[VB.NET] Not enough chars in SHA512 string

I'm trying to hash some data and bumped into a problem.

Code:

Dim SHA512 As New SHA512CryptoServiceProvider
Dim arrSHA512() As Byte
arrSHA512 = SHA512.ComputeHash(arrData)
Dim strSHA512Hex As String
For Each bytArrSHA512Element In arrSHA512
  strSHA512Hex += Conversion.Hex(bytArrSHA512Element)
Next

arrSHA512 has 64 elements, which is correct.
strSHA512Hex, witch is arrSHA512 converted to hex, only has 124 chars however, this should be 128.
Any ideas why 2 bytes just seem to disappear?

Thanks