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Despite, currently, “state-of-the-art” magnetic resonance imaging (MRI) protocols for head and neck (H&N) lesion assessment incorporate perfusion sequences, these acquisitions require the intravenous injection of exogenous gadolinium-based contrast agents (GBCAs), which may have potential risks. Alternative techniques such as arterial spin labeling (ASL) can provide quantitative microvascular information similar to conventional perfusion sequences for H&N lesions evaluation, as a potential alternative without GBCA administration. We review the existing literature and analyze the latest evidence regarding ASL in H&N area highlighting the technical adjustments needed for a proper ASL acquisition in this challenging region for lesion characterization, treatment monitoring, and tumor recurrence detection. ASL techniques, widely used for central nervous system lesions evaluation, can be also applied to the H&N region. Technical adjustments, especially regarding post-labeling delay, are mandatory to obtain robust and reproducible results. Several studies have demonstrated the feasibility of ASL in the H&N area including the orbits, skull base, paranasal sinuses, upper airway, salivary glands, and thyroid. ASL is a feasible technique for the assessment of H&N lesions without the need of GBCAs. This manuscript reviews ASL’s physical basis, emphasizing the technical adjustments necessary for proper ASL acquisition in this unique and challenging anatomical region, and the main applications in evaluating H&N lesions.

Editor's Note.-Articles in the RadioGraphics Update section provide current knowledge to supplement or update information found in full-length articles previously published in RadioGraphics. Authors of the previously published article provide a brief synopsis that emphasizes important new information such as technological advances, revised imaging protocols, new clinical guidelines involving imaging, or updated classification schemes. Articles in this section are published solely online and are linked to the original article. ©RSNA, 2021.

Context Muscle weakness is common in patients with Cushing’s syndrome (CS) and may persist after the resolution of hypercortisolism. Intramuscular fatty infiltration has been associated with the deterioration of muscle performance in several conditions. Objectives To quantify the degree of fatty infiltration in the thigh muscles of “cured” CS patients and evaluate the relationship between intramuscular fatty infiltration and physical performance. Design This was a cross-sectional study. Setting Tertiary referral center. Patients Thirty-six women with CS in remission, and 36 controls matched for age, BMI, menopausal status, and level of physical activity. Main Outcome Measures We analyzed the percentage fat fraction (FF) of the thigh muscles in the anterior, posterior, and combined anterior and posterior compartments using MRI and 2-point Dixon sequence. We assessed muscle function and strength using the following tests: gait speed (GS), timed up and go (TUG), 30-second chair stand, and hand grip strength. Results Fat fraction in all the compartments analyzed was increased in patients as compared with controls. The performance on TUG, 30-second chair stand, and GS was more impaired in CS patients versus controls. In patients, greater FF was negatively associated with performance on functional tests. Fat fraction in the combined anterior and posterior compartments predicted performance on TUG (ß 0.626, P < 0.000) and GS (ß -0.461, P = 0.007), after adjusting for age, BMI, menopausal status, and muscle mass. Conclusions Thigh muscle fatty infiltration is increased in “cured” CS patients and is associated with poorer muscle performance. Future studies are needed to establish therapeutic strategies to improve muscle weakness in these patients.

Altres ajuts: Asociación Española de Enfermos de Glucogenosis (AEEG) Quantitative MRI is an increasingly used method to monitor disease progression in muscular disorders due to its ability to measure changes in muscle fat content (reported as fat fraction) over a short period. Being able to objectively measure such changes is crucial for the development of new treatments in clinical trials. However, the analysis of the images involved continues to be a daunting task because of the time needed. Whether a more specific analysis selecting individual muscles or a global one analyzing the whole thigh or compartments could be a suitable alternative has only been marginally studied. In our study we compare three methods of analysis of 2-point-dixon images in a cohort of 34 patients with late onset Pompe disease followed over a period of one year. We measured fat fraction on MRIs obtained at baseline and at year 1, and we calculated the increment of fat fraction. We correlated the results obtained with the results of muscle function tests to investigate whether the three methods of analysis were equivalent or not. We observed significant differences between the three methods in the estimation of the fat fraction at both baseline and year 1, but no difference was found in the increment in fat fraction between baseline and year 1. When we correlated the fat fraction obtained with each method and the muscle function tests, we found a significant correlation with most tests in all three methods, although in most comparisons the highest correlation coefficient was found with the analysis of individual muscles. We conclude that the fastest strategy of analysis assessing compartments or the whole thigh could be reliable for certain cohorts of patients where the variable to study is the fat increment. In other sorts of studies, an individual muscle approach seems the most reliable technique.

Objectives: Magnetization transfer (MT) imaging exploits the interaction between bulk water protons and protons contained in macromolecules to induce signal changes through a special radiofrequency pulse. MT detects muscle damage in patients with neuromuscular conditions, such as limb-girdle muscular dystrophies or Charcot-Marie-Tooth disease, which are characterized by progressive fiber loss and replacement by fatty tissue. In Pompe disease, in which there is, in addition, an accumulation of glycogen inside the muscle fibers, MT has not been tested yet. Our aim is to estimate MT ratio (MTR) in the skeletal muscle of these patients and correlate it with intramuscular fat fraction (FF) and results of muscle function tests.Methods: We obtained two-point axial Dixon and Dixon-MT sequences of the right thigh on a 1.5 Teslas MRI scanner in 60 individuals, including 29 late onset Pompe disease patients, 2 patients with McArdle disease, and 29 age and sex matched healthy controls. FF and MTR were estimated. Muscle function using several muscle function tests, including quantification of muscle strength, timed test quality of life scales, conventional spirometry obtaining forced vital capacity while sitting and in the supine position, were assessed in all patients.Results: MTR was significantly lower in Pompe patients compared with controls (45.5 ± 8.5 vs. 51.7 ± 2.3, Student T-test, p < 0.05). There was a negative correlation between the MTR and FF muscles studied (correlation coefficient: −0.65, Spearman test: p < 0.05). MTR correlated with most of the muscle function test results. We analyzed if there was any difference in MTR values between Pompe patients and healthy controls in those muscles that did not have an increase in fat, a measure that could be related to the presence of glycogen in skeletal muscles, but we did not identify significant differences except in the adductor magnus muscle (48.4 ± 3.6 in Pompe vs. 51 ± 1.3 in healthy controls, Student T-test = 0.023).Conclusions: MTR is a sensitive tool to identify muscle loss in patients with Pompe disease and shows a good correlation with muscle function tests. Therefore, the MT technique can be useful in monitoring muscle degeneration in Pompe disease in clinical trials or natural history studies.

To propose and validate a novel imaging sequence that uses a single breath-hold whole-heart 3D T1 saturation recovery compressed SENSE rapid acquisition (SACORA) at 3T. The proposed sequence combines flexible saturation time sampling, compressed SENSE, and sharing of saturation pulses between two readouts acquired at different RR intervals. The sequence was compared with a 3D saturation recovery single-shot acquisition (SASHA) implementation with phantom and in vivo experiments (pre and post contrast; 7 pigs) and was validated against the reference inversion recovery spin echo (IR-SE) sequence in phantom experiments. Phantom experiments showed that the T1 maps acquired by 3D SACORA and 3D SASHA agree well with IR-SE. In vivo experiments showed that the pre-contrast and post-contrast T1 maps acquired by 3D SACORA are comparable to the corresponding 3D SASHA maps, despite the shorter acquisition time (15s vs. 188s, for a heart rate of 60 bpm). Mean septal pre-contrast T1 was 1453 ± 44 ms with 3D SACORA and 1460 ± 60 ms with 3D SASHA. Mean septal post-contrast T1 was 824 ± 66 ms and 824 ± 60 ms. 3D SACORA acquires 3D T1 maps in 15 heart beats (heart rate, 60 bpm) at 3T. In addition to its short acquisition time, the sequence achieves good T1 estimation precision and accuracy. TFdS has received funding from the European Union Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement N722427. CGA is a P-FIS fellow (Instituto deSalud Carlos III). This study was partially supported by the Comunidad de Madrid (S2017/BMD-3867 RENIM-CM) and cofunded with European structural and investment funds. The CNIC is supported by the Instituto de Salud Carlos III (ISCIII), the Ministerio de Ciencia, Innovación y Universidades (MCNU) and the Pro CNIC Foundation, and is a Severo Ochoa Center of Excellence (SEV-2015-0505). Sí

Diffusion-tensor imaging (DTI) has been used in the assessment of the central nervous system for the past 3 decades and has demonstrated great utility for the functional assessment of normal and pathologic white matter. Recent technical advances have permitted the expansion of DTI applications to the spinal cord. MRI of the spinal cord has traditionally been limited to conventional sequences, which provide information regarding changes in the anatomic shape of a structure or its signal intensity, suggesting the presence of a pathologic entity. However, conventional MRI lacks the ability to provide pathophysiologic information. DTI of the spinal cord can deliver pathophysiologic information on a molecular basis and thereby has several adjunctive uses. These advantages have yet to be fully evaluated, and therefore spinal DTI lacks widespread adoption. The barriers to implementation include a lack of understanding of the underlying physics principles needed to make necessary technical adjustments to obtain diagnostic images, as well as the need for standardization of protocols and postprocessing methods. The authors provide a comprehensive review of the physics of spinal cord DTI and the technical adjustments required to obtain diagnostic images and describe tips and tricks for accurate postprocessing. The primary clinical applications for spinal cord DTI are reviewed.

OBJECTIVES To use the mDIXON-Quant sequence to quantify the fat fraction of adrenal lesions discovered incidentally on CT studies. To analyze the relation between the signal loss between in-phase and out-of-phase T1-weighted sequences and the fat fraction in mDIXON-Quant. To compare the sensitivity and specificity of the two methods for characterizing adrenal lesions. MATERIAL AND METHODS This prospective descriptive study included 31 patients with incidentally discovered adrenal lesions evaluated with 3T MRI using in-phase and out-of-phase T1-weighted sequences and mDIXON-Quant; the fat fraction of the adrenal lesions was measured by mDIXON-Quant and by calculating the percentage of signal loss between in-phase and out-of-phase T1-weighted sequences. RESULTS The percentage of signal loss was significantly higher in the group of patients with adenoma (61.3% ± 20.4% vs. 5.1% ± 5.8% in the group without adenoma, p

Purpose Mesorectal lymph node staging plays an important role in treatment decision making. Here, we explore the benefit of higher-order diffusion MRI models accounting for non-Gaussian diffusion effects to classify mesorectal lymph nodes both 1) ex vivo at ultrahigh field correlated with histology and 2) in vivo in a clinical scanner upon patient staging. Methods The preclinical investigation included 54 mesorectal lymph nodes, which were scanned at 16.4 T with an extensive diffusion MRI acquisition. Eight diffusion models were compared in terms of goodness of fit, lymph node classification ability, and histology correlation. In the clinical part of this study, 10 rectal cancer patients were scanned with diffusion MRI at 1.5 T, and 72 lymph nodes were analyzed with Apparent Diffusion Coefficient (ADC), Intravoxel Incoherent Motion (IVIM), Kurtosis, and IVIM-Kurtosis. Results Compartment models including restricted and anisotropic diffusion improved the preclinical data fit, as well as the lymph node classification, compared to standard ADC. The comparison with histology revealed only moderate correlations, and the highest values were observed between diffusion anisotropy metrics and cell area fraction. In the clinical study, the diffusivity from IVIM-Kurtosis was the only metric showing significant differences between benign (0.80 ± 0.30 μm2 /ms) and malignant (1.02 ± 0.41 μm2 /ms, P = .03) nodes. IVIM-Kurtosis also yielded the largest area under the receiver operating characteristic curve (0.73) and significantly improved the node differentiation when added to the standard visual analysis by experts based on T2 -weighted imaging. Conclusion Higher-order diffusion MRI models perform better than standard ADC and may be of added value for mesorectal lymph node classification in rectal cancer patients.

Altres ajuts: This investigation was sponsored by the following grants, one from Sanofi Genzyme and another from the Spanish Ministry of Health, Fondos FEDER-ISCIII. Isabel Illa has received speaker honorarium from Grifols and Sanofi-Genzyme. Jordi Díaz-Manera has received speaker honorarium from PTC Therapeutics and Sanofi-Genzyme. The authors of this manuscript certify that they comply with the ethical guidelines for authorship and publishing in the Journal of Cachexia, Sarcopenia, and Muscle.42 Altres ajuts: MSCBS/PI18-01525 Altres ajuts: MSCBS/PI18-0111 Late-onset Pompe disease (LOPD) is a genetic disorder characterized by progressive degeneration of the skeletal muscles produced by a deficiency of the enzyme acid alpha-glucosidase. Enzymatic replacement therapy with recombinant human alpha-glucosidase seems to reduce the progression of the disease; although at the moment, it is not completely clear to what extent. Quantitative muscle magnetic resonance imaging (qMRI) is a good biomarker for the follow-up of fat replacement in neuromuscular disorders. The aim of this study was to describe the changes observed in fat replacement in skeletal muscles using qMRI in a cohort of LOPD patients followed prospectively. A total of 36 LOPD patients were seen once every year for 4 years. qMRI, several muscle function tests, spirometry, activities of daily living scales, and quality-of-life scales were performed on each visit. Muscle MRI consisted of two-point Dixon studies of the trunk and thigh muscles. Computer analysis of the images provided the percentage of muscle degenerated and replaced by fat in every muscle (known as fat fraction). Longitudinal analysis of the measures was performed using linear mixed models applying the Greenhouse-Geisser test. We detected a statistically significant and continuous increase in mean thigh fat fraction both in treated (+5.8% in 3 years) and in pre-symptomatic patients (+2.6% in 3years) (Greenhouse-Geisser p < 0.05). As an average, fat fraction increased by 1.9% per year in treated patients, compared with 0.8% in pre-symptomatic patients. Fat fraction significantly increased in every muscle of the thighs. We observed a significant correlation between changes observed in fat fraction in qMRI and changes observed in the results of the muscle function tests performed. Moreover, we identified that muscle performance and mean thigh fat fraction at baseline visit were independent parameters influencing fat fraction progression over 4 years (analysis of covariance, p < 0.05). Our study identifies that skeletal muscle fat fraction continues to increase in patients with LOPD despite the treatment with enzymatic replacement therapy. These results suggest that the process of muscle degeneration is not stopped by the treatment and could impact muscle function over the years. Hereby, we show that fat fraction along with muscle function tests can be considered a good outcome measures for clinical trials in LOPD patients.

Myopathy is a frequent feature in patients with Cushing’s syndrome (CS), long-term after eucortisolism is achieved. Muscle magnetic resonance imaging (MRI) is the gold standard technique to assess muscle architecture but cannot be performed in daily clinical practice. Ultrasonography (US) may be a useful and cost-effective tool to evaluate muscle impairment in the clinical setting. Utility of US to evaluate the impairment of muscle structure in “cured” CS patients is not established. The aim of our study was to assess the correlation between US- and MRI-measured parameters of muscle architecture. We included 21 female patients [mean (±SD) age, 50±12 years; mean (±SD) BMI, 26.7±3.8] and 21 age- and BMI-matched healthy women. Mean (±SD) duration of remission was 132±87 months. We obtained transverse ultrasound images of the rectus femoris and assessed muscle intensity at both the midpoint (QmitR) and the distal third (QtercR), between the anterior inferior iliac spine and the proximal end of the patella. We scored muscle intensity using the Heckmatt’s rating scale and classified our findings as follows: 1-normal, 2-mildy increased muscle echoes with normal bone reflection, 3-moderately increased muscle echoes with reduced bone, 4-severely increased muscle echoes with absent bone reflection. We found that mean US intensity score of the rectus femoris at midpoint (QmitR) was increased in patients vs. the control group (p

Sarcopenia, the loss of skeletal muscle mass and function, is a frequent finding in patients chronically exposed to glucocorticoids. Patients with active Cushing’s syndrome (CS) show reduced muscle mass and weakness. Decreased MRI-measured lean mass has been found in CS after 20 months since successful therapy vs. pre-treatment. Persistence and worsening of muscle strength has been described in CS despite long-term remission, suggesting that previous exposure to excessive cortisol may have induced irreversible alterations of muscle structure and function. Low muscle mass can be detected using several techniques, including dual-energy X-ray absorptiometry (DXA), ultrasonography (US), magnetic resonance imaging (MRI) and computed tomography (CT), while low muscle strength and performance can be diagnosed through functional testing. The Sarcopenia Index (SI),-(serum creatinine value [mg/dl]/serum cystatin C value[mg/L]) × 100, has been proposed as a potential, reliable surrogate marker of low muscle mass and function. Clinical usefulness of this parameter in CS is currently unknown. The aim of our study was to establish the correlation between SI and the techniques commonly used to evaluate muscle mass, including DXA, US, MRI, as well as tests of muscle function including gait speed velocity (GS), timed up and go (TUG), 30-second chair stand and hand grip strength (HGS). We studied 30 CS women [mean(±SD) age, 50±12 years; mean(±SD) BMI, 26.7±3.8] and 30 age- and BMI-matched healthy women. We studied whole-body composition by DXA, and calculated the Skeletal Muscle Index (SMI), defined as the ratio of the DXA-measured appendicular skeletal muscle mass (ASM) [Kg] and the height squared [m2]. We evaluated US muscle thickness using transverse images of rectus femoris and vastus intermedious at the midpoint and at the distal third. We measured the volume of lean mass (DxLean; ml) of the thigh muscles using MRI, 3-point Dixon sequences. SI was associated with both US-measured section of the distal third of the right rectus femoris (ρ=0.47, p=0.008), and the DxLean (ρ=-0.46, p=0.011) in patients. We found no correlations between SI and either SMI or DXA-measured lean mass (gr) (p=n.s.). SI was negatively associated with both total body fat mass (gr) (ρ=-0.45, p=0.010) and trunk fat mass (gr) (ρ=0.065 p

The presence of blood or calcium in the musculoskeletal (MSK) system may be linked to specific pathological conditions. The ability of MRI for calcium detection is usually limited compared with other techniques such as CT. In a similar manner, the accuracy of MRI for detection and evaluation of hemorrhage in soft tissues is closely linked to the degree of degradation of blood products. Blood and calcium are substances that cause local inhomogeneity of the magnetic field resulting in susceptibility artifacts. To try to evaluate these substances, specific MRI sequences which are highly sensitive to these local magnetic field inhomogeneities such as Susceptibility Weighted Imaging (SWI) have been developed and successfully applied in the Central Nervous System, but scarcely used in MSK. SWI may increase the overall sensitivity of MRI to detect blood and calcium in several clinical scenarios such as degenerative joint disease or bone and soft tissue lesion assessment and discriminate between both compounds, something which is not always possible with conventional MRI approaches. In this paper, physical basis and technical adjustment for SWI acquisition at MSK are detailed reviewing the potential application of SWI in different MSK clinical scenarios.

The purpose of this study was to develop a multi-platform automatic software tool for full processing of fMRI rodent studies. Existing tools require the usage of several different plug-ins, a significant user interaction and/or programming skills. Based on a user-friendly interface, the tool provides statistical parametric brain maps (t and Z) and percentage of signal change for user-provided regions of interest. The tool is coded in MATLAB (MathWorks(®)) and implemented as a plug-in for SPM (Statistical Parametric Mapping, the Wellcome Trust Centre for Neuroimaging). The automatic pipeline loads default parameters that are appropriate for preclinical studies and processes multiple subjects in batch mode (from images in either Nifti or raw Bruker format). In advanced mode, all processing steps can be selected or deselected and executed independently. Processing parameters and workflow were optimized for rat studies and assessed using 460 male-rat fMRI series on which we tested five smoothing kernel sizes and three different hemodynamic models. A smoothing kernel of FWHM = 1.2 mm (four times the voxel size) yielded the highest t values at the somatosensorial primary cortex, and a boxcar response function provided the lowest residual variance after fitting. fMRat offers the features of a thorough SPM-based analysis combined with the functionality of several SPM extensions in a single automatic pipeline with a user-friendly interface. The code and sample images can be downloaded from https://github.com/HGGM-LIM/fmrat .

Medical imaging has a key role in improving diagnosis and treatment of different diseases and has been used as a cost-effective solution to reduce costs in clinical trials [1]. Medical imaging overcomes the three main difficulties that traditional clinical endpoints have, such as (1) their difficulty to be standardized or quantified, (2) the long time required to be manifested, and (3) their high costs, particularly when long-term endpoints, such as mortality, are used. All these difficulties can be overcome by the so-called surrogate endpoints that are intended to substitute clinical endpoints and are expected to predict clinical benefits based on epidemiologic, therapeutic, pathophysiologic, or other scientific evidences. The utility of surrogate endpoints is defined based on their ability to be measured earlier and more frequently than traditional clinical endpoints, facilitating the access to the final results.

MotivationThis work presents the development of an open source tool for the quantification of dynamic susceptibility-weighted contrast-enhanced (DSC) perfusion studies. The development of this tool is motivated by the lack of open source tools implemented on open platforms to allow external developers to implement their own quantification methods easily and without the need of paying for a development license. Materials and methodsThis quantification tool was developed as a plugin for the ImageJ image analysis platform using the Java programming language. A modular approach was used in the implementation of the components, in such a way that the addition of new methods can be done without breaking any of the existing functionalities. For the validation process, images from seven patients with brain tumors were acquired and quantified with the presented tool and with a widely used clinical software package. The resulting perfusion parameters were then compared. ResultsPerfusion parameters and the corresponding parametric images were obtained. When no gamma-fitting is used, an excellent agreement with the tool used as a gold-standard was obtained (R2>0.8 and values are within 95% CI limits in Bland-Altman plots). ConclusionAn open source tool that performs quantification of perfusion studies using magnetic resonance imaging has been developed and validated using a clinical software package. It works as an ImageJ plugin and the source code has been published with an open source license. We have developed an open source tool for DSC-MRI quantification.The software runs as a plugin for the multiplatform public domain software ImageJ.It contains an open API that allows external users to implement new methods.It was validated, with good results, against a clinical tool, Philips IntelliSpace.

Purpose Compressed sensing (CS) has been widely applied to prospective cardiac cine MRI. The aim of this work is to study the benefits obtained by including motion estimation in the CS framework for small-animal retrospective cardiac cine. Methods We propose a novel B-spline-based compressed sensing method (SPLICS) that includes motion estimation and generalizes previous spatiotemporal total variation (ST-TV) methods by taking into account motion between frames. In addition, we assess the effect of an optimum weighting between spatial and temporal sparsity to further improve results. Both methods were implemented using the efficient Split Bregman methodology and were evaluated on rat data comparing animals with myocardial infarction with controls for several acceleration factors. Results ST-TV with optimum selection of the weighting sparsity parameter led to results similar to those of SPLICS; ST-TV with large relative temporal sparsity led to temporal blurring effects. However, SPLICS always properly corrected temporal blurring, independently of the weighting parameter. At acceleration factors of 15, SPLICS did not distort temporal intensity information but led to some artefacts and slight over-smoothing. At an acceleration factor of 7, images were reconstructed without significant loss of quality. Conclusion We have validated SPLICS for retrospective cardiac cine in small animal, achieving high acceleration factors. In addition, we have shown that motion modelling may not be essential for retrospective cine and that similar results can be obtained by using ST-TV provided that an optimum selection of the spatiotemporal sparsity weighting parameter is performed.

Over the lasts years many works have addressed the potential of compressed sensing techniques to accelerate acquisition of cardiac MRI. However, most of these works claimed the achievement of acceleration factors solely based on simulated data or on fully sampled acquisition data retrospectively undersampled. In this work the practical feasibility of compressed sensing acquisitions for the acceleration of cardiac cine imaging in small animals is proved with real acquisitions. Our experiments using a combined spatiotemporal technique confirm that high acceleration factors of about 10 are feasible. Future work involving the optimization of undersampling patterns and cardiac artifact correction might further improve this acceleration factor.

The acceleration of dynamic MRI studies such as fMRI would be a killing application of the recently developed compressed sensing techniques. We present the application of a spatiotemporal total variation reconstruction algorithm to undersampled rat fMRI series. In addition to the t maps extraction, a quantitative analysis of the percentage signal change has been performed to assess the maximum acceleration feasible. Undersampling up to 50%(x2 acceleration) can be applied without significant percentage signal change loss, and the activation maps preserve their shape within that range. To our knowledge, this is the first work performing quantitative analysis in compressed sensing reconstructions of rat fMRI data.

Motion-Based Reconstruction (MBR) and Prior-Based Reconstruction (PBR) are compressed sensing approaches for cardiac cine MRI that achieve high acceleration factors by exploiting temporal sparsity based on a prior image. It would be appealing to reconstruct only the image variation with respect to the prior image, as this is sparser than the image itself, but this leads to low signal-to-noise ratio and has been generally avoided.

Proceedings of: 2011 IEEE Nuclear Science Symposium and Medical Imaging Conference (NSS/MIC). Valencia, Spain, 23-29 October 2011 Dynamic cardiac magnetic resonance imaging in small animals is an important tool in the study of cardiovascular diseases. The reduction of the long acquisition times required for cardiovascular applications is crucial to achieve good spatiotemporal resolution and signal-to-noise ratio. Nowadays there are many acceleration techniques which can reduce acquisition time, including compressed sensing technique. Compressed sensing allows image reconstruction from undersampled data, by means of a non linear reconstruction which minimizes the total variation of the image. The recently appeared Split Bregman methodology has proved to be more computationally efficient to solve this problem than classic optimization methods. In the case of dynamic magnetic resonance imaging, compressed sensing can exploit time sparsity by the minimization of total variation across both space and time. In this work, we propose and validate the Split Bregman method to minimize spatial and time total variation, and apply this method to accelerate cardiac cine acquisitions in rats. We found that applying a quasi-random variable density pattern along the phase-encoding direction, accelerations up to a factor 5 are possible with low error. In the future, we expect to obtain higher accelerations using spatiotemporal undersampling. This work is supported in part by Ministerio de Ciencia e Innovacion (Red RECA VA), Comunidad de Madrid and Fondos FEDER (ARTEMIS project S2009DPI 1802). Publicado

In this work we evaluate a combination of a high-performance PET with a superconductive 3T MRI system. This PET/MRI system is implemented in a tandem configuration similar to some scanners used in clinical imaging but with both subsystems placed in proximity, what allows sharing a common animal holder that travels between both FOVs. The PET detector consists in two rings, each one having 18 DOI detectors, which provide a high sensitivity with a 1.0mm3 resolution at the centre and minimal degradation toward the edges of the 68mm diameter FOV. The MRI system is a compact, cryogen-free, auto-shielded and with a very tight fringe-field and no special room requirements. These characteristics enable the close location of the PET detector without deteriorating its performance. We have evaluated the system obtaining images of three mice in cardiology, oncology and neurology applications. All PET scans were performed 30m after intraperitoneal FDG injection of 25.2±5.8MBq and were reconstructed using a 3D-OSEM algorithm. For the cardiac MRI a gated FLASH sequence and a body coil were used. Tumor MRI was using an FSE T1w sequence and a body coil. Finally, brain MRI was done with an FSE T2w sequence. In all the cases registration of PET and MRI images was obtained following an equivalent protocol to the standard PET/CT preclinical system, and since the animals didn’t move from the bed the results were satisfactory. Attenuation correction was not applied to any image. The preliminary results from this prototype suggest that the tandem solution for preclinical PET/MRI is feasible and has the advantage of preserving the best image quality in both modalities without requiring any trade-off of specifications. The limitation of not being able to perform simultaneous acquisitions is compensated by the high quality results of studies that do not actually require such simultaneous data collection.