Biomedical subjects

Brian K Rutt

Publications and source records attributed to Brian K Rutt.

27 records · Page 2Linked to original sources

PubMed2003

Rapid combined T1 and T2 mapping using gradient recalled acquisition in the steady state.

A novel, fully 3D, high-resolution T(1) and T(2) relaxation time mapping method is presented. The method is based on steady-state imaging with T(1) and T(2) information derived from either spoiling or fully refocusing the transverse magnetization following each excitation pulse. T(1) is extracted from a pair of spoiled gradient recalled echo (SPGR) images acquired at optimized flip angles. This T(1) information is combined with two refocused steady-state free precession (SSFP) images to determine T(2). T(1) and T(2) accuracy was evaluated against inversion recovery (IR) and spin-echo (SE) results, respectively. Error within the T(1) and T(2) maps, determined from both phantom and in vivo measurements, is approximately 7% for T(1) between 300 and 2000 ms and 7% for T(2) between 30 and 150 ms. The efficiency of the method, defined as the signal-to-noise ratio (SNR) of the final map per voxel volume per square root scan time, was evaluated against alternative mapping methods. With an efficiency of three times that of multipoint IR and three times that of multiecho SE, our combined approach represents the most efficient of those examined. Acquisition time for a whole brain T(1) map (25 x 25 x 10 cm) is less than 8 min with 1 mm(3) isotropic voxels. An additional 7 min is required for an identically sized T(2) map and postprocessing time is less than 1 min on a 1 GHz PIII PC. The method therefore permits real-time clinical acquisition and display of whole brain T(1) and T(2) maps for the first time.

Analysis of Variance↗

PubMed2003

Imaging single mammalian cells with a 1.5 T clinical MRI scanner.

In the present work, we demonstrate that the steady-state free precession (SSFP) imaging pulse sequence FIESTA (fast imaging employing steady state acquisition) used in conjunction with a custom-built insertable gradient coil and customized RF coils can be used to detect individual SPIO-labeled cells using a commonly available 1.5 T clinical MRI scanner. This work provides the first evidence that single-cell tracking will be possible using clinical MRI scanners, opening up new possibilities for cell tracking and monitoring of cellular therapeutics in vivo in humans.

Cell Separation↗

PubMed2003

Peripheral nerve stimulation properties of head and body gradient coils of various sizes.

Peripheral nerve stimulation (PNS) caused by time-varying magnetic fields has been studied both theoretically and experimentally. A human volunteer study performed on three different body-size gradient coils and one head-size gradient coil is presented in this work. The experimental results were used to generate average PNS threshold parameters for the tested gradient systems. It was found that the average stimulation threshold increases while gradient-region-of-uniformity size decreases. In addition, linear relationships between PNS parameters and diameter of homogeneous gradient spherical volume (DSV) were discovered: SR(min) and DeltaG(min) both vary inverse linearly with DSV. More importantly, the chronaxie value was found to vary inversely linearly with the DSV. This finding indicates that, contrary to the general understanding, the parameter "chronaxie" in the commonly accepted simple stimulation models cannot be considered to be a single-value, nerve-specific constant. A modified linear model for gradient-induced PNS based on these results was developed, which may permit, for the first time, the general prediction of nerve stimulation properties for gradient coils of arbitrary linear region dimension.

Adolescent↗

PubMed2003

Quantitative assessment of carotid plaque composition using multicontrast MRI and registered histology.

MRI is emerging as a promising modality for monitoring carotid atherosclerosis. Multiple MR contrast weightings are required for identification of plaque constituents. In this study, eight MR contrast weightings with proven potential for plaque characterization were used to image carotid endarterectomy specimens. A classification technique was developed to create a tissue-specific map by incorporating information from all MR contrast weightings. The classifier was validated by comparison with micro-CT (calcification only) and with matched histological slices registered to MR images using a nonlinear warping algorithm (other components). A pathologist who was blinded to the classifier results manually segmented digitized histological images. The sensitivity of the classifier, as determined by pixel-by-pixel comparison with the pathologist's segmentation and micro-CT, was 60.4% for fibrous tissue, 83.9% for necrosis, 97.6% for calcification, and 65.2% for loose connective tissue. The corresponding values for specificity were 87.9%, 75.0%, 98.3%, and 94.9%, respectively. In conclusion, multicontrast MRI was successfully used in conjunction with a supervised classification algorithm to identify plaque components in endarterectomy specimens. Furthermore, this methodology will provide a framework for comparing different classification algorithms, and determining which combination of MR contrasts will be most valuable for in vivo plaque imaging.

Arteriosclerosis↗

PubMed2003

Reproducibility of image-based computational fluid dynamics models of the human carotid bifurcation.

Recent studies have demonstrated the ability of magnetic resonance imaging (MRI) to provide anatomically realistic boundary conditions for computational fluid dynamics (CFD) simulations of arterial hemodynamics. To date, however, little is known about the overall reproducibility of such image-based CFD techniques. Towards this end we used serial black blood and cine phase contrast MRI to reconstruct CFD models of the carotid bifurcations of three subjects with early atherosclerosis, each imaged three times at weekly intervals. The lumen geometry was found to be precise on average to within 0.15 mm or 5%, while measured flow and heart rates varied by less than 10%. Spatial patterns of a variety of wall shear stress (WSS) indices were largely preserved among the three repeat models. Time-averaged WSS was reproduced best, on average to within 5 dyn/cm2 or 37%, followed by WSS spatial gradients, angle gradients, and oscillatory shear index. The intrasubject flow rate variations were found to contribute little to the overall WSS variability. Instead, reproducibility was determined largely by the precision of the lumen boundary extraction from the individual MR images, itself shown to be a function of the image quality and proximity to the geometrically complex bifurcation region.

Aged↗

PubMed2002

Reconstruction of carotid bifurcation hemodynamics and wall thickness using computational fluid dynamics and MRI.

A thorough understanding of the relationship between local hemodynamics and plaque progression has been hindered by an inability to prospectively monitor these factors in vivo in humans. In this study a novel approach for noninvasively reconstructing artery wall thickness and local hemodynamics at the human carotid bifurcation is presented. Three-dimensional (3D) models of the lumen and wall boundaries, from which wall thickness can be measured, were reconstructed from black-blood magnetic resonance imaging (MRI). Along with time-varying inlet/outlet flow rates measured via phase contrast (PC) MRI, the lumen boundary was used as input for computational fluid dynamic (CFD) simulation of the subject-specific flow patterns and wall shear stresses (WSSs). Results from a 59-year-old subject with early, asymptomatic carotid artery disease show good agreement between simulated and measured velocities, and demonstrate a correspondence between wall thickening and low and oscillating shear at the carotid bulb. High shear at the distal internal carotid artery (ICA) was also colocalized with higher WSS; however, a quantitative general relationship between WSS and wall thickness was not found. Similar results were obtained from a 23-year-old normal subject. These findings represent the first direct comparison of hemodynamic variables and wall thickness at the carotid bifurcation of human subjects. The noninvasive nature of this image-based modeling approach makes it ideal for carrying out future prospective studies of hemodynamics and plaque development or progression in otherwise healthy subjects.

Adult↗

PubMed2002

Application of the static dephasing regime theory to superparamagnetic iron-oxide loaded cells.

The relaxation rates of iron-oxide nanoparticles compartmentalized within cells were studied and found to satisfy predictions of the static dephasing (SD) regime theory. THP-1 cells in cell culture were loaded using two different iron-oxide nanoparticles (superparamagnetic iron-oxide (SPIO) and ultrasmall SPIO (USPIO)) with four different iron concentrations (0.05, 0.1, 0.2, and 0.3 mg/ml) and for five different incubation times (6, 12, 24, 36, and 48 hr). Cellular iron-oxide uptake was assessed using a newly developed imaging version of MR susceptometry, and was found to be linear with both dose and incubation time. R(2)* sensitivity to iron-oxide loaded cells was found to be 70 times greater than for R(2), and 3100 times greater than for R(1). This differs greatly from uniformly distributed nanoparticles and is consistent with a cellular bulk magnetic susceptibility (BMS) relaxation mechanism. The cellular magnetic moment was large enough that R(2)' relaxivity agreed closely with SD regime theory predictions for all cell samples tested [R(2)'=2 pi/(9 x the square root of 3) x gamma LMD] where the local magnetic dose (LMD) is the sample magnetization due to the presence of iron-oxide particles). Uniform suspensions of SPIO and USPIO produced R(2)' relaxivities that were a factor of 3 and 8 less, respectively, than SD regime theory predictions. These results are consistent with theoretical estimates of the required mass of iron per compartment needed to guarantee SD-regime-dominant relaxivity. For cellular samples, R(2) was shown to be dependent on both the concentration and distribution of iron-oxide particles, while R(2)' was sensitive to iron-oxide concentration alone. This work is an important first step in quantifying cellular iron content and ultimately mapping the density of a targeted cell population.

Cell Compartmentation↗

PubMed2002

Acoustic noise reduction in a 4 T MRI scanner.

High-field, high-speed magnetic resonance imaging (MRI) can generate high levels of noise. There is ongoing concern in the medical and imaging research communities regarding the detrimental effects of high acoustic levels on auditory function, patient anxiety, verbal communication between patients and health care workers and ultimately MR image quality. In order to effectively suppress the noise levels inside MRI scanners, the sound field needs to be accurately measured and characterized. This paper presents the results of measurements of the sound radiation from a gradient coil cylinder within a 4 T MRI scanner under a variety of conditions. These measurement results show: (1) that noise levels can be significantly reduced through the use of an appropriately designed passive acoustic liner; and (2) the true noise levels that are experienced by patients during echo planar imaging.

Acoustics↗

PubMed2002

MRI gradient coil cylinder sound field simulation and measurement.

High-field, high-speed Magnetic Resonance Imaging (MRI) generates high sound levels within and nearby the scanner. The mechanism and process that produces the gradient magnetic field (a cylindrical electro-magnet, called the gradient coil cylinder, which produces a spatially and temporally varying magnetic field inside a static background magnetic field) is the primary source of this noise. This noise can cause difficulties in verbal communication in and around the scanner, heightened patient anxiety, temporary hearing loss and possible permanent hearing impairment for health care workers and patients. In order to effectively suppress the sound radiation from the gradient coil cylinder the sound field within and nearby the gradient coil needs to be characterized This characterization may be made using an analytical solution of the sound pressure field, computational simulation, measurement analysis or some combination of these three methods. This paper presents the computational simulation and measurement results of a study of the sound radiation from a head and neck gradient coil cylinder within a 4 Tesla MRI whole body scanner. The measurement results for the sound pressure level distribution along the centerline of the gradient coil cylinder are presented. The sound pressure distributions predicted from Finite Element Analysis of the gradient coil movement during operation and subsequent Boundary Element Analysis of the sound field generated are also presented. A comparison of the measured results and the predicted results shows close agreement. Because of the extremely complex nature of the analytical solution for the gradient coil cylinder, a treatment of the analytical solution and comparison to the computational results for a simple cylinder vibrating in a purely radial direction are also presented and also show close agreement between the two methods thus validating the computational approach used with the more complex gradient coil cylinder.

Computer Simulation↗