Ascending-descending aortic bypass surgery in aortic arch coarctation: four-dimensional magnetic resonance flow analysis.
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Aorta↗
Biomedical subjects
Jürgen Hennig
Publications and source records attributed to Jürgen Hennig.
Fast chemical shift mapping with multiecho balanced SSFP.
OBJECT: A method is proposed that provides spectroscopic images with high spatial resolution and moderate spectral resolution at very short total data acquisition times. MATERIALS AND METHODS: Balanced steady-state free precession (bSSFP, TrueFISP, FIESTA, b-FFE) is combined with a multiecho readout gradient and frequency-sensitive reconstruction such as Fourier reconstruction known from echo-planar spectroscopic imaging (EPSI) or matrix inversion. Balanced SSFP imaging requires short repetition times to minimize banding artefacts, thereby restricting the achievable frequency resolution. RESULTS: Two-dimensional (2D) high-resolution spectroscopic images were produced of three 1H resonances (water, acetone and fat) on phantoms and water/fat separation in vivo within 1-2 s. Additionally, fast 31P spectroscopic images were acquired from a phantom consisting of two resonances within 195 ms. CONCLUSION: Frequency-sensitive reconstruction of multiecho bSSFP data can provide spectroscopic images with high spatial and temporal resolution while the frequency resolution is moderate at around 100 Hz. The method can also separate more than three resonances, allowing for hetero-nuclei metabolite mapping, for example 13C and 31P.
Carbon Radioisotopes↗
Accelerated time-resolved 3D contrast-enhanced MR angiography at 3T: clinical experience in 31 patients.
PURPOSE: To evaluate whether time-resolved 3D MR-angiography at 3T with a net acceleration factor of eight is applicable in clinical routine and to evaluate whether good image quality and a low artifact level can be achieved with a temporal update rate that allows for additional information on pathologies. MATERIALS AND METHODS: Thirty-one consecutive patients underwent time-resolved 3D contrast-enhanced MR-angiography on a 3T system. Imaging consisted of accelerated 3D gradient echo sequences combining parallel imaging with an acceleration factor of four, partial Fourier acquisition along phase and slice encoding direction, and twofold temporal acceleration using view sharing. Data volumes representing the arterial and venous contrast phases were independently evaluated by two experienced radiologists by grading of image quality and artifact level on a 0-3 scale. RESULTS: Time-resolved MR-angiography was successfully performed in all subjects without the need for contrast agent bolus timing. Excellent arterial (average score = 2.65 +/- 0.32) and good venous (average score = 2.56 +/- 0.28) diagnostic image quality and little image degrading due to artifacts (average score = 2.20 +/- 0.16) were confirmed by both independent readers (agreement in 65.2% of all evaluations). In 14 patients vascular pathologies were identified in the arterial phases. In eight examinations temporal resolution and depiction of contrast agent dynamics provided additional information about pathology. DISCUSSION: Without the necessity for additional bolus timing, time-resolved 3D contrast-enhanced MR-angiography with imaging acceleration along both the spatial encoding direction and temporal domain revealed excellent diagnostic image quality in neurovascular and thoracic imaging. Despite the limited spatial resolution as compared to high-resolution imaging of the carotid artery bifurcation, the results demonstrate the applicability of contrast-enhanced MR-angiography in thoracic and abdominal MRA as well as cervical imaging with a temporal update rate allowing for additional information on pathologies. Future studies may include an evaluation of optimal trade-offs between spatial and temporal resolution, different acceleration factors and a comparison to the gold-standard for accuracy.
Adolescent↗
Imaging gene-substance interactions: the effect of the DRD2 TaqIA polymorphism and the dopamine agonist bromocriptine on the brain activation during the anticipation of reward.
Dopamine is known as the main neurotransmitter modulating the activation of the reward system of the brain. The DRD2 TaqIA polymorphism is associated with dopamine D2 receptor density which plays an important role in the context of reward. Persons carrying an A1 allele have a lower D2 receptor density and a higher risk to show substance abuse. The present study was designed to investigate the influence of the DRD2 TaqIA polymorphism and the selective D2 receptor agonist bromociptine on the activation of the reward system by means of functional magnetic resonance imaging (fMRI). In a double-blind crossover study with 24 participants we found an increase of reward system activation from placebo to bromocriptine only in subjects carrying the A1 allele. Furthermore, only A1 carrier showed an increase of performance under bromocriptine. The results are interpreted as reflecting a specific sensitivity for dopamine agonists in persons carrying an A1 allele and may complement actual data and theories of the development of addiction disorders postulating a higher genetic risk for substance abuse in carrier of the A1 allele.
Adolescent↗
Functional neuroimaging of emotional learning and autonomic reactions.
This article provides a selective overview of the functional neuroimaging literature with an emphasis on emotional activation processes. Emotions are fast and flexible response systems that provide basic tendencies for adaptive action. From the range of involved component functions, we first discuss selected automatic mechanisms that control basic adaptational changes. Second, we illustrate how neuroimaging work has contributed to the mapping of the network components associated with basic emotion families (fear, anger, disgust, happiness), and secondary dimensional concepts that organise the meaning space for subjective experience and verbal labels (emotional valence, activity/intensity, approach/withdrawal, etc.). Third, results and methodological difficulties are discussed in view of own neuroimaging experiments that investigated the component functions involved in emotional learning. The amygdala, prefrontal cortex, and striatum form a network of reciprocal connections that show topographically distinct patterns of activity as a correlate of up and down regulation processes during an emotional episode. Emotional modulations of other brain systems have attracted recent research interests. Emotional neuroimaging calls for more representative designs that highlight the modulatory influences of regulation strategies and socio-cultural factors responsible for inhibitory control and extinction. We conclude by emphasising the relevance of the temporal process dynamics of emotional activations that may provide improved prediction of individual differences in emotionality.
Animals↗
Visualization of tissue velocity data from cardiac wall motion measurements with myocardial fiber tracking: principles and implications for cardiac fiber structures.
OBJECTIVE: The spatial arrangement of myocardial fiber structure affects the mechanical and electrical properties of the heart. Therefore, information on the structure and dynamics of the orientation of the muscle fibers in the human heart might provide significant insight into principles of the mechanics of normal ventricular contraction and electrical propagation and may subsequently aid pre- and postsurgical evaluation of patients. Fiber orientation is inherently linked to cardiac wall motion, which can be measured with phase contrast magnetic resonance imaging (MRI), also termed tissue phase mapping (TPM). METHODS: This study provides initial results of the visualization of velocity data with fiber tracking algorithms and discusses implications for the fiber orientations. In order to generate datasets with sufficient volume coverage and resolution TPM measurements with three-dimensional (3D) velocity encoding were executed during breath-hold periods and free breathing. Subsequent postprocessing evaluation with a tracking algorithm for acceleration fields derived from the velocity data was performed. RESULTS: Myocardial acceleration tracking illustrated the dynamics of fiber structure during four different phases of left ventricular performance, that include isovolumetric contraction (IVC), mid-systole, isovolumetric relaxation (IVR), and mid-diastole. Exact reconstruction of the myocardial fiber structure from velocity data requires mathematical modeling of spatiotemporal evolution of the velocity fields. CONCLUSIONS: 'Acceleration fibers' were reconstructed at these four phases during the cardiac cycle, and these findings may become (a) surrogate parameters in the normal ventricle, (b) baseline markers for subsequent clinical studies of abnormal hearts with altered architecture, and (c) may help to explain and illustrate functional features of cardiac performance in structural models like the helical ventricular myocardial band.
Algorithms↗
Investigating myocardial motion by MRI using tissue phase mapping.
OBJECTIVE: Velocity-encoded phase contrast magnetic resonance imaging (MRI) provides a tool to quantify regional myocardial wall motion of the entire heart. It allows the acquisition of three-directional velocity vector fields with high spatial resolution that reflect the temporal evolution of myocardial velocities over the cardiac cycle. In contrast to other imaging modalities such as echocardiography left ventricular performance can be assessed without limited anatomical or functional coverage. METHODS: Compared to other techniques that quantify local myocardial contractility (e.g. implanted ultrasonic crystals) by means of regional displacement, phase contrast MRI provides information about local and global left ventricular velocities (i.e. motion) by utilizing the intrinsic motion sensitivity of MRI. The resultant motion components of contraction, expansion, rotation, lengthening, and shortening of the left ventricle are described in high spatial and temporal detail. Phase contrast measurements were performed in 12 healthy volunteers with a respiratory-gated technique in order to achieve a high temporal resolution of 13.8ms to demonstrate the detailed assessment of global and regional myocardial motion. RESULTS: Data revealed details in left ventricular motion patterns that were previously not seen in phase contrast measurements and are only known from echocardiography. For all volunteers, characteristic myocardial motion patterns and locally different radial (i.e. contraction and expansion), rotational (i.e. twisting and untwisting) and longitudinal (i.e. lengthening and shortening) motion components could be detected with high accuracy. CONCLUSIONS: The phase contrast MRI technique for high temporal resolution velocity mapping is therefore very promising for the investigation and better understanding of the myocardial motion in normal subjects and patients with disturbed left ventricular performance and may validate further testing of different models of cardiac structure.
Heart↗
Images in cardiovascular medicine. Time-resolved 3-dimensional magnetic resonance velocity mapping at 3 T reveals drastic changes in flow patterns in a partially thrombosed aortic arch.
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Adult↗
Identification of first candidate genes for creativity: a pilot study.
Studies from behavioral genetics have demonstrated the high heritability of intelligence. However, the endeavor to detect the genes forming the molecular basis of intelligence has been rather unsuccessful until now. Pharmacological studies have demonstrated the influence of the dopaminergic (DA) and the serotonergic (5-HT) system on subcomponents of cognitive functioning, and first studies from molecular genetics have demonstrated that genes related to the DA metabolism are associated with mental abilities. However, candidate genes for creativity have not been identified so far. Therefore, the influence of the catechol-O-methyltransferase (locus: COMT VAL158MET) gene and the dopamine D2 receptor gene (locus: DRD2 TAQ IA) on creativity was tested in addition to a serotonergic gene, TPH1 (locus: TPH-A779C), in a sample of N = 92 healthy Caucasian subjects while controlling for intelligence. Results showed that the DRD2 gene and the TPH gene were both associated with total creativity, explaining 9% of the variance, while COMT was not related to creativity at all. With respect to the subcomponents, the A1+ allele of DRD2 was related to higher verbal creativity as compared to the A1- allele, and carriers of the A allele of TPH1 showed significantly higher scores in figural and in numeric creativity, indicating that the two gene loci discriminate between higher cortical functions according to the organization of cognitive functions in the respective hemispheres.
Adolescent↗
High resolution 3T MRI for the assessment of cervical and superficial cranial arteries in giant cell arteritis.
A new high-resolution MR protocol for the combined assessment of neurovascular arterial anatomy and subsequent evaluation of inflammatory disease in cranial vessels walls has been investigated. First-pass contrast-enhanced MR angiography (CE-MRA) in combination with parallel imaging at high field permits the depiction of the neurovascular geometry with large coverage, including the aortic arch, supraaortic vessels, and almost the entire head, with high, submillimeter detail. Utilizing the remaining contrast agent, postcontrast T(1)-weighted turbo spin-echo (TSE) imaging was used to generate late enhancement images of the vessel walls to assess the morphology and potential inflammatory changes in cranial arteries with high in-plane (195 x 260 microm(2)) spatial resolution. As a result, a combined analysis of neurovascular arterial anatomy as well as cranial vessel wall inflammations could be achieved in less than 45 minutes in all studies. The feasibility and clinical value for the diagnosis of rheumatologic diseases and simultaneous arteriosclerotic involvement was demonstrated in seven patients with suspected giant cell arteritis (GCA). Excellent CE-MRA image quality could be achieved and even vascular geometry of small superficial cranial arteries could be successfully visualized using single dose (0.1 mmol/kg) contrast agent administration and a dedicated phased-array head and neck coil at 3T.
Aged↗
Detailed analysis of myocardial motion in volunteers and patients using high-temporal-resolution MR tissue phase mapping.
PURPOSE: To detect and investigate details in left ventricular (LV) motion patterns with a temporal resolution comparable to that of echocardiography. MATERIAL AND METHODS: To assess global and regional myocardial motion in high temporal detail, respiratory-gated MR phase-contrast measurements with three-directional velocity encoding (venc) were performed in 12 healthy volunteers and two patients with LV hypertrophy in basal, midventricular, and apical locations of the LV with a temporal resolution of 13.8 msec. RESULTS: The volunteer data revealed details in LV motion patterns that were known only from echocardiography. For all volunteers, characteristic myocardial motion patterns, such as triphasic global diastolic expansion, could be detected with high accuracy. One volunteer underwent an additional echocardiographic measurement in order to corroborate the complex motion features as measured by MRI. Patient examinations revealed substantial changes in diastolic function compared to motion patterns in healthy volunteers. CONCLUSION: The proposed high-temporal-resolution velocity-mapping technique provides previously undetectable information on LV performance, and is highly promising for the detection of local and global motion abnormalities in patients with disturbed LV performance, such as diastolic dysfunction.
Adult↗
2D axial moving table acquisitions with dynamic slice adaptation.
A method for axial multi-slice imaging during continuous table motion has been developed and implemented on a clinical scanner. Multiple axial slice packages are acquired consecutively and combined to cover an extended longitudinal FOV. To account for the table motion during the acquisition, the RF pulse frequencies are continuously updated according to the actual table velocity and slice position. Different strategies for the spatial-temporal acquisition sequence with extended FOV are proposed. They cover different regimes of scan requirements regarding table velocity, used scan range, and slice resolution. The method is easy to implement and compatible with most kinds of sequences. The robustness of the proposed approach has been tested in phantom studies and healthy volunteers using T1-, T2-, and STIR-weighted multi-slice techniques that are based on gradient and turbo spin echo sequences and compared to a stationary approach usually used in clinical routine. The method provides artifact free gradient echo based images during continuous table motion, while for turbo spin echo sequences limitations in choosing table translations occur due to gradient non-linearity effects.
Algorithms↗
Navigator gated high temporal resolution tissue phase mapping of myocardial motion.
Data acquisition for phase contrast velocity mapping of myocardial motion is typically based on multiple breath-held 2D measurements with limited acquisition duration and consequently relatively poor temporal resolution. In order to overcome the limitations of breath-hold acquisitions, an improved navigator-guided technique was implemented based on 2 navigator signals within each cardiac cycle in combination with paired acceptance and rejection criteria of successive navigator signals. Respiratory gated phase contrast measurements with 3-directional velocity encoding were performed in 12 healthy volunteers in basal, midventricular, and apical locations of the left ventricle during free breathing with a temporal resolution of 13.8 ms. Results were compared to standard breath-hold measurements with a temporal resolution of 69 ms. Data from the high temporal resolution study revealed details in left ventricular motion patterns that were previously not seen in phase contrast measurements and are only known from echocardiography. The proposed navigator gated technique for high temporal resolution velocity mapping is, therefore, highly promising for the detection of local and global motion abnormalities in patients with disturbed left ventricular performance, such as diastolic dysfunction.
Adult↗
Multicontrast sequences with continuous table motion: a novel acquisition technique for extended field of view imaging.
A novel acquisition technique called multicontrast imaging is presented that provides multiple datasets of different image contrasts covering an extended field of view within one measurement procedure. The technique uses a continuously moving table and is based on the repetitive acquisition of axial volume sections while the patient moves through the scanner once. To compensate for the table motion during the measurement, adaptive slice shifting is applied. Multicontrast imaging is designed to combine the comfort of a moving table examination with the high time efficiency of a multitask protocol and can be used for generating differences in both contrast and spatial parameters of the acquired data. The technique and its properties are demonstrated on healthy human volunteers.
Humans↗
T2-weighted balanced SSFP imaging (T2-TIDE) using variable flip angles.
A new technique for acquiring T2-weighted, balanced steady-state free precession (b-SSFP) images is presented. Based on the recently proposed transition into driven equilibrium (TIDE) method, T2-TIDE uses a special flip angle scheme to achieve T2-weighted signal decay during the transient phase. In combination with half-Fourier image acquisition, T2-weighted images can be obtained using T2-TIDE. Numerical simulations were performed to analyze the signal behavior of T2-TIDE in comparison with TSE and b-SSFP. The results indicate identical signal evolution of T2-TIDE and TSE during the transient phase. T2-TIDE was used in phantom experiments, and quantitative ROI analysis shows a linear relationship between TSE and T2-TIDE SNR values. T2-TIDE was also applied to abdominal and head imaging on healthy volunteers. The resulting images were analyzed quantitatively and compared with standard T2-weighted and standard b-SSFP methods. T2-TIDE images clearly revealed T2 contrast and less blurring compared to T2-HASTE images. In combination with a magnetization preparation technique, STIR-weighted images were obtained. T2-TIDE is a robust technique for acquiring T2-weighted images while exploiting the advantages of b-SSFP imaging, such as high signal-to-noise ratio (SNR) and short TRs.
Brain↗
Intrinsic fat suppression in TIDE balanced steady-state free precession imaging.
A novel fat-suppressed balanced steady-state free precession (b-SSFP) imaging method based on the transition into driven equilibrium (TIDE) sequence with variable flip angles is presented. The new method, called fat-saturated (FS)-TIDE, exploits the special behavior of TIDE signals from off-resonance spins during the flip angle ramp. As shown by simulations and experimental data, the TIDE signal evolution for off-resonant isochromats during the transition from turbo spin-echo (TSE)-like behavior to the true fast imaging with steady precession (TrueFISP) mode undergoes a zero crossing. The resulting signal notch for off-resonant spins is then used for fat suppression. The efficiency of FS-TIDE is demonstrated in phantoms and healthy volunteers on a 1.5T system. The resulting images are compared with standard TrueFISP data with and without fat suppression. It is demonstrated that FS-TIDE provides a fast and stable means for homogenous fat suppression in abdominal imaging while maintaining balanced SSFP-like image contrast and signal-to-noise ratio (SNR). The scan time of FS-TIDE is not increased compared to normal TrueFISP imaging without fat suppression and identical k-space trajectories. Because of the intrinsic fat suppression, no additional preparation is needed. Possible repetition times (TRs) are not firmly limited to special values and are nearly arbitrary.
Adipose Tissue↗
Advantages and limitations of prospective head motion compensation for MRI using an optical motion tracking device.
RATIONALE AND OBJECTIVES: Subject motion appears to be a limiting factor in numerous magnetic resonance (MR) imaging (MRI) applications. In particular, head tremor, which often accompanies stroke, may render certain high-resolution two- (2D) and three-dimensional (3D) techniques inapplicable. The reason for that is head movement during acquisition. The study objective is to achieve a method able to compensate for complete motion during data acquisition. The method should be usable for every sequence and easily implemented on different MR scanners. MATERIALS AND METHODS: The possibility of interfacing the MR scanner with an external optical motion-tracking system capable of determining the object's position with submillimeter accuracy and an update rate of 60 Hz is shown. Movement information on the object position (head) is used to compensate for motion in real time by updating the field of view (FOV) by recalculating the gradients and radiofrequency parameter of the MR scanner during acquisition of k-space data, based on tracking data. RESULTS: Results of rotation phantom, in vivo experiments, and implementation of three different MRI sequences, 2D spin echo, 3D gradient echo, and echo planar imaging, are presented. Finally, the proposed method is compared with the prospective motion correction software available on the scanner software. CONCLUSION: A prospective motion correction method that works in real time only by updating the FOV of the MR scanner is presented. Results show the feasibility of using an external optical motion-tracking system to compensate for strong and fast subject motion during acquisition.
Algorithms↗
Rapid vessel prototyping: vascular modeling using 3t magnetic resonance angiography and rapid prototyping technology.
OBJECT: Conversion of thoracic aortic vasculature as measured by Magnetic Resonance Imaging into a real physical replica. MATERIALS AND METHODS: Several procedural steps including data acquisition with contrast enhanced MR Angiography at 3T, data visualization and 3D computer model generation, as well as rapid prototyping were used to construct an in-vitro model of the vessel geometry. RESULTS: A rapid vessel prototyping process was implemented and used to convert complex vascular geometry of the entire thoracic aorta and major branching arteries into a real physical replica with large anatomical coverage and high spatial resolution. CONCLUSION: Rapid vessel prototyping permits the creation of a concrete solid replica of a patient's vascular anatomy.
Aorta, Thoracic↗