DicomDataSet ds = new DicomDataSet("Dataset.dcm");
int frame = 10;
bool cache = true;
var pixelBytes = ds.GetRawFrame(frame, cache);
                    
if (pixelBytes != null)
{
    int width = Convert.ToInt32(ds[Keyword.Columns].Value);
    int height = Convert.ToInt32(ds[Keyword.Rows].Value);
    
    using (Bitmap bitmap = new Bitmap(width, height, PixelFormat.Format24bppRgb))
    {
        BitmapData bmpData = bitmap.LockBits(new Rectangle(0, 0, width, height),
            ImageLockMode.WriteOnly, bitmap.PixelFormat);
        
        IntPtr ptr = bmpData.Scan0;
        Marshal.Copy(pixelBytes, 0, ptr, pixelBytes.Length);
        bitmap.UnlockBits(bmpData);          
        bitmap.Save(frame10.png", ImageFormat.Png);
    }
}