The aim of this study was to characterise pulmonary aspiration of refluxate in patients with gastroesophageal reflux disease (GORD) and laryngopharyngeal reflux (LPR) by continuous pulse oximetry (SpO2) during the supine phase of a scintigraphic reflux study. Variables assessed for significance included age, hiatus hernia, frequency, amplitude of reflux and clearance of reflux from the oesophagus/pharynx. The patients included in this study had established GORD and LPR by clinical history. All patients underwent fused three‐ dimensional scintigraphic/ X‐ray computed tomography (CT) and simultaneous continuous pulse oximetry when supine for 30 minutes. A total of 265 patients (40.4% M, 59.6% F) were studied. Mean age of aspirators was 57.0 years and non‐aspirators was 53.5 years. Seven patients had baseline oxygen saturation <95%, with 6/7 showing aspiration by scintigraphy. The remainder had mean baseline saturation of 97.7%. Continuous SpO2 monitoring showed a significant fall in pulmonary aspirators after 20 min of supine acquisition with significant variability. Analysis revealed a cyclic event every 1.5 min in aspirators only. Panel regression analysis showed a significant effect of age, hiatus hernia, pulse rate and reflux frequency on the fall in SpO2. Pulmonary aspiration in patients with LPR and GORD is characterised by acute oxygen desaturation. Variables affecting oxygen desaturation were age, hiatus hernia, pulse rate and reflux frequency. A cyclic event was observed every 1.5 min in aspirators and may be due to reflex homeostatic mechanism attempting to correct perceived hypoxia.

SummaryPurpose: Lung scintigraphy using single photon emission computed tomography (SPECT) allows accurate regional measurement of the ventilation/perfusion () relationship. Objective analysis has been shown to be useful in the diagnosis of pulmonary embolism (PE). By using anatomical information provided by co‐registered computed tomography, we describe methodology for determining the extent of heterogeneity at a lobar level. We investigate this methodology using simulated data, and demonstrate its potential application in the clinical setting of PE.Methods: Data representing an incremental perfusion defect involving the right lung, together with an unaffected ventilation dataset, were modelled using Monte Carlo simulation. For each increase in the size of the perfusion defect, the whole lung relationship was objectively determined. In addition, using an image mask of the pulmonary lobes, lobar relationships were also determined. heterogeneity was characterized using the log10 standard deviation of the ratio (log SDVQR), ventilation (log SDV) and perfusion (log SDQ) distributions. Finally, this methodology was explored in clinical cases.Results: As an increasing number of segments were involved by perfusion defects, there was a progressive increase in all objective parameters of heterogeneity. The relative change was greatest for log SDV. Analysis of both the simulated and clinical studies demonstrated sensitive changes in the lobar profiles to the presence of PE.Conclusions: Segmentation and analysis of SPECT ventilation–perfusion scintigraphy at a lobar level can be used to quantify regional relationships. This objective methodology is sensitive to the presence of PE, and may be useful in a clinical setting.

PurposeTo compare interpretation of traditional planar ventilation–perfusion lung scan images with planar images reformatted from single photon emission computed tomography (SPECT) data using two different techniques. MethodsPlanar and SPECT ventilation–perfusion (V/Q) data were acquired from 50 patients referred with suspected pulmonary embolism. In addition to traditional six-view planar images, six-view planar images were also generated from SPECT data using two methodologies: an angular summing technique (angular summed planar images) and a forward projection technique (reprojected planar images). Three experienced nuclear medicine clinicians reviewed the images in a blinded, randomized fashion. Results were analysed by comparing the two reprojected techniques with the traditional true planar scans, examining for differences in the defects seen (number, type and confidence), and the impact on final clinical interpretation. ResultsCompared with true planar scintigraphy, angular summed images demonstrated fewer mismatched defects (P<0.0001), while the reprojected planar images had more matched defects (P=0.013). In addition, there was a significant change in the clinical interpretation of the angular summed planar images resulting in clinicians perceiving a decreased likelihood of pulmonary embolism (P<0.016). No such difference in interpretation was observed for the reprojected planar images. ConclusionsAngular summed planar images result in a perceived decreased likelihood of pulmonary embolism compared with true planar images. In contrast, while reprojected planar images result in an increased number of matched defects compared to true planar scans, there was no change in the clinical interpretation. Caution should be exercised when interpreting SPECT derived angular summed planar images in isolation.

1299 Objectives: To produce an interactive graphical SPECT lung perfusion display based on a previously established computerised scintigraphic model of the segmental anatomy of the lungs. This model facilitates teaching, quantitation of perfusion defects and research as well as acting as a quality assurance tool for reporting of lung perfusion SPECT. Methods: We utilised a previously published scintigraphic monte carlo model of the three-dimensional segmental anatomy of the lungs. The model was based on colour-coded dyes injected into the pulmonary segments of cadaveric lungs. Transaxial sections were optically scanned and the segmental boundaries identified and transferred to the Zubal phantom with reference to normal variants. Projections were then generated by monte carlo techniques for whole lung, and whole lung minus segment for every segment. A graphical toolkit (WXWidgets) was used to transfer these segments into a C++ program that displays the whole lung with ability to subtract each segment individually. It also allowed volumetric quatitation of the defects. Results: This program allows segments of the lung to be switched off individually or in groups to simulate embolic disease. It allows the lungs to be viewed in the three standard SPECT projections and as a rotating volume-rendered image. The wire frames around the segmental boundaries are displayed separately to allows easy identification of segments, with automatic identification of all segments by name. Conclusions: The graphical display may be used as an aid for reporting clinical studies, quantitation tool for volume of lung involved, research, quality assurance of reporting accuracy and as a powerful teaching aid. Research Support (if any): Nuclear Medicine Research Foundation

V/Q (Ventilation / Perfusion) tests are used to diagnose pulmonary emboli predominantly using planar images. This study presents a quantitative, objective statistical analysis of SPECT V/Q scans for the detection of ventilation-perfusion mismatch. The method is based on a voxelwise statistical assessment of the V/Q images differences. A new acquisition protocol (externally triggered gating) is introduced for acquiring multiple frames for the voxelwise variance estimation. The V/Q datasets are then tested by applying a student's t-test in a voxelwise fashion seeking areas of mismatch. The resulting probability image is finally thresholded to display the detected differences. Two different datasets were used: 72 different cases of a computerised model of pulmonary embolism with emboli of varying magnitude and in different segments, plus seven clinical cases with physicians' reports. The method was shown to be robust irrespective of the location of the mismatch for large defects but greater count densities than those used in the simulation studies are needed for the detection of smaller defects. The results from the clinical datasets agree with the clinical reports but in some cases reveal unreported abnormalities.

An investigation of the complex boundaries between adjacent lobes and segments in human cadaveric lungs was undertaken to provide information for the later construction of a three-dimensional model of the segmental and subsegmental anatomy of the human lungs. This was performed by analyzing scanned cross-sections of the lungs after color-coded gelatin had been injected into segmental bronchi and the lungs embedded in gelatin and frozen. The resulting images provided information regarding the pattern of boundaries present between both lobes and segments. Clin. Anat. 14:10–14, 2001. © 2001 Wiley-Liss, Inc.

Emphysema is a common and debilitating disease that is the commonest cause of end-stage respiratory failure. Treatment is either by lung transplantation or by lung volume reduction surgery (LVRS) that improves the biomechanics of respiration. Patient selection for LVRS hinges on the demonstration of heterogeneous disease, predominantly involving the upper lobes, as a good surgical outcome is most likely in these patients. We used a virtual model of lung scintigraphy to compare planar with tomographic scintigraphy for the detection of diffuse lung disease. Lesions of the magnitude of the lung acinus, as well as larger and smaller lesions, were distributed throughout the lungs in volumes from 2% to 50%. Single-photon emission tomography does not add incremental value to planar images for the detection of diffuse lung disease.

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.

. 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.

A knowledge of the segmental anatomy of the lungs is the cornerstone for interpreting lung scintigraphy. Many attempts have been made to determine the best views for the appreciation of segmental defects and various theories have been formulated to explain the mechanisms of this process. In earlier work, we hypothesized that the arrangements of the segments was the principal determinant of this process. However, data subsequently derived from work on a model of diffuse lung disease indicates that the external shape of the lobes and lungs may be the most significant contributor to the optimal views of the lungs.

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.

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.

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.

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.