Single photon emission computed tomography in chronic thromboembolic pulmonary hypertension

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.

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.

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).

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.