Fast Imaging Technology Research Articles

Drosophila Heart as a Model for Cardiac Development and Diseases.

The Drosophila heart, also referred to as the dorsal vessel, pumps the insect blood, the hemolymph. The bilateral heart primordia develop from the most dorsally located mesodermal cells, migrate coordinately, and fuse to form the cardiac tube. Though much simpler, the fruit fly heart displays several developmental and functional similarities to the vertebrate heart and, as we discuss here, represents an attractive model system for dissecting mechanisms of cardiac aging and heart failure and identifying genes causing congenital heart diseases. Fast imaging technologies allow for the characterization of heartbeat parameters in the adult fly and there is growing evidence that cardiac dysfunction in human diseases could be reproduced and analyzed in Drosophila, as discussed here for heart defects associated with the myotonic dystrophy type 1. Overall, the power of genetics and unsuspected conservation of genes and pathways puts Drosophila at the heart of fundamental and applied cardiac research.

Epicardial Conduction Speed, Electrogram Abnormality, and ComputedTomography Attenuation Associations in Arrhythmogenic RightVentricular Cardiomyopathy.

This study sought to evaluate the association between contrast-enhanced multidetector computed tomography (CE-MDCT) attenuation and local epicardial conduction speed (ECS) and electrographic abnormalities in patients with arrhythmogenic right ventricular cardiomyopathy (ARVC) and ventricular tachycardia (VT). CE-MDCT is a widely available and fast imaging technology with high spatial resolution that is less prone to defibrillator generator-related safety issues and image artifacts. However, the association between hypoattenuation on MDCT and VT substrates in ARVC remains unknown. Patients with ARVC who underwent CE-MDCT followed by endocardial (n=30) and epicardial (n=21) electroanatomical mapping (EAM) and VT ablation were prospectively enrolled. Right ventricular (RV) mid-myocardial attenuation was calculated from 3-dimensional MDCT images and registered to EAM. Local ECS was calculated by averaging the ECS between each point and 5 adjacent points with concordant wave front direction. A total of 17,311 epicardial and 5,204 endocardial points were included. In multivariable regression analysis clustered by patient, RV myocardial attenuation was associated with epicardial bipolar voltage amplitude (2.5% decrease in amplitude per 10 HU decrease in attenuation; p<0.001), with endocardial unipolar voltage amplitude (0.9% decrease in amplitude per 10 HU decrease in attenuation; p<0.001), and with ECS (0.4% decrease in ECS per 10 HU decrease in attenuation; p=0.001). CE-MDCT attenuation distribution is associated with regional ECS and electrographic amplitude in ARVC. Regions with low attenuation likely reflect fibro-fatty involvement in the RV and may serve as important VT substrates in patients with ARVC who are undergoing VT ablation.

Simultaneous multi-slice (SMS) acquisition enhances the sensitivity of hemodynamic mapping using gas challenges.

Hemodynamic mapping using gas inhalation has received increasing interest in recent years. Cerebrovascular reactivity (CVR), which reflects the ability of the brain vasculature to dilate in response to a vasoactive stimulus, can be measured by CO2 inhalation with continuous acquisition of blood oxygen level-dependent (BOLD) magnetic resonance images. Cerebral blood volume (CBV) can be measured by O2 inhalation. These hemodynamic mapping methods are appealing because of their absence of gadolinium contrast agent, their ability to assess both baseline perfusion and vascular reserve, and their utility in calibrating the functional magnetic resonance imaging (fMRI) signal. However, like other functional and physiological indices, a major drawback of these measurements is their poor sensitivity and reliability. Simultaneous multi-slice echo planar imaging (SMS EPI) is a fast imaging technology that allows the excitation and acquisition of multiple two-dimensional slices simultaneously, and has been shown to enhance the sensitivity of several MRI applications. To our knowledge, the benefit of SMS in gas inhalation imaging has not been investigated. In this work, we compared the sensitivity of CO2 and O2 inhalation data collected using SMS factor 2 (SMS2) and SMS factor 3 (SMS3) with those collected using conventional EPI (SMS1). We showed that the sensitivity of SMS scans was significantly (p=0.01) higher than that of conventional EPI, although no difference was found between SMS2 and SMS3 (p=0.3). On a voxel-wise level, approximately 20-30% of voxels in the brain showed a significant enhancement in sensitivity when using SMS compared with conventional EPI, with other voxels showing an increase, but not reaching statistical significance. When using SMS, the scan duration can be reduced by half, whilst maintaining the sensitivity of conventional EPI. The availability of a sensitive acquisition technique can further enhance the potential of gas inhalation MRI in clinical applications.

Advanced MR Imaging Technologies in Fetuses.

Fetal Magnetic Resonance Imaging (MRI) on clinical scanners has increasingly been realized as a powerful imaging tool and applied for studying the brain abnormalities and the potential of neurodevelopmental disabilities in vivo. The primarily used multi-echo fast imaging sequences reduce the motion artifacts with a tradeoff of image Signal-to-Noise Ratio (SNR) and resolution. In Radio Frequency (RF) hardware for MR signal excitation and reception, there are lack of dedicated RF coils for fetal imaging providing optimized performance in acquisition and safety. There is an urgent demand for novel hardware and fast imaging technology developments to overcome motion artifacts and improve sensitivity and safety. Recent studies have demonstrated that dedicated fetal RF transceiver arrays can improve the SNR, image coverage, and safety. In addition, emerging fast imaging technologies such as parallel imaging and compressed sensing would be advantageous in improving imaging speed and thus reducing motion artifacts in fetal imaging.

Sodium imaging of the heart at 7T: design, evaluation and application of a four-channel transmit/receive surface coil array

Background Insight of physiological processes and cellular metabolism makes 23Na-MRI conceptually appealing as non-invasive imaging discipline. Several studies report the applicability of 23Na-MRI for the detection and assessment of acute and chronic heart disease due to increased sodium concentration after myocardial infarctions. Bi-exponential decay of the signal and a low SNR compared to 1H-MRI makes 23Na-MRI unattractive for clinical use. With a high SNR and fast imaging technologies ultrahigh field MRI brings 23Na-MRI back into focus, asking for dedicated radiofrequency (RF) technology.

Voltage effects on the nanoelectrospray characteristics in fully voltage-controlled atomisation of gold nanocolloids

The voltage effects on fully voltage-controlled nanoelectrospraying of aqueous gold nanocolloids were investigated. In the nanoelectrospray using 30 μm nozzle, with an increasing of voltage two stable spray regimes of pulsating and cone-jet mode were clearly observed by a combination of current measurement and fast imaging technology. In this nanoelectrospray uniquely determined by the electrical field voltage the current–voltage characteristics were analysed and evaluated based on an equivalent circuit method. At high field in cone-jet regime all the equivalent resistances derived by fitting appear close to a value of 0.53 ± 0.03 GΩ, showing independence to the conductivity of the nanocolloids. In low field pulsating regime a high pulsation frequency up to 100 kHz with relatively stable current pulse was exhibited in all the gold nanocolloids. A linear relationship between the DC components in the pulsating current and the voltage was found and the DC equivalent resistance obtained from the fitting varies between 0.90 and 1.47 GΩ. A strong correlation between the pulsating properties and the conductivity of the colloids was identified.

Evaluation of a new self-developing instant film for imaging and dosimetry

Radiation sensitive films are standard dosimetric tools in radiation therapy. Films are used for machine quality assurance (QA) and treatment planning software evaluation. With the advent of intensity modulated radiation therapy (IMRT), simple and fast imaging technology is needed for patient-specific verification of radiation fields. Conventional radiographic films are often used. Radiochromic films, e.g. Gafchromic films, were recently introduced to the market. But these films have some disadvantages. JP Laboratories have developed a prototype radiochromic film, called SIFID (self-developing, instant film for imaging and dosimetry) with superior performance such that SIFID is unaffected by ambient light for months, stable up to 90 degrees C and can be archived. SIFID is made of polymerisable diacetylene. The film develops blue colour instantly upon absorbing radiation. We evaluated the film for radiation therapy applications. Our preliminary data demonstrate its feasibility as a dosimetric tool for IMRT QA as well as for other applications.

Physiological foundations of temporal integration in the perception of speech

Speech understanding involves the integration and identification of acoustic cues that are distributed over multiple time scales. These range from the sub-millisecond intervals associated with spectral estimates, to the few-millisecond periods of the fundamental frequency (f0), to the tens of milliseconds spanning phonemic and syllabic segments, and the longer time scales involved in perceiving words and sentences. Much of what is known about the auditory representation of these cues comes from experimental studies in various animal species. Especially, well studied are the early stages of the cochlea and cochlear nucleus, and the later cortical stages (Sachs & Young, 1979; Young & Sachs, 1979; Young, 1997, Chap. 4; Clarey, Barone, & Imig, 1992; Calhoun & Schreiner, 1995; Shamma Versnel, & Kowalski, 1995; Kowalski, Depireux, & Shamma, 1996; deCharms, Blake, & Merzenich 1998). By contrast, the physiological underpinnings of the linguistic processes remain highly elusive despite extensive investigations employing a host of new human fast-imaging technologies and computational models over the last decade (Poeppel, 2001; Horwitz, Friston, & Taylor, 2000). These techniques do not yet have the resolution to give a clear insight into single units and the neural circuits and their responses and representations. Consequently, the review below concerns conceptions of auditory processes operating at the faster time scales found in the earlier auditory pathway where animal experimentation is possible. Furthermore, they are based on extrapolations from experiments that employ simpler stimuli than speech (such as tones and noise with various amplitude and frequency modulations), and hence the models discussed are not specific to speech perception. Temporal integration in the auditory system actually refers to integration of spectro-temporal features over several stages, giving rise to varied forms of spectro-temporal selectivity that have been deemed valuable for speech processing. One example is the selectivity to speed and direction of frequency-modulated (FM) tones that resemble formant transitions in speech (Nelken & ARTICLE IN PRESS