如何检查扫描仪是否已插入(C#,. NET TWAIN)

private static void RegisterScanner(TwainRegistryManager mgr)
{
    var properties = new[]
    {
        new VendorId PropertyName { VendorId = 0x0002, PropertyName = "DeviceCapabilities" },
        new PropertyName PropertyName { PropertyName = "Name" },
        new ProductId PropertyName { ProductId = 0x0903, PropertyName = "ProductName" },
        new ProductName PropertyName { PropertyName = "DeviceName" }
    };
    mgr.RegisterDevice(properties, 1, false);
    mgr.Initialize();
}

using System;
using System.Collections.Generic;
using System.Windows.Forms;
using TWAIN.ImageSource;

// 自定义扫描仪选项列表
private List<IScanSource> scannerOptions = new List<IScanSource>()
{
    new TWAIN.ImageDevice.ClientInfo()
    {
        Connect = () =>
        {
            var mgr = new TwainRegistryManager(new Dictionary<uint, string>() {
                { (uint)PropertyId.VendorId, "MINICOM">