@nycmusic, sure.
Of course, you know DXA the newer name (not catching on) for DEXA. Low radiation X-ray, two dimensional it registers areal (vs volumetric) measurement by a subtracting the light absorbed by soft tissue from the light absorbed by mineral in the bone. Two different wave lengths are used.
Qualitative Commuted Tomography QCT is also X-Ray with a CT scanner to yield a three dimensional image, capable of detecting osteoporosis earlier. QCT provides the most accurate measurements of bone mineral density in trabecular bone. Preferred for patients with high parathyroid hormone levels. Unlike DXA, QCT more accurately accounts for changes resulting osteophytes or vascular calcification and scoliosis. More accurate for older people. Expensive, it isn't widely used.
QUS qualitative ultrasound used mainly for the foot and hand, also a three d image
REMs is also ultrasound producing three dimensional images.
Some are finding that they have a better T score with REMS and it does address some of the failings of DEXA. Eco light has a nifty video on REMs that you can find hidden under the title of age and weight. https://iimhe.org/webinars/age-and-weight-webinar-deck/
I laughed when I finally saw your question, nycmusic, because the answer probably would sound like a crash of unfamiliar terms.
It is good to know that we can get REMs if we want to pay. I've noticed that most people have (consoling) higher bmd with REMs, but sometimes higher fragility scores.
I had a QCT early on; the results were the same as DEXA.
This is kind of interesting on DEXA https://cme.nof.org/sites/default/files/DXA%20Basics-%20Morgan_Jankowski.pdf, but I think the best time investment is the Australian on REMS.