

Object

Diffusion weighted imaging (DWI) of the liver suffers from low signal to noise making 3 Tesla (3 T) an attractive option, but 3 T data is scarce. It was the aim to study the influence of different b values and respiratory compensation methods (RCM) on the apparent diffusion coefficient (ADC) level and on ADC reproducibility at 3 T.

Materials and methods

Ten healthy volunteers and 12 patients with malignant liver lesions underwent repeated (2–22 days) breathhold, free-breathing and respiratory triggered DWI at 3 T using b values between 0 and 1,000 s/mm².

Results

The ADCs changed up to 150 % in healthy livers and up to 48 % in malignant lesions depending on b value combinations. Best ADC reproducibility in healthy livers were obtained with respiratory triggering (95 % limits of agreement: ±0.12) and free-breathing (±0.14). In malignant lesions equivalent reproducibility was obtained with less RCM dependence. The use of a lower maximum b value (b = 500) decreased reproducibility (±0.14 to ±0.32) in both normal liver and malignant lesions.

Conclusion

Large differences in absolute ADC values and reproducibility caused by varying combinations of clinically realistic b values were demonstrated. Different RCMs caused smaller differences. Lowering maximum b value to 500 increased limits of agreement up to a factor of two. Serial ADC changes larger than approximately 15 % can be detected confidently on an individual basis in both malignant lesions and normal liver parenchyma at 3 T using appropriate b values and respiratory compensation.     

Diffusion-weighted imaging of the liver: usefulness of ADC values in the differential diagnosis of focal lesions and effect of ROI methods on ADC measurements

Object

By measuring the apparent diffusion coefficient (ADC) of liver parenchyma and focal hepatic lesions (FHL) we proposed to investigate the utility of ADC in the differential diagnosis of hepatic disease and to determine the influence of region of interest (ROI) characteristics in those measurements.

Materials and methods

Ninety-three patients with at least one supracentimetric FHL, or parenchymal abnormality, were retrospectively evaluated. Diagnosis was based on histopathologic data or, alternatively, on a combination of consensus between imaging methods and 24 months of follow-up. Ninety lesions were evaluated with respiratory-triggered diffusion-weighted imaging (b values: 50 and 700 s/mm²): 14 hepatocellular carcinomas, 18 metastases, 10 focal nodular hyperplasias, four adenomas, 30 hemangiomas and 14 cysts. ADC of hepatic parenchyma was measured by placing ROIs in four different segments, and in FHLs by using three circular 1 cm² ROIs and one ROI encompassing the full lesion. Data was statistically analyzed (p < 0.05 considered significant), and a receiver operating characteristic curve was assessed to evaluate the accuracy for the diagnosis of malignancy.

Results

Our measurements showed that parenchyma ADC was significantly higher in segment II and that ADCs of malignant lesions were significantly lower than those of benign lesions (p < 0.001). There was significant overlap between benign solid lesions and malignant lesions and the area under the curve for malignancy was 0.939 (sensitivity 89.7 %, specificity 90.6 %), using a cutoff of 1.43 × 10^?3 mm²/s. No significant difference was found between ROIs of different characteristics.

Conclusion

ADC measurements can help to characterize FHLs and differentiate normal from pathological parenchyma. Any ROI above 1 cm² can provide accurate ADC measurements in homogenous lesions.     

Quantitative T 2 * assessment of acute and chronic myocardial ischemia/reperfusion injury in mice

Object

Imaging of myocardial infarct composition is essential to assess efficacy of emerging therapeutics. T ₂ ^* mapping has the potential to image myocardial hemorrhage and fibrosis by virtue of its short T ₂ ^* . We aimed to quantify T ₂ ^* in acute and chronic myocardial ischemia/reperfusion (I/R) injury in mice.

Materials and methods

I/R-injury was induced in C57BL/6 mice (n?=?9). Sham-operated mice (n?=?8) served as controls. MRI was performed at baseline, and 1, 7 and 28?days after surgery. MRI at 9.4?T consisted of Cine, T ₂ ^* mapping and late-gadolinium-enhancement (LGE). Mice (n?=?6) were histologically assessed for hemorrhage and collagen in the fibrotic scar.

Results

Baseline T ₂ ^* values were 17.1?±?2.0?ms. At day 1, LGE displayed a homogeneous infarct enhancement. T ₂ ^* in infarct (12.0?±?1.1?ms) and remote myocardium (13.9?±?0.8?ms) was lower than at baseline. On days 7 and 28, LGE was heterogeneous. T ₂ ^* in the infarct decreased to 7.9?±?0.7 and 6.4?±?0.7?ms, whereas T ₂ ^* values in the remote myocardium were 14.2?±?1.1 and 15.6?±?1.0?ms. Histology revealed deposition of iron and collagen in parallel with decreased T ₂ ^* .

Conclusion

T ₂ ^* values are dynamic during infarct development and decrease significantly during scar maturation. In the acute phase, T ₂ ^* values in infarcted myocardium differ significantly from those in the chronic phase. T ₂ ^* mapping was able to confirm the presence of a chronic infarction in cases where LGE was inconclusive. Hence, T ₂ ^* may be used to discriminate between acute and chronic infarctions.     

Comparison between different implementations of the 3D FLASH sequence for knee cartilage quantification

Objective

To compare several sequence implementations of the 3D FLASH sequence in the context of quantitative cartilage imaging.

Materials and methods

Test–retest coronal fast low angle shot (FLASH) sequences with water excitation were acquired in knees of 12 healthy participants, using two 1.5?T scanners from the same manufacturer. On one of the scanners, the FLASH was additionally compared with a FLASH VIBE, 75% with 100% slice resolution, a non-selective with a conventional spatial pulse, and “asymmetric echo allowed” with “not allowed”.

Results

Implementations of the FLASH showed systematic differences of up to 3.3%, but these were not statistically significant. Precision errors were similar between protocols, but tended to be smallest for the FLASH VIBE with 100% slice resolution (0.6–6.7%). In the medial tibia cartilage volume and thickness differed significantly (P?Conclusion Using a validated FLASH sequence, one can reduce slice resolution to 75% and allow asymmetric echo without sacrificing precision, in order to reduce the total acquisition time. However, in longitudinal studies, the scanner and the specific sequence implementation should be kept constant between baseline and follow-up, in order to avoid systematic off-sets in the measurements.     

Spatially resolved kinetics of skeletal muscle exercise response and recovery with multiple echo diffusion tensor imaging (MEDITI): a feasibility study

Objectives

We describe measurement of skeletal muscle kinetics with multiple echo diffusion tensor imaging (MEDITI). This approach allows characterization of the microstructural dynamics in healthy and pathologic muscle.

Materials and methods

In a Siemens 3-T Skyra scanner, MEDITI was used to collect dynamic DTI with a combination of rapid diffusion encoding, radial imaging, and compressed sensing reconstruction in a multi-compartment agarose gel rotation phantom and within in vivo calf muscle. An MR-compatible ergometer (Ergospect Trispect) was employed to enable in-scanner plantar flexion exercise. In a HIPAA-compliant study with written informed consent, post-exercise recovery of DTI metrics was quantified in eight volunteers. Exercise response of DTI metrics was compared with that of T2-weighted imaging and characterized by a gamma variate model.

Results

Phantom results show quantification of diffusivities in each compartment over its full dynamic rotation. In vivo calf imaging results indicate larger radial than axial exercise response and recovery in the plantar flexion-challenged gastrocnemius medialis (fractional response: nT2w?=?0.385?±?0.244, nMD?=?0.163?±?0.130, nλ₁?=?0.110?±?0.093, nλ_rad?=?0.303?±?0.185). Diffusion and T2-weighted response magnitudes were correlated (e.g., r?=?0.792, p?=?0.019 for nMD vs. nT2w).

Conclusion

We have demonstrated the feasibility of MEDITI for capturing spatially resolved diffusion tensor data in dynamic systems including post-exercise skeletal muscle recovery following in-scanner plantar flexion.

     

MR safety: simultaneous B 0, d��/dt, and dB/dt measurements on MR-workers up to 7 T

Object

The EU directive on safety requirements (2004/40/EC) limits the exposure to time varying magnetic fields to dB /dt = 200 mT/s. This action value is not clearly defined as it considers only the temporal change of the magnitude of ${\vec {B}}$ . Thus, only the translational motion in the magnet??s fringe field is considered and rotations are neglected.

Materials and methods

A magnetic field probe was constructed to simultaneously record the magnetic flux density ${\vec{B}}$ (x, y, z) with a 3-axis Hall sensor and the induced voltage due to movements with a set of three orthogonal coils. Voltages were converted into time-varying magnetic flux d ??(x, y, z)/dt serving as an exposition parameter for both translations and rotations. To separate the two types of motion, d B/dt was additionally calculated on the basis of the Hall sensor??s data. The calibrated probe was attached to the forehead of 8 healthcare workers and 17 MR physicists, and ${\vec {B}}$ and d??/dt were recorded during standard operating procedures at three different MR systems up to 7 T.

Results

The maximum percentage of the translational motion referring the data including both translations and rotations amounts to 32%. During volunteer measurements, maximum exposure values of d??/dt = 21 mWb/s, dB/dt = 1.40 T/s and ${\left| {\vec {B}}\right|= 2.75}$ Twere found.

Conclusion

The findings in this work indicate that both translations and rotations in the vicinity of an MR system should be taken into account, and that a single regulatory action level might not be sufficient.     

Increased hepatic fatty acid polyunsaturation precedes ectopic lipid deposition in the liver in adaptation to high-fat diets in mice

Objective

We monitored hepatic lipid content (HLC) and fatty acid (FA) composition in the context of enhanced lipid handling induced by a metabolic high-fat diet (HFD) challenge and fasting.

Materials and methods

Mice received a control diet (10% of kilocalories from fat, N = 14) or an HFD (45% or 60% of kilocalories from fat, N = 10 and N = 16, respectively) for 26 weeks. A subset of five mice receiving an HFD (60% of kilocalories from fat) were switched to the control diet for the final 7 weeks. At nine time points, magnetic resonance spectroscopy was performed in vivo at 14.1 T, interleaved with glucose tolerance tests.

Results

Glucose intolerance promptly developed with the HFD, followed by a progressive increase of fasting insulin level, simultaneously with that of HLC. These metabolic defects were normalized by dietary reversal. HFD feeding immediately increased polyunsaturation of hepatic FA, before lipid accumulation. Fasting-induced changes in hepatic lipids (increased HLC and FA polyunsaturation, decreased FA monounsaturation) in control-diet-fed mice were not completely reproduced in HFD-fed mice, not even after dietary reversal.

Conclusion

A similar adaptation of hepatic lipids to both fasting and an HFD suggests common mechanisms of lipid trafficking from adipose tissue to the liver. Altered hepatic lipid handling with fasting indicates imperfect metabolic recovery from HFD exposure.

     

Reproducibility and regional variations of an improved gagCEST protocol for the in vivo evaluation of knee cartilage at 7 T

Objective

The objective was to establish a gagCEST protocol that would enable robust and reproducible assessment of the glycosaminoglycan (GAG) content in knee cartilage at 7 T within a clinically feasible measurement time.

Materials and methods

Ten young healthy volunteers (mean age 26 years, range 24–28, five males, five females) were examined on a 7 T MR system. Informed consent was obtained from all individual participants prior to enrollment into the study. Each volunteer was measured twice for reproducibility assessment. The examined knee was immobilized using a custom-made fixation device. For the gagCEST measurement, a prototype segmented 3-D RF-spoiled gradient-echo sequence with an improved saturation scheme employing adiabatic pulses was used in a scan time of 19 min. The asymmetry of the Z-spectra (MTR_asym) in selected regions of interest in knee cartilage was calculated. Differences in MTR_asym between different regions were evaluated using ANOVA and the Bonferroni corrected post hoc test.

Results

The improvement of the saturation scheme reduced the influence of field inhomogeneities, resulted in more uniform saturation, and allowed for good reproducibility in a reasonable measurement time (19 min), as demonstrated by an intraclass correlation coefficient of 0.77. Improved fixation helped to reduce motion artifacts. Whereas similar MTR_asym values were found for weight-bearing and non-weight-bearing femoral cartilage, lower values were observed in the trochlear groove (p = 0.028), patellar (p = 0.015) and tibial cartilage (p < 0.001) when compared to non-weight-bearing femoral cartilage.

Conclusion

Reasonable reproducibility and sensitivity to regional differences in GAG content suggests that the improved gagCEST protocol might be useful for assessing the biochemical changes in articular cartilage that are associated with early stages of cartilage degeneration.

     

Topographical variations in zonal properties of canine tibial articular cartilage due to early osteoarthritis: a study using 7-T magnetic resonance imaging at microscopic resolution

Objective

Our aim was to determine topographical variations in zonal properties of articular cartilage over the medial tibia in an experimental osteoarthritis (OA) model using 7-T magnetic resonance imaging (MRI).

Materials and methods

An anterior cruciate ligament (ACL)-transection canine model was subjected to study at 8 (six) and 12 (seven) weeks after the surgery. Each medial tibia was divided into five topographical locations. For each specimen, T2 relaxation (at 0° and 55°) was quantified at microscopic resolution. The imaging data grouped the five locations into two topographical areas (meniscus-covered and -uncovered).

Results

The T2 (55°) bulk values from the meniscus-covered area were significantly lower than those from the uncovered area. The total cartilage thicknesses on the meniscus-covered area were significantly thinner than those on the meniscus-uncovered area. Significant differences in the T2 (0°) values were observed in most thicknesses of the four subtissue zones and whole-tissue from the uncovered area, while the same significant changes were detected in the superficial zone from the meniscus-covered area.

Conclusion

By quantifying high-resolution imaging data both topographically and depth-dependently (zonal-wise), this study demonstrates that the rate of disease progression varies topographically over the medial tibia. Future correlation with OA pathology could lead to better detection of early OA.

     

k-t BLAST and SENSE accelerated time-resolved three-dimensional phase contrast MRI in an intracranial aneurysm

Objective

The objective of this study was to investigate the performance of k-t BLAST (Broad-use Linear Acquisition Speed-up Technique) accelerated time-resolved 3D PC-MRI compared to SENSE (SENSitivity Encoding) acceleration in an in vitro and in vivo intracranial aneurysm.

Materials and methods

Non-accelerated, SENSE and k-t BLAST accelerated time-resolved 3D PC-MRI measurements were performed in vivo and in vitro. We analysed the consequences of various temporal resolutions in vitro.

Results

Both in vitro and in vivo measurements showed that the main effect of k-t BLAST was underestimation of velocity during systole. In the phantom, temporal blurring decreased with increasing temporal resolution. Quantification of the differences between the non-accelerated and accelerated measurements confirmed that in systole SENSE performed better than k-t BLAST in terms of mean velocity magnitude. In both in vitro and in vivo measurements, k-t BLAST had higher SNR compared to SENSE. Qualitative comparison between measurements showed good similarity.

Conclusion

Comparison with SENSE revealed temporal blurring effects in k-t BLAST accelerated measurements.     

A highly parallelized framework for computationally intensive MR data analysis

Object

The goal of this study was to develop a comprehensive magnetic resonance (MR) data analysis framework for handling very large datasets with user-friendly tools for parallelization and to provide an example implementation.

Materials and methods

Commonly used software packages (AFNI, FSL, SPM) were connected via a framework based on the free software environment R, with the possibility of using Nvidia CUDA GPU processing integrated for high-speed linear algebra operations in R. Three hundred single-subject datasets from the 1,000 Functional Connectomes project were used to demonstrate the capabilities of the framework.

Results

A framework for easy implementation of processing pipelines was developed and an R package for the example implementation of Fully Exploratory Network ICA was compiled. Test runs on data from 300 subjects demonstrated the computational advantages of a processing pipeline developed using the framework compared to non-parallelized processing, reducing computation time by a factor of 15.

Conclusion

The feasibility of computationally intensive exploratory analyses allows broader access to the tools for discovery science.     

Two-dimensional accelerated MP-RAGE imaging with flexible linear reordering

Object

Implementation of an accelerated Magnetization Prepared RApid Gradient Echo (MP-RAGE) sequence for T1 weighted neuroimaging; exploiting modern MRI technologies to minimize scan time while preserving the image quality.

Materials and methods

A custom MP-RAGE sequence was implemented on a state-of-the-art 3T MR scanner equipped with a 32-channel receiver array head coil. The sequence utilized a shifted CAIPIRINHA k _y –k _z under-sampling pattern combined with elliptical scanning and a two-dimensional view ordering scheme to achieve high parallel imaging acceleration factors at maintained image contrast.

Results

It could be shown that MP-RAGE accelerated in two k-space directions outperforms single direction acceleration, which is the common practice with standard view ordering. Applying the CAIPIRINHA technique in conjunction with elliptical scanning further increased this benefit.

Conclusion

By combining MP-RAGE with CAIPIRINHA sampling and elliptical scanning, the scan time can be reduced from 4–5 min to 2–3 min with insignificant reduction in image quality.     

Scan time minimization in hepatic diffusion-weighted imaging: evaluation of the simultaneous multislice acceleration technique with different acceleration factors and gradient preparation schemes

Objective

To evaluate simultaneous multislice (sms) accelerated diffusion-weighted imaging (DWI) of the liver in comparison to conventional sequences.

Materials and methods

Ten volunteers underwent DWI of the liver at 1.5 T. Four different sms-accelerated sequences with monopolar and bipolar gradient preparation (MP, BP) and acceleration factors 2 and 3 (sms2-DWI, sms3-DWI) were compared to conventional DWI (c-DWI). Image quality criteria rated on a 5-point Likert scale (5 = excellent), image quality sum scores (maximum 120), and ADC were compared using Friedman test and Dunn-Bonferroni post hoc test. Bland–Altman plots were calculated for ADC comparison. p values <0.05 were considered significant.

Results

Sms2-DWI offered scan time minimization of 67 % without significant difference in image quality (sum score: sms2-DWI MP/BP: 97 ± 8/92 ± 9; c-DWI MP/BP: 99 ± 8/97 ± 8). Sms3-DWI offered slight additional scan time minimization with significantly inferior image quality (sum score: sms3-DWI MP/BP: 75 ± 14/69 ± 14; p < 0.001). MP preparation provided slightly higher image quality in sms-DWI without statistical significance. ADC in sms-DWI were significantly lower (sms2-DWI MP 1.01 × 10^?3 mm²/s; c-DWI MP 1.20 × 10^?3 mm²/s; p < 0.001).

Conclusion

Sms2-DWI provides considerable scan time minimization without significant shortcomings in image quality. Sms3-DWI provides significantly inferior image quality without further scan time minimization. Potentially lower ADC in sms-DWI should be considered in clinical routine.

     

In vivo chlorine and sodium MRI of rat brain at 21.1 T

Object

MR imaging of low-gamma nuclei at the ultrahigh magnetic field of 21.1 T provides a new opportunity for understanding a variety of biological processes. Among these, chlorine and sodium are attracting attention for their involvement in brain function and cancer development.

Materials and methods

MRI of ³⁵Cl and ²³Na were performed and relaxation times were measured in vivo in normal rat (n = 3) and in rat with glioma (n = 3) at 21.1 T. The concentrations of both nuclei were evaluated using the center-out back-projection method.

Results

T ₁ relaxation curve of chlorine in normal rat head was fitted by bi-exponential function (T _1a = 4.8 ms (0.7) T _1b = 24.4 ± 7 ms (0.3) and compared with sodium (T ₁ = 41.4 ms). Free induction decays (FID) of chlorine and sodium in vivo were bi-exponential with similar rapidly decaying components of $ T_{{2{\text{a}}}}^{*} = 0.4 $  ms and $ T_{{2{\text{a}}}}^{*} = 0.53 $  ms, respectively. Effects of small acquisition matrix and bi-exponential FIDs were assessed for quantification of chlorine (33.2 mM) and sodium (44.4 mM) in rat brain.

Conclusion

The study modeled a dramatic effect of the bi-exponential decay on MRI results. The revealed increased chlorine concentration in glioma (~1.5 times) relative to a normal brain correlates with the hypothesis asserting the importance of chlorine for tumor progression.