Dual-isotope SPECT using simultaneous acquisition of 99mTc and 123I radioisotopes: a double-injection technique for peri-ictal functional neuroimaging.
The acquisition of multiple radiotracer studies at different time points during a neurological event permits the study of different functional activation states in humans. Peri-ictal SPECT is a promising technique for localizing the epileptogenic zone and would be enhanced by the ability to acquire sequentially coregistered ictal and postictal SPECT images of a single seizure. This study was designed to develop and validate an accurate method for the simultaneous acquisition of 99mTc and 123I SPECT images of the brain.


METHODS
A multicompartment, transaxial Hoffman brain-slice phantom was filled with 99mTc, 123I or a 3:1 mixture of the two isotopes. Planar and SPECT images were acquired by a dual-head gamma camera system equipped with parallel and fanbeam collimators, respectively. Thirty-two energy windows (2 keV width) were acquired over the energy range 120-184 keV. From the planar data, the signal-to-noise characteristics and crosstalk were measured for each energy window and used to devise an energy window acquisition strategy that was then applied to the SPECT data. Three summed energy windows were created: a primary 99mTc image (130-146 keV), a primary 123I image (152-168 keV) and a secondary 99mTc crosstalk image (134-140 keV). A fraction (0.041) of the 99mTc crosstalk image was subtracted from the 123I image. No crosstalk correction was performed on the primary 99mTc image.


RESULTS
(a) Planar images: results showed 1.3% crosstalk in the 123I image compared with 19.7% for a 10% asymmetric energy window alone. 123I crosstalk into the 99mTc window was 2.79% and was relatively constant with changes in the location of the 99mTc energy window. (b) Tomographic images: results showed 1.51% 99mTc crosstalk in the 123I image compared with 12.44% for the uncorrected image and 3.70% 123I crosstalk in the 99mTc image.


CONCLUSIONS
An effective technique for the simultaneous acquisition of 99mTc and 123I radiotracer distributions in the brain has been developed and validated in a phantom model and should have clinical application in peri-ictal functional activation studies of the brain.
Brinkmann
B H
BH
Department of Nuclear Medicine, Mayo Clinic, Rochester, Minnesota 55905, USA.
O'Connor
M K
MK
O'Brien
T J
TJ
Mullan
B P
BP
So
E L
EL
Robb
R A
RA
D001921:Brain / Q000000981:diagnostic imaging*; D004828:Epilepsies, Partial / Q000000981:diagnostic imaging*; D006801:Humans; D007091:Image Processing, Computer-Assisted; D007457:Iodine Radioisotopes; D019047:Phantoms, Imaging; D019275:Radiopharmaceuticals; D013670:Sodium Pertechnetate Tc 99m; D015899:Tomography, Emission-Computed, Single-Photon / Q000379:methods*
D007457:Iodine Radioisotopes; D019275:Radiopharmaceuticals; D013670:Sodium Pertechnetate Tc 99m