ORIGINAL ARTICLE 
Annals of Nuclear Medicine Vol, 11, No. 3, 201-206, 1997 
Comparison of 99mTc-Technegas SPECT with 133Xe dynamic SPECT in pulmonary emphysema 
Katashi SATOH,* Kazue TAKAHASHI,* Mayumi SASAKI,* Takuya KOBAYASHI,* Naomi HONJO,* Motoomi OHKAWA,* Masatada TANABE,* Jiro FUJITA** and Hirofumi MIYAWAKl** 
*Department of Rediology, and **First Department of Internal Medicine, School of Medicine, Kagawa Medical University 
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 1 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 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. 
Key words: Technegas, 133Xe gas, dynamic SPECT, pulmonary emphysema 
INTRODUCTION 
RECENTLY ultra fine 99mTc-labeled carbon particles are being used for ventilation scintigraphy including SPECT.1-10 Burch et al. reported that 99mTc-Technegas has considerably small particle size and can reach the peripheral parts of the lung,1 133Xe gas is also used for dynamic SPECT in addition to planar images.11 The present study was undertaken to compare axial images of 99mTc-Technegas (Technegas) SPECT with those of 133Xe dynamic SPECT in patients with pulmonary emphysema. 
Received March 31, 1997, revision accepted May 19, 1997. 
For reprint contact: Katashi Satoh. M.D.. Department of Radiology, School of Medicine, Kagawa Medical University, 1750-1 Ikenobe, Miki-cho, Kita-gun. Kagawa 761-07, JAPAN. 
e-mail: satoh@kms.ac.jp 
MATERIALS AND METHODS 
Patients 
Twenty patients were studied, 19 males and 1 female, with an age range of 49-78 years and a mean age of 68.1 years. All patients except one ex-smoker were heavy smokers and were diagnosed as having pulmonary emphysema on the basis of clinical symptoms, pulmonary function tests and CT (Table 1 ). 
Technegas SPECT 
Technegas was generated in a proprietary generator (Technegas Generator, Tetley Manufacturing Ltd., Sydney, Australia) by the resistive heating of a graphite crucible to 2,500deg.C in which a saline solution of 505 MBq of 99mTc-pertechnetate had been placed and dried. After generation of the aerosol, it was dispersed in a lead-lined chamber in an atmosphere of 100% argon. Following inhalation of 100% oxygen at 5 l/min for 3 minutes, all patients were given 505 MBq 99mTc-Technegas by inhalation in several tidal volume breaths without breath holding through a mouthpiece while wearing a nose clip and lying in the supine position. The SPECT system was a gamma camera with dual detectors (Picker model Prism 2000, Northford, Connecticut, USA) equipped with a low-energy, high-resolution collimator. Seventy-two images were acquired for 40 seconds each at 5deg. intervals. Each image was stored in a 128 x 128 pixel matrix. Reconstruction of images was performed by means of Butterworth and Ramp filters with no correction for attenuation.9 
Xe-133 dynamic SPECT 
Following inhalation of 100% oxygen at 5 l/min for 3 minutes, the patients also inhaled 370 MBq 133Xe gas through a mask over the nose and mouth connected to the 133Xe gas ventilation system (Xe-VSS set, Nippon Mediphysics, Osaka, Japan), as a single breath planar image and held their breath for 15 seconds. 133Xe dynamic SPECT was performed in the equilibrium phase for the last minute of the 3 minute breathing in a closed circuit, and in the washout phase for 6 minute breathing in semiclosed circuit, by means of a Picker model Prism 2000 equipped with a low energy general all purpose parallel collimator. Dynamic SPECT data acquisition by each detector was performed for 1.5 seconds per projection with 20 views encompassing a 180deg. arc. Each detector was rotated in clockwise and counterclockwise directions across the same projection arc for 30 sec. Each image was stored in a 64 x 64 pixel matrix. Reconstruction of images was performed with no correction for attenuation, by means of Butterworth and Ramp filters. Two sequential 30 second images were added to obtain one 1 minute image. 
Interpretation of SPECT images 
All SPECT images were interpreted independently by three radiologists. Abnormal findings on Technegas imaging were classified according to the extent of heterogeneity, defect, and hot spot formation as follows: peripheral heterogeneity in mild cases, additional hot spot formation in moderate cases, and additional regional defects in severe cases.12 Abnormal findings on 133Xe imaging were heterogeneity and defects on single breath images and on retention images 3 minutes after washout.15 
RESULTS 
According to the severity on Technegas planar images, there were 6 mild, 1 moderate and 13 severe cases, whereas on SPECT images there were 3 mild and 17 severe cases. Among these patients, there were 13 with equivalent severity in planar and SPECT images in which the degree of the severity was severe in all patients. In the remaining 7 patients, the severity in SPECT images was greater than on planar images: severe on SPECT and mild on planar in 2; severe on SPECT and moderate on planar in 1; and moderate on SPECT and mild on planar in 4 patients. 
On 133Xe dynamic SPECT, there were heterogeneity and peripheral defects in single breath and retention images in different segments in one or both lungs in all cases. 
Considering the extent of impairment, in 2 of 20 patients (10.0%), the extent of abnormal findings on Technegas was inferior to the area of 133Xe retention in the washout phase. In these patients, Technegas could not enter the emphysematous area in which there were peripheral defects and which showed remarkable retention images on 133Xe gas SPECT. In 3 of 20 patients (15.0%), the degree of abnormal findings in both Technegas and 133Xe dynamic SPECT were equivalent. In the above 5 patients, both planar and SPECT images of Technegas were equivalent with respect to severity but in the remaining 15 patients (75.0%), more detailed findings and a greater area of abnormality were shown on Technegas SPECT than on 133Xe dynamic SPECT. 
Two typical cases are shown in Figs. 1 and 2. In the case shown in Fig. 1 , 133Xe dynamic SPECT was estimated to be superior to Technegas SPECT. On the other hand, in the case shown in Fig. 2, Technegas SPECT was estimated to be superior to 133Xe dynamic SPECT. 
DISCUSSION 
A washout study with 133Xe gas is widely used to detect regional ventilation impairment in airways diseases.13-18 The late phases of these regional ventilation studies are helpful in evaluating cases of mild to moderate airway obstruction which would otherwise be misdiagnosed by radiographs.15,16 133Xe retention has been reported to be characterized as mild if retention is beyond three minutes but less than six minutes, moderate if between six and ten minutes, and severe if persisting longer than ten minutes.15 Nevertheless, the planar image has a two-dimensional character and has inherent limitations because of superimposition of the diseased and normal parts of the lung, and the background effect in the chest wall.13 Three-dimensional SPECT images, on the other hand, can more precisely assess the location or involvement in pulmonary disease.9-11 
With respect to recent ventilation studies, some advantages of the clinical use of Technegas has been reported and has an appropriate energy level,3,4,9 Previously the ideal size for aerosol droplets in order to get good uniformity in the lungs during deep tidal volume breathing was considered to be between 0.1 and 0.5 um.19 Because particles larger than 2 um are likely to be deposited in the proximal bronchial trunci, 99mTc-phytate aerosol images had a limitation due to intense bronchial foci or hot spot formation in cases with severe chronic obstructive pulmonary disease.7 Technegas is ultra fine carbon particles of the order of 0.005 ,um.1 Technegas imaging also gives similar or better diagnostic information on lung ventilation imaging in quantitative comparison with 133Xe and 81mKr due to the nesessity for preparation in advance and the latter two gases and a high cost.3,4 No need for a ventilation system in the case of Technegas is also an advantage over 133Xe scintigraphy. Technegas SPECT images assessed the pulmonary diseases better than planar images.9,10 
In 2 of 20 cases in the present study, 133Xe dynamic SPECT was estimated to be superior to and more prominent than Technegas SPECT in spite of the equivalent size of the abnormal area. These areas were of such a character that 133Xe gas could not enter in a single breath but could enter in the equilibrium phase following remarkable retention in the washout in contrast to the inability of Technegas to enter, suggesting that Technegas has the character of an aerosol in spite of its ultra fine particles. If rebreathing time is not long enough to allow 133Xe to accumulate in regions with poor air exchange, then 133Xe retention will not be seen during washout,16 
Although 133Xe scintigraphy is sensitive enough to detect the emphysematous regions due to its retention during washout, Technegas SPECT detected more detailed findings in areas where retention was not seen on 133Xe dynamic SPECT. In 15 cases, more detailed findings and greater area were provided by Technegas SPECT than by 133Xe dynamic SPECT. In our study, because of the short time, we could not assess SPECT images during a single breath but only planar images which cannot be compared with SPECT images during equilibrium and the washout phase. If these comparisons can be studied, more precise location or the nature of impairment will be assessed. 
X-ray CT can morphologically depict very tiny low attenuation as emphysematous areas,20,21 but ventilation study including SPECT can reveal more extensive or detailed findings, even very mild abnormalities, than the X-ray CT.9,11 Localized pulmonary emphysema, even if it is severe on X-ray CT or scintigraphy, may not influence the overall pulmonary function. Zhang et al. showed that the distribution of Technegas images became heterogeneous with the degree of severity of silicosis on SPECT images, which correlated to X-ray CT.10 
133Xe dynamic SPECT has the advantage of assessing severity by means of parameters such as Tl/2 and mean transit time (MTT).11 On the other hand, although Technegas images are static, they have an advantage over 133Xe dynamic SPECT images since the former do not require a ventilation system and there is no dyspnea in patients during examination. Technegas images may reveal not only emphysematous lesions but also other impairments. Morphological examination by means of radiologic-pathologic correlative studies may be necessary in cases with abnormal findings on Technegas SPECT even if there is no abnormality on 133Xe dynamic SPECT. 
In conclusion, in the present study Technegas SPECT provided more detailed findings of ventilation impairment than 133Xe dynamic SPECT in patients with pulmonary emphysema. 
REFERENCES 
l. Burch WM. Sullivan PJ, McLaren CJ. Technegas: a new ventilation agent for lung scanning. Nucl Med Commun 7: 865-871, 1986. 
2. Peltier P, Faucal P, Chetanneau A, Chatal JF. Comparison of technetium-99m aerosol and krypton-81m in ventilation studies for the diagnosis of pulmonary embolism. Nucl Med Commun 11: 631-638, 1990. 
3. Rimkus DS, Ashbum WL. Lung ventilation scanning with a new carbon particle radioaerosol (Technegas). Preliminary patient studies. Clin Nucl Med 15 : 222-226, 1990. 
4. Amis TC, Crawford ABH, Davison A, Engel LA. Distribution of inhaled 99mTechnetium labeled ultrafine carbon particle aerosol (Technegas) in human lungs. Eur Respir J 3: 679-685, 1990. 
5. Crawford ABH. Davison A. Amis TC. Engel LA. Intrapulmonary distribution of 99mTechnetium labeled ultrafine carbon aerosol (Technegas) in severe airflow obstruction. Eur Respir J 3: 686-692, 1990. 
6. Isawa T, Teshima T, Anazawa Y. Miki M. Motomiya M. Technegas for inhalation lung imaging. Nucl Med Commun 12: 47-55, 1991. 
7. Peltier P. Bardies M, Chetanneau A, Chatal JF. Comparison of technetium-99m C and phytate aerosol in ventilation studies. Eur J Nucl Med 19: 349-354, 1992. 
8. James JM, Lloyd JJ. Leahy BC. Church S, Hady CC, Shields RA, et al. 99Tcm Technegas and krypton-81m ventilation scintigraphy: a comparison in known respiratory disease. Br J Rediol 65: 1075-l082, 1992. 
9. Satoh K. Tanabe M, Nakano S, Nishiyama Y, Takahashi K, Kobayashi T, et al. Comparison of 99mTc-Technegas scintigraphy and high resolution CT in pulmonary emphysema. KAKU IGAKU (Jpn J Nucl Med) 32: 487-494, 1995. (Japanese, abstract in English) 
10. Zhang X, Hirano H. Yamamoto K. Kusaka Y. Sugimoto K, Kimoto T, et al. Technegas ventilation SPECT for evaluating silicosis in comparison with computed tomography. Ann Nucl Med 10: 165-170, 1996. 
11. Suga K, Nishigauchi K. Kume N. Koike S. Takano K, Tokuda O, et al. Dynamic pulmonary SPECT of Xe-133 gas washout. J Nucl Med 37: 807-814, 1996. 
12. Suzuki T. Evaluation of the regional lung function revealed in radioaerosol scintigram of chronic obstructive pulmonary disease. I. The comparison of radioaerosol scintigram with the lung function tests in chronic obstructive pulmonary disease. Nippon Acta Rediologica 40: 156-167, 1980. (Japanese, abstract in English) 
13. Secker-Walker RH, Hill RI. Markham J. The measurement of regional ventilation in man: a new method of quantitation. J Nuc Med 14: 725-732, 1973. 
14. Schor RA. Shames DM, Weber PM, Dos Remedios LV. Regional ventilation studies with 81mKr and 133Xe: a comparative analysis. J Nucl Med 19: 348-353, 1987.
l5. Alderson PO. Secker-Walker RH. Forrest JV. Detection of obstructive pulmonary disease. Relative sensitivity of ventilation-perfusion studies and chest radiography. Radiology 111: 643-648, 1974.
16. Alderson PO, Lee H, Summer WR, Motazedi A, Wagner HN. Comparison of Xe-133 washout and single-breath imaging for the detection of ventilation abnormalities. J Nucl Med 20: 917-922, 1979. 
17. Bunow B, Line BR, Horton MR, Weiss GH. Regional ventilatory clearance by xenon scintigraphy: a critical evaluation of two estimation procedure. J Nucl Med 20: 703-710, 1979. 
18. Van der Mark TW, Peset R, Beekhuis H. An improved method for analysis of 133 Xe washin and washout curves. J Nucl Med 21 : 1029-l034, 1980. 
19. Sirr SA, Junenemann PJ, Tom H, Boudreau RJ, Chandler RP, Loken MK. Effect of ethanol on droplet size, efficiency of delivery, and clearance characteristics of technetium-99m DTPA aerosol. J Nucl Med 26: 643-646, 1985. 
20. Murata K, Itoh H, Todo G. Centrilobular lesions of the lung: demonstration by high-resolution CT and pathologic correlation. Rediology 161: 641-645, 1986. 
21 . Webb WR, Stein MG, Finkbeiner WE, Im JG, Lynch D, Gamsu G. Normal and diseased isolated lungs: high-resolution CT. Radiology 166: 81-87, 1988.