We have been doing conventional QCT and scanning T1 through L3. If I scan only L1 and L2 now, will this have an adverse affect on longitudinal comparisons and precision?
There may be some adverse affect on longitudinal studies when using two different QCT BMD techniques. However, it has been observed clinically that the average BMD of L1/L2 is almost exactly the average BMD of T12/L1/L2/L3. QCT BMD shows a slight but consistent decrease going from T12 to L3. For consistency, the Mindways QCT PRO BMD modules only compare measurements of vertebral bodies in common between all serial exams. Thus, for example, QCT PRO would compare BMD measurements of L1/L2 from a 3D study with L1/L2 from a 2D study even though the 2D study might include results from T12/L1/L2/L3. This method of analysis better accommodates comparisons between other vertebral body pairs, for example T12/L1 or T12/L2, as may be necessary when vertebral abnormalities inhibit measurements in L1 or L2. That is, this serial analysis method favors comparison accuracy at the expense of some comparison precision.
