C# Definition:

    [StructLayout(LayoutKind.Explicit)]
    public struct IMAGE_NT_HEADERS32
    {
        [FieldOffset(0)]
        [MarshalAs(UnmanagedType.ByValArray, SizeConst = 4)]
        public char[] Signature;

        [FieldOffset(4)]
        public IMAGE_FILE_HEADER FileHeader;

        [FieldOffset(24)]
        public IMAGE_OPTIONAL_HEADER32 OptionalHeader;

        private string _Signature
        {
        get { return new string(Signature); }
        }

        public bool isValid
        {
        get { return _Signature == "PE\0\0" && (OptionalHeader.Magic == PE.MagicType.IMAGE_NT_OPTIONAL_HDR32_MAGIC || OptionalHeader.Magic == PE.MagicType.IMAGE_NT_OPTIONAL_HDR64_MAGIC); }
        }
    }
    [StructLayout(LayoutKind.Explicit)]
    public struct IMAGE_NT_HEADERS64
    {
        [FieldOffset(0)]
        [MarshalAs(UnmanagedType.ByValArray, SizeConst = 4)]
        public char[] Signature;

        [FieldOffset(4)]
        public IMAGE_FILE_HEADER FileHeader;

        [FieldOffset(24)]
        public IMAGE_OPTIONAL_HEADER64 OptionalHeader;

        private string _Signature
        {
        get { return new string(Signature); }
        }

        public bool isValid
        {
                               //What is PE? PE.MagicType doesn't exist
        get { return _Signature == "PE\0\0" && (OptionalHeader.Magic == PE.MagicType.IMAGE_NT_OPTIONAL_HDR32_MAGIC || OptionalHeader.Magic == PE.MagicType.IMAGE_NT_OPTIONAL_HDR64_MAGIC); }
        }
    }

VB Definition:

    <StructLayout(LayoutKind.Sequential)> _
    Public Structure IMAGE_NT_HEADERS32
        Public Signature As UInt32
        Public FileHeader As IMAGE_FILE_HEADER
        Public OptionalHeader As IMAGE_OPTIONAL_HEADER32
    End Structure

    <StructLayout(LayoutKind.Sequential)> _
    Public Structure IMAGE_NT_HEADERS64
        Public Signature As UInt32
        Public FileHeader As IMAGE_FILE_HEADER
        Public OptionalHeader As IMAGE_OPTIONAL_HEADER64
    End Structure

VB6 Definition:

    Public Type IMAGE_NT_HEADERS32
        Signature As Long
        FileHeader As IMAGE_FILE_HEADER
        OptionalHeader As IMAGE_OPTIONAL_HEADER32
    End Type

    Public Type IMAGE_NT_HEADERS64
        Signature As Long
        FileHeader As IMAGE_FILE_HEADER
        OptionalHeader As IMAGE_OPTIONAL_HEADER64
    End Type

User-Defined Field Types:

IMAGE_FILE_HEADER

IMAGE_OPTIONAL_HEADER32

IMAGE_OPTIONAL_HEADER64

Notes: