BMD interpretation mistakes - case 16

Radiologist report:
"This is a 39-year-old Hispanic female with a previous history of osteoporosis, to be compared to previous scans from the year 2000.
At the hip, total bone mineral content is 27.41 grams with an average bone mineral density of 0.786 grams/cm sq. . . . When these values at the hip are compared to previous hip measurements dating to 9-27-2000, there has been a significant improvement in hip BMD of +2.5%"

Why do these graphs look so different? Why did the total hip BMD and T-score get better while the Z-score hardly changed? In the femoral neck, why did the BMD get better, the T-score didn't change, while the Z-score got worse?

Updated 8/8/05