Search PubMed⌕ Search

Biomedical subjects

T R Nelson

Publications and source records attributed to T R Nelson.

At least 73 records · Page 4Linked to original sources
PubMed1995

Evaluation of normal and abnormal lips in fetuses: comparison between three- and two-dimensional sonography.

OBJECTIVE: The purpose of this study was to determine if three-dimensional (3D) sonography could improve prenatal evaluation of fetal lips in comparison with conventional two-dimensional (2D) sonography. MATERIALS AND METHODS: Sixty-one high-risk pregnant women and 10 low-risk pregnant women were examined with conventional 2D sonography followed by 3D sonography with a volume transducer. The ability to visualize cleft lips and normal lips was compared between the two techniques. RESULTS: Of the 71 fetuses studied, faces were seen in 68 and not seen in three by either 2D or 3D sonography. Abnormal lips were seen in five fetuses on both 2D and 3D sonograms. Of the remaining fetuses, 3D sonography was able to confirm the presence of a normal lip in 92% (58/63) compared with 76% (48/63) with 2D sonography. In the subgroup of fetuses less than 24 weeks' estimated gestational age, 3D sonography confirmed a normal lip in 93% (38/41) of fetuses as compared with 68% (28/41) for 2D sonography. There was no difference between 3D and 2D in the subgroup of fetuses older than 24 weeks. One false-positive finding of cleft lip was observed at 36 weeks' gestational age with the rendered surface display on 3D sonography, whereas the 3D planar views of the same volume showed the lips to be normal. CONCLUSION: 3D sonography was able to confirm the presence of normal lips more frequently than did 2D sonography in fetuses less than 24 weeks' gestational age. Abnormal lips were seen on both 2D and 3D sonograms; however, 3D images of cleft lip were easier to understand for both the family and clinical colleagues.

Cleft Lip↗
PubMed1995

Distance and volume measurement using three-dimensional ultrasonography.

The purpose of this study was to assess the accuracy of distance and volume measurements obtained by three-dimensional ultrasonography. A tissue-mimicking phantom was scanned using a prototype three-dimensional sonographic imaging system to verify distance measurements. Measurements were taken from the reconstructed three-dimensional sonographic data and compared to the real distances. Volume measurements were obtained by scanning 30 balloons of various shapes, sized 23 ml to 2400 ml. Each balloon was scanned twice in two orientations; three different masks were accomplished for each volume. Each volume measurement of 180 three-dimensional sonographic measurements was compared to conventional two-dimensional ultrasonographic volume estimates and to the actual, measured balloon size. Distance measurements had a mean error of 0.02 +/- 3.65% (range, -4.27 to 7.18%). Two-dimensional sonographic volume estimates using traditional scanner based methods had a mean error of 13.7 +/- 10.1%. Three-dimensional sonographic volume measurements had a mean error of 2.2 +/- 2.9% for regular and irregular objects over the entire range of volumes. The masking required 10 to 30 min. The field of view varied from 10 to 24 cm with a mean object depth of 9.8 cm. Three-dimensional ultrasonographic methods can provide accurate volume measurements of regular and irregular objects and offer improved accuracy compared to traditional two-dimensional methods.

Equipment Design↗
PubMed1995

Fetal face visualization using three-dimensional ultrasonography.

Evaluation of the fetal face is an essential part of the sonographic examination for high risk pregnancies. Even under optimal conditions, the complex curvature of the face makes it difficult to obtain adequate images with two-dimensional ultrasonography, and many cross-sectional images are required to obtain a complete impression. The purpose of this paper is to show preliminary work in assessing the utility of three-dimensional ultrasonographic visualization of the fetal face. Fetal facial features were evaluated with three-dimensional sonography by scanning with a volume transducer and compared to conventional two-dimensional ultrasonographic images in 27 fetuses (gestational ages 10 to 39 weeks). Surface rendered three-dimensional sonographic images of the fetal face were obtained in 24 of 27 fetuses. In four cases the upper lip was clearly imaged on three-dimensional ultrasonography when it could not be seen on two dimensional ultrasonography. Information requiring multiple planes with two-dimensional ultrasonography could be demonstrated on a single image from three-dimensional ultrasonography. Images of abnormal faces were seen with both two- and three-dimensional ultrasonography in two cases of cleft lip and one case of holoprosencephaly. Volume data acquisition required approximately 10 sec and reconstruction required approximately 5 sec with instantaneous review of planes through the volume data set. Surface rendering required 2 to 10 min depending on the angular viewing range. Three-dimensional ultrasonography has the potential to provide improved visualization of the fetal face compared with conventional two-dimensional sonographic imaging.

Anencephaly↗
PubMed1994

The cost of third-year clerkships at large nonuniversity teaching hospitals.

BACKGROUND: Large nonuniversity teaching hospitals are major providers of the clinical training component of undergraduate medical education, yet little information is available to policymakers, participating hospitals, or sponsoring medical schools on the institutional costs of this service. OBJECTIVE: To determine the costs associated with teaching students in required third-year clerkships for a group of large nonuniversity teaching hospitals. SETTING/PARTICIPANTS: A total of 201 medical students from nine large nonuniversity teaching hospitals affiliated with nine medical schools that participate in required third-year clerkships. METHODS: During a typical week, students completed 24-hour time and activity logs that classified each activity, instructor, and audience. From these logs, the number of teaching hours by full-time faculty and others were estimated and costs were calculated. RESULTS: Full-time faculty provided a mean of 0.242 h/d of formal teaching, 0.326 h/d of informal teaching, and 0.581 h/d of supervised patient care training per student, an estimated direct faculty cost of $412 per week per student. The cost of direct and indirect departmental and academic administration, as well as other direct out-of-pocket medical education costs, added $250 per week per student. The average annual clinical program cost of third-year clerkships to nonuniversity hospitals and their full-time faculties was $31,776 per student. This figure does not include the substantial contributions of teaching by other than paid faculty (eg, volunteer physicians and residents), which was important in terms of activity and service provided. CONCLUSIONS: Direct and indirect costs of third-year medical student education for most hospitals in this study was more than $1 million per year, well in excess of the average support provided by sponsoring medical schools.

Clinical Clerkship↗
PubMed1994

Mapping myocardial activation distributions using neural networks: 2-D simulation results.

The goal of this study was to explore the capabilities of neural networks to map with accuracy the sequence and location of myocardial activation using QRS complexes simulating normal and altered activation. A two-dimensional (2-D) fractal-based computer model of myocardial activation was used to develop training data for initial network learning. Two types of activation scenarios were used to evaluate network learning: 1) 450 training sets based on three activation foci per set using randomly chosen times and activation sites, and 2) 199 training sets based on a sequential, hierarchical blocking of the fractal-based model conduction network. Network learning was evaluated with training and test cases using trained weights. Network-calculated activation maps compared with the target activation maps had a mean error of < 5% in assigning the site and timing of activation. Pointwise mean correlation coefficients were > 0.98 for all conduction network cases and > 0.84 for the more demanding point foci cases. We conclude, based on these simulation results, that neural networks may be used to calculate activation maps using electrocardiogram lead data for a variety of activation patterns.

Animals↗
PubMed1994

Prenatal visualization of cranial sutures and fontanelles with three-dimensional ultrasonography.

The anatomy of the cranial sutures and fontanelles in the developing fetus is difficult to evaluate using conventional two-dimensional ultrasonography (2DUS). Three-dimensional sonographic imaging (3DUS) was performed on eight normal volunteer pregnant patients after informed consent with conventional 2DUS equipment that had been adapted to obtain 3DUS images. 3DUS images of the cranium were evaluated for the presence of specific cranial sutures and fontanelles. Cranial sutures and fontanelles were identified with 3DUS in all fetuses scanned. The sutures most commonly identified included coronal, lambdoidal, and squamosal. The fontanelles most often identified included anterior, posterior, mastoid, and sphenoid. 3DUS offers the capability of identifying cranial sutures and fontanelles more clearly because volume rendered images show the cranial surface in its entirely rather than as a cross-sectional slice, offering the potential to identify pathologic cranial lesions currently not seen with 2DUS.

Cranial Sutures↗
PubMed1992

Three-dimensional ultrasound of fetal surface features.

This paper presents preliminary results of techniques which permit acquisition and display of three-dimensional fetal anatomy using ultrasound image data collected as two-dimensional planar images with commercially available equipment. A precision translational stage was used which permitted the transducer position and orientation in the volume to be accurately determined. Ultrasound video image data were digitized into a personal computer together with transducer position and orientation information. All image and position data were subsequently transferred to a graphics workstation. Gray-scale ultrasound data were three-dimensionally filtered, thresholded and analyzed using maximum intensity, variable transparency and surface rendering techniques to evaluate the fetal surface. Images of arbitrary orientation were displayed interactively on a graphics workstation. Our results demonstrate the potential of three-dimensional ultrasound as a technique for visualization of fetal surfaces, extremities and internal anatomy. Three-dimensional ultrasound offers potential advantages over existing diagnostic methods since it is non-invasive and offers interactive review and viewing optimization after fetal scanning.

Journal Article↗
PubMed1992

AUR Memorial Award 1992. Quantification of amino acids in human body fluids by 1H magnetic resonance spectroscopy. A specific test for the identification of abscess.

RATIONALE AND OBJECTIVES: When polymorphonucleocytes are incubated in proteinaceous fluid, they cause extensive protein degradation, which leads to accumulation of free amino acids. The authors tested whether these free amino acids, particularly valine and leucine, also accumulate in human abscess fluids, but not in other body fluids, and thus could be a specific and distinguishing marker for the presence of an abscess. METHODS: Thirty fluids, obtained by percutaneous drainage from 28 patients, were lyophilized and reconstituted in 2H2O before in vitro 1H magnetic resonance (MR) spectroscopy. Concentrations of valine and leucine were determined by comparison of spectra before and after addition of known amounts of valine and leucine. Two chart reviewers, blinded to the spectroscopic results, categorized cases as abscess (n = 14), non-abscess (n = 15), or infection but not abscess (n = 1). RESULTS: The concentration of valine and leucine was significantly higher in the abscess fluids, 2.57 +/- 1.90 mM than in the non-abscess fluids, 0.25 +/- 0.33 mM (P < .001). The one infected fluid which was not an abscess had no amino acids. Using 0.8 mM as the threshold concentration of valine and leucine necessary for the diagnosis of abscess resulted in a sensitivity rate of 86% and a specificity rate of 94%. CONCLUSION: The authors conclude that identification of high concentrations of valine and leucine by 1H MR spectroscopy may be a specific test for the diagnosis of abscess. This technique merits further investigation in vivo.

Abscess↗
PubMed1992

3-dimensional sonographic analysis based on color flow Doppler and gray scale image data: a preliminary report.

This paper presents preliminary results of a technique that permits acquisition and display of three-dimensional (3D) anatomy using data collected from color flow Doppler and gray scale image sonography. 3D sonographic image data were acquired as two-dimensional planar images with commercially available equipment. A translational stage permitted the transducer position and orientation to be determined. Color flow sonographic video image data were digitized into a PC-AT computer along with transducer position and orientation information. Color flow velocity and gray scale data were separated, 3D filtered, and thresholded. A surface rendering program was used to define the vessel blood-lumen interface. Planar slices of arbitrary orientation and volume rendered images were displayed interactively on a graphics workstation. The technique was demonstrated in a lamb kidney in vitro and for the carotid artery at the bifurcation in vivo. Our results demonstrate the potential of 3D sonography as a technique for visualization of anatomy. Color flow data offer direct access to the vascular system, facilitating 3D analysis and display. 3D sonography offers potential advantages over existing diagnostic studies in that it is noninvasive, requires no intravenous contrast material, offers arbitrary plane extraction and review after the patient has completed the examination, and permits vascular anatomy to be visualized clearly via rendered images.

Animals↗
PubMed1990

The fractal lung: universal and species-related scaling patterns.

The mammalian lung exhibits features of a fractal tree: heterogeneity, self-similarity and the absence of a characteristic scale. The finite nature of the lung ultimately limits the range over which self-similarity scaling characteristics are applicable. However, generalization based on the scaling features of fractals, provides unique insight into geometric organization of anatomic structures. Furthermore, the mathematical theory of renormalization groups provides a description of the harmonically-modulated inverse power-law scaling observed for bronchial tree dimensions observed in different species. Compared to several mammalian species (dog, rat, hamster), the human lung shows marked differences in the phase of the harmonic modulation for both length and diameter measurements. These inter-species scaling differences suggest that evolutionary factors modify certain universal features of morphogenesis.

Anatomy, Comparative↗
PubMed1990

Device for the calibration of flow-velocity-measuring Doppler ultrasound equipment.

A new device is described for verifying the calibration accuracy of flow-velocity Doppler ultrasound (US) equipment. A rotating circular disk whose circumferential velocity may be fixed or modulated provides a strong signal source suitable for calibrating clinical Doppler US instruments. Circumferential edge velocity, derived from the disk angular frequency, is used to verify the accuracy of Doppler instrument calibration. A limited survey of routinely used Doppler US instruments demonstrates that calibration accuracy generally is satisfactory for clinical purposes, with minimal variation between instruments. Factors that affect measurements include transducer type, scale range, and display size. All transducers used on a specific piece of equipment need to be tested because the transducer design is an important part of the instrument operation. Variations were observed in reported velocities obtained from different transducers on the same equipment and for the same transducer with different scale ranges. In particular, some scales were more accurate than others, suggesting that individual scales should be tested when performing clinical Doppler US instrument calibration. Other measures of performance including scale display range, sample depth, aliasing, and transducer selection may be studied to identify their effect on measurement accuracy. Temporal modulation of angular velocity produces waveforms that may be used to simulate pulsatile velocity characteristics. The device is simple to construct and use, and it provides a convenient way to verify high-quality instrument performance.

Blood Flow Velocity↗
PubMed1990

Fractals. Physiologic complexity, scaling, and opportunities for imaging.

Fractal organization and behavior is an important and ubiquitous feature of biologic systems. Recognition of the properties and scaling relations can yield important clues regarding the underlying anatomy and physiology of most organs. Potential applications are many, and this brief article has considered only a few areas where there has been progress to date. Recognition of the importance of physiologic scaling has application regarding: proper extrapolation of drug doses from laboratory to human; understanding body mass and surface area relationships related to growth and development; the kinetics of basic biochemical reactions; stress-strain relationships of osteostructural development; and numerous other important processes. As imagers with access to a wide range of sophisticated instrumentation employing diverse probes to extract anatomic, and increasingly physiologic, information, radiologists are poised to use the features of fractals and nonlinear processes to expand the scope and precision of diagnostic information available for patient care.

Diagnostic Imaging↗
PubMed1988

The Doppler signal: where does it come from and what does it mean?

Doppler sonographic measurement of blood velocity and associated physiologic parameters is a powerful diagnostic technique. State-of-the-art instrumentation incorporates velocity measurement with two-dimensional imaging capability; it uses intensity and color coding to display complex physiologic and anatomic data to the observer in an easily understood format. Although the concepts underlying Doppler sonography are not complex, mastery of the technique requires extra training and commitment. The principal features and clinical practicalities associated with Doppler sonography are summarized in the following paragraphs. Continuous-wave Doppler is very sensitive to small vessels and has no upper velocity limit. In addition, the instrumentation is not complex and produces relatively low acoustic power. A significant drawback to continuous-wave Doppler is that there is no depth sensitivity, and thus complex structures or multiple vessels can give conflicting information. Pulsed Doppler (including duplex and color-flow) instrumentation has the capability of depth resolution and a variable sample volume. Pulsed Doppler equipment is prone to aliasing (false velocity indications) under some circumstances and also produces higher peak power levels than does continuous-wave equipment. Duplex equipment is more complex and expensive than continuous-wave equipment because the two-dimensional and Doppler modes must be synchronized in operation and display. Color-flow equipment is extremely complex and expensive. Color flow provides information of a qualitative and limited quantitative value. Absolute measurement still requires range-gate measurements. Technical and anatomic factors will affect the measured velocity profiles. Thus, it is important to fully appreciate the anatomy of the vessel and the angle between the vessel and the ultrasound beam when making quantitative measurements. Measurements that evaluate the velocity waveform and make use of ratios, such as the pulsatility index, eliminate the need for angular corrections; however, artifacts due to unappreciated anatomic or wall characteristics may lead to incorrect information if all parameters are not fully understood. Doppler sonographic measurements may be used to determine the presence of flow, determine the direction of flow, identify time-varying velocity characteristics, and detect velocity disturbances. Because flow and velocity are related, it is possible to estimate flow from velocity measurements with careful calibration and proper precautions. Velocity is related to flow, which, in turn, is related to both pressure and vascular resistance.(ABSTRACT TRUNCATED AT 400 WORDS)

Blood Flow Velocity↗
PubMed1988

Doppler ultrasound of twin transfusion syndrome.

Doppler sonography of umbilical arteries was used to evaluate eight cases of twin transfusion syndrome (TTS). Data were collected regarding the Doppler and real-time sonographic evaluation, clinical course, and outcome. In addition, the literature was reviewed. An abnormal peak systolic velocity (A) to end diastolic velocity (B) ratio, as defined by Giles et al, was seen in at least one twin in five cases. A difference in the A/B ratios between the two twins was greater than 0.4 in all eight cases. Doppler studies were able to suggest which fetus was encountering greater placental resistance, however they could not differentiate donor from recipient or provide prognostic data regarding outcome. Doppler evaluation was helpful when there was uncertainty as to whether growth discrepancy in a twin pregnancy was significant enough to suggest a pathologic state. In the future, Doppler sonography may be helpful in evaluating the effectiveness of therapy in TTS. Variable Doppler findings confirm that TTS is an extremely complex dynamic physiologic state.

Blood Flow Velocity↗
PubMed1987

High resolution proton NMR spectroscopy of human amniotic fluid.

Human amniotic fluid (HAF) is a dynamic system whose characteristics depend on continuous interchanges between fetal and maternal circulations. HAF reflects not only the environment of the fetus but may also provide information about fetal development or pathology. The concentration of HAF constituents varies with gestational age and pathological states. The number of the compounds currently implicated in fetal developmental pathology are relatively few. Currently used assay methods are not adequate to totally explain or predict the complex biochemistry of the fetus. The purpose of this work was to investigate HAF with NMR spectroscopy. In the present study HAF was obtained from 47 women undergoing routine amniocentesis. Cells were separated for karyological analysis and the supernatant was acid-extracted, lyophilized and re-suspended in D20 resulting in a concentration increase over native fluid. 1H NMR spectra were obtained at 360 MHz and 60 MHz. Eighteen compounds including several amino acids, were identified using parallel reference and standard addition protocols. NMR spectroscopy detected compounds of known clinical importance including glucose, leucine, isoleucine, lactate and creatinine. In conclusion, we have demonstrated that a number of physiologically relevant compounds are readily observable in HAF using 1H NMR spectroscopy. This technique can currently provide valuable information regarding HAF composition and has the potential of being used in vivo in the future.

Amniotic Fluid↗
PubMed1987

Temperature dependence of proton relaxation times in vitro.

Accurate measurement of tissue relaxation characteristics is dependent on many factors, including field strength and temperature. The purpose of this study was to evaluate the relationship between sample temperature, viscosity and proton spin-lattice relaxation time (T1) and spin-spin relaxation time (T2). A review of two basic models of relaxation the simple molecular motion model and the fast exchange two state model is given with reference to their thermal dependencies. The temperature dependence for both T1 and T2 was studied on a 0.15 Tesla whole body magnetic resonance imager. Thirteen samples comprising both simple and complex materials were investigated by using a standard spin-echo (SE) technique and a modified Carr-Purcell-Meiboom-Gill (CPMG) multi-echo sequence. A simple linear relationship between T1 and temperature was observed for all samples over the range of 20 degrees C to 50 degrees C. There is an inverse relationship between viscosity and T1 and T2. A quantity called the temperature dependence coefficient (TDC) is introduced and defined as the percent rate of change of the proton relaxation time referenced to a specific temperature. The large TDC found for T1 values, e.g. 2.37%/degrees C for CuSO4 solutions and 3.59%/degrees C for light vegetable oils at 22 degrees C, indicates that a temperature correction should be made when comparing in-vivo and in-vitro T1 times. The T2 temperature dependence is relatively small.

Magnetic Resonance Spectroscopy↗
PubMed1987

The effect of dexamethasone on tissue water distribution and proton relaxation in Panc02 tumors.

The present experiments were conducted to determine the effects of dexamethasone mediated changes in tumor water distribution on proton relaxation times (T1, T2) in a murine pancreatic adenocarcinoma (Panc02). Spin lattice (T1) and spin-spin(T2) relaxation times were determined by ex vivo methods (10 MHz) and by in vivo imaging techniques (6.25 MHz) at various intervals after single or multiple dexamethasone treatments. In complementary studies, dexamethasone mediated changes in tumor capillary permeability, tumor water distribution, relative tumor blood flow and tumor cell proliferation were also determined. Proton spin lattice (T1) and spin-spin (T2 relaxation times for Panc02 tumors shortened within two hours of a single dexamethasone treatment. The time course and magnitude of this response was dexamethasone dose dependent. The time dependent changes in T1 and T2 after dexamethasone were similar at 10 MHz (ex vivo) and 6.25 MHz (in vivo imaging). Although dexamethasone produced little or no change in total tumor water content and tumor cell proliferation, transient changes in the physiologic distribution of tumor water were clearly demonstrated. The data supports the idea that dexamethasone induced changes in the distribution of tumor water were mediated by changes in capillary permeability and tumor blood flow. These physiologic responses produced serial changes in tumor extracellular extravascular water content that were consistent with the observed changes in tumor T1 and T2. The results from these experiments might imply that therapy associated changes in tumor proton relaxation times may not only reflect changes in tissue water content, but may also reflect physiologic responses which alter the distribution of tissue water and solute.

Adenocarcinoma↗