Biomedical subjects

M H Buonocore

Publications and source records attributed to M H Buonocore.

At least 19 recordsLinked to original sources

PubMed1998

Visualizing blood flow patterns using streamlines, arrows, and particle paths.

A customized computer program (MRIView) is described for visualizing and quantifying complex blood flow patterns in major vessels, using nongated and cardiac-gated three-dimensional (3D) velocity data obtained with MR velocity-encoded phase pulse sequences. Streamlines, arrows, and particle paths (collectively referred to as "paths") can be computed interactively, using both forward and backward time integration of the velocity field. The program provides interactive cross-sectional and 3D perspective visualization of the paths, with quantification and statistical analysis of average speed, through-plane velocity, cross-sectional area, and flow. Normal flow patterns in the carotid artery, basilar artery tip, ascending aorta, coronary arteries, descending aorta, and renal arteries, as well as abnormal flow patterns in basilar tip aneurysms, have been investigated. The program revealed flow patterns in these regions with features that are well known from Doppler ultrasound and other features that have not been reported previously. The association between specific abnormal flow patterns and development of atherosclerosis suggests that particle paths can be used to assess risk of plaque formation and progression, as well as to evaluate flow dynamics and vascular patency before and after vascular interventions.

Adult↗

PubMed1998

ERP and fMRI measures of visual spatial selective attention.

In two prior studies, we investigated the neural mechanisms of spatial attention using a combined event-related potential (ERP) and positron emission tomography (PET) approach (Heinze et al. [1994]: Nature 392:543-546; Mangun et al. [1997]: Hum Brain Mapp 5:273-279). Neural activations in extrastriate cortex were observed in the PET measures for attended stimuli, and these effects were related to attentional modulations in the ERPs at specific latencies. The present study used functional magnetic resonance imaging (fMRI) and ERPs in single subjects to investigate the intersubject variability in extrastriate spatial attention effects, and to qualitatively compare this to variations in ERP attention effects. Activations in single subjects replicated our prior group-averaged PET findings, showing attention-related increases in blood flow in the posterior fusiform and middle occipital gyri in the hemisphere contralateral to attended visual stimuli. All subjects showed attentional modulations of the occipital P1 component of the ERPs. These findings in single subjects demonstrate the consistency of extrastriate attention effects, and provide information about the feasibility of this approach for integration of electrical and functional imaging data.

Attention↗

PubMed1997

Activation of left posterior cingulate gyrus by the auditory presentation of threat-related words: an fMRI study.

This study investigated the cortical response to hearing threat-related and neutral words using functional magnetic resonance imaging (fMRI) in 16 coronal planes. Right-handed volunteers listened to (i) neutral words alternating with no words as the control condition, and (ii) neutral words alternating with threat-related words as the experimental condition. Threat-related words compared to neutral words activated left posterior cingulate gyrus in eight of 10 subjects with activation most prominent in the retrosplenial region. Patterns of activation produced by neutral words compared to no words included bilateral temporal and frontal regions but not posterior cingulate. The retrosplenial cingulate region has recently been implicated in episodic memory processes. We discuss the possible role of the posterior cingulate cortex in processes involving emotion and memory and in anxiety disorders.

Adult↗

PubMed1997

Ghost artifact reduction for echo planar imaging using image phase correction.

An algorithm is described for reducing ghost artifacts in echo planar imaging (EPI) using phase corrections derived from images reconstructed using only even or odd k-space lines. The N/2 ghost, that arises principally from time-reversal of alternate k-space lines, was significantly reduced by this algorithm without the need for a calibration scan. In images obtained in eight subjects undergoing EPI for auditory functional MRI (fMRI) experiments, N/2 ghost intensity was reduced from 10.3% +/- 2.1% (range: 7.9-14.1%) to 4.5% +/- 0.2% (range: 4.1-4.9%) of parent image intensity, corresponding to a percent reduction in ghost intensity of 54% +/- 9% (range: 43-65%), and the algorithm restored this intensity to the parent image. It provided a significant improvement in image appearance, and increased the correlation coefficients related to neural activation in functional MRI studies. The algorithm provided reduction of artifacts from all polynomial orders of spatial phase errors in both spatial directions. The algorithm did not eliminate N/2 ghost intensity contributed by field inhomogeneities, susceptibility, or chemical shift.

Algorithms↗

PubMed1997

Noise suppression digital filter for functional magnetic resonance imaging based on image reference data.

The central decision in every functional magnetic resonance imaging (fMRI) experiment is whether pixels in brain tissues are showing activation in response to neural stimulus or as a result of noise. Images are degraded not only by random (e.g., thermal) noise, but also by structured noise due to MR system characteristics, cardiac and respiratory pulsations, and patient motion. A novel digital filter has been developed to suppress cardiac and respiratory structured noise in fMRI images, using estimates of structured and random noise power spectra obtained directly from the images. It is an adaptive filter based on stationary noise statistics, and is equivalent in form to a Wiener filter. A mathematical model of the filtering process was developed to understand how the strength and distribution of structured and random noise power influenced filter performance. The filter was tested using images from an auditory activation study in ten subjects. In subjects whose structured noise power was localized to a relatively narrow frequency range, a strong relationship was found, both experimentally (R = 0.975, P < 0.0004 for H0: R = 0) and using the model, between filter performance and the level of structured noise power contaminating the experiment frequency. The filter significantly reduced the rate of false-positive activations in the subset of subjects whose experiment frequency was relatively heavily contaminated by structured noise. Notch filters, that simply eliminate unwanted frequencies, performed poorly in all subjects. Unlike the proposed Wiener filter, these filters did not suppress structured noise power at the experiment frequency that contributes to false-positive activations.

Brain↗

PubMed1997

Isoflurane anesthesia blunts cerebral responses to noxious and innocuous stimuli: a fMRI study.

We used functional magnetic resonance imaging to determine how isoflurane affected cerebral neuronal activation resulting from noxious and innocuous stimuli. Five male volunteers were subjected to mild electrical shock and tactile stimuli applied to the hand. During low (0.7%) and moderate (1.3%) isoflurane anesthesia the stimuli were repeated and a supramaximal electrical shock was also applied. Tactile stimulation activated bilateral SI and SII, but resulted in no significant activation at low or moderate anesthesia. Electrical shock activated contralateral SI and bilateral SII; low anesthesia completely abolished this response. The supramaximal stimulus activated the caudate nucleus and bilateral thalamus at low anesthesia; these responses were diminished at moderate anesthesia. Isoflurane anesthesia blunts cerebral responses to somatosensory stimuli, and the absence of cortical activation during supramaximal stimulation suggests that noxious-induced movement is generated in lower CNS structures.

Adult↗

PubMed1995

A molecular receptor-binding contrast agent for magnetic resonance imaging of the liver.

RATIONALE AND OBJECTIVES: A gadolinium complex of polydiethylenetriamine pentaacetic acid polyneogalactosyl polylysine (Gd-DTPA-gal-PL) was developed and tested as a paramagnetic contrast agent for magnetic resonance (MR) imaging of the liver. The agent was designed for receptor-mediated uptake by the asialoglycoprotein receptor (ASGP-R), which is unique to hepatocytes and exhibits high specificity for galactose-terminated glycoconjugates. METHODS: Polylysine was alkylated with a mixed anhydride of diethylenetriamine pentaacetic acid. This product was complexed with gadolinium and N-alkylated with 3-oxopropyl-1-thio-beta-D-galactopyranoside. With this reaction sequence, we prepared a gadolinium complex consisting of 2284 galactose groups and 858 chelators per polylysine having 2136 amino groups. Hepatic enhancement was tested by MR imaging of nine rats with liver-implanted mammary adenocarcinoma before and after injection of 20 x 10(-9) mol/kg Gd-DTPA858-gal2284-PL2136. The conjugate was labeled with technetium-99m and tested (1.5 x 10(-10) mol/kg) for hepatic specificity via nuclear imaging. RESULTS: Mean hepatic enhancement was 86% within 10 min and remained constant for 25 min. Hepatic relative intensity exceeded preinjection intensities by at least four times the standard deviation of the preinjection values (p < .01). The tumors, which are devoid of ASGP-R, did not exhibit significant enhancement (p > .1). The liver accumulated 90% of the technetium-99m-labeled conjugate. CONCLUSION: A molecular paramagnetic ligand to the asialoglycoprotein receptor has been developed for hepatocyte-specific MR contrast enhancement.

Adenocarcinoma↗

PubMed1995

Functional magnetic resonance imaging depicts the brain in action.

In summary, FMRI is a new technique for discovering the organization and function of the brain. The ability rapidly and non-invasively to image regional cerebral blood flow, blood volume, and blood oxygenation may strengthen diagnoses in neurology, neurosurgery, and trauma medicine. The ability to localize specific functions in an individual's brain will have a large impact on the planning of therapeutic interventions, and in predicting outcomes after disease and injury. Substantial contributions to the diagnosis and treatment of psychiatric disorders are expected based on the ability to image subtle differences in a patient's response to auditory and visual stimuli of different emotional content.

Brain↗

PubMed1994

Algorithms for improving calculated streamlines in 3-D phase contrast angiography.

Streamline display is a unique alternative to cross-sectional slice or projection display, because streamlines more clearly show the patterns of blood flow within the vessel. Flow patterns associated with atherosclerosis, such as streamline separation and recirculation, can be quickly identified with this display. Streamlines can be calculated using velocity data obtained from 3-D phase contrast angiographic pulse sequences. However, these streamlines often pass through the wall of vessel or show intraluminal sources and sinks of blood. The author has developed iterative least squares algorithms to improve the realism of streamlines. The velocity data is modified so that the resulting streamlines do not pass through the vessel wall and there are no intraluminal sources or sinks. He has applied the algorithms to velocity data obtained from a flow phantom and the carotid arteries of normal volunteers. Streamlines derived from the processed velocity fields are more realistic and provide more precise flow quantitation.

Algorithms↗

PubMed1994

Experimental study of the effects of "fractional" gating on flow measurements.

Velocity encoded phase imaging is subject to errors from phase and amplitude variations of the k-space data caused by beat-to-beat variations of the flow. Fractional cardiac gating is defined as asynchronous gating with each phase encode step occupying a fixed fraction of the RR interval. The gating fraction is the inverse of the number of phase encode steps taken per RR interval. Studies in normal subjects show that deviations and standard errors of ascending and descending aorta flow measurements are significantly greater with decreased gating fraction. Significant errors occur when gating does not separate systolic and diastolic data. The studies establish a graded trade-off between flow measurement accuracy and precision with imaging time, and show that standard nongated phase contrast measurements of strongly pulsatile flow are unreliable.

Angiography↗

PubMed1994

Noninvasive measurement of renal hemodynamic functions using gadolinium enhanced magnetic resonance imaging.

A technique for the assessment of single kidney hemodynamic functions utilizing a novel MR pulse sequence in conjunction with MR contrast material administration is described. Renal extraction fraction (EF) is derived by measuring the concentration of the incoming contrast agent in the renal artery and the outgoing concentration in the renal vein. The glomerular filtration rate (GFR) can then be determined by the product of EF and renal plasma flow. A modified inversion recovery MR pulse sequence is used to measure the T1 of moving blood. This pulse sequence uses a spatially nonselective inversion pulse. A series of small flip angle detection pulses are then used to monitor the recovery of longitudinal spin magnetization in an image plane intersecting the renal vessels. The recovery rate is measured in each vessel and the T1 of blood determined. These T1 measurements are then used to determine the ratio of contrast concentration in the renal arteries and veins. Blood flow measurements can be obtained simultaneously with T1 measurements by inserting flow-encoding magnetic field gradients into the pulse sequence. Preliminary results in human volunteers suggest the feasibility of noninvasively determining hemodynamic functions with magnetic resonance.

Algorithms↗

PubMed1994

Estimation of total coronary artery flow using measurements of flow in the ascending aorta.

This paper describes a technique for estimation of total (right+left) coronary artery flow using MRI flow measurements in the ascending aorta. The technique is based on the principle that the flow in a vessel branch is equal to the difference of the net flow measured above and below the branch ostia. Aortic net flow is measured at four or more axial oblique slices from below the aortic valve to above the highest location of the coronary vessel ostia in late diastole. A flow model properly interprets the flow measurements in slices that contain the coronary ostia. Results in five normal subjects show that total coronary artery flow can be measured with a standard error of about 90 cc/min, 30% of total coronary artery flow. Potential clinical uses include noninvasive measurement of coronary flow reserve. Pulse sequence improvements are necessary to reduce examination time and improve accuracy and precision.

Algorithms↗

PubMed1993

Measurement of coronary artery flow reserve by magnetic resonance velocity mapping in the aorta.

Coronary artery flow occurs predominantly in diastole via retrograde flow in the ascending aorta, some of which supplies the coronary arteries while the remainder recirculates in the ascending aorta. We used magnetic resonance velocity mapping to measure global coronary artery diastolic flow in the ascending aorta. In eight normal subjects and in four patients with possible ischaemic heart disease but with normal perfusion scans, the mean coronary flow reserve (CFR) was 269 ml/min. CFR was zero in seven patients with coronary artery disease. We have shown that CFR can be measured non-invasively with this technique.

Aorta↗

PubMed1993

RF pulse design using the inverse scattering transform.

The inverse scattering transform (IST) is a mathematical transformation that can be used to derive RF pulses from functions called continuous spectra describing the final state of the spin system. This paper reviews three seemingly unrelated numerical algorithms that have appeared in the literature, and shows that they are all derivable from the IST. When the continuous spectra are rational, the finite rank kernel method is used to convert the IST to a matrix equation that is easily solved. Another algorithm, equivalent to the so-called "layer stripping" algorithm used in seismology, is derived by assuming that the spectra are Fourier series. Finally, the Shinnar-Le Roux (SLR) algorithm is derived by assuming that the spectra are ratios of Fourier series. With proper interconversion between the rational, series, and ratio of series forms of the continuous spectra, these algorithms generate RF pulses with identical or nearly identical shapes and performance properties, and can be regarded as equivalent.

Algorithms↗

PubMed1993

Blood flow measurement using variable velocity encoding in the RR interval.

Velocity-encoded phase imaging using asynchronous gating requires input of a velocity encoding value to set the velocity sensitivity of the pulse sequence. The raw data interpolation and reconstruction scheme that the pulse sequence uses forces the encoding value to be constant throughout the RR interval. The sequence and the raw data interpolation scheme were modified to allow two velocity encodings during the RR interval. Two-hundred cm/s encoding was used in systole, and 30 cm/s in diastole. Changing the encoding in diastole significantly improved the accuracy and precision of ascending aorta flow measurements.

Aorta↗

PubMed1992

The analytic theory, optimization, and performance of transparent pulses.

Transparent pulses are defined by the property of having no net effect on stationary spins, while selectively nutating and dephasing flowing spins. They are derived from the inverse scattering transform, a nonlinear extension of the inverse Fourier transform. They can be used as presaturation pulses to suppress selectively the signal from flowing spins. Their intended imaging application is suppression of blood flow artifacts arising from the heart and major vessels. Diastolic images of these areas have significant artifacts that hinder accurate delineation of vessel and chamber boundaries. Transparent pulses significantly improve delineation of these boundaries and therefore could be used to improve the accuracy and precision of cross-sectional area measurements. In this paper, the analytic theory, numerical optimization, and performance characteristics are described. Experimental evidence of flow signal suppression is provided in diastolic imaging of the heart in normal subjects. The long duration and power requirements of the present generation of transparent pulses currently limits their general clinical use.

Artifacts↗

PubMed1992

Factors influencing the accuracy and precision of velocity-encoded phase imaging.

Velocity-encoded phase contrast imaging is being used increasingly in clinical imaging for quantization of blood flow. In this study, the accuracy and precision of ascending aorta flow measurements were found to depend on several subtle aspects of the scan prescription and image analysis. While the usual scan parameters such as TR, TE, and flip angle gave incremental changes in the flow measurements, four additional factors that had a much greater effect on the measurements were identified. These factors were (1) the zero velocity (background) pixel value, (2) the size and shape of the vessel region of interest, (3) the maximum velocity encoded in diastole, and (4) the temporal resolution. Statistical analysis was done on a total of 48 scans on nine normal subjects to confirm the significance of the measured differences using the various choices for each of these factors. These factors must be considered if accurate and precise measurements of blood flow are desired. Estimates of accuracy and precision suggest that quantitative flow measurements from velocity-encoded MR imaging can be clinically useful.

Aorta↗

PubMed1991

Optimized pulse sequences for magnetic resonance measurement of aortic cross sectional areas.

This study was done to improve the ability of magnetic resonance (MR) imaging to provide clear cross-sectional images of the ascending and descending aorta in diastole. The study was motivated by interest in measuring the regional compliance of the ascending aorta, which requires determination of the change in cross sectional area of the vessel between systole and diastole. In diastolic images, residual signal from slow flowing blood and flow artifact consistently obscured the inner boundary of the aortic wall and precluded tracing and measurement of the cross sectional area. We concluded that cross sectional area measurement of the ascending aorta was impossible on our system using standard spin echo sequences. To improve wall delineation in diastolic images, SAT pulses were optimized with respect to pulse timing, slice thickness, and gap. Optimized SAT pulses greatly improved the delineation of the vessel wall by removing unwanted signal from flowing spins. Measurement precision was vastly improved by running two scans with and without flow compensation, and correlating visually and numerically the area measurements from each. We established that each image should be measured by two independent observers and traced three times by each. Using these procedures, diastolic cross-sectional areas of the mid-ascending aorta could be measured with a precision of 2.5%, and the change of cross-sectional area between systole and diastole could be measured with a precision of 10.8%. These measurements were precise enough to detect CAD patients with low aortic compliance from the age-matched controls previously reported in one study. The test based on cross sectional area measurement, with a false positive detection rate of 5%, had a false negative rate of 58%. Compliance measurements by MR at 1.5 T could become clinically useful if normal and abnormal populations are sufficiently separated.

Aorta↗