Mismatch between 99mTc-DTPA aerosol and 81mKr lung ventilation scintigraphy: a pitfall of radionuclide imaging

Pulmonary ventilation and perfusion scintigraphies were performed using 99mTc-MAA, 81mKr, and 99mTc-DTPA aerosol in a patient with asthma. Lung perfusion scintigraphy and 99mTc-DTPA aerosol scintigraphy showed multiple matching defects, however, 81mKr ventilation scintigraphy showed mismatch with lung perfusion scintigraphy. A pitfall of this examination was discussed.     

Comprehensive ventilation/perfusion SPECT.

Lung scintigraphy is the primary tool for diagnostics of pulmonary embolism. A perfusion study is often complemented by a ventilation study. Intermediate probability scans are frequent. Our goal was to develop a fast method for tomographic ventilation and perfusion scintigraphy to improve the diagnostic value of lung scintigraphy. METHODS: SPECT was performed with a dual-head gamma camera. Acquisition parameters were determined using a thorax phantom. Ventilation tomography after inhalation of 30 MBq (99m)Tc-diethylenetriaminepentaacetate (DTPA) aerosol was, without patient movement, followed by perfusion tomography after an intravenous injection of 100 MBq (99m)Tc-labeled macroaggregated albumin (MAA). Total SPECT acquisition time was 20 min. (99m)Tc-DTPA clearance, calculated from initial and final SPECT projections, was used for correction of the ventilation projection set before iterative reconstruction of ventilation and perfusion. The ventilation background was subtracted from the perfusion tomograms. A normalized ventilation/perfusion quotient (V/P quotient) image set was calculated. The method was evaluated on a trial group of 15 patients. RESULTS: Ventilation and perfusion images had adequate quality and showed ventilation/perfusion (V/Q quotient) relationships more clearly than did planar images. Frontal and sagittal slices were superior to planar scintigraphy for characterization of embolized areas. The V/Q quotient was supportive, particularly in the patients with chronic obstructive pulmonary disease. CONCLUSION: Fast, high-quality, ventilation/perfusion SPECT with standard isotopes doses is feasible and may contribute to higher objectivity in evaluating lung embolism as well as other lung diseases. The costs for the procedure and patient care until diagnosis are low because of the comprehensive system for the study and, particularly, the short time for its completion.     

Assessment of SPECT ventilation-perfusion imaging in patients with lung cancer

Ventilation and perfusion SPECT images during tidal breathing were studied in 15 cases of lung cancer using 81mKr gas and 99mTc-microspheres. Furthermore, functional images of V/Q ratio and Q/V ratio were prepared, and their clinical significance is discussed with reference to general lung function. There was a decrease in %VC and %FEV 1.0 in 7 of 15 cases, and an increase of AaDo2 in the blood gas analysis in 12 of 15 cases. Both planar and SPECT images showed ventilation and perfusion abnormalities in all 15 cases. Of these, 12 patients showed matched ventilation and perfusion defects, 2 patients a dead-space effect and 1 patient a shunt effect. In comparing planar and SPECT images, depiction of ventilation and perfusion impairments were equally clear in 11 cases, but in 3, showing a lobar or segmental defect with a shunt effect, the SPECT images were superior. In a patient with markedly impaired function of the affected lung, the remaining function could not be depicted by SPECT. From the above, it seems that better information can be obtained for understanding the ventilation and perfusion states of lung cancer by adding the SPECT images to the planar image.     

Lung ventilation/perfusion SPECT in the artificially embolized pig.

Planar lung scintigraphy is a standard method used for the diagnosis of lung embolism, but it is hampered by the high incidence of nondiagnostic tests. Ventilation/perfusion SPECT may possibly improve this situation. The objective of this study was to compare planar lung scintigraphy with ventilation/perfusion SPECT using pigs with artificially engendered lung emboli labeled with (201)Tl. METHODS: Sixteen anesthetized pigs were each injected with zero to 4 latex emboli. Cylindric emboli were used in the first 7 pigs and flat 3-tailed emboli were used in the remaining 9 pigs. The pigs spontaneously inhaled 30 MBq (99m)Tc-diethylenetriaminepentaacetic acid aerosol for ventilation scintigraphy. Planar scintigraphy and SPECT were performed using a double-head gamma camera in (99m)Tc and (201)Tl windows. Immediately thereafter, 100 MBq (99m)Tc-labeled macroaggregated albumin were injected intravenously followed by SPECT and, finally, planar scintigraphy. The ventilation background was subtracted from the perfusion tomograms for calculation of a normalized ventilation/perfusion (V/P) quotient image set. RESULTS: The cylindric emboli caused artifacts in the ventilation images; therefore, these were excluded from the final analysis. However, for the planar perfusion images of these pigs, sensitivity and specificity were 71% and 91%, respectively, whereas SPECT yielded 100% for both. For the 3-tailed emboli and ventilation/perfusion images, the sensitivity and specificity were 64% and 79%, respectively, for the planar modality, whereas SPECT yielded values of 91% and 87%, respectively. CONCLUSION: V/P SPECT may improve the diagnostic power of lung scintigraphy.     

Pulmonary perfusion and ventilation scintigraphies before and after cardiac catheterization in infants with congenital heart diseases

We performed 99mTc-MAA pulmonary perfusion scintigraphies before and after catheterization of 50 infants with congenital heart disease. 81mKr ventilation scintigraphies were also performed in 41 patients. Both right and left heart catheterization (23 patients) and right heart catheterization (27 patients) were performed by Seldinger's method. Pulmonary perfusion scintigraphies showed new perfusion defects in 6 patients (12%) following catheterization. Of six patients, three had ventilation defects. Clinical characteristics, duration of catheterization, hemodynamic variables were not significantly different between patients with and without lung perfusion defects. The lung perfusion defects seemed to be due to pulmonary embolism following cardiac catheterization.     

99mTc particle perfusion/99mTc aerosol ventilation imaging using a subtraction technique in suspected pulmonary embolism

It is generally acknowledged that ventilation-perfusion mismatch is diagnostic of pulmonary embolism. Lung ventilation imaging with radioactive gases is a good method for the detection of pulmonary embolism, but it is not in widespread use because of the limited availability of 81mKr gas and the poor physical properties of 133Xe. Aerosols have been proposed, instead of gases for use in lung ventilation imaging. As perfusion and ventilation distributions may change very rapidly, the two imaging procedures should be done in rapid succession. The cheapest way to perform the combined perfusion-ventilation (Q/V) imaging is to use 99mTc-labelled macroaggregates and aerosols. In our method the perfusion imaging was done first, immediately followed by the ventilation imaging with 99mTc-labelled aerosols. A computer program was used to subtract the contribution of the perfusion from the combined Q/V image so that the pure ventilation image alone was obtained. The method was tested in 41 patients with suspected pulmonary embolism.     

Effect of PEEP on regional ventilation and perfusion in the mechanically ventilated preterm lamb

Improvement of gas exchange through closer matching of regional ventilation (V) and lung perfusion (Q) with the application of positive end-expiratory pressure (PEEP) was evaluated in vivo in six mechanically ventilated preterm lambs (107-126 days/145 days gestation). Changes in V and Q were determined from in vivo scintigraphic measurements in four lung regions with inhaled radioactive 81mKr, and infused 81mKr/dextrose and/or [99mTc]MAA as PEEP was applied at 2, 4, and 6 cm H2O in each animal. Dynamic compliance varied between 0.02 and 0.40 ml/cm H2O, which was consistent with surfactant deficiency. As PEEP was increased, the regional distribution of Q shifted from the rostral to the caudal lung regions (p less than 0.02 to less than 0.05), while that of V remained unchanged. Regional V/Q matching improved together with a trend towards improvement of arterial blood gases as PEEP was increased from 2 to 4 cm H2O. Pulmonary scintigraphy offers a noninvasive methodology for the quantitative assessment of regional V and Q matching in preterm lambs and may be clinically applicable to ventilated neonates.     

81mKr gas and 99mTc-MAA V/Q ratio images for detection of V/Q mismatches

Methods for creating ventilation/perfusion ratio images have been reported previously using radioxenon. With the availability of 81mKr gas, corresponding ventilation and perfusion views in multiple projections to evaluate for V/Q mismatch may be performed more readily. A technique for the creation of a functional V/Q ratio image to highlight V/Q mismatches to aid in the evaluation of pulmonary embolism is described. By removing nonpertinent and distracting information and by converting a 'cold spot' imaging modality to a 'hot spot' modality, these functional images aid in the synthesis of the information provided by the ventilation and perfusion images. The limitations due to technical artifacts and the advantages of using these functional images are described.     

Is a lung perfusion scan obtained by using single photon emission computed tomography able to improve the radionuclide diagnosis of pulmonary embolism?

Planar pulmonary scintigraphy is still regularly performed for the evaluation of pulmonary embolism (PE). However, only about 50-80% of cases can be resolved by this approach. This study evaluates the ability of tomographic acquisition (single photon emission computed tomography, SPECT) of the perfusion scan to improve the radionuclide diagnosis of PE. One hundred and fourteen consecutive patients with a suspicion of PE underwent planar and SPECT lung perfusion scans as well as planar ventilation scans. The final diagnosis was obtained by using an algorithm, including D-dimer measurement, leg ultrasonography, a V/Q scan and chest spiral computed tomography, as well as the patient outcome. A planar perfusion scan was considered positive for PE in the presence of one or more wedge shaped defect, while SPECT was considered positive with one or more wedge shaped defect with sharp borders, three-plane visualization, whatever the photopenia. A definite diagnosis was achieved in 70 patients. After exclusion of four 'non-diagnostic' SPECT images, the prevalence of PE was 23% (n =15). Intraobserver and interobserver reproducibilities were 91%/94% and 79%/88% for planar/SPECT images, respectively. The sensitivities for PE diagnosis were similar for planar and SPECT perfusion scans (80%), whereas SPECT had a higher specificity (96% vs 78%; P =0.01). SPECT correctly classified 8/9 intermediate and 31/32 low probability V/Q scans as negative. It is concluded that lung perfusion SPECT is readily performed and reproducible. A negative study eliminates the need for a combined V/Q study and most of the 'non-diagnostic' V/Q probabilities can be solved with a perfusion image obtained by using tomography.     

Assessment of SPECT ventilation-perfusion imaging in patients with lung cancer

Ventilation and perfusion SPECT images during tidal breathing were studied in 15 cases of lung cancer using ^81mKr gas and ^99mTc-microspheres. Furthermore, functional images of V/Q ratio and Q/V ratio were prepared, and their clinical significance is descussed with reference to general lung function. There was a decreas in %VC and %FEV _1.0in 7 of 15 cases, and an increase of AaDo₂ in the blood gas analysis in 12 of 15 cases. Both planar and SPECT images showed ventilation and perfusion abnormalities in all 15 cases. Of these, 12 patients showed matched ventilation and perfusion defects, 2 patients a dead-space effect and 1 patient a shunt effect. In comparing planar and SPECT images, depiction of ventilation and perfusion impairments were equally clear in 11 cases, but in 3, showing a lobar or segmental defect with a shunt effect, the SPECT images were superior. In a patient with markedly impaired function of the affected lung, the remaining function could not be depicted by SPECT. From the above, it seems that better information can be obtained for understanding the ventilation and perfusion states of lung cancer by adding the SPECT images to the planar image.     

Technegas versus (81m)Kr ventilation-perfusion scintigraphy: a comparative study in patients with suspected acute pulmonary embolism.

81mKr is widely used as a ventilation agent to diagnose pulmonary embolism (PE). However, (81m)Kr is expensive, which limits its continuous availability. Technegas can be an alternative ventilation agent with the advantage of being less expensive and available daily. The aim of this study was to compare the value of technegas with that of (81m)Kr in the detection of PE. METHODS: Ninety-two consecutive patients (29 men; mean +/- SD, 53 +/- 17 y old) with at least one segmental perfusion defect (Hull criteria) were studied prospectively. Perfusion and ventilation (V/Q) lung scintigraphy with both technegas and (81m)Kr were performed within 24 h on all patients. V/Q lung scan results were classified as high probability for PE (normal ventilation study) or nondiagnostic (abnormal ventilation study). All V/Q lung scans were read by two experienced nuclear physicians in consensus. For the intra- and interobserver variabilities, two experienced observers independently read the V/Q lung scans. RESULTS: (81m)Kr and technegas showed a good agreement (kappa, 0.68; 95% confidence interval [CI], 0.53-0.82). However, technegas significantly increased the number of nondiagnostic V/Q lung scans (P: = 0.035). In 15 patients, a discrepancy was found between (81m)Kr and technegas. False-positive V/Q lung scan results occurred in 4 of 12 patients (33%) with (81m)Kr and in 2 of 3 patients (66%) with technegas. The intra- and interobserver variabilities were 0.71-0.88 (95% CI, 0.56-1.0) for perfusion/(81m)Kr and 0.74-0.96 (95% CI, 0.58-1.0) for perfusion/technegas. CONCLUSION: In comparison with (81m)Kr, technegas does not result in more false-positive V/Q lung scan results. The use of technegas, however, increases the number of nondiagnostic V/Q lung scan results, which would increase the demand for further additional testing to confirm or refute PE.     

The use of a computer in ventilation-perfusion scintigraphy with Tc-99m macroaggregates and Kr-81m, to obtain a physiological model

In this article we describe a computer program to demonstrate ventilation-perfusion relationships in the lungs, using 99mTc-MAA and 81mKr, with the patients sitting upright, the normal physiological situation. The ventilation and perfusion scans are performed simultaneously with both gamma camera and computer adjusted for dual isotope mode. Steady state images are acquired in the frontal, dorsal, and left and right posterior oblique positions. Additionally, in the dorsal and frontal projections, a sequence of 12 washout images (5 s) is registered, after closing the Krypton supply. After normalization and further computer processing, the following parameters are calculated in the frontal and dorsal projections, in the whole lung and in four horizontal subregions: washout values, ventilation-perfusion ratios, left to right ratios of ventilation and perfusion, and left to right ratios of the average pixel values for ventilation and perfusion. Results in a group of eight healthy volunteers are described and discussed.     

Lung scintigraphy clustering by texture analysis

The efficiency of texture analysis parameters, describing the organization of grey level variations of an image, was studied for lung scintigraphic data classification. Twenty one patients received a 99mTc-MAA perfusion scan and 81mKr and 127Xe ventilation scans. Scans were scaled to 64 grey levels and 100 k events for inter subject comparison. The texture index was the average of the absolute difference between a pixel and its neighbors. Energy, entropy, correlation, local homogeneity and inertia were computed using co-occurrence matrices. A principal component analysis was carried out on each parameter for each type of scan and the first principal components were selected as clustering indices. Validation was achieved by simulating 2 series of 20 increasingly heterogeneous perfusion and ventilation scans. For most of the texture parameters, one principal component could summarize the patients data since it corresponded to the relative variances of 67%-88% for perfusion scans, 53%-99% for 81mKr scans and 38%-97% for 127Xe scans. The simulated series demonstrated a linear relationship between the heterogeneity and the first principal component for texture index, energy, entropy and inertia. This was not the case for correlation and local homogeneity. We conclude that heterogeneity of lung scans may be quantified by texture analysis. The texture index is the easiest to compute and provides the most efficient results for clinical purpose.     

Clinical evaluation of Kr-81m inhalation study through a dead space

A new inhalation technique of 81mKr gas was applied to evaluate the pathophysiological abnormality of ventilation. 81mKr gas (370 MBq) was continuously supplied into a mouth piece directly (without dead space), VE, or through a dead space of 500 ml, VL, in 110 subjects with various lung diseases. Subjects were divided in four groups by a combination of distribution patterns of 81mKr gas obtained by these two inhalation techniques. Group 1: No ventilatory defect in both techniques. Group 2: Defects larger in VE than VL. Group 3: Defects larger in VL than VE. Group 4: No remarkable difference in defects in both techniques. Cases of group 1 were normal in pulmonary function test and chest X-ray. Finding of group 2 reflects early airway closure. This group consisted of cases in remission of bronchial asthma, small air way disease and pulmonary congestion. In group 3, restrictive disease and obstructive disease, especially emphysema, were included. Patients with severe obstructive disease and organized change of pulmonary parenchyma were belonged in group 4. In ventilation study with 81mKr gas, a combined study of inhalation technique through a dead space and by direct infusion may be useful to evaluate a pathophysiological change of various pulmonary diseases.     

Examination for quantitative evaluation of abnormality of regional pulmonary blood flow in patients with diffuse pulmonary diseases--an application of bull's eye analysis

Bull's eye analysis was applied to the 99mTc-MAA lung perfusion scintigraphy (planar or SPECT). Three kind of phantoms were used to examine spatial and density resolution. Filling defect of 3 cm in diameter was detected and 30% difference between one RI concentration and the other was also detected by this method. 99mTc-MAA lung perfusion scintigraphy was performed in 39, including 28 with diffuse pulmonary diseases and 11 normal subjects. Bull's eye image with its circumferential profile curve was compared visually with conventional planar or SPECT image. This method was superior or equal to conventional image in 78% (planar) and in 75% (SPECT). Especially in patients with interstitial pneumonia, 94% was superior or equal. The patient's Bull's eye map was compared with the lower limit of normal (mean-2SD), and the extent score (ES) and the severity score (SS) were calculated. The changes of ES and SS was useful to follow up the clinical course of the patients. This method would be effective to evaluate the regional pulmonary blood flow quantitatively.     

Segmental pulmonary anatomy in man: a method of study with angiography and single photon emission computed tomography

To study the appearance of the segmental pulmonary anatomy on single photon emission computed tomography (SPECT), 300 microCi of 99mTc-MAA was injected into one segmental pulmonary artery in patients who had elective cardiac catheterization for coronary artery disease and who had no pulmonary disease. Eighteen patients were enrolled in order to show the appearance of all pulmonary segments (10 in the right lung and 8 in the left lung). Planar and SPECT imaging were performed before and after peripheral intravenous injection of 3 mCi of 99mTc-MAA. Radioactivity in the segment was subtracted from that in the whole lung to show segmental perfusion defects on planar and SPECT whole lung images. Knowledge of the tomographic appearance of the pulmonary segments should make it easier to identify these segments on other imaging modalities that utilize sectional reconstruction, such as computed tomography and magnetic resonance imaging. This knowledge may also increase the specificity of pulmonary SPECT for the diagnosis of pulmonary emboli.     

Tomographic imaging in the diagnosis of pulmonary embolism: a comparison between V/Q lung scintigraphy in SPECT technique and multislice spiral CT.

Although ventilation/perfusion (V/Q) lung scintigraphy is a well-accepted and frequently performed procedure in the diagnosis of pulmonary embolism, there is growing controversy about its relevance, particularly due to the increasing competition between scintigraphy and CT. Even though comparative studies between both modalities have already been performed, their results were highly inconsistent. Remarkably, in most of those studies, conventional planar perfusion scans were compared with tomographic images acquired using state-of-the-art CT scanners-a study design that cannot give impartial results. Hence, the aim of our study was a balanced comparison between V/Q lung scintigraphy and CT angiography using advanced imaging techniques for both modalities. METHODS: A total of 83 patients with suspected pulmonary embolism were examined using V/Q lung scintigraphy in SPECT technique as well as 4-slice spiral CT. Ventilation scans were done using an ultrafine aerosol. Additionally, planar images in 8 views were extracted from the V/Q SPECT datasets. Two experienced referees assessed each of the 3 modalities. The final diagnosis was made at a consensus meeting while taking into account all of the imaging modalities, laboratory tests, clinical data, and evaluation of a follow-up period. RESULTS: In the course of the consensus conference, pulmonary embolism was diagnosed in 37 of the 83 patients (44.6%). Compared with planar scintigraphy, SPECT raised the number of detectable defects at the segmental level by 12.8% (+11 defects; P = 0.401) and at the subsegmental level by 82.6% (+57 defects; P < 0.01). The sensitivity/specificity/accuracy of planar V/Q scintigraphy and V/Q SPECT was 0.76/0.85/0.81 and 0.97/0.91/0.94, respectively, compared with 0.86/0.98/0.93 for multislice CT. CONCLUSION: SPECT and ultrafine aerosols are technical advancements that can substantially improve lung scintigraphy. Using advanced imaging techniques, V/Q scintigraphy and multislice spiral CT both yield an excellent and, in all aspects, comparable diagnostic accuracy, with CT leading in specificity while SPECT shows a superior sensitivity. Even though planar lung scintigraphy yields satisfactory results for a nontomographic modality, it does not compare with tomographic imaging.     

Ventilation-perfusion lung scan for the detection of pulmonary involvement in Takayasu's arteritis.

The aim of study was to analyse ventilation and perfusion (V/Q) lung scan findings in a series of Italian patients with Takayasu's arteritis. Eighteen consecutive patients underwent V/Q lung planar scintigraphy and single-photon emission tomography (SPET). Before perfusion scan acquisition was started, a first-pass study with (99m)Tc-macroaggregates of albumin was performed to assess the right ventricular ejection fraction (RVEF). All patients had normal chest X-rays and were symptom free at the time of the investigation. They also underwent echocardiography to evaluate pulmonary artery pressure and in 13 patients respiratory function tests were performed. In four patients, perfusion lung scan was repeated after 1 year. In 10/18 patients (55.5%), 43 unmatched lobar, segmental or subsegmental perfusion defects were found on planar images; ventilation scintigraphy was normal in all cases. On SPET images, 55 defects were found; no defects were found with SPET in the remaining patients who had normal planar images. All patients had normal RVEF and 5/13 patients had mild restrictive-obstructive lung disease. The pulmonary artery pressure was increased in two patients with perfusion defects. In the four patients who had repeat scintigraphy, all defects remained unchanged. The prevalence of lung perfusion abnormalities observed in Italian patients with Takayasu's arteritis is within the range of values reported in other countries, and V/Q planar scintigraphy is sufficient for the screening of patients.     

Correlation of pulmonary 99mTc-DTPA ventilation and 99mTc-MAA perfusion scans with pulmonary function tests in asymptomatic asthmatic children

Our objective was to examine and correlate 99mTc-diethylenetriaminopentaacetic acid (99mTc-DTPA) ventilation and 99mTc-macroaggregated albumin (99mTc-MAA) perfusion (V/Q) lung scans with spirometry in asymptomatic asthmatic children. We evaluated 89 subjects (age range, 6-15 years; mean age, 9.4 years), all with at least 70% predicted forced expiratory volume in 1 s (FEV(1)). There were four V/Q scan patterns: normal in 38 (42.7%), inhomogeneous ventilation in 11 (12.4%), matched defects in 25 (28.3%) and mismatched perfusion defects in 13 (14.6%). The maximal mid-expiratory flow rate (MMEF) of the normal scan group was significantly different from that in the other groups. The MMEF of the inhomogeneous group was significantly different from that in the matched defect group and the mismatched perfusion defect group. No other significant differences in spirometric indices were found. In two children with perfusion defects, pulmonary arteriograms demonstrated no obstructive lesions. In conclusion, lung scans provide diagnostic information in asymptomatic asthmatic children, even when they are uncooperative. Abnormal scans are common in these children and are significantly correlated with reduced MMEF (% predicted), reflecting small airway flow obstruction. The pathophysiology of V/Q defects in asymptomatic asthmatic children warrants further investigation.     

Ventilation-perfusion lung scan for the detection of pulmonary involvement in Takayasu's arteritis

The aim of study was to analyse ventilation and perfusion (V/Q) lung scan findings in a series of Italian patients with Takayasu's arteritis. Eighteen consecutive patients underwent V/Q lung planar scintigraphy and single-photon emission tomography (SPET). Before perfusion scan acquisition was started, a first-pass study with ^99mTc-macroaggregates of albumin was performed to assess the right ventricular ejection fraction (RVEF). All patients had normal chest X-rays and were symptom free at the time of the investigation. They also underwent echocardiography to evaluate pulmonary artery pressure and in 13 patients respiratory function tests were performed. In four patients, perfusion lung scan was repeated after 1 year. In 10/18 patients (55.5%), 43 unmatched lobar, segmental or subsegmental perfusion defects were found on planar images; ventilation scintigraphy was normal in all cases. On SPET images, 55 defects were found; no defects were found with SPET in the remaining patients who had normal planar images. All patients had normal RVEF and 5/13 patients had mild restrictive-obstructive lung disease. The pulmonary artery pressure was increased in two patients with perfusion defects. In the four patients who had repeat scintigraphy, all defects remained unchanged. The prevalence of lung perfusion abnormalities observed in Italian patients with Takayasu's arteritis is within the range of values reported in other countries, and V/Q planar scintigraphy is sufficient for the screening of patients.