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For diagnosing a pulmonary embolism, SPECT lung scintigraphy is a viable alternative to CT pulmonary angiography (CTPA), new research shows.

Plus, SPECT offers advantages, including fewer contraindications and a lower radiation dose.

"CTPA offers additional imaging information, but SPECT ventilation/perfusion (V/Q) scintigraphy produces a markedly lower radiation dose, which is important in women of reproductive age, and may have additional advantages of a higher rate of diagnostic scans and greater interobserver reproducibility than planar V/Q scintigraphy or CTPA," lead author Dr. Susan Miles, from Calvary Mater Newcastle, New South Wales, Australia, and colleagues note in the December issue of CHEST.

Their findings are from a study of 100 patients, age 50 and older, with suspected acute pulmonary embolism. Seventy-nine underwent diagnostic 16-detector CTPA as well as planar and SPECT V/Q scintigraphy.

Dr. Miles told Reuters Health that SPECT was performed with Technegas, "a radiotracer with properties that improves ventilation image quality particularly in patients with coexistent lung disease." She added that SPECT imaging for ventilation studies is not widely available yet because of "the non-availability of Technegas."

Overall, SPECT scintigraphy and CTPA agreed on a pulmonary embolism diagnosis 95% of the time.

In addition, based on a reference diagnosis analysis, SPECT was 83% sensitive and 98% specific in diagnosing pulmonary embolism, with a positive predictive value of 95% and a negative predictive value of 94%. The reference diagnosis was made by respiratory physicians who reviewed CTPA and planar V/Q scan results, clinical data, and 3-month follow-up data.

Regarding the non-agreement between the studies, in 3 cases, CTPA results were positive, while SPECT results were negative. In 1 case, just the opposite was true. In none of these patients did the clinicians diagnose pulmonary embolism based on imaging results. None received ongoing anticoagulation, and all were in good health at 3 months with no thromboembolic events.

The findings, the authors conclude, support the use of SPECT as an alternative to CTPA for diagnosing pulmonary embolism.

"If the clinician wants to know if their patient has had a pulmonary embolism, then V/Q SPECT and CTPA perform equally," Dr. Miles said. "The choice of modality depends on other factors such as the radiation dose, imaging availability, patient characteristics and the diagnostic question. SPECT is a safer modality than CTPA for use in women with proliferating breast tissue and for patients with contrast allergy or risk factors for contrast induced renal failure. CTPA may be preferable if other diagnoses are suspected, due to its utility in diagnosing multiple pathologies."

Source: Reuters Health

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