mtDNA

Hello group,
Are B2 and B4'5 mtDNA the same? My brother tested B2 (with NatGeo) and I B4'5 (with FTDNA).
On FTDNA Familyfinder, some of my matches are referred to as B2 and some as B4'5 in the mtDNA Haplogroups column.
Thank you for your help,
Alice Blake