Selection of healthy NP tissue based on MRI.

<p><b>a)</b> Healthy NP tissues exhibiting high signal intensity on T2-weighted MR imaging were selected and were classified as grade 1 by the Pfirrmann Grading System. <b>b–d)</b> Expression of <i>Col1A1</i>, <i>Col2A1</i>, and <i>ACAN</i> in NP tissues according to Pfirrmann’s grades 1–3 and HNP were analyzed using RT-PCR. Grade 3 NP and HNP tissues exhibited significantly higher expression of <i>Col1A1</i> than did grade1 NP tissues. For <i>Col2A1</i> and <i>ACAN</i>, there was a significant difference only in HNP (Fig. 1c, d), *p<0.05. <b>d)</b> Histochemical analysis of sections of NP tissues classified according to Pfirrmann’s grades 1–3 and HNP. Grade3 and HNP cells exhibited typical degenerative histological changes. Scale bar: 20 µm.</p>