Rationale and Objectives
Pulmonary enhancement imaging (PEI) derived from dual-energy computed tomographic (CT) imaging has been used to detect perfusion defects from pulmonary embolism (PE). The purpose of this study was to compare the ability of PEI, planar, single photon-emission CT (SPECT) perfusion scintigraphy, and SPECT-CT fusion images to detect perfusion defect in a PE rabbit model.
Materials and Methods
A PE model was made by injecting Gelfoam into the femoral veins of rabbits ( n = 16). After 2 hours, 16 experimental rabbits and three control rabbits underwent contrast-enhanced dual-energy CT scans, from which PEI and CT pulmonary angiography were created, and planar, SPECT, and SPECT-CT fusion images were then obtained and evaluated. Pathologic determination of locations and numbers of lung lobes with PE were recorded. The sensitivity and specificity of the above-mentioned modalities were calculated using the histopathologic results as reference standards.
Results
Emboli were present in 31 pulmonary lobes and absent in 64 lung lobes in histopathologic analysis. With the histopathologic findings as the gold standard, sensitivities and specificities of PEI, planar, SPECT, and SPECT-CT fusion images to detect PE were 100% and 96.9%, 71.0% and 84.4%, 77.4% and 90.6%, and 74.2% and 93.8%, respectively. McNemar’s tests showed that PEI had higher diagnostic accuracy for the detection of PE than three scintigraphic images (all P values < .05), while three scintigraphic images had similar diagnostic accuracy (all P values = NS).
Conclusions
This study demonstrates that PEI from dual-energy CT imaging can provide higher diagnostic accuracy for detecting PE than planar, SPECT, and SPECT-CT fusion images in a rabbit model.
Pulmonary embolism (PE) is ranked as the third leading cause of death in the United States, with as many as 300,000 fatalities per year . However, an estimated 400,000 diagnoses of PE are missed annually in the United States, largely because of nonspecific clinical signs and symptoms. The accurate diagnosis of PE continues to be a challenge for both clinicians and imaging specialists. Misdiagnosis is critically problematic because death occurs in up to 90% of patients with unrecognized PE, whereas in treated patients, PE accounts for <10% of deaths; furthermore, unnecessary treatment with anticoagulation can place a patient at risk for bleeding .
Imaging techniques, including pulmonary angiography, computed tomographic (CT) imaging, magnetic resonance imaging, and scintigraphy, play an important role in the detection of PE. Of these imaging modalities, pulmonary scintigraphy and CT pulmonary angiography (CTPA) are currently the most widely available and most widely used methods for imaging patients with suspected PE. Multidetector CT (MDCT) pulmonary angiography has been widely used in clinical practice, largely replacing conventional pulmonary angiography and scintigraphy for the evaluation of possible PE; MDCT pulmonary angiography is accepted as the reference standard for the diagnosis of acute PE . The Prospective Investigation of Pulmonary Embolism Diagnosis (PIOPED) II has recommended CTPA as the procedure of choice for the diagnosis of PE . However, many nuclear medicine practitioners have emphasized the merits of single photon-emission CT (SPECT) scintigraphy compared to planar scintigraphy and/or MDCT pulmonary angiography for imaging of PE, citing fewer contraindications, reduced radiation dose, and fewer nondiagnostic findings compared to CTPA as well as improved sensitivity and specificity and fewer nondiagnostic findings compared to planar scintigraphy . Prior studies have also demonstrated that coregistered SPECT-CT fusion images can provide important anatomic and functional information serving as a useful adjunct to CTPA for the diagnosis of acute PE . With recently available dual-source CT scanners, functional and anatomic information can be provided with a single contrast-enhanced dual-energy CT (DECT) scan; DECT methods may overcome the limitations of prior MDCT approaches to improve sensitivity for the detection of PE .
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Materials and methods
Animal Model
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DECT Imaging
Imaging protocols
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Image reconstruction and analysis
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Perfusion Planar and SPECT Scintigraphy
Imaging protocols
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Image analysis
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Coregistered SPECT-CT Imaging
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Image analysis
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Pathologic Processing
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Statistical Analysis
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Results
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Table 1
Location and Total Number of Pulmonary Emboli Detected for Each Imaging Modality
Modality Right Lung ( n ) Left Lung ( n ) Summary Upper Middle Lower Upper Lower PEI 0 6 (2 ∗ ) 11 3 13 33 Planar scintigraphy 2 (2 ∗ ) 2 (1 ∗ , 3 † ) 11 (3 ∗ , 3 † ) 2 (1 ∗ , 2 † ) 13 (1 ∗ , 1 † ) 30 SPECT 2 (2 ∗ ) 1 (1 ∗ , 4 † ) 13 (3 ∗ , 1 † ) 1 (2 † ) 13 30 SPECT-CT 1 (1 ∗ ) 1 (1 ∗ , 4 † ) 12 (2 ∗ , 1 † ) 1 (2 † ) 12 (1 † ) 27 Histopathology 0 4 11 3 13 31
CT, computed tomography; PEI, pulmonary enhancement imaging; SPECT, single photon-emission computed tomography.
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Table 2
Diagnostic Performance of Each Imaging Modality for the Detection of Pulmonary Embolism
Modality Results ( n ) Statistical Analysis (%) TP TN FP FN Sensitivity Specificity PPV NPV Accuracy PEI 31 62 2 0 100 (31/31) 96.9 (62/64) 93.9 (31/33) 100 (62/62) 97.9 (93/95) Planar scintigraphy 22 56 8 9 71.0 (22/31) 84.4 (56/64) 73.3 (22/30) 86.2 (56/65) 82.1 (78/95) SPECT 24 58 6 7 77.4 (24/31) 90.6 (58/64) 80.0 (24/30) 89.2 (58/65) 86.3 (82/95) SPECT-CT 23 60 4 8 74.2 (23/31) 93.8 (60/64) 85.2 (23/27) 88.2 (60/68) 87.4 (83/95)
CT, computed tomography; FN, false-negative results; FP, false-positive results; NPV, negative predictive value; PEI, pulmonary enhancement imaging; PPV, positive predictive value; SPECT, single photon-emission computed tomography; TN, true-negative results; TP, true-positive results.
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Discussion
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Conclusions
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Acknowledgment
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