Figure 7. Measurements and calculations of vertebral body height and IVD height based on radiographs. The IVD height should be quantified using a relative value, %DHI, which measures changes in the DHI of punctured discs. DHI = 2 × (D + E + F) /(A + B + C + G + H + I); %DHI = post-punctured DHI /pre-punctured DHI × 100. DHI: disc height index; IVD: intervertebral disc.³¹³ .