In Vivo Dual-Isotope SPECT Imaging with Improved Energy Resolution

Cadmium zinc telluride or CZT cameras offer dual-isotope imaging capabilities impossible to duplicate using any other pre-clinical molecular imaging system. This new technology will enable the investigation of multiple biological processes in parallel and open new areas in research and drug development. The dual-isotope capability is due to the improved energy resolution of CZT (4.5% for ^99mTc), which is 2-3 times better than in existing systems. This improved energy resolution allows for the rejection of more scattered photons, yielding higher contrast images. In addition, CZT provides increased sensitivity compared to traditional pixellated NaI(Tl) systems due to the absence of any escape peaks. These properties combine to give a higher sensitivity detector with significantly improved contrast. The present work demonstrates the use of CZT in dual-isotope imaging of mice using two radiopharmaceuticals with very close energy peaks. These included ^99mTc-labelled MDP (bone agent) and ¹²³I (thyroid) and a mouse bone (^99mTc-MDP) image with a ⁵⁷Co fiducial marker. The results show the first ever simultaneous ^99mTc/¹²³I mouse images. The individual isotope peaks showed significant separation and yielded an image with the thyroid (2-3 mm) clearly distinguished from the bone structure. GM-I´s new FLEX Triumphtrade Pre-clinical system is the first in the field to offer CZT SPECT detectors.