Ventricular Distribution Pattern of the Novel Sympathetic Nerve PET Radiotracer F-18-LMI1195 in Rabbit Hearts

We aimed to determine a detailed regional ventricular distribution pattern of the novel cardiac nerve PET radiotracer F-18-LMI1195 in healthy rabbits. Ex-vivo high resolution autoradiographic imaging was conducted to identify accurate ventricular distribution of F-18-LMI1195. In healthy rabbits, F-18-LMI1195 was administered followed by the reference perfusion marker Tl-201 for a dual-radiotracer analysis. After 20 min of F-18-LMI1195 distribution time, the rabbits were euthanized, the hearts were extracted, frozen, and cut into 20-mu m short axis slices. Subsequently, the short axis sections were exposed to a phosphor imaging plate to determine F-18-LMI1195 distribution (exposure for 3 h). After complete F-18 decay, sections were re-exposed to determine Tl-201 distribution (exposure for 7 days). For quantitative analysis, segmental regions of Interest (ROIs) were divided into four left ventricular (LV) and a right ventricular (RV) segment on mid-ventricular short axis sections. Subendocardial, midportion, and subepicardial ROIs were placed on the LV lateral wall. F-18-LMI1195 distribution was almost homogeneous throughout the LV wall without any significant differences in all four LV ROIs (anterior, posterior, septal and lateral wall, 99 +/- 2, 94 +/- 5, 94 +/- 4 and 97 +/- 3%LV, respectively, n.s.). Subepicardial Tl-201 uptake was significantly lower compared to the subendocardial portion (subendocardial, midportion, and subepicardial activity: 90 +/- 3, 96 +/- 2 and *80 +/- 5%LV, respectively, *p < 0.01 vs. midportion). This was in contradistinction to the transmural wall profile of F-18-LMI1195 (90 +/- 4, 96 +/- 5 and 84 +/- 4%LV, n.s.). A slight but significant discrepant transmural radiotracer distribution pattern of Tl-201 in comparison to F-18-LMI1195 may be a reflection of physiological sympathetic innervation and perfusion in rabbit hearts.