V/Q SPECT Interpretation for Pulmonary Embolism Diagnosis: Which Criteria to Use?

Abstract

Ventilation-perfusion (V/Q) SPECT has been reported to improve the diagnostic performance of V/Q imaging for the diagnosis of pulmonary embolism (PE). However, only sparse data based on an objective reference test are available, and the criteria used for interpretation have varied widely. Therefore, the aim of our study was to assess the performance of V/Q SPECT using various criteria for interpretation, in comparison with a validated independent diagnostic strategy. Methods: The SPECT study included patients for whom V/Q SPECT data were compared with the results of an independent and validated diagnostic algorithm for PE. V/Q SPECT scans were performed after intravenous injection of 99m Tc-macroaggregated albumin and simultaneous ventilation with 81m Kr gas. Interpretation was performed independently by 2 nuclear medicine physicians who were not aware of the clinical history, diagnostic strategy conclusion, or patient's outcome. Sensitivity, specificity, and likelihood ratios were evaluated for various combinations of mismatched defect numbers and sizes (segmental or subsegmental). Generation of receiver-operating-characteristic curves was based on the number of mismatch defects and the number of subsegmental mismatch defects or equivalent. Results: Of the 249 patients who were analyzed, the diagnosis of PE was confirmed in 49 and ruled out in 200 according to the previously validated independent strategy. Of all the tested criteria, the best performance was achieved using a diagnostic cutoff of at least 1 segmental or 2 subsegmental mismatches, with sensitivity and specificity of 0.92 (95% confidence interval, 0.84-1) and 0.91 (95% confidence interval, 0.87-0.95), respectively. With a negative V/Q SPECT result, the posttest probability of PE was 0.010, 0.037, and 0.119 for a low, intermediate, and high clinical probability. With a positive V/Q SPECT result, the posttest probability of PE was 0.531, 0.814, and 0.939 for a low, intermediate, and high probability. Conclusion: For V/Q SPECT interpretation, a diagnostic cutoff of 1 segmental or 2 subsegmental mismatches seems best for confirming or excluding acute PE. Pl anar ventilation-perfusion (V/Q) lung scintigraphy was the first validated noninvasive procedure for the diagnosis of pulmonary embolism (PE). In the late 1980s, chest CT overtook V/Q scanning in most institutions as the initial imaging modality for suspected PE, mainly because of the high rate of inconclusive results from planar V/Q scintigraphy using the probabilistic interpretation proposed in the PIOPED study (prospective investigation of pulmonary embolism diagnosis) (1).More recently, there has been a renewed interest in V/Q imaging, primarily in response to concerns about high radiation exposure from CT angiography (2). Indeed, the radiation dose is lower with V/Q scintigraphy than with chest multidetector CT (MDCT), particularly to the female breast (3-5). Another drawback of MDCT is that it cannot be performed in many patients because of contraindications such as renal failure or an allerg...

Additional value of combining low-dose computed tomography to V/Q SPECT on a hybrid SPECT-CT camera for pulmonary embolism diagnosis

“…V/Q SPECT was interpreted by the nuclear medicine physician in charge using a diagnostic cutoff of one segmental or two subsegmental mismatched defects [16]. The final diagnostic conclusion was established by the physician in charge of patient care on the basis of clinical symptoms, laboratory tests, V/Q SPECT and other imaging procedures performed.…”

“…Compared with traditional planar V/Q imaging, V/Q SPECT offers a better spatial resolution and a limitation of the overlapping of perfusion defects by other structures [8][9][10]. The diagnostic performance of V/Q SPECT has been reported in several accuracy and cohort studies [11][12][13][14][15], and interpretation criteria dedicated to V/Q SPECT have been validated [16][17][18]. Improved performance of V/Q SPECT could allow safe and simplified algorithm strategies while maintaining the advantages of V/Q scintigraphy (i.e.…”

Pulmonary Scintigraphy for the Diagnosis of Acute Pulmonary Embolism: A Survey of Current Practices in Australia, Canada, and France

“…For V/Q SPECT, the most commonly used criteria (60%) were those proposed by the EANM, that is, a binary approach (PE or no PE) with a diagnostic cutoff of "1 segmental or 2 subsegmental perfusion mismatched defects" (18). This diagnostic cutoff has been reported to be optimal for PE diagnosis (36), and a recent observational study confirmed the diagnostic exclusion safety of a diagnostic management including a V/Q SPECT study interpreted with these criteria (37). Only 8% of institutions used the probabilistic approach for interpretation of SPECT, compared with 29% for planar.…”

Critical review of SPECT imaging in pulmonary embolism

“…The agents used for V SPECT differed (Table 1) and the diagnostic criteria for interpretation of SPECT also differed among investigations (Table 1). Le Roux et al [39], in a subset of patients reported by Le Duc-Pennec et al [26], showed the best performance of SPECT with a diagnostic cutoff of C1 segmental or C2 subsegmental mismatches [sensitivity: 45 out of 49 (92 %), specificity: 182 out of 200 (91 %)].…”