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Biomedical subjects

Warren B Gefter

Publications and source records attributed to Warren B Gefter.

15 recordsLinked to original sources
PubMed2006

Mechanical effects of genioglossus muscle stimulation on the pharyngeal airway by MRI in cats.

To examine the regional mechanical effects of selective genioglossus muscle activation on pharyngeal airway size and function, magnetic resonance images of the pharyngeal airway were obtained in five paralyzed, anesthetized cats over a range of positive and negative pressures in an isolated, sealed upper airway. When all results across pressure levels and pharyngeal regions were analyzed, genioglossus stimulation significantly increased the cross-sectional area (CSA) of the nasopharyngeal airway. Within specific regions, stimulation tended toward significantly increasing cross-sectional airway area in the mid-nasopharynx. Despite its dilating effect, genioglossus muscle stimulation did not alter compliance in the nasopharyngeal airway, as evidenced by the similar slopes of the pressure versus cross-sectional area relationships with and without stimulation. Finally, airway shape in the mid pharynx became more circular with either increased airway pressure or genioglossus stimulation. The results indicate that selective stimulation of the genioglossus muscle dilates the nasopharynx and provide evidence that stimulation of the genioglossus alone does not alter airway compliance.

Anatomy, Cross-Sectional↗
PubMed2006

Pulmonary nodule detection in CT images with quantized convergence index filter.

A novel filter termed quantized convergence index filter (QCI filter) that is capable of enhancing the conspicuity of rounded lesions is proposed as part of a CAD (computer-aided diagnosis) scheme for detecting pulmonary nodules in computed tomography (CT) images. In this filter and its predecessor, the convergence index filter (CI filter), the output at a pixel represents the degree of convergence toward the pixel shown by the directions of gray-level gradients at surrounding pixels. The QCI filter and the CAD scheme were evaluated using five clinical datasets containing 50 nodules. With the support region of 9 x 9 pixels, the QCI filter showed more selective response to the nodules than the CI filter. In the CAD scheme, intermediate nodule candidates are generated based on the QCI filter output and then classified using linear discriminant analysis of eight features that are attributed to each intermediate nodule candidate. The QCI filter output level itself was used as one of the features. The scheme achieved a sensitivity of 90% with 1.67 false positives per slice. The QCI filter output level was most effective among the features in correctly classifying intermediate nodule candidates. The QCI filter is promising as a tool of preprocessing for automated pulmonary nodule detection in CT images.

Algorithms↗
PubMed2006

Use of an optical flow method for the analysis of serial CT lung images.

RATIONALE AND OBJECTIVES: Serial CT lung studies are difficult to compare due to misregistration between image sets. An optical flow method (OFM) was adapted for use on CT lung images to register images and visualize changes between studies. Three applications were investigated: lung nodule assessment; evaluation of pulmonary enhancement; and functional changes due to air trapping. MATERIALS AND METHODS: From an initial clinical study, a follow-up study was created by digitally manipulating the images to simulate patient positioning errors and nodule growth. Nodule growth was measured from the temporal subtraction of registered images. In application to the assessment of pulmonary enhancement, pre and postcontrast images from a patient with acute pulmonary embolism (PE) were registered. A map of the perfused blood volume was computed from the ratio of aligned lung volumes. Functional changes in the lung were demonstrated using images from a patient with air trapping. End-inspiratory and end-expiratory volumes were aligned and displacement fields estimated using the OFM. Principal strains were computed from the displacement fields. RESULTS: All image volumes were aligned with at least 0.95 correlation. OFM estimates of displacement showed excellent agreement with the prescribed displacements with 0.33 pixel RMS error. Nodule growth was evident in the presence of significant positioning errors. In the PE case, enhancement ratios indicated a hypoperfused area consistent with an occlusive hypodense filling defect. For the air trapping case, a strain map showed functional changes along the interface of the air trap. CONCLUSIONS: The OFM can facilitate the detection and quantification of changes between serial CT lung studies.

Humans↗
PubMed2005

Mediastinal Castleman disease mimicking mediastinal pulmonary sequestration.

We describe a 39-year-old woman who presented with anterior mediastinal Castleman disease that mimicked an anterior mediastinal pulmonary sequestration due to the presence of both prominent systemic arterial feeding vessels and a systemic draining vein as seen on computed tomography and magnetic resonance imaging.

Adult↗
PubMed2005

The electronic viewbox.

OBJECTIVE: We describe an effective, resource-free method for facilitating the comparison of film-based and PACS-based radiographic studies. CONCLUSION: Side-by-side comparison of film-based and PACS-based radiographic studies is often inconvenient because of the absence of an ergonomically satisfactory viewbox near the workstation. With a simple maneuver, any PACS display monitor can be used as a rudimentary viewbox, providing a convenient and ergonomically effective alternative.

Computer Terminals↗
PubMed2004

Single-shot half-Fourier RARE sequence with ultra-short inter-echo spacing for lung imaging.

PURPOSE: To improve the image quality of pulmonary magnetic resonance (MR) imaging using an ultra-short inter-echo spacing half-Fourier single shot rapid acquisition with relaxation enhancement (USHA-RARE) sequence. MATERIALS AND METHODS: Pulmonary MR images were acquired by USHA-RARE sequence with various inter-echo spacings. The sequence parameters were as follows: repetition time (TR)/effective TE: infinite/39-41 msec; section thickness: 10 mm; acquisition matrix: 128 x 128; field of view: 450 x 450 mm. Inter-echo spacing varied (2.5 msec, 3.0 msec, 3.5 msec, 4.0 msec, 4.5 msec, 5.0 msec), and the respective phase-encoding steps were 80, 77, 75, 74, 73, and 72. Signal-to-noise ratios (SNRs), the signal ratios between lung and fat (lung-to-fat ratio: LFRs), and the signal ratios between the lung and the serratus anterior muscle (lung-to-muscle ratio: LMRs) of each inter-echo spacing were calculated, and statistically evaluated. RESULTS: The SNRs at inter-echo spacings of < or = 3.0 msec were significantly higher than those > or = 4.0 msec (P < 0.05). The LFRs and LMRs at inter-echo spacing < or = 3.0 msec were significantly higher than those > or = 4.0 msec (P < 0.05). CONCLUSION: USHA-RARE sequence does improve signal intensity from the lung.

Adult↗
PubMed2003

A direct comparison of signal behavior between 4.0 and 1.5 T: a phantom study.

INTRODUCTION: Higher magnetic fields (>or=3 T) afford higher spatial and/or temporal resolution in MR imaging with contrast agents, however, studies containing direct comparisons of signal intensity among different magnetic fields are substantially sparse. Our aim was to quantify the differences in terms of signal-to-noise ratios (SNRs) and contrast-to-noise ratios (CNRs) between higher and lower (<or=1.5 T) magnetic fields and to clarify the benefit of higher magnetic fields. METHODS: The same sets of phantom experiments were conducted at both 4 and 1.5 T on whole-body MR scanners with head coils. Phantoms included different concentrations of Gd chelate water solution. A standard contrast-enhanced MR angiographic sequence with the same imaging parameters was utilized to confirm changes in signal intensities. Furthermore, the results were compared with a computer simulation. RESULTS: Peak SNRs at 4 T increased at least 2.21 times higher compared with those at 1.5 T. Moreover, peak CNRs at 4 T increased at least 1.59 times higher compared with those at 1.5 T in the range of Gd concentration expected during clinical use. CONCLUSION: Higher magnetic fields benefit CNRs as well as SNRs. These advantages may lead to a high resolution imaging and reduction of scan time.

Computer Simulation↗
PubMed2003

Voxelwise mapping of magnetic resonance ventilation-perfusion ratio in a porcine model by multimodality registration: technical note.

RATIONALE AND OBJECTIVES: The purpose of this study was to demonstrate the construction of voxelwise ventilation-perfusion (V/Q) ratio maps in a porcine model by nonrigidly aligning the respective ventilation and perfusion images using a multimodality registration algorithm. MATERIALS AND METHODS: The first-pass contrast agent technique for a blood flow map and 3He used for ventilation imaging were performed using a normal porcine model. The registered 3He-ventilation image was then aligned to the blood flow map using a multimodality registration algorithm. The voxelwise V/Q ratios were calculated by dividing the registered 3He-ventilation image by the blood flow map. The V/Q ratios were also semi-logarithmically scatter-plotted against the number of voxels. RESULTS: From perfusion magnetic resonance images, a voxel-by-voxel blood flow map was produced. Registered 3He ventilation image was successfully obtained as well as V/Q ratio map. Plots of the V/Q ratios obtained by this registration approach were similar to the logarithmic normal distribution. CONCLUSION: Registration of MR perfusion and ventilation images can potentially enable quantitative evaluation of regional pulmonary function and thus yield deeper insight into the physiology and pathophysiology of the lung.

Animals↗
PubMed2003

Alignment of CT lung volumes with an optical flow method.

RATIONALE AND OBJECTIVES: This study was performed to evaluate an optical flow method for registering serial computed tomographic (CT) images of lung volumes to assist physicians in visualizing and assessing changes between CT scans. MATERIALS AND METHODS: The optical flow method is a coarse-to-fine model-based motion estimation technique for estimating first a global parametric transformation and then local deformations. Five serial pairs of CT images of lung volumes that were misaligned because of patient positioning, respiration, and/or different fields of view were used to test the method. RESULTS: Lung volumes depicted on the serial paired images initially were correlated at only 28%-68% because of misalignment. With use of the optical flow method, the serial images were aligned to at least 95% correlation. CONCLUSION: The optical flow method enables a direct comparison of serial CT images of lung volumes for the assessment of nodules or functional changes in the lung.

Humans↗
PubMed2003

Videofluoroscopic studies of swallowing dysfunction and the relative risk of pneumonia.

OBJECTIVE: The purpose of our investigation was to determine the relationship between the degree of swallowing dysfunction observed on barium studies and the likelihood of developing pneumonia in a large series of patients. MATERIALS AND METHODS: The findings on videofluoroscopic swallowing studies in 381 patients were used to classify these patients into one of five groups: those with normal swallowing; those with abnormal swallowing but no laryngeal penetration or tracheobronchial aspiration; those with laryngeal penetration; those with tracheobronchial aspiration; and those with silent tracheobronchial aspiration. Clinical data were also reviewed to determine how many patients had developed pneumonia during the 6 months before or after the barium studies. The data were then analyzed to determine whether the risk of developing pneumonia increased significantly with each level of swallowing dysfunction seen on barium studies. RESULTS: No significant difference was found in the frequency of pneumonia in patients with abnormal swallowing but no laryngeal penetration or tracheobronchial aspiration compared with patients with normal swallowing on barium studies (p = 0.85). In contrast, patients with laryngeal penetration, tracheobronchial aspiration, or silent tracheobronchial aspiration were approximately four times (p = 0.008), 10 times (p < 0.0001), and 13 times (p < 0.0001), respectively, more likely to develop pneumonia than those with normal swallowing. CONCLUSION: Our findings indicate that the likelihood of developing pneumonia is directly related to the degree of swallowing dysfunction seen on videofluoroscopic studies. Patients with no laryngeal penetration-regardless of whether they had normal or abnormal swallowing-have the lowest risk of developing pneumonia. Patients with laryngeal penetration, tracheobronchial aspiration, or silent tracheobronchial aspiration are, in increasing order of magnitude, significantly more likely to develop pneumonia than patients with normal swallowing.

Adult↗
PubMed2002

CT and MR in pulmonary embolism: A changing role for nuclear medicine in diagnostic strategy.

The goal of this article is to summarize current data on computed tomography (CT) and magnetic resonance (MR) in the diagnosis of acute pulmonary embolism (PE) in relation to the radionuclide ventilation perfusion scan. It is important for the nuclear medicine, CT, and MR communities to develop a shared approach to this disorder. Triage using chest radiographs appears to be a practical method for enhancing both nuclear medicine and CT/MR performance. The realization that there is no clinically available gold standard for the diagnosis of PE suggests that the imaging community should replace impractical and idealistic discussions with more realistic outcome-oriented approaches. A simplified one-step evaluation of the pulmonary arteries and the lower extremity veins for deep venous thrombus can provide a comprehensive examination for PE. CT is currently a more practical diagnostic tool, whereas MR offers a scientific probe for pulmonary physiology including the regional mapping of ventilation-perfusion relationships. Nuclear medicine, CT, and MR thus form an imaging triad for the diagnosis of acute PE.

Humans↗