Merits of V/Q SPECT Scintigraphy Compared with CTPA in Imaging of Pulmonary Embolism

Radiologic Aspects of the Diagnosis of Pulmonary Embolism in Pregnancy

Pulmonary embolism in pregnancy is a leading cause of maternal mortality. The clinical presentation is often nonspecific, making imaging essential for accurate diagnosis. After reviewing the literature on the radiologic diagnosis of pulmonary embolism in pregnancy, we concluded that both computed tomography pulmonary angiography and lung perfusion scintigraphy are sensitive with high positive predictive values in the presence of high clinical suspicion, but lung perfusion scintigraphy is recommended given lower maternal breast exposure to ionizing radiation and lower fetal contrast exposure. However, if a chest x-ray is abnormal, computed tomography pulmonary angiography is preferred due to high nondiagnostic rates of lung perfusion scintigraphy.

Impact of CT perfusion imaging on the assessment of peripheral chronic pulmonary thromboembolism: clinical experience in 62 patients

PURPOSE

To evaluate the impact of CT perfusion imaging on the detection of peripheral chronic pulmonary embolisms (CPE).

MATERIALS AND METHODS

62 patients underwent a dual-energy chest CT angiographic examination with (a) reconstruction of diagnostic and perfusion images; (b) enabling depiction of vascular features of peripheral CPE on diagnostic images and perfusion defects (20 segments/patient; total: 1240 segments examined). The interpretation of diagnostic images was of two types: (a) standard (i.e., based on cross-sectional images alone) or (b) detailed (i.e., based on cross-sectional images and MIPs).

RESULTS

The segment-based analysis showed (a) 1179 segments analyzable on both imaging modalities and 61 segments rated as nonanalyzable on perfusion images; (b) the percentage of diseased segments was increased by 7.2 % when perfusion imaging was compared to the detailed reading of diagnostic images, and by 26.6 % when compared to the standard reading of images. At a patient level, the extent of peripheral CPE was higher on perfusion imaging, with a greater impact when compared to the standard reading of diagnostic images (number of patients with a greater number of diseased segments: n = 45; 72.6 % of the study population).

CONCLUSION

Perfusion imaging allows recognition of a greater extent of peripheral CPE compared to diagnostic imaging.

KEY POINTS

• Dual-energy computed tomography generates standard diagnostic imaging and lung perfusion analysis. • Depiction of CPE on central arteries relies on standard diagnostic imaging. • Detection of peripheral CPE is improved by perfusion imaging.

Single photon emission computed tomography in chronic thromboembolic pulmonary hypertension

BACKGROUND AND OBJECTIVE

The management of chronic thromboembolic pulmonary hypertension (CTEPH) is largely dependent on the extent of obstruction in the pulmonary arteries. Planar perfusion scans are commonly used to quantify perfusion defects in CTEPH patients. However, planar scans typically under-represent the extent of vascular obstruction in CTEPH. We conducted this study to test the hypothesis that SPECT lung perfusion scans are more accurate than planar scans for determining the location and extent of perfusion defects in patients with CTEPH.

METHODS

Planar ventilation scans, planar and SPECT perfusion scans were performed preoperatively in patients undergoing pulmonary thromboendarterectomy for treatment of CTEPH. Two clinical experts independently documented the segmental anatomy of the vascular obstructions by reviewing clinical records, pulmonary and CT angiograms, and surgical specimens. A nuclear medicine expert documented the segmental anatomy of the perfusion defects observed by planar and SPECT scans independently.

RESULTS

Clinical/pathological evaluation disclosed 241 obstructed and 99 unobstructed lung segments in 17 patients. Sensitivity for detecting obstructed segments was significantly higher for SPECT than for planar scanning (63.5 ± 3.1% vs. 42.7 ± 3.2%, respectively; P < 0.01). Specificities of SPECT and planar scanning were not significantly different (62.6 ± 4.8% vs. 76.8 ± 4.2%, respectively; P = 0.092).

CONCLUSIONS

The SPECT is more sensitive than planar perfusion scanning for identifying obstructed segments in CTEPH. However, even SPECT under-represents the true extent of the vascular occlusions in CTEPH.

Pulmonary enhancement imaging with dual energy CT for the detection of pulmonary embolism in a rabbit model: comparison to perfusion planar scintigraphy, SPECT and SPECT-CT modalities

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.

Ventilation/Perfusion SPECT for diagnostics of pulmonary embolism in clinical practice

AIM

The aim of this retrospective study is to illustrate clinical utility and impact of pulmonary embolism (PE) diagnostics of up to date Ventilation/Perfusion SPECT (V/P (SPECT)) applying holistic interpretation criteria.

MATERIAL AND METHODS

During a 2-year period 2328 consecutive patients referred to V/P(SPECT) for clinically suspected PE were examined. Final diagnosis was established by physicians clinically responsible for patient care. To establish the performance of V/P(SPECT) negative for PE, patients were followed up by medical records for 6 months.

RESULTS

Ventilation/Perfusion SPECT was feasible in 99% of the patients. Data for follow-up were available in 1785 patients (77%). PE was reported in 607 patients (34%). Normal pattern was described in 420 patients (25%). Pathology other than PE such as a pneumonia, left heart failure, obstructive lung disease, tumour was described in 724 patients (41%). Report was nondiagnostic in 19 patients (1%). Six cases were classified as falsely negative because PE was diagnosed at follow-up and was fatal in one case. Six cases were classified as falsely positive because the clinician decided not to treat. In 608 patients with final PE diagnosis, 601 patients had positive V/P(SPECT) (99%). In 1177 patients without final PE diagnosis 1153 patients had negative V/P(SPECT) (98%).

CONCLUSIONS

Holistic interpretation of V/P(SPECT,) yields high negative and positive predictive values and only 1% of nondiagnostic findings and was feasible in 99% of patients. It is a responsibility and a challenge of nuclear medicine to provide optimal care of patients with suspected PE by making V/P(SPECT) available.