Effective Temporal Resolution Research Articles

Two-Dimensional Strain Imaging to Assess the Origin and Extent of Ventricular Preexcitation Associated With an Accessory Bypass

A 51-year-old, otherwise healthy man with drug refractory Wolff-Parkinson-White syndrome was referred for radio-frequency catheter ablation (RFCA). His ECG exhibited a typical pattern of preexcitation, suggestive of an inferior or inferoseptal bypass (Figure 1A). Before and after RFCA, we acquired B-mode images on a Vivid 7 echocardiography machine (Vingmed Ultrasound, Horten, Norway) from a parasternal short-axis view and 5 apical views (AP2C, AP4C, APLAX, and 2 intermediate planes) at 77 to 91 frames/s, offering an effective temporal resolution of 22 to 26 ms. Off-line, B-mode–based, 2-dimensional (2-D) strain curves were extracted using commercially available software (Echopac version 4.0.2, GE Vingmed Ultrasound, Horten, Norway). The software program performs a frame-by-frame autocorrelation analysis to track the typical speckled myocardial patterns generated by irregularities in acoustic backscatter. In this manner, we were able to obtain angle-independent information on strain (or contraction), which we applied to assess the site of …

Laminar specificity in monkey V1 using high-resolution SE-fMRI

The lamination of mammalian neocortex is widely used as reference for describing a wide range of anatomical and physiological data. Its value lies in the observation that in all examined species, cortical afferents, intrinsic cells and projection neurons organize themselves with respect to the laminae. The comprehension of the computations, carried out by the neocortical microcircuits, critically relies on the study of the interlaminar connectivity patterns and the intralaminar physiological processes in vivo. High-resolution functional neuroimaging, enabling the visualization of activity in individual cortical laminae or columns, may greatly contribute in such studies. Yet, the BOLD effect, as measured with the commonly used GE-EPI, contains contributions from both macroscopic venous blood vessels and capillaries. The low density of the cortical veins limits the effective spatial specificity of the fMRI signal and yields maps that are weighted toward the macrovasculature, which thus can be significantly different from the actual site of increased neuronal activity. Spin-echo (SE) sequences yielding apparent T2-weighted BOLD images have been shown to improve spatial specificity by increasing the sensitivity of the signal to spins of the parenchyma, particularly at high magnetic fields. Here we used SE-fMRI at 4.7 T to examine the specificity and resolution of functional maps obtained by stimulating the primary visual cortex of monkeys. Cortical layers could be clearly visualized, and functional activity was predominantly localized in cortical layer IV/Duvernoy layer 3. The choice of sequence parameters influences the fMRI signal, as the SE-EPI is by nature sensitive to T2* in addition to its T2 dependency. Using parameters that limit T2* effects yielded higher specificity and better visualization of the cortical laminae. Because the demands of high-spatial resolution using SE severely decreases temporal resolution, we used a stimulus protocol that allows sampling at higher effective temporal resolution. This way, it was possible to acquire high-spatial and high-temporal resolution SE-fMRI data.

Volumetric cine imaging for four-dimensional radiation therapy planning using the second model of the 256-detector row CT-scanner: Initial experience in lung cancer

This is an initial demonstration of volumetric cine imaging under free breathing in lung cancer patients using the second model of the 256-detector row CT (256MDCT). Scan range is 128 mm in the cranio-caudal direction with a 0.5 mm slice thickness and effective temporal resolution of 250 ms. Volumetric cine images are satisfactorily obtained for the thin sections which can be used to create cine loops in multiple planes. Thus, the 256MDCT overcomes some of the limitations of current respiratory-gated CT or 4D-CT scan techniques and has the potential for use in 4D-IMRT planning and 4D radiation therapy.

Analysis of Atelectasis, Ventilated, and Hyperinflated Lung During Mechanical Ventilation by Dynamic CT

To study the dynamics of lung compartments by dynamic CT (dCT) imaging during uninterrupted pressure-controlled ventilation (PCV) and different positive end-expiratory pressure (PEEP) settings in healthy and damaged lungs. Experimental animal investigation. Experimental animal facility of a university department. In seven anesthetized pigs, static inspiratory pressure volume curves were obtained to identify the individual lower inflection point (LIP) before and after saline solution lung lavage. During PCV, PEEP was adjusted 5 millibars (mbar) below the individually determined LIP (LIP - 5), at the LIP, and 5 mbar above the LIP (LIP + 5). Measurements were repeated before and after induction of lung damage. Hemodynamics, arterial and mixed venous blood gases, and dCT imaging in one juxtadiaphragmatic slice (effective temporal resolution of 100 ms) were assessed during uninterrupted PCV in series of three successive respiratory cycles. The mean fractional area (FA) of the hyperinflated lung (FA-H), mean FA of ventilated lung, mean FA of poorly ventilated lung, and mean FA of nonventilated lung (FA-NV), and the change in FA of the whole lung area (DeltaFA) were compared at different PEEP settings. Calculated pulmonary shunt (Qs/Qt) was compared to FA-NV. LIP + 5 decreased the amount of atelectasis (FA-NV) and increased hyperinflation (FA-H) in healthy and injured lungs. Cyclic changes of atelectasis (DeltaFA-NV) and hyperinflation (DeltaFA-H) were observed in both healthy and injured lungs. In the injured but not in the healthy lungs, the amount of cyclic changes of atelectasis and hyperinflation were independent from the adjusted PEEP level. FA-NV correlated with the calculated Qs/Qt, with a slight overestimation (mean +/- SEM, 2.1 +/- 4.1%). dCT imaging allows the following: (1) the quantification of the extent of atelectasis, ventilated, poorly ventilated, and hyperinflated lung parenchyma during ongoing mechanical ventilation; (2) the detection and quantification of repeated recruitment and derecruitment, as well as hyperinflation; and (3) an estimation of Qs/Qt. dCT adds promising functional information for the respiratory treatment of early ARDS.

高心拍領域におけるMDCTの心臓イメージングの画質に関する評価 : 心臓動態ファントムによる検討を中心に

The multi-sector reconstruction (MSR) algorithm and cardiac half-reconstruction (CHR) algorithm are the main algorithms used in cardiac reconstruction. Analysis of effective temporal resolution (TR) confirmed that optimal rotation speed depends on different heart rates when using MSR. During visualization (3D/MPR image) and quantitative (EF: ejection fraction) evaluations, it was found that image quality and measurement accuracy are well correlated with effective temporal resolution (TR) by the different algorithms. The CHR algorithm resulted in less desirable image quality at TR 250 ms than that from MSR at high heart rates (>75 bpm) in the phantom experiment. We determined that the combination of the MSR algorithm and the optimal selection of gantry rotation speed is important for obtaining high-quality cardiac imaging in the high heart rate region.

Time resolved neutron flux diagnostics for quasi-steady-state operation study of the HT-7 tokamak

Time resolved neutron flux diagnostic systems based on BF3 proportional counter and ZnS(Ag) scintillator have been developed and implemented on the HT-7 superconducting tokamak. A ten-channel flexible data acquisition system designed with a PCI-8554 general digital counter and industry PC is equipped. Calibrations are made with several neutron sources. The consistencies of experimental data from two techniques have been proven; the BF3 based system is more reliable with better detection efficiency. The measured neutron yield shows good agreement with the simple numerical calculation. The observed photo–neutron production indicates that photon–nuclear reactions are dominant in several special cases such as low density and disruption conditions. Good agreement on ion temperature deduced from neutron diagnosis and neutral particle analyzer under high parameter plasma conditions implies that neutron flux diagnostics can be used as an effective higher temporal resolution ion temperature monitor.

Perceptual consequences of normal and abnormal peripheral compression: Potential links between psychoacoustics and speech perception

Cochlear damage can lead to a reduction in the overall amount of peripheral auditory compression, presumably due to outer hair cell (OHC) loss or dysfunction. The perceptual consequences of functional OHC loss include loudness recruitment and reduced dynamic range, poorer frequency selectivity, and poorer effective temporal resolution. These in turn may lead to a reduced ability to make use of spectral and temporal fluctuations in background noise when listening to a target sound, such as speech. We tested the effect of OHC function on speech reception in hearing-impaired listeners by comparing psychoacoustic measures of cochlear compression and sentence recognition in a variety of noise backgrounds. In line with earlier studies, we found weak (nonsignificant) correlations between the psychoacoustic tasks and speech reception thresholds in quiet or in steady-state noise. However, when spectral and temporal fluctuations were introduced in the masker, speech reception improved to an extent that was well predicted by the psychoacoustic measures. Thus, our initial results suggest a strong relationship between measures of cochlear compression and the ability of listeners to take advantage of spectral and temporal masker fluctuations in recognizing speech. [Work supported by NIH Grants Nos. R01DC03909, T32DC00038, and R01DC00117.]

Embedded MR fluoroscopy: high temporal resolution real-time imaging during high spatial resolution 3D MRA acquisition.

A method termed "embedded fluoroscopy" for simultaneously acquiring a real-time sequence of 2D images during acquisition of a 3D image is presented. The 2D images are formed by periodically sampling the central phase encodes of the slab-select direction during the 3D acquisition. The tradeoffs in spatial and temporal resolution are quantified by two parameters: the "redundancy" (R), the fraction of the 3D acquisition sampled more than once; and the "effective temporal resolution" (T), the time between temporal updates of the central views. The method is applied to contrast-enhanced MR angiography (CE-MRA). The contrast bolus dynamics are portrayed in real time in the 2D image sequence while a high-resolution 3D image is being acquired. The capability of the 2D acquisition to measure contrast enhancement with only a 5% degradation of the spatial resolution of the 3D CE-MR angiogram is shown theoretically. The method is tested clinically in 15 CE-MRA patient studies of the carotid and renal arteries.

Motion artifacts in subsecond conventional CT and electron-beam CT: pictorial demonstration of temporal resolution.

To visually demonstrate the effective temporal resolution of subsecond conventional (slip-ring) and electron-beam computed tomographic (CT) systems, two phantoms containing high-contrast test objects were scanned with a slip-ring CT system (effective exposure time, 0.5 second) and an electron-beam CT system (exposure time, 0.1 second). Images were acquired of each phantom at rest, during translation along the x axis at speeds of 10-100 mm/sec, and during rotation about isocenter at speeds of 0.1 and 0.5 revolution per second. Motion artifacts and loss of spatial resolution were judged to be absent, noticeable, or severe. For 0.5-second conventional CT images, motion artifacts and loss of spatial resolution were noticeable at 10 mm/sec and 0.1 revolution per second and were severe at speeds greater than or equal to 20 mm/sec and at 0.5 revolution per second. For 0.1-second electron-beam CT scans, noticeable, but not severe, motion artifacts and loss of spatial resolution occurred at speeds between 40 and 100 mm/sec and at 0.5 revolution per second. Over the range of physiologic speeds examined, the images provide visually compelling evidence of the effect of improving temporal resolution in CT.

Multi-rotation CT during continuous ventilation: comparison of different density areas in healthy lungs and in the ARDS lavage model

In this animal study, density ranges for CT-based quantification of ventilated lung area were determined. Healthy lungs and ARDS lungs were compared during artificial respiration. CT-scans were performed in 5 anesthetized pigs using a dynamic multiscan CT option on a predefined transverse slice (slice thickness 1 mm; effective temporal resolution, 250 ms). During continuous CT acquisition, airway pressure was increased or decreased in a stepwise manner. In all images, areas of defined HU ranges were determined planimetrically. The lower threshold was set to -910 HE in all images. The upper threshold was varied from -800 HE to -200 HE in steps of 100 HE. During inspiration in healthy lungs the HU-range of -910 to -700 HU showed the largest increase in area. During inspiration in ARDS lungs the HU range from -910 to -300 HU allowed the most sensitive assessment of area changes. These findings can be explained by recruitment of atelectases (HU-range > -300 HU) and their transition to a HU range from -700 to -300 HU. Dynamic multiscan CT acquisitions are a useful method to determine changes of ventilated lung area during a respiratory cycle. Different HU-ranges are required to access volume changes in healthy lungs and in ARDS lungs.

Functional MR microscopy of the lung using hyperpolarized 3He

A new strategy designed to provide functional magnetic resonance images of the lung in small animals at microscopic resolution using hyperpolarized 3He is described. The pulse sequence is based on a combination of radial acquisition (RA) and CINE techniques, referred to as RA-CINE, and is designed for use with hyperpolarized 3He to explore lung ventilation with high temporal and spatial resolution in small animal models. Ventilation of the live guinea pig is demonstrated with effective temporal resolution of 50 msec and in-plane spatial resolution of <100 μm using hyperpolarized 3He. The RA-CINE sequence allows one to follow gas inflow and outflow in the airways as well as in the distal part of the lungs. Regional analysis of signal intensity variations can be performed and can help assess functional lung parameters such as residual gas volume and lung compliance to gas inflow. Magn Reson Med 41:787–792, 1999. © 1999 Wiley-Liss, Inc.

Functional MR microscopy of the lung using hyperpolarized 3He.

A new strategy designed to provide functional magnetic resonance images of the lung in small animals at microscopic resolution using hyperpolarized 3He is described. The pulse sequence is based on a combination of radial acquisition (RA) and CINE techniques, referred to as RA-CINE, and is designed for use with hyperpolarized 3He to explore lung ventilation with high temporal and spatial resolution in small animal models. Ventilation of the live guinea pig is demonstrated with effective temporal resolution of 50 msec and in-plane spatial resolution of <100 microm using hyperpolarized 3He. The RA-CINE sequence allows one to follow gas inflow and outflow in the airways as well as in the distal part of the lungs. Regional analysis of signal intensity variations can be performed and can help assess functional lung parameters such as residual gas volume and lung compliance to gas inflow.

心拍動によるモーションアーチファクト軽減のための高時間分解能再構成アルゴリズム

Cardiac pulsation is the most important cause of serious image degradation on high resolution CT(HRCT) images of lung adjacent to heart and cardiac images. The purpose of this study was to propose a special high temporal resolution reconstruction(HTRR) algorithm, and to assess the effects on the reduction in motion artifacts caused by cardiac pulsation on HRCT images of lung and cardiac images by using this algorthm combined with sub-second CT. The HTRR algorithm was developed on the basis of a special weighting function. The results of phantom and clinical studies demonstrated that the HTRR algorithm can provide high temporal resolution, substantially reduce moting artifacts and noise, and markedly improve the quality of cardiac images and HRCT lung images at the cost of a slight degradation in spatial resolution. Further, the HTRR algorithm can obtain phase information by combining subsecond CT with the overlapping cine reconstruction technique and ECG information. Using the HTRR algorithm, the effective temporal resolution(FWHM) is 0.4 sec for a 0.8 sec scan.

Event-Related fMRI: Characterizing Differential Responses

We present an approach to characterizing the differences among event-related hemodynamic responses in functional magnetic resonance imaging that are evoked by different sorts of stimuli. This approach is predicated on a linear convolution model and standard inferential statistics as employed by statistical parametric mapping. In particular we model evoked responses, and their differences, in terms of basis functions of the peri-stimulus time. This facilitates a characterization of the temporal response profiles that has a high effective temporal resolution relative to the repetition time. To demonstrate the technique we examined differential responses to visually presented words that had been seen prior to scanning or that were novel. The form of these differences involved both the magnitude and the latency of the response components. In this paper we focus on bilateral ventrolateral prefrontal responses that show deactivations for previously seen words and activations for novel words.

Improved ejection fraction and flow velocity estimates with use of view sharing and uniform repetition time excitation with fast cardiac techniques.

To improve the accuracy of ventricular volume estimates and effective temporal resolution in fast cardiac acquisitions. Data sets at intermediate temporal phases were generated by means of sharing of views from two temporally adjacent data sets. A simulated model was used, and studies with patients and volunteers were conducted. View sharing was implemented in both fast gradient-echo and fast phase-contrast cine acquisitions; breath holding was used when possible. Uniform repetition time (TR) radio-frequency (RF) excitation allowed a better assessment of the end-diastolic ventricular volume. In addition, view sharing provided a better estimate of end-systolic ventricular volume in cases in which rapid changes in volume occurred at or about the temporal boundary of the source images. View sharing also provided a much smoother representation of dynamic cardiac motion when viewed in a cine loop. View sharing and uniform TR RF excitation improve the accuracy of end-systolic and end-diastolic ventricular volume measurements by improving the effective temporal resolution.