ORIGINAL ARTICLE Annals of Nuclear Medicine Vol. 11, No. 2. 109-113, 1997 Assessment of Technetium-99m Technegas scintigraphy for ventilatory impairment in pulmonary emphysema: Comparison of planar and SPECT images Katashi SATOH,* Masatada TANABE,* Kazue TAKAHASHI,* Takuya KOBAYASHI,* Yoshihiro NISHIYAMA,* Yuka YAMAMOTO,* Naomi HONJO,* Mayumi SASAKI,* Motoomi OHKAWA,* Jiro FUJITA** and Hiroki OKADA** *Department of Rodiology, and **First Department of Internal Medicine, Kagawa Medical University. School of Medicine 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. Key words: technegas, pulmonary emphysema, ventilation study, planar images, SPECT images INTRODUCTION RECENTLY, ultrafine Technetium-99m labeled carbon particles (Technegas) are being used for ventilation scintigraphy.1-6 Ventilation scintigraphy can be performed with inert gases such as Xe-133 and Kr-81m, but there are some limitations. Tc-99m phytate aerosol and Techengas can be generated in any institution. However, Peltier et al. reported that Tc-99m phytate aerosol images were not superior to Technegas images and had a limitation where there is a possible existence of intense high bronchial foci or hot spot formation in cases of severe chronic obstructive pulmonary disease.5 On the other hand, morphologically CT can depict pulmonary emphysema as small low attenuation areas.7,8 The purpose of this study was to assess the usefulness of Technegas scintigraphy by both planar and SPECT images in patients with pulmonary emphysema. MATERIALS AND METHODS Patients Twenty patients (all males with age range of 32-78 years and a mean age of 67 years: 18 heavy smokers, 1 non-smoker, and I ex-smoker) underwent X-ray CT (CT) and Technegas scintigraphy. All patients were diagnosed as having pulmonary emphysema by clinical symptoms. pulmonary function test and CT. The patients were ar-ranged from 1-20 by % forced expiratory volume in one second (%FEV 1.0) from mild to severe (Table 1). Pulmonary function test were performed by Chestac-35K and Chestac-55V (Chest MI, Tokyo, Japan). Technegas Technegas is generated in a proprietary generator (Technegas Generator, Tetley Manufacturing Ltd., Sydney, Australia) by the resistive heating of a graphite crucible up to 2,500degC in which a saline solution of 505 MBq of Tc-99m pertechnetate has been placed and dried. After generation of the aerosol in an atmosphere of 100% argon, it is dispersed in a lead-lined chamber. Following inhalation of 100% oxygen at 5 l/min for 3 minutes, all patients were given Technegas by inhalation through a mouthpiece while wearing a nose clip and lying in the supine position, in several tidal volume breaths without breath holding. Following the administration of Technegas, planar imaging was performed in 6 projections: anterior, posterior, right lateral, left lateral, right posterior oblique and left posterior oblique. The SPECT system used was Picker model Prism 2000 (Northford, Connecticut, USA) with a low-energy, high-resolution collimator. SPECT was rotated through 360deg. Seventy-two images were collected at 5deg intervals for 40 seconds each with 128 x 128 matrix size. A low pass filter and a Ramp filter were used. No correction was made for attenuation. SPECT imaging was also performed in 3 projections with 4.95 mm thickness: axial, coronal, and sagittal. The axial images were compared with CT. The lower cut level of display was 0% in planar images and 0-5% in SPECT images. We classified the findings of Technegas imaging into 4 stages according to the extent of peripheral irregularity and central hot spot formation: Stage I) normal homogeneous distribution; Stage II) peripheral heterogeneity; Stage III) additional hot spot formation; and Stage IV) further regional defect.10 CT CT was performed after Technegas scintigraphy making 12 slices from above the aortic arch to the diaphragm with 5 mm collimation in a bone detail algorithm during moderate inspiration using two CT scanners, CT9800 and HiSpeed Advantage (General Electric, Milwaukee, Wisconsin, USA). CT images from each lung were displayed with window level - 600 and window width 1,500. RESULTS Table 2 shows the results of images of planar and SPECT according to Technegas stages. Cases 3, 4 and 5 had normal pulmonary function tests. They showed localized severe bullous changes on CT. In cases 3 and 4, both images of planar and SPECT revealed Stage IV, whereas in case 5, planar images revealed Stage II whereas SPECT revealed Stage IV. In 14 of the 20 cases (70%), SPECT and planar images of Technegas were equivalent in terms of the degree and range of involvement (Table 2, Group A). With Technegas SPECT all stages observed were IV in Group A except in case 9, which was shown as Stage III. In the remaining 6 cases (30%), more detailed findings were shown by SPECT than by planar images (Table 2, Group B). Stages of planar images in Technegas were: 3 as Stage I and 3 as Stage II. All 3 Stage I cases in planar corresponded to stage II in SPECT, and all 3 Stage II cases corresponded to Stage IV in SPECT. In these cases SPECT showed heterogeneity and hot spot formation which was not observed in planar images. Findings in planar and SPECT images were the same in the more severe cases, Stages 111 and IV. Figure 1 shows a case (#20) in which planar and SPECT were equivalent. Figure 2 shows a case (#1) in which SPECT was superior to planar. DISCUSSION CT can demonstrate tiny low attenuation areas less than 5 mm in diameter, confirmed by radiologic-pathologic correlative studies.8,9 Although spatial resolution of the scintigram in nuclear medicine is inferior to CT, nuclear medicine can depict the physiological kinetic movement and assess the regional pulmonary function in contrast with overall function11,12 as with CT.13 Ventilation 11,12 scintigraphy by inert gases such as Xe-133 and Kr-8lm has some limitations, such as the necessity for preparation of gases in advance. Furthermore, Xe-133 requires a ventilator system or bag-box spirometer, and Kr-81m is high in cost in spite of the "gold standard."6 Although particle size of Technegas is in the order of 0.005 um^2 different authors agree that they are more likely less to be than 0.2 um.4,6 Because particles larger than 2 p:m are likely to be deposited in the proximal bronchial trunks, Tc-99m phytate aerosol images are not superior to Technegas images and have a limitation due to a intense bronchial foci or hot spot formation in cases with severe chronic obstructive pulmonary disease.5 Since the appropriate energy of the Technetium-99m made Technegas delineates the outline of the lung in multiple projections, Technegas is reported to be superior to or not different from Xe-133.1,2 However, there have been only few re-ports about SPECT using Technegas.7,13 Zhang et al. reported that an index expressing the subliminal heterogeneous distribution by Technegas SPECT correlated well with severity of silicosis.7 Localized pulmonary emphysema, even if it is severe in images on CT or Technegas, does not influence the overall pulmonary function. In comparing planar and SPECT images of Technegas, SPECT showed more detailed findings of advanced stages than planar images in mild Stage I and II cases. This implies that SPECT could be excluded in advanced stages, such as Stage III and IV and replaced by planar images. In Stages III and IV, the more severe cases, images of SPECT and planar are equivalent. REFERENCES 1. Rimkus DS, Ashburn WL. Lung ventilation scanning with a new carbon particle radioaerosol (Technegas). Prelimi-nary patient studies. Clin Nucl Med 15: 222-226, 1990. 2. AmisTC, 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. 3. 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. 4. Isawa T, Teshima T, Anazawa Y, Miki M, Motomiya M. 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