Biomedical subjects

J H Downs

Publications and source records attributed to J H Downs.

13 recordsLinked to original sources

PubMed2000

Occipital atrophy is associated with visual hallucinations in Alzheimer's disease.

In this study of patients with Alzheimer's disease (AD), patients with visual hallucinations were compared with patients who did not have visual hallucinations to determine if selective occipital lobe atrophy is associated with visual hallucinations. Seven AD patients with visual hallucinations were matched by cognitive score to 7 AD patients without visual hallucinations and 3-D MRI images obtained. A ratio of measured occipital volumes to whole brain volumes was compared between the two groups. AD patients with visual hallucinations had a significantly smaller occipital/whole brain ratio than AD patients without visual hallucinations. These results suggest visual hallucinations in AD may be associated with neuropathology of the occipital lobe.

Aged↗

PubMed2000

A new vibrotactile stimulator for functional MRI.

Presenting various stimuli in an MRI scanner can be difficult due to the high magnetic field associated with the scanner. Mechanical vibration stimuli are difficult to deliver to subjects in the MRI environment because most vibration devices contain internal circuitry that can adversely interact with the high magnetic field. Piezoelectric ceramics can provide a solution to this problem since they do not require any internal circuitry to vibrate. Piezoceramics are nonmagnetic and they can be made to vibrate if supplied with an alternating current from a straight wire. We designed a piezoceramic vibrotactile stimulator that is safe and effective in functional MRI experiments. The stimulator was tested in an fMRI experiment at 35 and 150 Hz. The results yielded activation sites in the primary sensory cortex and Brodmann area 40 at both frequencies.

Adult↗

PubMed1998

Nutritional assessment in the critically ill.

Essentially, there have not been any outstanding recent developments in nutritional assessment techniques. However, it would appear that the acceptance that there is no absolute gold standard for nutritional assessment has led to the development of disease specific and clinically relevant subjective global type-assessments, which are user-friendly and effective tools. The further development of dual frequency bioelectrical impedance models may allow for greater accuracy in the differentiation of alterations in body composition.

Anthropometry↗

PubMed1997

MR imaging and spectroscopy using hyperpolarized 129Xe gas: preliminary human results.

Using a new method of xenon laser-polarization that permits the generation of liter quantities of hyperpolarized 129Xe gas, the first 129Xe imaging results from the human chest and the first 129Xe spectroscopy results from the human chest and head have been obtained. With polarization levels of approximately 2%, cross-sectional images of the lung gas-spaces with a voxel volume of 0.9 cm3 (signal-to-noise ratio (SNR), 28) were acquired and three dissolved-phase resonances in spectra from the chest were detected. In spectra from the head, one prominent dissolved-phase resonance, presumably from brain parenchyma, was detected. With anticipated improvements in the 129Xe polarization system, pulse sequences, RF coils, and breathing maneuvers, these results suggest the possibility for 129Xe gas-phase imaging of the lungs with a resolution approaching that of current conventional thoracic proton imaging. Moreover, the results suggest the feasibility of dissolved-phase imaging of both the chest and brain with a resolution similar to that obtained with the gas-phase images.

Adult↗

PubMed1997

Telepresence in neurosurgery: the integrated remote neurosurgical system.

This paper describes the Integrated Remote Neurosurgical System (IRNS), a remotely-operated neurosurgical microscope with high-speed communications and a surgeon-accessible user interface. The IRNS will allow high quality bidirectional mentoring in the neurosurgical suite. The research goals of this effort are twofold: to develop a clinical system allowing a remote neurosurgeon to lend expertise to the OR-based neurosurgical team and to provide an integrated training environment. The IRNS incorporates a generic microscope/transport model, Called SuMIT (Surgical Manipulator Interface Translator). Our system is currently under test using the Zeiss MKM surgical transport. A SuMIT interface is also being constructed for the Robotics Research 1607. The IRNS Remote Planning and Navigation Workstation incorporates surgical planning capabilities, real-time, 30 fps video from the microscope and overhead video camera. The remote workstation includes a force reflecting handcontroller which gives the remote surgeon an intuitive way to position the microscope head. Bidirectional audio, video whiteboarding, and image archiving are also supported by the remote workstation. A simulation mode permits pre-surgical simulation, post-surgical critique, and training for surgeons without access to an actual microscope transport system. The components of the IRNS are integrated using ATM switching to provide low latency data transfer. The research, along with the more sophisticated systems that will follow, will serve as a foundation and test-bed for extending the surgeon's skills without regard to time zone or geographic boundaries.

Humans↗

PubMed1997

The props-based interface for neurosurgical visualization.

We describe a three-dimensional human-computer interface for neurosurgical visualization. The interface is based on the two-handed physical manipulation of hand-held tools, or "props", in free space. These user interface "props" facilitate transfer of the user's skills for manipulating tools with two hands to the operation of a user interface for visualizing 3D medical images, without need for training. The interface allows neurosurgeons to explore a 3D MRI scan of a patient's brain during presurgical planning. From the surgeon's perspective, the interface is analogous to holding a miniature head in one hand which can be "sliced open" or "pointed to" using a cross-sectioning plane or a stylus tool, respectively, held in the other hand. Cross-sectioning a 3D volume, for example, simply requires the surgeon to hold a plastic plate (held in the preferred hand) up to the miniature head (held in the nonpreferred hand) to demonstrate the desired cross-section.

Computer Simulation↗

PubMed1997

Basic principles and neurosurgical applications of positron emission tomography.

Positron emission tomography (PET) is a technique for studying functional processes in the human body in vivo. The important clinical applications of PET in neurosurgery include localization of epileptic foci, diagnosis of brain tumors, preoperative brain mapping, and the study of plasticity of the brain following brain damage. The basic physics and neurosurgical applications of PET are presented.

Brain Neoplasms↗

PubMed1996

A PET study of the neural systems of stuttering.

The cause of stuttering is unknown. Failure to develop left-hemispheric dominance for speech is a long-standing theory although others implicated the motor system more broadly, often postulating hyperactivity of the right (language nondominant) cerebral hemisphere. As knowledge of motor circuitry has advanced, theories of stuttering have become more anatomically specific, postulating hyperactivity of premotor cortex, either directly or through connectivity with the thalamus and basal ganglia. Alternative theories target the auditory and speech production systems. By contrasting stuttering with fluent speech using positron emission tomography combined with chorus reading to induce fluency, we found support for each of these hypotheses. Stuttering induced widespread overactivations of the motor system in both cerebrum and cerebellum, with right cerebral dominance. Stuttered reading lacked left-lateralized activations of the auditory system, which are thought to support the self-monitoring of speech, and selectively deactivated a frontal-temporal system implicated in speech production. Induced fluency decreased or eliminated the overactivity in most motor areas, and largely reversed the auditory-system underactivations and the deactivation of the speech production system. Thus stuttering is a disorder affecting the multiple neural systems used for speaking.

Adult↗

PubMed1995

Use of implicit motor imagery for visual shape discrimination as revealed by PET.

Positron emission tomography (PET) can be used to map brain regions that are active when a visual object (for example, a hand) is discriminated from its mirror form. Chronometric studies suggest that viewers 'solve' this visual shape task by mentally modelling it as a reaching task, implicitly moving their left hand into the orientation of any left-hand stimulus (and conversely for a right-hand stimulus). Here we describe an experiment in which visual and somatic processing are dissociated by presenting right hands to the left visual field and vice versa. Frontal (motor), parietal (somatosensory) and cerebellar (sensorimotor) regions similar to those activated by actual and imagined movement are strongly activated, whereas primary somatosensory and motor cortices are not. We conclude that mental imagery is realized at intermediate-to-high order, modality-specific cortical systems, but does not require primary cortex and is not constrained to the perceptual systems of the presented stimuli.

Adult↗

PubMed1994

Evaluation of new algorithms for the interactive measurement of surface area and volume.

The maximum unit normal component (MUNC) method used for surface area measurement and the divergence theorem algorithm (DTA) used for volume measurement were evaluated. The accuracy and precision of these methods were investigated at varying signal-to-noise ratios (SNRs), sampling, spatial averaging, and orientation. The accuracy of the MUNC measured surface area, as indicated by the mean error, was 2.0% for seven spherical samples, with SNRs ranging from 5:1 to 39:1. The precision, as indicated by the percent coefficient of variation (% CV) for these samples, was less than 3.0%. Likewise, the accuracy and precision of the DTA measured volume for these samples were both less than 1.0%. MUNC surface area measurement from 23 samples of a computed tomography (CT) image of a wooden sphere (51.44-mm diameter) with x,y voxel size ranging from 1 to 10 mm and z voxel size ranging from 2 to 14 mm yielded an accuracy of 1.3% and a precision of 2.2%. The DTA volume measurements from 18 samples of the wooden sphere with x,y vowel size ranging from 1 to 8 mm and z size ranging from 2 to 14 mm provided an accuracy of 1.2% and a precision of 1.8%. Measurement of surface area for a cylindrical rod scanned by CT in five different orientations, ranging from along each axis to between all three axes, yielded an accuracy of 3.7% and a precision of 2.0%. The volume of the cylindrical rod measured by the DTA method for these orientations produced an accuracy of 4.0% and a precision of 3.7%. The volume measured by DTA compared well with the volume measured by a modified voxel counting method. The MUNC surface area method was superior to counting surface voxels. The accuracy and precision for five interactive surface area and volume measurements, using paired cut planes to select subsets of a computer-generated sphere with radius 25 pixels, were both less than 1.0%.

Algorithms↗

PubMed1986

Effect of dietary chloride on salt-sensitive and renin-dependent hypertension.

We have previously reported that 1) selective dietary sodium loading (without chloride) does not produce hypertension in rats of the Dahl salt-sensitive strain (DS) and 2) selective chloride loading (without sodium) lowers plasma renin activity in the intact Sprague-Dawley rat maintained on a low NaCl diet. The present study examined the effect of selective dietary chloride loading on two models of hypertension: the DS and the renin-dependent one-kidney, one clip Sprague-Dawley rat. The DS were pair-fed (n = 7/group) a "normal" NaCl, a high NaCl (4%), or a "normal" sodium-high chloride diet for 11 weeks. From Week 7 until the end of the experiment, the high NaCl-fed animals had higher (p less than or equal to 0.05) blood pressures than animals fed either the normal NaCl or normal sodium-high chloride diet, which were not different from each other. Thus, in the DS, hypertension depends on high dietary intakes of both sodium and chloride. In one-kidney, one clip hypertensive rats, selective chloride loading failed to lower plasma renin activity (9 +/- 1 vs 7 +/- 1 ng angiotensin I/ml/hr) or to prevent hypertension (160 +/- 10 vs 166 +/- 9 mm Hg). Thus, selective dietary chloride loading (without sodium) does not alter blood pressure in either salt-sensitive or renin-dependent hypertension.

Animals↗

PubMed1985

Mechanism for inhibition of renin release by acute plasma volume expansion in the dog.

Plasma volume expansion alters renal tubular sodium chloride transport and renal nerve activity. The purpose of this study was to determine the mechanism(s) for inhibition of renin secretion by acute volume expansion with albumin in the anesthetized dog. In dogs with a single intact kidney, albumin infusion decreased renin release by 86% and significantly increased renal blood flow, glomerular filtration rate, and sodium excretion. Albumin volume expansion inhibited renin secretion to a lesser extent in dogs with denervated filtering kidneys and in dogs with innervated nonfiltering kidneys. In dogs with denervated nonfiltering kidneys, albumin infusion did not change renin secretion. Comparable volume expansion was produced in all groups. Thus, inhibition of renin release by acute plasma volume expansion is dependent on both a renal tubular mechanism and the integrity of the renal nerves. Partial inhibition of renin release was observed with interruption of either one of the mechanisms, whereas interruption of both mechanisms totally abolished the effect of acute plasma volume expansion on renin secretion.

Albumins↗

PubMedDate not supplied

A geometric model for measurement of surface distance, surface area, and volume from tomographic images.

Surface area and volume are essential measurements in the morphometric assessment of anatomical structures. New algorithms were developed to measure (1) distance along a curve, (2) surface area, and (3) volume using data extracted from tomographic images as a geometrical surface model. The model is a list of coordinates and normal vectors for each voxel or point gathered from the surface of a selected object. The resulting surface-based pointlist is also used for high-speed rendering of surfaces. Differential arclength and surface area are measured with high numeric precision by using the absolute value of the maximum component of the unit normal vector (MUNC) to approximate their values. These differential values are summed to measure distance along a curve and surface area. A discrete form of the Divergence theorem, also using the MUNC, is used to calculate volume. The intrinsic accuracy of the measurement algorithms was evaluated using computer generated pointlists of circles, ellipses, spheres, and ellipsoids. Compared to standard measurement techniques, the new algorithms provided the greatest accuracy and least shape-related bias for measurement of distance, surface area, and volume. Feasibility of using the new algorithms to measure physical objects was tested with CT images of spherical, egg-shaped, and irregular shaped objects. The Dividing Cubes algorithm was used to segment and create pointlists from the CT data. Volume and surface area measurements from CT data compared extremely well with reference values for most objects tested (errors less than 2%).

Algorithms↗