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Biomedical subjects

John Palmer

Publications and source records attributed to John Palmer.

At least 19 recordsLinked to original sources
PubMed2006

Lightness constancy in 4-month-old infants.

In the present study, discrete trial familiarization/novelty techniques were used to study lightness constancy in 4-month-old infants. The test stimuli were real objects (paper smiley faces) of two different reflectances, dark gray (17% reflectance) and light gray (54% reflectance). In Experiment 1, the test stimuli were viewed against a white (90% reflectance) surround, and in Experiment 2, against a black (4.6% reflectance) surround. In Experiments 1 and 2, the illumination was changed between familiarization and test phases of each trial. In Experiment 3, the reflectance of the surround was changed from white to mid gray (28.5% reflectance) between familiarization and test phases of each trial. With the white surround, the infants preferred the face with the novel reflectance, consistent with the presence of lightness constancy. With the black surround, the infants showed no preference between faces with novel reflectance vs. novel luminance. With the changing surround, the infants showed a small preference for the stimulus with the novel ratio, as opposed to the stimulus with the novel reflectance and the novel luminance. The results are discussed in the context of adult cues for lightness constancy, including white anchor points and local luminance ratios.

Adult↗
PubMed2006

Metabolic syndrome in the elderly.

The prevalence of metabolic syndrome is increasing worldwide, especially among the elderly. Due to multiple age-related physiologic mechanisms, the elderly are at increased risk of developing intra-abdominal obesity and the metabolic syndrome, including nonalcoholic steatohepatitis. Metabolic syndrome consists of obesity, insulin resistance, dyslipidemia, and hypertension leading to increased risk of cardiovascular disease (CVD) and renal events. With the future population dynamics, the metabolic syndrome should be emphasized among the health care field, researchers, and clinicians. Without proactive and preventative efforts, elderly patients and the health care system will likely experience an epidemic of the metabolic syndrome and the associated CVD.

Aged↗
PubMed2006

A model that accounts for the interdependence of extent and severity in the automatic evaluation of myocardial defects.

BACKGROUND: The extent and severity are two important parameters when describing a regional defect in myocardial single-photon emission computed tomography (SPECT) perfusion imaging. Intuitively, these two parameters should be independent of each other, but we have shown in a previous study that there is an interdependence. This interdependence has been investigated in two commercially available analysis programs (AutoQUANT and 4D-MSPECT) using Monte Carlo-simulated SPECT data. METHODS: An anthropomorphic digital computer phantom and a Monte Carlo program were used to generate SPECT data. Several defects of different volumes and lesion activity uptake reductions were simulated and evaluated. Comparison of the measures of extent and severity with their corresponding known values led to the development of a correction model based on least-squares parameter estimation. This model was then applied to a test group consisting of 10 different computer-simulated patients. RESULTS: Our results showed that the interdependence was reduced significantly for most of our test cases after applying the correction method. The application of the correction model to the test group demonstrated that the model was robust with respect to different patient geometries. A further test with projections that simulated a perfect SPECT system revealed that the interdependence between the extent and severity was not caused by the limited spatial resolution of the SPECT system, but rather the inherent design of the algorithms of the analysis programs. CONCLUSIONS: A model has been developed to take into account the interdependence of the extent and severity.

Algorithms↗
PubMed2006

Hypertension--a treatable component of the cardiometabolic syndrome: challenges for the primary care physician.

Patients with the cardiometabolic syndrome (CMS) have an adverse cardiovascular risk factor profile, placing them at increased risk of stroke, coronary artery disease, chronic kidney disease, and type 2 diabetes mellitus. Although no specific treatments for CMS are available per se, prompt recognition and treatment of the individual components of the condition can prevent or delay the development of comorbidities. Primary care physicians are ideally positioned to identify patients with CMS and implement early intervention strategies. Hypertension contributes to many complications of CMS, and rigorous blood pressure control will help to delay or prevent end-organ vascular damage. Achieving blood pressure control to current guideline standards should be eagerly sought in the majority of patients through a combination of lifestyle modifications and appropriate pharmacologic therapy. Antihypertensive drug choice should be personalized, taking into account the CMS determinants present and any compelling indications for specific agents. As an initial approach, a thiazide diuretic is suitable for most cases of uncomplicated hypertension, although many patients will require additional antihypertensives from other classes to achieve their blood pressure goal. It is predicted that, due to the increase in unhealthy lifestyles, the prevalence of CMS will rise in the coming years. Therefore, by meeting the challenge of attaining and maintaining blood pressure control in patients with CMS, primary care physicians have the unique opportunity to markedly improve the health of the nation.

Albuminuria↗
PubMed2005

The effect of stimulus strength on the speed and accuracy of a perceptual decision.

Both the speed and the accuracy of a perceptual judgment depend on the strength of the sensory stimulation. When stimulus strength is high, accuracy is high and response time is fast; when stimulus strength is low, accuracy is low and response time is slow. Although the psychometric function is well established as a tool for analyzing the relationship between accuracy and stimulus strength, the corresponding chronometric function for the relationship between response time and stimulus strength has not received as much consideration. In this article, we describe a theory of perceptual decision making based on a diffusion model. In it, a decision is based on the additive accumulation of sensory evidence over time to a bound. Combined with simple scaling assumptions, the proportional-rate and power-rate diffusion models predict simple analytic expressions for both the chronometric and psychometric functions. In a series of psychophysical experiments, we show that this theory accounts for response time and accuracy as a function of both stimulus strength and speed-accuracy instructions. In particular, the results demonstrate a close coupling between response time and accuracy. The theory is also shown to subsume the predictions of Piéron's Law, a power function dependence of response time on stimulus strength. The theory's analytic chronometric function allows one to extend theories of accuracy to response time.

Decision Making↗
PubMed2005

Development of a measure of knowledge and attitudes about obstructive sleep apnea in children (OSAKA-KIDS).

BACKGROUND: Primary care physicians play an important role in screening for childhood obstructive sleep apnea syndrome (OSAS) that, if untreated, can result in serious complications. OBJECTIVE: To describe the development of the Obstructive Sleep Apnea Knowledge and Attitudes in Children (OSAKA-KIDS) questionnaire for use in measuring physicians' knowledge and attitudes about childhood OSAS and its treatment. DESIGN: Cross-sectional survey to pilot administration of the 23-item OSAKA-KIDS questionnaire, mailed to 1195 community- and academic-based physicians in Louisville, Ky; Philadelphia, Pa; and St Louis, Mo. MAIN OUTCOME MEASURES: Analysis of variance measured differences in knowledge and attitudes between academic- and community-based physicians and between pediatricians and family practitioners. Using stepwise multiple linear regression, we analyzed the associations between various predictors (including specialty, practice setting, and years since medical school graduation) and each item of knowledge and attitudes. All tests were 2-tailed. RESULTS: Questionnaires for 497 respondents (44% female; mean [SD] age, 45.7 [10.5] years; and mean [SD] number of years since medical school graduation, 18.7 [11.0] years) were analyzed. The mean (SD) knowledge score (percentage of 18 possible) was 69.6% (14.6%). In regression analyses, more knowledge was associated with more positive attitudes overall and more recent graduation from medical school; having a more positive attitude was associated with having completed a pediatrics residency and more knowledge about OSAS. CONCLUSIONS: Deficits in basic knowledge about childhood OSAS were observed regardless of physician practice setting and specialty training. More education focusing on the diagnosis and treatment of childhood OSAS and identifying children at risk for OSAS is recommended.

Analysis of Variance↗
PubMed2005

Achromatic contrast effects in infants: adults and 4-month-old infants show similar deviations from Wallach's ratio rule.

When adults view a disk of light embedded in a higher luminance surround, the perceived lightness of the disk is largely determined by the surround to disk luminance ratio (Wallach's ratio rule). In the present study, both adult and infant subjects were tested with multiple discrete trial procedures in which the surround luminance was decreased between the study and test phases of each trial. Tested with sequential lightness matching, adult subjects showed an approximate ratio rule, with a small but consistent deviation in the direction of a luminance match. Tested with a forced-choice novelty preference technique in combination with a cross-familiarization paradigm, 4-month-old infants showed preference minima that fell closer to the mean adult match than to the ratio rule. This finding suggests that, at least for a relatively simple visual display, 4-month-old infants' looking preferences are governed by an adult-like achromatic contrast system.

Adult↗
PubMed2005

Interdependence between measures of extent and severity of myocardial perfusion defects provided by automatic quantification programs.

AIM: To evaluate the accuracy of the values of lesion extent and severity provided by the two automatic quantification programs AutoQUANT and 4D-MSPECT using myocardial perfusion images generated by Monte Carlo simulation of a digital phantom. The combination between a realistic computer phantom and an accurate scintillation camera simulation tool allows the generation of realistic single-photon emission computed tomography (SPECT) images similar to those obtained in clinical patient studies. METHODS: The NCAT phantom and the SIMIND Monte Carlo program were used to simulate myocardial perfusion studies. Perfusion defects with sizes ranging from 5 to 17% of the left ventricular wall volume and reductions in tracer uptake of 20, 60 and 100% were simulated in three vascular territories. RESULTS: The values of the extent provided by the programs were dependent on the reduction in tracer uptake, i.e. the severity. Similarly, the measures of severity were dependent on the size of the lesions. The severity provided by AutoQUANT for different defects was not dependent on the location, whereas 4D-MSPECT presented different values depending on the location in the left ventricle. The measures of extent and severity of the defects with the same true extent and activity uptake reduction provided by the two programs were different. CONCLUSIONS: The NCAT phantom and the SIMIND Monte Carlo program were shown to be useful in simulating clinical myocardial SPECT studies. The quantification programs gave values of lesion extent that were dependent on the magnitude of the severity. Users should therefore consider this dependence when interpreting results from these programs.

Automation↗
PubMed2005

Evaluation of left ventricular volumes and ejection fraction by automated gated myocardial SPECT versus cardiovascular magnetic resonance.

BACKGROUND: Electrocardiogram-gated myocardial single-photon emission computed tomography (SPECT) with (99m)Tc-tetrofosmin allows simultaneous evaluation of myocardial perfusion and function. In this study, left ventricular volumes, ejection fraction (LVEF), and left ventricular wall volume (LVWV) derived from gated SPECT were compared with measurements from cardiovascular magnetic resonance (CMR), performed within a few hours. METHODS: The study population included 55 patients with known or suspected coronary artery disease, including 13 patients with recent acute myocardial infarction. End-diastolic (EDV) and end-systolic (ESV) volumes, LVEF and LVWV were derived automatically from gated SPECT using commercially available software (QGS). In the CMR studies, manually delineated endocardial and epicardial borders on short-axis slices were used to calculate the volumes. RESULTS: Gated SPECT underestimated EDV by 35 +/- 14 ml (mean +/- SD) (P < 0.001), ESV by 10 +/- 13 ml (P < 0.001), and LVEF by 4 +/- 7 percentage points (P < 0.001). There were no systematic difference in EDV, ESV or LVEF between the methods. SPECT underestimated LVWV by 49 +/- 30 ml (P < 0.001), with a trend towards increasing underestimation by SPECT for larger wall volumes. CONCLUSION: These findings show that gated SPECT slightly underestimates EDV, ESV and LVEF compared with CMR. This underestimation is systematic, however, indicating that ventricular volumes derived from gated SPECT are robust enough to guide clinical management. Estimates of LVWV in patients with large wall volumes are less accurate.

Adult↗
PubMed2005

Comparison of 1- and 2-day protocols for myocardial SPECT: a Monte Carlo study.

BACKGROUND: Myocardial perfusion single-photon emission computed tomography (SPECT) is carried out by combining a rest and a stress study that are performed either on one day or two separate days. A problem when performing the two studies on 1 day is that the residual activity from the first study contributes to the activity measured in the second study. AIM: Our aim was to identify and evaluate trends in the quantification parameters of myocardial perfusion images as a function of separation time between rest and stress. METHODS: A digital phantom was used for the generation of heart images and a Monte Carlo-based scintillation camera program was used to simulate SPECT projection images. In our simulations, the rest images were normal and the stress images included lesions of different types and localization. Two programs for quantification of myocardial perfusion images were used to assess the different images in an automated and objective way. RESULTS: The summed difference scores observed with the 2-day protocol were 3 +/- 1 (mean +/- SD) higher for AutoQUANT and 2 +/- 1 higher for 4D-MSPECT compared with those observed with the 1-day protocol. The extent values were 2% points higher for the 2-day protocol compared with the 1-day protocol for both programs. CONCLUSIONS: There are differences in the quantitative assessment of perfusion defects depending on the type of protocol used. The contribution of residual activity is larger when a 1-day protocol is used compared with the 2-day protocol. The differences, although small, are of a magnitude that results in a clear shift in quantification parameters.

Coronary Artery Disease↗
PubMed2005

Quantitative polar representation of left ventricular myocardial perfusion, function and viability using SPECT and cardiac magnetic resonance: initial results.

BACKGROUND: The clinical management of patients with coronary artery disease (CAD) often involves a complex assessment of the extent and severity of changes in left ventricular (LV) myocardial perfusion, function and viability. We aimed to explore the feasibility of integrative quantitative representation of LV perfusion, function and viability in adjacent polar plots. In order to assess the clinical usefulness of the quantitative methods, we also explored the relationship and determined the agreement between visual scoring and quantitative measurement of regional perfusion and function. METHODS: Ten patients with CAD underwent rest and stress (99m)Tc-tetrofosmin single photon emission computed tomography (SPECT) and cardiac magnetic resonance (CMR) imaging. Software was developed in-house for generating polar plots from semi-automatic quantification of rest and stress perfusion from SPECT, function from cine CMR and viability from delayed contrast enhancement (DE) CMR. The agreement between visual assessment and quantification of both perfusion and function was tested by Kendall's coefficient of concordance (W). RESULTS: Polar plots were created using quantitative data from the semi-automatic analysis of perfusion, function and viability. Kendall's W for agreement between quantitative measurement and visual scoring was 1.0 (P<0.001) for perfusion and 0.85 (P<0.001) for function. CONCLUSIONS: Side-by-side quantitative polar representation of LV perfusion, function and viability is feasible and may aid in the complex assessment of these parameters. The agreement between quantitative measurement and visual scoring was very good for both perfusion and function.

Aged↗
PubMed2004

Diagnostic evaluation of planar and tomographic ventilation/perfusion lung images in patients with suspected pulmonary emboli.

Planar lung ventilation/perfusion scintigraphy (V/P(PLANAR)) is a standard method for diagnosis of pulmonary embolism (PE). The goals of this study were to test whether the diagnostic information of ventilation/perfusion tomography (V/P(SPET)) applied in clinical routine might enhance information compared with V/P(PLANAR) and to streamline data processing for the demands of clinical routine. This prospective study includes 53 patients suspected for PE referred for lung scintigraphy. After inhalation of (99m)Tc-DTPA planar ventilation imaging was followed by tomography, using a dual-head gamma camera. (99m)Tc-MAA was injected i.v. for perfusion tomography followed by planar imaging. Patients were examined in supine position, unchanged during V/P tomography. Two reviewers evaluated V/P(PLANAR) and V/P(SPET) images separately and randomly. Mismatch points were calculated on the basis of extension of perfusion defects with preserved ventilation. Patients were followed up clinically for at least 6 months. With V/P(SPET) the number of patients with PE was higher and 53% more mismatch points were found. In V/P(SPET) interobserver variation was less compared with V/P(PLANAR). Ancillary findings were observed by both techniques in half of the patients but more precisely interpreted with V/P(SPET). V/P(SPET) shows more and better delineated mismatch defects, improved quantification and less interobserver variation compared with V/P(PLANAR). V/P(SPET) is amenable to implementation for clinical routine and suitable even when there is demand for a high patient throughput.

Administration, Inhalation↗
PubMed2004

Determination of the left ventricular long-axis orientation from a single short-axis MR image: relation to BMI and age.

Accurate determination of imaging planes in relation to the left ventricular (LV) long-axis orientation is important for anatomical and functional evaluation as well as for serial comparisons with cardiac magnetic resonance (CMR) imaging. Therefore, a fast and reliable method to test the accuracy of CMR imaging for measuring the orientation of the LV long-axis was developed and validated. In addition, the relationship between LV long-axis orientation and body mass index (BMI), gender and age was assessed. Two approaches were used, a long-axis approach (based on a manually defined vector) and a short-axis approach (based on a calculated vector). The concordance between the two approaches was assessed in 72 healthy volunteers. The accuracy and precision of MR imaging for measuring three-dimensional orientations were tested using a LV phantom. The mean difference between the long- and short-axis approaches for measuring the LV long-axis orientation in the study population was 0 +/- 3 degrees, 0 +/- 2 degrees, and -1 +/- 3 degrees in the frontal, transverse and sagittal plane, respectively. BMI and age were shown to influence LV long-axis orientation, especially in the frontal and sagittal planes. A significant difference in LV long-axis orientation in the frontal and sagittal planes was found between genders. The correlation coefficient between MR-measured phantom orientation and true phantom orientation was >0.98 in all three orthogonal planes. These observations suggest that a single LV short-axis MR image can be used for measuring LV long-axis orientation in patients with no cardiac disease.

Adult↗
PubMed2004

Myocardial SPECT perfusion defect size compared to infarct size by delayed gadolinium-enhanced magnetic resonance imaging in patients with acute or chronic infarction.

BACKGROUND: Single photon emission computed tomography (SPECT) perfusion imaging has been considered a reference method for non-invasive estimation of infarct size in man. Recently, delayed gadolinium-enhanced magnetic resonance imaging (DE-MRI) has evolved as an accurate tool to quantify infarct size. Therefore, the present study was designed to compare perfusion defect size by SPECT to hyperenhanced volume by DE-MRI. METHODS: DE-MRI was performed in 30 patients. Fourteen were patients with revascularized first-time acute infarctions, eight revascularized chronic infarctions, and eight clinically referred non-revascularized patients. SPECT was performed in the same patients and analysed by a commercial package. RESULTS: The hypoperfused volume by SPECT was larger than the hyperenhanced volume by DE-MRI by 8 +/- 8 ml (6% +/- 5 percentage points), 10 +/- 18 ml (6% +/- 11 percentage points), and 26 +/- 30 ml (12% +/- 10 percentage points) in the acute, chronic and clinical populations, respectively. Left ventricle wall volume was smaller by SPECT in all settings. CONCLUSION: The SPECT perfusion defect size was comparable with but generally slightly larger than the hyperenhanced volume by DE-MRI in both absolute and relative terms in patients with acute and chronic infarction. The results may be related to systematic differences between modalities but could also be influenced by biological phenomena such as wall thinning or hypoperfused but viable myocardium.

Acute Disease↗
PubMed2004

Visual search and attention: an overview.

This special feature issue is devoted to attention and visual search. Attention is a central topic in psychology and visual search is both a versatile paradigm for the study of visual attention and a topic of study in itself. Visual search depends on sensory, perceptual, and cognitive processes. As a result, the search paradigm has been used to investigate a diverse range of phenomena. Manipulating the search task can vary the demands on attention. In turn, attention modulates visual search by selecting and limiting the information available at various levels of processing. Focusing on the intersection of attention and search provides a relatively structured window into the wide world of attentional phenomena. In particular, the effects of divided attention are illustrated by the effects of set size (the number of stimuli in a display) and the effects of selective attention are illustrated by cueing subsets of stimuli within the display. These two phenomena provide the starting point for the articles in this special issue. The articles are organized into four general topics to help structure the issues of attention and search.

Attention↗