Dual Energy CT lung perfusion imaging--correlation with SPECT/CT

Objective

Aims were (1) to determine the diagnostic accuracy of Dual Energy CT (DECT) in the detection of perfusion defects and (2) to evaluate the potential of DECT to improve the sensitivity for PE.

Methods

15 patients underwent Dual Energy pulmonary CT angiography (DE CTPA) and a combination of lung perfusion SPECT/CT and ventilation scintigraphy. CTPA and DE iodine distribution maps as well as perfusion SPECT/CT and inhalation scintigrams were reviewed for pulmonary embolism (PE) diagnosis. DECT and SPECT perfusion images were assessed regarding localization and extent of perfusion defects. Diagnostic accuracy of DE iodine (perfusion) maps was determined with reference to SPECT/CT. Diagnostic accuracies for PE detection of DECT and of SPECT/CT with ventilation scintigraphy were calculated with reference to the consensus reading of all modalities.

Results

DE CTPA had a sensitivity/specificity of 100%/100% for acute PE, while the combination of SPECT/CT and ventilation scintigraphy had a sensitivity/specificity of 85.7%/87.5%. For perfusion defects, DECT iodine maps had a sensitivity/specificity of 76.7% and 98.2%.

Conclusion

DECT is able to identify pulmonary perfusion defects with good accuracy. This technique may potentially enhance the diagnostic accuracy in the assessment of PE.     

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.     

Planar ventilation-perfusion imaging for pulmonary embolism: the case for "outcomes" medicine

Single-photon emission computed tomography (SPECT) has been a significant advancement in scintigraphy, impacting many areas of diagnosis. It has begun to find use in ventilation-perfusion (V/Q) scintigraphy. However, its utility has been limited in the United States because of a lack of an optimal and Food and Drug Administration-approved SPECT ventilatory agent. Although SPECT V/Q can show more and smaller mismatches than planar studies, there is persistent debate regarding the clinical significance of these smaller pulmonary emboli (PE); they may be neither clinically significant nor require treatment. Available data suggest that planar V/Q, SPECT V/Q, and computed tomographic pulmonary angiography (CTPA) have similar false-negative rates and thus have a similar impact on outcomes. In most cases, emergency department physicians are the first to encounter patients who may have PE, and they frequently use an imaging study as part of the evaluation. We discuss the rational for triaging patients to different imaging modalities with the use of chest radiography and the strengths and weaknesses of each modality. Detailed anatomy is an advantage of CTPA, breast radiation dose is reduced with scintigraphy, and imaging is quicker and more detailed with SPECT. We also review planar and SPECT V/Q and CTPA from the differing vantage points of diagnostic accuracy vs patient outcomes. Whatever modality their patients require, physicians can be confident that they are all similarly efficacious at diagnosing clinically relevant emboli.     

Improving the diagnostic performance of lung scintigraphy in suspected pulmonary embolic disease

AIM: to determine the effectiveness of a new imaging algorithm in the investigation of suspected pulmonary embolism (PE). MATERIALS AND METHODS: A new imaging algorithm for suspected PE was introduced following the installation of a multisection computed tomography (CT) machine at our institution. Before its installation, patients with suspected PE were evaluated with ventilation/perfusion (V/Q) scintigraphy. Subsequently, patients were triaged according to chest radiography (CR) and respiratory history to either lung scintigraphy or CT pulmonary angiography (CTPA). Patients with a normal CR and no history of lung disease were evaluated using perfusion (Q) scintigraphy [ventilation (V) scintigraphy was no longer performed]. Patients with an abnormal CR, asthma or chronic lung disease were evaluated using CTPA. All V/Q images in a continuous 3-year period before the introduction of the new imaging algorithm and all Q images performed in a 3-year period after its introduction were retrospectively reviewed. Imaging reports were categorized into normal, non-diagnostic (low or intermediate probability) or high probability for PE. Patients in the later group who subsequently underwent CTPA, were also reviewed. RESULTS: After the policy change the percentage of normal scintigrams significantly increased (39 to 60%; p<0.001). There was a non-significant increase in the percentage of high probability scintigrams (15 to 18%; p=0.716). Overall the diagnostic yield of lung scintigraphy improved significantly (54 to 78%; p<0.001). CONCLUSION: the diagnostic performance of lung scintigraphy can be improved by careful triage of patients to either Q scintigraphy or CTPA based on clinical history and CR findings. Q scintigraphy remains a valuable diagnostic test in the investigation of suspected PE in carefully selected 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 (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.     

Relation between lung perfusion defects and intravascular clots in acute pulmonary thromboembolism: assessment with breath-hold SPECT-CT pulmonary angiography fusion images

PURPOSE: The relation between lung perfusion defects and intravascular clots in acute pulmonary thromboembolism (PTE) was comprehensively assessed on deep-inspiratory breath-hold (DIBrH) perfusion SPECT-computed tomographic pulmonary angiography (CTPA) fusion images. MATERIALS AND METHODS: Subjects were 34 acute PTE patients, who had successfully performed DIBrH perfusion SPECT using a dual-headed SPECT and a respiratory tracking system. Automated DIBrH SPECT-CTPA fusion images were used to assess the relation between lung perfusion defects and intravascular clots detected by CTPA. RESULTS: DIBrH SPECT visualized 175 lobar/segmental or subsegmental defects in 34 patients, and CTPA visualized 61 intravascular clots at variable locations in 30 (88%) patients, but no clots in four (12%) patients. In 30 patients with clots, the fusion images confirmed that 69 (41%) perfusion defects (20 segmental, 45 subsegmental and 4 lobar defects) of total 166 defects were located in lung territories without clots, although the remaining 97 (58%) defects were located in lung territories with clots. Perfusion defect was absent in lung territories with clots (one lobar branch and three segmental branches) in four (12%) of these patients. In four patients without clots, nine perfusion defects including four segmental ones were present. CONCLUSION: Because of unexpected dissociation between intravascular clots and lung perfusion defects, the present fusion images will be a useful adjunct to CTPA in the diagnosis of acute PTE.     

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.     

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.     

Methodology for ventilation/perfusion SPECT

Ventilation/perfusion single-photon emission computed tomography (V/Q SPECT) is the scintigraphic technique of choice for the diagnosis of pulmonary embolism and many other disorders that affect lung function. Data from recent ventilation studies show that the theoretic advantages of Technegas over radiolabeled liquid aerosols are not restricted to the presence of obstructive lung disease. Radiolabeled macroaggregated human albumin is the imaging agent of choice for perfusion scintigraphy. An optimal combination of nuclide activities and acquisition times for ventilation and perfusion, collimators, and imaging matrix yields an adequate V/Q SPECT study in approximately 20 minutes of imaging time. The recommended protocol based on the patient remaining in an unchanged position during the initial ventilation study and the perfusion study allows presentation of matching ventilation and perfusion slices in all projections as well as in rotating volume images based upon maximum intensity projections. Probabilistic interpretation of V/Q SPECT should be replaced by a holistic interpretation strategy on the basis of all relevant information about the patient and all ventilation/perfusion patterns. PE is diagnosed when there is more than one subsegment showing a V/Q mismatch representing an anatomic lung unit. Apart from pulmonary embolism, other pathologies should be identified and reported, for example, obstructive disease, heart failure, and pneumonia. Pitfalls exist both with respect to imaging technique and scan interpretation.     

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.     

肺通气/灌注显像与多层螺旋CT诊断慢性血栓栓塞性肺动脉高压的对比研究

目的 对比肺通气/灌注(V/Q)显像与多层螺旋CT肺血管造影(CTPA)诊断慢性血栓栓塞性肺动脉高压(CTEPH)的准确性,评价2种影像学方法的诊断符合程度.方法 49例肺动脉高压患者,经超声心动图排除瓣膜性心脏病和先天性心脏病,既往无急性肺栓塞病史.所有患者先后行肺V/Q显像和CTPA检查,并以肺动脉造影为"金标准"进行对比评价.对V/Q显像和CTPA检查结果比较进行χ2检验,采用SPSS 12.0统计软件.结果 肺V/Q显像对CTEPH的诊断灵敏度、特异性和准确性分别为100.0%(17/17),71.9%(23/32)和81.6%(40/49),CTPA分别为94.1%(16/17),81.2%(26/32)和85.7%(42/49).肺V/Q显像与CTPA的诊断符合率为75.5%(37/49),Kappa值为0.513,2种影像学方法的诊断结果差异无统计学意义(χ2=0.75,P>0.05).结论 肺V/Q显像和CTPA均是诊断CTEPH有效的无创性影像学方法,两者结合应用有助于更好地诊断CTEPH.     

Ventilation-perfusion scintigraphy is more sensitive than multidetector CTPA in detecting chronic thromboembolic pulmonary disease as a treatable cause of pulmonary hypertension.

Pulmonary hypertension (PH) is a progressive disease with a poor prognosis. Identifying chronic thromboembolic pulmonary disease as a cause of PH has major clinical implications as these patients could be potentially offered a surgical cure. Ventilation-perfusion (V/Q) scintigraphy has a high sensitivity to detect embolic disease but its value has been challenged with the emergence of multidetector CT pulmonary angiography (CTPA). We compared the value of V/Q scintigraphy with CTPA in detecting chronic thromboembolic pulmonary disease. METHODS: We retrospectively reviewed the results of V/Q scintigraphy and CTPA performed on patients who had been referred to the Pulmonary Hypertension Service at Hammersmith Hospital between 2000 and 2005. A total of 227 patients (85 males, 142 females; age range, 18-81 y; mean age, 42 y) had all tests done at Hammersmith Hospital and were included in the study. Interpretation of scans was according to the modified PIOPED (Prospective Investigation of Pulmonary Embolism Diagnosis) criteria. CTPA was considered as suggestive of chronic thromboembolic pulmonary disease if it showed visualization of the thrombus or webs, recanalization, perfusion abnormalities, stenosis, or strictures. Standard pulmonary angiography was performed via femoral approach. In 90% of the cases, CTPA and V/Q scintigraphy were performed within 10 d. RESULTS: Seventy-eight patients (group A) had a final diagnosis of chronic thromboembolic pulmonary hypertension (CTEPH) and 149 (group B) had non-CTEPH etiology. Among group A, V/Q scintigraphy was reported as high probability in 75 patients, intermediate probability in 1 patient, and low probability in 2 patients. CTPA was positive in 40 patients and negative in 38 patients. Among group B, V/Q scintigraphy was reported as low probability in 134, intermediate probability in 7, and high probability in 8 patients. CTPA was negative in 148 patients and false-positive in 1 patient. Statistical analysis showed V/Q scintigraphy to have a sensitivity of 96%-97.4% and a specificity of 90%-95%. CTPA showed a sensitivity of 51% and a specificity of 99%. CONCLUSION: Our results demonstrate that V/Q scintigraphy has a higher sensitivity than CTPA in detecting CTEPH as a potential curable cause of PH.     

V/Q SPECT and computed tomographic pulmonary angiography

Planar ventilation and perfusion (V/Q) scintigraphy has been largely displaced by computed tomography pulmonary angiography (CTPA) in recent years for the diagnosis of pulmonary embolism (PE). This change can be attributed to multiple studies that demonstrate CTPA has a reasonable sensitivity and good prognostic value in negative cases, associated with the ability to deliver few indeterminate results and provide an alternate diagnosis in a significant number of patients. However, the technique has significant limitations. The Prospective Investigation of Pulmonary Embolism Diagnosis II (PIOPED II) study has shown a sensitivity of 83%, which is not optimal. However, CT technology has greatly progressed since this time, and therefore it is likely that this number has improved. The PIOPED II study has also shown that there may be a problem in positive or negative predictive value when the imaging results are discordant with the clinical probability. Additional concerns include allergies, contrast nephropathy associated with the use of intravenous contrast in patients with impaired creatinine clearance, suboptimal results in pregnant women, and high radiation exposure. In recent years, V/Q single-photon emission computed tomography has emerged as a mature technique for the diagnosis of PE and has been shown to be clearly superior to planar V/Q. The technique has excellent sensitivity for PE and is not associated with most of the limitations of CTPA, although it has its own set of limitations in patients with very severe chronic obstructive pulmonary disease or with a severely abnormal chest x-ray. V/Q single-photon emission computed tomography can be used as the initial modality for PE diagnosis in a wide variety of situations although CTPA remains invaluable in specific scenarios.     

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 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.     

SPECT imaging in the diagnosis of pulmonary embolism: automated detection of match and mismatch defects by means of image-processing techniques.

SPECT of ventilation/perfusion (V/Q) lung scans not only improves the diagnostic accuracy of the method but also facilitates the application of advanced image-processing techniques. On the basis of such techniques, our study aimed at developing a procedure that automatically analyzes V/Q lung scans with regard to match and mismatch defects. METHODS: Fifty-three patients with suspected pulmonary embolism had lung scans using the SPECT technique as well as 16-slice multidetector-row spiral CT within an interval of 48 h. After iterative image reconstruction and computerized linear registration of the V/Q scans, the ventilation was normalized to the perfusion. For the automated detection of mismatch defects, the perfusion was subtracted from the ventilation, whereas for the detection of match defects, the perfusion was subtracted from the inverted ventilation. Two experienced referees assessed all images. 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: The sensitivity, specificity, and accuracy of the conventional visual assessment were 0.91, 0.97, and 0.94, respectively, compared with 0.95, 0.84, and 0.89, respectively, for the automated algorithm. Artifacts imitating mismatch defects in the pulmonary recesses accounted for the relatively low specificity of the automated analysis. Artifacts of that kind were found in 15 patients and led to a false-positive diagnosis in 5 patients. However, by combining the visual and the automated approach, all artifacts could be easily identified leading to a sensitivity, specificity, and accuracy of 0.95, 1.0, and 0.98, respectively. Additionally, in all 12 patients of the cohort with highly heterogeneous ventilation and perfusion, the automated analysis made correct diagnoses. CONCLUSION: Because of the 3-dimensional properties of the SPECT data, the analysis of lung scans can be automated and objectified. The algorithm produces images that are easy to read and well suited for demonstration. Because of artifacts in the pulmonary recesses introduced by the automated approach, its diagnostic accuracy does not reach the level of the conventional analysis yet. Could these artifacts be overcome, the efficiency of the automated algorithm would be at least equivalent to that of conventional image interpretation. At present, best results can be achieved by combining both approaches.     

Dual nuclides SPECT for ventilation and perfusion study]

Dual nuclides SPECT using 81mKr and 99mTc-MAA for ventilation and perfusion study was performed in 24 subjects. Crosstalk of 81mKr to 99mTc-energy window was about 7.5% when ventilation and perfusion study were performed by 370 MBq of 81mKr gas and 185 MBq of 99mTc-MAA. Areas of low V/Q was significantly larger in SPECT study than in planar study, in 11 cases with various pulmonary diseases. High V/Q mismatches were also more clearly delineated in SPECT than in planar study. Dual nuclides SPECT study has advantages of obtaining V/Q distribution without movement artifacts and of simultaneous acquisition of ventilation and perfusion image. Area of high V/Q became larger in SPECT with crosstalk than in SPECT without crosstalk, but in the low V/Q area no significant difference was noted between SPECT with crosstalk and without crosstalk.     

Assessment of anatomic relation between pulmonary perfusion and morphology in pulmonary emphysema with breath-hold SPECT-CT fusion images

OBJECTIVE: Anatomic relation between pulmonary perfusion and morphology in pulmonary emphysema was assessed on deep-inspiratory breath-hold (DIBrH) perfusion single-photon emission computed tomography (SPECT)-CT fusion images. METHODS: Subjects were 38 patients with pulmonary emphysema and 11 non-smoker controls, who successfully underwent DIBrH and non-BrH perfusion SPECT using a dual-headed SPECT system during the period between January 2004 and June 2006. DIBrH SPECT was three-dimensionally co-registered with DIBrH CT to comprehend the relationship between lung perfusion defects and CT low attenuation areas (LAA). By comparing the appearance of lung perfusion on DIBrH with non-BrH SPECT, the correlation with the rate constant for the alveolar-capillary transfer of carbon monoxide (DLCO/VA) was compared between perfusion abnormalities on these SPECTs and LAA on CT. RESULTS: DIBrH SPECT provided fairly uniform perfusion in controls, but significantly enhanced perfusion heterogeneity when compared with non-BrH SPECT in pulmonary emphysema patients (P < 0.001). The reliable DIBrH SPECT-CT fusion images confirmed more extended perfusion defects than LAA on CT in majority (73%) of patients. Perfusion abnormalities on DIBrH SPECT were more closely correlated with DLCO/VA than LAA on CT (P < 0.05). CONCLUSIONS: DIBrH SPECT identifies affected lungs with perfusion abnormality better than does non-BrH SPECT in pulmonary emphysema. DIBrH SPECT-CT fusion images are useful for more accurately localizing affected lungs than morphologic CT alone in this disease.     

Scintigraphic Evidence for Overdiagnosis of Small PE on CT Pulmonary Angiography

A 68-year-old man with recent history of a fall presented with dyspnea on exertion, and underwent computed tomography pulmonary angiography (CTPA) for possible pulmonary embolism (PE). The CTPA was first read by the radiology resident as nondiagnostic for segmental PE. Subsequent planar perfusion (Q) images were normal; meanwhile, the attending radiologist revised the CTPA results as subsegmental PE in the left upper lobe. Further Q-SPECT images were obtained and fused with CTPA for clarification, which showed normal perfusion in the region of PE. The patient was monitored without anticoagulation treatment and remained uneventful for 12 months. This case illustrates that CTPA can lead to overdiagnosis and overtreatment of nonocclusive subsegmental PE.     

V/Q SPECT imaging of acute pulmonary embolus - A practical perspective

The following article is intended to illustrate the place of scintigraphy and computed tomography pulmonary angiography (CTPA) in the investigation of acute PE in current practice, and to guide non-radionuclide radiologists and other medical professionals to the best test for patients. We share our early experiences with ventilation-perfusion (V/Q) single-photon-emission computed tomography (SPECT) including image acquisition and interpretation. A comparison of the two techniques is given, along with practical considerations in a variety of clinical scenarios.