Dynamic SPECT with technetium-99m HM-PAO in meningiomas--a comparison with iodine-123 IMP

Technetium-99m hexamethylpropyleneamine oxime ([99mTc]HM-PAO) has recently been introduced as an alternative to N-isopropyl-p-[123I]iodoamphetamine ([123I]IMP) for measurement of regional cerebral blood flow. This study compares dynamic SPECT studies using the two tracers in seven patients with meningiomas. Regions of interest were placed over the lesion and contralateral homologous presumed normal area. The counting-rate ratio for the lesion to the contralateral homologous area (L/N ratio) was then calculated in the first image. L/N ratios of [99mTc]HM-PAO single photon emission computed tomography (SPECT) were lower than those of [123I])IMP SPECT, particularly in hypervascular meningiomas. Furthermore, time-activity curves showed that the washout of [99mTc]HM-PAO in the tumors was very slow or incomplete, preventing an accurate assessment of vascularity of meningiomas with [99mTc]HM-PAO, as is generally possible with [123I]IMP.