Philippe R. Franken

Feasibility of in vivo dual-energy myocardial SPECT for monitoring the distribution of transplanted cells in relation to the infarction site

PurposeCell therapy using bone marrow mesenchymal stem cells (BMSCs) shows promise in the treatment of myocardial infarction (MI) but accurate cell delivery within MI areas remains critical. In the present study, we tested the feasibility of in vivo pinhole SPECT imaging for monitoring the sites of intramyocardial implanted BMSCs in relation to targeted MI areas in rats.MethodsBMSCs were labelled with 111In-oxine and injected within the fibrotic areas of 3-month-old MI in ten rats. Two days later, dual 111In/99mTc-sestamibi pinhole SPECT was recorded for localisation of 111In-BMSCs on a 15-segment left ventricular (LV) division. Additional 99mTc-sestamibi pinhole SPECT had been performed 1 month earlier and on the day before transplantation. In vitro counting on histological sections was used to validate the pinhole SPECT determination of 111In-BMSC activity within LV segments.ResultsThe underperfused MI area (segments with <70% uptake) was stable between the 99mTc-sestamibi SPECT study recorded at 1 month (4.6±1.9 segments) and at 1 day (4.7±2.3 segments) before transplantation. 111In-BMSCs were detected by dual-energy SPECT in 56 segments: 33 (59%) were underperfused MI segments but 23 (41%) were not (14 adjacent and nine remote segments). Finally, 111In-labelled BMSCs were not detected in 14 out of the 47 (30%) underperfused MI segments.ConclusionWhen BMSCs are injected within MI areas in rats, sites of early cell retention do not always match the targeted MI areas. The dual-energy pinhole SPECT technique may be used for monitoring the sites of early retention of implanted BMSCs and the data obtained may have critical importance when analysing the effects of cardiac cell therapy.

Measurement of left-ventricular volumes using an internal standard

When performing equilibrium radionuclide angiocardiography with two successive acquisition views, absolute left-ventricular volumes can be calculated using an ‘internal standard’ generated by a computer in the left-ventricular cavity. The method is based on the computed ratio of maximum to global activity in the 40°-left-anterior-oblique view after background correction and on the measured depth of the left ventricle in almost-orthogonal, 30°-left-posterior-oblique Fourier first-harmonic images. The method does not require blood sampling or correction for self attenuation. The intra- and interobserver reproducibility is excellent, even in patients with severe impairment of the ventricular-contractility pattern. When compared with a classical method requiring venous-blood counting and an attenuation correction factor, the accuracy of the internalstandard method was fairly good, with a regression coefficient of 0.90.