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A W Palmer

Publications and source records attributed to A W Palmer.

14 recordsLinked to original sources
PubMed2000

Creation of a three-dimensional model of human segmental lung anatomy.

OBJECTIVE: The investigation of pulmonary embolism using scintigraphic tomography requires a model of the internal architecture of the segments and subsegments in the human lung. Such a model has been developed by the segmentation and subsegmentation of an existing whole-body tissue-segmented phantom. MATERIALS AND METHODS: By using information from suitably windowed human axial CT scans, combined with the information gained from the injection of color-coded dyes into the segmental bronchi of human cadaveric lungs, the lobar and segmental boundaries were added to the existing phantom. Further refinements were added from reports in the literature regarding the predominant pattern of subsegmental bronchi in a series of human cadavers, enabling the creation of subsegmental boundaries. RESULTS: A digitized model of the segmental and subsegmental anatomy of the human lung was successfully created. External, or pleural, projections of the complex internal arrangement of the segments closely corresponded with the projections of the best available authorities on the subject. CONCLUSION: The model provides the opportunity to address several issues germane to scintigraphy and important for diagnosing pulmonary embolic disease. In particular, the model allows the manipulation of three-dimensional data sets to explore issues of importance to tomographic lung scanning.

Computer Simulation↗
PubMed1999

Single-photon emission tomography of a computerised model of pulmonary embolism.

Planar pulmonary scintigraphy is currently the standard investigation for the diagnosis of pulmonary embolism. There are a number of problems with the technique, particularly in patients with an intermediate scan report under the PIOPED criteria. The technique is also under threat from the increasing use of spiral CT angiography. A putative improvement may be gained by use of tomography. The incremental value of tomography over planar studies was therefore evaluated in a virtual model of pulmonary scintigraphy. A model of the segmental anatomy of the lungs was developed from computed tomography, cadaveric human lungs and available anatomical texts. Counts were generated within the phantom by Monte Carlo simulation of photon emission. Eighteen single segmental lesions were interspersed with 47 subsegmental defects and displayed on an Icon reporting station. These were presented in the transaxial, sagittal and coronal planes to four experienced reporters to obtain assessment of defect size. Planar studies of the same defects were displayed to the same observers in the standard eight views with a normal study for comparison. With planar studies, the accuracy of estimation of defect size was 51% compared with 97% using tomographic studies. Defects in the medial basal segment of the right lower lobe were not identified in planar studies but were easily seen by all observers in the tomographic study. It is concluded that there is marked improvement in the accuracy of determination of defect size for tomographic studies over the planar equivalents. This is especially important in the lung bases, the most common reported site of pulmonary emboli. Tomography permits visualisation of defects in the medial basal segment of the right lung, which are not seen in planar studies.

Cadaver↗
PubMed1999

Threshold of detection of diffuse lung disease.

UNLABELLED: A scintigraphic model of the lungs was used to study the threshold of detection of diffuse disease of the lungs. METHODS: Randomly distributed cold lesions of 4, 8, 12 and 16 mm3 block sizes were created, occupying 0%-50% of lung tissue in steps of 1%. These were submitted for reporting to five observers each with a normal study for comparison. RESULTS: No observer detected lesions of 4-mm3 block size even when up to 50% of the lung was involved. All observers detected lesions of 8-mm3 block size when a mean of 27% of lung tissue was involved with lesions. As lesion size increased to 12 and 16 mm3, observers detected lesions when a mean of 10% and 6% of lung tissue was involved, respectively. Comparison between views for each observer showed that the lateral and anterior oblique views were used more often than the anterior, posterior oblique and posterior views. CONCLUSION: This model suggests that pulmonary scintigraphy has the potential to detect a diffuse disease such as emphysema at an early stage of lung involvement. In general, small anatomic lesions appear to have more profound scintigraphic consequences. However, even scintigraphic lesions of the order of size of the pulmonary acinus are easily detected.

Humans↗
PubMed1998

Variability of perceived defect size in virtual lung scintigraphy.

UNLABELLED: The diagnosis of pulmonary embolism is based on the presence of mismatched segmental or subsegmental defects. An important axiom is the classification of defect sizes into small, moderate and large. Little information about the recognition and classification of such defects has been published. We undertook a study of the perception of defect size using a model of the virtual scintigraphic anatomy of the lungs to address this issue. METHODS: Segmental anatomy of the lungs was modeled with CT, cadaveric lungs and standard anatomical tests. The emission, scatter and attenuation of photons were modeled within these virtual lungs and the surrounding tissues. Single segmental lesions, each 100% of a segment, were created in eight projections and submitted for blinded reporting by four experienced nuclear medicine physicians to obtain their assessment of the size of each defect on two occasions. RESULTS: Of the 144 defects submitted for reporting, 15% were reported as <25% of a segment, 35% were reported as 25%-75% and 50% were reported as 75%-100%. The accuracy of each reporter and the intraobserver agreement were calculated; the weighted kappa value ranged from 0.34 to 0.60. The segmental defects that were most likely to be underestimated in size were in the right lower lobe. CONCLUSION: It is clear that segmental defect sizes were underestimated, particularly in the right lower lobe. Although the intraobserver agreement in reporting was fair, the accuracy of estimation was only 50%. The variability and inaccuracy might be reduced by the use of a guide to segmental anatomy.

Computer Simulation↗
PubMed1998

Enhanced accuracy and reproducibility in reporting of lung scintigrams by a segmental reference chart.

UNLABELLED: The diagnostic probability of pulmonary embolic disease is based on the recognition of unmatched segmental perfusion defects. Although interobserver and intraobserver reproducibility have been studied, accuracy has been an elusive goal due to the lack of a gold standard. We investigated the accuracy and reproducibility of reporting in a virtual scintigraphic model of the lungs, with and without the use of a lung segmental reference chart. METHODS: A Monte Carlo package was used to model lung scintigraphy from a digital phantom of the human lungs. An ideal lung segmental reference chart was created from the phantom. Five experienced nuclear medicine physicians reported a set of all possible defects involving 100% of a segment, without and with the chart. A further set of defects involving 45%-55% of a segment in the lower lobes was investigated using the chart. RESULTS: There was a significant improvement in accuracy (from 48% to 72%) and intraobserver agreement (from 61% to 77%) with the chart. The accuracy of reporting defects in the upper and middle lobes was consistently better than that in the lower lobes. There was no significant difference between the accuracy of reporting large defects and that of reporting moderate defects in the lower lobes. CONCLUSION: The lung segmental reference chart significantly improves both the accuracy and reproducibility of reporting lung scintigrams; however, although reporting in the lung bases is improved, absolute accuracy is substantially less than that in the upper and middle lobes. This emphasizes the need for caution because the lung bases are the most common site of embolic disease.

Computer Simulation↗
PubMed1997

Optimization of the scintigraphic segmental anatomy of the lungs.

UNLABELLED: Accurate and reproducible reporting of lung scintigraphy is predicated on a sound knowledge of the segmental anatomy of the lungs. A limited amount of hard data exists about the true segmental anatomy of the lungs. A virtual model of human lungs was created using a CT-based dataset and a Monte Carlo simulation technique to examine the optimal projections for the visualization of each segment in the lungs. METHODS: Segmental anatomy of the lungs was modeled using CT, cadaveric lungs and standard anatomical texts. The emission, scatter and attenuation of photons was modeled within these virtual lungs and the surrounding tissues. Single segmental lesions were created in eight projections and submitted for blinded reporting to four experienced nuclear medicine physicians to obtain the best views for each segment. RESULTS: The anterior and posterior oblique projections yielded the best views for 10 of 18 segments, with the laterals contributing four views, the anterior contributing two views and the posterior contributing one view. The majority of basal segments (six of nine) were best seen in the anterior and posterior oblique projections. CONCLUSION: This model overcomes the major problems associated with experimentation in the normal human and has the potential to provide answers to the major problems of scatter, attenuation and "shine-through" in lung scintigraphy.

Cadaver↗
PubMed1991

Does the administration of oral Bicitra before elective cesarean section affect the incidence of nausea and vomiting in the parturient?

Soluble oral antacids are commonly used before anesthesia for cesarean section. The purpose of this prospective, single institution, randomized experimental study was to examine the relationship of oral administration of Bicitra (sodium citrate and citric acid) to the incidence of nausea and vomiting in patients undergoing elective cesarean section utilizing regional anesthesia, and to evaluate its effectiveness in neutralizing gastric acid. Eighty-six patients were studied (39 in a control group and 47 in a Bicitra treatment group) to ascertain if there was any difference with regard to height, weight, parity, gravity, age, race, incidence of heartburn with pregnancy, incidence of nausea with pregnancy, length of NPO status, preoperative systolic blood pressure (SBP), perioperative low level of SBP, and cumulative drop in SBP. Pearson chi square analysis showed no significant difference between the two groups for all variables or the incidence of nausea and vomiting. No significant difference was noted in the mean pH and volume of emesis of seven subjects analyzed using pooled t tests. After initial hypothesis testing was concluded, the sample was divided into two groups, those who experienced nausea and those who were free from nausea. The nausea group demonstrated a significantly greater cumulative decrease in SBP than did the non-nausea group. Larger patients (mean cube root weight index of 2.78) tended to become nauseated more frequently.

Administration, Oral↗
PubMed1986

An infra-red fibre optic device for cardiac cycle timing and photoplethysmography.

In this work a simple fibre optic device using infra-red radiation is used to obtain information on the timing of the cardiac cycle and blood volume changes in the flow of blood in the body. The device is small, non-invasive and free from interference by surrounding electromagnetic fields enabling it to be used in the environment of such devices as NMR scanners.

Cardiography, Impedance↗
PubMed1985

Optical fibre plethysmograph.

We describe a method for obtaining blood volume information from the external jugular vein or carotid artery by means of an optical fibre transducer. The device may be used to obtain accurate predictions of the state of the cardiac cycle, thereby enabling a range of physiological measurements to be made. The transducer is entirely non-invasive and non-magnetic; it is extremely robust and is unaffected by the electrically and magnetically hostile environment created by an NMR scanner.

Biomedical Engineering↗
PubMed1984

Interrupted reflection fibre optic communication device for the severely disabled.

The difference between light reflected from the open eye and that reflected from the closed lid is detected by means of an optic fibre attached to a spectacle frame. That difference is processed electronically to produce a pulse train which may be interpreted either subjectively by a 'listener', or physically for the purpose of controlling external devices. Involuntary blinks may be suppressed. Potential developments of the technique are discussed.

Biomedical Engineering↗