Robitaille P M, Merkle H, Lew B, Path G, Hendrich K, Lindstrom P, From A H, Garwood M, Bache R J, Uğurbil K
Department of Biochemistry, University of Minnesota, Navarre 55392.
Magn Reson Med. 1990 Oct;16(1):91-116. doi: 10.1002/mrm.1910160110.
Spatially localized phosphorus-31 nuclear magnetic resonance (31P NMR) spectroscopy has been applied to the study of the normal canine myocardium to measure the relative content of high energy phosphates across the left ventricular wall. Transmural NMR data were acquired in five voxels spanning the wall of the left ventricle using the FLAX-ISIS technique. The validity of the FLAX-ISIS approach in acquiring localized spectra for transmural studies and in providing quantitative information from the localized spectra was examined rigorously by studies involving phantoms, intact rats, and the canine myocardium in vivo. The results indicated that (1) this technique yields spatially resolved spectra with partial overlap between adjacent voxels and virtually no overlap between every other voxel; (2) in the canine heart, signals from subepicardium, midwall, and subendocardium can be detected separately without cross contamination; and (3) relative metabolite contents within a voxel and among voxels can be quantitated. Transmural 31P NMR spectra were acquired with cardiac gating on 29 separate animals either at early systole or late diastole, and at three different workloads with the heart rate peak systolic pressure product (RPP) increasing from 6000 mmHg/min to 35,000 mmHg/min. The data revealed that in the normal canine myocardium, the creatine phosphate (CP) content and the CP/ATP ratio was significantly lower in the subendocardium than in the subepicardium. ATP levels were transmurally constant. Both the CP content and the CP/ATP ratio measured for each voxel remained unaltered in relation to either the phase of the cardiac cycle or approximately fourfold increase in workload. Free ADP levels calculated for each voxel showed that ADP was relatively higher in the subendocardium than the subepicardium, and in all transmural layers was higher than its apparent Km for oxidative phosphorylation. In this domain changes in ADP content with workload and MVO2 are not expected and were not observed.
空间定位磷-31核磁共振（31P NMR）光谱已被应用于正常犬心肌的研究，以测量左心室壁上高能磷酸盐的相对含量。使用FLAX-ISIS技术在跨越左心室壁的五个体素中获取透壁NMR数据。通过涉及体模、完整大鼠和犬心肌活体的研究，严格检验了FLAX-ISIS方法在获取用于透壁研究的定位光谱以及从定位光谱中提供定量信息方面的有效性。结果表明：（1）该技术产生空间分辨光谱，相邻体素之间部分重叠，每隔一个体素之间几乎没有重叠；（2）在犬心脏中，心外膜下、心肌中层和心内膜下的信号可被分别检测到，无交叉污染；（3）一个体素内以及不同体素间的相对代谢物含量可被定量。在29只不同的动物身上，于心脏门控下在早期收缩期或晚期舒张期，以及在三种不同工作负荷下获取透壁31P NMR光谱，此时心率收缩压乘积（RPP）从6000 mmHg/min增加到35000 mmHg/min。数据显示，在正常犬心肌中，心内膜下的磷酸肌酸（CP）含量和CP/ATP比值显著低于心外膜下。ATP水平在透壁方向上保持恒定。每个体素测量的CP含量和CP/ATP比值相对于心动周期的阶段或工作负荷大约四倍的增加均保持不变。为每个体素计算的游离ADP水平表明，心内膜下的ADP相对高于心外膜下，并且在所有透壁层中均高于其氧化磷酸化的表观Km。在该范围内，预计且未观察到ADP含量随工作负荷和心肌耗氧量（MVO2）的变化。
