Three-dimensional quantitation of regional cerebral blood flow in mice using a high-resolution pinhole SPECT system and 123I-iodoamphetamine.

INTRODUCTION: This study is intended to evaluate the feasibility of using a high-resolution pinhole SPECT system and iodine-123-N-isopropyl-4-iodoamphetamine ((123)I-IMP) for three-dimensional (3D) absolute quantitation of regional cerebral blood flow (rCBF) in mice. METHODS: The pinhole SPECT system consists of a rotating stage and a pinhole collimator attached to a clinical gamma camera. The collimator's focal length is 251 mm. Phantom studies were performed to evaluate sensitivity and full-width half-maximum (FWHM) spatial resolution. The aperture-to-object distance was 15 mm. Six mice were studied. Cerebral infarctions were induced by ligating and disconnecting the distal portion of the left middle cerebral artery. Ex vivo SPECT studies were performed using harvested brains and skulls. The CBF volumetric image was computed using the standardized input function. RESULTS: Excellent spatial resolution of 0.9-mm FWHM and uniform sensitivity throughout the 3D volume were demonstrated in the phantom experiments. The CBF images showed a defect in the infarcted areas and a reduction of CBF values in the infarcted region as compared with the control region. CONCLUSIONS: This study demonstrated the feasibility of the 3D quantitation of rCBF in mice using a high-resolution pinhole SPECT system and (123)I-IMP.

Biological in vitro and in vivo studies of a series of new asymmetrical cationic [99mTc(N)(DTC-Ln)(PNP)]+ complex (DTC-Ln = alicyclic dithiocarbamate and PNP = diphosphinoamine).

(99m)Tc(N)-DBODC5 is a cationic mixed compound under clinical investigation as potential myocardial imaging agent. In spite of this, analogously to the other cationic (99m)Tc-agents, presents a relatively low first-pass extraction. Thus, modification of (99m)Tc(N)-DBODC(5) direct to increase its first-pass extraction keeping unaltered the favorable imaging properties would be desirable. This work describes the synthesis and biological evaluation of a series of novel cationic (99m)Tc-nitrido complexes, of general formula [(99m)TcN(DTC-Ln)(PNP)](+) (DTC-Ln= alicyclic dithiocarbamates; PNP = diphosphinoamine), as potential radiotracers for myocardial perfusion imaging. The synthesis of cationic (99m)Tc-(N)-complexes were accomplished in two steps. Biodistribution studies were performed in rats and compared with the distribution profiles of (99m)Tc(N)-DBODC5 and (99m)Tc-Sestamibi. The metabolisms of the most promising compounds were evaluated by HPLC methods. Biological studies revealed that most of the complexes have a high initial and persistent heart uptake with rapid clearance from nontarget tissues. Among tested compounds, 2 and 12 showed improved heart uptake with respect to the gold standard (99m)Tc-complexes with favorable heart-to-liver and slightly lower heart-to-lung ratios. Chromatographic profiles of (99m)Tc(N)-radioactivity extracted from tissues and fluids were coincident with the native compound evidencing remarkable in vivo stability of these agents. This study shows that the incorporation of alicyclic dithiocarbamate in the [(99m)Tc(N)(PNP)](+) building block yields to a significant increase of the heart uptake at early injection point suggesting that the first-pass extraction fraction of these novel complexes may be increased with respect to the other cationic (99m)Tc-agents keeping almost unaltered the favorable target/nontarget ratios.

99mTc-N-DBODC5, a new myocardial perfusion imaging agent with rapid liver clearance: comparison with 99mTc-sestamibi and 99mTc-tetrofosmin in rats.

UNLABELLED: (99m)Tc-[bis (dimethoxypropylphosphinoethyl)-ethoxyethylamine (PNP5)]-[bis (N-ethoxyethyl)-dithiocarbamato (DBODC)] nitride (N-PNP5-DBODC or N-DBODC5) is a new monocationic myocardial perfusion tracer. We sought to compare the myocardial uptake and clearance kinetics and organ biodistribution of (99m)Tc-N-DBODC5 with (99m)Tc-sestamibi and (99m)Tc-tetrofosmin. METHODS: Seventy-five anesthetized Sprague-Dawley rats were injected intravenously with 22.2-29.6 MBq (99m)Tc-N-DBODC5 (n = 25), (99m)Tc-sestamibi (n = 25), or (99m)Tc-tetrofosmin (n = 25). Rats were euthanized at either 2, 10, 20, 30, or 60 min after injection and gamma-well counting was performed on excised organ (heart, lung, and liver) and blood samples. In 3 additional rats, serial in vivo whole-body gamma-camera imaging with each tracer was performed. RESULTS: (99m)Tc-N-DBODC5 cleared rapidly from the blood pool. At 2 min after injection, (99m)Tc-N-DBODC5 blood activity was significantly lower than either (99m)Tc-sestamibi or (99m)Tc-tetrofosmin (P < 0.01) and remained lower over 60 min. Myocardial (99m)Tc-N-DBODC5 uptake was rapid (2.9% +/- 0.1% injected dose/g at 2 min), and there was no significant clearance over 60 min, similar to (99m)Tc-sestamibi and (99m)Tc-tetrofosmin. All 3 tracers exhibited rapid lung clearance. Importantly, (99m)Tc-N-DBODC5 cleared more rapidly from the liver than either (99m)Tc-sestamibi or (99m)Tc-tetrofosmin. As early as 30 min after injection, (99m)Tc-N-DBODC5 heart-to-liver ratio was 5.7 +/- 1.0 versus 1.6 +/- 0.1 and 2.9 +/- 0.3 for (99m)Tc-sestamibi and (99m)Tc-tetrofosmin (P < 0.05). By 60 min, (99m)Tc-N-DBODC5 heart-to-liver ratio further increased to 18.4 +/- 2.0 compared with 2.6 +/- 0.2 and 5.8 +/- 0.7 for (99m)Tc-sestamibi and (99m)Tc-tetrofosmin (P < 0.001). The rapid blood pool, lung, and liver clearance of (99m)Tc-N-DBODC5 resulted in excellent-quality myocardial images within 30 min after injection. CONCLUSION: (99m)Tc-N-DBODC5 is a promising new myocardial perfusion tracer with superior biodistribution properties. The rapid (99m)Tc-N-DBODC5 liver clearance may shorten the duration of imaging protocols by allowing earlier image acquisition and may markedly reduce the problem of photon scatter from the liver into the inferoapical wall on myocardial images.