Hepatic fat quantification in dual-layer computed tomography using a three-material decomposition algorithm.

OBJECTIVES: The purpose of this study was to evaluate a three-material decomposition algorithm for hepatic fat quantification using a dual-layer computed tomography (DL-CT) and MRI as reference standard on a large patient cohort. METHOD: A total of 104 patients were retrospectively included in our study, i.e., each patient had an MRI exam and a DL-CT exam in our institution within a maximum of 31 days. Four regions of interest (ROIs) were positioned blindly and similarly in the liver, by two independent readers on DL-CT and MRI images. For DL-CT exams, all imaging phases were included. Fat fraction agreement between CT and MRI was performed using intraclass correlation coefficients (ICC), determination coefficients R2, and Bland-Altman plots. Diagnostic performance was determined using sensitivity, specificity, and positive and negative predictive values. The cutoff for steatosis was 5%. RESULTS: Correlation between MRI and CT data was excellent for all perfusion phases with ICC calculated at 0.99 for each phase. Determination coefficients R2 were also good for all perfusion phases (about 0.95 for all phases). Performance of DL-CT in the diagnosis of hepatic steatosis was good with sensitivity between 89 and 91% and specificity ranging from 75 to 80%, depending on the perfusion phase. The positive predictive value was ranging from 78 to 93% and the negative predictive value from 82 to 86%. CONCLUSION: Multi-material decomposition in DL-CT allows quantification of hepatic fat fraction with a good correlation to MRI data. CLINICAL RELEVANCE STATEMENT: The use of DL-CT allows for detection of hepatic steatosis. This is especially interesting as an opportunistic finding CT performed for other reasons, as early detection can help prevent or slowdown the development of liver metabolic disease. KEY POINTS: • Hepatic fat fractions provided by the dual-layer CT algorithm is strongly correlated with that measured on MRI. • Dual-layer CT is accurate to detect hepatic steatosis ≥ 5%. • Dual-layer CT allows opportunistic detection of steatosis, on CT scan performed for various indications.

Assessment of exposure, coping and adaptation strategies for elements at risk to climate change-induced flooding in urban areas. The case of Jangwani Ward in Dar es Salaam City, Tanzania.

Urban areas are the engines of socioeconomic growth and the homes of billions of people around the globe. In a changing climate, urban areas are inexorably from vulnerability to climate hazards including flooding which deters their social, economic, and environmental sustainability. The main objective of this paper was to explore exposure to elements at risk due to climate change-induced flooding in urban areas. In addition, the paper analyses the coping and adaptation strategies practiced at the community and national levels and recommends appropriate policy measures for enhanced climate resilience in urban areas. The study adopted purposeful sampling in which n = 95 households were selected for the study. Data collection methods involved household interviews with structured questionnaires, focused group discussions, documentary reviews, transect walks, surveys, and observations. Data analysis was done with a statistical package for social sciences. The results revealed that the elements at risk of exposure to climate change-induced flooding in the study area were physical infrastructures, socio-economic activities, livelihoods, and ecosystems. The study recommends enhancing resilience of elements at risk to climate change-induced flooding at national and local levels in urban areas. This is through promoting flood policies, strategies, laws, planning and management measures; enhance non-structural actions including flood forecasting, mapping, emergency evacuation plans and land use zoning and structural measures namely dams, dikes, storm surge barriers for adaptation to urban flooding.

Scribble Controls Social Motivation Behavior through the Regulation of the ERK/Mnk1 Pathway.

Social behavior is a basic domain affected by several neurodevelopmental disorders, including ASD and a heterogeneous set of neuropsychiatric disorders. The SCRIB gene that codes for the polarity protein SCRIBBLE has been identified as a risk gene for spina bifida, the most common type of neural tube defect, found at high frequencies in autistic patients, as well as other congenital anomalies. The deletions and mutations of the 8q24.3 region encompassing SCRIB are also associated with multisyndromic and rare disorders. Nonetheless, the potential link between SCRIB and relevant social phenotypes has not been fully investigated. Hence, we show that Scribcrc/+ mice, carrying a mutated version of Scrib, displayed reduced social motivation behavior and social habituation, while other behavioral domains were unaltered. Social deficits were associated with the upregulation of ERK phosphorylation, together with increased c-Fos activity. Importantly, the social alterations were rescued by both direct and indirect pERK inhibition. These results support a link between polarity genes, social behaviors and hippocampal functionality and suggest a role for SCRIB in the etiopathology of neurodevelopmental disorders. Furthermore, our data demonstrate the crucial role of the MAPK/ERK signaling pathway in underlying social motivation behavior, thus supporting its relevance as a therapeutic target.

Vangl2 in the Dentate Network Modulates Pattern Separation and Pattern Completion.

The organization of spatial information, including pattern completion and pattern separation processes, relies on the hippocampal circuits, yet the molecular and cellular mechanisms underlying these two processes are elusive. Here, we find that loss of Vangl2, a core PCP gene, results in opposite effects on pattern completion and pattern separation processes. Mechanistically, we show that Vangl2 loss maintains young postmitotic granule cells in an immature state, providing increased cellular input for pattern separation. The genetic ablation of Vangl2 disrupts granule cell morpho-functional maturation and further prevents CaMKII and GluA1 phosphorylation, disrupting the stabilization of AMPA receptors. As a functional consequence, LTP at lateral perforant path-GC synapses is impaired, leading to defects in pattern completion behavior. In conclusion, we show that Vangl2 exerts a bimodal regulation on young and mature GCs, and its disruption leads to an imbalance in hippocampus-dependent pattern completion and separation processes.

Mitotic activity, modulation of DNA processing, and purinergic signalling in the adult rat auditory brainstem following sensory deafferentation.

A complex scenario of cellular network reorganization is caused by unilateral sensory deafferentation (USD) in the adult rat central auditory system. We asked whether this plasticity response involves mitosis. Immunohistochemistry was applied to brainstem sections for the detection and localization of mitotic markers Ki67 and PCNA, the growth-associated protein Gap43 and purine receptor P2X4. Fluorescent double staining was done for Ki67:PCNA and for both of them with HuC/HuD (neurons), S100 (astrocytes), Iba1 (microglia) and P2X4. Inquiring 1-7 days after USD, we found Ki67 expression to be changed in cellular profiles of cochlear nucleus (CN) with a significant increase in number by 1-3 days, followed by reset to control level within 1 week. USD-induced mitosis exclusively occurred in microglia and was absent elsewhere in the auditory brainstem. PCNA staining of small cellular profiles increased similarly but remained elevated. PCNA staining intensity also changed in CN, superior olive and inferior colliculus in neuronal nuclei, suggesting shifts in DNA processing. No apoptotic cell death was detected in any region of the adult auditory brainstem after USD. A comparison of anterograde and retrograde effects of nerve damage revealed proliferating microglia expressing P2X4 receptors in CN upon USD, but not in the facial nucleus after facial nerve transection. In conclusion, the deafferentation model studied here permits insight into the capacity of the adult mammalian brain to invoke mitosis among glia cells, adjustment of gene processing in neurons and purinergic signalling between them, jointly accounting for a multilayered neuro- and glioplastic response.

Sensory deafferentation modulates and redistributes neurocan in the rat auditory brainstem.

INTRODUCTION: Cochlear ablation causing sensory deafferentation (SD) of the cochlear nucleus triggers complex re-arrangements in the cellular and molecular communication networks of the adult mammalian central auditory system. Participation of the extracellular matrix (ECM) in these processes is not well understood. METHODS: We investigated consequences of unilateral SD for the expression and distribution of the chondroitin sulfate proteoglycans, neurocan (Ncan) and aggrecan (Agg), alongside various plasticity markers in the auditory brainstem of the adult rat using immunohistochemical techniques. RESULTS: In the deafferented ventral cochlear nucleus (VCN), Ncan expression increased massively within 3 postoperative days (POD), but rapidly decreased thereafter. Agg showed a similar but less pronounced progression. Decrease in Ncan was spatially and temporally related to the re-innervation of VCN documented by the emergence of growth-associated protein Gap43 contained in nerve fibers and presynaptic boutons. Concurrently, astrocytes grew and expressed matrix metalloproteinase-2 (MMP2), an enzyme known to emerge only under re-innervation of VCN. MMP2 is capable of cleaving both Ncan and Agg when released. A transient modulation of the ECM in the central inferior colliculus on the side opposite to SD occurred by POD1. Modulations of glutamatergic synapses and Gap43 expression were detected, reflecting state changes of the surrounding tissue induced by transsynaptic effects of SD. CONCLUSIONS: The ECM variously participates in adaptive responses to sudden deafness by SD on several levels along the central auditory pathway, with a striking spatial and temporal relationship of Ncan modulation to astrocytic activation and to synaptogenesis.

Monaural Neonatal Deafness Induces Inhibition among Bilateral Auditory Networks under Binaural Activation.

Worldwide, almost 500 million people are hearing impaired, making hearing loss the most common sensory impairment among humans. For people with single-sided deafness (SSD), cochlear implants (CIs) can be enormously beneficial by providing binaural information. However, binaural benefits in CI users have been only incompletely realized. Overcoming these limitations requires a better knowledge of how neuronal circuits adapt to SSD and how unilateral CI stimulation can compensate a deaf ear. We investigated effects of neonatal SSD on auditory brainstem circuitry using acoustic (AS), electric (ES), or acoustic stimulation on one ear and electric stimulation on the other ear (AS + ES). The molecular marker Fos was used to investigate changes in interneuronal communication due to SSD. To induce SSD, neonatal rats obtained a unilateral intracochlear injection of neomycin. In adulthood, rats were acutely stimulated by AS, ES, or AS + ES. AS and ES were applied correspondingly in terms of intracochlear stimulation side and intensity resulting in bilaterally comparable Fos expression in hearing rats. In contrast, SSD rats showed a loss of tonotopic order along the deafened pathway, indicated by a massive increase and spread of Fos expressing neurons. We report three major results: First, AS of the hearing ear of SSD rats resulted in bilateral activation of neurons in the cochlear nucleus (CN). Second, ES of the deaf ear did not activate contralateral CN. Third, AS + ES of SSD rats resulted in bilateral reduced Fos expression in the auditory brainstem compared to monaural stimulations. These findings indicate changes in inhibitory interactions among neuronal networks as a result of monaural deafness.

Astrocyte Hypertrophy and Microglia Activation in the Rat Auditory Midbrain Is Induced by Electrical Intracochlear Stimulation.

Neuron-glia interactions contribute to tissue homeostasis and functional plasticity in the mammalian brain, but it remains unclear how this is achieved. The potential of central auditory brain tissue for stimulation-dependent cellular remodeling was studied in hearing-experienced and neonatally deafened rats. At adulthood, both groups received an intracochlear electrode into the left cochlea and were continuously stimulated for 1 or 7 days after waking up from anesthesia. Normal hearing and deafness were assessed by auditory brainstem responses (ABRs). The effectiveness of stimulation was verified by electrically evoked ABRs as well as immunocytochemistry and in situ hybridization for the immediate early gene product Fos on sections through the auditory midbrain containing the inferior colliculus (IC). Whereas hearing-experienced animals showed a tonotopically restricted Fos response in the IC contralateral to electrical intracochlear stimulation, Fos-positive neurons were found almost throughout the contralateral IC in deaf animals. In deaf rats, the Fos response was accompanied by a massive increase of GFAP indicating astrocytic hypertrophy, and a local activation of microglial cells identified by IBA1. These glia responses led to a noticeable increase of neuron-glia approximations. Moreover, staining for the GABA synthetizing enzymes GAD65 and GAD67 rose significantly in neuronal cell bodies and presynaptic boutons in the contralateral IC of deaf rats. Activation of neurons and glial cells and tissue re-composition were in no case accompanied by cell death as would have been apparent by a Tunel reaction. These findings suggest that growth and activity of glial cells is crucial for the local adjustment of neuronal inhibition to neuronal excitation.

Magnetization transfer from inhomogeneously broadened lines (ihMT): Improved imaging strategy for spinal cord applications.

PURPOSE: Inhomogeneous magnetization transfer (ihMT) shows great promise for specific imaging of myelinated tissues. Whereas the ihMT technique has been previously applied in brain applications, the current report presents a strategy for cervical spinal cord (SC) imaging free of cerebrospinal fluid (CSF) pulsatility artifacts. METHODS: A pulsed ihMT preparation was combined with a single-shot HASTE readout. Electrocardiogram (ECG) synchronization was used to acquire all images during the quiescent phase of SC motion. However ihMT signal quantification errors may occur when a variable recovery delay is introduced in the sequence as a consequence of variable cardiac cycle. A semiautomatic retrospective correction algorithm, based on repetition time (TR) -matching, is proposed to correct for signal variations of long T1 -components (e.g., CSF). RESULTS: The proposed strategy combining ECG synchronization and retrospective data pairing led to clean SC images free of CSF artifacts. Lower variability of the ihMT metrics were obtained with the correction algorithm, and allowed for shorter TR to be used, hence improving signal-to-noise ratio efficiency. CONCLUSION: The proposed methodology enabled faster acquisitions, while offering robust ihMT quantification and exquisite SC image quality. This opens great perspectives for widening the in vivo characterization of SC physiopathology using MRI, such as studying white matter tracts microstructure or impairment in degenerative pathologies. Magn Reson Med 77:581-591, 2017. © 2016 International Society for Magnetic Resonance in Medicine.

Induction of single-sided deafness in the newborn rat and its consequence for cochlear nucleus volume development.

Aim of this study was to induce a single-sided deafness (SSD) in rats before hearing onset. Rats were operated at postnatal day 10 by approaching the tympanic cavity along a retroauricular path without manipulating ossicles or tympanic membrane. The ototoxic aminoglycoside neomycin was injected intracochlearly through the round window membrane on one side. When the animals have reached young adult stages, their hearing threshold was determined by their auditory brainstem response (ABR). Monaural deafening was considered successful when the hearing threshold was at least 95 dB above the threshold of the normal hearing ear. Growing up with one non-functional ear, rats developed a striking anatomical asymmetry of their cochlear nuclei (CN). The CN from age-matched normal hearing brains and from both sides of single-sided deaf brains were cut into series of frontal sections and their volumes calculated. No difference was detected between the volume of the normal hearing CN and the contralateral CN in SSD rats. By contrast, growth retardation was found for the ventral CN on the deaf side to result in a volume of only 57% compared to the normal hearing side. Marginal growth retardation was also observed for the dorsal CN on the deaf side. Thus, loss of sensory activation leads mainly, but not exclusively, to a reduction of tissue volume in the ventral CN of the deaf side, leaving the contralateral side apparently unaffected.

In vivo free-breathing DTI and IVIM of the whole human heart using a real-time slice-followed SE-EPI navigator-based sequence: A reproducibility study in healthy volunteers.

PURPOSE: In this study, we proposed an efficient free-breathing strategy for rapid and improved cardiac diffusion-weighted imaging (DWI) acquisition using a single-shot spin-echo echo planar imaging (SE-EPI) sequence. METHODS: A real-time slice-following technique during free-breathing was combined with a sliding acquisition-window strategy prior Principal Component Analysis temporal Maximum Intensity Projection (PCAtMIP) postprocessing of in-plane co-registered diffusion-weighted images. This methodology was applied to 10 volunteers to quantify the performance of the motion correction technique and the reproducibility of diffusion parameters. RESULTS: The slice-following technique offers a powerful head-foot respiratory motion management solution for SE-EPI cDWI with the advantage of a 100% duty cycle scanning efficiency. The level of co-registration was further improved using nonrigid motion corrections and was evaluated with a co-registration index. Vascular fraction f and the diffusion coefficients D and D* were determined to be 0.122 ± 0.013, 1.41 ± 0.09 × 10(-3) mm(2) /s and 43.6 ± 9.2 × 10(-3) mm(2) /s, respectively. From the multidirectional dataset, the measured mean diffusivity was 1.72 ± 0.09 × 10(-3) mm(2) /s and the fractional anisotropy was 0.36 ± 0.02. CONCLUSION: The slice-following DWI SE-EPI sequence is a promising solution for clinical implementation, offering a robust improved workflow for further evaluation of DWI in cardiology. Magn Reson Med 76:70-82, 2016. © 2015 Wiley Periodicals, Inc.

Qualitative and quantitative evaluation of skeletal muscle fatty degenerative changes using whole-body Dixon nuclear magnetic resonance imaging for an important reduction of the acquisition time.

In recent years, MRI has proven its usefulness for the diagnostic workup of patients with musculo-skeletal diseases, and also shown great promise as a non-invasive, quantitative outcome measure in clinical studies. The characterization of patterns of fatty degenerative lesions, which now plays an important part in the diagnosis of some diseases, is typically performed by the radiologist on routine T1-weighted images. We propose to rationalize acquisitions and reduce patients' time in the scanner by allowing radiologists to perform the qualitative grading of the muscles on images derived from fat/water acquisitions. These maps are color-coded, where the different colors correspond to classes of fatty infiltration degree. This allows a quick visual assessment of the muscles, equivalent to the standard method. Using the weighted Kappa agreement test, the agreement between the proposed method and the traditional one, as well as the reproducibility of the results with two raters, was measured on twenty patients suffering from various neuromuscular pathologies. The presented comparisons show that the use of color coded fat fraction maps is statistically equivalent to using the traditional T1-weighted images when performing visual assessment of degenerative lesions with fatty infiltrations in patients with neuromuscular disorders.

BLOCH equations-based reconstruction of myocardium t1 maps from modified look-locker inversion recovery sequence.

Modified Look-Locker Inversion recovery (MOLLI) sequence is increasingly performed for myocardial T1 mapping but is known to underestimate T1 values. The aim of the study was to quantitatively analyze several sources of errors when T1 maps are derived using standard post-processing of the sequence and to propose a reconstruction approach that takes into account inversion efficacy (η), T2 relaxation during balanced steady-state free-precession readouts and B1+ inhomogeneities. Contributions of the different sources of error were analyzed using Bloch equations simulations of MOLLI sequence. Bloch simulations were then combined with the acquisition of fast B1+ and T2 maps to derive more accurate T1 maps. This novel approach was evaluated on phantoms and on five healthy volunteers. Simulations show that T2 variations, B1+ heterogeneities and inversion efficiency represent major confounders for T1 mapping when MOLLI is processed with standard 3-parameters fitting. In vitro data indicate that T1 values are accurately derived with the simulation approach and in vivo data suggest that myocardium T1 are 15% underestimated when processed with the standard 3-parameters fitting. At the cost of additional acquisitions, this method might be suitable in clinical research protocols for precise tissue characterization as it decorrelates T1 and T2 effects on parametric maps provided by MOLLI sequence and avoids inaccuracies when B1+ is not homogenous throughout the myocardium.

The pattern of Fos expression in the rat auditory brainstem changes with the temporal structure of binaural electrical intracochlear stimulation.

The immediate-early-gene c-fos with its protein product Fos has been used as a powerful tool to investigate neuronal activity and plasticity following sensory stimulation. Fos combines with Jun, another IEG product, to form the dimeric transcription factor activator protein 1 (AP-1) which has been implied in a variety of cellular functions like neuronal plasticity, apoptosis, and regeneration. The intracellular emergence of Fos indicates a functional state of nerve cells directed towards molecular and morphological changes. The central auditory system is construed to detect stimulus intensity, spectral composition, and binaural balance through neurons organized in a complex network of ascending, descending and commissural pathways. Here we compare monaural and binaural electrical intracochlear stimulation (EIS) in normal hearing and early postnatally deafened rats. Binaural stimulation was done either synchronously or asynchronously. The auditory brainstem of hearing and deaf rats responds differently, with a dramatically increasing Fos expression in the deaf group so as if the network had no pre-orientation for how to organize sensory activity. Binaural EIS does not result in a trivial sum of 2 independent monaural EIS, as asynchronous stimulation invokes stronger Fos activation compared to synchronous stimulation almost everywhere in the auditory brainstem. The differential response to synchronicity of the stimulation puts emphasis on the importance of the temporal structure of EIS with respect to its potential for changing brain structure and brain function in stimulus-specific ways.

Parallel-transmission-enabled three-dimensional T2 -weighted imaging of the human brain at 7 Tesla.

PURPOSE: A promise of ultra high field MRI is to produce images of the human brain with higher spatial resolution due to an increased signal to noise ratio. Yet, the shorter radiofrequency wavelength induces an inhomogeneous distribution of the transmit magnetic field and thus challenges the applicability of MRI sequences which rely on the spin excitation homogeneity. In this work, the ability of parallel-transmission to obtain high-quality T2 -weighted images of the human brain at 7 Tesla, using an original pulse design method is evaluated. METHODS: Excitation and refocusing square pulses of a SPACE sequence were replaced with short nonselective transmit-SENSE pulses individually tailored with the gradient ascent pulse engineering algorithm, adopting a kT -point trajectory to simultaneously mitigate B1 (+) and ΔB0 nonuniformities. RESULTS: In vivo experiments showed that exploiting parallel-transmission at 7T with the proposed methodology produces high quality T2 -weighted whole brain images with uniform signal and contrast. Subsequent white and gray matter segmentation confirmed the expected improvements in image quality. CONCLUSION: This work demonstrates that the adopted formalism based on optimal control, combined with the kT -point method, successfully enables three-dimensional T2 -weighted brain imaging at 7T devoid of artifacts resulting from B1 (+) inhomogeneity.

Myocardial perfusion assessment in humans using steady-pulsed arterial spin labeling.

PURPOSE: Although arterial spin labeling (ASL) has become a routinely performed method in the rodent heart, its application to the human heart remains challenged by low tissue blood flow and cardiac and respiratory motion. We hypothesized that an alternative steady-pulsed ASL (spASL) method would provide more efficient perfusion signal averaging by driving the tissue magnetization into a perfusion-dependent steady state. METHODS: We evaluated the feasibility of spASL in the human heart by combining pulsed labeling in the aortic root with a balanced steady state free precession sequence. The spASL scheme was applied to 13 subjects under free breathing. Breathing motion was addressed using retrospective image exclusion based on a contour-based cross-correlation algorithm. RESULTS: The measured signal with spASL was due to labeled blood. We found that the perfusion signal was larger than that obtained with the earlier flow-sensitive alternating inversion recovery (FAIR) method. Averaged myocardial blood flow (MBF) over four myocardial regions was 1.28 ± 0.36 mL·g(-1) ·min(-1) . CONCLUSION: spASL was able to quantify MBF in healthy subjects under free breathing. Because quantification with ASL is more direct than with first-pass perfusion MRI, it appears particularly suited for pathologies with diffuse microvascular alterations, MBF reserve, and follow-up studies.

Gap43 transcription modulation in the adult brain depends on sensory activity and synaptic cooperation.

Brain development and learning is accompanied by morphological and molecular changes in neurons. The growth associated protein 43 (Gap43), indicator of neurite elongation and synapse formation, is highly expressed during early stages of development. Upon maturation of the brain, Gap43 is down-regulated by most neurons with the exception of subdivisions such as the CA3 region of hippocampus, the lateral superior olive (LSO) and the central inferior colliculus (CIC). Little is known about the regulation of this mRNA in adult brains. We found that the expression of Gap43 mRNA in specific neurons can be modulated by changing sensory activity of the adult brain. Using the central auditory system of rats as a model, Gap43 protein and mRNA levels were determined in LSO and CIC of hearing-experienced rats unilaterally or bilaterally deafened or unilaterally stimulated by a cochlear implant (CI). Our data indicate that Gap43 is a marker useful beyond monitoring neuronal growth and synaptogenesis, reflecting also specific patterns of synaptic activities on specific neurons. Thus, unilateral loss of input to an adult auditory system directly causes asymmetrical expression of Gap43 mRNA between LSOs or CICs on both sides of the brainstem. This consequence can be prevented by simple-patterned stimulation of a dysfunctional ear by way of a CI. We suggest that as a function of input balance and activity pattern, Gap43 mRNA expression changes as cells associate converging afferent signals.

Time-resolved spin-labeled MR angiography for the depiction of cerebral arteriovenous malformations: a comparison of techniques.

PURPOSE: To assess time-resolved spin-labeled (SL) magnetic resonance (MR) angiographic imaging with a large acquisition time window over two cardiac cycles for characterization of cerebral arteriovenous malformations (AVMs). MATERIALS AND METHODS: This study was institutional review board-approved. Sixteen patients presented with an AVM, provided informed consent, and were prospectively included. Time-resolved SL MR angiographic images with acquisition window that covered two cardiac cycles (acquisition time, 10-12 min; temporal resolution, 60 msec) or one cardiac cycle and time-of-flight (TOF) MR angiographic images were acquired with a 3-T MR imager. A diagnostic confidence index was used for image quality evaluation; scores were 0, no diagnosis, to 3, high image quality. AVM characterization consisted of arterial feeder, nidus size, and venous drainage type identification compared with those at digital subtraction angiography (DSA). κ coefficients were computed to determine interobserver and intermodality agreement. RESULTS: Time-resolved SL MR angiographic imaging over two cardiac cycles provided a median diagnostic confidence index of 2.5 for arterial feeders, 3.0 for nidus, and 3.0 for venous drainage. Venous drainage depiction quality was higher with time-resolved SL MR angiography over two cardiac cycles than with time-resolved SL MR angiography over one cardiac cycle (P < .001) and TOF MR angiography (P < .001). For AVM characterization, interobserver agreement was very good to excellent, and agreement with DSA showed κ of 0.85 for arterial feeders, κ of 1.00 for nidus size, and κ of 0.82 for venous drainage. CONCLUSION: Time-resolved SL MR angiographic imaging over two cardiac cycles is a reliable clinical tool for cerebral AVM characterization, which showed very good to excellent agreement with DSA.

Magnetic resonance imaging for the exploitation of bubble-enhanced heating by high-intensity focused ultrasound: a feasibility study in ex vivo liver.

Bubble-enhanced heating (BEH) may be exploited to improve the heating efficiency of high-intensity focused ultrasound in liver and to protect tissues located beyond the focal point. The objectives of this study, performed in ex vivo pig liver, were (i) to develop a method to determine the acoustic power threshold for induction of BEH from displacement images measured by magnetic resonance acoustic radiation force imaging (MR-ARFI), and (ii) to compare temperature distribution with MR thermometry for HIFU protocols with and without BEH. The acoustic threshold for generation of BEH was determined in ex vivo pig liver from MR-ARFI calibration curves of local tissue displacement resulting from sonication at different powers. Temperature distributions (MR thermometry) resulting from "conventional" sonications (20 W, 30 s) were compared with those from "composite" sonications performed at identical parameters, but after a HIFU burst pulse (0.5 s, acoustic power over the threshold for induction of BEH). Displacement images (MR-ARFI) were acquired between sonications to measure potential modifications of local tissue displacement associated with modifications of tissue acoustic characteristics induced by the burst HIFU pulse. The acoustic threshold for induction of BEH corresponded to a displacement amplitude of approximately 50 µm in ex vivo liver. The displacement and temperature images of the composite group exhibited a nearly spherical pattern, shifted approximately 4 mm toward the transducer, in contrast to elliptical shapes centered on the natural focal position for the conventional group. The gains in maximum temperature and displacement values were 1.5 and 2, and the full widths at half-maximum of the displacement data were 1.7 and 2.2 times larger than in the conventional group in directions perpendicular to ultrasound propagation axes. Combination of MR-ARFI and MR thermometry for calibration and exploitation of BEH appears to increase the efficiency and safety of HIFU treatment.