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Jonathan M Links

Publications and source records attributed to Jonathan M Links.

At least 19 recordsLinked to original sources
PubMed2006

Three-class ROC analysis--a decision theoretic approach under the ideal observer framework.

Receiver operating characteristic (ROC) analysis is well established in the evaluation of systems involving binary classification tasks. However, medical tests often require distinguishing among more than two diagnostic alternatives. The goal of this work was to develop an ROC analysis method for three-class classification tasks. Based on decision theory, we developed a method for three-class ROC analysis. In this method, the objects were classified by making the decision that provided the maximal utility relative to the other two. By making assumptions about the magnitudes of the relative utilities of incorrect decisions, we found a decision model that maximized the expected utility of the decisions when using log-likelihood ratios as decision variables. This decision model consists of a two-dimensional decision plane with log likelihood ratios as the axes and a decision structure that separates the plane into three regions. Moving the decision structure over the decision plane, which corresponds to moving the decision threshold in two-class ROC analysis, and computing the true class 1, 2, and 3 fractions defined a three-class ROC surface. We have shown that the resulting three-class ROC surface shares many features with the two-class ROC curve; i.e., using the log likelihood ratios as the decision variables results in maximal expected utility of the decisions, and the optimal operating point for a given diagnostic setting (set of relative utilities and disease prevalences) lies on the surface. The volume under the three-class surface (VUS) serves as a figure-of-merit to evaluate different data acquisition systems or image processing and reconstruction methods when the assumed utility constraints are relevant.

Algorithms↗
PubMed2006

Establishing evidence-informed core intervention competencies in psychological first aid for public health personnel.

A full-scale public health response to disasters must attend to both the physical and mental health needs of affected communities. Public health preparedness efforts can be greatly expanded to address the latter set of needs, particularly in light of the high ratio of psychological to physical casualties that often rapidly overwhelms existing mental health response resources in a large-scale emergency. Psychological first aid--the provision of basic psychological care in the short term aftermath of a traumatic event--is a mental health response skill set that public health personnel can readily acquire with proper training. The application of psychological first aid by public health workers can significantly augment front-line community-based mental health responses during the crisis phase of an event. To help achieve this augmented response, we have developed a set of psychological first aid intervention competencies for public health personnel. These competencies, empirically grounded and based on best practice models and consensus statements from leading mental health organizations, represent a necessary step for developing a public health workforce that can better respond to the psychological needs of impacted populations in disasters.

Clinical Competence↗
PubMed2006

Expanding disaster mental health response: a conceptual training framework for public health professionals.

The available research literature suggests that in disasters, individuals presenting acutely with psychologically-related complaints tend to outnumber those presenting with physical symptoms directly stemming from the injury-causing agent or event. This acute "mental health surge" can rapidly overwhelm existing community mental health resources, especially in the context of terrorism. Training professionals from outside the traditional mental health workforce in basic psychological crisis intervention may promote more efficient use of mental health services through a gatekeeper process of early intervention and appropriate referrals to mental health specialists. With their experience in patient and client services at the community level, public health professionals represent a cohort well-suited for training in and delivery of acute mental health services in disasters. In this paper, we outline a conceptual model and rationale for training public health professionals in basic crisis-oriented mental health functions (psychological first aid) in order to augment community-based mental health services for affected populations in a disaster.

Clinical Competence↗
PubMed2006

Understanding radiologic and nuclear terrorism as public health threats: preparedness and response perspectives.

Terrorism dates back to antiquity, but our understanding of it as a public health threat is still in its nascent stages. Focusing on radiation and nuclear terrorism, we apply a public health perspective to explore relevant physical health and psychosocial impacts, the evolving national response infrastructure created to address terrorism, and the potential roles of nuclear medicine professionals in preparing for and responding to radiologic and nuclear terrorism.

Disaster Planning↗
PubMed2005

Applying educational gaming to public health workforce emergency preparedness.

From natural disasters to terrorism, the demands of public health emergency response require innovative public health workforce readiness training. This training should be competency-based yet flexible, and able to foster a culture of professional and personal readiness more traditionally seen in non-public health first-response agencies. Building on the successful applications of game-based models in other organizational development settings, the Johns Hopkins Center for Public Health Preparedness piloted the Road Map to Preparedness curriculum in 2003. Over 1500 employees at six health departments in Maryland have received training via this program through November 2004. Designed to assist public health departments in creating and implementing a readiness training plan for their workforce, the Road Map to Preparedness uses the core competencies of the Centers for Disease Control and Prevention for all public health workers as its basic framework.

Disaster Planning↗
PubMed2005

Applying risk perception theory to public health workforce preparedness training.

Since 9/11, public health has seen a progressive culture change toward a 24/7 emergency response organizational model. This transition entails new expectations for public health workers, including (1) a readiness and willingness to report to duty in emergencies and (2) an ability to effectively communicate risk to an anxious public about terrorism or naturally occurring disasters. To date, however, research on readiness education for health department workers has focused little attention upon the risk perceptions that may influence their willingness to report to duty during disasters, as well as their ability to provide effective emergency risk communication to the public. Here, we apply risk perception factors to explore the potential barriers and remedies to effective public health workforce emergency response.

Attitude of Health Personnel↗
PubMed2005

The application of the Haddon matrix to public health readiness and response planning.

State and local health departments continue to face unprecedented challenges in preparing for, recognizing, and responding to threats to the public's health. The attacks of 11 September 2001 and the ensuing anthrax mailings of 2001 highlighted the public health readiness and response hurdles posed by intentionally caused injury and illness. At the same time, recent natural disasters have highlighted the need for comparable public health readiness and response capabilities. Public health readiness and response activities can be conceptualized similarly for intentional attacks, natural disasters, and human-caused accidents. Consistent with this view, the federal government has adopted the all-hazards response model as its fundamental paradigm. Adoption of this paradigm provides powerful improvements in efficiency and efficacy, because it reduces the need to create a complex family of situation-specific preparedness and response activities. However, in practice, public health preparedness requires additional models and tools to provide a framework to better understand and prioritize emergency readiness and response needs, as well as to facilitate solutions; this is particularly true at the local health department level. Here, we propose to extend the use of the Haddon matrix--a conceptual model used for more than two decades in injury prevention and response strategies--for this purpose.

Disaster Planning↗
PubMed2004

Application of MRI-based partial-volume correction to the analysis of PET images of mu-opioid receptors using statistical parametric mapping.

UNLABELLED: The accurate quantification of brain radioactivity concentration is limited by the spatial resolution of the PET scanner for structures smaller than 2-3 times the resolution. In the presence of enlarged cerebrospinal fluid spaces or regions of cortical neuronal loss, a significant underestimation of gray-matter radioactivity concentration due to the resulting partial-volume averaging can potentially occur. To recover the true radioactivity concentration from PET data, algorithms that use the high-resolution anatomic information provided by MRI have been developed. Their effect on PET quantification has been assessed using regions of interest and non-operator-dependent voxel-based analyses such as statistical parametric mapping (SPM), although the mechanisms that lead to an improvement in PET quantification after partial-volume correction (PVC), compared with no PVC, have not been addressed. METHODS: We studied the influence of our previously described MRI-based PVC algorithm on SPM analysis of age effects on mu-opioid receptor (mu -OR) binding using (11)C-carfentanil PET in 14 healthy subjects (age range, 29-74 y). RESULTS: Mu-OR binding increased with age at a rate of about 0.9% per year in the left temporal cortex after PVC, consistent with the results obtained from human autoradiographic studies. Without PVC, no significant relationship with age was observed. PVC decreased mainly the residual variability of voxel mu-OR binding values around the age regression line. CONCLUSION: MRI-based PVC improves the sensitivity and accuracy of voxel-based statistical analysis of PET data.

Adult↗
PubMed2003

Interactive specification of regions of interest on brain surfaces.

We describe Surface Editor-a tool for interactive specification of regions of interest (ROIs) on brain surfaces. The tool allows users to define subsurfaces by tracing around areas within a triangle-mesh brain surface. The input to the program is a triangle-mesh representation of a brain volume and a set of user-defined input points on the mesh. The program connects each pair of successive input points with a polyline that results from the intersection of the mesh with a plane that is approximately normal to the mesh. The polyline comprises coplanar line segments. The boundary of an ROI is a connected set of polylines that intersects triangle edges to form a continuous path. To validate Surface Editor we demonstrated that the program could be used to interactively delineate gyri on brain surfaces, and we showed that paths that the program generated were comparable to paths that a user generated and to shortest paths.

Brain↗
PubMed2003

The longitudinal association of lead with blood pressure.

BACKGROUND: Several investigators have reported an association of blood lead or bone lead with increased blood pressure and hypertension, but questions remain concerning whether these effects are acute or chronic in nature. METHODS: In this longitudinal study, we evaluated the relation of lead, measured in blood and tibia, to changes in blood pressure between 1994 and 1998. We studied 496 current and former employees of a chemical-manufacturing facility in the eastern United States who had previous occupational exposure to inorganic and organic lead. Cohort members who provided three or four blood pressure measurements during the study were included. RESULTS: Mean age at baseline was 55.8 years with a mean of 18 years since last occupational exposure to lead. Blood lead at baseline averaged 4.6 microg/dL (standard deviation [SD] = 2.6) or 0.22 micromole/Liter (SD = 0.13). Tibia lead at year three averaged 14.7-microg/gm (SD = 9.4) bone mineral. Change in systolic blood pressure during the study was associated with lead dose, with an average annual increase of 0.64 mmHg (standard error [SE] = 0.25), 0.73 mmHg (SE = 0.26), and 0.61 mmHg (SE = 0.27) for every standard deviation increase in blood lead at baseline, tibia lead at year three, or peak past tibia lead, respectively. CONCLUSIONS: The results support an etiologic role for lead in the elevation of systolic blood pressure among adult males and are consistent with both acute and chronic modes of action.

Adult↗
PubMed2003

Initial experience with oral contrast in PET/CT: phantom and clinical studies.

UNLABELLED: The aims of the study were to evaluate the effects of oral contrast on apparent tracer activity measured with PET/CT when using CT attenuation correction and to report our initial experience in the use of oral contrast with PET/CT. METHODS: Phantom studies with (18)F activity and saline bags or syringes filled with barium or gastrografin of varying densities were performed using a PET/CT scanner (CT attenuation correction). In the study, 91 clinical patients received dilute oral contrast and were evaluated by whole-body (18)F-FDG PET. RESULTS: A phantom experiment with CT contrast (1.3% weight/volume [w/v] barium) showed a "cold" area in the cold stomach whereas a phantom with high-density barium (98% w/v) showed an artifactual focus of intense "activity" in the cold stomach. In clinical studies, stomach and right colon were opacified by CT contrast. Maximal measured contrast density was 239 Hounsfield units. CONCLUSION: High-density barium causes overestimation of tissue (18)F-FDG concentration. Low-density barium does not cause significant artifacts and appears suitable for clinical use.

Administration, Oral↗
PubMed2002

Neural systems and cue-induced cocaine craving.

We have extended our previous work investigating the neural correlates of cue-induced cocaine craving through the use of positron emission tomography with greater spatial resolution (<4.6 mm), an evocative script, and a pixel-by-pixel analysis. Craving and cerebral glucose metabolism were measured after presentation of cocaine-related or neutral cues to 11 cocaine abusers. Cocaine cues elicited a higher degree of craving than has been previously reported and resulted in left hemispheric activation of lateral amygdala, lateral orbitofrontal cortex, and rhinal cortex and right hemispheric activation of dorsolateral prefrontal cortex and cerebellum. The intensity of activation in these areas (except cerebellum), as well as left insula, was also correlated with craving. Deactivation occurred in left ventral pole and left medial prefrontal cortex. The results suggest that induction of drug craving involves a neural network that assigns incentive motivational value to environmental stimuli through the coactivation of brain regions that process information about memories and emotions.

Adult↗
PubMed2002

PET/CT: comparison of quantitative tracer uptake between germanium and CT transmission attenuation-corrected images.

UNLABELLED: In PET, transmission scanning for attenuation correction has most commonly been performed with an external positron-emitting radionuclide source, such as (68)Ge. More recently, combined PET/CT scanners have been developed in which the CT data can be used for both anatometabolic image formation and attenuation correction of the PET data. The purpose of this study was to assess the quantitative differences between CT-based and germanium-based attenuation-corrected PET images. METHODS: Twenty-eight patients with known or suspected cancer underwent whole-body (18)F-FDG PET/CT scanning for clinical diagnostic purposes. For each patient, attenuation maps were obtained from both the CT scan and the (68)Ge transmission data, and 2 different attenuation-corrected emission datasets were produced. Measured activity concentrations (both mean and maximum) from identical regions of interest in representative normal organs and in 36 pathologic foci of uptake were compared. RESULTS: CT-corrected emission images generally showed slightly higher radioactive concentration values than did germanium-corrected images (P < 0.01) for all lesions and all normal organs except the lung. Mean and maximum radioactivity concentrations were 4.3%-15.2% higher for CT-corrected images than for germanium-corrected images. Calculated radioactivity concentrations were significantly greater in osseous lesions than in nonosseous lesions (11.0% vs. 2.3%, P < 0.05, for mean value; 11.1% vs. 2.1%, P < 0.01, for maximum value). A weak positive correlation was observed between the CT Hounsfield units within the regions of interest and the percentage difference in apparent tracer activity in the CT-corrected images. CONCLUSION: Although quantitative radioactivity values are generally comparable between CT- and germanium-corrected emission PET images, CT-based attenuation correction produced radioactivity concentration values significantly higher than the germanium-based corrected values. These effects, especially in radiodense tissues, should be noted when using and comparing quantitative PET analyses from PET and PET/CT systems.

Algorithms↗
PubMedDate not supplied

Clinical significance of apical thinning after attenuation correction.

BACKGROUND: Apical thinning and other image changes at the apex have been described after attenuation correction of myocardial perfusion single photon emission computed tomography (SPECT) studies, but their clinical significance is unknown. METHODS AND RESULTS: We studied 102 subjects from a multicenter trial of attenuation correction, 46 with angiographic coronary artery disease and 56 normal subjects. We graded the presence and magnitude (on a 4-point scale) of apical thinning (decrease in wall thickness, best assessed in the vertical long-axis view) in both noncorrected and attenuation-corrected images. In attenuation-corrected images, apical thinning of any degree was present in 78% of the abnormal patients and 63% of the normal subjects (P = not significant [NS]). However, moderate or severe apical thinning was present in 30% of the abnormal patients compared with 5% of the normal subjects (relative risk = 2.2, P <.001). In noncorrected images, apical thinning of any degree was present in 87% of the abnormal patients and 71% of the normal subjects (P = NS). However, moderate or severe apical thinning was present in 28% of the abnormal patients compared with 4% of the normal subjects (relative risk = 2.3, P <.001). CONCLUSION: The presence of mild apical thinning is common in both noncorrected and attenuation-corrected SPECT images and does not imply coronary artery disease. Moderate or severe apical thinning is 7 times more common in patients than in normal subjects, but it is relatively uncommon and thus is not a generally useful clinical tool.

Coronary Angiography↗
PubMedDate not supplied

Comparison of 180 degrees and 360 degrees acquisition for myocardial perfusion SPECT with compensation for attenuation, detector response, and scatter: Monte Carlo and mathematical observer results.

BACKGROUND: The optimal projection data acquisition strategy for myocardial perfusion (MP) single photon emission computed tomography (SPECT) remains controversial. METHODS: We compared MP SPECT using 180 degrees and 360 degrees projection data obtained with the same acquisition time, reconstructed either with filtered back projection (FBP) or the iterative ordered-subsets expectation maximization (OS-EM) algorithm with various combinations of attenuation, detector response, and scatter compensation using mathematical observers and a myocardial defect detection task. We used Monte Carlo-simulated projection data from a population of 3-dimensional nurbs-based cardiac-torso (NCAT) phantoms with ranges of variability in patient anatomy, organ uptake, defect location, defect size, and noise level based on clinical data. Projection data from 180 degrees and 360 degrees acquisitions were generated by assuming the same acquisition time. After iterative or FBP reconstruction, standard postprocessing methods were applied. For each acquisition and reconstruction method, we optimized the number of iterations and cut-off frequency of the Butterworth filter using the Channelized Hotelling Observer methodology. The optimum set of parameters was that which gave the maximum area under the curve. RESULTS: For both acquisition protocols, OS-EM with compensations provided better performance than FBP or OS-EM without compensation. For FBP, the optimized 180 degrees acquisition provided a statistically significant increase in AUC as compared with optimized 360 degrees acquisition. For OS-EM, the AUCs for 180 degrees were slightly larger than for 360 degrees acquisitions when comparing images reconstructed with the same compensations. However, the differences were smaller and not statistically significant. CONCLUSION: With optimized reconstruction and filtering parameters, 180 degrees acquisition provided a statistically significant improvement over 360 degrees acquisition for FBP reconstruction. However, for OS-EM the differences were small and not statistically significant.

Algorithms↗
PubMedDate not supplied

Attenuation correction and gating synergistically improve the diagnostic accuracy of myocardial perfusion SPECT.

BACKGROUND: The diagnostic accuracy of myocardial perfusion single photon emission computed tomography is limited by soft tissue attenuation. Artifacts may be reduced by attenuation correction (AC) or compensated for by assessment of wall motion in gated images. We studied the benefit of gating and AC, both separately and combined, in improving accuracy. METHODS AND RESULTS: Sixty-six subjects (27 with > or =50% angiographic stenosis, 5 with <50% stenosis, and 34 Bayesian normal volunteers) underwent gated AC single photon emission computed tomography. Images were reconstructed and independently viewed in 4 ways: static with motion correction (MC) only, gated with MC only, static with MC plus blur correction plus AC (referred to as combined corrections [CC]), and gated with CC. Images were interpreted by 2 blinded observers for overall presence of coronary disease and for vascular territory (left anterior descending [LAD], left circumflex [LCx], and right coronary artery [RCA]). Statistical analysis of sensitivity and normalcy was done by means of the Cochran Q test. Overall diagnostic accuracy showed statistically significant improvement (P =.05 for sensitivity, P <.001 for normalcy), progressing from static MC to gated MC to static CC to gated CC (sensitivity/normalcy = 85%/54%, 78%/62%, 93%/77%, and 96%/85%, respectively, for the 4 reconstruction and viewing approaches). Sensitivity was highest in all 3 vascular territories for the combination of gating and CC; normalcy was also highest with the same combination for the LAD and RCA territories; sensitivity/normalcy with this combination was 85%/87% for the LAD, 69%/87% for the LCx, and 89%/87% for the RCA territory. CONCLUSIONS: The combination of gating and CC provides the highest diagnostic accuracy, and gating and AC should thus be considered complementary and synergistic.

Artifacts↗