Dynamic contrast material-enhanced gradient-echo magnetic resonance (MR) imaging was performed on 15 patients with 18 renal masses (seven simple renal cysts, nine renal cell carcinomas, one angiomyolipoma, and one oncocytoma). Fifteen sequential images were obtained while the patients held their breath during a 2.5-3.5-minute interval during and immediately after the intravenous administration of gadolinium diethylenetriaminepentaacetic acid (DTPA); delayed images were also obtained for 15 minutes. Time-intensity curves showed that renal cortical enhancement reached maximal intensity 80 seconds after the injection of Gd-DTPA. Medullary enhancement reached maximal intensity at 120 seconds. None of the simple renal cysts showed enhancement; each cyst displayed a signal intensity less than that of the renal cortex on precontrast images. All renal cell carcinomas were isointense with the renal cortex and demonstrated variable enhancement. Three patterns of enhancement were observed: predominantly peripheral, heterogeneous, and homogeneous. Both the angiomyolipoma and the oncocytoma showed brisk, homogeneous enhancement. This MR imaging technique appears to be useful in the detection and characterization of simple renal cysts and solid neoplasms.

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Although the magnetic field may be homogeneous, the positioning of a human subject in the bore of the magnet to perform imaging studies induces inhomogeneous fields. Least effect is generated when the object is cylindrical. In regions of marked contour abnormalities such as the leg to foot junction and trunk to neck or neck to head, the inhomogeneity can be so dramatic that errors in fat saturation occur that can lead to misdiagnoses. This manuscript is intended to explain the principle of magnetic susceptibility, fat saturation, and how Sat Pads help improve magnetic field homogeneity. The improved homogeneity results in higher quality MR images, improved homogeneous fat/water saturation to allow for true anatomic representation.Magnetic Resonance (MR) imaging is a modality that utilizes a magnetic field and radio-waves to interact with hydrogen atoms (protons) inside the body to create non-invasive sectional images of internal organs [ 11. The basic and most important principle upon which this technique relies is that protons will respond to a specific radio-frequency dependent upon the local magnetic field strength they experience. Therefore, to properly interact with specific protons, their local magnetic field must be homogeneous and known. When a linearly ramped 1477

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