Evaluation of pulmonary perfusion in lung regions showing isolated xenon-133 ventilation washout defects

Xenon-133 washout phase imaging is often used to help determine whether the etiology of a perfusion defect is embolic or due to pulmonary parenchymal pathology, such as chronic obstructive pulmonary disease. This study was designed to evaluate the pulmonary blood flow patterns associated with isolated defects on xenon washout images. Scintigraphic lung studies were reviewed until 100 cases with abnormal ventilation results were obtained. Ventilation abnormalities were compared with the corresponding perfusion scan results at the same anatomic site. Of the 208 individual lung regions with xenon abnormalities, 111 showed isolated washout defects (that is, with normal washin). Ninety-four of these 111 sites showed either normal perfusion or a small, nonsegmental corresponding perfusion defect. Three segmental perfusion defects were noted in association with isolated xenon retention. In each of these cases, however, the patient was felt actually to have pulmonary embolism. Thus, it is recommended that, for interpretation of scintigraphic images in the assessment of pulmonary embolism, lung pathology associated with isolated xenon retention not be considered a potential cause for large or segmental perfusion defects.     

An unusual ventilation perfusion scintigram in a case of immunologic pulmonary edema clinically simulating pulmonary embolism

A case of immunologic pulmonary edema secondary to hydrochlorothiazide allergy developed in a 55-year-old woman that clinically simulated pulmonary embolism. The patient had abnormal washin images with normal washout images on an Xe-133 ventilation study. On the perfusion study, large bilateral central and posterior perfusion defects were present that showed an unusual "mirror image" pattern on the lateral and posterior oblique views. Resolution of radiographic and scintigraphic abnormalities occurred over a 3-day period in conjunction with corticosteroid therapy.     

Ventilation imaging of the lung: Comparison of hyperpolarized helium-3 MR imaging with Xe-133 scintigraphy

RATIONALE AND OBJECTIVES: To compare hyperpolarized helium-3 (HHe) magnetic resonance imaging (MRI) of the lung with standard Xe-133 lung ventilation scintigraphy. MATERIALS AND METHODS: We performed a retrospective review of 15 subjects who underwent HHe MRI and Xe-133 lung ventilation imaging. Coronal MRI sections were acquired after a single inhalation of HHe gas, and standard posterior planar lung ventilation scintigraphy was performed during continuous breathing of Xe-133 gas. The first breath scintigram of each patient was compared with a composite MR image composed of the sum of the individual MR images and with the individual helium-3 MR images. Ventilation defects on the two imaging modalities were compared for size, conspicuity, and concordance in presence and location. Assessment was done separately for each of four lung quadrants. RESULTS: Comparing the composite HHe MR images with Xe-133 scintigraphy, ventilation defect size, conspicuity and concordance were the same in 67% (40/60), 63% (38/60), and 62% (37/60) quadrants, respectively. Comparing the individual HHe MR image sections with the Xe-133 ventilation scan, there was concordance between the ventilation defects in 27% (16/60) of quadrants. More defects were identified on the individual HHe MR images in 62% (37/60) of quadrants. CONCLUSION: There was good agreement between composite HHe MR image and first breath Xe-133 scintigraphic images, supporting the widely held assumption that HHe MRI likely depicts first breath lung ventilation.     

Bilateral basal Xe-133 retention and ventilation/perfusion patterns in mild and subclinical congestive heart failure

The Xe-133 ventilation pattern in congestive heart failure (CHF) was assessed using 24 inpatient ventilation/perfusion studies performed to rule out pulmonary embolism. Patients with histories of CHF, myocardial infarction (MI), and cardiomyopathy were included in the study. Frank pulmonary edema, pulmonary embolism, and other known lung diseases such as chronic obstructive lung disease, tumor, and pneumonia were excluded. Fifteen of the 24 patients had abnormal ventilation scans. Twelve of the 15 showed bilateral basal Xe-133 retention on washout; the remaining 3 showed diffuse, posterior regional retention. On perfusion scans, 14 of the 15 abnormal ventilation patients showed evidence of CHF such as inverted perfusion gradient, enlarged cardiac silhouette, or patchy perfusion, and all of them had a history of CHF or cardiac disease. Nine of the 24 patients had normal ventilation scans, including normal washout patterns. Seven of the nine had normal perfusion (p less than 0.01). Four of the nine normal ventilation patients had a history of cardiac disease or CHF but no recent acute MI. Bilateral basal regional Xe-133 retention, coupled with perfusion scan evidence of CHF such as inverted perfusion gradient, enlarged cardiac silhouette, and patchy perfusion pattern, appears to be a sensitive and characteristic ventilation/perfusion finding in mild or subclinical CHF.     

Ventilation-perfusion scintigram in diabetics

We carried out ventilation and perfusion scintigraphies and pulmonary function tests in 20 diabetics under 50 years of age. 99mTc-MAA perfusion scintigrams showed evidence of minimal nonuniformity (MNU) in four cases (20%) and nonsegmental defect (NSD) in eight cases (40%). There was a ventilation defect in the single-breath image in one case (5%) and a delayed washout in three cases (15%) upon 133Xe ventilation scintigram. In the NSD group, the mean diffusing capacity value was abnormally low and the mean duration of the diabetes was long compared with other groups. The frequency of perfusion defects was higher than that of ventilation abnormalities; moreover, abnormal findings on ventilation scintigrams were very mild compared with those of perfusion defects. Perfusion defects correlated significantly with a decrease in diffusing capacity. These findings suggest that the disturbance in pulmonary arterial perfusion caused a decrease in diffusing capacity in diabetics.     

Regional comparison of technetium-99m DTPA aerosol and radioactive gas ventilation (xenon and krypton) studies in patients with suspected pulmonary embolism

The regional distribution of [99mTc]DTPA aerosol was compared with that of 133Xe (n = 30) and krypton (n = 24) in a group of patients with suspected pulmonary embolism. All patients had an aerosol study using a recently available commercial generator system, a ventilation study with one of the gases, and perfusion imaging. Regional information was assessed visually on xenon, krypton, and aerosol studies independently by considering each lung as three equal-sized zones. In addition, gas ventilation findings peripheral to regions of aerosol turbulence ("hot spots") were evaluated. Only 64% of the zones were in complete agreement on xenon and aerosol. Most of the discordance between xenon and aerosol was accounted for by minor degrees of 133Xe washout retention in zones that appeared normal in the aerosol study. An agreement rate of 85% was noted between 81mKr and aerosol regionally. The regions of discordance between aerosol and gas studies, however, usually were associated with unimpressive perfusion defects that did not change the scintigraphic probability for pulmonary embolism in any patient. Regarding zones of aerosol hyperdeposition, 76% had associated washout abnormalities on xenon; however, there was no correlation between the presence of these abnormalities or perfusion abnormalities. The results confirm the high sensitivity of 133Xe washout imaging, but suggest that radioaerosol imaging will detect most parenchymal abnormalities associated with perfusion defects of significance.     

Usefulness of ventilation and perfusion scans in patients with collagen-vascular diseases

We studied 32 patients with collagen-vascular diseases with Xe-133 ventilation scans (V) and Tc-99m MAA perfusion scans (Q). Five patients underwent sequential studies at intervals of more than 3 months. Mean transit time (MTT) was calculated from the Xe-133 wash-out curve. V, Q images and MTT were compared with chest X-ray films and the values of %DLco. Of 32 patients, 17 had no abnormal finding on the chest X-ray films. Of the 17 patients, however, V and/or Q abnormalities were found in 10 (59%), 14 patients (82%), respectively. Every patient with abnormal findings on the chest X-ray film showed both V and Q abnormalities. Overall, Q abnormality was more frequent and severer than V one. Of the 5 patients with the sequential studies, 3 showed prolongation of MTT in concordance with deterioration of pulmonary fibrosis. V and Q abnormalities were not necessarily relevant to %DLco. In conclusion, ventilation and perfusion studies are useful in assessing the regional pulmonary function in patients with collagen-vascular diseases.     

Ventilation-perfusion scan in the acutely ill patient with unilateral hyperlucent lung

A patient with a unilateral hyperlucent lung with acute respiratory complaints is presented. A ventilation-perfusion scan was performed to rule out pulmonary embolism. The perfusion scan ( [99mTC]MAA) showed peripheral perfusion defects in the hyperlucent lung. The ventilation study (133Xe) demonstrated peripheral ventilatory defects on the single breath image in the hyperlucent lung, the filling in of these on the equilibrium view, and diffusely delayed washout in the affected lung. These findings were suggestive of the Swyer-James syndrome and critical in excluding the numerous other causes of unilateral hyperlucent lung, which are discussed. The importance of the ventilation-perfusion study (and particularly the ventilation scan) in the patient with unilateral hyperlucent lung and acute respiratory symptoms is stressed. In addition, a discussion of the Swyer-James syndrome is included.     

Fibrosing Mediastiniti<Emphasis Type="Bold">s</Emphasis>: a Rare Cause of Unilateral Absent Lung Perfusion on a V/Q Scan

We report a case of a 29-year-old female with a history of asthma, post-partum ARDS, and pulmonary hypertension who presents with severe shortness of breath. The patient describes her shortness of breath as progressive over the past 10 years. Chest radiography and CT angiography of the thorax showed findings consistent with fibrosing mediastinitis with severe stenosis of the left main pulmonary artery. This resulted in appearance of unilateral absent left lung perfusion on quantitative Tc-99-MAA perfusion and Xe-133 ventilation (V/Q) scan.     

Ventilation imaging with Kr-81m

Sixty-five patients with suspected pulmonary embolism were studied prospectively with both Kr-81 m and Xe-133 ventilation imaging and Tc-99m MAA perfusion imaging. The krypton images, perfusion scintigrams and chest radiographs were read independently of the xenon images, perfusion scintigrams and chest radiographs by three observers. The studies of 53 patients were interpreted as normal or as indicative of a low or intermediate probability for pulmonary embolism with both gases. One study indicated intermediate probability with Xe-133 due to diffuse, severe xenon retention but low probability with Kr-81 m because of close ventilation-perfusion correspondence. The studies of 9 patients indicated a high probability of embolism with both gases, while those of two additional patients (one with emboli at angiography) indicated a high probability only with Kr-81m. While essential agreement between Xe-133 and Kr-81m ventilation imaging was found in most patients, the significant difference in interpretation in 2 of 11 patients with probable pulmonary embolism suggests that a controlled, prospective trial with pulmonary angiography is warranted before Kr-81m is employed for routine clinical use.     

Tc-99m-DTPA aerosol and radioactive gases compared as adjuncts to perfusion scintigraphy in patients with suspected pulmonary embolism

To evaluate the clinical utility of improved methods for radioaerosol inhalation imaging, we obtained preperfusion radioaerosol images in 107 patients (mean age = 62 years), who were referred for evaluation of suspected pulmonary embolism (PE). For each patient, we compared six-view aerosol images with accompanying perfusion scans and chest radiographs and with Xenon-133 (Xe-133) or Krypton-81m (Kr-81m) studies. Four observers at four different institutions independently evaluated aerosol-perfusion and gas-perfusion pairs, classifying the probability of PE as low, high, or indeterminate. The radioaerosol images were good to excellent in quality; excessive central deposition of activity was infrequent and did not interfere with image interpretation. The aerosol-perfusion studies showed 86% agreement with Xe-133 perfusion interpretations (n = 299) and 80% agreement with Kr-81m perfusion interpretations (n = 99). These rates of agreement were comparable with those of intraobserver agreement for gas-to-gas and aerosol-to-aerosol comparisons, and higher than interobserver agreement rates. In a limited number (n = 9) of angiographically documented cases, aerosol-perfusion and gas-perfusion studies provided accurate and equivalent diagnoses. The results suggest that radioaerosol inhalation studies, performed with improved nebulizers, are diagnostically equivalent to ventilation imaging as an adjunct to perfusion scintigraphy in evaluating patients with suspected PE.     

Lateral-view ventilation images with 133Xe.

For better delineation of regional ventilation abnormalities, a lateral-view imaging has been employed when one or more areas of abnormal retention were visible in posterior views of 133Xe washout images. It is technically simple to obtain lateral views during the 133Xe washout phase. The resulting images were found to be very useful in detecting regions of ventilation-perfusion mismatch and in evaluating regional obstructive lung disease.     

Pulmonary ventilation/perfusion and reverse mismatches in an infant

A male infant, with bronchopulmonary dysplasia and ventilator dependence, had lung ventilation (Xe-133 gas) and perfusion (Tc-99m MAA) imaging performed. The examination revealed a region that was ventilated but not perfused (mismatch) and a separate area that was perfused but not ventilated (reverse mismatch). The basis of both abnormalities is suspected to be related to bronchopulmonary dysplasia, atelectasis and/or mechanical ventilation. Ventilation/perfusion mismatches and reverse mismatches can occur in the same patient.     

Sensitivity of Kr-81m and Xe-127 in evaluating nonembolic pulmonary disease

The relative sensitivities of Kr-81m and Xe-127 in detecting lung ventilation defects was evaluated in 80 patients with nonembolic pulmonary diseases. Krypton-81m ventilation images (500,000 count) were interdigitated with Tc-99m MAA perfusion images; both were compared with Xe-127 images. The distributions of the two gases were also compared on the basis of point-by-point computer analyses. Xenon-127 was found to be more sensitive than Kr-81m in clinical evaluations of scintiphotos--although they were equivalent by computer analyses--in indicating regions of impaired ventilation in patients with obstructive airways disease.     

Postperfusion xenon-133 ventilation scintigraphy with a narrow window

Xenon-133 postperfusion lung scintigraphy using 10% windows was compared with standard posterior preperfusion 133Xe ventilation scanning in 33 patients. The postperfusion 133Xe study identified all major defects and washout abnormalities. In five patients, the assessment of match or mismatch of defects was improved because of optimal positioning of the postperfusion ventilation study. Computer subtraction of background technetium-99m macroaggregated albumin activity improved detection of mild washout abnormalities in eight patients but did not change the diagnostic category in any case. Postperfusion ventilation scanning using 10% windows (with or without background computer subtraction) is an alternative to preperfusion ventilation scanning for major V/Q abnormalities.     

Lung ventilation scanning with a new carbon particle radioaerosol (Technegas). Preliminary patient studies

A new Tc-99m labeled carbon particle aerosol ("Technegas") has been developed for lung ventilation scanning. This is the first reported clinical study of this agent in the United States. A total of 23 subjects were studied. Thirteen had comparative Xe-133 studies, and in seven patients pulmonary angiograms were available. The Technegas study agreed closely with the Xe-133 results in 10 out of 13 patients, while the pulmonary angiogram confirmed the Technegas and perfusion scan findings in seven out of seven cases. The Technegas scan was easily performed and well tolerated by all patients. If further clinical trials confirm these preliminary findings, Technegas may become the preferred agent for lung ventilation scanning.     

Regional lung perfusion and ventilation with radioisotopes in cervical cord-injured patients

In general, cervical cord-injured patients present with restrictive pulmonary dysfunction resulting from paralysis of the intercostal muscles. Vital capacity frequently decreases below 50% of that in normal subjects, and their respiratory pattern frequently includes paradoxical movement in which the intercostal spaces sink and the abdomen distends at inspiration. Ventilation scintigraphy using Xe-133 and pulmonary perfusion scintigraphy using Tc-99m macroaggregated albumin (MAA) were performed on nine cervical cord-injured patients and four normal subjects to investigate regional lung functions in the cervical cord-injured patients. Pulmonary perfusion scintigraphy, in which measurement was made in the supine position, revealed no differences between the patients and the normal subjects. The inhomogeneous ventilation/perfusion distribution was presumed to have resulted from change in regional intrapleural pressure due to paradoxical movement of the thoracic cage. Washing and washout times were prolonged by paralysis of the intercostal muscles. These phenomena were particularly apparent in the upper and middle lung regions where compensating action by movement of the diaphragm is small.     

Compression of the Right Pulmonary Artery by a Massive Descending Aortic Aneurysm Causing Bilateral Perfusion Defects on Pulmonary Scintigraphy

A 67-year-old woman, who presented with a 2 month history of dyspnea, had a ventilation and perfusion lung scan that showed absent perfusion of the entire right lung with normal ventilation, as well as a rounded matched defect in the left lower lung adjacent to midline, suspicious for an aortic aneurysm or dissection. CT pulmonary angiography revealed a massive descending aortic aneurysm compressing the right pulmonary artery as well as the left lung parenchyma, accounting for the bilateral perfusion scan defects. We present the Xe-133 ventilation, Tc-99m MAA perfusion and CT pulmonary angiography imaging findings of this rare case.     

Computer processing of perfusion,ventilation, and V/Q images to highlight pulmonary embolism

A method is described for generating regional ventilation/perfusion (V/Q) images of the lung to aid assessment of suspected pulmonary embolism, especially in patients with obstructive airways disease. The radionuclide scans used for this are stored on a computer and comprise: lung perfusion (P) with Tc-99 m MAA, lung ventilation at equilibrium (E) with Xe-127, and the sum of the Xe-127 washout images (W). A functional ventilation image is calculated as V=E/W and a functional perfusion image as Q=P/E. Finally a ventilation perfusion ratio image is obtained by taking V/Q. This is normalised by a factor determined from the cumulative frequency distributions of the counts per pixel in the Q and V images so that areas which are well ventilated and perfused are given a V/Q value of 1.0.Areas with normalised V/Q values>1.5 suggest pulmonary embolism. In 100 studies on patients with abnormal perfusion scans this method proved very helpful by assisting the recognition or exclusion of areas with abnormally high V/Q values.     

Indeterminate lung imaging. Can the number be reduced?

During a 2 1/2-year period, 1131 patients with suspected pulmonary embolism had ventilation-perfusion lung scans; 150 of these patients also underwent pulmonary angiography. In a retrospective study, these 150 patients were re-evaluated using the reference criteria of Biello and Alderson, with 62% read as indeterminate. Twenty patients who had chronic obstructive pulmonary disease with retention of Xe-133 in greater than 50% of the lung fields without corresponding radiographic abnormality were included. Ventilation/perfusion matches and mismatches could be correctly determined in 15 of these patients. These 15 of 20 studies could be correctly reclassified as low-probability, while the other five remained indeterminate. With increasing intervals between ventilation/perfusion lung imaging and the onset of symptoms, the percentage of patients with proven pulmonary emboli correctly diagnosed as high probability continuously decreased, and the percentage of studies read as indeterminate constantly increased. Serial chest radiographs suggested that the development of infiltrates in the region of the embolus convert high-probability ventilation/perfusion scans to indeterminate.