Very low probability interpretation of V/Q lung scans in combination with low probability objective clinical assessment reliably excludes pulmonary embolism: data from PIOPED II.

Use of a very low probability interpretation of ventilation/perfusion (V/Q) lung scans, if verified by prospective evaluation to have a low positive predictive value (PPV), will reduce the number of nondiagnostic interpretations of V/Q scans and may be particularly useful in patients with a relative contraindication to CT. The purpose of this investigation was to test the hypothesis that a very low probability interpretation of the V/Q scan has a PPV of <10%. METHODS: Data are from PIOPED II (Prospective Investigation of Pulmonary Embolism Diagnosis II). Very low probability criteria are (a) nonsegmental perfusion abnormalities, (b) perfusion defect smaller than corresponding radiographic lesion, (c) > or =2 matched V/Q defects with regionally normal chest radiograph, (d) 1-3 small segmental perfusion defects (<25% of a segment), (e) solitary triple matched defect in middle or upper lung zones, (f) stripe sign around the perfusion defect(s), and (g) perfusion defect from pleural effusion equal to one third or more of the pleural cavity with no other perfusion defect. RESULTS: A very low probability consensus interpretation of the V/Q scan was made in 56% of patients. The PPV of a very low probability interpretation of the V/Q scans was 36 of 440 patients (8.2%). Among patients with suspected pulmonary embolism who had a low clinical probability objective clinical assessment and a very low probability V/Q scan, the PPV was 8 of 259 patients (3.1%). Among women < or =40 y, the PPV of the very low probability V/Q with a low objective clinical assessment was 1 of 50 (2%). CONCLUSION: The very low probability V/Q scan together with a low probability clinical assessment reliably excludes pulmonary embolism.     

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.     

核素肺通气/灌注显像在肺动脉血栓栓塞症中的应用

目的 应用肺通气／灌注（V／Q）显像研究下肢深静脉血栓（DVT）患者肺栓塞（PE）发病情况，并与CT血管造影（CTA）或MR血管造影（MRA）结果进行比较。方法 85例DVT患者进行肺通气（Technegas）／^99Tc^m-聚合白蛋白（MAA）灌注显像和X线胸片检查，其中13例同期进行肺CTA或MRA检查。根据PIOPED诊断标准（1995年修正版），综合分析肺V／Q显像和X线胸片结果，划分为PE高、中、低、极低度可能性和正常5类，并以低、中和高度PE可能性者为阳性，极低可能性和正常者为阴性。结果 85例患者中，PE高度可能性34.1％，中度可能性8．2％，低度可能性7．1％，极低度可能性1．2％，正常49．4％，共计阳性率49．4％，阴性率50．6％。13例同期进行CTA或MRA检查的患者中，3例V／Q显像和CTA或MRA发现病灶数量和范围一致，10例不一致。肺动脉部分栓塞时，由于血流可通过，肺组织灌注可能正常，V／Q显像往往不能发现病变血管。而外周肺段、亚分段较小肺动脉栓塞时，CTA或MRA容易漏诊。结论 V／Q显像可以提供优良、准确的PE诊断结果，CTA检查与其可优势互补。     

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.     

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.     

Lung perfusion in patients with pulmonary hypertension: comparison between MDCT pulmonary angiography with minIP reconstructions and 99mTc-MAA perfusion scan

OBJECTIVES: Alterations in lung perfusion are a well-known feature of pulmonary hypertension (PH) seen on nuclear medicine studies. Abnormal radiotracer distribution in patients with PH may be caused by arterial thromboembolic occlusion, like in chronic thromboembolic pulmonary hypertension, by parenchymal destruction as in interstitial lung disease and pulmonary emphysema or by distal arteriopathy, like in idiopathic pulmonary arterial hypertension and other nonembolic forms. The different imaging pattern on radionuclide perfusion studies represents an important element for differential diagnosis. The aim of this study was to evaluate minimum intensity projection (minIP) images as an alternative to perfusion scintigraphy. We compared lung parenchyma attenuation patterns as depicted in minIP reconstructions with scintigraphic findings of lung perfusion in patients affected by pulmonary hypertension from various etiologies. METHODS: One hundred and seven consecutive patients affected by PH of different etiology (37 of those had chronic thromboembolic pulmonary hypertension) who had undergone both multidetector computed tomography pulmonary angiography and 99mTc-MAA perfusion scan were included. Five-millimeter thickness contiguous axial, coronal, and sagittal minIP images were reconstructed from the contrast enhanced computed tomography datasets. Two radiologists evaluated the images and qualitatively graded pulmonary attenuation as homogeneous, inhomogeneous with nonsegmental patchy defects, or inhomogeneous with segmental defects. The presence of parenchymal and pleural alterations was recorded. MinIP perfusion grading results were then compared with those of perfusion scintigraphy. RESULTS: In 87 of 107 patients (81.3%), the attenuation pattern seen on minIP images (39 homogeneous patterns, 13 with nonsegmental patchy defects, and 39 with segmental defects) correlated with the nuclear medicine scans. In the remaining 20 patients (18.7%), the imaging pattern was discordant because of 7 false-positive and 2 false-negative thromboembolic patterns at minIP and 11 false-positive thromboembolic patterns at perfusion scan. Air-trapping and parenchymal disease caused false-positive findings at minIP and perfusion scans, respectively. The sensitivity and specificity of minIP in detection of a chronic thromboembolic perfusion pattern were 94.5% and 90%, whereas perfusion scan had 100% sensitivity and 84% specificity. CONCLUSION: MinIP reconstructions can identify different patterns of pulmonary parenchymal attenuation, which show high concordance with perfusion patterns seen on radionuclide studies in patients with pulmonary hypertension. MinIP is a promising technique to evaluate lung perfusion in PH and may be used as an alternative to scintigraphy in the diagnostic work-up of these patients.     

Clearance of Tc-99m DTPA aerosol in mismatched and matched pulmonary perfusion defects

PURPOSE: To evaluate clearance changes of Tc-99m DTPA aerosol in mismatched and matched pulmonary perfusion defects. MATERIALS AND METHODS: Twenty-one patients (14 women, 7 men; mean age, 51 +/- 14 years) with possible pulmonary embolism were included in the study. On the day after perfusion (Q) scintigraphy with 5 mCi Tc-99m MAA, radioaerosol inhalation scintigraphy was performed using 45 mCi Tc-99m DTPA. Immediately and 45 minutes after the inhalation, early and delayed inhalation images (EI and DI, respectively) were obtained. Group 1 included 11 patients with mismatched defects who had a high probability of pulmonary embolism according to the Q/EI scan results. Group 2 included 10 patients with matched defects who had a low probability of PE. Contralateral normal lungs of 7 patients in group 2 served as controls (group 3). In groups 1 and 2, regions of interest were drawn over the mismatched and matched perfusion defects where they were best visualized, and this region of interest was mirrored to the same region on EI and DI images. For the control group, this was done in the contralateral normal lung. Mean counts in each region of interest were used for quantitative analysis, and the percentage clearance ratio was calculated using the following formula: early counts - late counts/early counts x 100. RESULTS: The average percentage clearances for the three groups were as follows: group 1, 37% +/- 10%; group 2, 21% +/- 4%; group 3, 24% +/- 7%. Differences between groups 1 and 3 were significant, as were those between groups 1 and 2 (P < 0.05). Patients with mismatched perfusion defects had increased DTPA clearance compared with the control group and those with matched defects. CONCLUSIONS: Vascular occlusion may lead to impairment of the alveolar-capillary barrier and consequently an increase in the clearance of Tc-99m DTPA aerosol in embolized regions. Immediately after inhalation, Tc-99m DTPA imaging should be started in the projection where perfusion defects are best seen to avoid potential misinterpretation of pulmonary embolism.     

Distribution of ventilation/perfusion ratios in pulmonary embolism: an adjunct to the interpretation of ventilation/perfusion lung scans.

Diagnosis of pulmonary embolism (PE) by visual interpretation of ventilation/perfusion (V/Q) scans is limited by the high percentages of patients classified in the intermediate- and low-probability categories. This study proposes a quantitative analysis of the distribution of V/Q ratios to better identify patients with PE. METHODS: We studied 99 consecutive patients who underwent dual-isotope (81m)Kr/(99m)Tc-macroaggregate V/Q scanning and arterial blood gas analysis within 48 h. The 8-view V/Q scans were visually analyzed by 2 observers according to the revised criteria of the Prospective Investigation of Pulmonary Embolism Diagnosis (PIOPED) (normal scan or low, intermediate, or high probability of PE). Quantitative analysis of the posterior-view distribution histogram of V/Q ratios was performed using dedicated software. Briefly, regions of interest were drawn around the lungs on the matched V/Q images, smooth filtering was applied, normalized regional V/Q ratios were calculated within each pixel, and a distribution histogram was built. RESULTS: Patients with normal scans (n = 16) had a predominance of V/Q ratios (63.3% +/- 13.0%) between 0.8 and 1.2. They had only 9.8% +/- 5.8% of ratios > 1.2, and the remaining 26.9% +/- 7.5% of ratios were <0.8. By contrast, patients with PE (n = 34) were characterized by a significant increase (15.5 +/- 10.0%, P = 0.04) in high V/Q ratios (>1.2) and a significant increase (34.5% +/- 8.2%, P = 0.003) in low V/Q ratios (<0.8). Interestingly, a similar pattern was found in patients with a high PIOPED probability of PE, 21.3% +/- 11.0% and 37.5% +/- 9.2%, respectively. Within the nondiagnostic group (intermediate- + low-probability scans, n = 58), 17 patients were finally diagnosed with PE. Analysis of the distribution histogram in this group allowed the identification of 5 patients with PE (specificity, 78%). CONCLUSION: A quantitative approach to lung scan interpretation, based on the distribution histogram of V/Q ratios, may be helpful for categorizing patients with suspected PE.     

Assessment of ventilation-perfusion scans in patients with chronic thromboembolic pulmonary hypertension before and after surgery and correlation with clinical parameters

PurposeWe did a comparative analysis of matched and mismatched defects in pre- and post-operative V/Q scans in CTEPH patients. We correlated the number of these defects with pre-operative clinical and hemodynamic parameters.MethodsThis was a retrospective study on 27 patients with CTEPH who underwent surgery. Pre- and post-operative V/Q scans were graded for each lung segment as normal, matched or mismatched defect. Additional pre- and post-operative clinical and hemodynamic parameters that were collected include New York Heart Association functional class, six-minute walk distance in feet, N-terminal pro b-type natriuretic peptide, forced expiratory volume in one second/forced vital capacity, diffusing capacity of the lung for carbon monoxide, pulmonary arterial pressure (systolic, diastolic and mean), right atrial pressure, cardiac output and cardiac index. Pulmonary vascular resistance was then calculated.ResultsOn a segmental basis, 176 mismatched defects were noted in 27 patients, of which 111 improved post-surgery (63%). 22 of the 34 matched defects improved following surgery (64%). 31 new mismatched defects were observed. The number of pre-operative matched defects per patient ranged from 0 to 6. No statistically significant associations were observed between the number of pre-operative matched defects and pre-operative clinical parameters. No statistically significant associations were observed between the number of improved matched defects and the change in clinical parameters (pre- to post-surgery).ConclusionBoth matched and mismatched defects on preoperative V/Q scans can show normalization post-surgery. The extent of matched defects on a preoperative V/Q scan does not correlate significantly with other clinical and hemodynamic parameters.     

Pulmonary embolism: comprehensive evaluation with MR ventilation and perfusion scanning with hyperpolarized helium-3, arterial spin tagging, and contrast-enhanced MRA

PURPOSE: Development of a comprehensive magnetic resonance (MR) examination consisting of MR angiography (MRA) and MR ventilation and perfusion (MR V/Q) scan for the detection of pulmonary emboli (PE) and assessment of the technique in a rabbit model. MATERIALS AND METHODS: Reversible PE was induced by inflating a non-detachable silicon balloon in the left pulmonary artery of five New Zealand White rabbits. MR V/Q scans were obtained prior to, during, and after balloon deflation. MRA was performed during balloon inflation. MR ventilation imaging was performed after the inhalation of hyperpolarized helium-3. MR perfusion imaging was performed with Flow-sensitive Alternating Inversion Recovery with an Extra Radiofrequency pulse technique (FAIRER). High-resolution contrast-enhanced MR pulmonary angiography was used to confirm the occlusion of the pulmonary artery. All imaging was performed on a 1.5-T whole body scanner with broadband capabilities. RESULTS: High-resolution ventilation images of the lungs were obtained. No ventilation defects were detected before, during, or after resolution of simulated PE. FAIRER imaging allowed visualization of pulmonary perfusion. No perfusion defects were detected prior to balloon inflation. During balloon inflation (PE), there was decreased perfusion in the left lower lobe. After reversal of the PE, there was improved perfusion to the left lower lobe. In analogy to nuclear medicine techniques, acute PE produced a mismatched defect in the MR V/Q scan. MRA verified the occlusive filling defect in the left pulmonary artery. CONCLUSION: High-resolution MRA and MR V/Q imaging of the lung is feasible and allows comprehensive assessment of pulmonary embolism in one imaging session.     

81mKr ventilation and 99mTc perfusion scans in chest disease: comparison with standard radiographs.

In 75 patients with various pulmonary disorders, ventilation and perfusion scans were obtained in multiple views with the 81mKr/99mTc technique and compared with an evaluation of regional ventilation and perfusion derived from the standard chest radiograph. In emphysema, the chest film correlated poorly with ventilation-perfusion scans, showing a trend to underestimate the functional impairment. In chronic bronchitis and asthma, large segmental defects observed on both ventilation and perfusion scans were associated with a normal chest radiograph. Typical findings in pulmonary embolism were segmental defects on perfusion scan with normal ventilation scan and clear lung fields on the chest film. In chronic left heart disease, plain films were inaccurate in predicting alteration of the base-to-apex perfusion gradient observed on the scan.     

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.     

False-positive ventilation-perfusion scan in a patient with a transplanted lung

A false-positive ventilation perfusion (V/Q) scan in a patient with a transplanted lung and secondary pulmonary artery stenosis is reported. The patient was examined for tachypnea and shortness of breath after single lung transplantation. A V/Q scan revealed multiple perfusion defects in the transplanted lung, with no corresponding ventilation defects. A pulmonary angiogram revealed pulmonary artery stenosis and no pulmonary emboli. The authors describe a false-positive V/Q scan in a patient after lung transplantation.     

Lung scintigraphy in the diagnosis and follow-up of pulmonary thromboembolism in children with nephrotic syndrome

Thromboembolic phenomenon and pulmonary embolism is quite frequent in children with nephrotic syndrome (NS). The incidence of pulmonary thromboembolism in children with NS is as common as in adults, and severity is also reported to be relatively high. The mortality rate in NS with thromboembolic complications may be significantly increased if not diagnosed and treated well in time. For establishing the diagnosis of pulmonary embolism, although the combined use of magnetic resonance venography and CT angiography has been proposed, V/Q scan is still the best modality. We performed serial lung perfusion scans in two young patients with NS who developed sudden onset tachypnea during their stay in the hospital. Initial lung perfusion scans showing marked perfusion defects and normal chest X-rays indicated a high probability for pulmonary embolism. The patients were treated with streptokinase, and the study was repeated. Marked improvement was seen in lung perfusion, thereby highlighting the importance of lung perfusion scan in the follow-up of such patients.     

Utility of ventilation and perfusion scan in the diagnosis of young military recruits with an incidental finding of hyperlucent lung

Swyer-James-MacLeod syndrome (SJMS) is considered to be a relatively uncommon disease presenting with unilateral hyperlucent lung due to hypoplasia of a pulmonary artery and bronchiectasis of the affected lung. In this report, we describe the ventilation-perfusion (V/Q) scan findings of nine male recruits (aged 20-29 years, mean 24.4+/-2.96 years) with SJMS in whom the diagnosis was first established in adulthood. V/Q scan findings of all patients were compared with those on planar radiographs, pulmonary function studies, high resolution computed tomography (HRCT) and digital subtraction angiography (DSA). The ventilation (133Xe) and perfusion (99Tcm-macro-aggregated albumin) scans showed the characteristic pattern of a matched V/Q defect and marked air trapping on the washout phase on 133Xe scintigraphy. HRCT displayed hypodense lung with integrity of main airways, and markedly diminished vasculature on the affected side in all patients. A smaller pulmonary artery on the affected side with poor peripheral vasculature was observed with DSA in all patients. All patients had features of obstructive airway disease in varying degrees on pulmonary function studies. In contrast to other imaging methods, bronchiectasis as an etiological factor was displayed on HRCT. Some pulmonary areas, which were normal on HRCT and planar radiographs, showed air trapping on V/Q scan. Although a V/Q scan was more helpful in determining the extent of the disease and correlates well with conventional imaging methods, HRCT was the most valuable imaging method for the evaluation of aetiology in unilateral hyperlucent lung.     

99mTc-DTPA aerosol for same-day post-perfusion ventilation imaging: Results of a multicentre study

A multicentre study was performed in an attempt to evaluate a submicronic technetium-99m diethylene triamine penta-acetic acid aerosol generated by a newly developed delivery system, the aerosol production equipment (APE nebulizer), for same-day post-perfusion ventilation imaging in patients with clinically suspected pulmonary embolism. Quantitative comparison between the DTPA aerosol and krypton gas demonstrated a close correlation with respect to regional pulmonary distribution of activity and peripheral lung penetration (n=14,r=0.94,P<0.001 andr=0.75,P<0.0025, respectively). In 169 consecutive patients, DTPA aerosol images performed immediately following perfusion (inhalation scan I) were compared to those carried out on the next day (inhalation scan 11) with respect to image quality and assessment of perfusion-ventilation matches or mismatches. Agreement between inhalation scans I and II with respect to perfusion defects matched or mismatched to ventilation was found in 166/169 (98%) studies. The image quality of inhalation scan I was equal to that of scan II in 72%; inhalation scan I was superior in 11% of cases, while scan 11 was superior in 17%. This submicronic^99mTc-labelled DTPA aerosol is well suited for fast same-day post-perfusion ventilation imaging in patients with clinical suspicion of pulmonary embolism.     

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.     

Ventilation-perfusion scintigraphy in suspected pulmonary embolism: correlation with pulmonary angiography and refinement of criteria for interpretation

Retrospective analysis of 139 ventilation-perfusion (V/Q) lung scans obtained for suspected pulmonary embolism (PE) was undertaken, using the Biello criteria for interpretation. All scans were correlated with chest radiographs obtained within 24 hours and with pulmonary angiograms obtained within 72 hours of the V/Q study. The prevalence of PE in the high-, intermediate-, and low-probability groups was 89.5%, 49.3%, and 3.6%, respectively. Using minor modifications of these criteria, V/Q scans interpreted as high or low probability had a sensitivity of 97.1%, specificity of 94.3%, and accuracy of 95.7%. Perfusion defects corresponding to radiographic abnormalities that were present for at least 10 days were less likely to be associated with PE. Separate analysis of 27 perfusion-only lung scans that met all other criteria for inclusion in the study confirmed the nonspecificity of perfusion-only lung imaging and indicated the need for ventilation imaging with Tc-99m-DTPA aerosol or Kr-81m gas for portable studies.     

Value of oxygen-enhanced MRI of the lungs in patients with pulmonary hypertension: a qualitative and quantitative approach

Purpose:

To assess the clinical value of oxygen‐enhanced magnetic resonance imaging (oeMRI) in patients with pulmonary hypertension (PH) by correlation with ventilation/perfusion (V/Q) scintigraphy.

Materials and Methods:

In all, 33 patients with known PH underwent V/Q scintigraphy and oeMRI. oeMRI was used to assess the regional pulmonary function based on relative‐signal‐enhancement (RSE) and cross‐correlation‐coefficient (CCC) maps, evaluating mean RSE (mRSE), fraction of oxygen‐activated pixels (fOAP), and mean CCC (mCCC). Two reviewers, blinded to the results of scintigraphy, performed visual detection of diseased lung areas.

Results:

In 26 of the 33 patients (79%) the image quality of oeMRI reached a diagnostic level. In total, 150 lung areas were analyzed and compared. Sensitivities/specificities of oeMRI for detecting these defects were: RSE vs. ventilation scintigraphy 92%/73%; RSE vs. perfusion scintigraphy 60%/87%; CCC vs. ventilation scintigraphy 89%/81%; CCC vs. perfusion scintigraphy 50%/87%. The number of diseased lung areas in oeMRI correlated significantly with the number in V/Q scintigraphy (P < 0.01). mRSE showed a significant correlation with the number of diseased lung areas in ventilation scintigraphy (P < 0.05).

Conclusion:

oeMRI is feasible in PH patients, yielding an overall moderate agreement between oeMRI and V/Q scans, with a good sensitivity of oeMRI for the detection of ventilation defects as compared with ventilation scintigraphy. J. Magn. Reson. Imaging 2012;35:86‐94. © 2011 Wiley Periodicals, Inc.     

Spontaneous abrupt changes in the distribution of ventilation: a cause for apparent mismatching on ventilation/perfusion scintigraphy

A defect seen in the perfusion scan in a region of lung that is normally ventilated is usually interpreted as indicating pulmonary vascular disease. Since the distribution of 99Tcm macro-aggregated albumin (MAA) represents the distribution of perfusion (Q) only at the time of MAA injection, the assumption is required that the distribution of ventilation (V) remains unchanged between MAA injection and the commencement of imaging. We report the V/Q scintigraphic findings in six patients (including four children), in whom this assumption could not be sustained. Thus ventilation imaged with 81Krm was seen to change during image acquisition in lobes that showed perfusion abnormalities. In some, but not all, views the appearances were typical for pulmonary vascular disease, which might easily have been misdiagnosed if the changes in the distribution of ventilation had not announced themselves by occurring during image acquisition. A ventilation image obtained immediately before injection of 99Tcm-MAA may be useful.