An evolution of low-field strength MRI.

The paper describes the evolution of low-field MRI from the very early pioneering days in the late 70 s until today. It is not meant to give a comprehensive historical account of the development of MRI, but rather to highlight the different research environments then and now. In the early 90 s, when low-field systems below 1.5 T essentially vanished, there were just no reasonable means available to make up for the factor of roughly three in signal-to-noise-ratio (SNR) between 0.5 and 1.5 T. This has drastically changed. Improvements in hardware-closed Helium-free magnets, RF receiver systems and especially much faster gradients, much more flexible sampling schemes including parallel imaging and compressed sensing and especially the use of AI at all stages of the imaging process have made low-field MRI a clinically viable supplement to conventional MRI. Ultralow-field MRI with magnets around 0.05 T are also back and constitute a bold and courageous endeavor to bring MRI to communities, which have neither the means nor the infrastructure to sustain a current standard of care MRI.

Common and dissociable effects of oxytocin and lorazepam on the neurocircuitry of fear.

Benzodiazepines (BZDs) represent the gold standard of anxiolytic pharmacotherapy; however, their clinical benefit is limited by side effects and addictive potential. Consequently, there is an urgent need to develop novel and safe anxiolytics. The peptide hormone oxytocin (OXT) exhibits anxiolytic-like properties in animals and humans, but whether OXT and BZDs share similar effects on the neural circuitry of fear is unclear. Therefore, the rationale of this ultra-high-field functional MRI (fMRI) study was to test OXT against the clinical comparator lorazepam (LZP) with regard to their neuromodulatory effects on local and network responses to fear-related stimuli. One hundred twenty-eight healthy male participants volunteered in this randomized double-blind, placebo-controlled, between-group study. Before scanning using an emotional face-matching paradigm, participants were randomly administered a single dose of OXT (24 IU), LZP (1 mg), or placebo. On the behavioral level, LZP, but not OXT, caused mild sedation, as evidenced by a 19% increase in reaction times. On the neural level, both OXT and LZP inhibited responses to fearful faces vs. neutral faces within the centromedial amygdala (cmA). In contrast, they had different effects on intra-amygdalar connectivity; OXT strengthened the coupling between the cmA and basolateral amygdala, whereas LZP increased the interplay between the cmA and superficial amygdala. Furthermore, OXT, but not LZP, enhanced the coupling between the cmA and the precuneus and dorsomedial prefrontal cortex. These data implicate inhibition of the cmA as a common denominator of anxiolytic action, with only OXT inducing large-scale connectivity changes of potential therapeutic relevance.

Single shot spiral TSE with annulated segmentation.

PURPOSE: To develop, optimize, and implement a single shot spiral turbo spin echo (TSE) sequence at 3T and to demonstrate its feasibility to acquire artifact free images of the central nervous system with 1 mm spatial resolution in <200 ms. THEORY AND METHODS: Spiral TSE sequences with annulated spiral segmentation have been implemented with different acquisition modes. In fixed mode, the duration of each spiral segment is fixed to fill the available acquisition time tacq . In tangential mode, the beginning of each spiral segment is reached via a straight tangential trajectory. Tangential mode allows faster transition and thus longer tacq for a given echo spacing (ESP), but less data points can be acquired per acquisition interval. Alternating between spiral-in and spiral-out readout in alternating echoes leads to a somewhat different point spread function for off-resonant spins. RESULTS: Images of the brain with 1 mm spatial resolution acquired with a variable density spiral with ∼40% undersampling can be acquired in a single shot. All acquisition modes produce comparable image quality. Only mild artifacts in regions of strong susceptibility effects can be observed for ESP of 10 ms and below. The use of variable flip angle schemes allows seamless acquisition of consecutive slices and/or dynamic scans without waiting time between consecutive acquisitions. Comparison with images acquired at 1.5T shows reduced susceptibility artifacts within the brain and facial structures. CONCLUSION: Single shot spiral TSE has been demonstrated to enable highly efficient acquisition of high-resolution images of the brain in <200 ms per slice.

15 Years MR-encephalography.

OBJECTIVE: This review article gives an account of the development of the MR-encephalography (MREG) method, which started as a mere 'Gedankenexperiment' in 2005 and gradually developed into a method for ultrafast measurement of physiological activities in the brain. After going through different approaches covering k-space with radial, rosette, and concentric shell trajectories we have settled on a stack-of-spiral trajectory, which allows full brain coverage with (nominal) 3 mm isotropic resolution in 100 ms. The very high acceleration factor is facilitated by the near-isotropic k-space coverage, which allows high acceleration in all three spatial dimensions. METHODS: The methodological section covers the basic sequence design as well as recent advances in image reconstruction including the targeted reconstruction, which allows real-time feedback applications, and-most recently-the time-domain principal component reconstruction (tPCR), which applies a principal component analysis of the acquired time domain data as a sparsifying transformation to improve reconstruction speed as well as quality. APPLICATIONS: Although the BOLD-response is rather slow, the high speed acquisition of MREG allows separation of BOLD-effects from cardiac and breathing related pulsatility. The increased sensitivity enables direct detection of the dynamic variability of resting state networks as well as localization of single interictal events in epilepsy patients. A separate and highly intriguing application is aimed at the investigation of the glymphatic system by assessment of the spatiotemporal patterns of cardiac and breathing related pulsatility. DISCUSSION: MREG has been developed to push the speed limits of fMRI. Compared to multiband-EPI this allows considerably faster acquisition at the cost of reduced image quality and spatial resolution.

Analysis of accelerated 4D flow MRI in the murine aorta by radial acquisition and compressed sensing reconstruction.

Preclinical 4D flow MRI remains challenging and is restricted for parallel imaging acceleration due to the limited number of available receive channels. A radial acquisition with combined parallel imaging and temporal compressed sensing reconstruction was implemented to achieve accelerated preclinical 4D flow MRI. In order to increase the accuracy of the measured velocities, a quantitative evaluation of different temporal regularization weights for the compressed sensing reconstruction based on velocity instead of magnitude data is performed. A 3D radial retrospectively triggered phase contrast sequence with a combined parallel imaging and compressed sensing reconstruction with temporal regularization was developed. It was validated in a phantom and in vivo (C57BL/6 J mice), against an established fully sampled Cartesian sequence. Different undersampling factors (USFs [12, 15, 20, 30, 60]) were evaluated, and the effect of undersampling was analyzed in detail for magnitude and velocity data. Temporal regularization weights λ were evaluated for different USFs. Acceleration factors of up to 20 compared with full Nyquist sampling were achieved. The peak flow differences compared with the Cartesian measurement were the following: USF 12, 3.38%; USF 15, 4.68%; USF 20, 0.95%. The combination of 3D radial center-out trajectories and compressed sensing reconstruction is robust against motion and flow artifacts and can significantly reduce measurement time to 30 min at a resolution of 180 µm3 . Concisely, radial acquisition with combined compressed sensing and parallel imaging proved to be an excellent method for analyzing complex flow patterns in mice.

Oxytocin enhances the pain-relieving effects of social support in romantic couples.

Social support plays a vital role in physical and mental well-being. The neuropeptide hormone oxytocin (OXT) has been implicated in modulating pair-bonding and affiliative behaviors, but whether OXT contributes to the analgesic effects of a romantic partner's touch remains elusive. In the present randomized placebo-controlled, between-group, functional magnetic resonance imaging study involving 194 healthy volunteers (97 heterosexual couples), we tested the effects of intranasal OXT (24 IU) on handholding as a common mode of expressing emotional support in romantic couples. We scanned the subjects while brief electric shocks were administered. The subjects assumed that they received social support from either their romantic partner or an unfamiliar person. Unbeknown to the subject, in the partner and stranger support conditions, the same male experimenter always held the subject's left hand. Partner support was most effective in reducing the unpleasantness of electric shocks, and OXT further attenuated the unpleasantness across conditions. On the neural level, OXT significantly augmented the beneficial effects of partner support, as evidenced by a stronger decrease of neural responses to shocks in the anterior insula (AI), a stronger activity increase in the middle frontal gyrus (MFG), and a strengthened functional coupling between the AI and MFG. Our results support the notion that OXT specifically modulates the beneficial effects of social support in romantic couples by concomitantly reducing pain-associated activity and increasing activity linked to cognitive control and pain inhibition. We hypothesize that impaired OXT signaling may contribute to the experience of a lack of partner support.

Fearfulness, neuroticism/anxiety, and COMT Val158Met in long-term fear conditioning and extinction.

Individual differences in long-term stability of fear memories are of potential relevance for stable dispositions related to threat processing, such as neuroticism/anxiety and fearfulness. As previous research suggests a prominent role of dopamine for the retention of conditioned and extinguished fear, dopaminergic gene polymorphisms may also relate to individual differences in fear stability. While the COMT Val158Met polymorphism causes individual differences in prefrontal dopamine, its associations with human long-term fear extinction are currently unknown. Here, n = 30/29/28 healthy male Val/Val, Val/Met and Met/Met carriers, respectively, underwent a two-day differential conditioning paradigm with fear acquisition and extinction on Day 1 and a recall test on Day 2 with recordings of EEG and ECG. Fearfulness but not neuroticism/anxiety predicted fear bradycardia (i.e., heart period slowing) during Day 1 fear acquisition while it did not affect extinction or Day 2 fear recall. In contrast, COMT Val158Met significantly modulated Day 2 fear recall as evident in fear bradycardia and Late Positive Potential (LPP) amplitudes while it did not affect Day 1 fear or extinction learning. Furthermore, exploratory analyses revealed that individual differences in fear bradycardia during Day 2 extinction recall depended on Day 1 extinction success. Importantly, this contingency was (a) modulated by COMT Val158Met and (b) significantly reduced in high vs. low neuroticism/anxiety. The present study indicates that (a) individual differences in dopaminergic genotypes may affect the long-term stability of fear memories and (b) fearfulness vs. neuroticism/anxiety might play distinct roles in initial fear reactions vs. long-term stability of fear memories, respectively.

How the brain codes intimacy: The neurobiological substrates of romantic touch.

Humans belong to a minority of mammalian species that exhibit monogamous pair-bonds, thereby enabling biparental care of offspring. The high reward value of interpersonal closeness and touch in couples is a key proximate mechanism facilitating the maintenance of enduring romantic bonds. However, surprisingly, the neurobiological underpinnings mediating the unique experience of a romantic partner's touch remain unknown. In this randomized placebo (PLC)-controlled, between-group, pharmacofunctional magnetic resonance imaging (fMRI) study involving 192 healthy volunteers (96 heterosexual couples), we intranasally administered 24 IU of the hypothalamic peptide oxytocin (OXT) to either the man or the woman. Subsequently, we scanned the subjects while they assumed that they were being touched by their romantic partners or by an unfamiliar person of the opposite sex, although in reality an identical pattern of touch was always given by the same experimenter. Our results show that intranasal OXT compared to PLC selectively enhanced the subjective pleasantness of the partner's touch. Importantly, intranasal OXT selectively increased responses to partner touch in the nucleus accumbens (NAcc) and anterior cingulate cortex. Under OXT, NAcc activations to partner touch positively correlated with the subjects' evaluation of their relationship quality. Collectively, our results suggest that OXT may contribute to the maintenance of monogamous relationships in humans by concomitantly increasing the reward value of partner touch and diminishing the hedonic quality of stranger touch. Hum Brain Mapp 38:4525-4534, 2017. © 2017 Wiley Periodicals, Inc.

The ventral fiber pathway for pantomime of object use.

The current concept of a dual loop system of brain organization predicts a domain-general dual-pathway architecture involving dorsal and ventral fiber connections. We investigated if a similar dichotomy of brain network organization applies for pantomime (P) and imitation of meaningless gestures (I). Impairments of these tasks occur after left hemispheric brain lesions causing apraxia. Isolated impairments and double-dissociations point towards an anatomical segregation. Frontal and parietal areas seem to contribute differently. A special role of the inferior frontal gyrus and underlying fiber pathways was suggested recently. Using a combined fMRI/DTI-approach, we compared the fiber pathway architecture of left hemispheric frontal, temporal and parietal network components of pantomime and imitation. Thereby, we separated object effects from pantomime-specific effects. P and I both engage a fronto-temporo-parietal network of cortical areas interconnected by a dorsal fiber system (superior longitudinal fascicle) for direct sensory-motor interactions. The pantomime-specific effect additionally involved the triangular part of the inferior frontal gyrus, the middle temporal gyrus, the inferior parietal cortex and the intraparietal sulcus, interconnected by ventral fibers of the extreme capsule, likely related to higher-order conceptual and semantic operations. We discuss this finding in the context of the dual loop model and recent anatomical concepts.

Impact of COMT Val158Met-polymorphism on appetitive conditioning and amygdala/prefrontal effective connectivity.

Appetitive conditioning is an important mechanism for the development, maintenance, and treatment of psychiatric disorders like substance abuse. Therefore, it is important to identify genetic variations, which impact appetitive conditioning. It has been suggested that the Val(158) Met-polymorphism in the Catechol-O-Methyl-Transferase (COMT) is associated with the alteration of neural processes of appetitive conditioning due to the central role of the dopaminergic system in reward processing. However, no study has so far investigated the relationship between variations in the COMT Val(158) Met-polymorphism and appetitive conditioning. In this fMRI study, an appetitive conditioning paradigm was applied, in which one neutral stimulus (CS+) predicted appetitive stimuli (UCS) while a second neutral stimulus (CS-) was never paired with the UCS. As a main result, we observed a significant association between the COMT Val(158) Met-genotype and appetitive conditioning: skin conductance responses (SCRs) revealed a significant difference between CS+ and CS- in Val/Val-allele carriers but not in the other genotype groups. Val/Val-allele carriers showed increased hemodynamic responses in the amygdala compared with the Met/Met-allele group in the contrast CS+ > CS-. In addition, psychophysiological-interaction analysis revealed increased effective amygdala/ventromedial prefrontal cortex connectivity in Met/Met-allele carriers. The increased amygdala activity points to facilitated appetitive conditioning in Val/Val-allele carriers while the amygdala/prefrontal connectivity results could be regarded as a marker for altered emotion regulation during conditioning, which potentially impacts appetitive learning sensitivity. The SCRs finding indicates a stronger conditioned response in the Val/Val-allele group and dovetails with the neural differences between the groups. These findings contribute to the current research on COMT in emotional processing.

Parallel imaging with phase scrambling.

PURPOSE: Most existing methods for accelerated parallel imaging in MRI require additional data, which are used to derive information about the sensitivity profile of each radiofrequency (RF) channel. In this work, a method is presented to avoid the acquisition of separate coil calibration data for accelerated Cartesian trajectories. METHODS: Quadratic phase is imparted to the image to spread the signals in k-space (aka phase scrambling). By rewriting the Fourier transform as a convolution operation, a window can be introduced to the convolved chirp function, allowing a low-resolution image to be reconstructed from phase-scrambled data without prominent aliasing. This image (for each RF channel) can be used to derive coil sensitivities to drive existing parallel imaging techniques. As a proof of concept, the quadratic phase was applied by introducing an offset to the x(2) - y(2) shim and the data were reconstructed using adapted versions of the image space-based sensitivity encoding and GeneRalized Autocalibrating Partially Parallel Acquisitions algorithms. RESULTS: The method is demonstrated in a phantom (1 × 2, 1 × 3, and 2 × 2 acceleration) and in vivo (2 × 2 acceleration) using a 3D gradient echo acquisition. CONCLUSION: Phase scrambling can be used to perform parallel imaging acceleration without acquisition of separate coil calibration data, demonstrated here for a 3D-Cartesian trajectory. Further research is required to prove the applicability to other 2D and 3D sampling schemes.

Reproduction of motion artifacts for performance analysis of prospective motion correction in MRI.

PURPOSE: Despite numerous publications describing the ability of prospective motion correction to improve image quality in magnetic resonance imaging of the brain, a reliable approach to assess this improvement is still missing. A method that accurately reproduces motion artifacts correctable with prospective motion correction is developed, and enables the quantification of the improvements achieved. METHODS: A software interface was developed to simulate rigid body motion by changing the scanning coordinate system relative to the object. Thus, tracking data recorded during a patient scan can be used to reproduce the prevented motion artifacts on a volunteer or a phantom. The influence of physiological motion on image quality was investigated by filtering these data. Finally, the method was used to reproduce and quantify the motion artifacts prevented in a patient scan. RESULTS: The accuracy of the method was tested in phantom experiments and in vivo. The calculated quality factor, as well as a visual inspection of the reproduced artifacts shows a good correspondence to the original. CONCLUSION: Precise reproduction of motion artifacts assists qualification of prospective motion correction strategies. The presented method provides an important tool to investigate the effects of rigid body motion on a wide range of sequences, and to quantify the improvement in image quality through prospective motion correction.

Interplay between sexual excitation and inhibition: impact on sexual function and neural correlates of erotic stimulus processing in women.

Background: As outlined by the dual control model (DCM), individual differences in the regulation of sexual arousal following sexual stimulation depend on two distinct neurophysiological processes: sexual excitation (SE) and sexual inhibition (SI). Although associations with sexual function, behavior, and cue processing have been demonstrated in previous research, underlying neural correlates remain insufficiently explored. Moreover, interactive effects of SE/SI as proposed by the DCM, as well as factors impacting SE/SI properties, such as the use of oral contraceptives (OCs), have not received adequate attention in existing research. Methods: 90 healthy, sexually active women (n = 51 using OCs, n = 39 naturally cycling) completed an Emotional-Picture-Stroop-Paradigm (EPSP) while a 64-channel EEG was recorded. LPP amplitudes toward erotic and neutral stimuli were consecutively computed as a marker of motivational salience and approach motivation. Additionally, women provided self-reports of SE/SI and sexual function. Moderation analyses were performed to assess interactive effects of SE/SI in predicting LPP amplitudes and sexual function. Results: Sexual function was negatively associated with SI levels but unrelated to SE. Higher SI was associated with reduced LPP amplitudes in response to erotic stimuli. This negative association was, however, attenuated for women high in SE, suggesting interactive effects of SE/SI. Furthermore, women using OCs reported lower SE compared to naturally cycling women. Conclusion: The observed findings provide additional psychophysiological evidence supporting the DCM and underscore the relevance of interactive SE/SI effects in stimulus processing and approach motivation. They also highlight the possible impact of OCs on psychosexual variables that warrants further research.

The 5-HTTLPR polymorphism is associated with altered hemodynamic responses during appetitive conditioning.

BACKGROUND: Current models suggest that a variation in the promoter region of the serotonin transporter gene (5-HTTLPR) is associated with altered amygdala reactivity not only towards negative but also towards positive stimuli, which has been neglected in the past. This association may possibly convey an elevated vulnerability for psychopathology like abuse, craving, and relapses. Since appetitive conditioning is a crucial mechanism in the pathogenesis of these psychiatric disorders, the identification of specific factors contributing to interindividual variation is important. METHODS: In the present study (N = 86), an appetitive conditioning paradigm was conducted, in which a neutral stimulus (CS+) was associated with appetitive stimuli, while a second stimulus (CS-) predicted their absence. Subjects were genotyped according to the 5-HTTLPR genotype. RESULTS: As the main result, we report a significant association between the 5-HTTLPR genotype and hemodynamic responses. Individuals with the s-allele displayed elevated conditioned bilateral amygdala activity in contrast to l/l-allele carriers. Further, increased hemodynamic responses in s-allele carriers were also found in the extended emotional network including the orbitofrontal cortex, the thalamus, and the ventral striatum. CONCLUSION: The present findings indicate an association of the 5-HTTLPR and altered conditioned responses in appetitive conditioning. Further, the findings contribute to the ongoing debate on 5-HTTLPR dependent hemodynamic response patterns by emphasizing that s-allele carriers are not exclusively biased towards fearful, but also towards positive stimuli. In conclusion, our results imply that s-allele carriers might be better described as hyper-reactive towards salient stimuli, which may convey vulnerability for the development of psychiatric disorders.

Accelerated point spread function mapping using signal modeling for accurate echo-planar imaging geometric distortion correction.

Echo-planar imaging is a fast and commonly used magnetic resonance imaging technique with applications in diffusion weighted and functional MRI. Fast data acquisition in echo-planar imaging is accomplished by the extended readout, which also introduces sensitivity to off-resonance effects such as amplitude of static (polarizing) field inhomogeneities and eddy-currents. These off-resonance effects produce geometric distortions in the corresponding echo-planar images. To correct for these distortions, an acceleration of point spread function (PSF) acquisition using a special sampling pattern is presented in this work. The proposed technique allows for reliable and fully automated distortion correction of echo-planar images at a field strength of 3 T. Additionally, a new approach to visualize and determine the distortions in a hybrid (x, y, kPSF) three-dimensional space is proposed. The accuracy and robustness of the proposed technique is demonstrated in phantom and in vivo experiments. The accuracy of the presented method here is compared to previous techniques for echo-planar imaging distortion correction such as PLACE.

Segmental myocardial velocities in dilated cardiomyopathy with and without left bundle branch block.

PURPOSE: To quantify three-directional left ventricular (LV) myocardial velocities and intraventricular synchrony in dilated cardiomyopathy (DCM) with and without left bundle branch block (LBBB) using MR tissue phase mapping (TPM). MATERIALS AND METHODS: Regional velocities were assessed by TPM (spatial/temporal resolution = 1.3 × 1.3 mm(2) × 8 mm/14 ms) in DCM patients with (n = 12) and without LBBB (n = 7) compared with age-matched volunteers (n = 20). For the evaluation the AHA 16-segment and an extended LV visualization model was used. RESULTS: Radial velocities in DCM patients were reduced in 75% (systole) and in 94% (diastole) (P = 0.0001 - P = 0.0360), long-axis velocities in 31% (systole) and in 75% (diastole) of the 16 segments compared with controls (P = 0.0001 - P = 0.0310). LBBB resulted in inferolaterally delayed diastolic long-axis velocities (P = 0.0012 - P = 0.0464) and shortened TTP for septal systolic radial velocities (P = 0.0002). Intra-ventricular radial systolic TTP differed up to 150 ms between segments in patients with LBBB (89 ms without LBBB, 34 ms in volunteers) reflecting an increased dyssynchrony. LV twist was altered in all patients with reduced and delayed systolic and diastolic peak velocities. CONCLUSION: TPM identified previously not described alterations of the spatial distribution and timing of all myocardial velocities in patients with DCM and LBBB. This may help to optimize therapy management in future.

Prospective motion correction with continuous gradient updates in diffusion weighted imaging.

Despite the existence of numerous motion correction methods, head motion during MRI continues to be a major source of artifacts and can greatly reduce image quality. This applies particularly to diffusion weighted imaging, where strong gradients are applied during long encoding periods. These are necessary to encode microscopic movements. However, they also make the technique highly sensitive to bulk motion. In this work, we present a prospective motion correction method where all applied gradients are adjusted continuously to compensate for changes of the object position and ensure the desired phase evolution in the image coordinate frame. Additionally, in phantom experiments this new technique is used to reproduce motion artifacts with high accuracy by changing the position of the imaging frame relative to the measured object. In vivo measurements demonstrate the validity of the new correction method.

Reconstruction of MRI data encoded by multiple nonbijective curvilinear magnetic fields.

Parallel imaging technique using localized gradients (PatLoc) uses the combination of surface gradient coils generating nonbijective curvilinear magnetic fields for spatial encoding. PatLoc imaging using one pair of multipolar spatial encoding magnetic fields (SEMs) has two major caveats: (1) The direct inversion of the encoding matrix requires exact determination of multiple locations which are ambiguously encoded by the SEMs. (2) Reconstructed images have a prominent loss of spatial resolution at the center of field-of-view using a symmetric coil array for signal detection. This study shows that a PatLoc system actually has a higher degree of freedom in spatial encoding to mitigate the two challenges mentioned above. Specifically, a PatLoc system can generate not only multipolar but also linear SEMs, which can be used to reduce the loss of spatial resolution at the field-of-view center. Here, we present an efficient and generalized image reconstruction method for PatLoc imaging using multiple SEMs without explicitly identifying the locations where SEM encoding is not unique. Reconstructions using simulations and empirical experimental data are compared with those using conventional linear gradients to demonstrate that the general combination of SEMs can improve image reconstructions.

In vivo noninvasive 4D pressure difference mapping in the human aorta: phantom comparison and application in healthy volunteers and patients.

In this work, we present a systematic phantom comparison and clinical application of noninvasive pressure difference mapping in the human aorta based on time-resolved 3D phase contrast data. Relative pressure differences were calculated based on integration and iterative refinement of pressure gradients derived from MR-based three-directional velocity vector fields (flow-sensitive 4D MRI with spatial/temporal resolution ∼ 2.1 mm(3)/40 ms) using the Navier-Stokes equation. After in vitro study using a stenosis phantom, time-resolved 3D pressure gradients were systematically evaluated in the thoracic aorta in a group of 12 healthy subjects and 6 patients after repair for aortic coarctation. Results from the phantom study showed good agreement with expected values and standard methods (Bernoulli). Data of healthy subjects showed good intersubject consistency and good agreement with the literature. In patients, pressure waveforms showed elevated peak values. Pressure gradients across the stenosis were compared with reference measurements from Doppler ultrasound. The MRI findings demonstrated a significant correlation (r = 0.96, P < 0.05) but moderate underestimation (14.7% ± 15.5%) compared with ultrasound when the maximum pressure difference for all possible paths connecting proximal and distal locations of the stenosis were used. This study demonstrates the potential of the applied approach to derive additional quantitative information such as pressure gradients from time-resolved 3D phase contrast MRI.

Volumetric analysis of MRI data monitoring the treatment of polycystic kidney disease in a mouse model.

OBJECT: The human condition autosomal dominant polycystic kidney disease (ADPKD) is characterized by the growth of cysts in the kidneys that increase renal volume and lead to kidney failure. Mice studies are performed for treatment development monitored with imaging. The analysis of the imaging data is typically manual, which is costly and potentially biased. This paper presents a reliable and reproducible method for the automated segmentation of polycystic mouse kidneys. MATERIALS AND METHODS: Treated and untreated mice have been imaged longitudinally with high field anatomic MRI. The region of interest (ROI) of the kidneys in the images is identified and restored for artifacts. It is then analyzed statistically and geometric models are estimated for each kidney. The statistical and geometric information are provided to the graph cuts algorithm that delineates the kidneys. RESULTS: The accuracy of the analysis has been demonstrated by showing consistency with results obtained with previous methods as well as by comparing with manual segmentations. CONCLUSION: The method developed can accelerate and improve the accuracy of kidney volumetry in preclinical treatment trials for ADPKD.