Combining CT and nuclear: a winning hybrid team

Novel 99mTc(III)-azide complexes [99mTc(N3)(CDO)(CDOH)2B-R] (CDOH2=cyclohexanedione dioxime) as potential radiotracers for heart imaging

INTRODUCTION

In this study, novel ^99mTc(III)-azide complexes [^99mTc(N₃)(CDO)(CDOH)₂B-R] (^99mTc-ISboroxime-N₃: R=IS; ^99mTc-MPboroxime-N₃: R=MP; ^99mTc-PAboroxime-N₃: R=PA; ^99mTc-PYboroxime-N₃: R=PY; and ^99mTc-Uboroxime-N₃: R=5U) were evaluated as heart imaging agents.

METHODS

Complexes [^99mTc(N₃)(CDO)(CDOH)₂B-R] (R=IS, MP, PA, PY and 5U) were prepared by ligand exchange between NaN₃ and [^99mTcCl(CDO)(CDOH)₂B-R]. Biodistribution and imaging studies were carried out in Sprague-Dawley rats. Image quantification was performed to compare their initial heart uptake and myocardial retention.

RESULTS

^99mTc-ISboroxime-N₃, ^99mTc-PYboroxime-N₃ and ^99mTc-Uboroxime-N₃ were prepared with high RCP (93-98%) while the RCP of ^99mTc-MPboroxime-N₃ and ^99mTc-PAboroxime-N₃ was 80-85%. The myocardial retention curves of ^99mTc-ISboroxime-N₃, ^99mTc-PYboroxime-N₃ and ^99mTc-Uboroxime-N₃ were best fitted to the bi-exponential decay function. The half-time of the fast component was 1.6±0.4min for ^99mTc-ISboroxime-N₃, 0.7±0.1min for ^99mTc-PYboroxime-N₃ and 0.9±0.4min for ^99mTc-Uboroxime-N₃. The 2-min heart uptake from biodistribution studies followed the ranking order of ^99mTc-ISboroxime-N₃ (3.60±0.68%ID/g)>^99mTc-PYboroxime-N₃ (2.35±0.37%ID/g)≫^99mTc-Uboroxime-N₃ (1.29±0.06%ID/g). ^99mTc-ISboroxime-N₃ had the highest 2-min heart uptake among ^99mTc radiotracers revaluated in SD rats. High quality SPECT images were obtained with the right and left ventricular walls being clearly delineated. The best image acquisition window was 0-5min for ^99mTc-ISboroxime-N₃.

CONCLUSION

Both azide coligand and boronate caps had significant impact on the heart uptake and myocardial retention of complexes [^99mTc(N₃)(CDO)(CDOH)₂B-R]. Among the radiotracers evaluated in SD rats, ^99mTc-ISboroxime-N₃ has the highest initial heart uptake with the heart retention comparable to that of ^99mTc-Teboroxime. ^99mTc-ISboroxime-N₃ is a promising alternative to ^99mTc-Teboroxime for SPECT MPI.

Effect of co-ligands on chemical and biological properties of (99m)Tc(III) complexes [(99m)Tc(L)(CDO)(CDOH)2BMe] (L=Cl, F, SCN and N3; CDOH2=cyclohexanedione dioxime)

INTRODUCTION

(99m)Tc-Teboroxime ([(99m)TcCl(CDO)(CDOH)2BMe]) is a member of the BATO (boronic acid adducts of technetium dioximes) class of (99m)Tc(III) complexes. This study sought to explore the impact of co-ligands on solution stability, heart uptake and myocardial retention of [(99m)Tc(L)(CDO)(CDOH)2BMe] ((99m)Tc-Teboroxime: L=Cl; (99m)Tc-Teboroxime(F): L=F; (99m)Tc-Teboroxime(SCN): L=SCN; and (99m)Tc-Teboroxime(N3): L=N3).

METHODS

Radiotracers (99m)Tc-Teboroxime(L) (L=F, SCN and N3) were prepared by reacting (99m)Tc-Teboroxime with NaF, NaSCN and NaN3, respectively. Biodistribution and imaging studies were carried out in Sprague-Dawley rats. Image quantification was performed to compare their heart retention and liver clearance kinetics.

RESULTS

Complexes (99m)Tc-Teboroxime(L) (L=F, SCN and N3) were prepared in high yield with high radiochemical purity. All new radiotracers were stable for >6h in the kit matrix. In its HPLC chromatogram, (99m)Tc-Teboroxime showed one peak at ~15.5 min, which was shorter than that of (99m)Tc-Teboroxime(F) (~16.4 min). There were two peaks for (99m)Tc-Teboroxime(SCN) at 16.5 and 18.3 min. (99m)Tc-Teboroxime(N3) appeared as a single peak at 18.4 min. Their heart retention and liver clearance curves were best fitted to the bi-exponential decay function. The half-times of fast/slow components were 1.6±0.4/60.7±8.9 min for (99m)Tc-Teboroxime, 0.8±0.2/101.7±20.7 min for (99m)Tc-Teboroxime(F), 1.2±0.3/84.8±16.6 min for (99m)Tc-Teboroxime(SCN), and 2.9±0.9/51.6±5.0 min for (99m)Tc-Teboroxime(N3). The 2-min heart uptake followed the order of (99m)Tc-Teboroxime (3.00±0.37%ID/g)>(99m)Tc-Teboroxime(N3) (2.66±0.01 %ID/g)≈(99m)Tc-Sestamibi (2.55±0.46 %ID/g)>(99m)TcN-MPO (2.38±0.15 %ID/g). (99m)Tc-Teboroxime remains the best in first-pass extraction. The best image acquisition window is 0-5 min for (99m)Tc-Teboroximine and 0-15 min for (99m)Tc-Teboroximine(N3).

CONCLUSION

Co-ligands had significant impact on the heart uptake and myocardial retention of complexes [(99m)Tc(L)(CDO)(CDOH)2BMe] (L=Cl, F, SCN and N3). Future studies should be directed towards minimizing the liver uptake and radioactivity accumulation in the blood vessels while maintaining their high heart uptake.

PET and PET/CT in cardiovascular disease

The present review provides an overview of the role of cardiac positron emission tomography in the diagnosis and management of cardiovascular disease. It expands on the relative advantages and disadvantages over other imaging modalities as well as the available evidence supporting its value in the diagnosis and management of patients with coronary artery disease, the assessment of myocardial viability, and evaluation of the cardiac sympathetic nervous system. Furthermore, the recent developments, such as the implementation of high-end computed tomography devices to form hybrid systems, and the advances of molecular imaging probes in experimental applications are briefly discussed.

Integration of coronary anatomy and myocardial perfusion imaging

Advances in cardiovascular imaging have resulted in the development of multiple noninvasive techniques to evaluate myocardial perfusion and coronary anatomy, each of which has unique strengths and limitations. For example, CT angiography can directly visualize the presence of atherosclerosis, but the hemodynamic effect of many lesions identified by this technique is unknown. Alternatively, myocardial perfusion imaging enables a physiological assessment, but it may underestimate the extent of atherosclerosis in patients with multivessel disease. Dual-modality simultaneous imaging or multimodal sequential imaging techniques facilitate integration of information on both myocardial perfusion and coronary anatomy, and thus have the potential to improve diagnostic and prognostic evaluation, which could translate into improved care of patients. This Review discusses the strengths and limitations of the currently available individual noninvasive techniques for imaging coronary anatomy and myocardial perfusion. Approaches to integration of these imaging modalities are described, followed by an exploration of the clinical utility and future directions of hybrid imaging.