123I-metaiodobenzylguanidine single-photon emission computerized tomography in brain tumors - a preliminary study

(123)I-metaiodobenzylguanidine (MIBG) has been developed as a functional analog of the neurotransmitter norepinephrine. The success of MIBG as an imaging agent for neural crest tumors is derived from its chemical similarities to norepinephrine. The present study aimed to explore a potential of (123)I-MIBG to differentiate embryonal tumors from other types of brain tumors.

Sixteen patients with brain tumors including three medulloblastomas, one neuroblastoma, six gliomas, and six meningiomas were examined with single-photon emission computerized tomography (SPECT) using (123)I-MIBG. The (123)I-MIBG uptake of tumors was defined as the ratios of tumor/nontumor (early and delayed T/NT) on SPECT images scanned 30 min and 6 h after intravenous injection of the tracer, respectively. Retention index was calculated as (delayed T/NT - early T/NT)/early T/NT.

The T/NT ratios on the early images for embryonal tumors (medulloblastomas and neuroblastoma), gliomas, and meningiomas were 3.2+/-1.7 (mean+/-SD), 1.4+/-0.3, and 1.6+/-0.5, respectively. The early uptake was significantly higher in the embryonal tumors than in gliomas (P<0.05). Delayed T/NT ratios for embryonal tumors were increased compared to the early T/NT ratios, while in contrast delayed T/NT ratios for the other tumors remained low (1.2-1.7). The high retention indices of the embryonal tumors indicate specific uptake of (123)I-MIBG in the tumors.

Early high accumulation and high retention on delayed imaging may indicate a possibility of (123)I-MIBG SPECT in differentiating embryonal brain tumors from gliomas and meningiomas.