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The purpose of this study was to use MR imaging to accurately measure the thickness of hyaline cartilage and determine the MR contrast parameters for differentiation of cartilage zones in normal human cartilage samples. Cartilage samples were examined using three dimensional spin-echo MR microscopy at 9.4 T with a voxel size of 31 x 31 x 300 microns. Effects of T2 signal loss, susceptibility, and partial volume on measured thickness of cartilage were investigated. Thickness measurements were obtained on corresponding histological sections for comparison. Optimal contrast parameters for delineation of cartilage zones were evaluated using magnetization transfer, inversion recover, T1, and T2 contrast. T2 relaxation losses were identified as the primary source of discrepancy between the measured thickness of cortical bone and hyaline cartilage. Good contrast for zonal differentiation was obtained using T1 weighting. We conclude that images obtained using short TE MR microscopy can be used to accurately measure cartilage and bone thickness in human specimens, and can demonstrate zones within normal cartilage.

An imaging method is described that makes use of proton double quantum nuclear magnetic resonance (NMR) to construct images based on selected metabolites such as lactic acid. The optimization of the method is illustrated in vitro, followed by in vivo determination of lactic acid distribution in a solid tumor model. Water suppression and editing of lipid signals are such that two-dimensional spectra of lactic acid may be obtained from a radiation-induced fibrosarcoma (RIF-1) tumor in under 1 min and lactic acid images from the same tumor in under 1 hr at 2.0 T. This technique provides a fast and reproducible method at moderate magnetic field strength for mapping biologically relevant metabolites. This paper describes an efficient proton nuclear magnetic resonance (NMR) imaging method that can be used to noninvasively map the distribution and levels of certain biologically significant metabolites in vivo. Metabolites of clinical interest include lactic acid (1), N-acetylaspartate (2), alanine (3), and taurine (4). Lactate was chosen for these initial studies because of its biochemical and pathological importance. An elevated level of tissue lactate may indicate (i) the presence of hypoxia, characterized by an increased rate of anaerobic glycolysis, as is found in certain solid tumor centers; (ii) conditions of reduced blood flow (ischemia), such as occurs in coronary infarct and cerebral stroke; (iii) certain inborn errors of metabolism-for example, pyruvate dehydrogenase and pyruvate carboxylase deficiency, or (iv) diabetes (type I)-in which oral phenformin overdose might be implicated.To generate an in vivo proton magnetic resonance image based on a metabolite such as lactate requires the elimination, or reduction, of signals from the large population of water and lipid protons present in vivo, as well as separation of metabolites, residual water, and residual lipid signals. Because metabolite concentrations and magnetic field strength are the limiting factors for in vivo studies, the method must maintain a high level ofefficiency in terms ofselectivity, sensitivity, and minimum data acquisition time. In a previous study (5), two-dimensional double quantum coherence transfer spectroscopy (Fig. 1A) was used to determine steady-state lactate levels in vivo (Fig. 1B). Because of high residual water and lipid levels observed in data collected by the method shown in Fig. 1, both the double quantum (w1) and chemical shift (w2) dimensions are needed for spectral editing. This means that a four-dimensional matrix would be required to obtain an image based on this method.For practical in vivo imaging, the aim was to eliminate the requirement for the chemical shift (W2) dimension by improving the performance of the double quantum method. The w2 dimension can then be used for encoding space rather than chemical shift.The efficiency and limits of detection of double quantum coherence methods were evaluated by using aqueous solutions of lactic acid or its NMR analogue N-acetyl alanine. Metabolite specific images usin...

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