Spiral Resonance Research Articles

Prospective evaluation of ultrasonography, multi-slice spiral CT, endoscopic ultrasonography, and magnetic resonance imaging in assessment of TNM staging and assessment of resectability in pancreatic carcinoma

To evaluate prospectively the efficacy and clinical significance of ultrasonography (US), multi-slice spiral CT (MSCT), magnetic resonance imaging (MRI), and endoscopic ultrasonography (EUS) in assessment of the TNM staging and resectability of pancreatic carcinoma. Consecutive 68 patients with pancreatic carcinoma underwent US, MSCT, MRI, and EUS to assess their efficacies in assessment of the size of carcinoma, lymph node metastasis, and distant metastasis. The results of theses imaging techniques were compared with the surgical and pathological findings. EUS was the most precise technique in evaluating the T staging of pancreatic carcinoma with the coefficients of regression of maximum and minimum radii of 1.025 (P=0.043) and 0.987 (P<0.0001). In the assessment of lymph node metastasis, EUS had the highest sensitivity (75.0%), accuracy (87.5%), and negative predictive values (91.7%). Univariate logistic regression showed that EUS was significantly correlated with the surgical findings (OR: 33.00, 95%CI: 7.18-151.77 P<0.0001). Multivariate logistic regression analysis confirmed that EUS had an independent predictive value (OR: 34.50, 95%CI: 6.54-182.09, P<0.0001). MSCT had the highest sensibility (88.9%) in the assessment of distant metastasis and had the highest accuracy (61.8%) in preoperative TNM staging of pancreatic carcinoma. All 4 imaging techniques were correlated with surgical findings in assessment of the resectability. Multivariate logistic regression analysis confirmed that none of the imaging techniques had independent predictive value. MSCT is the best method in preoperative TNM staging of pancreatic carcinoma. EUS is the best methods in the assessment of tumor size and lymph node metastasis. Preoperative assessment of pancreatic carcinoma needs combination of at least two kinds of imaging techniques.

Impaired Coronary Vasodilation by Magnetic Resonance Angiography Is Associated With Advanced Coronary Artery Calcification

This study evaluated the hypothesis that impaired nitroglycerin (NTG)-induced coronary vasodilation is associated with advanced coronary atherosclerosis in asymptomatic older patients. Atherosclerosis is associated with both structural and functional abnormalities of the vessel wall. Noninvasive functional measures of subclinical coronary atherosclerosis may help characterize high-risk subjects and guide preventive therapy. A total of 236 older patients (age 60 to 72 years, 33% female) without a history of cardiovascular disease were studied. Nitroglycerin-induced coronary vasodilation was measured by magnetic resonance angiography (MRA). Cross-sectional images of the right coronary artery were acquired before and 5 min after 0.4-mg sublingual NTG using a gated, breath-held spiral coronary MRA sequence (0.7-mm resolution). Quantitative analysis of the increase in cross-sectional area was performed in the 90% of patients (n = 212) with adequate image quality. Quantitation of coronary artery calcification (CAC) was performed by multidetector computed tomography using the Agatston method. Forty patients (19%) had advanced CAC (> or =400). Coronary vasodilation to NTG was significantly impaired (p = 0.02) in patients with advanced CAC (median [interquartile range] = 15.9% [4.2% to 28.0%] vs. 21.5% [9.6% to 36.6%] for CAC <400). Importantly, NTG-induced coronary vasodilation remained independently associated with advanced CAC after multivariate analysis incorporating risk factors (p = 0.02) and other potential confounders (p = 0.04). There was no significant difference in coronary vasodilation between men and women, but few women (n = 3) had advanced CAC. Impaired NTG-induced coronary vasodilation by MRA is associated with advanced coronary atherosclerosis in a community-based cohort of older asymptomatic subjects. Coronary MRA may provide a noninvasive functional assessment of subclinical coronary atherosclerosis.

Improved spiral compact microstrip resonance cell low‐pass filter with wide stopband characteristics

AbstractAn improved spiral compact microstrip resonance cell (SCMRC) structure is proposed in this article. Good low pass performance and wide stopband characteristics can be achieved with a simple single cell, two transmission zeros are introduced within the stopband and thus improve the bandwidth significantly. The measured results of the prototype show that the insertion loss is less than 0.55 dB in the passband, and the bandwidth of the stopband is about 90%, nearly two times of the original SCMRC structure. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 121–124, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22032

Reducing gradient imperfections for spiral magnetic resonance spectroscopic imaging

Spiral k-space magnetic resonance spectroscopic imaging (MRSI) requires high performance from gradient hardware systems. During the readout phase, oscillating gradients are continuously played out, which can cause undesired effects. These effects on the quality of SI data are non-intuitive because of their time-varying nature. In this work we describe the effects of undesirable gradient performance on SI. Measurements of the true readout trajectories were performed and the results were then used in the reconstruction process. The effects of these imperfections resulted in a spatially and spectrally varying amplitude and frequency modulation. The use of the measured trajectories in the reconstruction process yielded an up to 20% increase in signal amplitude recovery.

Treatment of Aortic Disease in Patients With Marfan Syndrome

Marfan syndrome (MFS) is a heritable disorder of the connective tissue with a prevalence of ≈1 in 3000 to 5000 individuals. The condition is inherited in an autosomal dominant manner with complete penetrance but demonstrates variable expression with significant intra- and interfamilial variation. Approximately 25% of patients do not have a family history and represent sporadic, new mutations for the condition. The cardinal features of MFS involve the cardiovascular, ocular, and skeletal systems. The most life-threatening complication of MFS is thoracic aortic aneurysms leading to aortic dissection, rupture, or both. This article focuses on medical and surgical treatment of aortic disease in patients with MFS and addresses the treatment of aortic disease in children and pregnant women with the condition. The most common cardiovascular complication in patients with MFS is progressive aortic root enlargement initially occurring at the sinuses of Valsalva. Ascending aortic aneurysm can precipitate acute type A aortic dissection, aortic rupture, aortic regurgitation (AR), or all 3, and these complications were the primary cause of death before the advent of successful preventive therapies. Treatment of the aorta consists of regular imaging to detect and quantify progression of aortic dilation, β-adrenergic receptor antagonist therapy, and prophylactic aortic repair when the dilation reaches a sufficient size to threaten dissection or cause AR. Before the era of open-heart surgery, the majority of patients with MFS died prematurely of rupture of the aorta, with an average life expectancy of 45 years.1 The success of current medical and surgical treatment of aortic disease in MFS has substantially improved the average life expectancy, extending it up to 70 years.2,3 Cardiovascular manifestations in MFS also include valvular disease involving the mitral valve, aortic valve, or both. Mitral valve prolapse is the most prevalent valvular abnormality, affecting 35% to 100% of patients.4 Mitral …

Spiral magnetic resonance coronary angiography with rapid real-time localization

Spiral magnetic resonance coronary angiography with rapid real-time localization

Spiral magnetic resonance coronary angiography with rapid real-time localization

ObjectivesA spiral high-resolution coronary artery imaging sequence (SH) interfaced with real-time localization system (RT) has been developed. A clinical study of 40 patients suspected of coronary artery disease (CAD) was conducted. BackgroundSegmented k-space acquisition techniques have dominated magnetic resonance coronary angiography (MRCA) over the last decade. Although a recent multicenter trial using this technique demonstrated encouraging results, the technique was hampered by low specificity. Spiral k-space acquisition had demonstrated several advantages for MRCA. Therefore, a first clinical trial implementing spiral high-resolution coronary imaging sequence with real-time localization (SH-RT) was performed. MethodsA clinical study of 40 patients suspected of CAD undergoing X-ray angiography was conducted to analyze the clinical reliability of this novel imaging system. The SH-RT had been designed to exploit the unique capability of two imaging sequences. The RT allowed a rapid localization of the coronary arteries. Then SH achieved multislice acquisition during a short breath-hold with submillimeter resolution. The MRCA data were analyzed for scan time, anatomic coverage, image quality, and accuracy in detecting CAD. ResultsIn 40 subjects, SH achieved 0.7 to 0.9 mm resolution with 14-heartbeat breath-holds. Excellent or good image quality was achieved in 78% (263/337) of the coronary segments. Blinded consensus reading among three observers generated sensitivity of 76% and specificity of 91% in the detection of CAD compared with X-ray angiography. ConclusionsThe MRCA imaging sequence implementing a novel spiral k-space acquisition technique enabled rapid and reliable imaging of the CAD in submillimeter resolution with short breath-holds.

Spiral magnetic resonance coronary angiography with real-time localization at 3T

Spiral magnetic resonance coronary angiography with real-time localization at 3T

Multislice breath-hold spiral magnetic resonance coronary angiography in patients with coronary artery disease: effect of intravascular contrast medium.

First, to apply a breath-hold multislice 2D spiral magnetic resonance (MR) approach in patients acquiring within 16 heartbeats (acquisition window, 116 msec) a 10-mm-thick stack of four slices (resolution, 1.3 x 1.3 mm(2)); and second, to evaluate the effect of an intravascular Fe-based contrast medium (CM) on a signal-to-noise ratio (SNR) and a contrast-to-noise ratio (CNR). In each patient one or two coronary arteries were imaged prior to and following cumulative doses of 0.25, 0.5, and 0.75 mg of Fe/kg of body weight (bw) of an intravascular CM (CLARISCAN trade mark, Nycomed-Amersham, Princeton, NJ, USA) containing ultrasmall superparamagnetic iron oxide (USPIO) particles. On precontrast maximum intensity projection (MIP) images generated from the stack of slices, 10 and 11 stenoses of 12 stenoses confirmed by coronary angiography were detected by readers 1 and 2, respectively. SNR and CNR in the coronary arteries peaked at 0.50 mg of Fe/kg of bw, yielding a slight increase of 15.5% and 18.4%, respectively (P < 0.05 vs. precontrast), which did not improve detection of coronary artery stenoses. The presented multislice spiral approach allows display of coronary anatomy in MIP formats for convenient display of coronary stenoses. The pulse sequence did not benefit from an intravascular USPIO-based CM, since little improvement in SNR and CNR was achieved.

Single-Shot Magnetic Resonance Imaging of a Moving ObjectBased on the High-Speed Spiral-Scan Echo Planner Technique at 4.7 T

The single-shot spiral magnetic resonance imaging (MRI) technique wasimplemented and optimized on a Bruker Biospec47/30 scanner. Thetechnique includes the pulse sequence for generation and detection ofthe k-space MRI signal (free induction decay (FID)), and PC-basedprograms for the data grid and image reconstruction. The temporalresolution is 70 ms (14 images per second), which consists of a dataacquisition time as short as 13.7 ms, a spin-echo time of 13.6 ms anda magnetization recovery time of 43 ms. This makes it possible totake real-time images of moving objects. The technique is demonstratedusing a pendulum (tube) filled with water.

Platform-independent image reconstruction for spiral magnetic resonance imaging

The distinct feature of data acquisition for magnetic resonance imaging (MRI) is that the data are sampled in frequency domain instead of spatial domain. Therefore, the acquired data must be inverse Fourier transformed to generate images. To apply fast Fourier transform (FFT), the data are usually acquired on rectilinear grids. However, acquiring data on rectilinear grids is not very efficient in MRI. A spiral trajectory, which starts at the origin of the frequency domain and spins out to higher spatial frequency is more efficient and faster than the conventional method. Since the spiral trajectories do not sample on rectilinear grids, raw data must be re-interpolated onto rectilinear grids prior to inverse FFT. This re-gridding process is done using a reconstruction program. When the platforms to run the program grow, the efforts required to maintain the program become prohibitive. This problem can be solved through the platform-independent Java programming language. In this paper, we report on our attempt to implement the spiral MRI reconstruction program in Java. We show that the performance is not significantly affected and that it is practical to use a platform-independent reconstruction software.

Triggering the Formation of Young Clusters

Star formation is triggered in essentially three ways: (1) the pressures from existing stars collect and squeeze nearby dense gas into gravitationally unstable configurations, (2) random compression from supersonic turbulence makes new clouds and clumps, some of which are gravitationally unstable, and (3) gravitational instabilities in large parts of a galaxy disk make giant new clouds and spiral arms that fragment by the other two processes into a hierarchy of smaller star-forming pieces. Examples of each process are given. Most dense clusters in the solar neighborhood were triggered by external stellar pressures. Most clusters and young stars on larger scales are organized into hierarchical patterns with an age-size correlation, suggestive of turbulence. Beads-on-a-string of star formation in spiral arms and resonance rings indicate gravitational instabilities. The turbulence model explains the mass spectrum of clusters, the correlation between the fraction of star formation in the form of clusters and the star formation rate, found by Larsen &amp; Richtler, and the correlation between the size of the largest cluster and the number of clusters in a galaxy.

Seeing Galaxies through Thick and Thin. I. Optical Opacity Measures in Overlapping Galaxies

We describe the use of partially overlapping galaxies to provide direct measurements of the effective absorption in galaxy disks, independent of assumptions about internal disk structure. The nonoverlapping parts of the galaxies and symmetry considerations are used to reconstruct, via differential photometry, how much background galaxy light is lost in passing through the foreground disks. Extensive catalog searches and follow-up imaging yield ~15-25 nearby galaxy pairs suitable for varying degrees of our analysis; 11 of the best such examples are presented here. From these pairs, we find that interarm extinction is modest, declining from AB ~ 1 mag at 0.3R to essentially zero by R; the interarm dust has a scale length consistent with that of the disk starlight. In contrast, dust in spiral arms and resonance rings may be optically thick (AB > 2) at virtually any radius. Some disks have flatter extinction curves than the Galaxy, with AB/AI ≈ 1.6; this is probably the signature of clumpy dust distributions. Even though typical spirals are not optically thick throughout their disks, where they are optically thick is correlated with where they are most luminous: in spiral arms and inner disks. This correlation between absorption and emission regions may account for their apparent surface brightness being only mildly dependent on inclination, erroneously indicating that spirals are generally optically thick. Taken as an ensemble, the opacities of spiral galaxies may be just great enough to significantly affect QSO counts, though not enough to cause their high-redshift cutoff.

Radiodiagnosis of the lung

Radiological cross-sectional imaging modalities, particularly computed tomography (CT) have become the mainstays for diagnosing lung disease in recent years. These enable morphological visualization of pathological processes with the greatest possible spatial resolution. Modern technical developments and complementary strategies have led to new applications and new functional assessments which need to be reviewed together with state-of-the-art techniques in nuclear imaging. The diagnosis of pulmonary embolism using spiral CT angiography and magnetic resonance (MR) angiography certainly belongs in this category. CT has become the an alternative modality of first choice, and it is also challenging pulmonary angiography as the gold standard. Direct visualization of patent pulmonary arteries and thromboembolic material is complemented by that of effects on the pulmonary parenchyma and right heart function; it also provides perfusion studies and MR-based flow measurement to assess hemodynamic compromise. Ventilation studies have long been a domain of nuclear imaging, and new techniques for the direct visualization of ventilation are emerging from recent developments in the field of MR imaging, for example, using hyperpolarized inert gases. New functional parameters of ventilation can be derived from these studies. For the diagnosis of metabolically active disease, such as tumor and pneumonia, CT offers very high sensitivity, for example, in screening for intrapulmonary nodules using low-dose CT and in the early detection of pulmonary infiltrates in high-risk patients. Especially for characterizing pulmonary nodules there is a need to combine nuclear medicine techniques, such as in positron-emission tomography.

Real-time image reconstruction for spiral MRI using fixed-point calculation.

Because spiral magnetic resonance imaging (MRI) is more robust to motion artifacts than echo planar imaging (EPI), spiral imaging method is more suitable in real-time imaging applications where dynamic processes are to be observed. The major hurdle to use spiral imaging method in real-time applications is its slow reconstruction speed. Since spiral trajectories do not sample data on rectilinear grids, raw data must be regridded before inverse fast Fourier transform (FFT). At present, the computational cost for the spiral reconstruction algorithm is still too high and it is not fast enough to achieve the minimum speed requirement of 20 frames/s for real-time imaging applications. In this paper, we propose to replace floating-point calculations with fixed-point calculations in the reconstruction algorithm to remove the computational bottlenecks. To overcome the quantization and round-off errors introduced by fixed-point calculations, we devise a method to find the optimal precision for the fixed-point representation. Adding with a highly efficient vector-radix two-dimensional (2-D) FFT algorithm and modifications to speed up the gridding convolution, we have cut the reconstruction time by 42% and achieved real-time reconstruction at 30 frames/s for 128 x 128 matrices on low-cost PC's.

On the optimality of the gridding reconstruction algorithm

Gridding reconstruction is a method to reconstruct data onto a Cartesian grid from a set of nonuniformly sampled measurements. This method is appreciated for being robust and computationally fast. However, it lacks solid analysis and design tools to quantify or minimize the reconstruction error. Least squares reconstruction (LSR), on the other hand, is another method which is optimal in the sense that it minimizes the reconstruction error. This method is computationally intensive and, in many cases, sensitive to measurement noise. Hence, it is rarely used in practice. Despite their seemingly different approaches, the gridding and LSR methods are shown to be closely related. The similarity between these two methods is accentuated when they are properly expressed in a common matrix form. It is shown that the gridding algorithm can be considered an approximation to the least squares method. The optimal gridding parameters are defined as the ones which yield the minimum approximation error. These parameters are calculated by minimizing the norm of an approximation error matrix. This problem is studied and solved in the general form of approximation using linearly structured matrices. This method not only supports more general forms of the gridding algorithm, it can also be used to accelerate the reconstruction techniques from incomplete data. The application of this method to a case of two-dimensional (2-D) spiral magnetic resonance imaging shows a reduction of more than 4 dB in the average reconstruction error.

Fast Spiral Magnetic Resonance Imaging with Trapezoidal Gradients

A modified spiral imaging technique is presented, in which the conventional sinusoidal gradient waveforms are replaced by trapezoidal ones. In addition to allowing a reduced data acquisition time, the new waveforms circumvent specific hardware restrictions on the minimum scan repetition time.

Capillary penetration in fibrous matrices studied by dynamic spiral magnetic resonance imaging

The dynamic spiral nuclear magnetic resonance (NMR) imaging technique was used to investigate the water imbibition into cellulose fiber matrices. The advancing water boundary, water concentration distribution, and swelling degree within the fiber matrix samples were monitored as a function of time over the entire absorption process. A combined image that shows the time evolution of the absorbed water concentration distribution within the fiber matrix was synthesized from the dynamically acquired NMR image data set. The NMR imaging data clearly demonstrated that water imbibition into a fiber matrix consists of two different processes: water penetration into capillaries between fibers and water diffusion into the cellulose fibers. The advancing liquid front is primarily determined by the water capillary flow and can be quantitatively described by Washburn equation. The slower water diffusion process in fibers is mainly responsible for the fiber swelling. The time evolution of the absorbed water concentration distribution can be qualitatively interpreted in terms of steady capillary flow and concentration-gradient-driven diffusion into fibers with a constant permeability. The effects of pore morphology, tortuosity, and surface heterogeneity to the water absorption process are also discussed.

Spiral Wave Dynamics under Pulsatory Modulation of Excitability

The dynamics of meandering spiral waves in the photosensitive Belousov−Zhabotinsky reaction is investigated under external forcing by single light pulses, periodic pulses, and feedback-controlled sequences of light pulses. The effect of a single stimulus on the trajectory of the spiral tip is related to the phase of the tip motion on the trajectory at the moment when the stimulus is applied. Periodic stimulation of the medium can produce spiral wave entrainment and resonance. A connection between the phase of the stimuli and the stability of the regime of entrainment is shown. In the feedback-controlled system each stimulus is applied at a moment corresponding to the passage of a wave front through a particular detection point. The introduction of such a feedback results in two new dynamic regimes, the entrainment and resonance attractor. Size and stability of these attractors are determined by the value of a time delay in the feedback loop. The experimental results are corroborated by numerical simulations performed with a modified two-component Oregonator model.

Exercise-related changes in aortic flow measured with spiral echo-planar MR velocity mapping.

Spiral echo-planar magnetic resonance (MR) velocity mapping was used to measure exercise-related changes in flow in the descending thoracic aorta in 10 healthy volunteers. Flow was measured at rest and immediately after dynamic exercise, with a 0.5-T imager with a surface receiving coil and electrocardiographic triggering. Supine exercise was performed with a home-built pedaling apparatus. Spiral velocity mapping was performed in a transverse plane through the descending thoracic aorta with the subject at rest. The subject was then asked to perform maximum exercise, stop, and hold his breath during a four-heartbeat acquisition time. Eight cine frames with a temporal resolution of 50 msec were acquired through systole. Each image was acquired in 40 msec during spiral acquisition of k-space data, starting at the center, 6 msec after the excitation pulse. Reproducibility of the technique was established by repeating the flow measurement in four consecutive heartbeats. At rest, the heart rate (mean +/- standard deviation), mean aortic flow, peak aortic flow, and time to peak flow were 68 beats per minute +/- 6, 41 milliliters per beat +/- 8, 107 mL/sec +/- 20, and 175 msec +/- 25, respectively. After exercise, the heart rate and mean and peak aortic flow were significantly increased (P < .001), measuring 101 beats per minute +/- 12, 57 milliliters per beat +/- 11, and 158 mL/sec +/- 29, respectively, while the time to peak flow (115 msec +/- 32) was significantly reduced (P < .001). The four sets of values obtained for the first four consecutive heartbeats measured at rest were similar, as were those obtained for the first four heartbeats after exercise.