How to parse xmlns fields in php?

I've a little problem, I look old questions for this, but i couldn't find correctly answer for my problem.

How can access "price" or "product_type" fields values with php from below xml code ?

    <rss xmlns:g="http://ift.tt/15FVsV8" version="2.0">
    <channel>
    <item>
    <g:id>1000092</g:id>
    <title>BCI-3EBK Siyah Kartuş</title>
    <g:product_type>Bilgisayar > Ofis Malzemeleri > Kartuşlar</g:product_type>
    <g:brand>CANON</g:brand>
    <g:price>45.0 TRY</g:price>
    <g:gtin>4960999865300</g:gtin>
    <g:image_link>http://ift.tt/1AphKd3;
    <link>
    http://ift.tt/1zDMWyd
    </link>
    <description>BCI-3EBK Siyah Kartuş</description>
    <g:condition>new</g:condition>
    <g:availability>in stock</g:availability>
    </item>
    </channel>
    </rss>

Thanks in advance