SPET of a computerised model of diffuse lung disease

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.

Accuracy in gamma camera measurements of point source velocities

Mucociliary clearance is impaired in many diseases of the respiratory system. We have developed a method for measuring tracheal mucus velocity by the dynamic study of a single point source of radioactivity deposited in the trachea by cricothyroid injection. Preliminary results suggest that patients with airways disease have very low tracheal mucus velocities (<2 mm x min(-1)). The aim of this experiment was to explore the ability of current scintillation detection systems to track a single point as it moves in a dynamic study in small increments and at low velocity (movements of the order of 1 mm). Background noise was estimated to contribute an error in positioning of 0.16 mm (1 standard deviation). Overall errors in velocity were estimated at 0.2 mm x min(-1). This suggests that standard instrumentation in use in most nuclear medicine departments has the capacity to measure accurately velocities as low as 1 mm x min(-1).

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.

Rationalization of the optimal views in planar lung scintigraphy

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.

Threshold of detection of diffuse lung disease

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.

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

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.

Variability of perceived defect size in virtual lung scintigraphy

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.

Optimization of the scintigraphic segmental anatomy of the lungs

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.

Recognition of subsegmental scintigraphic defects in virtual lung scintigraphy

A virtual model of the segmental scintigraphic anatomy of the lungs was used to investigate the threshold at which small defects are perceptible. A model of the segmental anatomy of the lungs was developed from a number of sources and counts generated within the phantom by Monte-Carlo simulation of photon emission. Multiple subsegmental defects were created in both lungs and submitted for blinded reporting to detect the presence of any defect. A total of 36 of the 47 (77%) defects were seen. Of those defects in the lower lobes, 16 of 22 (73%) were visible. All the defects in the left lung (n = 21) were visible, while 15 of 26 (58%) of the defects on the right were visible. In the lower lobe of the right lung, 4 of 10 defects were visible. The defects that were not visible were all in the right lung. We conclude that absolute size and location are critical in the perception of defects. The perception of defects was dependent on absolute defect size rather than the proportion of a segment involved. Defects less than 3% of the volume of a lung were not detected.

Simulation of the stripe sign in a scintigraphic model of the lungs

Using a virtual model of the lungs, we investigated the nature of the 'stripe sign' which is sometimes encountered in pulmonary scintigraphy. A model of the segmental anatomy of the lungs was developed from a number of sources and counts generated within the phantom by Monte-Carlo simulation of photon emission. Multiple segmental and subsegmental defects were created in both lungs and submitted for blinded reporting of the 'stripe sign'. Images were resubmitted for reporting with the contralateral lung removed. The stripe sign was reported in 32 of the 117 studies performed. Nearly half of these were present in defects involving approximately 25% of a segment and the sign was most commonly seen in the lateral projection. Removal of activity from the contralateral lung abolished the sign in only 2 of 32 cases. We conclude that shine through of activity from the contralateral lung is a mechanism rarely responsible for the stripe sign. Most occurrences of the sign are due to interposition of activity from unaffected areas of the same lung between the defect and the periphery of the lung. Orientation of the segments, particularly in the lung bases, accounts for the lateral projection being the most common view in which the sign is present.

Physical properties and use of pertechnegas as a ventilation agent

Pertechnegas, a variant of technegas, produces similar ventilation images with a much increased clearance rate. This work aims to determine the properties of pertechnegas and its use as a ventilatory agent.

METHODS

Fourteen men and 11 women were scanned for PE, after pertechnegas ventilation. Six were reimaged with technegas within 1 wk. Studies were reported according to PIOPED criteria. Pertechnegas samples were analyzed by transmission electron microscopy (TEM), cascade impaction (CI), aerosol mobility analysis (AMA), Fourier transform mass spectrometry (FTMS), x-ray photoelectron spectroscopy (XPS), paper strip (PC) and gas chromatography (GC).

RESULTS

Post-test probabilities were normal in 5, low in 8, high in 5 and indeterminate in 7. There were 15 Grade 1, 6 Grade 2 and 4 Grade 3 studies. All Grade 3 patients had FEV1 < 1.5 liters, 3 with rates < 1.0 liter. Patients with high probability had proven deep venous thrombosis in three by venography and in one by doppler. TEM identified 0.3 micron salt particles. CI demonstrated a 7-min time to half clearance from the chamber for particles in the < 0.1 micron range. AMA indicated all particles were < 0.032 micron when salt was excluded. Pertechnegas behaves in PC as pertechnetate, GC demonstrated CO levels below 516 ppm. CO2 concentrations were 0.146 +/- 0.0009%. FTMS found molecular pertechnetate species including 99TcO3(OH)+, Na99TcO3(OH)3+ and Na99TcO3(OH)3+. XPS confirmed that these Tc species exist in oxidation state +7.

CONCLUSION

Comparison with technegas images in the follow-up group proved equivalent in the first five views, but indistinct lung boundaries and a high background activity characterized the final anterior images. The active component of pertechnegas is molecular pertechnetate.

A study of Technegas employing X-ray photoelectron spectroscopy, scanning transmission electron microscopy and wet-chemical methods

Scanning transmission electron microscopy (STEM), coupled with energy dispersive X-ray analysis (EDS), X-ray photoelectron spectroscopy (XPS) or radionuclear chemical methods, indicates that the active agent in Technegas is either polymeric TcO2[i.e. (TcO2)n] or (TcO2)n bound to a carbon nanoparticle. The particle size observed using STEM is in good agreement with other published results. XPS has also been used to investigate technetium residues remaining on spent crucibles. The chemical form of technetium in this residue is quite different to the form detected in the aerosol particles. We conclude that the small fraction that migrates into the crucible framework upon resistive heating is reduced to either metallic technetium or carbidic forms, with the remaining nuclide evaporating as (TcO2)n with or without carbon before complete reduction can occur.

The observation of fullerenes in a Technegas lung ventilation unit

Evidence is provided to show that Technegas has structure compatible with the Buckminsterfullerene model C60 in which 99Tcm atoms are trapped.

Nomograms of renal length in children obtained from DMSA scintigraphy

The aim of this study was to establish nomograms of renal length in children comparing age, body weight, and height. Renal lengths were obtained from data derived from Tc-99m DMSA scintigraphy in 266 patients with 532 kidneys that appeared normal on DMSA studies. The children's ages ranged from 6 days to 19 years. Renal length appeared to have nonlinear relationships with patient weight and age, but was found to correlate linearly with patient height. On average, scintigraphic renal length exceeded sonographic renal length by approximately 1 cm. The most likely explanation for this is the effect of respiration causing renal motion during the acquisition of the scintigraphic images. It is hoped that the nomograms derived from these data will be of use in routine clinical practice for nuclear medicine departments performing DMSA scintigraphy in children.

An improved radionuclide technique for the detection of altered pulmonary permeability

Technegas, an ultra-fine dry aerosol with prolonged retention in the lungs, can be modified by altering the atmosphere in which the carbon particles are generated. The modified Technegas has much faster clearance from the lung. The half-time pulmonary clearances with modified Technegas were compared to those obtained with conventional 99mTc DTPA aerosol in 50 patients. Interstitial lung disease was suspected in 12 while 38 were infected with the human immunodeficiency virus and suspected of having opportunistic lung infection. In 22 nonsmokers in whom no evidence of active pulmonary pathology was demonstrable, the mean half-time with DTPA was 52.5 min whereas the mean half-time with modified aerosol was 10.1 min. The mean half-time in 14 smokers in whom there was also no evidence of active pulmonary disease was 28.3 min with DTPA and 7.0 min with the modified method. In the 14 patients in whom altered pulmonary permeability was demonstrated by a short DTPA half-time (mean 4.8 min) there was also an accelerated half-time with modified Technegas (mean 2.5 min). It is concluded that the modified Technegas procedure offers a simple but accurate method of identifying individuals having opportunistic infection or other diffuse lung pathology.

Optimising technetium 99m diethylene triamine penta-acetate lung clearance in patients with the acquired immunodeficiency syndrome

Pneumocystis carinii pneumonia (PCP) has become a major cause of morbidity and mortality due to infectious diseases, largely as a result of the acquired immunodeficiency syndrome (AIDS) epidemic. Since the mortality from recurrent infection is between 40% and 60%, early diagnosis and therapy are the keys to survival. The role of technetium 99m diethylene triamine penta-acetate (DTPA) aerosol pulmonary clearance was studied in 81 patients with AIDS. The mathematical technique of curve stripping was found to be the optimal method of analysis and to provide an overall sensitivity of 94% for the detection of interstitial pneumonitis. The procedure was superior to standard pathology parameters and radiography and more convenient than gallium 67 scintigraphy.

Pediatric solid tumors: evaluation by gallium-67 SPECT studies

A retrospective review of 37 children with a variety of solid tumors who underwent 60 67Ga single-photon emission computed tomographic (SPECT) studies was performed. These studies were correlated with clinical and radiological findings and, where possible, histopathologic confirmation. In all studies, SPECT gave better definition and better anatomic localization of disease sites than obtained with planar views. SPECT detected more lesions in the head and neck (planar 16, SPECT 19), chest (planar 39, SPECT 45), and abdomen (planar 22, SPECT 24). In six of 20 patients scanned following chemotherapy, SPECT was useful in demonstrating that tracer accumulation in a normally located and shaped thymus indicated uptake resulting from thymic regeneration rather than tumor recurrence. It is concluded that 67Ga SPECT studies are very useful in the pediatric population, where perhaps because of their small size, interpretation of standard planar views may be difficult.