Biomedical subjects

D C Noll

Publications and source records attributed to D C Noll.

52 records · Page 3Linked to original sources

PubMed1996

Localizing the lexicon for reading aloud:replication of a PET study using fMRI.

Functional magnetic resonance imaging (fMRI) was used to investigate the neural basis of written word recognition in two normal subjects. With a 1.5T scanner and temporal surface coil, T2 gradient echo images were obtained while subjects read words aloud. As a control condition, subjects visualized false font strings and said the word "range' each time such a string appeared. These two conditions were presented in an oscillatory pattern, alternating 30 s of each condition for a total of 4 min. Comparison of the two conditions using cross-correlation demonstrated strong activation in both subjects in the left posterior superior temporal gyrus, near the site predicted for the visual input lexicon by Déjerine and recently demonstrated by positron emission tomography.

Adult↗

PubMed1996

Improved image registration by using Fourier interpolation.

This paper presents a technique for performing two-dimensional rigid-body image registration for functional magnetic resonance images (fMRI). The method provides accurate motion correction without local distortion. The approach is to perform the translation and rotation in the Fourier domain. For images sampled on a grid, such as in echo-planar imaging (EPI), one potential stumbling block to this approach is the computational burden of reconstruction, since the rotated image will no longer be on the Cartesian grid. A method of approximating rotations via local translations (shearing) is presented, which keeps the data on the Cartesian grid. This can provide quite accurate approximations with only a moderate amount of computation. A mean squared error (MSE) criterion is used for determining the registration parameters. This method is tested on several sets of simulated images and shown to have an accuracy ranging from 0.02 to 0.3 pixels for images with SNRs ranging from 100 to 10, respectively. These techniques have been tested on several sets of images. They are shown to work well on real subjects, for both echo-planar and spiral data acquisition schemes. The techniques are used in an activation study in which the subject moved his head during image collection. After use of this registration technique, the activation is easily detected.

Fourier Analysis↗

PubMed1996

Preoperative cortical localization with functional MRI for use in stereotactic radiosurgery.

Accurate localization of the lesion with respect to functionally significant brain is essential to safe stereotactic radiosurgical dose planning. We report the use of functional MR imaging in 3 patients to identify critical areas of surrounding brain and to provide assistance with dose planning, especially with regard to shaping the peripheral isodose around the lesion. We used a functional MRI system employing a conventional 1.5-tesla MRI unit that can detect decreases in deoxyhemoglobin concentration occurring with performance of specific tasks. Two of the patients had supratentorial arteriovenous malformations and 1 patient had a recurrent parasagittal meningioma. Functional MRI provided information on the location of speech, motor, and sensory cortex in these patients. Radiosurgical dose plans were constructed that kept these cortical areas outside of the 30% isodose curves. We believe that the safety of supratentorial parenchymal radiosurgery will be enhanced by the localization of critical brain regions around the target.

Adult↗

PubMed1995

Comparison of functional magnetic resonance imaging with positron emission tomography and magnetoencephalography to identify the motor cortex in a patient with an arteriovenous malformation.

Alterations in gyral contour made it difficult to identify the motor cortex thought to be near an arteriovenous malformation (AVM) in a 24-year-old man considered for stereotactic radiosurgery. Functional imaging in three modalities was performed preoperatively to compare the reliability of localization using functional magnetic resonance imaging (fMRI) on a conventional scanner with positron emission tomography (PET) and magnetoencephalography (MEG). Similar tasks were used for each imaging modality in an attempt to activate and identify the sensory and motor cortex. Data from all three modalities converged for the sensory task, and fMRI and PET data converged for the motor task. The right hemisphere motor strip was localized adjacent and anterior to the AVM. These data were used in planning the radiosurgery isodose configuration to the AVM in order to reduce the irradiation of motor cortex parenchyma. A postoperative fMRI study was also performed using newer techniques to reduce head motion artifact and to improve signal-to-noise ratio. The data confirmed the conclusions derived from the preoperative evaluations. This study demonstrates how conventional MRI scanners can be used for functional studies of use in surgical planning.

Adult↗

PubMed1995

Improved assessment of significant activation in functional magnetic resonance imaging (fMRI): use of a cluster-size threshold.

The typical functional magnetic resonance (fMRI) study presents a formidable problem of multiple statistical comparisons (i.e., > 10,000 in a 128 x 128 image). To protect against false positives, investigators have typically relied on decreasing the per pixel false positive probability. This approach incurs an inevitable loss of power to detect statistically significant activity. An alternative approach, which relies on the assumption that areas of true neural activity will tend to stimulate signal changes over contiguous pixels, is presented. If one knows the probability distribution of such cluster sizes as a function of per pixel false positive probability, one can use cluster-size thresholds independently to reject false positives. Both Monte Carlo simulations and fMRI studies of human subjects have been used to verify that this approach can improve statistical power by as much as fivefold over techniques that rely solely on adjusting per pixel false positive probabilities.

Brain↗

PubMed1995

Activation of prefrontal cortex in children during a nonspatial working memory task with functional MRI.

Functional magnetic resonance imaging (fMRI) was used to examine the pattern of activity of prefrontal cortex in prepubertal children during performance of a nonspatial working memory task. The children observed sequences of letters and responded whenever a letter repeated with exactly one nonidentical letter intervening. In a comparison task, subjects monitored similar sequences of letters for any occurrence of a single, prespecified target letter. Location of activation closely approximated that observed in a recent fMRI study with adults using exactly the same task. Activation of the inferior and middle frontal gyri was reliably observed within individual subjects during performance of the working memory task relative to the comparison task. Activation increased and decreased with a time course that was highly consistent with the task manipulations and correlated with behavioral performance. To our knowledge, this study is one of the first to demonstrate the applicability of fMRI to a normative developmental population. Issues of age dependence of the hemodynamic responses of fMRI are discussed.

Adult↗

PubMed1994

Variable-averaging RARE.

The RARE method and its variants have become popular, rapid-imaging alternatives to conventional spin-echo imaging, particularly for long repetition time proton density and T2-weighted imaging. One variant is to generate both early and late echo images using the same pulse sequence, which has the added benefit of reduced edge artifacts and blurring. Described in this paper is variable-averaging RARE (VA-RARE), a method by which independent amounts of averaging can be set for the early and late echo images generated by a single scanning sequence. Through the use of this method, the signal-to-noise ratio (SNR) of late echo images can be improved without unnecessarily increasing the number of averages for the early echo image, thus saving scanning time. Comparisons to various alternatives are made with respect to scanning time and image quality. Phantom measurements and in vivo images are given to demonstrate the effectiveness of VA-RARE as an efficient method for improving SNR of late echo time images in RARE imaging.

Humans↗

PubMed1993

Functional topographic mapping of the cortical ribbon in human vision with conventional MRI scanners.

The human brain has anatomically distinct areas in which processing is laid out in space at the millimetre level with substantial variation across individuals. Activity occurs along a cortical ribbon 1.5-3 mm thick in response to specific stimuli. Here we report the first use of cortical ribbon analysis on humans using non-invasive functional magnetic resonance imaging techniques performed with a conventional 1.5 T MRI scanner. Changes in activation were detected using T2*-weighted, gradient echo imaging sequences. Subjects observed partial field, flashing checkerboard patterns (left-right, top-bottom, half rings, and wedges). Stimuli produced magnetic resonance signal changes in the 1-8% range, varying at the millimetre scale, which showed contralateral vertically reflected patterns of activation in the visual cortex. To compare the spatial topographies across subjects, computer algorithms were used to control for the subject-unique folding of cortex, providing a flattened cortical ribbon identifying four topographically distinct areas.

Brain Mapping↗

PubMed1993

Consistent projection reconstruction (CPR) techniques for MRI.

Motion of the subject causes inconsistencies in MR scan data which in turn produce streaks in projection reconstruction (PR) scans or ghosts in 2DFT imaging. It is shown that a data manifold consistent with a static object may be extracted from input scan data by applying consistency criteria based on moment or Fourier expansions of the object's projections. The criteria limit the spectrum of azimuthal variation relative to the radial moments or radial spectral components, and their application diminishes k-space inconsistencies from motion or flow by discarding unallowed expansion terms. This consistent projection reconstruction (CPR) algorithm was applied to the reconstruction of projection data from a moving phantom and from human abdominal sections, and in each case provided reduced motion streaks relative to conventional reconstructions. In addition, CPR was found to be effective when used with 2DFT data by resampling the Cartesian data as radial projections, but to a lesser extent.

Abdomen↗

PubMed1992

Deblurring for non-2D Fourier transform magnetic resonance imaging.

For several non-2D Fourier transform imaging methods, off-resonant reconstruction does not just cause geometric distortion, but changes the shape of the point spread function and causes blurring. This effect is well known for projection reconstruction and spiral k-space scanning sequences. We introduce here a method that automatically removes blur introduced by magnetic field inhomogeneity and susceptibility without using a resonant frequency map, making these imaging methods more useful. In this method, the raw data are modulated to several different frequencies and reconstructed to create a series of base images. Determination of degree of blur is done by calculating a focusing measure for each point in each base image and a composite image is then constructed using only the unblurred regions from each base image. This method has been successfully applied to phantom and in vivo images using projection-reconstruction and spiral-scan sequences.

Algorithms↗

PubMed1992

MR imaging of lung parenchyma: a solution to susceptibility.

The authors have developed a pulse sequence for imaging lung parenchyma with projection reconstruction magnetic resonance (MR) imaging that reduces the effects of motion and susceptibility. In this study, the projection reconstruction technique was further modified by optimizing MR signal frequencies for reconstructing the images. This was done by means of one of two methods. With the first method, a susceptibility map was derived from the raw image data and this map was used to indicate the optimal frequencies for reconstructing the images. The second method of susceptibility correction was a postprocessing technique in which the optimal reconstruction frequencies were selected with use of specific focusing criteria to generate the least blurred image. The effect of using susceptibility map correction on a phantom was demonstrated, and both of these methods were used to improve the visibility of pulmonary structures on images of subjects with normal and abnormal lungs.

Humans↗

PubMedDate not supplied

Spiral K-space MR imaging of cortical activation.

Brain function can be mapped with magnetic resonance (MR) imaging sensitized to regional changes in blood oxygenation due to cortical activation. Several MR imaging methods, including conventional imaging and echo-planar imaging, have been successfully used for this purpose. The authors investigated spiral k-space MR imaging, implemented with an unmodified 1.5-T clinical imager, for imaging of cortical activation. A gradient-echo, spiral k-space imaging method was used to measure activation in the primary visual cortex (number sequence task), primary motor cortex (fist-clenching task), and prefrontal cortex (verbal fluency task). Comparison of conventional and spiral k-space imaging in the visual and motor cortex, in which signal-to-noise ratio, voxel size, and imaging time were matched, showed that artifacts were reduced with the spiral k-space method, while the area and degree of activation were similar. The number of sections that could be imaged in a fixed time interval was increased by a factor of four with this implementation of spiral k-space imaging compared with conventional imaging.

Brain Mapping↗

PubMedDate not supplied

Tracking of cyclic motion with phase-contrast cine MR velocity data.

A method of computing trajectories of objects by using velocity data, particularly as acquired with phase-contrast magnetic resonance (MR) imaging, is presented. Starting from a specified location at one time point, the method recursively estimates the trajectory. The effects of measurement noise and eddy current-induced velocity offsets are analyzed. When the motion is periodic, trajectories can be computed by integrating in both the forward and backward temporal directions, and a linear combination of these trajectories minimizes the effect of velocity offsets and maximizes the precision of the combined trajectory. For representative acquisition parameters and signal-to-noise ratios, the limitations due to measurement noise are acceptable. In a phantom with reciprocal rotation, the measured and true trajectories agreed to within 3.3%. Sample trajectory estimates of human myocardial regions are encouraging.

Heart↗

PubMedDate not supplied

Deming, quality and the small medical group administrator.

As administrators, writes Douglas Noll, we can coordinate and implement quality measures affecting our practices and which impact the patient's total medical experience. Unfortunately, many smaller groups cannot hire an outside consultant or single employee whose sole purpose would be to monitor quality. Noll offers several simple practices that administrators can use to improve the quality of service in their groups.

Administrative Personnel↗

PubMedDate not supplied

Of chaos, Merlin and the future of medicine.

Chaos theory is a good way to describe what has taken place in the recent history of health care. A prevailing dynamic in nature is for seemingly small variations in an initial set of circumstances to cause very large variations in behavior. In health care, an innocuous policy made at some point in the system may have drastic effects on other parts. Merlin was the fabled wizard of King Arthur's court who was born in the future and lived backward through time, enabling him to foretell events. Similarly, medical practice administrators should envision the future they want for themselves and make the changes now that will result in that future. A methodology for accomplishing that is presented.

Delivery of Health Care, Integrated↗

PubMedDate not supplied

Complexity theory 101.

Health care exhibits the same attributes of self-organization that are evident in the world in general. Systems are at a critical state where there is change and upheaval in all dimensions. Health care is inching closer to a major reorganization as the fundamental issues of cost, access and quality are moving toward a critical state. This article explores some of the aspects of complexity and how they are impacting the future of the health care system.

Continuity of Patient Care↗