A simple process using technetium-99m generator eluate in a graphite crucible at 2500ºC, produces a structured ultra-fine dispersion of labelled carbon. Particle sizes are 5.0 nm (0.0051µm) and less and adhere to the walls of the alveoli on inhalation. Penetration characteristics are gas-like and the radioactivity per litre of carrier argon allows single breath inhalations of a diagnostic dose.

Over 190 patients have been studied including 50 within a formal clinical trial with xenon-133. Results of tomography, dynamic inhalation, and image subtraction using this new agent- 'Technegas'- are presented. 

Combined vent/perf scintigraphy has been shown to have high sensitivity and specificity in the diagnosis of PTE. Using a radioaerosol with high alveolar deposition SPECT data acquisition is possible. In 50 pat. with suspected PTE we used the following technique: after inhalation of 37MBq Technegas in supine position SPECT data acquisition was performed. Immediately after the ventilation study perfusion SPECT scans were obtained after injection of 185M8q 99m Tc-MAA in the same position. By comparing the transversal, coronal and sagittal vent and perf SPECT slices, diagnosis was made. In some special cases the V/P- quotient was calculated slice by slice. During SPECT-acquisition conventional planar scans were performed. Results: 32 of the 50 examined pat. showes pathologic results, 15 of them were embolic and 17 embolic and partially obstructive. All planar findings could also be represented by SPECT. In 72% of all pathologic findings SPECT showed a better spatial resolution. In 2 cases small PTE could only be documented by SPECT. No central deposition was seen in the vent scan in any case. In summary Technegas is an excellent tool for SPECT studies. Vent/perf lung SPECT is the better procedure to screen patients suspected of having PTE. 

Technegas (TcG) was produced by a commercially available TcG-Generator. Structure and size distribution of TcG-Particles were examined using the following methods:

- Transmission electron microscopy (TEM) range: I nm - 100 um

- Time of flight mass spectroscopy (MS) range: < 3 nm

- Photon correlation spectroscopy (PCS) range 3 nm - 3 um

Results: TEM images show graphite particles (size 4-50 nm) agglomerated into larger secondary aggregates. The size distribution of these aggregates was determined from PCS and TEM-measurements and ranges typically from 80 to 250 nm. No single particles smaller than 3 nm could be detected by MS.

Conclusion: TcG particles consist of ⁹⁹Tc^m tagged agglomerated graphite particles and have an average size of 80 to 250 nm.

Airway closure is common during induced broncho-constriction in asthma but closure of large airways (sub-segmental or larger bronchi) during broncho-constriction may occur in ‘severe asthmatics’.

To detect closure of large airways, a technique of topographically imaging ventilation distribution at residual volume (RV, when airway closure is greatest) was developed. Five normal and five asthmatic subjects inhaled a 250-300ml bolus of Technegas slowly from RV while upright, continuing to inhale to total lung capacity with air. The breath was then held for 10 secs. This was repeated in 4 of the asthmatic subjects following methacholine. Technegas is an ultra fine aerosol of Tc-99m labelled carbon particles 10-100 nm in diameter. Simultaneous emission and transmission tomographic data were acquired simultaneously using a gamma camera and a scanning line source. Transmission data were used to apply attenuation correction and to provide an anatomical reference for definition of lung outlines. This allowed accurate measurement of both lung volumes at functional residual capacity (FRC) in which ventilation was completely absent and the distribution of ventilation relative to the regional lung volume at FRC.

In normals, Technegas distributed according to the known presence of basal airway closure and compliance near residual volume. The distribution in one stable asthmatic suggested large airway closure. Following induced bronchoconstriction, segmental or larger defects developed in 4 asthmatics suggesting closure of large airways.

In conclusion, SPECT scanning using Technegas is a simple but powerful technique of detecting subsegmental or larger ventilation defects due to closure of airways at RV and semi-quantitive data on ventilation distribution. In asthmatics, the results suggest closure of large airways during induced bronchoconstriction.

Technegas, a newly developed ultra-fine dry dispersion of Tc-99m labeled carbon with a particle size of approximately 5 nm to 20 nm, possesses the properties for lung ventilation imaging using SPECT. The authors observed a discrepancy between krypton-81m gas and Technegas lung ventilation SPECT in two patients with idiopathic pulmonary fibrosis who demonstrated heterogeneously decreased distribution of technegas without regions of high count density (focal hot spots) of tracer in their lungs in spite of the almost homogenous distribution of krypton-81m gas. This finding could be explained by the duration of radioactive gas inhalation. Technegas lung ventilation SPECT images reflected lung ventilation with tidal breathing. Conversely, Kr-81m gas lung ventilation SPECT images reflected not only lung ventilation, but also lung volumes. These two radioactive agents for lung ventilation SPECT show different findings. 

Scintigraphy with ^99mTc-Technegas was recently introduced for clinical imaging of lung ventilation.

This method has been found to be useful in emergencies, to be more suitable for single photon emission computed tomography (SPECT) than other agents used in ventilation scintigraphy, and could reveal abnormalities in ventilation more easily than high resolution computed tomography (HRCT) in pulmonary emphysema. We compared ^99mTc-Technegas SPECT with HRCT in six regions: the right upper, middle, and lower lobes, the left upper lobe, the lingula, and the left lower lobe, in 15 patients with pulmonary emphysema. Patients with centrilobular emphysema tended to show stronger changes in upper lobes than in lower lobes on both ^99mTc-Technegas SPECT and HRCT. Some regions showed no change on HRCT but various changes on ^99mTc-SPECT. Patients with panlobular emphysema showed severe changes on ^99mTc-SPECT in lower lung fields in which well-demarcated areas of low attenuation were not seen on HRCT. We conclude that ^99mTC-SPECT is useful for detecting early changes and panlobular changes in pulmonary emphysema.

To evaluate regional lung function in patients with interstitial lung disease (IP), five healthy controls (HC) and 32 patients with IP were performed Tc-99m Technegas and Tc-99m MAA SPECT. From the each data, 4 lung transverse slices excepting the part of apex and bottom including diaphragm were obtained. And ROI were designated in the anterior and posterior regions of each slice. The ratio of counts per voxel in a given ROI to the counts of the whole lung was regarded as the Technegas deposition index (T) and perfusion rate (Q). Then the ratio of T to Q (T/Q) was obtained each slice. In HC, the T/Q decreased from the upper to lower region. In the IP patients with mild restrictive disorder, the T/Q pattern was similar to that of HC. But, in moderate disorder patients, the T/Q was tend to equal at any slices, then in severe disorder group, the T/Q at lower slice was tend to be higher than the other. This method was enable to evaluate the three-dimensional regional lung function in sitting position which was not possible with other conventional methods. We concluded that regional function differed among patients with IP by the degree of restrictive disorder. 

This study was undertaken to compare axial images of 99mTc-Technegas SPECT (Technegas) with those of ¹³³Xe gas dynamic SPECT in patients with pulmonary emphysema. There were 20 patients, 19 males and I female. All patients except one ex-smoker were heavy smokers with a mean age of 68.1 years. For Technegas scintigraphy, the patients inhaled 505 MBq ⁹⁹Tc-Technegas in several tidal volume breaths in the supine position without breath holding. For ¹³³Xe gas scintigraphy, the patients inhaled 370 MBq ¹³³Xe gas. ¹³³Xe gas dynamic SPECT was performed in the equilibrium phase for the last minute of the 3 minute inhalation in a closed circuit, and in the washout phase for 6 minutes of inhalation in a semi-closed circuit, by means of a gamma camera with dual detectors (Picker model Prism 2000). Abnormal findings included heterogeneity, defects and hot spots on Technegas images and on retention images taken 3 minutes after ¹³³Xe gas washout. In 2 of 20 patients, the degree of abnormal findings on Technegas images depended on the area of ¹³³Xe gas retention in the washout phase. In 3 patients, the degrees of abnormal findings on both Technegas SPECT and ¹³³Xe gas dynamic SPECT images were equivalent. In the remaining 15 patients, more detailed findings and a greater area were shown by Technegas SPECT than ¹³³Xe gas dynamic SPECT. We conclude that in patients with pulmonary emphysema Technegas SPECT can demonstrate ventilation impairment more easily than ¹³³Xe gas dynamic SPECT.

Absence of a maximal dose-response plateau and mathematical modeling suggest that asthmatic airways close,during bronchoconstriction. Finding segmental areas affected by closure would be important in understanding asthmatic airway function. The aim of this study was to evaluate singie-photon emission computed tomography (SPECT) as a method of investigating airway closure. Simultaneous SPECT transmission and emission studies were performed on a thoracic phantom to develop analysis methodology, and on 13 normal subjects after they inhaled a Techriegas bolus from residual volume (RV), to measure airway closure. Single-breath nitrogen test values and lung volumes were measured.

Airway closure was defined as the percent of Technegas-free lung volurne (LV_closed). The mean error ± 95% Cl of the error, as determined by transmission scan, was 1. 1 ml ± 165 ml ( (0.8% ±15% lung volume) in the phantom studies, and 112 ml ± 419ml (4% ± 31 % of supine functional residual capacity [FRC]) in the human studies. LV_closed correlated with closing capacity

(r = 0.86, p < 0.01) and closing volume (r = 0.86, p < 0.01), but not with RV/total lung capacity (TLC). This study indicates that simultaneous SPECT emission and transmission scans, using a Technegas bolus, are a valid method of measuring airway closure in vivo, with the added advantage of providing three-dimensional data that allow the detection of small, discrete areas of airway closure and determination of their volumes and shapes.

To compare the subtle pulmonary parenchymal morphologic changes with ventilation function in patients with silicosis, the conventional CT, high resolution CT and technegas ventilation SPECT were performed. In 25 silicotic patients and six controls, the pulmonary ventilation state was evaluated by an index called the coefficient of variation (CV), which expresses the subliminal heterogeneous distribution of technegas in the lungs. The results showed that with silicosis the CV value is significantly higher than that without silicosis. The CV value was proved by multifactorial analysis to independently reflect the extent of the appearance of small scattered interstitial findings such as nodules, septal thickening and bullæ, which were typical findings for silicosis. The CV value calculated from the technegas SPECT correlated well with the severity of silicosis. It is considered that the CV value can also express the functional state of the silicotic lung.

Extent of airway closure may be an important indication of functional abnormality of asthmatic airways. However, regional distribution of airway closure has been difficult to assess with traditional methods. We investigated the use of simultaneous emission/transmission SPECT (SET SPECT) to provide 3-dimensional distribution of lung regions subtended by closed airways. Airway closure was estimated by inhalation from residual volume (RV) of a Tc-99m Technegas bolus, which distributes similarly to an inert gas, but remains in the lungs to allow SPECT imaging. The simultaneously acquired transmission study was segmented into lung and soft tissue regions to give total lung volume. Regions subtended by closed airways (LVclosed) were defined as lung regions (defined by transmission scan) with Technegas activity below a defined threshold. To assess the accuracy, "lung" volumes ranging from 670-2600 ml with defects (ranging from 70-2100 ml) representing closed airway regions were placed into a thorax phantom and SET SPECT studies were performed. The known volumes were compared to those determined from the SPECT studies. The technique was also applied to 23 asthmatics and 13 age and sex matched normal volunteers.

Mean±SD difference between measured and actual phantom lung volume was 1.1±108 ml, with a COV of 9.8%. Regression equation for measured vs actual was y=1.035x50.9, r=0.987. Mean±SD difference between measured and actual defects was 35±131ml, with a COV of 22.9%. There was a strong correlation between LV_closed and age in normals (r=0.94), but not in asthmatics (r=0.46). LV_closed in normals was largely restricted to the base of the lung, while in asthmatics it was more widely distributed and patchy. However, total LV_closed (expressed as a percentage of total lung volume) was not significantly different between normal (30±7.8%) and asthmatics (31±6.0%).

SET SPECT after Technegas inhalation not only provides accurate estimation of airway closure, but also the distribution of airway closure, which is not readily available with other techniques.

Pulmonary emphysema can be diagnosed easily by X-ray CT (CT) as a low attenuation area. Recently Tc-99m-Technegas (Technegas) has been used for ventilation scintigraphy. The present study was undertaken to assess the usefulness of planar and SPECT images by using Technegas scintigraphy in patients with pulmonary emphysema. Technegas scintigraphy, CT and pulmonary function tests were performed in 20 patients (males, age 32-78 years). We classified the findings of Technegas images into 4 grades. Comparing planar and SPECT images of Technegas, more detailed findings were shown by SPECT than by planar images in mild cases (6 cases, 30%). In more severe cases, findings of SPECT and planar images were equivalent (14 cases, 70%). The degree of abnormal findings obtained by SPECT was equivalent to that obtained by CT in severe cases (6 cases, 30%). SPECT should be excluded in advanced stages as indicated by planar images.

Planar pulmonary scintigraphy is limited to diagnose subsegmental pulmonary embolism (PE) which is improved by "normal" SPECT (nSPECT) acquisition but still hampered by movement artefacts. Gated SPECT (gSPECT) might be helpful (dual head, 64x64 matrix, 64 views. 8 time-bins, 15 breath cycles per view) to overcome this limitation. The cyclic movement of a sphere (in coincidence with a trigger pulse) in a body shaped phantom containing an appropriate activity (negative contrast) was used for simulation studies. In patients (pts) gSPET was realised by the registration of the temperature difference of the in- and exhaled air from which gating was derived. The gated phantom studies showed a significant increase of resolution and contrast compared with nSPET read by visual analysis. In 36 pts suffering from deep vein thrombosis (proven by duplex sonography) V/Q scintigraphy was performed using Tc-99m-labeled Technegas and MAA using n- and gSPET immediately before and 10 days after initialisation of two different therapy regimes (standard or low-molecular-weight heparin: early versus late mobilisation). All scans were blindly read by two experienced physicians. Inter-observer agreement was 82% and 94% for nSPECT and gSPECT, respectively. Initially 58% of pts had PE. 55% of pts showed no clinical change. In the two groups with different therapies improvement of PE was diagnosed in both in 6 (17%) pts whereas in 2 pts (5.5%) a worsening was found. We conclude, that by gated pulmonary SPECT there is an improvement of spatial resolution and contrast which leads to a more reliable diagnosis of pulmonary embolism in V/Q scintigraphy.

This study was undertaken to compare axial images of ^99mTc-Technegas SPECT (Technegas) with those of ¹³³Xe gas dynamic SPECT in patients with pulmonary emphysema. There were 20 patients, 19 males and I female. All patients except one ex-smoker were heavy smokers with a mean age of 68.1 years. For Technegas scintigraphy, the patients inhaled 505 MBq ^99mTc-Technegas in several tidal volume breaths in the supine position without breath holding. For ¹³³Xe scintigraphy, the patients inhaled 370 MBq ¹³³Xe gas. ¹³³Xe gas dynamic SPECT was performed in the equilibrium phase for the last minute of the 3 minute inhalation in a closed circuit, and in the washout phase for 6 minutes of inhalation in a semi-closed circuit, by means of a gamma camera with dual detectors (Picker model Prism 2000). Abnormal findings included heterogeneity, defects and hot spots on Technegas images and on retention images taken 3 minutes after ¹¹³Xe gas washout. In 2 of 20 patients, the degree of abnormal findings on Technegas images depended on the area of ¹³³Xe gas retention in the washout phase. In 3 patients, the degrees of abnormal findings on both Technegas SPECT and ¹³³Xe gas dynamic SPECT images were equivalent. In the remaining 15 patients, more detailed findings and a greater area were shown by Technegas SPECT than ¹³³Xe gas dynamic SPECT. We conclude that in patients with pulmonary emphysema Technegas SPECT can demonstrate ventilation impairment more easily than ¹³³Xe gas dynamic SPECT.

The aim of the study was to evaluate the performance of pixel based 3-D-Imaging of Inhalation / Perfusion SPET data in comparison with the subjective interpretation of static image characteristics in various long diseases (COPD n=5, PE n=8, COPE and PE n=3, emphysema n=5, lung transplantation n=7, and in 5 cases of suspected PE having a normal scan and no PE.

Methods: Inhalation of 74 MBq 99m Tc-Technegas was followed by planar and SPET imaging. The lying patient then received 111 MBq 99m Tc-MAP without changing his position. Image fusion and data processing was done using a SUN workstation with multimodality software (HERMES). Subtracted images were interpreted by three independent trained observers. Interobserver agreement was defined.

Results: All mismatches found in the static images were also identified in the 3-D-images. In 2 patients which were considered to have matched defects in the static images, mismatched areas were observed by the 3-D-studies. The aquisition time of the combined SPET is 30 minutes, the duration of the static image sampling varies. (30-60 min)

Conclusions: Combined 3-D-Ventilation/Perfusion Imaging by SPET is a helpful tool in the investigation of lung diseases. allowing quantification and precise localisation of perfusion defects with regular ventilation. The aquisition and processing time is similar to that of simple planar imaging.

Purpose; Usually practiced planar lung scintigraphy is insufficient in detection of subsegmental pulmonary embolization. SPECT might be helpful. Unfortunately movement of lung reduces both resolution and contrast. Therefore. what about gated SPECT?

Methods; A prepared body phantom is used for simulation. The cyclic movement of a sphere in m appropriate activity containing medium (negative contrast) is correlated with a pulse for camera control. For clinical purposes gating was realized by a thermosensor of an electrical flowmeter which registered the beginning of inhalation. A TTL-pulse enables breath-corresponding imaging.

Results; The gated phantom studies show a clear increase of resolution and contrast compared with non-gated SPECT. Though realistic acquisition parameters and activity concentrations we used the detection of the defect is quite similar to that of the non-gated study if the sphere is fixed. The practised SPECT acquisition parameters (dual head camera, 64x64 matrix, 64 steps, 8 time segments and 15 accepted breath cycles per view) result from compromising count statistics and total acquisition time tolerated by the patient.

Conclusion; Phantom studies with a moved individually filled sphere (diameters 25mm, shift 25mm and ,,cold") is resolved with a gated SPECT study only. The phantom studies demonstrate that gated SPECT is more effective for detection of small defects in lung scintigraphy. The clinical gated SPECT studies showed a clew increase of resolution and contrast (20% of patients (n=36) had m increase of contrast>20% ) compared with non-gated SPECT.