Clinical Magnetic Resonance Scanners Research Articles

Application Value of a Novel Micro-Coil in High-Resolution Imaging of Experimental Mice Based on 3.0 T Clinical MR.

The clinical magnetic resonance scanner (field strength ≤ 3.0 T) has limited efficacy in the high-resolution imaging of experimental mice. This study introduces a novel magnetic resonance micro-coil designed to enhance the signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR), thereby improving high-resolution imaging in experimental mice using clinical magnetic resonance scanners. Initially, a phantom was utilized to determine the maximum spatial resolution achievable by the novel micro-coil. Subsequently, 12 C57BL/6JGpt mice were included in this study, and the novel micro-coil was employed for their scanning. A clinical flexible coil was selected for comparative analysis. The scanning methodologies for both coils were consistent. The imaging clarity, noise, and artifacts produced by the two coils on mouse tissues and organs were subjectively evaluated, while the SNR and CNR of the brain, spinal cord, and liver were objectively measured. Differences in the images produced by the two coils were compared. The results indicated that the maximum spatial resolution of the novel micro-coil was 0.2 mm. Furthermore, the subjective evaluation of the images obtained using the novel micro-coil was superior to that of the flexible coil (p < 0.05). The SNR and CNR measurements for the brain, spinal cord, and liver using the novel micro-coil were significantly higher than those obtained with the flexible coil (p < 0.001). Our study suggests that the novel micro-coil is highly effective in enhancing the image quality of clinical magnetic resonance scanners in experimental mice.

Noninvasive 3-Dimensional 1 H-Magnetic Resonance Spectroscopic Imaging of Human Brain Glucose and Neurotransmitter Metabolism Using Deuterium Labeling at 3T : Feasibility and Interscanner Reproducibility.

Noninvasive, affordable, and reliable mapping of brain glucose metabolism is of critical interest for clinical research and routine application as metabolic impairment is linked to numerous pathologies, for example, cancer, dementia, and depression. A novel approach to map glucose metabolism noninvasively in the human brain has been presented recently on ultrahigh-field magnetic resonance (MR) scanners (≥7T) using indirect detection of deuterium-labeled glucose and downstream metabolites such as glutamate, glutamine, and lactate. The aim of this study was to demonstrate the feasibility to noninvasively detect deuterium-labeled downstream glucose metabolites indirectly in the human brain via 3-dimensional (3D) proton ( 1 H) MR spectroscopic imaging on a clinical 3T MR scanner without additional hardware. This prospective, institutional review board-approved study was performed in 7 healthy volunteers (mean age, 31 ± 4 years, 5 men/2 women) after obtaining written informed consent. After overnight fasting and oral deuterium-labeled glucose administration, 3D metabolic maps were acquired every ∼4 minutes with ∼0.24 mL isotropic spatial resolution using real-time motion-, shim-, and frequency-corrected echo-less 3D 1 H-MR spectroscopic Imaging on a clinical routine 3T MR system. To test the interscanner reproducibility of the method, subjects were remeasured on a similar 3T MR system. Time courses were analyzed using linear regression and nonparametric statistical tests. Deuterium-labeled glucose and downstream metabolites were detected indirectly via their respective signal decrease in dynamic 1 H MR spectra due to exchange of labeled and unlabeled molecules. Sixty-five minutes after deuterium-labeled glucose administration, glutamate + glutamine (Glx) signal intensities decreased in gray/white matter (GM/WM) by -1.63 ± 0.3/-1.0 ± 0.3 mM (-13% ± 3%, P = 0.02/-11% ± 3%, P = 0.02), respectively. A moderate to strong negative correlation between Glx and time was observed in GM/WM ( r = -0.64, P < 0.001/ r = -0.54, P < 0.001), with 60% ± 18% ( P = 0.02) steeper slopes in GM versus WM, indicating faster metabolic activity. Other nonlabeled metabolites showed no significant changes. Excellent intrasubject repeatability was observed across scanners for static results at the beginning of the measurement (coefficient of variation 4% ± 4%), whereas differences were observed in individual Glx dynamics, presumably owing to physiological variation of glucose metabolism. Our approach translates deuterium metabolic imaging to widely available clinical routine MR scanners without specialized hardware, offering a safe, affordable, and versatile (other substances than glucose can be labeled) approach for noninvasive imaging of glucose and neurotransmitter metabolism in the human brain.

FSMP-06. IN VIVO MONITORING OF LDHA EXPRESSION IN GLIOBLASTOMA USING QUANTITATIVE EXCHANGED-LABEL TURNOVER 1H MRS TECHNIQUE

Most cancers, including glioblastomas (GBMs), rely extensively on glycolysis to support growth, proliferation, and survival. A hallmark of this elevated glycolysis is overexpression of Lactate dehydrogenase-A (LDHA) protein leading to increased uptake of glucose and overproduction of lactate. Various clinical trials using LDHA as a target for diagnosis and treatment have yielded encouraging results. However, in vivo monitoring of LDHA expression has been challenging due to either requirement of administration of radioactive substrates or specialized hardware. In this presentation, we will demonstrate a new method-quantitative exchanged-label turnover MRS (QELT, or simply qMRS)-that increases the sensitivity of magnetic resonance-based metabolic mapping without the requirement for specialized hardware. qMRS relies on the administration of deuterated (2H-labeled) substrates to track the production of downstream metabolites. Since 2H is invisible on 1H MRS, replacement of 1H with 2H due to metabolic turnover leads to an overall reduction in 1H MRS signal for the corresponding metabolites. We applied our qMRS technique to monitor the rate of lactate production in a preclinical GBM model. Infusion of [6,6’-2H2]glucose led to downstream deuterium labeling of lactate, thereby resulting in a reduction in the 1.33 ppm lactate-CH3 peak on 1H MRS over time. The subtraction of post-administration 1H MR spectra from the pre-infusion spectra aided in the determination of the kinetics of the lactate turnover. We believe that the detection and quantification of lactate production kinetics may provide crucial information regarding tumor LDHA expression non-invasively in GBMs without requiring biopsies. Hence, qMRS is expected to open up new opportunities to probe LDHA expression differences in a variety of gliomas, including GBMs and astrocytomas. This method takes advantage of the universal availability and ease of implementation of 1H MRS on all clinical and preclinical magnetic resonance scanners.

Quantifying dog meniscal volume at 1.5T and 3.0T MRI

The dog has been used extensively as an experimental model to study meniscal treatments such as meniscectomy, meniscal repair and regeneration. Accurate quantification of meniscal size and morphology are a crucial step for developing models of the meniscus. 3.0T magnetic resonance imaging (MRI) has been found to be highly accurate in analyzing the meniscus in both clinical and research fields. However, 3.0T MRI systems are still uncommonly used in veterinary medicine. The goal of the study was to compare meniscal volume measurements from 1.5T MRI system with 3.0T MRI system using proton density sequence, a clinically relevant protocol. The MR images were segmented to reconstruct 3D surface representations of both medial and lateral menisci to compare the meniscal volumes measurements. Average volume differences were 8.8% (P=0.42) and 8.9% (P=0.535) for medial and lateral meniscus, respectively. No significant volume differences were found between 1.5T and 3.0T magnetic resonance (MR) measurements, with high Pearson’s correlation coefficient of r > 0.8 and the intraclass correlation coefficient (ICC) of 0.899. For inter- and intra-observer reproducibility, high correlation (ICC = 0.942 and 0.814) was observed, but with high variability for intra-observer reproducibility (lower bound 0.478, upper bound 0.949). We have shown that common clinical MR scanners and pulse sequences can be used to quantify dogs’ meniscal volumes with good reproducibility. We believe that repeatable measurements of meniscal volumes using MR may provide a useful capability for assessment of postoperative results following meniscal treatments such as meniscectomy and meniscal regeneration.

Establishment of novel technical methods for evaluating brain edema and lesion volume in stroked rats: A standardization of measurement procedures

Stroke plays a role in high morbidity and mortality. Deciphering its mechanisms and pathophysiology is critical for the creation of new drugs and therapies. Most of the previous animal models of stroke, aimed at identifying the extent and location of brain injury following stroke, require animal sacrifice, which, besides ethical considerations, also negates the ability for follow up studies with the same rats. Because of these failures, the use of clinical magnetic resonance scanners for evaluating small animal models has been increasing. Magnetic resonance imaging scanners used particularly for small-bore animals are eligible for use in high-resolution magnetic resonance imaging of rodent brains. However, high costs and scarcity factor heavily in the rare availability of these scanners.In our investigation, we sought to establish a unitary magnetic resonance imaging protocol for stroke assessment in rats. We made use of a 3-Tesla magnetic resonance imaging clinical scanner, as well as another clinical equipment, with the purpose of increasing its reproducibility. The results of inquest validated a new magnetic resonance imaging protocol, comparing a magnetic resonance imaging-measured infarcted zone to the “gold standard” of histological examination. We carried out the experimental procedure on a 3 Tesla magnetic resonance imaging clinical scanner using a conventional eight-channel receive-only coil.The two methods produced remarkable quantitative and qualitative correlations between them. Conclusively, we showed the clinical magnetic resonance imaging scanner to be a high-precision and sensitive image analysis instrument for evaluating both the infarct zone and the brain edema in a stroke experimental rat model.

Automated low-contrast pattern recognition algorithm for magnetic resonance image quality assessment.

Low contrast (LC) detectability is a common test criterion for diagnostic radiologic quality control (QC) programs. Automation of this test is desirable in order to reduce human variability and to speed up analysis. However, automation is challenging due to the complexity of the human visual perception system and the ability to create algorithms that mimic this response. This paper describes the development and testing of an automated LC detection algorithm for use in the analysis of magnetic resonance (MR) images of the American College of Radiology (ACR) QC phantom. The detection algorithm includes fuzzy logic decision processes and various edge detection methods to quantify LC detectability. Algorithm performance was first evaluated using a single LC phantom MR image with the addition of incremental zero mean Gaussian noise resulting in a total of 200 images. A c-statistic was calculated to determine the role of CNR to indicate when the algorithm would detect ten spokes. To evaluate inter-rater agreement between experienced observers and the algorithm, a blinded observer study was performed on 196 LC phantom images acquired from nine clinical MR scanners. The nine scanners included two MR manufacturers and two field strengths (1.5 T, 3.0 T). Inter-rater and algorithm-rater agreement was quantified using Krippendorff's alpha. For the Gaussian noise added data, CNR ranged from 0.519 to 11.7 with CNR being considered an excellent discriminator of algorithm performance (c-statistic = 0.9777). Reviewer scoring of the clinical phantom data resulted in an inter-rater agreement of 0.673 with the agreement between observers and algorithm equal to 0.652, both of which indicate significant agreement. This study demonstrates that the detection of LC test patterns for MR imaging QC programs can be successfully developed and that their response can model the human visual detection system of expert MR QC readers.

Quantitative Evaluation of Rabbit Brain Injury after Cerebral Hemisphere Radiation Exposure Using Generalized q-Sampling Imaging.

Radiation therapy is widely used for the treatment of brain tumors and may result in cellular, vascular and axonal injury and further behavioral deficits. The non-invasive longitudinal imaging assessment of brain injury caused by radiation therapy is important for determining patient prognoses. Several rodent studies have been performed using magnetic resonance imaging (MRI), but further studies in rabbits and large mammals with advanced magnetic resonance (MR) techniques are needed. Previously, we used diffusion tensor imaging (DTI) to evaluate radiation-induced rabbit brain injury. However, DTI is unable to resolve the complicated neural structure changes that are frequently observed during brain injury after radiation exposure. Generalized q-sampling imaging (GQI) is a more accurate and sophisticated diffusion MR approach that can extract additional information about the altered diffusion environments. Therefore, herein, a longitudinal study was performed that used GQI indices, including generalized fractional anisotropy (GFA), quantitative anisotropy (QA), and the isotropic value (ISO) of the orientation distribution function and DTI indices, including fractional anisotropy (FA) and mean diffusivity (MD) over a period of approximately half a year to observe long-term, radiation-induced changes in the different brain compartments of a rabbit model after a hemi-brain single dose (30 Gy) radiation exposure. We revealed that in the external capsule, the GFA right to left (R/L) ratio showed similar trends as the FA R/L ratio, but no clear trends in the remaining three brain compartments. Both the QA and ISO R/L ratios showed similar trends in the all four different compartments during the acute to early delayed post-irradiation phase, which could be explained and reflected the histopathological changes of the complicated dynamic interactions among astrogliosis, demyelination and vasogenic edema. We suggest that GQI is a promising non-invasive technique and as compared with DTI, it has better potential ability in detecting and monitoring the pathophysiological cascades in acute to early delayed radiation-induced brain injury by using clinical MR scanners.

Brain White Matter Tracts: Functional Anatomy and Clinical Relevance

Diffusion tensor imaging is increasingly available on clinical magnetic resonance scanners and can be acquired in a relatively short time. There has been an explosion of applications in the research field but the use to the practicing radiologist may seem obscure. This paper aims to highlight how diffusion tensor imaging can be used to prompt a dedicated neuroanatomical search for white matter lesions in clinical presentations relating to motor, sensory, language, and visuospatial deficits. The enhanced depiction of white matter tracts in the temporal stem is also highlighted, which is a region of importance in epilepsy surgery planning.

Reproducibility of small animal cine and scar cardiac magnetic resonance imaging using a clinical 3.0 tesla system

BackgroundTo evaluate the inter-study, inter-reader and intra-reader reproducibility of cardiac cine and scar imaging in rats using a clinical 3.0 Tesla magnetic resonance (MR) system.MethodsThirty-three adult rats (Sprague–Dawley) were imaged 24 hours after surgical occlusion of the left anterior descending coronary artery using a 3.0 Tesla clinical MR scanner (Philips Healthcare, Best, The Netherlands) equipped with a dedicated 70 mm solenoid receive-only coil. Left-ventricular (LV) volumes, mass, ejection fraction and amount of myocardial scar tissue were measured. Intra-and inter-observer reproducibility was assessed in all animals. In addition, repeat MR exams were performed in 6 randomly chosen rats within 24 hours to assess inter-study reproducibility.ResultsThe MR imaging protocol was successfully completed in 32 (97%) animals. Bland-Altman analysis demonstrated high intra-reader reproducibility (mean bias%: LV end-diastolic volume (LVEDV), -1.7%; LV end-systolic volume (LVESV), -2.2%; LV ejection fraction (LVEF), 1.0%; LV mass, -2.7%; and scar mass, -1.2%) and high inter-reader reproducibility (mean bias%: LVEDV, 3.3%; LVESV, 6.2%; LVEF, -4.8%; LV mass, -1.9%; and scar mass, -1.8%). In addition, a high inter-study reproducibility was found (mean bias%: LVEDV, 0.1%; LVESV, -1.8%; LVEF, 1.0%; LV mass, -4.6%; and scar mass, -6.2%).ConclusionsCardiac MR imaging of rats yielded highly reproducible measurements of cardiac volumes/function and myocardial infarct size on a clinical 3.0 Tesla MR scanner system. Consequently, more widely available high field clinical MR scanners can be employed for small animal imaging of the heart e.g. when aiming at serial assessments during therapeutic intervention studies.

Resolution enhancement as a key step towards clinical implementation of Padé-optimized magnetic resonance spectroscopy for diagnostic oncology

Our overall aim is for the full potential of magnetic resonance spectroscopy (MRS) and magnetic resonance spectroscopic imaging (MRSI) to be realized in oncology. This requires mathematics, without which encoded MRS data are entirely uninterpretable. Mathematics based on the conventional approach, the fast Fourier transform (FFT), and ambiguous fittings of Fourier spectra cannot fulfill the rigorous demands of oncology. It is vital to go beyond the FFT and fitting, to obtain reliable quantitative information via MRS about the metabolic content of tissue. None of the available MRS fitting algorithms could provide the clinically needed information with certainty, namely, the metabolite concentrations. Our more advanced method, the fast Pade transform (FPT) is firmly established as a stable, high-resolution processor, with which metabolite concentrations are unequivocally generated for in vitro MRS data associated with prostate, breast and ovarian cancer. Validation of the FPT has also been performed for in vivo MRS of normal human brain from clinical magnetic resonance scanners (1.5 T) as well as from 4 to 7 T scanners. The FPT successfully handles major problems hindering more widespread clinical application of MRS and MRSI, such as separation of noise from signal, resolution of very dense spectra with multiplet resonances (prostate) and overlapping metabolite resonances (breast, brain). In the present paper, we focus upon the implications of resolution enhancement by the FPT. We conclude that the manner by which the FPT achieves its high resolution accuracy dictates a major reformulation of the concept of data acquisition by encoding a small number of short transient time signals to secure good signal-noise ratio. Pade-guided MRS has distinct clinical advantages in combining improved diagnostic accuracy of MRS with shorter examination times. This shortens turn-around time for patients, making MRS efficient and cost-effective. With Pade-based quantification plus FPT-guided encoding of MRS and MRSI data, MRS can become a reliable, cost-effective tool for diagnostics and various aspects of patient care within oncology.

Cardiovascular magnetic resonance imaging of isolated perfused pig hearts in a 3T clinical MR scanner

An isolated perfused pig heart model has recently been proposed for the development of novel methods in standard clinical magnetic resonance (MR) scanners. The original set-up required the electrical system to be within the safe part of the MR-room, which introduced significant background noise. The purpose of the current work was to refine the system to overcome this limitation so that all electrical parts are completely outside the scanner room. Four pig hearts were explanted under terminal anaesthesia from large white cross landrace pigs. All hearts underwent cardiovascular magnetic resonance (CMR) scanning in the MR part of a novel combined 3T MR and x-ray fluoroscopy (XMR) suite. CMR scanning included real-time k-t SENSE functional imaging, k-t SENSE accelerated perfusion imaging and late gadolinium enhancement imaging. Interference with image quality was assessed by spurious echo imaging and compared to noise levels acquired while operating the electrical parts within the scanner room. Imaging was performed successfully in all hearts. The system proved suitable for isolated heart perfusion in a novel 3T XMR suite. No significant additional noise was introduced into the scanner room by our set-up. We have substantially improved a previous version of an isolated perfused pig heart model and made it applicable for MR imaging in a state of the art clinical 3T XMR imaging suite. The use of this system should aid novel CMR sequence development and translation into clinical practice.

MR imaging near metal with undersampled 3D radial UTE‐MAVRIC sequences

Recently developed techniques such as the multiple acquisition with variable resonance image combination and slice encoding for metal artifact correction techniques have improved the ability of clinical magnetic resonance scanners to image near metal implants. These sequences are based on fast spin echo sequences which preclude detection of short T(2) tissues such as tendons, ligaments, and cortical bone. Ultrashort echo time sequences have the potential to detect signals from these tissues. In this study, we investigate the potential of combining ultrashort echo time with multiple acquisition with variable resonance image combination to image short T(2) musculoskeletal tissues adjacent to metallic implants. Different radio frequency excitation pulse types and spectral binning strategies were studied. We found that ultrashort echo time-multiple acquisition with variable resonance image combination sequences were able to significantly reduce typical artifacts near metal, as well as detect very short T(2) signals that are usually not visualized using clinical pulse sequences.

Cardiac magnetic resonance imaging of isolated perfused pig hearts in a 3T clinical MR scanner

Purpose: An isolated perfused pig heart model has recently been proposed for the development of novel methods in standard clinical magnetic resonance (MR) scanners. The original set-up required the electrical system to be within the safe part of the MR-room, which introduced significant background noise. The purpose of the current work was to refine the system to overcome this limitation so that all electrical parts are completely outside the scanner room. Methods: four pig hearts were explanted under terminal anaesthesia from large white cross landrace pigs. All hearts underwent cardiovascular magnetic resonance (CMR) scanning in the MR part of a novel combined 3T MR and x-ray fluoroscopy (XMR) suite. CMR scanning included real-time k-t SENSE functional imaging, k-t SENSE accelerated perfusion imaging and late gadolinium enhancement imaging. interference with image quality was assessed by spurious echo imaging and compared to noise levels acquired while operating the electrical parts within the scanner room. Results: imaging was performed successfully in all hearts. The system proved suitable for isolated heart perfusion in a novel 3T XMR suite. No significant additional noise was introduced into the scanner room by our set-up. Conclusions: We have substantially improved a previous version of an isolated perfused pig heart model and made it applicable for MR imaging in a state of the art clinical 3T XMR imaging suite. The use of this system should aid novel CMR sequence development and translation into clinical practice.

Usefulness of clinical magnetic resonance scanners for imaging experimental changes in laboratory rodents' central nervous system

Abstract Introduction Magnetic resonance imaging (MRI) is a noninvasive technique applied in medical diagnosis and for studying animal models of human diseases. MRI offers longitudinal in vivo studies without the need to sacrifice animals, thus making data easier to compare. The number of required animals can be limited. Aim The aim of this article was to present the potential role of clinical MRI scanners in the management of central nervous system visualization and injury in rodents on the basis of the current literature. Materials and methods Clinical small bore scanners with field strength from 0.1 T to 3 T are used for imaging the nervous system of rodents in vivo . Results and discussion The employment of clinical scanners equipped with dedicated human coils, for small objects imaging, results in the reduction of image quality. It is caused by a small signal-to-noise ratio (SNR). The way to increase the SNR is to use clinical scanners for imaging particular parts of the human body, e.g. head, or dedicated coils for imaging small parts of the human body, e.g., thumb or wrist, or to use dedicated small animal coils to image multiple animals in the larger bore of the clinical scanner at the same time. For some neurobiological experiments clinical scanners seem to be sufficient. Although clinical MRI scanners are widespread, not many laboratories use them for small animal research. Conclusions Clinical scanners with surface coils dedicated to small human organs, or with dedicated small animal coils, are useful for imaging experimental changes in the central nervous system of laboratory rodents.

Three-Dimensional Ultrashort Echo Time Imaging of Solid Polymers on a 3-Tesla Whole-Body MRI Scanner

With the introduction of ultrashort echo time (UTE) sequences solid polymeric materials might become visible on clinical whole-body magnetic resonance (MR) scanners. The aim of this study was to characterize solid polymeric materials typically used for instruments in magnetic resonance guided interventions and implants. Relaxation behavior and signal yield were evaluated on a 3-Tesla whole-body MR unit. Nine different commonly used solid polymeric materials were investigated by means of a 3-dimensional (3D) UTE sequence with radial k-space sampling. The investigated polymeric samples with cylindrical shape (length, 150 mm; diameter, 30 mm) were placed in a commercial 8-channel knee coil. For assessment of transverse signal decay (T2*) images with variable echo times (TE) ranging from 0.07 milliseconds to 4.87 milliseconds were recorded. Spin-lattice relaxation time (T1) was calculated for all MR visible polymers with transverse relaxation times higher than T2* = 300 mus using an adapted method applying variable flip angles. Signal-to-noise ratio (SNR) was calculated at the shortest achievable echo time (TE = 0.07 milliseconds) for standardized sequence parameters. All relaxation times and SNR data are given as arithmetic mean values with standard deviations derived from 5 axially oriented slices placed around the isocenter of the coil and magnet. Six of the 9 investigated solid polymers were visible at TE = 0.07 milliseconds. Visible solid polymers showed markedly different SNR values, ie, polyethylene SNR = 1146 +/- 41, polypropylene SNR = 60 +/- 6. Nearly mono-exponential echo time dependent signal decay was observed: Transverse relaxation times differed from T2*=36 +/- 5 mus for polycarbonate to T2*=792 +/- 7 mus for polyvinylchloride (PVC). Two of the investigated solid polymers were applicable to T1 relaxation time calculation. Polyurethane had a spin-lattice relaxation time of T1 = 172 +/- 1 milliseconds, whereas PVC had T1 = 262 +/- 7 milliseconds, respectively. A variety of solid polymers can be visualized by means of clinical whole-body MR scanners and 3D ultrashort echo time (UTE) sequences. The investigated polymers differ substantially in signal yield, signal-decay, and spin-lattice relaxation time. The knowledge of the signal behavior of solid polymers on whole-body clinical MR scanners may help to select suitable polymeric materials for instruments and implants which are visible using UTE sequences.

Measuring muscle lipids with 1H-MR spectroscopy

Fat is a key element of normal skeletal muscle. It is stored inside muscle cells as droplets called intramyocellular lipids (IMCL), or in adipocytes scattered between muscle cells, called extramyocellular lipids (EMCL). Since the 1980s, IMCL droplets have been of particular interest because they were noted to be in contact with mitochondria when examined under electron microscopy. This observation led to the concept that IMCL served as nearby fuel during prolonged exercise [1]. The focus on IMCL, however, intensified after a link with the etiology of diabetes was uncovered. In 1997, 38 Pima Indians—a group of Native Americans living in central and southern Arizona—participated in a study on diabetes [2]. Pima Indians have a marked predisposition to developing Type 2 diabetes and are less sensitive to insulin action. Such a condition, called insulin resistance, generally precedes the clinical development of Type 2 diabetes by 10 to 20 years [3]. Biopsies from the vastus lateralis muscle of these participants showed increased amounts of lipids that strongly correlated with their insulin resistance. This finding pioneered further research that established a connection between IMCL accumulation and insulin resistance. Recent studies indicate that IMCL may act indirectly: increased sub-products of IMCL, such as fatty acyl-CoA and diacylglycerol, hamper signals from insulin that promote transport of glucose into the cell [4]. Interestingly, increased IMCL is not always a herald of disease. Elite athletes show high levels of IMCL and are very insulin-sensitive. This paradox is explained by the fact that muscles of highly trained persons have enhanced fatburning (oxidative) capacity, being very efficient at lipid utilization [4]. Sedentary and obese individuals, on the other hand, have decreased muscle oxidative capacity in which IMCL accumulation may be harmful. Such observations relied on several techniques to measure muscle lipids. Biochemical analysis, histochemistry, and electron microscopy represent methods that directly assess lipid content. Yet they require biopsy, which limits multiple measures of the same area and application in children. On the other hand, non-invasive methods such as computerized tomography and magnetic resonance (MR) imaging have been optimized for muscle lipid quantification. However, only proton magnetic resonance spectroscopy (1H-MRS) succeeded in discriminating the IMCL and EMCL compartments. An important principle behind 1H-MRS is that protons resonate at different frequencies depending on the molecules they are linked to. For example, methylene protons in lipids compared with methyl protons in creatine resonate differently by about 1.5 ppm (ppm is a measure of frequency independent of magnetic field strength). MR spectroscopy data is displayed as a graphic where frequency is along the x-axis, allowing identification of metabolites. Peak intensity is plotted on the y-axis. The area under a peak corresponds to its concentration, which is measured by software that compares one peak with another (relative quantitation), or compares peaks with in vitro data (absolute quantitation). Several important metabolites can be identified in the proton spectrum of muscle, including: IMCL (0.9 and 1.3 ppm), EMCL (1.1 and 1.5 ppm), creatine (2.8, 3.0, and 3.2 ppm), trimethylamines (3.2 ppm), and an assumed taurine signal (3.5 ppm; Fig. 1) [5]. A signal of acetylcarnitine can be seen at 2.13 ppm, immediately after strenuous exercise. These data can be gathered by most clinical MR scanners, using pulse sequences that measure metabolites from very specific areas while ignoring the surrounding tissues. The most popular pulse sequence for IMCL measurement is single-voxel short echo time point-resolved spectroscopy (PRESS). Using this technique, Schick et al. [6] and later Boesch et al. [5] demonstrated that IMCL and EMCL showed slightly different frequencies due to contrasting spatial arrangements in muscle. While IMCL droplets are roughly spherical, EMCL are within sheets of adipocytes, causing each compartment to experience the magnetic field differentSkeletal Radiol (2007) 36:607–608 DOI 10.1007/s00256-006-0252-8

T1 and T2 relaxivity of intracellular and extracellular USPIO at 1.5T and 3T clinical MR scanning

In this study we evaluated the effects of intracellular compartmentalization of the ultrasmall superparamagnetic iron oxide (USPIO) ferumoxtran-10 on its proton T1 and T2 relaxivities at 1.5 and 3T. Monocytes were labeled with ferumoxtran-10 by simple incubation. Decreasing quantities of ferumoxtran-10-labeled cells (2.5x10(7)-0.3x10(7) cells/ml) and decreasing concentrations of free ferumoxtran-10 (without cells) in Ficoll solution were evaluated with 1.5 and 3T clinical magnetic resonance (MR) scanners. Pulse sequences comprised axial spin echo (SE) sequences with multiple TRs and fixed TE and SE sequences with fixed TR and increasing TEs. Signal intensity measurements were used to calculate T1 and T2 relaxation times of all samples, assuming a monoexponential signal decay. The iron content in all samples was determined by inductively coupled plasma atomic emission spectrometry and used for calculating relaxivities. Measurements at 1.5T and 3T showed higher T1 and T2 relaxivity values of free extracellular ferumoxtran-10 as opposed to intracellularly compartmentalized ferumoxtran-10, under the evaluated conditions of homogeneously dispersed contrast agents/cells in Ficoll solution and a cell density of up to 2.5x10(7) cells/ml. At 3T, differences in T1-relaxivities between intra- and extracellular USPIO were smaller, while differences in USPIO T2-relaxivities were similar compared with 1.5T. In conclusion, cellular compartmentalization of ferumoxtran-10 changes proton relaxivity.

Method for Cortical Bone Structural Analysis From Magnetic Resonance Images 1

Quantitative evaluation of cortical bone architecture as a means to assess bone strength typically is accomplished on the basis of images obtained by means of dual-energy X-ray absorptiometry (DXA) or computed tomography. Magnetic resonance (MR) imaging has potential advantages for this task in that it allows imaging in arbitrary scan planes at high spatial resolution. However, several hurdles have to be overcome to make this approach practical, including resolution of issues related to nonlinear receive coil sensitivity, variations in marrow composition, and the presence of periosteal isointense tissues, which all complicate segmentation. The aim of this study is to develop MR acquisition and analysis methods optimized for the detection of cortical boundaries in such complex geometries as the femoral neck. Cortical boundary detection is achieved by radially tracing intensity profiles that intersect the periosteal and endosteal boundaries of bone. Profiles subsequently are normalized to the intensity of the marrow signal, processed with morphologic image operators, and binarized. The resulting boundaries are mapped back onto the spatial image, and erroneous boundary points are removed. From the detected cortical boundaries, cortical cross-sectional area and thickness are computed. The method was evaluated on cortical bone specimens and human volunteers on the basis of high-resolution images acquired at a 1.5-Tesla field strength. To assess whether the method is sensitive to detect the expected dependencies of cortical parameters in weight-bearing bone on overall habitus, 10 women aged 46-73 years (mean age, 56 years) underwent the cortical imaging protocol in the proximal femur, and results were compared with DXA bone mineral density parameters of the hip and spine. Reproducibility was approximately 2%. Double oblique images of the femoral neck in the 10 women studied showed that cortical cross-sectional area correlated strongly with height (r = 0.88; p = .0008), whereas cortical diameter versus age approached significance (r = 0.61; p = .06). Measurements in specimens of some cortical parameters indicated resolution dependence. However, note that specimen ranking within each parameter remained constant across all resolutions studied. Data suggest the new method to be robust and applicable on standard clinical MR scanners at arbitrary anatomic locations to yield clinically meaningful quantitative results.

Efficacy of Proton Magnetic Resonance Spectroscopy in Neurological Diagnosis and Neurotherapeutic Decision Making

Anatomic and functional neuroimaging with magnetic resonance imaging (MRI) includes the technology more widely known as magnetic resonance spectroscopy (MRS). Now a routine automated "add-on" to all clinical magnetic resonance scanners, MRS, which assays regional neurochemical health and disease, is therefore the most accessible diagnostic tool for clinical management of neurometabolic disorders. Furthermore, the noninvasive nature of this technique makes it an ideal tool for therapeutic monitoring of disease and neurotherapeutic decision making. Among the more than 100 brain disorders that fall within this broad category, MRS contributes decisively to clinical decision making in a smaller but growing number. In this review, we will cover how MRS provides therapeutic impact in brain tumors, metabolic disorders such as adrenoleukodystrophy and Canavan's disease, Alzheimer's disease, hypoxia, secondary to trauma or ischemia, human immunodeficiency virus dementia and lesions, as well as systemic disease such as hepatic and renal failure. Together, these eight indications for MRS apply to a majority of all cases seen. This review, which examines the role of MRS in enhancing routine neurological practice and treatment concludes: 1) there is added value from MRS where MRI is positive; 2) there is unique decision-making information in MRS when MRI is negative; and 3) MRS usefully informs decision making in neurotherapeutics. Additional efficacy studies could extend the range of this capability.

Importance of exactb-tensor calculation for quantitative diffusion tensor imaging and tracking of neuronal fiber bundles

Quantitative diffusion tensor imaging (DTI) is a novel method of magnetic resonance (MR) imaging providing information on the brain’s microstructure in vivo. DTI can be effectively measured with modern clinical MR scanners. However, imaging sequence details required for accurateb matrix calculation and for following DTI quantification are normally unknown to the user. In this work, we investigated the accuracy ofb value approximation if theb matrix is calculated without taking into account the effect of imaging gradients. It was found that an error of more than 4% in DTI estimation arises for a quite typical brain imaging protocol. The errors in mean diffusivity and fractional anisotropy index depend on diffusion tensor shape and eigenvectors orientation and exceed noise level in DTI quantification. These errors however have a strong impact on fiber tracking — up to 30% difference was found between the fiber tracks corresponding to exact and approximate calculated DTI data. Since these errors are dependent on imaging parameters and sequence implementation, accurateb matrix calculations are important for adequate comparison between data acquired on different MR scanners and also for data measured with the different imaging protocols.