Assessment of myocardial triglyceride oxidation with PET and 11C-palmitate

Background  The goal of this study was to test whether myocardial triglyceride (TG) turnover including oxidation of TG-derived fatty acids (FA) could be assessed with PET and ¹¹C-palmitate. Methods and Results  A total of 26 dogs were studied fasted (FAST), during Intralipid infusion (IL), during a hyperinsulinemic-euglycemic clamp without (HIEG), or with Intralipid infusion (HIEG + IL). ¹¹C-palmitate was injected, and 45 minutes were allowed for labeling of myocardial TG pool. 3D PET data were then acquired for 60 minutes, with first 15 minutes at baseline followed by 45 minutes during cardiac work stimulated with constant infusion of either phenylephrine (FAST, n = 6; IL, n = 6; HIEG + IL, n = 6) or dobutamine (FAST, n = 4; HIEG, n = 4). Myocardial ¹¹C washout during adrenergic stimulation (AS) was fitted to a mono-exponential function (Km(PET)). To determine the source of this ¹¹C clearance, Km(PET) was compared to direct coronary sinus-arterial measurements of total ¹¹C activity, ¹¹C-palmitate, and ¹¹CO₂. Before AS, PET curves in all groups were flat indicating absence of net clearance of ¹¹C activity from heart. In both FAST groups, AS resulted in negligible net ¹¹C activity and ¹¹CO₂ production higher than net ¹¹C-palmitate uptake. AS with phenylephrine resulted in net myocardial uptake of total ¹¹C activity and ¹¹C-palmitate in IL and HIEG + IL, and ¹¹CO₂ production lower than ¹¹C-palmitate uptake. In contrast, AS with dobutamine in HIEG resulted in net clearance of all ¹¹C metabolites (total ¹¹C activity, ¹¹C-palmitate and ¹¹CO₂) with ¹¹CO₂ contributing 66% to endogenous FA oxidation. The AS resulted in significant Km(PET) in all the groups, except HIEG + IL. However, positive correlation between Km(PET) and ¹¹CO₂ was observed only in HIEG (R ² = 0.83, P = .09). Conclusions  This is the first study to demonstrate that using PET and pre-labeling of intracardiac TG pool with ¹¹C-palmitate, noninvasive assessment of myocardial TG use is feasible under metabolic conditions that favor endogenous TG use such as increased metabolic demand (β-adrenergic stimulation of cardiac work) with limited availability of exogenous substrate (HIEG).     

Visualization of the lenticulostriate artery with flow‐sensitive black‐blood acquisition in comparison with time‐of‐flight MR angiography

Purpose

To evaluate the capability of flow‐sensitive black blood (FSBB) acquisition to visualize the lenticulostriate artery (LSA) in comparison with time‐of‐flight (TOF) angiography.

Materials and Methods

Twenty‐one healthy subjects (13 males and 8 females, 19–44 years old) were enrolled in this study after obtaining written informed consent. Magnetic resonance imaging (MRI) examinations were performed with FSBB and TOF to visualize the LSA using a 1.5T MRI unit. In FSBB acquisition a motion probing gradient of b = 4 sec/mm² was applied to dephase blood flow. Images were reconstructed into coronal sections and were evaluated in terms of number, length, and image quality at origins and distal areas of visualized LSA branches with a four‐point scale.

Results

In all, 145 LSA branches were visualized with FSBB and 66 branches with TOF. There was no LSA visualized only with TOF. In all evaluated terms, FSBB was significantly better than TOF.

Conclusion

We could better visualize the LSA with FSBB than with TOF, both quantitatively and qualitatively. FSBB is a promising method, although it remains to be evaluated in clinical cases. J. Magn. Reson. Imaging 2009;29:65–69. © 2008 Wiley‐Liss, Inc.