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PURPOSE: To accelerate whole-brain quantitative T 2 $$ {\mathrm{T}}_2 $$ mapping in preclinical imaging setting. METHODS: A three-dimensional (3D) multi-echo spin echo sequence was highly undersampled with a variable density Poisson distribution to reduce the acquisition time. Advanced iterative reconstruction based on linear subspace constraints was employed to recover high-quality raw images. Different subspaces, generated using exponential or extended-phase graph (EPG) simulations or from low-resolution calibration images, were compared. The subspace dimension was investigated in terms of T 2 $$ {\mathrm{T}}_2 $$ precision. The method was validated on a phantom containing a wide range of T 2 $$ {\mathrm{T}}_2 $$ and was then applied to monitor metastasis growth in the mouse brain at 4.7T. Image quality and T 2 $$ {\mathrm{T}}_2 $$ estimation were assessed for 3 acceleration factors (6/8/10). RESULTS: The EPG-based dictionary gave robust estimations of a large range of T 2 $$ {\mathrm{T}}_2 $$ . A subspace dimension of 6 was the best compromise between T 2 $$ {\mathrm{T}}_2 $$ precision and image quality. Combining the subspace constrained reconstruction with a highly undersampled dataset enabled the acquisition of whole-brain T 2 $$ {\mathrm{T}}_2 $$ maps, the detection and the monitoring of metastasis growth of less than 500 µ m 3 $$ \mu {\mathrm{m}}^3 $$ . CONCLUSION: Subspace-based reconstruction is suitable for 3D T 2 $$ {\mathrm{T}}_2 $$ mapping. This method can be used to reach an acceleration factor up to 8, corresponding to an acquisition time of 25 min for an isotropic 3D acquisition of 156 µ $$ \mu $$ m on the mouse brain, used here for monitoring metastases growth.
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Algoritmos , Encéfalo , Imagenología Tridimensional , Fantasmas de Imagen , Animales , Ratones , Encéfalo/diagnóstico por imagen , Imagenología Tridimensional/métodos , Neoplasias Encefálicas/diagnóstico por imagen , Imagen por Resonancia Magnética/métodos , Reproducibilidad de los Resultados , Procesamiento de Imagen Asistido por Computador/métodosRESUMEN
OBJECTIVES: To assess feasibility of a three-dimensional ultrashort echo time (3D-UTE)-sequence to evaluate normal and pathological disco-vertebral complex (DVC), with assessment of its different portions in a rat model of degenerative disk disease (DDD) with histological correlation. To assess whether this sequence, in comparison with long echo time T2-weighted sequence, is able to monitor DDD with differentiation of early from chronic DVC changes in pathological mechanical conditions. METHODS: Five rats were induced with DDD model by percutaneous disk trituration of the tail with an 18-G needle under US-guidance and imaged at 4.7 T. MRI protocol included fat-saturated-T2 (RARE) and 3D-UTE-sequences performed at baseline (day 0. n = 5 animals /10 DVC) and each week (W) from W1 to W10 postoperatively. Visual analysis and signal intensity measurements of SNR and CNR of all DVC portions were performed on RARE and UTE images. Following killing (baseline, n = 1/2 DVC; W2, n = 2/4 DVC; W10, n = 2/4 DVC), histological analysis was performed and compared with MRI. RESULTS: In normal DVC, unlike conventional RARE-sequences, 3D-UTE allowed complete identification of DVC zonal anatomy including on visual analysis and CNR measurements. In pathological conditions, SNR and CNR measurements of the annulus fibrosus and nucleus pulposus on 3D-UTE distinguished early discitis at W1 from chronic discopathy (P < 0.001 for SNR and P < 0.001 for CNR). Neither the normal complete anatomy of the DVC nor its pathological patterns could be assessed on conventional sequences. CONCLUSIONS: Unlike conventional sequences, 3D-UTE enables visualization of the complete normal DVC anatomy and enables monitoring of DDD differentiating between early DVC changes from chronic ones. LEVEL OF EVIDENCE I: Diagnostic: individual cross-sectional studies with the consistently applied reference standard and blinding.
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Imagenología Tridimensional , Imagen por Resonancia Magnética , Animales , Estudios Transversales , Estudios de Factibilidad , RatasRESUMEN
PURPOSE: To develop a 2D radial multislice MP2RAGE sequence for fast and reliable T1 mapping at 7 T in mice and for MR thermometry. METHODS: The 2D-MP2RAGE sequence was performed with the following parameters: TI1 -TI2 -MP2RAGETR = 1000-3000-9000 ms. The multiple dead times within the sequence were used for interleaved multislice acquisition, enabling one to acquire six slices in 9 seconds. The excitation pulse shape, inversion selectivity, and interslice gap were optimized. In vitro comparison with the inversion-recovery sequence was performed. The T1 variations with temperature were measured on tubes with T1 ranging from 800 ms to 2000 ms. The sequence was used to acquire T1 maps continuously during 30 minutes on the brain and abdomen of healthy mice. RESULTS: A three-lobe cardinal sine excitation pulse, combined with an inversion slice thickness and an interslice gap of respectively 150% and 50% of the imaging slice thickness, led to a SD and bias of the T1 measurements below 1% and 2%, respectively. A linear dependence of T1 with temperature was measured between 10°C and 60°C. In vivo, less than 1% variation was measured between successive T1 maps in the mouse brain. In the abdomen, no obvious in-plane motion artifacts were observed but respiratory motion in the slice dimension led to 6% T1 underestimation. CONCLUSION: The multislice MP2RAGE sequence could be used for fast whole-body T1 mapping and MR thermometry. Its reconstruction method would enable on-the-fly reconstruction.
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Imagen por Resonancia Magnética , Termometría , Animales , Artefactos , Interpretación de Imagen Asistida por Computador , Ratones , Fantasmas de ImagenRESUMEN
PURPOSE: To develop a Compressed Sensing (CS)-MP2RAGE sequence to drastically shorten acquisition duration and then detect and measure the T1 of brain metastases in mice at 7 T. METHODS: The encoding trajectory of the standard Cartesian MP2RAGE sequence has been modified (1) to obtain a variable density Poisson disk under-sampling distribution along the ky -kz plane, and (2) to sample the central part of the k-space exactly at TI1 and TI2 inversion times. In a prospective study, the accuracy of the T1 measurements was evaluated on phantoms containing increasing concentrations of gadolinium. The CS acceleration factors were increased to evaluate their influence on the contrast and T1 measurements of brain metastases in vivo. Finally, the 3D T1 maps were acquired with at 4-fold increased spatial resolution. The volumes and T1 values of the metastases were measured while using CS to reduce scan time. RESULTS: The implementation of the CS-encoding trajectory did not affect the T1 measurements in vitro. Accelerating the acquisition by a factor of 2 did not alter the contrast or the T1 values of the brain metastases. 3D T1 maps could be obtained in < 1 min using a CS factor of 6. Increasing the spatial resolution enabled more accurately measurement of the metastasis volumes while maintaining an acquisition duration below 5 min. CONCLUSION: The CS-MP2RAGE sequence could be of great interest in oncology to either rapidly obtain mouse brain 3D T1 maps or to increase the spatial resolution with no penalty on the scan duration.
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Neoplasias Encefálicas/diagnóstico por imagen , Neoplasias de la Mama/diagnóstico por imagen , Compresión de Datos/métodos , Imagen por Resonancia Magnética , Algoritmos , Animales , Encéfalo/diagnóstico por imagen , Neoplasias Encefálicas/patología , Neoplasias Encefálicas/secundario , Neoplasias de la Mama/patología , Línea Celular Tumoral , Femenino , Gadolinio/química , Humanos , Aumento de la Imagen , Interpretación de Imagen Asistida por Computador , Procesamiento de Imagen Asistido por Computador , Imagenología Tridimensional , Espectroscopía de Resonancia Magnética , Ratones , Ratones Desnudos , Metástasis de la Neoplasia , Trasplante de Neoplasias , Fantasmas de Imagen , Distribución de Poisson , Estudios Prospectivos , Reproducibilidad de los ResultadosRESUMEN
OBJECTIVES: The T1 longitudinal recovery time is regarded as a biomarker of cancer treatment efficiency. In this scope, the Magnetization Prepared 2 RApid Gradient Echo (MP2RAGE) sequence relevantly complies with fast 3D T1 mapping. Nevertheless, with its Cartesian encoding scheme, it is very sensitive to respiratory motion. Consequently, a radial encoding scheme was implemented for the detection and T1 measurement of hepatic metastases in mice at 7T. METHODS: A 3D radial encoding scheme was developed using a golden angle distribution for the k-space trajectories. As in that case, each projection contributes to the image contrast, the signal equations had to be modified. Phantoms containing increasing gadoteridol concentrations were used to determine the accuracy of the sequence in vitro. Healthy mice were repetitively scanned to assess the reproducibility of the T1 values. The growth of hepatic metastases was monitored. Undersampling robustness was also evaluated. RESULTS: The accuracy of the T1 values obtained with the radial MP2RAGE sequence was > 90% compared to the Inversion-Recovery sequence. The motion robustness of this new sequence also enabled repeatable T1 measurements on abdominal organs. Hepatic metastases of less than 1-mm diameter were easily detected and T1 heterogeneities within the metastasis and between the metastases within the same animal were measured. With a twofold acceleration factor using undersampling, high-quality 3D T1 abdominal maps were achieved in 9 min. CONCLUSIONS: The radial MP2RAGE sequence could be used for fast 3D T1 mapping, to detect and characterize metastases in regions subjected to respiratory motion. KEY POINTS: ⢠The Cartesian encoding of the MP2RAGE sequence was modified to a radial encoding. The modified sequence enabled accurate T 1 measurements on phantoms and on abdominal organs of mice. ⢠Hepatic metastases were easily detected due to high contrast. Heterogeneity in T 1 was measured within the metastases and between each metastasis within the same animal. ⢠As implementation of this sequence does not require specific hardware, we expect that it could be readily available for clinical practice in humans.
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Cavidad Abdominal/diagnóstico por imagen , Imagenología Tridimensional/métodos , Neoplasias Hepáticas/diagnóstico , Imagen por Resonancia Magnética/métodos , Neoplasias Experimentales , Fantasmas de Imagen , Animales , Femenino , Humanos , Neoplasias Hepáticas/secundario , Masculino , Ratones , Ratones Endogámicos C57BL , Reproducibilidad de los ResultadosRESUMEN
PURPOSE: To develop a fast three-dimensional (3D) k-space encoding method based on spiral projection imaging (SPI) with an interleaved golden-angle approach and to validate this novel sequence on small animal models. METHODS: A disk-like trajectory, in which each disk contained spirals, was developed. The 3D encoding was performed by tilting the disks with a golden angle. The sharpness was first calculated at different T2* values. Then, the sharpness was measured on phantom using variable undersampling ratios. Finally, the sampling method was validated by whole brain time-of-flight angiography and ultrasmall superparamagnetic iron oxide (USPIO) enhanced free-breathing liver angiography on mouse. RESULTS: The in vitro results demonstrated the robustness of the method for short T2* and high undersampling ratios. In vivo experiments showed the ability to properly detect small vessels in the brain with an acquisition time shorter than 1 min. Free-breathing mice liver angiography showed the insensitivity of this protocol toward motions and flow artifacts, and enabled the visualization of liver motion during breathing. CONCLUSIONS: The method implemented here allowed fast 3D k-space sampling with a high undersampling ratio. Combining the advantages of center-out spirals with the flexibility of the golden angle approach could have major implications for real-time imaging. Magn Reson Med 77:1831-1840, 2017. © 2016 International Society for Magnetic Resonance in Medicine.
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Encéfalo/diagnóstico por imagen , Imagenología Tridimensional/métodos , Hígado/diagnóstico por imagen , Imagen por Resonancia Magnética/métodos , Angiografía , Animales , Artefactos , Compuestos Férricos/química , Aumento de la Imagen/métodos , Interpretación de Imagen Asistida por Computador/métodos , Hígado/patología , Magnetismo , Ratones , Ratones Endogámicos C57BL , Movimiento (Física) , Fantasmas de ImagenRESUMEN
PURPOSE: To develop and assess a 3D-cine self-gated method for cardiac imaging of murine models. MATERIALS AND METHODS: A 3D stack-of-stars (SOS) short echo time (STE) sequence with a navigator echo was performed at 7T on healthy mice (n = 4) and mice with acute myocardial infarction (MI) (n = 4) injected with ultrasmall superparamagnetic iron oxide (USPIO) nanoparticles. In all, 402 spokes were acquired per stack with the incremental or the golden angle method using an angle increment of (360/402)° or 222.48°, respectively. A cylindrical k-space was filled and repeated with a maximum number of repetitions (NR) of 10. 3D cine cardiac images at 156 µm resolution were reconstructed retrospectively and compared for the two methods in terms of contrast-to-noise ratio (CNR). The golden angle images were also reconstructed with NR = 10, 6, and 3, to assess cardiac functional parameters (ejection fraction, EF) on both animal models. RESULTS: The combination of 3D SOS-STE and USPIO injection allowed us to optimize the identification of cardiac peaks on navigator signal and generate high CNR between blood and myocardium (15.3 ± 1.0). The golden angle method resulted in a more homogeneous distribution of the spokes inside a stack (P < 0.05), enabling reducing the acquisition time to 15 minutes. EF was significantly different between healthy and MI mice (P < 0.05). CONCLUSION: The method proposed here showed that 3D-cine images could be obtained without electrocardiogram or respiratory gating in mice. It allows precise measurement of cardiac functional parameters even on MI mice. J. Magn. Reson. Imaging 2016;44:355-365.
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Técnicas de Imagen Sincronizada Cardíacas/métodos , Dextranos , Interpretación de Imagen Asistida por Computador/métodos , Imagenología Tridimensional/métodos , Imagen por Resonancia Cinemagnética/métodos , Nanopartículas de Magnetita , Infarto del Miocardio/diagnóstico por imagen , Procesamiento de Señales Asistido por Computador , Animales , Medios de Contraste , Aumento de la Imagen/métodos , Ratones , Reproducibilidad de los Resultados , Sensibilidad y EspecificidadRESUMEN
PURPOSE: To develop an undersampled anatomical, three-dimensional (3-D) time-resolved magnetic resonance angiography (MRA) method for small animals based on time-of-flight (TOF) effect and radial sampling. METHODS: Mouse carotid arteries and Circle of Willis images were acquired on a 7T scanner with an electrocardiogram (ECG)-triggered sequence. Preliminary experiments were used to generate an approximately uniform distribution of radial projections with a first golden angle and to produce anatomical TOF images. A second golden angle ratio between consecutive projections of cine acquisitions was added to make it possible to use a temporal filter during reconstruction of time-resolved angiography. A decreasing number of projections were tested, and their impact on signal-to-noise ratio (SNR) and spatial resolution was assessed. RESULTS: In anatomical MRA, the undersampled radial approach efficiently allows fast acquisition of mouse angiogram in 3D (22 sec). It was also only slightly sensitive to motion and flow artifacts. The time-resolved sequence can be performed with only 2,500 projections per cine and a temporal resolution under 4 ms in a relatively short acquisition time (less than 5 min). CONCLUSION: This technique simultaneously provided high 3D isotropic spatial resolution and excellent temporal resolution with a good SNR level, allowing blood flow to be visualized in a restricted acquisition time.
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Arterias Carótidas/anatomía & histología , Círculo Arterial Cerebral/anatomía & histología , Aumento de la Imagen/métodos , Interpretación de Imagen Asistida por Computador/métodos , Imagenología Tridimensional/métodos , Angiografía por Resonancia Magnética/métodos , Algoritmos , Animales , Técnicas de Imagen Sincronizada Cardíacas/métodos , Interpretación Estadística de Datos , Ratones , Ratones Endogámicos C57BL , Modelos Biológicos , Modelos Estadísticos , Reproducibilidad de los Resultados , Tamaño de la Muestra , Sensibilidad y Especificidad , Procesamiento de Señales Asistido por Computador , Relación Señal-RuidoRESUMEN
Mapping longitudinal relaxation times in 3D is a promising quantitative and non-invasive imaging tool to assess cardiac remodeling. Few methods are proposed in the literature allowing us to perform 3D T1 mapping. These methods often require long scan times and use a low number of 3D images to calculate T1 . In this project, a fast 3D T1 mapping method using a stack-of-spirals sampling scheme and regular RF pulse excitation at 7 T is presented. This sequence, combined with a newly developed fitting procedure, allowed us to quantify T1 of the whole mouse heart with a high spatial resolution of 208 × 208 × 315 µm(3) in 10-12 min acquisition time. The sensitivity of this method for measuring T1 variations was demonstrated on mouse hearts after several injections of manganese chloride (doses from 25 to 150 µmol kg(-1) ). T1 values were measured in vivo in both pre- and post-contrast experiments. This protocol was also validated on ischemic mice to demonstrate its efficiency to visualize tissue damage induced by a myocardial infarction. This study showed that combining spiral gradient shape and steady RF excitation enabled fast and robust 3D T1 mapping of the entire heart with a high spatial resolution.
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Algoritmos , Ventrículos Cardíacos/patología , Interpretación de Imagen Asistida por Computador/métodos , Imagenología Tridimensional/métodos , Cloruro de Magnesio , Infarto del Miocardio/patología , Animales , Medios de Contraste , Aumento de la Imagen/métodos , Ratones , Ratones Endogámicos C57BL , Dosis de Radiación , Ondas de Radio , Reproducibilidad de los Resultados , Sensibilidad y EspecificidadRESUMEN
BACKGROUND: To develop and evaluate three-dimensional (3D) self-gated balanced steady state free precession (bSSFP) imaging at high magnetic fields to track iron-labeled cells and metastases in murine abdomens. METHODS: Mice were injected intravenously with iron-labeled melanoma cells and imaged at 7 Tesla (T). Respiration peaks were identified using Free Induction Decay acquired immediately after the radiofrequency pulse. Respiration-corrupted k-space lines were deleted. Four images were acquired to reconstruct final images using the Sum-Of-Square technique. Image sharpness, metastasis contrast and iron-labeled cell detection with SG-bSSFP sequence (acquired with echo time [TE] = 3 ms or TE = 6 ms) were compared with standard methods (gradient echo (GRE) and RARE). RESULTS: After reconstruction, the 3D SG-bSSFP images were 75-80% sharper, free from banding (75% liver signal-to-noise ratio recovery) and respiratory motion (26-42% improvement in signal homogeneity) artifacts. Metastasis contrast was twice higher on SG-bSSFP with TE = 3 ms than on RARE images. Iron-labeled cells and metastases were simultaneously detected on SG-bSSFP images with TE = 6 ms, with similar void intensity and tumor contrast to GRE and RARE, respectively. Halving acquisition time preserved iron sensitivity and metastasis contrast, allowing for 3D abdomen imaging in 13 min (TE = 3 ms) or 26 min (TE = 6 ms). CONCLUSION: Combining a self-gating technique with bSSFP sequences at 7T provides high-resolution 3D artifact-free abdominal images of small animals.
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Compuestos Férricos , Imagenología Tridimensional/métodos , Neoplasias Hepáticas/patología , Neoplasias Hepáticas/secundario , Melanoma/patología , Melanoma/secundario , Animales , Línea Celular Tumoral , Rastreo Celular/métodos , Medios de Contraste , Femenino , Aumento de la Imagen/métodos , Interpretación de Imagen Asistida por Computador/métodos , Ratones , Ratones Endogámicos C57BL , Reproducibilidad de los Resultados , Sensibilidad y Especificidad , Coloración y Etiquetado/métodosRESUMEN
BACKGROUND: To show that 3D sequences with ultra-short echo times (UTEs) can generate a positive contrast whatever the magnetic field (4.7, 7 or 9.4 T) and whatever Ultra Small Particles of Iron Oxide (USPIO) concentration injected and to use it for 3D time-resolved imaging of the murine cardiovascular system with high spatial and temporal resolutions. METHODS: Three different concentrations (50, 200 and 500 µmol Fe/kg) of USPIO were injected in mice and static images of the middle part of the animals were acquired at 4.7, 7 and 9.4 T pre and post-contrast with UTE (TE/TR = 0.05/4.5 ms) sequences. Signal-to-Noise Ratio (SNR) and Contrast-to-Noise Ratio (CNR) of blood and static tissus were evaluated before and after contrast agent injection. 3D-cine images (TE/TR = 0.05/3.5 ms, scan time < 12 min) at 156 µm isotropic resolution of the mouse cardiopulmonary system were acquired prospectively with the UTE sequence for the three magnetic fields and with an USPIO dose of 200 µmol Fe/kg. SNR, CNR and signal homogeneity of blood were measured. High spatial (104 µm) or temporal (3.5 ms) resolution 3D-cine imaging (scan time < 35 min) isotropic resolution were also performed at 7 T with a new sequence encoding scheme. RESULTS: UTE imaging generated positive contrast and higher SNR and CNR whatever the magnetic field and the USPIO concentration used compared to pre-contrast images. Time-resolved 3D acquisition enables high blood SNR (66.6 ± 4.5 at 7 T) and CNR (33.2 ± 4.2 at 7 T) without flow or motion artefact. Coronary arteries and aortic valve were visible on images acquired at 104 µm resolution. CONCLUSIONS: We have demonstrated that by combining the injection of iron nanoparticles with 3D-cine UTE sequences, it was possible to generate a strong positive contrast between blood and surrounding tissues. These properties were exploited to produce images of the cardiovascular system in small animals at high magnetic fields with a high spatial and temporal resolution. This approach might be useful to measure the functional cardiac parameters or to assess anatomical modifications to the blood vessels in cardio-vascular disease models.
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Sistema Cardiovascular/anatomía & histología , Medios de Contraste , Dextranos , Interpretación de Imagen Asistida por Computador/métodos , Imagenología Tridimensional/métodos , Imagen por Resonancia Cinemagnética/métodos , Nanopartículas de Magnetita , Animales , Artefactos , Ratones Endogámicos C57BL , Valor Predictivo de las Pruebas , Reproducibilidad de los Resultados , Relación Señal-RuidoRESUMEN
Lungs are the most frequent site of metastases growth. The amount and size of pulmonary metastases acquired from MRI imaging data are the important criteria to assess the efficacy of new drugs in preclinical models. While efficient solutions both for MR imaging and the downstream automatic segmentation have been proposed for human patients, both MRI lung imaging and segmentation in preclinical animal models remains challenging due to the physiological motion (respiratory and cardiac movements), to the low amount of protons in this organ and to the particular challenge of precise segmentation of metastases. As a consequence post-mortem analysis is currently required to obtain information on metastatic volume. In this work, we have developed a complete methodological pipeline for automated analysis of lungs and metastases in mice, consisting of an MR sequence for image acquisition and a deep learning method for automatic segmentation of both lungs and metastases. On one hand, we optimized an MR sequence for mouse lung imaging with high contrast for high detection sensitivity. On the other hand we developed DeepMeta, a multiclass U-Net 3+ deep learning model to automatically segment the images. To assess if the proposed deep learning pipeline is able to provide an accurate segmentation of both lungs and pulmonary metastases, we have longitudinally imaged mice with fast- and slow-growing metastasis. Fifty-five balb/c mice were injected with two different derivatives of renal carcinoma cells. Mice were imaged with a SG-bSSFP (self-gated balanced steady state free precession) sequence at different time points after the injection of cancer cells. Both lung and metastases segmentations were manually performed by experts. DeepMeta was trained to perform lung and metastases segmentation based on the resulting ground truth annotations. Volumes of lungs and of pulmonary metastases as well as the number of metastases per mouse were measured on a separate test dataset of MR images. Thanks to the SG method, the 3D bSSFP images of lungs were artifact-free, enabling the downstream detection and serial follow-up of metastases. Moreover, both lungs and metastases segmentation was accurately performed by DeepMeta as soon as they reached the volume of â¼ 0.02 m m 3 . Thus we were able to distinguish two groups of mice in terms of number and volume of pulmonary metastases as well as in terms of the slow versus fast patterns of growth of metastases. We have shown that our methodology combining SG-bSSFP with deep learning, enables processing of the whole animal lungs and is thus a viable alternative to histology alone.
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OBJECTIVES: The magnetization-prepared 2 rapid acquisition gradient echo (MP2RAGE) sequence provides quantitative T1 maps in addition to high-contrast morphological images. Advanced acceleration techniques such as compressed sensing (CS) allow its acquisition time to be compatible with clinical applications. To consider its routine use in future neuroimaging protocols, the repeatability of the segmented brain structures was evaluated and compared with the standard morphological sequence (magnetization-prepared rapid gradient echo [MPRAGE]). The repeatability of the T1 measurements was also assessed. MATERIALS AND METHODS: Thirteen healthy volunteers were scanned either 3 or 4 times at several days of interval, on a 3 T clinical scanner, with the 2 sequences (CS-MP2RAGE and MPRAGE), set with the same spatial resolution (0.8-mm isotropic) and scan duration (6 minutes 21 seconds). The reconstruction time of the CS-MP2RAGE outputs (including the 2 echo images, the MP2RAGE image, and the T1 map) was 3 minutes 33 seconds, using an open-source in-house algorithm implemented in the Gadgetron framework.Both precision and variability of volume measurements obtained from CAT12 and VolBrain were assessed. The T1 accuracy and repeatability were measured on phantoms and on humans and were compared with literature.Volumes obtained from the CS-MP2RAGE and the MPRAGE images were compared using Student t tests (P < 0.05 was considered significant). RESULTS: The CS-MP2RAGE acquisition provided morphological images of the same quality and higher contrasts than the standard MPRAGE images. Similar intravolunteer variabilities were obtained with the CS-MP2RAGE and the MPRAGE segmentations. In addition, high-resolution T1 maps were obtained from the CS-MP2RAGE. T1 times of white and gray matters and several deep gray nuclei are consistent with the literature and show very low variability (<1%). CONCLUSIONS: The CS-MP2RAGE can be used in future protocols to rapidly obtain morphological images and quantitative T1 maps in 3-dimensions while maintaining high repeatability in volumetry and relaxation times.
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Sustancia Gris , Imagen por Resonancia Magnética , Algoritmos , Encéfalo/anatomía & histología , Encéfalo/diagnóstico por imagen , Humanos , Imagen por Resonancia Magnética/métodos , NeuroimagenRESUMEN
Purpose: To confirm the interest of 3-dimensional ultrashort echo-time (3D-UTE) sequences to assess morphologic aspects in normal and pathological Achilles entheses in a rat model of spondyloarthropathy (SpA) with histological correlations, in comparison with conventional RARE T2 Fat-Sat sequences, and, furthermore, to evaluate the feasibility of a 3D multiecho UTE sequence performed before and after the intravenous injection of ultrasmall superparamagnetic iron oxide (USPIO) particles to assess macrophagic involvement in the Achilles enthesis in the same rat model of SpA. Materials and Methods: Fourteen rats underwent in vivo MRI of the ankle at 4.7 T, including a 3D RARE T2 Fat-Sat sequence and a 3D ultrashort echo-time (UTE) sequence for morphologic assessment at baseline and day 3 after induction of an SpA model, leading to Achilles enthesopathy in the left paw (right paw serving as a control). A 3D multiecho UTE sequence was also performed at day 3 before and then 24 (4 rats) and 48 (2 rats) hours after intravenous injection of USPIO. Visual analysis and signal intensity measurements of all images were performed at different locations of the Achilles enthesis and preinsertional area. Visual analysis and T2∗ measurements were performed before and after USPIO injection, on the 3D multiecho UTE sequence in the same locations. Normal and pathological values were compared by Wilcoxon signed-rank tests. MR findings were compared against histological data. Results: 3D-UTE sequences enabled morphologic identification of the anterior fibrocartilage and posterior collagenic areas of the Achilles enthesis. Visual analysis and signal intensity measurements distinguished SpA-affected entheses from healthy ones at day 3 (P=0.02). After administration of USPIO, no differences in signals were detected. Similarly, both visual analysis and signal T2∗ measurements in the enthesis were unable to distinguish the SpA-affected tendons from healthy ones (P=0.914). Neither the normal anatomy of the enthesis nor its pathological pattern could be distinguished using the standard RARE sequence. Histology confirmed the absence of USPIO in Achilles entheses, despite marked signs of inflammation. Conclusion: Unlike conventional RARE T2 Fat-Sat sequences, 3D-UTE sequences enable morphologic assessment of normal enthesis anatomy and early detection of abnormalities in pathological conditions. However, 3D multiecho UTE sequences combined with USPIO injections with T2∗ measurements were unable to detect macrophagic involvement in these pathological conditions.
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Tendón Calcáneo/patología , Imagenología Tridimensional/métodos , Imagen por Resonancia Magnética/métodos , Espondiloartropatías/diagnóstico por imagen , Animales , Tobillo/diagnóstico por imagen , Colágeno/análisis , Modelos Animales de Enfermedad , Compuestos Férricos/análisis , Fibrocartílago/diagnóstico por imagen , Inflamación , Macrófagos/patología , Tamaño de la Partícula , Ratas , Espondiloartropatías/patología , Factores de TiempoRESUMEN
Magnetic Resonance Imaging (MRI) appears as a good surrogate to Computed Tomography (CT) scan as it does not involve radiation. In this context, a 3D anatomical and perfusion MR imaging protocol was developed to follow the evolution of bone regeneration and the neo-vascularization in femoral bone defects in rats. For this, three different biomaterials based on Pullulan-Dextran and containing either Fucoidan or HydroxyApatite or both were implanted. In vivo MRI, ex vivo micro-CT and histology were performed 1, 3 and 5 weeks after implantation. The high spatially resolved (156 × 182 × 195 µm) anatomical images showed a high contrast from the defects filled with biomaterials that decreased over time due to bone formation. The 3D Dynamic Contrast Enhanced (DCE) imaging with high temporal resolution (1 image/19 s) enabled to detect a modification in the Area-Under-The-Gadolinium-Curve over the weeks post implantation. The high sensitivity of MRI enabled to distinguish which biomaterial was the least efficient for bone regeneration, which was confirmed by micro-CT images and by a lower vessel density observed by histology. In conclusion, the methodology developed here highlights the efficiency of longitudinal MRI for tissue engineering as a routine small animal exam.
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Materiales Biocompatibles , Regeneración Ósea , Fémur , Imagenología Tridimensional , Angiografía por Resonancia Magnética , Animales , Biomarcadores , Modelos Animales de Enfermedad , Femenino , Fémur/diagnóstico por imagen , Fémur/lesiones , Fémur/patología , Inmunohistoquímica , Angiografía por Resonancia Magnética/métodos , Ratas , Ingeniería de Tejidos , Microtomografía por Rayos XRESUMEN
The goal of this study was to develop a 3D diffusion weighted sequence for free breathing liver imaging in small animals at high magnetic field. Hepatic metastases were detected and the apparent diffusion coefficients (ADC) were measured. A 3D SE-EPI sequence was developed by (i) inserting a water-selective excitation radiofrequency pulse to suppress adipose tissue signal and (ii) bipolar diffusion gradients to decrease the sensitivity to respiration motion. Mice with hepatic metastases were imaged at 7T by applying b values from 200 to 1100 s/mm(2). 3D images with high spatial resolution (182 × 156 × 125 µm) were obtained in only 8 min 32 s. The modified DW-SE-EPI sequence allowed to obtain 3D abdominal images of healthy mice with fat SNR 2.5 times lower than without any fat suppression method and sharpness 2.8 times higher than on respiration-triggered images. Due to the high spatial resolution, the core and the periphery of disseminated hepatic metastases were differentiated at high b-values only, demonstrating the presence of edema and proliferating cells (with ADC of 2.65 × 10(-3) and 1.55 × 10(-3) mm(2)/s, respectively). Furthermore, these metastases were accurately distinguished from proliferating ones within the same animal at high b-values (mean ADC of 0.38 × 10(-3) mm(2)/s). Metastases of less than 1.7 mm(3) diameter were detected. The new 3D SE-EPI sequence enabled to obtain diffusion information within liver metastases. In addition of intra-metastasis heterogeneity, differences in diffusion were measured between metastases within an animal. This sequence could be used to obtain diffusion information at high magnetic field.
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Imagen de Difusión por Resonancia Magnética/métodos , Procesamiento de Imagen Asistido por Computador/métodos , Imagenología Tridimensional/métodos , Neoplasias Hepáticas/diagnóstico , Neoplasias Hepáticas/secundario , Animales , Ratones , Ratones Endogámicos C57BL , RespiraciónRESUMEN
INTRODUCTION: The purpose of this paper is to develop an easy method to generate both fat signal and banding artifact free 3D balanced Steady State Free Precession (bSSFP) images at high magnetic field. METHODS: In order to suppress fat signal and bSSFP banding artifacts, two or four images were acquired with the excitation frequency of the water-selective binomial radiofrequency pulse set On Resonance or shifted by a maximum of 3/4TR. Mice and human volunteers were imaged at 7 T and 3 T, respectively to perform whole-body and musculoskeletal imaging. "Sum-Of-Square" reconstruction was performed and combined or not with parallel imaging. RESULTS: The frequency selectivity of 1-2-3-2-1 or 1-3-3-1 binomial pulses was preserved after (3/4TR) frequency shifting. Consequently, whole body small animal 3D imaging was performed at 7 T and enabled visualization of small structures within adipose tissue like lymph nodes. In parallel, this method allowed 3D musculoskeletal imaging in humans with high spatial resolution at 3 T. The combination with parallel imaging allowed the acquisition of knee images with ~500 µm resolution images in less than 2 min. In addition, ankles, full head coverage and legs of volunteers were imaged, demonstrating the possible application of the method also for large FOV. CONCLUSION: In conclusion, this robust method can be applied in small animals and humans at high magnetic fields. The high SNR and tissue contrast obtained in short acquisition times allows to prescribe bSSFP sequence for several preclinical and clinical applications.