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Embolic Distribution Through Patent Foramen Ovale Demonstrated by ^99mTc-MAA Brain SPECT After Valsalva Radionuclide Venography

Departments of Radiology and Medicine, National Cardiovascular Center, Osaka, Japan

Cryptogenic stroke might relate to paradoxical embolism stemming from right-to-left shunt caused by patent foramen ovale (PFO). We performed radionuclide venography using the Valsalva maneuver, followed by ^99mTc-macroaggregated albumin (MAA) brain SPECT to investigate the fate of emboli originating from the lower extremities. Methods: Ten patients (9 men, 1 woman; mean age, 61 ± 17 y) with PFO underwent radionuclide venography with and without the Valsalva maneuver on the whole-body image, followed by brain SPECT with ^99mTc-MAA to determine the cortical uptake that would detect right-to-left shunt. After counts in each region of interest (ROI) were normalized by comparison with the averaged count, the distribution of MAA was compared with that of ^99mTc–hexamethyl-propyleneamine oxime (HMPAO) brain SPECT by drawing ROIs on frontal, temporoparietal (anterior circulation territory), occipital, and cerebellar areas (posterior circulation territory). Results: The thyroid on the whole-body scan was visualized after the Valsalva maneuver in 2 of the 10 patients. In 7 of 10 patients, 56 ROIs in the visualized cortical uptake showed that the distribution of MAA correlated well with that of HMPAO according to the equation: HMPAO = -71.21 + 1.71 x MAA, (r = 0.575, P < 0.01). The excess difference in the relative counts in the posterior over anterior circulation territory was 5.6% and 16.1% of the HMPAO and MAA values, respectively. Conclusion: Brain SPECT with ^99mTc-MAA was more sensitive than thyroid visualization in detecting right-to-left shunt. The excess flow in the posterior cerebral circulation indicated an increased likelihood of cerebral emboli originating from the lower extremities and indicated that the flow difference between HMPAO and MAA probably resulted from poor linearization of HMPAO in the high-flow area.

Key Words: cerebral embolism • patent foramen ovale • radionuclide venography • ^99mTc-microaggregated albumin • brain SPECT

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