The future of CMR: All-in-one vs. real-time CMR (Part 2).

Cardiac Magnetic Resonance (CMR) protocols can be lengthy and complex, which has driven the research community to develop new technologies to make these protocols more efficient and patient-friendly. Two different approaches to improving CMR have been proposed, specifically "all-in-one" CMR, where several contrasts and/or motion states are acquired simultaneously, and "real-time" CMR, in which the examination is accelerated to avoid the need for breathholding and/or cardiac gating. The goal of this two-part manuscript is to describe these two different types of emerging rapid CMR protocols. To this end, the vision of all-in-one and real-time imaging are described, along with techniques which have been devised and tested along the pathway of clinical implementation. The pros and cons of the different methods are presented, and the remaining open needs of each are detailed. Part 1 tackles the "All-in-One" approaches, and Part 2 focuses on the "Real-Time" approaches along with an overall summary of these emerging methods.

Parahydrogen-Polarized Fumarate for Preclinical in Vivo Metabolic Magnetic Resonance Imaging.

We present a versatile method for the preparation of hyperpolarized [1-13C]fumarate as a contrast agent for preclinical in vivo MRI, using parahydrogen-induced polarization (PHIP). To benchmark this process, we compared a prototype PHIP polarizer to a state-of-the-art dissolution dynamic nuclear polarization (d-DNP) system. We found comparable polarization, volume, and concentration levels of the prepared solutions, while the preparation effort is significantly lower for the PHIP process, which can provide a preclinical dose every 10 min, opposed to around 90 min for d-DNP systems. With our approach, a 100 mM [1-13C]-fumarate solution of volumes up to 3 mL with 13-20% 13C-hyperpolarization after purification can be produced. The purified solution has a physiological pH, while the catalyst, the reaction side products, and the precursor material concentrations are reduced to nontoxic levels, as confirmed in a panel of cytotoxicity studies. The in vivo usage of the hyperpolarized fumarate as a perfusion agent in healthy mice and the metabolic conversion of fumarate to malate in tumor-bearing mice developing regions with necrotic cell death is demonstrated. Furthermore, we present a one-step synthesis to produce the 13C-labeled precursor for the hydrogenation reaction with high yield, starting from 13CO2 as a cost-effective source for 13C-labeled compounds.

Tiny golden angle ultrashort echo-time lung imaging in mice.

Imaging the lung parenchyma with MRI is particularly difficult in small animals due to the high respiratory and heart rates, and ultrashort T2* at high magnetic field strength caused by the high susceptibilities induced by the air-tissue interfaces. In this study, a 2D ultrashort echo-time (UTE) technique was combined with tiny golden angle (tyGA) ordering. Data were acquired continuously at 11.7 T and retrospective center-of-k-space gating was applied to reconstruct respiratory multistage images. Lung (proton) density (fP ), T2*, signal-to-noise ratio (SNR), fractional ventilation (FV) and perfusion (f) were quantified, and the application to dynamic contrast agent (CA)-enhanced (DCE) qualitative perfusion assessment tested. The interobserver and intraobserver and interstudy reproducibility of the quantitative parameters were investigated. High-quality images of the lung parenchyma could be acquired in all animals. Over all lung regions a mean T2* of 0.20 ± 0.05 ms was observed. FV resulted as 0.31 ± 0.13, and a trend towards lower SNR values during inspiration (EX: SNR = 12.48 ± 6.68, IN: SNR = 11.79 ± 5.86) and a significant (P < 0.001) decrease in lung density (EX: fP  = 0.69 ± 0.13, IN: fP  = 0.62 ± 0.13) were observed. Quantitative perfusion results as 34.63 ± 9.05 mL/cm3 /min (systole) and 32.77 ± 8.55 mL/cm3 /min (diastole) on average. The CA dynamics could be assessed and, because of the continuous nature of the data acquisition, reconstructed at different temporal resolutions. Where a good to excellent interobserver reproducibility and an excellent intraobserver reproducibility resulted, the interstudy reproducibility was only fair to good. In conclusion, the combination of tiny golden angles with UTE (2D tyGA UTE) resulted in a reliable imaging technique for lung morphology and function in mice, providing uniform k-space coverage and thus low-artefact images of the lung parenchyma after gating.

Two-dimensional UTE overview imaging for dental application.

PURPOSE: To investigate the applicability of a 2D-UTE half-pulse sequence for dental overview imaging and the detection of signal from mineralized dental tissue and caries lesions with ultra-short T2∗ as an efficient alternative to 3D sequences. METHODS: A modified 2D-UTE sequence using 240-µs half-pulses for excitation and a reduction of the coil tune delay from the manufacturer preset value allowed for the acquisition of in vivo dental images with a TE of 35 µs at 1.5T. The common occurrence of out-of-slice signal for half-pulse sequences was avoided by applying a quadratic-phase saturation pulse before each half-RF excitation. A conventional 2D-UTE sequence with a TE of 750 µs, using slice selection rephasing, was used for comparison. RESULTS: Quadratic phase saturation pulses adequately improve the slice profile of half-pulse excitations for dental imaging with a surface coil. In vivo images and SNR measurements show a distinct increase in signal in ultrashort T2∗ tissues for the proposed 2D-UTE half-pulse sequence compared with a 2D-UTE sequence using conventional slice selection, leading to an improved detection of caries lesions. CONCLUSION: The proposed pulse sequence enables the acquisition of in vivo images of a comprehensive overview of bone structures and teeth of a single side of the upper and lower jaw and signal detection from mineralized dental tissues in clinically acceptable scan times.

Feasibility of real-time cardiac MRI in mice using tiny golden angle radial sparse.

Cardiovascular magnetic resonance imaging has proven valuable for the assessment of structural and functional cardiac abnormalities. Even although it is an established imaging method in small animals, the long acquisition times of gated or self-gated techniques still limit its widespread application. In this study, the application of tiny golden angle radial sparse MRI (tyGRASP) for real-time cardiac imaging was tested in 12 constitutive nexilin (Nexn) knock-out (KO) mice, both heterozygous (Het, N = 6) and wild-type (WT, N = 6), and the resulting functional parameters were compared with a well-established self-gating approach. Real-time images were reconstructed for different temporal resolutions of between 16.8 and 79.8 ms per image. The suggested approach was additionally tested for dobutamine stress and qualitative first-pass perfusion imaging. Measurements were repeated twice within 2 weeks for reproducibility assessment. In direct comparison with the high-quality, self-gated technique, the real-time approach did not show any significant differences in global function parameters for acquisition times below 50 ms (rest) and 31.5 ms (stress). Compared with WT, the end-diastolic volume (EDV) and end-systolic volume (ESV) were markedly higher (P < 0.05) and the ejection fraction (EF) was significantly lower in the Het Nexn-KO mice at rest (P < 0.001). For the stress investigation, a clear decrease of EDV and ESV, and an increase in EF, but maintained stroke volume, could be observed in both groups. Combined with ECG-triggering, tyGRASP provided first-pass perfusion data with a temporal resolution of one image per heartbeat, allowing the quantitative assessment of upslope curves in the blood-pool and myocardium. Excellent inter-study reproducibility was achieved in all the functional parameters. The tyGRASP is a valuable real-time MRI technique for mice, which significantly reduces the scan time in preclinical cardiac functional imaging, providing sufficient image quality for deriving accurate functional parameters, and has the potential to investigate real-time and beat-to-beat changes.

Magnetic resonance spectroscopy in the rodent brain: Experts' consensus recommendations.

In vivo MRS is a non-invasive measurement technique used not only in humans, but also in animal models using high-field magnets. MRS enables the measurement of metabolite concentrations as well as metabolic rates and their modifications in healthy animals and disease models. Such data open the way to a deeper understanding of the underlying biochemistry, related disturbances and mechanisms taking place during or prior to symptoms and tissue changes. In this work, we focus on the main preclinical 1H, 31P and 13C MRS approaches to study brain metabolism in rodent models, with the aim of providing general experts' consensus recommendations (animal models, anesthesia, data acquisition protocols). An overview of the main practical differences in preclinical compared with clinical MRS studies is presented, as well as the additional biochemical information that can be obtained in animal models in terms of metabolite concentrations and metabolic flux measurements. The properties of high-field preclinical MRS and the technical limitations are also described.

2D Ultrashort Echo-Time Functional Lung Imaging.

BACKGROUND: Imaging of the lung by MRI is challenging due to the intrinsic low proton density and rapid T2 * relaxation. MRI methods providing lung parenchyma and function are in demand. PURPOSE: To investigate the feasibility of two-dimensional ultrashort echo-time (2D UTE) imaging for lung function assessment. STUDY TYPE: Prospective. POPULATION: Eleven healthy volunteers. FIELD STRENGTH/SEQUENCE: 3T, 2D tiny golden angle UTE (2D-tyUTE). ASSESSMENT: The applicability of breath-hold (BH) and self-gated (SG) 2D-tyUTE for quantification of the lung parenchyma signal-to-noise ratio (SNR), proton fraction (fP ), fractional ventilation (FV), and perfusion (f) was investigated. Dependencies on repetition time (BHS/I1/I2 ) and respiratory phase (expiration [EX], inspiration [IN]) were investigated and compared between smokers and nonsmokers. STATISTICAL TESTS: Analysis of variance (ANOVA), Kendell's W. RESULTS: Significant differences of SNR (EX: 10.98 ± 3.19(BHS ), 14.58 ± 3.89(BHI1 ), 17.59 ± 4.92(BHI2 ), 11.00 ± 5.42(SG); IN: 7.17 ± 2.07(BHS ), 9.51 ± 2.37(BHI1 ), 10.49 ± 2.33(BHI2 ), 10.00 ± 4.14(SG)) (P < 0.05 for all cases) were observed between the different approaches. Where fP in expiration (0.41 ± 0.13) was independent of the BH imaging technique, it was slightly higher in SG (0.44 ± 0.06). FV was reproducible among the BH techniques (0.41 ± 0.10), but significantly lower in SG (0.21 ± 0.06) (P < 0.05). A moderate correlation (R2 = 0.47, P < 0.01) was observed between the breathing amplitude and FV. No significant differences between BH and SG were observed for the perfusion analysis (EX: 3.50 ± 1.29 mL/min/mL [BHS ]; IN: 2.36 ± 1.05 mL/min/mL [BHS ]). Significant differences in fP were found between smokers (0.48 ± 0.11 BH) and nonsmokers (0.37 ± 0.12 BH) in expiration. DATA CONCLUSION: This study demonstrates the feasibility of 2D-tyUTE for successful quantification of relevant lung function parameters at 3T within clinically attractive acquisition times. The low spatial resolution into the slice selection direction may limit the final sensitivity and needs further clinical evaluation. LEVEL OF EVIDENCE: 2 TECHNICAL EFFICACY STAGE: 1 J. MAGN. RESON. IMAGING 2020;52:1637-1644.

Cell competition is a tumour suppressor mechanism in the thymus.

Cell competition is an emerging principle underlying selection for cellular fitness during development and disease. Competition may be relevant for cancer, but an experimental link between defects in competition and tumorigenesis is elusive. In the thymus, T lymphocytes develop from precursors that are constantly replaced by bone-marrow-derived progenitors. Here we show that in mice this turnover is regulated by natural cell competition between 'young' bone-marrow-derived and 'old' thymus-resident progenitors that, although genetically identical, execute differential gene expression programs. Disruption of cell competition leads to progenitor self-renewal, upregulation of Hmga1, transformation, and T-cell acute lymphoblastic leukaemia (T-ALL) resembling the human disease in pathology, genomic lesions, leukaemia-associated transcripts, and activating mutations in Notch1. Hence, cell competition is a tumour suppressor mechanism in the thymus. Failure to select fit progenitors through cell competition may explain leukaemia in X-linked severe combined immune deficiency patients who showed thymus-autonomous T-cell development after therapy with gene-corrected autologous progenitors.

IKK2/NF-κB signaling protects neurons after traumatic brain injury.

Traumatic brain injury (TBI) is the leading cause of death in young adults. After the initial injury, a poorly understood secondary phase, including a strong inflammatory response determines the final outcome of TBI. The inhibitor of NF-κB kinase (IKK)/NF-κB signaling system is the key regulator of inflammation and also critically involved in regulation of neuronal survival and synaptic plasticity. We addressed the neuron-specific function of IKK2/NF-κB signaling pathway in TBI using an experimental model of closed-head injury (CHI) in combination with mouse models allowing conditional regulation of IKK/NF-κB signaling in excitatory forebrain neurons. We found that repression of IKK2/NF-κB signaling in neurons increases the acute posttraumatic mortality rate, worsens the neurological outcome, and promotes neuronal cell death by apoptosis, thus resulting in enhanced proinflammatory gene expression. As a potential mechanism, we identified elevated levels of the proapoptotic mediators Bax and Bad and enhanced expression of stress response genes. This phenotype is also observed when neuronal IKK/NF-κB activity is inhibited just before CHI. In contrast, neuron-specific activation of IKK/NF-κB signaling does not alter the TBI outcome. Thus, this study demonstrates that physiological neuronal IKK/NF-κB signaling is necessary and sufficient to protect neurons from trauma consequences.-Mettang, M., Reichel, S. N., Lattke, M., Palmer, A., Abaei, A., Rasche, V., Huber-Lang, M., Baumann, B., Wirth, T. IKK2/NF-κB signaling protects neurons after traumatic brain injury.

Quantitative 19F MRI of perfluoro-15-crown-5-ether using uniformity correction of the spin excitation and signal reception.

OBJECTIVES: A common limitation of all 1H contrast agents is that they only allow indirect visualization through modification of the intrinsic properties of the tissue, making quantification of this effect challenging. 19F compounds, on the contrary, are measured directly, without any background signal. There is a linear relationship between the amount of 19F spins and the intensity of the signal. However, non-uniformity of the radiofrequency field may lead to errors in the quantified 19F signal and should be carefully addressed for any quantitative imaging. MATERIALS AND METHODS: Adaptation of the previously introduced [Formula: see text] mapping technique to the problem of quantifying the 19F signal from perfluoro-15-crown-5-ether (PFCE) is proposed in this work. Initial evaluation of the proposed technique simultaneously accounting for transmit [Formula: see text] and receive [Formula: see text] field inhomogeneities is performed in a PFCE phantom. As a proof of concept, in vivo quantification of the 19F signal is performed in a murine model after application of custom-designed hollow mesoporous silica spheres (HMSS) loaded with PFCE. RESULTS: A phantom experiment clearly shows that only compensation for both transmit and receive characteristics outperforms inaccurate quantification based on the non- or partly-corrected signal intensities. Furthermore, an optimized protocol is proposed for in vivo application. CONCLUSION: The proposed [Formula: see text]/[Formula: see text] mapping technique represents a simple to implement and easy-to-use solution for quantification of the 19F signal from PFCE in the presence of B1-field inhomogeneities.

Low dietary protein content alleviates motor symptoms in mice with mutant dynactin/dynein-mediated neurodegeneration.

Mutations in components of the molecular motor dynein/dynactin lead to neurodegenerative diseases of the motor system or atypical parkinsonism. These mutations are associated with prominent accumulation of vesicles involved in autophagy and lysosomal pathways, and with protein inclusions. Whether alleviating these defects would affect motor symptoms remain unknown. Here, we show that a mouse model expressing low levels of disease linked-G59S mutant dynactin p150(Glued) develops motor dysfunction >8 months before loss of motor neurons or dopaminergic degeneration is observed. Abnormal accumulation of autophagosomes and protein inclusions were efficiently corrected by lowering dietary protein content, and this was associated with transcriptional upregulations of key players in autophagy. Most importantly this dietary modification partially rescued overall neurological symptoms in these mice after onset. Similar observations were made in another mouse strain carrying a point mutation in the dynein heavy chain gene. Collectively, our data suggest that stimulating the autophagy/lysosomal system through appropriate nutritional intervention has significant beneficial effects on motor symptoms of dynein/dynactin diseases even after symptom onset.

Respiratory self-gated 3D UTE for lung imaging in small animal MRI.

PURPOSE: To investigate retrospective respiratory gating of three-dimensional ultrashort echo time (3D UTE) lung acquisition in free-breathing rats using k-space center self gating signal (DC-SG) and 3D image-based SG (3D-Img-SG). METHODS: Seven rats were investigated with a quasi-random 3D UTE protocol. Low-resolution time-resolved sliding-window images were reconstructed with a 3D golden-angle radial sparse parallel (GRASP) reconstruction to extract a 3D-Img-SG signal, whereas DC-SG was extracted from the center of k-space. Both signals were sorted into 10 respiratory bins. Signal-to-noise ratio (SNR) and normalized signal intensity (NSI) in lung parenchyma, image sharpness, and lung volume changes were studied in the resulting images to show feasibility of the method. An algorithm for bulk movement identification and removal was implemented. RESULTS: Three-dimensional Img-SG allows reconstruction of different respiratory stages in all acquired datasets, showing clear differences in diaphragm position and significantly different lung volumes, SNR, and NSI in lung parenchyma. Improved sharpness in expiration images was observed compared to ungated images. DC-SG did not result in clear different diaphragm position in all cases. Bulk motion removal improved final image sharpness. CONCLUSION: Low-resolution 3D GRASP reconstruction allowed for extraction of an effective gating signal for 3D-Img-SG. The DC-SG method did not work in cases for which respiratory frequencies were inconsistent. Magn Reson Med 78:739-745, 2017. © 2016 International Society for Magnetic Resonance in Medicine.

Multistage self-gated lung imaging in small rodents.

PURPOSE: To investigate the exploitation of the self-gating signal in ultrashort echo time (UTE) two-dimensional (2D) acquisitions of freely breathing rats to reconstruct multiple respiratory stages. METHODS: Twelve rats were investigated with a 2D golden angle UTE protocol (12 coronal slices, echo time 0.343 ms, repetition time 120 ms, thickness 1 mm, flip angle 30°, matrix 256 × 256, 20-fold oversampling). The self-gating signal was extracted from the k-space center and sorted into five respiration bins (expiration, inspiration, three intermediate stages). Lung volume, sharpness, signal to noise ratio (SNR) and normalized signal intensity (NSI) were investigated. Time resolved images were reconstructed to visualize global animal motion. RESULTS: The method delineated that the lung volume decreased gradually from inspiration to expiration. Sharpness index resulted higher in expiration than in the ungated images. SNR was higher in ungated images and in expiration, decreasing gradually toward inspiration. NSI values presented a similar trend, with ungated images showing lower values than the expiration images. In one animal clear global motion and in seven animals minor movements were identified. CONCLUSION: The presented respiratory gating method allows the reconstruction of different respiratory positions. Improved sharpness in expiration images was observed compared with ungated images. SNR and NSI changes in parenchyma reflect the expected variation of lung tissue density during respiration. Magn Reson Med 75:2448-2454, 2016. © 2015 Wiley Periodicals, Inc.

Multistage three-dimensional UTE lung imaging by image-based self-gating.

PURPOSE: To combine image-based self-gating (img-SG) with ultrashort echo time (UTE) three-dimensional (3D) acquisition for multistage lung imaging during free breathing. METHODS: Three k-space ordering schemes (modified spiral pattern, quasirandom numbers and multidimensional Golden Angle) providing uniform coverage of k-space were investigated for providing low-resolution sliding-window images for image-based respiratory self-gating. The performance of the proposed techniques were compared with the conventional spiral pattern and standard DC-based self-gated methods in volunteers during free breathing. RESULTS: Navigator-like respiratory signals were successfully extracted from the sliding-window data by monitoring the lung-liver interface displacement. A temporal resolution of 588 ms was adequate to retrieve gating signals from the lung-liver interface. Images reconstructed with the img-SG technique showed significantly better sharpness and apparent diaphragm excursion than any of the DC-SG methods. Direct comparison of the three implemented ordering schemes did not demonstrate any clear superiority of one with respect to the others. CONCLUSION: Image-based respiratory self gating in UTE 3D lung images allows successful retrospective respiratory gating, also enabling reconstruction of intermediate respiratory stages.

Self-gated tissue phase mapping using golden angle radial sparse SENSE.

PURPOSE: To investigate the combination of Golden Angle Radial Sparse SENSE reconstruction with image-based self-gating (SG) for deriving high-quality TPM data from radial golden angle (GA) k-space data. METHODS: In 10 healthy volunteers, a self-gated radial GA TPM sequence (TPMSG ) was compared with a prospectively triggered radial TPM acquisition with conventional respiratory (RNAV) compensation (TPMref ). Image quality and velocities were compared for different regularization strengths λ in the CS reconstruction. RESULTS: Acquisitions and retrospective self-gating was successful in all cases. Contrast in TPMSG was superior to TPMref , because the blood saturation bands could be applied with full thickness without interference with the RNAV. Velocities from both acquisitions visually showed the same motion patterns and were quantitatively highly similar (correlation 0.81-0.97 and RMSE 0.08-0.21 cm/s). Strong temporal regularization ( λ∈0.3,0.4) led to reduced velocity peaks in TPMSG . For λ=0.2, image sharpness as well as velocity peaks of TPMSG were comparable to TPMRef . CONCLUSION: The combination of Golden Angle Radial Sparse SENSE with image-based self-gating allows measurement of velocities of the myocardium with superior black-blood contrast and full coverage of the cardiac cycle.

A self-gating method for time-resolved imaging of nonuniform motion.

PURPOSE: To develop a self-gating method capable of assessing nonuniform motion, e.g., in cardiovascular magnetic resonance imaging of patients with severe arrhythmia, or for imaging of the temporomandibular joint. METHODS: The proposed method allows cyclic motion trajectories with a nonuniform pace by replacing the one-dimensional gating signal of conventional image-based self-gating with a two-dimensional gating matrix. The resulting image quality is compared with conventional self-gating and real-time MRI. RESULTS: Nonuniform self-gating resulted in superior image quality compared with conventional self-gating and the feasibility study showed significantly improved image sharpness (P < 0.01). Further, improvements in image quality were shown compared with golden angle radial parallel sparse MRI. CONCLUSION: A new self-gating method was proposed that allows cardiovascular magnetic resonance of arrhythmic patients, which is a common problem in clinical practice. Further, the proposed method enables self-gated imaging of the temporomandibular joint. Magn Reson Med 76:919-925, 2016. © 2015 Wiley Periodicals, Inc.

Golden ratio sparse MRI using tiny golden angles.

PURPOSE: The combination of fully balanced SSFP sequences with iterative golden angle radial sparse parallel (iGRASP) MRI leads to strong image artifacts due to eddy currents caused by the large angular increment of the golden angle ordering. The purpose of this work is to enable the combination of iterative golden angle radial sparse parallel MRI with balanced SSFP using the recently presented tiny golden angles. METHODS: The tiny golden angle trajectories are analyzed for their incoherence properties in relation to sparse imaging using the time-resolved point-spread functions. Tiny golden angle radial sparse parallel (tyGRASP) MRI is introduced and evaluated with applications in cardiac imaging and dynamic imaging of the temporomandibular joint. The results are analyzed in detail for 3 T and verified for 1.5 T. RESULTS: The incoherence properties of the tiny golden angle trajectory are comparable to the incoherence properties of the golden angle trajectory and are well suited for sparse MRI reconstruction. The proposed tiny golden angle radial sparse parallel MRI method strongly reduces eddy current related artifacts for both applications. CONCLUSION: This work enables sparse, golden-ratio-based imaging with balanced SSFP sequences. Magn Reson Med 75:2372-2378, 2016. © 2015 Wiley Periodicals, Inc.

Pulmonary perfusion quantification with flow-sensitive inversion recovery (FAIR) UTE MRI in small animal imaging.

Blood perfusion in lung parenchyma is an important property for assessing lung function. In small animals, its quantitation is limited even with radioactive isotopes or dynamic contrast-enhanced MRI techniques. In this study, the feasibility flow-sensitive alternating inversion recovery (FAIR) for the quantification of blood flow in lung parenchyma in free breathing rats at 7 T has been investigated. In order to obtain sufficient signal from the short T2 * lung parenchyma, a 2D ultra-short echo time (UTE) Look-Locker read-out has been implemented. Acquisitions were segmented to maintain acquisition time within an acceptable range. A method to perform retrospective respiratory gating (DC-SG) has been applied to investigate the impact of respiratory movement. Reproducibilities within and between sessions were estimated, and the ability of FAIR-UTE to identify the decrease of lung perfusion under hyperoxic conditions was tested. The implemented technique allowed for the visualization of lung parenchyma with excellent SNR and no respiratory artifact even in ungated acquisitions. Lung parenchyma perfusion was obtained as 32.54 ± 2.26 mL/g/min in the left lung, and 34.09 ± 2.75 mL/g/min in the right lung. Application of retrospective gating significantly but minimally changes the perfusion values, implying that respiratory gating may not be necessary with this center-our acquisition method. A decrease of 10% in lung perfusion was found between normoxic and hyperoxic conditions, proving the feasibility of the FAIR-UTE approach to quantify lung perfusion changes.

On the influence of respiratory motion in radial tissue phase mapping cardiac MRI.

PURPOSE: To investigate the impact of respiratory motion on radial tissue phase mapping (TPM) measurements, and to improve image quality and scan efficiency without compromising velocity fidelity by increasing the respiratory acceptance window with and without motion correction. MATERIALS AND METHODS: A radial golden angle TPM sequence was measured in 10 healthy volunteers in three short axis slices at 3T. Ungated ( CFREE), self-gated with a single acceptance window ( CREF), motion-corrected averaging using all ( CMCall), or selected ( CMC) data reconstructions were compared by means of various image quality measures and resulting velocities. RESULTS: Using all data ( CFREE) resulted in significantly higher perceived signal-to-noise ratio (SNR) (P < 0.001), but significantly reduced sharpness (P < 0.001) and contrast (P = 0.02), when compared to CREF. Coefficient of variation (CV) and perceived sharpness were not significantly different (P > 0.05). With motion-correction, perceived sharpness could be significantly improved ( CMC: P = 0.002; CMCall: P = 0.002) in comparison to CFREE. Velocity peaks of CFREE were significantly reduced compared to CREF (all peaks: P < 0.001; except the longitudinal "E" peak: P = 0.03). The peak velocities in CMC and CMCall were not significantly different from CREF (all peaks: P > 0.08; except longitudinal "E"/"A" peaks: P > 0.01). CONCLUSION: Free-breathing reconstruction results in good perceived image sharpness and velocity information with slightly, but significantly, reduced peak velocities. For achieving velocities and image quality comparable to data from a single acceptance window, but higher gating efficiency, selected motion-corrected TPM (CMC) can be applied. J. Magn. Reson. Imaging 2016;44:1218-1228.

T2-prepared segmented 3D-gradient-echo for fast T2-weighted high-resolution three-dimensional imaging of the carotid artery wall at 3T: a feasibility study.

BACKGROUND: The multi-contrast assessment of the carotid artery wall has become an important diagnostic tool for the characterization of atherosclerotic plaque and vessel wall thickening. For providing the required T1-, T2-, and proton density weighted contrast, multi-slice turbo spin echo (TSE) techniques are normally applied. The straightforward extension of the TSE techniques to volumetric imaging of large sections of the carotid arteries is limited by the resulting long acquisition times. Where the acquisition of a T1-weighted contrast can be accelerated by applying a T1-weighted fast gradient echo technique, acceleration of the T2-weighted contrast is not as straightforward. METHODS: In this work, the combination of a T2 preparation and a conventional fast gradient echo technique (T2P-3DGE) was evaluated for rapid acquisition of a T2-weighted image contrast. Acquisition parameters were optimized in an initial in vitro study in direct comparison to the conventional T2-weighted TSE (T2W-3DTSE) technique. Subsequently, the T2P-3DGE technique was evaluated in vivo. RESULTS: In direct comparison, the T2P-3DGE sequence provided similar T2 contrast as the respective T2W-3DTSE sequence. After correction of an observed intensity offset, most likely caused by the additional T1-weighting of the T2P-3DGE sequence, no significant difference between the two T2-weighted sequences were observed in phantom data. The good correlation of the image contrast between the two sequences was confirmed in the initial in-vivo study, proving a potential reduction of the scan time for T2P-3DGE to 25% of the respective T2W-3DTSE technique. CONCLUSION: The in vitro as well as the in vivo results clearly indicate the potential of the T2P-3DGE technique for providing similar T2 image contrast as in the conventional techniques. Thereby, the acquisition times could be substantially reduced to about 25% of the respective 3D-TSE technique.