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Three-dimensional spin-lattice relaxation time in the rotating frame (3D-T 1 ) with parallel imaging at 3.0T was implemented on a whole-body clinical scanner. A 3D gradient-echo sequence with a self-compensating spin-lock pulse cluster was combined with generalized autocalibrating partially parallel acquisitions (GRAPPA) to acquire T 1 -weighted images. 3D-T 1 maps of an agarose phantom and three healthy subjects were constructed using an eight-channel phased-array coil without parallel imaging and with parallel imaging acceleration factors of 2 and 3, in order to assess the reproducibility of the method. The coefficient of variation (CV) of the median T 1 of the agarose phantom was 0.44%, which shows excellent reproducibility. The reproducibility of in vivo 3D-T 1 maps was also investigated in three healthy subjects. The CV of the median T 1 of the patellar cartilage varied between ϳ1.1% and 4.3%. Similarly, the CV varied between ϳ2.1-5.8%, ϳ1.4 -8.7%, and ϳ1.5-4.1% for the biceps femoris and lateral and medial gastrocnemius muscles, respectively. The preliminary results demonstrate that 3D-T 1 maps can be constructed with good reproducibility using parallel imaging. 3D-T 1 with parallel imaging capability is an important clinical tool for reducing both the total acquisition time and RF energy deposition at 3T. Magn Reson Med 56:563-571, 2006.

Purpose: To produce in vivo high-resolution images of the knee and to determine the feasibility of using 7T MR to detect changes in trabecular bone microarchitecture in elite athletes (Olympic fencers) who undergo high impact activity. Materials and Methods:The dominant knees of four males from the U.S. Olympic Fencing Team and three matched healthy male controls were scanned in a 7T whole-body scanner using a quadrature knee coil with three-dimensional (3D) fast low angle shot (FLASH): 50 axial images at the distal femur (0.156 mm ϫ 0.156 mm) and 80 axial images at the knee joint (0.195 mm ϫ 0.195 mm). Bone volume fraction (BVF) and marrow volume fraction (MVF) images were computed and fuzzy distance transform (FDT) and digital topological analysis (DTA) were applied to determine: trabecular number (Tb.N), trabecular thickness (Tb.Th), and trabecular separation (Tb.Sp); BVF (BV/TV); trabecular and marrow space surface-to-curve ratio (SC, marker of plate to rod ratio); and trabecular and marrow space erosion index (EI, inverse marker for network connectivity). Quadriceps muscle volume (MV) was calculated as well. We calculated group means and performed twotailed t-tests to determine statistical significance.Results: Compared to controls, fencers had: decreased Tb.Sp (P ϭ 0.0082 at femur, P ϭ 0.051 at joint); increased Tb.N (P Ͻ 0.05 at both femur and joint) and BV/TV (P Ͻ 0.001 at both femur and joint); increased trabecular SC and decreased marrow space SC (P Ͻ 0.01 at both femur and joint); decreased trabecular EI and increased marrow space EI (P Ͻ 0.01 at both femur and joint); and increased MV (P ϭ 0.038). There was no difference in Tb.Th at the distal femur (P ϭ 0.92) or joint (P ϭ 0.71) between groups. Conclusion:To our knowledge, this is the first study to perform 7T MRI of the knee in vivo. Elite athletes who undergo high impact activity have increased MV and improved trabecular bone structure compared to controls.

Non-invasive thermometry using hyperfine-shifted MR signals from paramagnetic lanthanide complexes has attracted attention recently because the chemical shifts of these complexes are many times more sensitive to temperature than the water 1H signal. Among all the lanthanide complexes examined thus far, thulium tetramethyl-1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetate (TmDOTMA-) appears to be the most suitable for MR thermometry. In this paper, the feasibility of imaging the methyl 1H signal from TmDOTMA- using a frequency-selective radiofrequency excitation pulse and chemical shift-selective (CHESS) water suppression is demonstrated. A temperature imaging method using a phase-sensitive spin-echo imaging sequence was validated in phantom experiments. A comparison of regional temperature changes measured with fiber-optic probes and the temperatures calculated from the phase shift near each probe showed that the accuracy of imaging the temperature with TmDOTMA- is at least 0.1-0.2 degrees C. The feasibility of imaging temperature changes in an intact rat at 0.5-0.6 mmol/kg dose in only a few minutes is demonstrated. Similar to commonly used MRI contrast agents, the lanthanide complex does not cross the blood-brain barrier. TmDOTMA- may prove useful for temperature imaging in many biomedical applications but further studies relating to acceptable dose and signal-to-noise ratio are necessary before clinical applications.

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