Converting SqlDataReader to SequentialAccess to avoid out-of-memory errors?

I'm currently hitting out of memory errors with the code shown here, and I want to move my SqlDataReader to SequentialAccess to see if that helps.

I originally stumbled across this via the following answer - https://stackoverflow.com/a/15146498

public static void PopulateDataTable(DataTable dt, SQLiteDataReader reader, TableSchema schema)
{
    while (reader.Read())
    {
        var row = dt.NewRow();

        for (int i = 0; i < schema.ColumnCount; ++i)
        {
            if (schema[i].IsBigInteger)
            {
                row[i] = new BigInteger((byte[])reader[i]);
            }
            else
            {
                row[i] = reader[i];
            }
        }

        dt.Rows.Add(row);
    }
}

I'm pretty sure I can use

row[i] = reader.GetString(i);

but I'm unsure how best to convert the BigInt read line. Should I actually be utilising GetChars() with a buffer offset to be seeing any benefit?

Any advice is greatly appreciated.