An audio system includes a circuit for processing an audio signal, this circuit having an input for receiving the audio signal and an output for supplying an output signal. A region that does not contain the upper catalyst layer is disposed on the exhaust gas upstream side of this exhaust gas purification catalyst. Also, a source electrode is formed of source tungsten layers buried in source trenches and an AlSi layer in contact with the source tungsten layers and covering source layers and the gate electrodes with a thick insulating film interposed therebetween. The present invention utilizes novel computational techniques for blending between geometric objects, wherein weighted sums of points on the geometric objects are used in deriving a new blended geometric object. The lead through is particularly suited for use in the production of polarized gases, such as 3He. The method includes segmenting the imaging data to identify one or more suspect regions in the imaging data near which localized artifacts are expected to occur, defining an artifact-containing region of interest in the imaging data around each suspect region, and applying a local bias field within the artifact-containing regions to correct for the localized artifacts.