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SPECT may have advantages over CT for diagnosing pulmonary embolism

Reuters Health and The Doctor's Channel Daily Newscast

NEW YORK (Reuters Health) – For diagnosing pulmonary embolism, single-photon emission CT (SPECT) lung scintigraphy is a viable alternative to CT pulmonary angiography (CTPA), and it offers advantages as well, including fewer contraindications and a lower radiation dose, new research shows.

“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 both diagnostic 16-detector CTPA as well as planar and SPECT V/Q scintigraphy.

Overall, the SPECT scintigraphy and CTPA data 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.

“SPECT lung scintigraphy is recommended for patients in whom CPTA is contraindicated due to allergy, critical illness, renal impairment, or diabetes and in those who have proliferating breast tissue,” the researchers advise.

Also, they add, “Perfusion-only lung scintigraphy may be the preferred test in women who are pregnant.”

But in other situations, the researchers note, CTPA might help clinicians confirm additional or alternative diagnoses – “an important consideration when choosing” which test to perform.

Chest 2009;136:1546-1553.